complex evolution of paleolacustrine systems on mars an example from the holden crater 1 the 150 km wide holden crater lies in an area characterized by high density of valley networks implying conditions conducive to forming of water related environments we undertook geological mapping and a stratigraphic survey in order to probe the evolution of water related landforms and their paleoenvironmental implications our investigations lead us to propose that the holden area was subjected to a wet lacustrine phase of hesperian age and an icy phase during the amazonian deltaic coastal and lacustrine environments occurred during the wet phase some displaying a cyclic depositional pattern presumably related to autogenic processes water was delivered to the basin by the uzboi vallis and by surface runoff channels from a series of drainage basins along the crater walls fan delta geometries and coastal onlap enabled estimation of major water levels two levels of major stand of the water have been recognized possibly reflecting allogenic controls geologic units related to this wet lacustrine phase were subsequently eroded by glacial abrasion and plucking and were disconformably overlain by glacial deposits of amazonian age defining an icy phase these features are consistent with a warm based glacier entering the holden crater through the wide uzboi vallis to form a proglacial lake in the central part of the crater changes in sedimentary units reflect changes of depositional environments probably connected with climatic variation

the timing of martian valley network activity constraints from buffered crater counting abstract valley networks concentrations of dendritic channels that often suggest widespread pluvial and fluvial activity have been cited as indicators that the climate of mars differed significantly in the past from the present hyperarid cold desert conditions some researchers suggest that the change in climate was abrupt while others favor a much more gradual transition thus the precise timing of valley network formation is critical to understanding the climate history on mars we examine thirty valley network incised regions on mars including both cratered upland valley networks and those outside the uplands and apply a buffered crater counting technique to directly constrain when valley network formation occurred the crater populations that we derive using this approach allow assessment of the timing of the last activity in a valley network independent of the mapping of specific geological units from these measurements we find that valley networks cluster into two subdivisions in terms characteristics and age 1 valley network activity in the cratered highlands has an average cessation age at the noachian hesperian boundary and all valleys that we crater counted are early hesperian or older no evidence is found for valley networks in the cratered uplands of late hesperian or amazonian age the timing of the cessation of cratered upland valley network activity at the noachian hesperian boundary also corresponds to a decline in the intensity of large crater formation and degradation and to the apparent end of phyllosilicate type weathering 2 a few valley network incised regions formed outside of the cratered uplands on volcanic edifices in association with younger impact craters and on the rim of valles marineris we applied our buffered crater counting technique to four such valleys on the volcanoes ceraunius tholus hecates tholus and alba patera and on the rim of echus chasma and find that each has distinctive and different late hesperian or early amazonian ages indicating that valley networks formed from time to time in the post noachian period unlike the cratered upland valley networks these isolated occurrences are very local and have been interpreted to represent local conditions e g snowpack melted during periods of intrusive volcanic activity in contrast to a gradual cessation in the formation of valley networks proposed by some workers our new buffered crater counting results indicate a relatively abrupt cessation in the formation of the widespread cratered upland valley networks at approximately the end of the noachian followed only by episodic and very localized valley network formation in later mars history very likely due to specific conditions e g local magmatic heating these valley network ages and correlations are thus consistent with a major change in the near surface aqueous environment on mars at approximately the noachian hesperian boundary the noachian environment supported surface running water and fluvial erosion across mars in the cratered uplands enhanced crater degradation and a weathering environment favoring the formation of phyllosilicates the hesperian amazonian environment was more similar to the hyperarid cold desert of today with valley networks forming only extremely rarely and confined to localized special conditions sources of water for these latter occurrences are likely to be related to periodic mobilization and equatorward migration of polar volatiles due to variations in spin axis orbital parameters and to periodic catastrophic emergence of groundwater

cooling and uplift patterns in the lepontine alps south central switzerland and an age of vertical movement on the insubric fault line 96 new fission track ft apatite and zircon k ar and rb sr biotite and muscovite ages are presented for 19 samples mainly acid gneisses from a 40 km traverse through the lepontine alps in the maggia valley south central switzerland plotting measured mineral ages against assumed system closure temperatures yields cooling rates for each sample the entire profile shows a fairly uniform late neogene recent mean uplift rate of 0 5 mm a confirmed by a gradient of ft apatite age with elevation cooling from higher temperatures occurred earlier in the south where uplift rates of 2 2 mm a in the steep belt root zone indicate 9 km early miocene uplift of the northern pennine block this uplift started before 23 ma and is interpreted as resulting from a major phase of backthrusting along the insubric line and as dating the formation of the mylonite belt estimated cooling rates constrain the timing of lepontine mid tertiary metamorphism 3 schematic models are proposed which also consider published rb sr k ar mica and hornblende and u pb monazite ages slow cooling differential initial heating and subsequent cooling of different parts of the central alps and post 38 ma cooling with syntectonic metamorphism at 27 ma are postulated as alternative interpretations of isotopic data and geologic evidence from extrapolation between k ar and rb sr mica ages and apatite ft ages 240 50 c is proposed as the closure temperature for the retention of fission tracks in zircon

evolution of clastic piles in an arc arc collision zone late cenozoic depositional history around the tanzawa mountains central honshu japan abstract late cenozoic clastic piles around the tanzawa mountains represent trough trench landward and seaward basin fills developed in an arc arc collision zone in central honshu japan the landward basin fills are clastic wedges prograded from the northern orogenic highlands and are characterized by fan deltaic successions succeeding submarine volcano submarine fan slope successions on basin plain deposits the landward basin fills were generally developed intermittently from north to south since the middle miocene evolution of the landward basin fills depended on the interplay of the northward buoyant subduction and suturing of the izu bonin arc in central honshu honshu arc together with submarine magmatism on the landward basin slope emplaced by the subducting pacific plate beneath the izu bonin arc to the west the seaward basin fills however generally lack terrigenous detritus derived from the northern highlands except for a trough fill which received some detritus shed from the rising highs just to the north and are characterized by pyroclastic flow deposits prograded from the southern submarine volcanoes or a volcanic island on the ocean basin the northward progradation of the pyroclastic flow deposits may have been emplaced by the northward drifting of the ocean basin the tanzawa mountains on the other hand consist mainly of early to middle miocene subaqueous volcaniclastic rocks intercalated with some volcanic conglomerates and shallow marine coquinas and can be interpreted as a miocene volcanic island punctuated initiation and propagation of the late cenozoic basin fills diachronously from the north to the south of the tanzawa mountains can be explained by northward drifting and collision of the tanzawa block a paleo volcanic island with central honshu during middle to late miocene and the consequent jump of the subduction zone to the south of it since late miocene preceding the collision of the izu peninsula izu block with the south of the youngest basin fills developed in the southern front of the tanzawa mountains since the middle pleistocene after collision of the izu block with the southernmost basin fills the late cenozoic clastics in and around the tanzawa mountains were uplifted and deformed into northward imbricated structures by rapid slip on the faults framing this area

