reading the climate record of the martian polar layered deposits abstract the martian polar regions have layered deposits of ice and dust the stratigraphy of these deposits is exposed within scarps and trough walls and is thought to have formed due to climate variations in the past insolation has varied significantly over time and caused dramatic changes in climate but it has remained unclear whether insolation variations could be linked to the stratigraphic record we present a model of layer formation based on physical processes that expresses polar deposition rates of ice and dust in terms of insolation in this model layer formation is controlled by the insolation record and dust rich layers form by two mechanisms 1 increased summer sublimation during high obliquity and 2 variations in the polar deposition of dust modulated by obliquity variations the model is simple yet physically plausible and allows for investigations of the climate control of the polar layered deposits pld we compare the model to a stratigraphic column obtained from the north polar layered deposits npld fishbaugh k e hvidberg c s byrne s russel p s herkenhoff k e winstrup m kirk r 2010a geophys res lett 37 l07201 and show that the model can be tuned to reproduce complex layer sequences the comparison with observations cannot uniquely constrain the pld chronology and it is limited by our interpretation of the observed stratigraphic column as a proxy for npld composition we identified however a set of parameters that provides a chronology of the npld tied to the insolation record and consistently explains layer formation in accordance with observations of npld stratigraphy this model dates the top 500 m of the npld back to 1 million years with an average net deposition rate of ice and dust of 0 55 mm a 1 the model stratigraphy contains a quasi periodic 30 m cycle similar to a previously suggested cycle in brightness profiles from the npld laskar j levrard b mustard f 2002 nature 419 375 377 milkovich s head j w 2005 j geophys res 110 but here related to half of the obliquity cycles of 120 and 99 kyr and resulting from a combination of the two layer formation mechanisms further investigations of the non linear insolation control of pld formation should consider data from other geographical locations and include radar data and other stratigraphic datasets that can constrain the composition and stratigraphy of the npld layers

orbital forcing of the martian polar layered deposits since the first images of polar regions on mars revealed alternating bright and dark layers there has been speculation that their formation might be tied to the planet s orbital climate forcing1 2 3 4 but uncertainties in the deposition timescale exceed two orders of magnitude estimates based on assumptions of dust deposition ice formation and sublimation and their variations with orbital forcing suggest a deposition rate of 10 3 to 10 2 cm yr 1 refs 5 6 whereas estimates based on cratering rate result in values as high as 0 1 to 0 2 cm yr 1 ref 7 here we use a combination of high resolution images of the polar layered terrains8 high resolution topography9 and revised calculations of the orbital and rotational parameters of mars to show that a correlation exists between ice layer radiance as a function of depth obtained from photometric data of the images of the layered terrains and the insolation variations in summer at the martian north pole similar to what has been shown for palaeoclimate studies of the earth10 11 12 for the best fit between the radiance profile and the simulated insolation parameters we obtain an average deposition rate of 0 05 cm yr 1 for the top 250 m of deposits on the ice cap of the north pole of mars

new martian climate constraints from radar reflectivity within the north polar layered deposits the north polar layered deposits npld of mars represent a global climate record reaching back millions of years potentially recorded in visible layers and radar reflectors however little is known of the specific link between those layers reflectors and the global climate to test the hypothesis that reflectors are caused by thick and indurated layers known as marker beds the reflectivity of three reflectors was measured mapped and compared to a reflectivity model the measured reflectivities match the model and show a strong sensitivity to layer thickness implying that radar reflectivity may be used as a proxy for short term accumulation patterns and that regional climate plays a strong role in layer thickness variations comparisons to an orbitally forced npld accumulation model show a strong correlation with predicted marker bed formation but dust content is higher than expected implying a stronger role for dust in mars polar climate than previously thought

metamorphic facies and tectonics in part of the cascade range and puget lowland of northwestern washington metamorphic assemblages in pre tertiary rocks of northwestern washington can be grouped into eight facies types which represent recrystallization under widely diverse p t conditions consideration of these assemblages together with their regional distribution and age allows speculation concerning some aspects of the regional metamorphic and tectonic history 1 high pressure assemblages indicate that much of the metamorphosed rock has been affected by subduction 2 two ages of subduction are represented carboniferous to permian and early cretaceous 3 during the cretaceous event rock masses of local to regional extent gained mutually distinctive metamorphic assemblages indicating that the rock units acted as separate tectonic elements during the subduction process 4 sea floor metamorphism may be indicated by the occurrence of low pressure assemblages in ophiolitic rocks 5 in some rock units low pressure assemblages are overprinted by high pressure minerals suggesting a history of sea floor followed by subduction metamorphism 6 some rock units contain only low pressure assemblages and thus may have escaped subduction 7 diverse origins of rock units and profound movement on unit bounding faults are suggested by the disparity of ages and facies type

stratigraphy of the north polar layered deposits of mars from high resolution topography nasa earth and space science fellowship nnx13ao55h nasa s mars reconnaissance orbiter project hirise

detrital zircon constraints on terrane ages and affinities and timing of orogenic events in the san juan islands and north cascades washington detrital zircon geochronology of this report pertains to cretaceous orogeny in northwest washington an event that involved blueschist metamorphism and emplacement of nappes in the san juan islands northwest cascades thrust system and continental arc magmatism and associated barrovian metamorphism in the neighboring coast plutonic complex structurally low in the thrust system quartzose gneiss of the yellow aster complex yields an entirely precambrian suite of detrital zircons with an age pattern that is similar to that of ordovician miogeoclinal rocks and the outboard yukon tanana yreka and shoo fly terranes elsewhere in the cordillera midway in the nappe pile of the northwest cascades sandstone in the bell pass melange has a zircon age population of 110 ma an age that together with the spectrum of exotic materials associated with the sandstone suggests the melange was a major zone of dislocation during mid cretaceous nappe emplacement at a high level in the thrust system are nappes of the fida

fragment of the coast range ophiolite and the great valley sequence in the san juan islands washington the decatur terrane is a small allochthonous fragment of upper jurassic oceanic crust with an overlying blanket of upper jurassic lower cretaceous sedimentary rocks in the san juan islands the stratigraphy and petrotectonic elements are dissimilar to those of coeval sequences in the pacific northwest oregon washington and southern british columbia but are virtually identical to those of the coast range ophiolite and overlying great valley sequence south of san francisco california this stratigraphic correlation together with regional considerations suggests that the decatur terrane was detached and transported during cretaceous time the resultant displacement is in excess of 1000 km

earliest accumulation history of the north polar layered deposits mars from sharad abstract the approximately 2 km thick north polar layered deposits npld are often considered to contain the most complete and detailed stratigraphic records of recent climate of mars exposures of the dense layering within troughs and scarps allowed detailed reconstructions of the latest accumulation history of these water ice deposits but we lack knowledge of their initial emplacement the shallow radar sharad onboard mars reconnaissance orbiter mro penetrates the npld to their base and detects their internal layering overcoming the limitation of scarce and scattered visible outcrops of the lowermost sequences in this study we map reflectors in sharad data that result from discrete stratigraphic horizons in order to delineate the three dimensional stratigraphy of the lowermost 500 m npld sequence and reconstruct their accumulation history we confirm the large scale lateral continuity and thickness uniformity of the deposits previously detected within the lowermost npld however stratigraphic complexity in the form of pinch outs and significant thickness variations arises when we examine single radar units we find evidence of an initially limited geographic stability of water ice within two deposits that are centered at the north pole and present day gemina lingula a period of lateral ice sheet growth followed interrupted only once by a retreat episode lower net accumulation is observed on pre existing slopes suggesting a reduction of water ice stability due to increased solar radiation incidence and or transport by katabatic winds lateral transport of water ice by wind is also suggested by thickness undulations toward the top of the sequence resembling cyclic steps water ice accumulation models based on orbital forcing predict a sequence of deposition and retreat events that is generally compatible with our reconstructed accumulation history therefore we interpret the stratigraphic complexity that we observe as regional and possibly global climate change induced by orbital forcing we also find that at least two units are completely buried within the npld and do not outcrop and that npld deposition in some places was contemporaneous with deposition of the stratigraphically underlying cavi unit in other places both of these findings show that radar reflector mapping is a necessary complement to any stratigraphic reconstruction based on visible exposures

models of climate cycles recorded in martian polar layered deposits abstract layered strata observed in orbital images of polar sedimentary terrains on mars have been hypothesized to contain information about recent variations in the martian climate celestial mechanicians have determined that mars has experienced large amplitude quasi periodic variations in obliquity and eccentricity planetary meteorologists have inferred that the resulting changing patterns of solar heating must have had dramatic effects on martian climate accordingly it might be possible to link the known recent history of orbit axial variations with the physical characteristics of the most recently deposited strate determined from orbital imagery our paper explores that possibility quantitatively for various models of the formation of the polar layered deposits and the layering developed within them we modeled the formation of polar layered deposits during the past 10 my for two general classes of model uniform deposition rate udr models assume that the major constituent of the layered deposits is deposited at a uniform rate and that layering is established by climate induced variations in the concentration of a minor constituent climate modulated deposition rate cmdr models assume that the deposition rate of the major constituent is controlled by climate and that layer boundaries correspond to intervals of nondeposition in both models abrupt changes in deposition regime occur when a function of the orbit axial parameters crosses a threshold value detailed physical mechanisms for the control of sedimentation by orbit axial variations were developed for two specific models of the cmdr type in one model the deposits are assumed to be primarily composed of dust in the other they are assumed to be predominantly water ice we calculated the times at which abrupt changes in deposition regime occur and determined the relative thicknesses of successive layers which can be compared against layer thicknesses made from orbital imagery in all these models obliquity variations exert the dominant influence on the sequential variations in layer thickness although eccentricity and precession index longitude of perihelion may take recognizable contributions as well the layer patterns for the north and south polar deposits are identical for the dust model and only slightly different for the ice model but this is at least partly a consequence of simplifying assumptions the sequential variation in layer thickness is also very sensitive to those model parameters which control the fraction of time for which deposition occurs when the climate threshold for deposition is low deposition occurs a large fraction of the total time and characteristic patterns form with one thick layer and a number of much thinner ones such patterns would be easily recognized in photogeological measurements of layer thickness when the threshold for deposition lies in the mid range with respect to excursions of the climate function deposition occurs approximately half of the time and there is only slight modulation of layer thickness when the threshold for deposition is high deposition occurs only a small fraction of the total time and groups of layers form which are separated form other groups by long periods of nondeposition the stratigraphic unconformities that separate groupings of five to ten layers in the polar deposits may indicate that the martian polar region has experienced such a depositional history the feasibility of using these model results to verify the theory of climate control of polar stratigraphy on mars and to gain additional insights into the significant processes is considered the stratigraphy issues raised here are also explored in the context of recent work on the interpretation of stratigraphy of ocean margins from this comparison there emerge some valuable insights into the stratigraphic effects of periods of nondeposition and the uncertaintiesin interpreting images of exposed polar strata on mars

timescales of the climate record in the south polar ice cap of mars the south polar layered deposits spld are the largest water ice reservoirs on mars their accumulation is believed to result from climate oscillations that drive the movement of ice and dust on the surface the high resolution imaging science experiment and the colour and stereo surface imaging system have imaged exposures of its internal structure in troughs and marginal scarps here we use the stereo imaging products of these instruments to extract stratigraphic pro les representative of various locations throughout the spld through wavelet and series matching analyses of these pro les we reveal periodicities in the stratigraphy that correlate to the orbital oscillations that drive climate change on mars and that have been observed to force the accumulation of the north polar cap we infer that the water ice and dust of the spld were deposited at variable rates of 0 13 0 39 mm year taking a minimum of 10 30 myr to accumulate

the transitional depositional environment and sequence stratigraphy of chasma boreale abstract the depositional system within chasma boreale is unique in that it contains active aeolian environments expressed as dune fields and active cryosphere environments present as layered ice deposits as well as environments that transition between these this work presents a new analysis of the chasma boreale sediment system that creates an interpretative framework addressing a controls on the balance between aeolian and cryospheric processes in the modern depositional system b the stratigraphic architecture of related sedimentary deposits and c processes of sediment accumulation and preservation images from context camera ctx 6 m pixel are used to classify and map sedimentary environments surfaces and deposits on the reentrant floor to refine the established geologic map of the reentrant and to infer the stratigraphic record of the accumulation from chasma boreale s depositional system a spectrum of sedimentary environments occurring between those dominated by aeolian and by cryospheric processes are identified through time the boundaries of these sedimentary environments have shifted resulting in complex lateral changes in the configuration of sedimentary environments on the reentrant s floor vertically the stratigraphic record is characterized by the punctuation of sandy aeolian deposits by icy surfaces that indicate episodes of ice growth that preserve underlying deposits resulting in accumulation stabilized icy surfaces occur at multiple vertical temporal scales and lateral extents suggesting the influence of both regional climate change due to allogenic forcing as well as autogenic dynamics within the transitional system these observations demonstrate that the chasma boreale accumulation can be interpreted in an aeolian sequence stratigraphic framework this work contributes the first detailed description of the processes forming polar aeolian sequences with an emphasis on the competing and complementary dynamics between aeolian and cryospheric systems

a revised surface age for the north polar layered deposits of mars this work was funded by nasa grant nnx13ag72g m e l was supported by the national science foundation graduate research fellowship program grant dge 1143953 hirise images referenced are available on the instrument s public website https hirise lpl arizona edu the crater catalog used in this work is included with this paper as supporting information the authors thank s sutton for help with socet set software m m sori for useful discussion on viscous relaxation and m e banks for useful discussion on the impact population the authors additionally thank j a skinner p becerra d laikko m sori n barlow and an anonymous reviewer for helpful comments on the manuscript

stratigraphic relationships within martian polar cap deposits abstract deposits of layered ice and dust accumulate on the smooth and banded terrains of the north and south polar cap deposits while erosion of equator facing slopes of layered terrain expose these layers banded terrain occurs at exposures of irregular layers resulting from slight erosion of the feather edges of layers deposited on pole facing trough walls these deposits unconformably overlap onto adjacent layered terrain stripping of layers occurs in areas of strong multidirectional wind forming striped terrain local wind scour has also produced steep scarps with crescentic planform often associated with dune fields positioned immediately downwind unconformities are common within layered deposits in areas of complex topography at the north pole these indicate that episodes of deposition of 5 10 layers alternate with slight erosion of pole facing trough walls troughs that strike north south alternate between erosional widening and deepening and depositional infilling creating multiple unconformities troughs near the equatorward limit of polar deposits increase in relief by deposition on adjacent smooth terrain and locally by erosional deepening troughs may migrate poleward replacing the relief increase by depositional infilling when they near the poles

kinematic analysis of the san juan thrust system washington shear related fabric in the middle to late cretaceous san juan thrust system washington is observed in imbricated blocks and in fault zones a few millimeters to tens of meters thick foliation and lineation are defined in tectonic blocks by alignment of 1 newly grown muscovite and chlorite and 2 flattened and stretched radiolaria mineral porphyroclasts and rock fragments thin argillaceous shear zones bear a pronounced lineation defined by lithologic streaks and slickenside corrugations the slickenside and stretching lineations show a well defined preferred orientation in a horizontal northwest southeast direction widespread s c fabrics asymmetric pressure shadows fault drag features and asymmetric folds in the x z plane yield a sense of tectonic transport at most localities of upper plate to the northwest aragonite prehnite lawsonite pumpellyite and rare na amphibolite and na pyroxene characterize the metamorphism during the thrusting the findings of this study indicate north west orogen parallel transport of the san juan thrust system we suggest that this structure is a large step over zone transferring dextral strike slip from the western cascades to the oceanward side of wrangellia