hydraulic modeling of the tributary and the outlet of a martian paleolake located in the memnonia quadrangle we present a steady state hydraulic model of the tributary and the outlet of a martian paleolake located in the memnonia quadrangle between 167 0 0 w and 167 30 0 w longitude and between 9 25 0 s and 9 45 0 s latitude the mars express high resolution stereo camera hrsc digital elevation model h31850000da4 with a spatial resolution of 75 m is used to describe the geometrical features of the hydraulic system a steady state hydraulic model through a monte carlo procedure is adopted to investigate the assumption that the tributary lake outlet hydraulic system was acting simultaneously during its last water related evolutionary phase through our analysis we infer the roughness coefficient and the discharge of both the tributary and the outlet channels geomorphic evidence such as river terraces were used to constrain the water discharge and the manning s roughness coefficient thereby obtaining estimates of the water level in the lake during the last evolutionary phase of the system our analysis of the outlet reveals a median paleodischarge of 7135 m3 s 1 and a median manning s roughness coefficient of 0 067 m 1 3 s tributary analysis provides a median flow and a median roughness coefficient of 6405 m3 s 1 and 0 123 m 1 3 s respectively moreover the hydraulic analysis suggests that the paleolake water surface level was 1397 m median value hrsc elevation which is consistent with the observed paleoshoreline the results imply that the tributary the lake and the outlet were hydraulically synchronized therefore confirming the presence of a connected water system this study demonstrates that hydraulic analysis can provide valuable information regarding ancient martian water fluxes

bed thickness distributions on mars an orbital perspective studies on earth show that sedimentary bed thickness and bed thickness distributions record information about the processes controlling sediment deposition high resolution digital terrain models dtms such as those derived from the high resolution imaging science experiment hirise now provide the opportunity to quantify bed thickness properties on mars over several orders of magnitude down to the submeter scale this study uses hirise dtms and visible images to measure bed thickness distributions at 10 deposits on mars with the aim of determining whether statistical techniques can provide useful criteria for distinguishing sedimentary depositional processes basic statistics including mean thickness and range are examined as are histograms cumulative frequency plots and log log plots statistical tests interrogate these deposits for thinning or thickening upward trends and the presence of normal lognormal and exponential distributions although there are challenges associated with these methods the statistical analysis of bed thickness coupled with morphological and mineralogical interpretations has the potential to be a powerful tool for characterizing and classifying sedimentary rocks on mars in particular bed thickness statistics are particularly well suited for examining changes in sediment supply and accommodation within martian sedimentary sequences

the effects of secular disequilibrium on u th he systematics and dating of quaternary volcanic zircon and apatite the u th he dating method applied to u rich phases such as zircon and apatite has sufficient sensitivity and precision to be of potential use for dating relatively recent geologic events such as volcanic eruptions however in phases with crystallization ages less than 1 ma chemical fractionation within the 238 u decay series may modify the he ingrowth rate causing he ages computed from the secular equilibrium age equation to be incorrect the resulting systematic error depends on the 230 th 238 u activity ratio of the dated phase when it is erupted and on the eruption age zircons which exclude th relative to u will likely have secular equilibrium he ages that underestimate the eruption age by up to a few tens of decreasing with increasing eruption age apatites tend to accommodate u and th with little fractionation so apatite secular equilibrium he ages will be nearly concordant with eruption age if minerals are erupted immediately after crystallization the disequilibrium effect can be reasonably accounted for based on th u systematics however crystals are likely to reside for unknown but potentially long periods in a magma chamber such that the degree of secular disequilibrium will be reduced prior to the onset of he accumulation u th he analyses of co genetic phases that fractionate the u th ratio differently like apatite and zircon can be used to better constrain eruption age as well as to provide insights into magma chamber residence time we illustrate this approach with u th he analyses of zircons and apatites of the pleistocene age rangitawa tephra new zealand

orographic precipitation in valley network headwaters constraints on the ancient martian atmosphere 1 we examine the martian valley networks in the framework of topographic influences on precipitation we use an analytical model and the laboratoire de meteorologie dynamique lmd early mars global circulation model gcm to explore the local scale distribution of orographically forced precipitation as a function of atmospheric pressure in simulations with 500 mbar and 1 bar co2 atmospheres orographic lifting results in enhanced snowfall upslope of the observed valley network tributaries our framework also suggests that a 2 bar atmosphere cannot create the observed valley pattern at the highest relief valley network warrego valles as in previous work the gcm does not generate temperatures warm enough for rain or significant snowmelt in the highlands with co2 greenhouse warming alone thus while transient periods of unusual warming are still required to melt the deposits and carve the valleys our model predicts snow deposition in the correct locations

a lake in uzboi vallis and implications for late noachian early hesperian climate on mars abstract uzboi vallis centered at 28 s 323 e is 400 km long and comprises the southernmost segment of the northward draining uzboi ladon morava ulm meso scale outflow system that emerges from argyre basin bond and holden craters blocked the valley to the south and north respectively forming a late noachian to hesperian paleolake basin that exceeded 4000 km 3 limited crism data suggest lake deposits in uzboi and underlying basin floor incorporate relatively more mg clays and more fe clays respectively the short lived lake overflowed and breached holden crater s rim at an elevation of 350 m and rapidly drained into the crater fan deltas in holden extend 25 km from the breach and incorporate meter sized blocks and longitudinal grooves along the uzboi basin floor are hundreds of meters long and average 60 m wide suggesting high discharge drainage of the lake precipitation derived runoff rather than regional groundwater or overflow from argyre dominated contributions to the uzboi lake although the failure of most tributaries to respond to a lowering of base level indicates their incision largely ended when the lake drained the uzboi lake may have coincided with alluvial and or lacustrine activity in holden eberswalde and other craters in southern margaritifer terra where fluvial lacustrine activity may have required widespread synoptic precipitation rain or snow perhaps associated with an ephemeral global hydrologic system during the late noachian into the hesperian on mars