orbital change experiments with a mars general circulation model abstract we use a mars general circulation model to examine the effect of orbital changes on the planet s general circulation and climate system experiments are performed for obliquities ranging from 0 to 60 for two different longitudes of perihelion each experiment simulates a full mars year assuming a fixed atmospheric dust distribution and fixed amount of co 2 in the atmosphere cap system we find that global mean surface temperatures and pressures decline with increasing obliquity due to the increasing extent of the winter polar caps the seasonal co 2 cycle and intensity of the solstice circulation amplify considerably with increasing obliquity such that global dust storms are likely at both solstices the most significant feature of the high obliquity solstice circulations is the development of an intense low level jet associated with the return branch of the hadley circulation model surface stresses are used to map regions of preferred dust lifting which are defined in terms of an annual deflation potential for the present obliquity the model predicted regions of high deflation potential are in good agreement with cantor et al s 2001 j geophys res 106 23653 23688 observations which gives us some confidence in the model s ability to predict where lifting might occur when mars orbit parameters are different than they are today in general we find that the dust lifting potential increases sharply with obliquity and is greatest at times of high obliquity when perihelion coincides with northern summer solstice over an obliquity cycle the model global annual deflation potential ranges from several tenths of a millimeter at 0 obliquity to almost 15 mm at 60 obliquity much higher values are possible when the atmosphere is very dusty we find a strong correlation between the deflation potential and surface thermal inertia regions of high deflation potential correspond to regions of high thermal inertia high rock abundance and regions of low deflation potential correspond to regions of low thermal inertia high dust sand abundance furthermore while the regions of preferred lifting high deflation potential expand somewhat with increasing obliquity and dust loading the central parts of tharsis arabia and elysium show no tendency for significant lifting at any obliquity or longitude of perihelion these regions may therefore be very old and represent net long term sinks for atmospheric dust it is the topography of the planet through its influence on surface pressure and wind systems which ultimately determines where dust accumulates finally as was found by fenton and richardson 2001 j geophys res 106 32885 32909 we find no tendency for the development of east southeasterly winds at the pathfinder site for any of our orbital change experiments this suggests that the ancient wind regime discussed by greeley et al 2000 j geophys res 105 1829 1840 was produced by other factors such as polar wander

a procedure for testing the significance of orbital tuning of the martian polar layered deposits layered deposits of dusty ice in the martian polar caps have been hypothesized to record climate changes driven by orbitally induced variations in the distribution of incoming solar radiation attempts to identify such an orbital signal by tuning a stratigraphic sequence of polar layered deposits plds to match an assumed forcing introduce a risk of identifying spurious matches between unrelated records we present an approach for evaluating the significance of matches obtained by orbital tuning and investigate the utility of this approach for identifying orbital signals in the mars plds using a set of simple models for ice and dust accumulation driven by insolation we generate synthetic pld stratigraphic sequences with nonlinear time depth relationships we then use a dynamic time warping algorithm to attempt to identify an orbital signal in the modeled sequences and apply a monte carlo procedure to determine whether this match is significantly better than a match to a random sequence that contains no orbital signal for simple deposition mechanisms in which dust deposition rate is constant and ice deposition rate varies linearly with insolation we find that an orbital signal can be confidently identified if at least 10 of the accumulation time interval is preserved as strata addition of noise to our models raises this minimum preservation requirement and we expect that more complex deposition functions would generally also make identification more difficult in light of these results we consider the prospects for identifying an orbital signal in the actual pld stratigraphy and conclude that this is feasible even with a strongly nonlinear relationship between stratigraphic depth and time provided that a sufficient fraction of time is preserved in the record and that ice and dust deposition rates vary predictably with insolation independent age constraints from other techniques may be necessary for example if an insufficient amount of time is preserved in the stratigraphy

first high resolution stratigraphic column of the martian north polar layered deposits 1 this study achieves the first high spatial resolution layer scale measured stratigraphic column of the martian north polar layered deposits using a 1m posting dem the marker beds found throughout the upper north polar layered deposits range in thickness from 1 6 m 16 0 m 1 4 m and 6 of 13 marker beds are separated by 25 35 m thin layer sets have average layer separations of 1 6 m these layer separations may account for the spectral power peaks found in previous brightness profile analyses marker bed layer thicknesses show a weak trend of decreasing thickness with depth that we interpret to potentially be the result of a decreased accumulation rate in the past for those layers however the stratigraphic column reveals that a simple rhythmic or bundled layer sequence is not immediately apparent throughout the column implying that the relationship between polar layer formation and cyclic climate forcing is quite complex

north polar cap of mars polar layered deposit characterization and identification of a fundamental climate signal of the cap 6 10 5 km 2 in the 13 images analyzed to date 3 assessment of geometric relationships shows that layers are not horizontal but rather have an apparent dip of approximately 0 5 degrees we interpret these results as follows 1 the fundamental 30 m signal is interpreted as a climate signal that may correspond to a 51 kyr insolation cycle 2 the lateral correlation and broad distribution of these layer sequences strongly imply that layer accumulation processes are widespread across the cap rather than confined within a single trough or region 3 local to regional variability in individual layer thicknesses and thus accumulation and sublimation rates is typically less than a factor of 2 5 providing the ability to study regional trends but often making it difficult to correlate visually the vertical sequences in individual cores finally initial examination of layers located deeper in the stratigraphic sequence within the north polar cap than the 300 m thick zone 1 provides evidence for a unit less than 100 m thick zone 2 in which the fundamental 30 m sequence is not detected we interpret this as a deposit having formed during a recent high obliquity phase of mars during which time polar volatiles underwent mobilization and were transport equatorward leaving a polar lag of dust rich material the most recent ice age 0 5 2 ma offers a plausible candidate for this period of ice cap removal and lag deposit formation an underlying zone 3 200 m contains a dominant 35 m signal and a lowermost zone 4 200 m contains multiple signals but no dominant one together these four zones represent 800 m of vertical stratigraphic section about one fourth of the total thickness of the cap these findings support earlier interpretations that orbital parameter variations could cause significant erosion and possibly complete removal of the polar caps the interpreted crater retention ages of the layered terrain are consistent with the correlations and vertical sequences described here suggesting that the polar caps wax and wane throughout geological history depending on the evolution of orbital parameters definition of the 30 m unit signal holds promise for determining 1 the detailed origin of individual layer types 2 the nature of deposition and sublimation processes and their relation to insolation geometry across the polar cap and 3 correlation with and comparison to the south polar layered terrain record

meter scale morphology of the north polar region of mars mars north pole is covered by a dome of layered ice deposits detailed 30 centimeters per pixel images of this region were obtained with the high resolution imaging science experiment on board the mars reconnaissance orbiter mro planum boreum basal unit scarps reveal cross bedding and show evidence for recent mass wasting flow and debris accumulation the north polar layers themselves are as thin as 10 centimeters but appear to be covered by a dusty veneer in places which may obscure thinner layers repetition of particular layer types implies that quasi periodic climate changes influenced the stratigraphic sequence in the polar layered deposits informing models for recent climate variations on mars

onset and migration of spiral troughs on mars revealed by orbital radar the northern polar cap of mars containing enough water to cover the entire planet to a depth of several metres features two major landforms that stand above all others these are the enormous canyon chasma boreale and a series of spiral troughs the processes leading to their formation have remained unclear now two papers in this issue present detailed histories of both systems john holt and colleagues use penetrating radar imagery from mars reconnaissance orbiter s radar sounder to show that depositional processes rather than a catastrophic event formed the chasma boreale isaac smith and john holt use mars reconnaissance orbiter data to rule out erosional cutting of polar ice as the cause of the central troughs and instead conclude that they too are largely depositional having migrated polewards and upwards in elevation in the past two million years a pinwheel array of deep troughs has been one of the most perplexing features of the north polar layered deposits on mars many ideas have been put forward about how it formed but there is as yet no consensus here penetrating radar has been used to rule out erosional cutting as a mechanism for the formation of the array instead it is concluded that the troughs are largely depositional in origin and have migrated to the poles and upwards in elevation over the past two million years or so the landscape of the north polar layered deposits of mars npld is dominated by a pinwheel array of enigmatic spiral troughs1 the troughs have intrigued planetary scientists since the mariner 9 spacecraft returned the first close up image in 1972 but conclusive evidence of their origin has remained elusive debate continues regarding all aspects of the troughs including the possibility that they have migrated2 3 4 5 their age in relation to the current npld surface6 and whether they are fundamentally erosional6 7 or constructional2 4 features the troughs are probably related to climatic processes2 8 yet the nature of this relationship has remained a mystery previous data characterizing only the exposed nlpd surface were insufficient to test these hypotheses here we show that the central spiral troughs initiated after deposition of three quarters of the npld quickly reached a stable morphology and migrated approximately 65 kilometres poleward and 600 metres in altitude over the past two million years or so our radar stratigraphy rules out hypotheses of erosional incision post dating deposition6 7 9 10 and instead largely validates an early hypothesis for constructional trough migration2 3 4 5 with wind transport and atmospheric deposition as dominant processes these results provide hard constraints for palaeo climate models and a new context for evaluating imagery spectral data and now radar sounding data the better to understand the link between orbital parameters and climate the role of climate in shaping the polar ice of mars and eventually the age of the polar deposits themselves8 11 12 13