tectonic history of granitic bodies in the south fossa magna region central japan new evidence from fission track analysis of zircon abstract a fission track ft analysis of zircons has been performed to clarify tectonic history of the tertiary granitic bodies in the northern part of the izu bonin arc and the south fossa magna region of central japan a total of 30 ft ages was obtained from the kaikoma tsuburai ashigawa tokuwa and tanzawa granitic bodies confined ft lengths were also measured on 11 zircon samples from the granitic rocks to obtain more information on the thermal history of the region the ft ages and confined ft length data from the kaikoma indicate that this granitic body cooled below the isotherm of zircon 240 c at 9 4 0 4 ma 2 the tsuburai ashigawa tokuwa and tanzawa granitic bodies which have a similar lithology and tectonic setting lie from northwest to southeast respectively the ft ages for these bodies are 15 0 0 6ma for the tsuburai 11 9 0 4 ma for the ashigawa 12 5 1 4 ma for the tokuwa which is comparable with the ft age of the ashigawa 7 1 2 0 ma for the tanzawa which is the youngest the data indicate a differential uplift of the granitic bodies in the south fossa magna region in general the ft ages become younger as one proceeds southeastwards approaching the izu bonin arc the ft age data provide constraints on the tectonic effects of the collision of the izu bonin arc with the central honshu of the japan arc

paleohydrology of eberswalde crater mars abstract eberswalde crater mars contains a well preserved fluvial distributary network in a likely deltaic setting the meandering inverted paleochannels and closed drainage basin of this deposit support relatively well constrained estimates of channel forming discharge over an individual event flood timescale runoff production event and annual timescales and longevity of deposition geologic timescale during the late hesperian to early amazonian epochs the width and meander dimensions of two inverted paleochannels reflect the channel forming discharge from event floods 200 to 400 m 3 s the deposit surface indicates the level 1400 to 1350 m and surface area 410 to 810 km 2 of the likely paleolake and the topography and mapped extent of tributaries constrain the watershed area 5000 to 17 000 km 2 based on these results and terrestrial empirical constraints on evaporation and sediment concentration we evaluated three hypothetical water sources meltwater liberated by the nearby holden crater impact continuous deposition over 10 1 10 2 years intermittent rainfall or snowmelt during finite periods controlled by orbital evolution deposition over 10 4 10 6 years and highly infrequent runoff or melting of accumulated snowpacks following distant impacts or secular changes in orbital parameters local impact generated runoff and highly infrequent rainfall or snowmelt require unreasonably high and low rates of evaporation respectively to maintain the paleolake level the local impact hypothesis alternatively depends on one flooding episode with very high concentrations of fluvial sediment that are inconsistent with morphologic considerations multiple primary impact craters in the area postdate holden ejecta but were later dissected indicating fluvial erosion long after the holden impact intermittent rainfall of 1 cm day and seasonal snowmelt are both consistent with our results over a deposition timescale totaling 10 4 10 6 years

co2 solubility in primitive martian basalts similar to yamato 980459 the effect of composition on co2 solubility of basalts and the evolution of the martian atmosphere to determine the influence of basalt composition on the co2 solubility in martian lavas we investigated experimentally a synthetic melt based on the martian meteorite yamato 980459 y 980459 an olivine phyric shergottite and a picritic rock 19 wt mgo thought to be a near primary liquid derived from high temperature 1540 c partial melting of the martian mantle experiments were performed in a piston cylinder apparatus at 1 2 gpa and 1600 1650 c co2 contents in quenched glasses were determined using fourier transform infrared spectroscopy ftir and range from 0 45 1 26 wt despite large differences in feo and mgo contents the co2 solubilities in y 980459 are similar to that in a less primitive synthetic martian basalt based on the humphrey rock and to a hawaiian tholeiite the lack of enhanced solubility in fe2 and mg2 rich melts is likely owing to the complex structural role of these cations in silicate melts acting partly as network formers rather than network modifiers the small sensitivity of co2 solubility to compositional variations among martian and tholeiitic basalts means that the experimentally determined solubilities may be applicable to a wide spectrum of martian magmatic products using experimentally determined co2 solubilities of y 980459 and humphrey allows the calibration of the thermodynamic parameters governing dissolution of co2 vapor as carbonate in martian basalts this relation facilitates calculation of the co2 dissolved in magmas derived from graphite saturated martian basalt source regions as a function of p t and f o2 the hot conditions in the source of y 980459 1540 10 c and 1 2 0 5 gpa are plausible for plume related magmas forming the giant tharsis volcanic complex which accounts for 50 of martian igneous activity since stabilization of the primordial crust if oxygen fugacity in the sources of hot tharsis magmatism were equivalent to that at the iron wustite buffer iw or 1 log unit above iw 1 respectively then the entire tharsis event would outgas 30 300 mbars of co2 to the martian atmosphere which is far from the 2 bars required to stabilize an equable climate in the late noachian and early hesperian epochs this mismatch could be reconciled if significant martian igneous activity derived from comparatively oxidized mantle sources i e iw 2 similar to those responsible for the nakhlite meteorites

confined fission track length measurement of zircon assessment of factors affecting the paleotemperature estimate abstract we carried out a series of laboratory annealing experiments in order to understand the factors affecting observed confined track lengths in thermally annealed zircon the variation of confined fission track lengths according to both experimental and analytical conditions was determined on zircons from nisatai dacite it was found that etching temperature track etching criteria measurement criteria of horizontal confined tracks hct s and the orientation of hct s significantly control the observed track lengths if samples are highly annealed i e 600 c for 1 hr annealing the first three factors may be related to the presence of gap zones in an annealed track whilst the fourth is caused by anisotropic annealing and etching characteristics for reliable thermal history reconstruction therefore it should be the minimum requirement to document explicitly the experimental and analytical conditions of these factors in zircon fission track analysis