glaciological response to distal tephra fallout from the 1947 eruption of hekla south iceland glacier responses to tephra deposition are shown to be highly variable where wind transported eruption plumes produce narrow distal fallout zones with steep lateral thickness gradients significant but short lived advances of faster flowing glaciers can be triggered by deposition from modest eruptions the 1947 eruption of hekla south iceland covered nearby glaciers with variable thicknesses of tephra causing dramatic spatial variations in ablation rate relative snow ablation increased by an estimated 80 at the eastern margin of eyjafjallajokull but decreased by 54 at the western margin relative ice ablation increased by only 4 in the east but decreased by 75 at the western margin only 15 km distant the effect on mass balance therefore depends on tephra distribution as well as on the nature of the glacier surface on gigjokull retardation of ablationwas greatest at the terminus associated with an anomalous advance of 328 m between 1947 and 1954 other glaciers in the fallout zone show either no recognizable response or accelerated retreat advances will be short lived due to the rapid redistribution of supraglacial tephra in a maritime climate and the potential for discriminating between volcanically and climatically forced advances in the glacio geomorphological record is low the long term glaciological effect of volcanism is to create thin low albedo covers after reworking which make conditions less favourable for glaciation

geochemistry of the shuksan greenschists and blueschists north cascades washington variably fractionated and altered metabasalts of oceanic affinity the shuksan schist comprises a structurally coherent metabasaltic member of the easton formation the uppermost allochthon shuksan thrust plate in the thrust system of the western north cascades of washington state late jurassic metamorphism at moderately high p t produced interlayering of actinolite bearing greenschist assemblages with blue amphibole bearing rocks major and trace element analyses of twelve greenschist and blueschist samples have been used to establish similarities between the basaltic protolith and moderately to strongly fractionated type i morb to distinguish the effects of seafloor alteration superimposed on the primary igneous chemistry and to evaluate the origin and nature of the chemical controls which produced the two mineral assemblages

optical determination of topotactic aragonite calcite growth kinetics metamorphic implications textures produced by the partial recrystallization of aragonite to calcite in the blueschist facies show that heterogeneous topotactic nucleation is rapid enough to permit growth kinetics to dominate the overall geologic rate of transformation both grain boundary velocities measured microscopically between 375 c and 455 c and analysis of topotactic relations predict a growth mechanism involving only small atomic displacements near a highly coherent boundary between the two phases the kinetic equation of turnbull for interface controlled growth based on that mechanism accurately describes the experimental results when calculated rates are integrated over geologically plausible pressure temperature time paths for convergent plate margins even the most extreme values lead to the conclusion that aragonite bearing rocks enroute to the surface must enter the calcite stability field between 125 c and 175 c the widespread occurrence of aragonite along the pacific margin of north america and by contrast

geology and insolation driven climatic history of amazonian north polar materials on mars a wealth of image and topographic data from the mars global surveyor and mars odyssey missions has been combined in a detailed geological map of the north polar region of mars one intriguing finding is a cycle of ice deposition similar in duration to a 1 470 year climate cycle of unknown origin on earth if both are externally driven a mechanism that affects both planets such as variation in solar luminosity must be involved mariner 9 and viking spacecraft images revealed that the polar regions of mars like those of earth record the planet s climate history however fundamental uncertainties regarding the materials features ages and processes constituting the geologic record remained1 2 3 4 5 6 recently acquired mars orbiter laser altimeter data7 and mars orbiter camera high resolution images8 from the mars global surveyor spacecraft and moderately high resolution thermal emission imaging system visible images9 from the mars odyssey spacecraft permit more comprehensive geologic and climatic analyses10 11 12 13 14 15 16 17 here i map and show the history of geologic materials and features in the north polar region that span the amazonian period 3 0 gyr ago to present 18 19 erosion and redeposition of putative circumpolar mud volcano deposits15 formed by eruption of liquefied fine grained material led to the formation of an early amazonian polar plateau consisting of dark layered materials crater ejecta superposed on pedestals indicate that a thin mantle was present during most of the amazonian suggesting generally higher obliquity and insolation conditions at the poles than at present brighter polar layered deposits rest unconformably on the dark layers and formed mainly during lower obliquity over the past 4 5 myr ref 20 finally the uppermost layers post date the latest downtrend in obliquity 20 000 years ago20

mars north polar deposits stratigraphy age and geodynamical response the shallow radar sharad on the mars reconnaissance orbiter has imaged the internal stratigraphy of the north polar layered deposits of mars radar reflections within the deposits reveal a laterally continuous deposition of layers which typically consist of four packets of finely spaced reflectors separated by homogeneous interpacket regions of nearly pure ice the packet interpacket structure can be explained by approximately million year periodicities in mars obliquity or orbital eccentricity the observed 100 meter maximum deflection of the underlying substrate in response to the ice load implies that the present day thickness of an equilibrium elastic lithosphere is greater than 300 kilometers alternatively the response to the load may be in a transient state controlled by mantle viscosity both scenarios probably require that mars has a subchondritic abundance of heat producing elements

the state and future of mars polar science and exploration as the planet s principal cold traps the martian polar regions have accumulated extensive mantles of ice and dust that cover individual areas of 10 6 km 2 and total as much as 3 4 km thick from the scarcity of superposed craters on their surface these layered deposits are thought to be comparatively young preserving a record of the seasonal and climatic cycling of atmospheric co 2 h 2o and dust over the past 10 5 10 8 years for this reason the martian polar deposits may serve as a rosetta stone for understanding the geologic and climatic history of the planet documenting variations in insolation due to quasiperiodic oscillations in the planet s obliquity and orbital elements volatile mass balance atmospheric composition dust storm activity volcanic eruptions large impacts catastrophic floods solar luminosity supernovae and perhaps even a record of microbial life beyond their scientific value the polar regions may soon prove important for another reason providing a valuable and accessible reservoir of water to support the long term human exploration of mars in this paper we assess the current state of mars polar research identify the key questions that motivate the exploration of the polar regions discuss the extent to which current missions will address these questions and speculate about what additional capabilities and investigations may be required to address the issues that remain outstanding

crater population and resurfacing of the martian north polar layered deposits present day accumulation in the north polar layered deposits npld is thought to occur via deposition on the north polar residual cap understanding current mass balance in relation to current climate would provide insight into the climatic record of the npld to constrain processes and rates of npld resurfacing a search for craters was conducted using images from the mars reconnaissance orbiter context camera one hundred thirty craters have been identified on the npld 95 of which are located within a region defined to represent recent accumulation high resolution imaging science experiment images of craters in this region reveal a morphological sequence of crater degradation that provides a qualitative understanding of processes involved in crater removal a classification system for these craters was developed based on the amount of apparent degradation and infilling and where possible depth diameter ratios were determined the temporal and spatial distribution of crater degradation is interpreted to be close to uniform through comparison of the size frequency distribution of these craters with the expected production function the craters are interpreted to be an equilibrium population with a crater of diameter d meters having a lifetime of 30 75d 1 14 years accumulation rates within these craters are estimated at 7 2d 0 14 mm yr which corresponds to values of 3 4 mm yr and are much higher than rates thought to apply to the surrounding flat terrain the current crater population is estimated to have accumulated in the last 20 kyr or less

sublimation waves geomorphic markers of interactions between icy planetary surfaces and winds abstract sublimation waves are periodic linear and transverse bedforms that grow by sublimation of icy substrates under turbulent winds they occur in different environments of the earth and other planets where the climate is favorable to sublimation their morphological and kinematic characteristics wavelength migration velocity characteristic time of formation depend on the environmental conditions in which they develop atmosphere viscosity wind speed sublimation rate to highlight these relations we designed a theoretical model for their formation based on models previously designed for dissolution bedforms from a linear stability analysis of the model we derived a dispersion relation and three scaling laws these are validated by comparison with measurements available for two natural terrestrial examples blue ice areas of the antarctic ice sheets and ice caves and with new measurements in a laboratory experiment they are applied to linear bedforms of hitherto unknown origin that we identified on the martian north polar cap we thus demonstrate that sublimation waves are convenient geomorphic markers to constrain surface compositions atmospheric properties climates and winds on terrestrial ice sheets and other icy planetary surfaces

the role of sublimation for the formation of the northern ice cap results from the mars orbiter laser altimeter abstract the evolutionary history of the martian ice caps is practically unknown and the caps are key to understanding the climatic history of mars sublimation and ice flow are two hypotheses that have recently been suggested to explain the observed form of the northern ice cap here we present a sublimation model and compare the shape of the cap obtained from this model with mars orbiter laser altimeter mola observations of the north polar region this model can reproduce the shape of the cap and individual troughs sublimation is an important process as are flow and wind erosion we were able to constrain the time scales of sublimation only to about two orders of magnitude 1 100 million years this estimate depends on many unknown parameters such as friction velocity and wind speed over the ice caps these can be determined only by direct measurement over the surface

seasonal variability in winds in the north polar region of mars abstract surface features near mars polar regions are very active suggesting that they are among the most dynamic places on the planet much of that activity is driven by seasonal winds that strongly influence the distribution of water ice and other particulates morphologic features such as the spiral troughs chasma boreale and prominent circumpolar dune fields have experienced persistent winds for several myr therefore detailing the pattern of winds throughout the year is an important step to understanding what processes affect the martian surface in contemporary and past epochs in this study we provide polar focused mesoscale simulations from northern spring to summer to understand variability from the diurnal to the seasonal scales we find that there is a strong seasonality to the diurnal surface wind speeds driven primarily by the retreat of the seasonal co 2 until about summer solstice when the co 2 is gone the fastest winds are found when the co 2 cap boundary is on the slopes of the north polar layered deposits providing a strong thermal gradient that enhances the season long katabatic effect mid summer winds while not as fast as spring winds may play a role in dune migration for some dune fields late summer wind speeds pick up as the seasonal cap returns

detrital zircon geochronology and regional correlation of metasedimentary rocks in the coast mountains southeastern alaska u pb ages have been determined for 55 detrital zircon grains from a metasedimentary sequence along the west flank of the coast mountains in southeastern alaska these rocks belong to the port houghton assemblage which consists of upper paleozoic pelitic and psammitic schist metaconglomerate metabasalt and marble the port houghton assemblage rests unconformably on metamorphosed and deformed mid paleozoic arc type volcanics endicott arm assemblage which gradationally overlie upper proterozoic lower paleozoic continental margin strata tracy arm assemblage three main clusters of ages are present 330 365 ma 19 grains 1710 2000 ma 27 grains and 2450 2680 ma 6 grains additional grains are approximately 2334 2364 and 3324 ma comparison of these ages with detrital zircon ages in other cordilleran assemblages supports previous interpretations that metasedimentary rocks in the coast mountains i form a southwestern continuation of the yukon tanana terrane of eastern alaska and yukon

north polar deposits of mars extreme purity of the water ice 1 the polar layered deposits are the largest reservoir of water on the surface of mars the physical properties of the ice and their spatial distribution are largely unknown 140 000 data points from the sounding radar sharad on the mars reconnaissance orbiter were analyzed over the gemina lingula region one fourth of the north polar layered deposits area maps of the dielectric properties of the bulk ice were drawn up there is no basal melting signature a drop of the dielectric constant in north west of gemina lingula could be explained by an abrupt 250 meter uplift of the base the bulk ice of the studied region has an average dielectric constant of 3 10 0 12 and a loss tangent 0 0026 0 0005 analytic interpretations shown the volume of ice is pure at 95 the impurities have a radial distribution with higher concentrations at margins

martian north polar layered deposits stratigraphy implications for accumulation rates and flow 1 we have used mars orbiter camera moc images and mars observer laser altimeter mola data to correlate specific layers within the upper 500 m of the martian north polar layered deposits in many troughs using these correlation results we derive relative accumulation rates across the polar layered deposits and through time we identify two major layer sequences one lying stratigraphically above the other each consistent with an overall curving downward layer structure with shallow slopes but with significant localized variations in layer height major disruptions of stratigraphy such as angular unconformities do not appear within the correlated layer sequences on local and broad scales each layer sequence exhibits a different relative accumulation rate pattern indicating that this rate has not remained constant through time and has been affected by localized processes the overall pattern of the lower layer sequence is similar to that of a classic terrestrial ice sheet with a decreasing relative accumulation rate away from the center of the polar layered deposits southward the upper layer sequence exhibits no obvious overall trends we also compare our correlation results to predictions of the effects of simple ice flow on layer structure finding that mass balance patterns have overprinted any effects of large scale ice flow flow has not been significant compared to mass balance in forming the overall structure of the correlated layers

structural geology and accretionary history of the northwest cascades system washington and british columbia pre tertiary rock units on the western flank of the cascades in washington and southern british columbia constitute the northwest cascades system nwcs this litho tectonic package is characterized by predominantly oceanic lithologies subjected to high p t metamorphism and structurally mixed to form a regional melange although the focus of this report is on rocks of the nwcs as originally defined survey of the regional geology suggests broadening of the limits of this system to include the san juan islands the pacific rim complex and pre tertiary rocks on the western flank of the central and southern washington cascades the shuksan metamorphic suite a relatively coherent and broadly exposed unit of the nwcs contains a regionally consistent stretching lineation which provides evidence of east northeast directed underthrusting subduction during the early cretaceous blue schist metamorphism metamorphic f2 folds are approximately normal to the stretching lineation and appear to have developed late in the same deformational event the melange structure postdates the high pressure regional metamorphism it is characterized by a tectonic assemblage of diverse and unrelated rock units occurring as fragments as much as 10 or more kilometres in breadth and separated by a network of low to high angle north northwest striking faults pre fault restoration is impossible argillaceous or serpentinitic material commonly occurs in deformation zones between more competent lithologies mylonite zones as much as several metres thick are widely developed and display stretched clast lineations indicating a north northwest south southeast transport direction for both low and high angle faults the high angle faults are therefore strike slip in nature shear sense indicators are mixed in thrust fault zones but many indicate dextral movement for the strike slip faults k ar whole rock ages of mylonites range from 20 127 ma but two late cretaceous ages of 87 and 91 3 ma are considered as best representing the time of faulting the inferred shift in direction of tectonic transport from east northeast west southwest during early cretaceous metamorphism to north northwest south southeast during late cretaceous faulting and melange formation is correlated with a mid cretaceous change in plate interaction between the north american and farallon kula plates from high to low angle convergence the nwcs melange is interpreted to have formed during large dextral transform motion along the continental margin and to have reached final emplacement by thrusting against the southern end of wrangellia and the coast plutonic complex

remagnetization during cretaceous normal superchron in eastern san juan islands wa implications for tectonic history abstract the eastern san juan islands expose an island arc ophiolite sequence and one or more ocean floor terranes cover rocks of the former including red radiolarian tuff and arc derived sandstone have no penetrative fabric and lack high pressure minerals in contrast pillow basalts and ribbon cherts of the latter are strongly deformed and the overlying metagraywacke is folded with a penetrative axial plane cleavage all ocean floor rocks have aragonite in veins indicative of higher pressure conditions than experienced by the island arc rocks a downward magnetization is common to the ocean floor rocks consistent with widespread remagnetization during the cretaceous normal superchron this magnetization is carried by magnetite and in red rocks by hematite fluid flow during or after deformation and high p metamorphism likely facilitated remagnetization at low temperature the magnetic directions are somewhat scattered but most are moderately to steeply down to the southeast they are far from directions expected with or without northward transport of baja bc rotation of observed directions into agreement with those expected for either present or more southerly locations also rotate structural elements in the host rocks three alternative rotation histories explored here all produce structural reconstructions that differ considerably from the present structure a tectonic history of the eastern san juan islands based on any of these reconstructions would be superior to one based on present attitudes of structures this is because at least a constraint that the restored paleomagnetic directions match a paleomagnetic field direction is satisfied choices among alternative reconstructions would become clearer with better understanding of relative ages of specific structures and their magnetizations improved geologic understanding of the regional setting where the rocks could have been deformed and remagnetized would also help