vertical groundwater flow in permo triassic sediments underlying two cities in the trent river basin uk the vertical component of groundwater flow that is responsible for advective penetration of contaminants in sandstone aquifers is poorly understood this lack of knowledge is of particular concern in urban areas where abstraction disrupts natural groundwater flow regimes and there exists an increased density of contaminant sources vertical hydraulic gradients that control vertical groundwater flow were investigated using bundled multilevel piezometers and a double packer assembly in dedicated boreholes constructed to depths of between 50 and 92 m below ground level in permo triassic sediments underlying two cities within the trent river basin of central england birmingham nottingham the hydrostratigraphy of the permotriassic sediments indicated by geophysical logging and hydraulic packer testing demonstrates considerable control over observed vertical hydraulic gradients and hence vertical groundwater flow the direction and magnitude of vertical hydraulic gradients recorded in multilevel piezometers and packers are broadly complementary and range within error from 0 1 to 2 0 7 groundwater is generally found to flow vertically toward transmissive zones within the hydrostratigraphical profile though urban abstraction from the sherwood sandstone aquifer also influences observed vertical hydraulic gradients bulk downward darcy velocities at two locations affected by abstraction are estimated to be in the order of several metres per year consistency in the distribution of hydraulic head with depth in permo triassic sediments is observed over a one year period and adds support the deduction of hydrostratigraphic control over vertical groundwater flow q 2003 elsevier b v all rights reserved

interior channels in martian valley networks discharge and runoff production the highland valley networks are perhaps the most compelling evidence for widespread fluvial activity on mars 3 5 ga however determining the hydrology of these features has been difficult owing to poor image resolution and the lack of available topographic data new orbital imaging reveals 21 late stage channels within valley networks which we use to estimate formative discharges and to evaluate water supply mechanisms we find that channel width and associated formative discharge are comparable to terrestrial valley networks of similar area and relief for 15 narrow channels in basin filling networks likely episodic runoff production rates up to centimeters per day and first order formative discharges of 300 3000 m 3 s are similar to terrestrial floods supplied by precipitation geothermal melting of ground ice would produce discharges 100 times smaller per unit area and would require pulsed outbursts to form the channels in four large valleys with few tributaries wider channels may represent large subsurface outflows or paleolake overflows as these four channels originate at breached basin divides and or near source regions for the catastrophic outflow channels

context camera investigation on board the mars reconnaissance orbiter 1 the context camera ctx on the mars reconnaissance orbiter mro is a facility instrument i e government furnished equipment operated by a science team not responsible for design and fabrication designed built and operated by malin space science systems and the mro mars color imager team marci ctx will 1 provide context images for data acquired by other mro instruments 2 observe features of interest to nasa s mars exploration program e g candidate landing sites and 3 conduct a scientific investigation led by the marci team of geologic geomorphic and meteorological processes on mars ctx consists of a digital electronics assembly a 350 mm f 3 25 schmidt type telescope of catadioptric optical design with a 5 7 field of view providing a 30 km wide swath from 290 km altitude and a 5000 element ccd with a band pass of 500 700 nm and 7 m pixels giving 6 m pixel spatial resolution from mro s nearly circular nearly polar mapping orbit raw data are transferred to the mro spacecraft flight computer for processing e g data compression before transmission to earth the ground data system and operations are based on 9 years of mars global surveyor mars orbiter camera on orbit experience ctx has been allocated 12 of the total mro data return or about 3 terabits for the nominal mission this data volume would cover 9 of mars at 6 m pixel but overlapping images for stereo mosaics and observation of changes and meteorological events will reduce this area ctx acquired its first instrument checkout images of mars on 24 march 2006

provenance and thermal history of the franciscan accretionary complex constraints from zircon fission track thermochronology the franciscan accretionary complex of california contains large belts of sediments that were subducted to depths of 10 to 30 km metamorphosed under high pressure and low temperature conditions and later returned to the surface reconnaissance zircon fission track ft data 21 samples place constraints on the sedimentary provenance thermal history and or exhumation history of various franciscan units in a transect across the northern coast ranges through mendocino pass metagraywacke samples from the valantine springs formation of the franciscan eastern belt experienced maximum temperatures tmax ranging from 250 to 310 c zircon ft and previously reported apatite ft data indicate that parts of the western eastern and eastern central belts cooled at about 100 70 ma from 300 c to 100 c considering the low paleogeothermal gradient of roughly 9 c km during franciscan subduction these rocks were apparently uplifted and exhumed from 30 to 10 km depth at this time one sample from the eyler mountain sequence in the northwestern diablo range similarly shows tmax 310 c and major cooling at 100 70 ma this uplift and exhumation may have reflected accelerated accretion at the base as well as the front of the franciscan wedge accompanied by extensional thinning at shallower levels as a result of massive sediment influx into the franciscan trench from the sierra nevada magmatic arc in the northern coast ranges the western part of the central belt and the coastal belt experienced lower tmax probably 200 c and retain source area detrital zircon ft ages burnt hills terrane samples in the diablo range also experienced tmax 230 c and retain detrital ages the detrital single grain age patterns from these areas are compatible with those expected from the sierra nevada magmatic arc and its country rocks this is consistent with derivation of franciscan sediments from arc terranes in california and provides no particular suggestion that these parts of the franciscan are highly allochthonous paleogene coastal belt sandstones also yield detrital ages compatible with derivation from the sierra nevada but also include early tertiary zircon populations compatible with reconstructions suggesting these sandstones were sourced partly from the idaho batholith

timescales of alluvial fan development by precipitation on mars 1 dozens of large low gradient alluvial fans are present within impact crater basins on the cratered highlands of mars the timescales and climate conditions that were required to generate such fans are unknown but testable through our understanding of terrestrial hill slope erosion in the presence of precipitation previous estimates of fan formation time vary from years to millions of years here we use an idealised physical model of 2 d catchment fan evolution to present a framework within which the development of martian alluvial fans should be considered we simplify the erosional and depositional system so that there are only three variables erodibility due to gravity amount of water runoff due to precipitation and catchment fan boundary elevation within this framework to generate large low gradient 108 yr if the substrate is extremely erodible relative to terrestrial examples

continental crust crustal underplating and low q upper mantle beneath an oceanic island arc a detailed structural model of the crust subducting slab and underlying upper mantle across the northern izu ogasawara bonin island arc system is derived from a marine seismic reflection and ocean bottom seismographic refraction survey and subsequent forward modeling combined with tomographic inversion the model indicates that the crust is thickest beneath the presently active rift zone and a granitic crust may have formed in the mid crust a highly attenuative mantle that is one with low quality q seems to be confined mainly beneath the presently active rift zone in contrast high p wave velocity persists in the lower crust between the forearc and eastern margin of the back arc basin suggesting a large scale magma input responsible for the arc formation