revised ages of blueschist metamorphism and the youngest pre thrusting rocks in the san juan islands washington new ages of rocks in the san juan islands northwest washington significantly change our understanding of the evolution of the san juan islands thrust system re examination of foraminifera bearing mudstones at richardson on lopez island indicates a late aptian 112 115 ma not late albian 100 ma age as currently presented in the literature the age brackets of thrusting marked by these pre thrusting mudstones and 84 ma post thrusting sedimentary rocks span a much longer period than previously thought diminishing controls on rates of displacement in the thrust system and the timing of regional deformation in western washington new 40 ar 39 ar plateau ages of phengite in blueschist facies meta volcanic rock also at richardson are 124 0 7 ma 2 late barremian these blueschist facies volcanic rocks are in fault contact with the fossiliferous mudstones therefore the blueschist facies metamorphism at richardson previously inferred to be associated with the thrusting now appears to have occurred prior to thrusting further the ar ages demonstrate that blueschist facies fabric formed earlier than the thrust event and is therefore not directly useful in analyzing the thrusting kinematics the richardson 40 ar 39 ar age is similar to isotopic ages found in the eastern san juan islands and in the shuksan blueschist terrane in the northwest cascades and thus fits into an emerging regional age pattern of blueschist facies metamorphism during late jurassic early cretaceous up to barremian but not late albian cenomanian if this pattern is more broadly confirmed for the san juan islands all the blueschist facies metamorphism can be regarded as having formed in subduction zones elsewhere along the continental margin rather than in the anomalous setting of an on land thrust system as in the san juan islands resume de nouveaux ges pour les roches des iles san juan dans le nord ouest de l etat de washington changent profondement notre comprehension de l evolution du systeme de chevauchement san juan un reexamen des mudstones foraminiferes a richardson sur l ile lopez indique un ge aptien tardif 112 115 ma et non albien tardif 100 ma tel qu indique actuellement dans la litterature les plages d ges pour le chevauchement marquees par ces mudstones precedant le chevauchement et des roches sedimentaires 84 ma posterieures au chevauchement couvrent une periode beaucoup plus grande que stipulee anterieurement diminuant les controles sur les taux de deplacement dans le systeme de chevauchement et le moment de la deformation regionale dans l ouest de l etat de washington de nouveaux ges plateaux 40 ar 39 ar de la phengite dans des roches volcaniques au facies des schistes bleus aussi a richardson datent

evaluating the meaning of layer in the martian north polar layered deposits and the impact on the climate connection abstract using data from the high resolution imaging science experiment hirise aboard the mars reconnaissance orbiter we reassess the methods by which layers within the north polar layered deposits npld can be delineated and their thicknesses measured apparent brightness and morphology alone are insufficient for this task high resolution topographic data are necessary from these analyses we find that the visible appearance of layers depends to a large degree on the distribution of younger mantling deposits which in turn is partially influenced by inherent layer properties and on the shape and location of the particular outcrop this younger mantle partially obscures layer morphology and brightness and is likely a cause of the gradational contacts between individual layers at this scale high resolution images reveal that there are several layers similar in appearance to the well known marker bed discovered by malin m edgett k 2001 j geophys res 106 23429 23570 the morphology thicknesses 4 8 2 m and separation distances 5 32 2 m of these marker beds as gleaned from a high resolution stereo digital elevation model lend insight into the connection between stratigraphy and climate

modeling sublimation of ice exposed by new impacts in the martian mid latitudes abstract new impacts in the martian mid latitudes have exposed near surface ice this ice is observed to slowly fade over timescales of months in the present martian climate exposed surface ice is unstable during summer months in the mid latitudes and will sublimate we model the sublimation of ice at five new impact sites and examine the implications of its persistence even with generally conservative assumptions for most reasonable choices of parameters it is likely that over a millimeter of sublimation occurred in the period during which the ice was observed to fade the persistence of visible ice through such sublimation suggests that the ice is relatively pure rather than pore filling such ice could be analogous to the nearly pure ice observed by the phoenix lander in the dodo goldilocks trench and suggests that the high ice contents reported by the mars odyssey gamma ray spectrometer at high latitudes extend to the mid latitudes our observations are consistent with a model of the martian ice table in which a layer with high volumetric ice content overlies pore filling ice although other structures are possible

in situ measurements of antarctic snow compaction compared with predictions of models 1 we describe in situ measurements of the compaction of antarctic snow at three different sites in antarctica the rate of compaction was measured hourly over various depth intervals for up to two years these measurements show that compaction at each of the sites occurs through slow viscous deformation of the snowpack with no significant contribution from sudden collapse of weak layers the measured rates of compaction at the coldest site exhibit a strong seasonality consistent with a temperature dependent sintering mechanism having activation energy of 70 kj mol 1 at the two warmer sites activation energies of 80 and 120 kj mol 1 provide slightly better agreement with the observations published models of snow compaction underestimate the temperature sensitivity a good match to our observations is provided by a semi empirical model based on rate equations for lattice diffusion nabarro herring creep of material around pores combined with normal grain growth this model also provides a theoretical basis for a widely used empirical model of snow compaction the rate coefficient for lattice diffusion inferred from our measurements is considerably higher than published values however and other creep mechanisms cannot be ruled out

cyclostratigraphy and its revolutionizing applications in the earth and planetary sciences over the past 25 yr the science of stratigraphy has evolved to include time correlative data from vastly disparate components of the earth system not least of these is the global signal afforded by cyclostratigraphy which has recorded the evolution of earth s astronomical milankovitch forcing of insolation and the paleoclimate system fossil astronomical signals are collected from cyclic sedimentary sequences by detailed sampling and study of facies geochemistry mineralogy rock magnetism color etc in step with the documentation of astronomically forced paleoclimate from ever older older geologic times innovations in computational science have provided ever longer high accuracy astronomical model targets that can be used for time scale calibration the earth s orbit is affected by motions of other planets notably the orbital perihelia of venus and jupiter which impose a dominant 405 k y eccentricity cycle on earth s orbital evolution the large mass of jupiter stabilizes this cycle over hundreds of millions of years the cyclostratigraphic record of 405 k y cycles is therefore often used to correct chronologies affected by variable sedimentation earth s shape and rotation rate are influenced by tidal dissipation and climate friction these effects affect earth s precession rate through time thus a record of earth moon evolution is also embedded in cyclostratigraphy the geochronologic value of cyclostratigraphy has been affirmed through intercalibration with high precision radioisotope dating which today has the potential to define the ages of stratigraphic horizons with 2 uncertainties at the scale of a precession cycle precession index phasing relative to that of the obliquity elucidates the seasonal nature of astronomical forcing of the paleoclimate system cyclostratigraphy contributes to our knowledge of planetary dynamics for times prior to the current ca 50 ma limit of accurate astronomical solutions and it will guide our future understanding of solar system evolution and the evidence for chaotic diffusion astronomical modeling is undergoing its own revolution with development of new numerical integrators to extend accuracy further back in time finally space exploration has revealed prominent sedimentary bedding and ice stratigraphy on the surface of mars with patterns suggestive of astronomical forcing analogous to earth

the spiral troughs of mars as cyclic steps we combine observations of stratigraphy morphology and atmospheric processes to relate the spiral troughs on mars polar layered deposits to a class of features known as cyclic steps cyclic steps are quasi stable repeating and upstream migrating bed forms that have been studied in terrestrial and submarine environments the repeating pattern is bounded by hydraulic jumps which act to stabilize the form we use radar stratigraphy from the shallow radar instrument on mars reconnaissance orbiter to examine trough evolution and constrain lateral transport we examine visible images from the thermal emission imaging system and observe low altitude clouds that we interpret to be the result of katabatic jumps i e the aeolian counterpart of hydraulic jumps in open channel flow we then devise a theoretical framework for understanding the origin of the spiral troughs that agree with 10 criteria that should be explained for any scenario to satisfactorily model the spiral troughs finally we use froude and geometrical analysis to estimate the rate of upstream migration caused by katabatic winds for the spiral troughs

introduction to the 4th mars polar science and exploration conference special issue five top questions in mars polar science abstract as an introduction to this icarus special issue for the 4th mars polar science and exploration conference we discuss five key questions in mars polar science gleaned from plenary discussions and presentations held at the conference these questions highlight major unknowns in the field 1 what are the physical characteristics of the polar layered deposits pld and how are the different geologic units within beneath and surrounding the pld related 2 how old are the pld and what are their glacial fluvial depositional and erosional histories 3 what are the mass and energy budgets of the pld and what processes control these budgets on seasonal and longer timescales 4 what chronology compositional variability and record of climatic change is expressed in the stratigraphy of the pld 5 how have volatiles and dust been exchanged between polar and non polar reservoirs and how has this exchange affected the past and present distribution of surface and subsurface ice

dispersed remnants of a northeast pacific fringing arc upper paleozoic terranes of permian mccloud faunal affinity western u s two fragmentary subparallel belts of terranes within the western north american cordillera contain upper paleozoic rocks and are characterized by contrasting lithotectonic assemblages and contrasting permian faunal affinity these two belts are a volcanic arc related successions of permian mccloud faunal affinity mccloud belt and b subduction related accretionary complexes of permian tethy an faunal affinity cache creek belt this paper supports the hypothesis that the fragmentary terranes of the mccloud belt once constituted parts of a northeast pacific fringing arc system and in constrast to some earlier interpretations concludes that the volcanic arc evolved above an eastward dipping subduction zone the absolute distance between this arc and western north america during the late paleozoic cannot be constrained however there is little evidence to suggest closure of a major 10 km ocean basin or protracted periods of westward dipping subduction parts of devonian to permian volcanic island arc sequences of the western u s cordillera are represented in the northern sierra eastern klamath bilk creek grindstone and chilliwack terranes these scattered volcanic arc remnants share several fundamental characteristics 1 the sequences were constructed across continental affinity basement assemblages 2 they underwent similar tectonic evolution during late paleozoic time such as coeval pulses in volcanism and related depositional histories 3 they contain early permian mccloud type fauna of distinctive biogeographic affinity 4 mccloud belt terranes are spatially and possibly genetically related to westward lying accretionary complexes of the cache creek belt which contain fragments of upper triassic blueschist and permian limestone blocks bearing tethyan permian fusulinids and corals based on the presence of distinctive early permian mccloud fauna the island arc remnants discussed in this paper are referred to as the mccloud belt the similarities between mccloud belt terranes suggest that they were once parts of a long lived late paleozoic volcanic arc complex the stratigraphy of these terranes records the tectonic evolution of the volcanic arc volcanism within the paleozoic arc began as early as the early devonian and was succeeded or accompanied by carbonate and epiclastic sedimentation during the middle and late devonian an influx of detritus derived from sedimentary and metasedimentary rocks during the late devonian and mississippian records the uplift and erosion of arc basement sequences an event that was at least locally accompanied by ongoing volcanism a pulse in volcanism during the pennsylvanian and coeval uplift led to the establishment of shallow marine and deltaic volcanogenic and carbonate sedimentation and locally subaerial exposure which persisted into the early early permian elsewhere during the early permian shallow water carbonate deposition was established with only minor influx of volcanogenic debris during the late permian and locally as early as late early permian a major pulse in volcanism occurred and is now represented by voluminous sequences of volcanogenic debris and lavas most of these sequences are overlain by upper triassic carbonate platformal sequences arc volcanism was recorded at least locally until the middle jurassic paleomagnetic data are used to constrain a schematic pre cretaceous reconstruction of these volcanic arc sequences and their associated subduction assemblages the inferred paleogeography of island arc sequences and the adjacent accretionary terranes suggests that volcanism occurred above an east dipping subduction zone with a long lived paleogeographic relation to north america the current structural position of these terranes is largely the result of mesozoic and locally younger deformation

signals of astronomical climate forcing in the exposure topography of the north polar layered deposits of mars nasa earth and space science fellowship nnx13ao55h nasa s mars reconnaissance orbiter project

correlation of early cretaceous blueschists in washington oregon and northern california the protolith and metamorphic histories of early cretaceous blueschists that occur in washington oregon and california are remarkably similar these blueschists are the shuksan metamorphic suite of northwestern washington the condrey mountain schist of northern california and southern oregon and the pickett peak terrane of northern california and southwestern oregon we suggest that these bodies were coextensive during their formation dispersion of the blueschists occurred in late cretaceous time by lateral translation of up to 900 km along the continental margin in response to oblique plate convergence

interplay of plutonism and regional deformation in an obliquely convergent arc southern coast belt british columbia the coast plutonic complex is an extensive zone of continental growth that formed along the mesozoic convergent margin of northwestern north america the orogeny creating this belt involved terrane accretion and assembly massive upward transfer and emplacement of sial in the form of batholiths constituting a magmatic arc and transformation of broad tracts of sedimentary and volcanic rocks into crystalline continental crust all operating in more or less the same space and time the mechanisms and interplay of these orogenic processes are well displayed in the harrison lake area of the southern coast belt british columbia great structural relief across the area exhibits a present day architecture defined by thin thrust stacked terrane sheets and early concordant pluton sheets folded on a macroscopic scale all truncated by oblique dextral reverse faults and overlain by later floored plutons construction of this complex began with terrane assembly on orogen normal thrusts during a lull in plutonism in the early cretaceous low grade metamorphism during this event indicates only modest crustal thickening subsequent plutons intruded into the assembled terranes appear to be composites of sheets early pluton sheets are now steeply dipping due to folding but were likely intruded as horizontal bodies large ovoid post folding plutons are mostly subhorizontal floored bodies at least in part sheeted these plutons are underlain by barrovian mineralogic aureoles that indicate downward vertical displacement of 10 km or more during plutonism suggesting pluton emplacement by vertical inflation magmatic fabrics in these bodies and the discordant relation of plutons to regional structures preclude emplacement in active fault zones penetrative strain aureoles flanking plutons are mostly limited to zones a few hundred meters wide and regional tectonic structures are widely preserved tectonic deformation of the arc is characterized by contraction and strike slip not orogen normal extension plutons played a greater role than terrane accretion in causing crustal thickening and high grade metamorphism

correlation of the tonga formation and the chiwaukum schist north cascades washington implications for late cretaceous orogenic mechanisms the tonga formation of the north cascades washington consists of weakly deformed bedded feldspathic graywacke and shale metamorphosed at chlorite to staurolite grade analysis of protolith lithology rb sr isotopic signature and plutonic metamorphic and deformational evolution in the tonga formation suggests that this unit is correlative with the chiwaukum schist of the cascades crystalline core the tonga formation occurs on the flank of the late cretaceous orogen whereas high grade chiwaukum schist is exposed in the core of the orogen metamorphic pressure as reflected by the distribution of metamorphic minerals and thermobarometry increases continuously northward in the tonga formation from the chlorite zone 4 kbar to the staurolite zone 7 kbar and then to the kyanite zone 7 kbar in the chiwaukum schist the findings reported herein do not support the previously advanced concept that the cascades crystalline core represents the easton blueschist terrane that was converted into higher temperature metamorphic rock by thermal relaxation after cessation of subduction the results of this study suggest a relatively simple two stage metamorphic history for the chiwaukum schist represented by 90 93 ma shallow contact metamorphism overprinted by harrovian metamorphism that increased sharply in pressure from south west to northeast and reached peak conditions after 90 ma all events occurring in a plutonic magmatic arc setting

dynamic and isotopic evolution of ice reservoirs on mars abstract the layered polar caps of mars have long been thought to be related to variations in orbit and axial tilt we dynamically link mars s past climate variations with the stratigraphy and isotopic composition of its ice by modeling the exchange of h2o and hdo among three reservoirs the model shows that the interplay among equatorial mid latitude and north polar layered deposits npld induces significant isotopic changes in the cap the diffusive properties of the sublimation lags and dust content in our model result in a cap size consistent with current mars the layer thicknesses are mostly controlled by obliquity variations but the precession period of 50 kyr dominates the variations in the isotopic composition during epochs of relatively low and nearly constant obliquity such as at present isotopic sampling of the top 100 m may reveal climate oscillations unseen in the layer thicknesses and would thus probe recent precession driven climate cycles

spiral trough diversity on the north pole of mars as seen by shallow radar sharad we combine observations from ground penetrating radar and optical instruments to conduct a comprehensive survey of spiral troughs on the north polar layered deposits of mars our survey reveals that all north polar troughs have common characteristics but there is strong regional diversity we divide the north polar layered deposits npld into eight regions based on observations of morphology and stratigraphy in order to classify the spiral troughs morphologic features that separate the regions include central promontories topographic undulations bedrock floors and trough asymmetry among others we demonstrate here that the troughs formed during two periods the first generation of troughs formed on the main lobe and in part of gemina lingula during accumulation of 600 m of ice and dust the second generation of troughs formed stratigraphically higher and immediately after large scale erosion in gemini scopuli which we conclude created the slopes necessary for troughs to form we test scenarios of trough evolution and find that only three concurrent processes are required for their formation wind transport insolation induced sublimation and atmospheric deposition our observations are inconsistent with other hypothesized processes to produce spiral troughs including incision after the formation of the npld fracturing due to flowing ice and sublimation driven patterns from insolation