large alluvial fans on mars 1 several dozen distinct alluvial fans 10 to 40 km long downslope have been observed in highlands craters within a search region between 0 and 30 s alluvial fan containing craters were found only between 18 and 29 s and they all occur at around 1 km of the mola defined martian datum within the study area they are not randomly distributed but instead form three distinct clusters fans typically descend 1 km from where they disgorge from their alcoves longitudinal profiles show that their surfaces are very slightly concave with a mean slope of 2 many fans exhibit very long narrow low relief ridges radially oriented downslope often branching at their distal ends suggestive of distributaries morphometric data for 31 fans were derived from mola data and compared with terrestrial fans with high relief source areas terrestrial low gradient alluvial ramps in inactive tectonic settings and older martian alluvial ramps along crater floors the martian alluvial fans generally fall on the same trends as the terrestrial alluvial fans whereas the gentler martian crater floor ramps are similar in gradient to the low relief terrestrial alluvial surfaces for a given fan gradient martian alluvial fans generally have greater source basin relief than terrestrial fans in active tectonic settings this suggests that the terrestrial source basins either yield coarser debris or have higher sediment concentrations than their martian counterpoints martian fans and terrestrial basin and range fans have steeper gradients than the older martian alluvial ramps and terrestrial low relief alluvial surfaces which is consistent with the construction of martian fans from dominantly gravel sized sediment rather than sand and silt martian fans are relatively large and of low gradient similar to terrestrial fluvial fans rather than debris flow fans although gravity scaling uncertainties make the flow regime forming martian fans uncertain however evidence of bedforms accentuated by differential erosion such as scroll bars supports the contention that these are fluvially formed fans martian fans at least those in holden crater apparently formed around the time of the noachian hesperian boundary we infer that these fans formed during an episode of enhanced precipitation probably snow and runoff which exhibited both sudden onset and termination

assessment of overetching factor for confined fission track length measurement in zircon abstract the effect of prolonged etching provides a fundamental bias in observed confined track lengths in minerals particularly those having highly anisotropic etching characteristics such as zircon in this paper the anisotropic prolonged etching factor around the ends of horizontal confined tracks hct s which are practically used for track length analysis was assessed quantitatively by step etch of spontaneous tracks in zircon the observed etching characteristics are two fold 1 the track etch rate for the direction perpendicular to the crystallographic c axis is significantly smaller than that parallel to it and 2 for a particular crystallographic direction the growth rate of track length is consistently greater than the bulk etch rate measured as the growth rate of track width for the direction perpendicular to that of interest to further constrain the etching characteristics of hct s the shape of their ends were compared and contrasted with that of track etch pits on a prismatic surface in contrast to the diamond shape of surface tracks the ends of hct s are generally convex outward with the core of etched track longest regardless of track orientation this suggests that at the ends of hct s the core of track has a growth rate greater than the surrounding bulk region probably with decreasing rate outward hence the traditional model of track etching dividing a latent track into the etchable and unetchable ranges should be refined etch rate of a latent track decreases rather continuously toward both ends this model is concordant with the ionization pattern in a mineral detector produced by nuclear fission and explains reasonably the experimental results because the correction of such a complicated overetching factor for an individual sample is extremely laborious for routine analysis it is recommended that hct s nearly perpendicular to the crystallographic c axis e g 70 should be used for track length measurement nevertheless the reduction in number of tracks to be measured may be rather small since hct s with smaller angles to the c axis are less detectable due to the etching anisotropy

the geologic history of margaritifer basin mars in this study we investigate the fluvial sedimentary and volcanic history of margaritifer basin and the uzboi ladon morava outflow channel system this network of valleys and basins spans more than 8000 km in length linking the fluvially dissected southern highlands and argyre basin with the northern lowlands via ares vallis compositionally thermophysically and morphologically distinct geologic units are identified and are used to place critical relative stratigraphic constraints on the timing of geologic processes in margaritifer basin our analyses show that fluvial activity was separated in time by significant episodes of geologic activity including the widespread volcanic resurfacing of margaritifer basin and the formation of chaos terrain the most recent fluvial activity within margaritifer basin appears to terminate at a region of chaos terrain suggesting possible communication between surface and subsurface water reservoirs we conclude with a discussion of the implications of these observations on our current knowledge of martian hydrologic evolution in this important region

martian layered fluvial deposits implications for noachian climate scenarios 1 fluvial deposits in a basin north of holden crater exhibiting a sinuous anabranching pattern are of deltaic or fan origin channel width and meander wavelength indicate persistent flow magnitudes of about 700 m3 s if these flows were produced by quasi periodic climate episodes involving typical terrestrial style precipitation the deposit required thousands to millions of years to accumulate however a scenario of deposition during a few short episodes of constant heavy precipitation resulting from large impacts cannot be excluded

postcollisional exhumation history of the tanzawa tonalite complex inferred from u th he thermochronology and fission track analysis 1 the tanzawa mountains in the south fossa magna region in the middle of the japan arc were formed due to collision of the izu bonin arc against the japan arc during the last several million years the tanzawa tonalite complex is exposed in the tanzawa mountains and is inferred to represent middle crust of the izu bonin arc we performed new thermochronometry consisting of u th he dating fission track dating and fission track length analysis for the complex to investigate the exhumation history of the tanzawa tonalite complex caused by arc arc collision typical u th he ages were 2 0 0 2 ma on apatite 3 3 0 2 ma on zircon and 4 5 to 6 9 ma on zircon using the fission track method the mean fission track length was 9 7 0 6 m 2 se the cooling rate of the tonalite has been calculated to be in the range of 20 60 c ma 1 from 7 to 3 3 ma 80 c ma 1 from 3 3 to 2 0 ma and 30 c ma 1 from 2 0 to 0 ma assuming a surface temperature of 10 c the exhumation rate has been calculated to be 0 5 to 1 5 mm a 1 from 7 to 3 3 ma 2 mm a 1 from 3 3 to 2 0 ma and 0 8 mm a 1 from 2 0 to 0 ma with an assumed geothermal gradient of 40 c km 1 the exhumation rate has not changed significantly despite the simultaneous tectonic changes around the tanzawa mountains after 7 ma

reconstruction of the largest holocene jokulhlaup within jokulsa a fjollum ne iceland abstract glacial outburst floods jokulhlaups have a significant role for landscape evolution in ne iceland a number of jokulhlaups have routed from the northern margin of vatnajokull during the holocene in this study reconstruction of the largest holocene jokulhlaup along jokulsa a fjollum ne iceland was undertaken using the hec ras hydraulic modelling and hec georas flood mapping techniques with a digital elevation model dem derived from ers insar data and field based wash limit evidence the largest jokulhlaup produced extensive erosional and depositional landforms across an inundated area of 1390 km2 and is calculated to have had a peak discharge of 0 9 106 m3 s 1 power per unit area within this jokulhlaup varied from 6 to 46 000 w m 2 jokulhlaup hydraulics are related to geomorphogical evidence at three key sites in va alda upptyppingar and mo rudalur sub areas in order to explain the abrupt spatial variation of the flood characteristics on a regional scale and to relate erosional and depositional features to spatial variations in jokulhlaup hydraulics these process form relationships of the largest jokulhlaup along the jokulsa a fjollum are compared with large outburst floods elsewhere the largest jokulsa a fjollum jokulhlaup had a factor of 20 times smaller discharge and a factor of 20 times lower power per unit area than altai palaeoflood the largest known flood on the earth

fluvial geomorphology on earth like planetary surfaces a review morphological evidence for ancient channelized flows fluvial and fluvial like landforms exists on the surfaces of all of the inner planets and on some of the satellites of the solar system in some cases the relevant fluid flows are related to a planetary evolution that involves the global cycling of a volatile component water for earth and mars methane for saturn s moon titan in other cases as on mercury venus earth s moon and jupiter s moon io the flows were of highly fluid lava the discovery in 1972 of what are now known to be fluvial channels and valleys on mars sparked a major controversy over the role of water in shaping the surface of that planet the recognition of the fluvial character of these features has opened unresolved fundamental questions about the geological history of water on mars including the presence of an ancient ocean and the operation of a hydrological cycle during the earliest phases of planetary history other fundamental questions posed by fluvial and fluvial like features on planetary bodies include the possible erosive action of large scale outpourings of very fluid lavas such as those that may have produced the remarkable canali forms on venus the ability of exotic fluids such as methane to create fluvial like landforms as observed on saturn s moon titan and the nature of sedimentation and erosion under different conditions of planetary surface gravity planetary fluvial geomorphology also illustrates fundamental epistemological and methodological issues including the role of analogy in geomorphological geological inquiry

the structure and evolution of ancient impact basins on mars the number of martian impact basins once thought deficient owing to a low number of impactors has been significantly increased through the identification of structural imprints that remain even after nearly complete erasure of basin massifs five ancient multiringed impact basins were selected for detailed study and exhibit a systematic pattern of rejuvenation of the multiring plan through endogenic modification concentric zones of unstable terrain are believed to reflect deep seated impact related fractures that have localized regional igneous processes in a manner analogous with the basin controlled distribution of basalts on the moon most martian outflow channels were found to originate along the unstable ring zones hydrothermal melting and temporary confinement of channel source materials at sites analogous to lunar sinuous rille source regions are proposed to play an important role in the distribution of martian outflow channels ancient basins also can be delineated by the concentric pattern of topographically and structurally controlled narrow valley networks that are particularly abundant along the outer rings where basin ejecta deposits occur remnant massifs and scarps commonly exhibit extensive furrowing by narrow valley networks perhaps due to a different paleoclimate or sapping during a period of geothermal melting of trapped ices the systematic patterns of valley networks stable and unstable annuli scarps and massifs provide bases for interpreting impact structure in general and for recognizing multiringed structures elsewhere the chryse basin in particular is proposed to represent a major multiringed structure that controlled the formation and distribution of eastern valles marineris and the chaotic terrains of margaritifer sinus in response to volcanism tectonism related to tharsis we conclude that 1 mars is probably not deficient in large body impactors 2 the multiring patterns of basins represent deep seated fracture zones that can be reexposed through subsequent volcanism hydrothermal activity sapping and differential erosion 3 many martian terrains and features e g chaotic terrains and outflow channels are controlled by ancient basins and 4 the resurrection and destruction of impact basins reveal an important third dimension depth for interpreting impact basin formation

evidence for persistent flow and aqueous sedimentation on early mars landforms representative of sedimentary processes and environments that occurred early in martian history have been recognized in mars global surveyor mars orbiter camera and mars odyssey thermal emission imaging system images evidence of distributary channelized flow in particular flow that lasted long enough to foster meandering and the resulting deposition of a fan shaped apron of debris indicate persistent flow conditions and formation of at least some large intracrater layered sedimentary sequences within fluvial and potentially lacustrine environments

u th he geochronology of single zircon grains of known tertiary eruption age we performed a systematic study of u th he ages of volcanic zircons of known eruption age to establish a reliable protocol for zircon he dating and to validate the resulting ages using laser he extraction and dissolution by lithium borate flux melting we analyzed many aliquots of single zircon grains separated from four rapidly cooled rocks fish canyon tuff accepted age 27 8 0 7 ma buluk tuff 16 3 0 2 ma tardree rhyolite 58 4 0 7 ma and utaosa rhyolite 2 52 0 02 ma he ages of fish canyon tuff buluk tuff and utaosa rhyolite zircons are in good agreement with their reference ages mean emission corrected ages were 28 6 1 4 1 16 1 0 8 and 2 61 0 18 ma respectively however the zircon he ages of tardree rhyolite are irreproducible and consistently too old with a mean he age of 78 8 7 0 ma spontaneous fission track densities of tardree rhyolite zircons indicate that about 80 of these zircons are strongly zoned in u with high track density i e high u content in the core and low density on the rim this causes an overestimation of the ejection correction that likely explains the erratic and excessively high he ages from these zircons assessment of the degree and style of u zonation within a zircon population is thus prudent before application of the u th he method step heating experiments indicate that for most zircons he extraction is 99 complete after 1 h at 1300 c however for as yet unknown reasons occasional grains seem to retain substantial amounts of he under these conditions

comparison of experimental techniques to increase the number of measurable confined fission tracks in zircon abstract we compared three experimental techniques for increasing the number of measurable horizontal confined fission tracks hcts in annealed and unannealed zircon these techniques are irradiation of 252 cf spontaneous fission fragments irradiation of heavy ions 58 ni 11 using a tandem van de graaff accelerator and artificial fracturing of the zircon grains all these techniques increased the number of measurable hcts and they introduced no significant change in the measured length of annealed hcts for the samples with low track density 10 5 cm 2 heavy ion irradiation was far more effective than irradiation of 252 cf fission fragments because relatively long artificial tracks could be formed by the heavy ion irradiation the artificial fracturing method is recommended when an accelerator facility is not easily available because its effect was comparable to heavy ion irradiation and it is practicable in ordinary laboratories using these techniques a preliminary comparison of annealing characteristics was performed for three zircon samples with different spontaneous track densities of 4 10 5 4 10 6 and 2 10 7 cm 2 with fission track ages of 3 1 22 8 and 367 6 ma respectively the length reduction due to the thermal annealing of these zircons appeared to be different with the possibility that the thermal stability of spontaneous fission tracks depends on the initial spontaneous track density i e the higher the initial spontaneous track density of a sample the slower the rate of track annealing

annealing kinetics of fission tracks in zircon an experimental study a series of laboratory annealing experiments on zircon fission tracks has been carried out under heating conditions of 350 750 c for 10 1 103 hr i e 4 5 min 40 days variation in the confined lengths of spontaneous fission tracks was determined using zircon grains from nisatai dacite the fading contours of normalized mean track length r on the arrhenius diagram showed as sets of straight lines we performed a series of model fittings called the parallel and fanning models in order to describe the decrease in r with increasing temperature or heating time the lowest temperature limit of the zircon partial annealing zone zpaz was defined as r 0 95 and the highest as r 0 4 which approximately corresponded to the total fading of surface tracks extrapolation of the results of the laboratory experiments to the geological timescale gives for a heating duration of 106 yr estimated values of the zpaz of 210 320 c 60 c 2 with the parallel model 190 350 c 50 c 2 with the fanning model critical temperature t0 and 170 390 c 50 c 2 with the fanning model t0 the temperatures of the zpaz decrease by 20 c for an annealing duration that is an order of magnitude longer because the estimated closure temperature of zircon fission track analysis approximately corresponds to the middle of the zpaz these results support the previously estimated closure temperature of 240 c by varying the etching time it was revealed that significant removal of radiation damage occurs at r 0 93

planetary geomorphology some historical analytical perspectives abstract three broad themes from the history of planetary geomorphology provide lessons in regard to the logic valid reasoning processes for the doing of that science the long controversy over the origin of lunar craters which was dominated for three centuries by the volcanic hypothesis provides examples of reasoning on the basis of authority and a priori presumptions percival lowell s controversy with geologists over the nature of linear markings on the surface of mars illustrates the role of tenacity in regard to the beliefs of some individual scientists finally modern controversies over the role of water in shaping the surface of mars illustrate how the a priori method i e belief produced according to reason can seductively cloud the scientific openness to the importance of brute facts that deviate from a prevailing paradigm

diverse aqueous environments on ancient mars revealed in the southern highlands high resolution spectral images reveal many new exposures of hydrated minerals across the noachian southern highlands of mars several different phyllosilicates are observed with inferred accompanying phases ranging from zeolites to sulfates to chlorides each in distinct geologic settings hydrated sulfates are observed in several locations at mid latitudes and likely formed independently from the equatorial sulfates these assemblages suggest a greater diversity of aqueous environments on ancient mars than has previously been recognized and their distribution implies that alteration was widespread during the noachian period not restricted to a few locations

collision of the izu block with central japan during the quaternary and geological evolution of the ashigara area abstract the ashigara area is located in the northern part of the izu collision zone and has been suspected as a possible location of the boundary between the eurasian and the philippine sea plates in order to analyse its evolution during the collision we have determined the age of the ashigara group and studied its depositional environments and its deformation the age of the ashigara group is early to middle pleistocene the lower part was deposited in a 1000 2000 m deep trough which lay between the izu peninsula and central japan at that time the sedimentary facies show subsequent upward coarsening and shallowing the beginning of the collision resulted in the uplift of the tanzawa mountains which are the source of the voluminous conglomerates deposited in this area soon after the deposition of the upper part of the ashigara group this area was over thrust by the tunzawa mountains along the kannawa fault and strongly folded under a nw se compressional stress field then about 0 3 ma ago the direction of compression drastically changed to n s or ne sw when the colliding izu peninsula was finally locked against central japan

melange forming processes in the development of an accretionary prism evidence from fission track thermochronology to give thermotectonic constraints on melange forming processes and to understand the significance of melange in the evolution of accretionary complexes fission track analysis was carried out on samples collected from sandstone blocks in melange matrix and coherent sandstone sequences adjacent to melange units in the cretaceous to miocene shimanto accretionary complex southwest japan which is one of the typical accretionary complexes with an accumulation of geological information nineteen zircon ages and 15 track length distributions from melanges indicate with some local variation that materials with higher maximum paleotemperatures are exposed at the rear part of the prism as is the case of the coherent units two apatite ages are contemporaneous with previously reported apatite ages of 10 ma obtained from coherent units in the region emphasizing the regional cooling through the apatite closure temperature of 100 c at that time there is no evidence for substantial relative motion of the melanges with respect to the surrounding coherent units melange formation is explained by processes that exclude large vertical transport i e 5 km of melange forming materials these thermotectonic characteristics observed in the shimanto accretionary complex are maintained during subsequent local internal deformation caused by the successive growth of the wedge

catastrophic flooding origin of shelf valley systems in the english channel britain became geographically isolated from continental europe when high interglacial seas flooded the shallow english channel and north sea shelf areas but a tenuous link remained the weald artois chalk ridge between southeast england and northwest france just how this isthmus was breached making britain an island has been a matter of conjecture a new bathymetric map of the sea floor may solve the mystery it reveals a large bedrock floored valley containing landforms including grooves and streamlined islands consistent with a megaflood event caused when a rock dam at the dover strait breached draining a large pro glacial lake in the north sea basin a hypothesis for the permanent isolation of britain from mainland europe during interglacial high sea levels has been confirmed gupta et al analysed a new regional bathymetric map of part of the area finding a valley with landforms indicating large scale subaerial erosion by high magnitude water discharges they suggest breaching of a rock dam at the dover strait instigated drainage of a large lake in the north sea basin megaflood events involving sudden discharges of exceptionally large volumes of water are rare but can significantly affect landscape evolution continental scale drainage patterns and climate change1 it has been proposed that a significant flood event eroded a network of large ancient valleys on the floor of the english channel the narrow seaway between england and france2 3 4 this hypothesis has remained untested through lack of direct evidence and alternative non catastrophist ideas have been entertained for valley formation5 6 here we analyse a new regional bathymetric map of part of the english channel derived from high resolution sonar data which shows the morphology of the valley in unprecedented detail we observe a large bedrock floored valley that contains a distinct assemblage of landforms including streamlined islands and longitudinal erosional grooves which are indicative of large scale subaerial erosion by high magnitude water discharges our observations support the megaflood model in which breaching of a rock dam at the dover strait instigated catastrophic drainage of a large pro glacial lake in the southern north sea basin2 we suggest that megaflooding provides an explanation for the permanent isolation of britain from mainland europe during interglacial high sea level stands7 and consequently for patterns of early human colonisation of britain together with the large scale reorganization of palaeodrainage in northwest europe4

catalogue of large alluvial fans in martian impact craters abstract we conducted a systematic global survey using thermal emission imaging system infrared themis ir coverage 100 m pixel to search for large alluvial fans in impact craters on mars our survey has focused on large fans apron areas greater than 40 km 2 usually located in craters greater than 20 km in diameter due to the resolution of the themis images and mars orbiter laser altimeter mola coverage we find that the host craters are found to have a distinctive diameter range from 30 150 km the fans generally cluster in three geographic areas southern margaritifer terra southwestern terra sabaea and southwestern tyrrhena terra however several outliers do exist the alluvial fans do not form in a particular orientation along the crater rim nor are they associated with the location of current high rim topography fan area magnitude and variability increase with crater diameter while fan concavity magnitude and variability increase with decreasing crater diameter smaller fan aprons in general have higher more variable concavity the source of the water forming these fans is uncertain given the challenges of accommodating the global distribution pattern and formation patterns within the craters

hirise imaging of impact megabreccia and sub meter aqueous strata in holden crater mars high resolution imaging science experiment hirise images of holden crater mars resolve impact megabreccia unconformably overlain by sediments deposited during two noachian age phases of aqueous activity a lighter toned lower unit exhibiting phyllosilicates was deposited in a long lived quiescent distal alluvial or lacustrine setting an overlying darker toned and often blocky upper unit drapes the sequence and was emplaced during later high magnitude flooding as an impounded uzboi vallis lake overtopped the crater rim the stratigraphy provides the first geologic context for phyllosilicate deposition during persistent wet and perhaps habitable conditions on early mars

geologic characteristics of relatively high thermal inertia intracrater deposits in southwestern margaritifer terra mars 1 twenty one craters in southwestern margaritifer terra exhibit unusually warm interior deposits in nighttime thermal emission imaging system themis infrared images these deposits exhibit nighttime temperatures as high as 223 k and are 5 18 warmer than the surrounding plain thermal inertia values derived from thermal emission spectrometer tes data are greater for the deposits than the plains with maximum values between 455 and 675 j m 2 k 1 s 1 2 analysis of themis thermal inertia data having nearly an order of magnitude better spatial resolution shows that the deposits can have a thermal inertia as high as 1060 j m 2 k 1 s 1 2 albedo and dust cover index values suggest that both the deposits and the surrounding region are generally dust free compositional analysis with tes and themis data show that though a small number of the deposits may have isolated compositional differences the majority of the deposits have a composition similar to that of the surrounding plains the geomorphology of the craters as viewed from mars orbiter camera moc images shows that the deposits are coherent units rather than sand deposits an observation that is consistent with the relatively high thermal inertia values if these deposits are coherent rock units as the results of our study suggest possible methods of formation include emplacement of primary igneous material or lithification of sediments from surrounding terrain

the channeled scabland a retrospective the channeled scabland of east central washington in the united states is a complex of anastomosing rock cut fluvial channels cataracts loess islands rock basins broad gravel deposits and immense gravel bars in the 1920s j harlen bretz demonstrated that the channeled scabland formed by cataclysmic erosion and deposition from pleistocene megaflooding derived from the margins of the cordilleran ice sheet particularly glacial lake missoula in western montana and northern idaho studies of this region and the high energy flood processes that generated it are stimulating a discoveries of similar megaflood related landscapes around the world and on mars b enhanced understanding of the processes involved in the fluvial erosion of bedrock and c the use of paleoflood indicators for understanding the magnitudes and frequency of flooding

zircon fission track thermochronology and applications to fault studies zircon is one of the most useful minerals used to unravel the earth s history recorded in rocks after the success of etching fission tracks in zircon fleischer et al 1964 naeser 1969 krishnaswami et al 1974 early studies focused primarily on dating young volcanic horizons for stratigraphic purposes e g naeser et al 1973 hurford et al 1976 seward 1979 gleadow 1980 kowallis et al 1986 kohn et al 1992 subsequently fission track analysis of zircon has been extensively employed along with other radiometric dating methods such as u pb and u th he techniques e g davis et al 2003 reiners 2005 to understand the thermochronology of rocks in a variety of geological settings i e thermal history analysis of basement rocks for orogenic studies e g zeilter et al 1982 hurford 1986 kamp et al 1989 sorkhabi 1993 seward and mancktelow 1994 hasebe and tagami 2001 spikings et al 2001 thermochronology using detrital zircon grains in sedimentary rocks for provenance analysis and thermal history analysis in or near faults which will be highlighted below in this present chapter the thermal sensitivity of the zircon fission track thermochronometry is reviewed in the context of laboratory and field studies then laboratory procedures of the zircon fission track analysis using the external detector method are outlined as practiced in the fission track laboratory of kyoto university for basic fundamentals of these fission track analyses including data analysis and graphical displays see the chapter by tagami and o sullivan 2005 finally as an example of recent geological applications of the technique the results of zircon fission track analysis of the nojima fault zone japan are presented these rocks were the target of systematic drilling of an active fault system using five boreholes and a trench applications to other geological settings and the