regional stratigraphy of the south polar layered deposits promethei lingula mars discontinuity bounded units in images and radargrams abstract the mars south polar layered deposits spld are the result of depositional and erosional events which are marked by different stratigraphic sequences and erosional surfaces to unambiguously define the stratigraphic units at regional scale we mapped the spld on the basis of observed discontinuities i e unconformities correlative discontinuities and conformities as commonly done in terrestrial modern stratigraphy this methodology is defined as discontinuity bounded units or allostratigraphy and is complemented by geomorphological mapping our study focuses on promethei lingula pl and uses both high resolution images ctx hirise and radargrams sharad to combine surface and sub surface observations and obtain a 3d geological reconstruction of the spld one regional discontinuity named aur1 was defined within the studied stratigraphic succession and is exposed in several non contiguous outcrops around pl as well as observed at depth within the ice sheet this is the primary contact between two major depositional sequences showing a different texture at ctx resolution the lower sequence is characterized mainly by a ridge and trough morphology ridge and trough sequence rts and the upper sequence shows mainly by a stair stepped morphology stair stepped sequence sss on the basis of the observations we defined two regional discontinuity bounded units in pl respectively coinciding with rts and sss sequences our stratigraphic reconstruction provides new hints on the major scale events that shaped this region oscillations in martian axial obliquity could have controlled local climate conditions in the past affecting the pl geological record

is there an orbital signal in the polar layered deposits on mars do the polar layered deposits on mars refl ect orbital control or stochastic variability it is fi useful to determine whether an orbital signal would be detected even if present an estimate of the uncertainty in the time depth relationship of the polar stratigraphy shows that nonlinearities in this relationship and noise in the signal will hamper or preclude detection of orbital forcing even if layer composition is directly proportional to insolation indeed stratigraphic sections of the north polar layered deposits reconstructed from spacecraft images yield no clear evidence of orbital control and are largely consistent with an autoregressive stochastic formation process there is however a broad rise in spectral power centered on a wavelength of roughly 1 6 m that appears in many of the stratigraphic sections this bedding may record a time scale associated with processes internal to mars climate system perhaps related to dust storms alternatively if formed in response to variations in mars obliquity or orbital precession the 1 6 m bedding implies that the 1 km thick upper north polar layered deposits formed over 30 70 myr

local site effects in latur india an empirical study based on the aftershocks of the killari earthquake of september 29 1993 abstract the site amplification is estimated at five seismic stations of the latur region using the horizontal to vertical spectral ratios of 33 aftershocks of the main killari earthquake of september 29 1993 utc spectral amplifications ranging from a factor of 2 6 are found to vary with frequency at different places significant amplification is found at four sites within the latur region at basavakalyan kasgi killari and mudgad eakoji villages our results show a positive correlation between the site amplification and the damage pattern in area the pattern and the nature of the site amplification estimated in the present study corroborates also with the analytical models and the borehole data indicating alternating layers of unconsolidated sediments and basaltic rocks

sequence architecture of the cavi unit chasma boreale mars abstract the principles of terrestrial sequence stratigraphy provide a proven approach for evaluating the cavi unit where it transitions into the north polar layered deposits npld three cavi unit outcrops at the head of chasma boreale were examined using high resolution imagery and topography and interpreted in a sequence stratigraphic framework lithofacies present in the cavi unit were identified and consist of 1 dark lithic material 2 dark material with icy foresets 3 icy cavi 4 isolated dunes 5 dirty ice and 6 layered ice these lithofacies represent a progression in the dominance of aeolian to cryosphere processes and have analogs in the modern chasma boreale depositional environment parasequences were defined as aeolian units bounded by outcrop scale unconformities permafrost layers and layered ice deposits the northern outcrop is dominated by sandy lithofacies with large bodies of sand also dominating the northern parts of the central and southern outcrops in the central and southern outcrops sandy lithofacies yield southward to icier accumulations concurrently vertical trends in lithofacies distribution indicate an increasing prevalence of ice deposits through time considered across all three outcrops the parasequences form a set that expresses the northward retreat of the cavi aeolian system coincident with transgression of an ice sheet originating in gemini lingula this retrogradational stacking pattern of cavi aeolian parasequences with gradual transgression of the npld environment implies that the transitional cavi unit and npld form a single sequence that may correspond to allogenic forcing by orbital parameters the dynamics between aeolian and cryosphere processes revealed at the parasequence scale indicate that preservation of the stratigraphic record is driven by the ice transgression suggesting that during episodes of ice sheet collapse the north polar sedimentary environment reverts to one dominated by aeolian erosion and reworking as represented by the basal cavi unit

subsurface structure of planum boreum from mars reconnaissance orbiter shallow radar soundings abstract we map the subsurface structure of planum boreum using sounding data from the shallow radar sharad instrument onboard the mars reconnaissance orbiter radar coverage throughout the 1 000 000 km2 area reveals widespread reflections from basal and internal interfaces of the north polar layered deposits npld a dome shaped zone of diffuse reflectivity up to 12 s 1 km thick underlies two thirds of the npld predominantly in the main lobe but also extending into the gemina lingula lobe across chasma boreale we equate this zone with a basal unit identified in image data as amazonian sand rich layered deposits byrne s murray b c 2002 j geophys res 107 5044 12 pp doi 10 1029 2001je001615 fishbaugh k e head j w 2005 icarus 174 444 474 tanaka k l rodriguez j a p skinner j a bourke m c fortezzo c m herkenhoff k e kolb e j okubo c h 2008 icarus 196 318 358 elsewhere the npld base is remarkably flat lying and co planar with the exposed surface of the surrounding vastitas borealis materials within the npld we delineate and map four units based on the radar layer packets of phillips et al phillips r j and 26 colleagues 2008 science 320 1182 1185 that extend throughout the deposits and a fifth unit confined to eastern gemina lingula we estimate the volume of each internal unit and of the entire npld stack 821 000 km3 exclusive of the basal unit correlation of these units to models of insolation cycles and polar deposition laskar j levrard b mustard j f 2002 nature 419 375 377 levrard b forget f montmessin f laskar j 2007 j geophys res 112 e06012 18 pp doi 10 1029 2006je002772 is consistent with the 4 2 ma age of the oldest preserved npld obtained by levrard et al levrard b forget f montmessin f laskar j 2007 j geophys res 112 e06012 18 pp doi 10 1029 2006je002772 we suggest a dominant layering mechanism of dust content variation during accumulation rather than one of lag production during periods of sublimation

recent formation and evolution of northern martian polar layered deposits as inferred from a global climate model 1 we present a time marching model which simulates the exchange of water ice between the martian northern cap the tropics and a high latitude surface reservoir net annual exchange rates of water and their sensitivity to variations in orbital rotational parameters are examined using the martian water cycle modeled by the lmd three dimensional global climate model these rates are propagated over the last 10 myr to follow the thickness of the reservoirs the effect of a sublimation dust lag is taken account to test simple models of layer formation periods of high mean polar summer insolation 5 10 ma ago lead to a rapid exhaustion of a northern polar cap and a prolonged formation of tropical glaciers the formation of a northern cap and of a high latitude icy mantle may have started 4 ma ago with the average decrease of polar insolation tropical ice may have disappeared around 2 7 ma ago but small glaciers could have formed during the last peaks of polar summer insolation over the last 4 myr most of the present cap may have formed at the expense of tropical and high latitude reservoirs forming distinct layers at almost each 51 kyr 120 kyr insolation cycle layers thickness ranges from 10 to 80 m variations being produced by the modulation of the obliquity with 2 4 and 1 3 myr periods because only 30 insolation cycles have occurred since 4 ma ago we found an inconsistency between the recent astronomical forcing the observed number of layers and simple astronomically based scenarios of layers formation

aeolian processes as drivers of landform evolution at the south pole of mars abstract we combine observations of surface morphology topography subsurface stratigraphy and near surface clouds with mesoscale simulations of south polar winds and temperature to investigate processes governing the evolution of spiral troughs on the south pole of mars in general we find that the south polar troughs are cyclic steps that all formed during an erosional period contrary to the troughs at the north pole which are constructional features the shallow radar instrument sharad onboard mars reconnaissance orbiter detects subsurface stratigraphy indicating relatively recent accumulation that occurred post trough formation in many locations using optical instruments especially the thermal emission imaging system themis we find low altitude trough clouds in over 500 images spanning 6 mars years the locations of detected clouds correspond to where recent accumulation is detected by sharad and offers clues about surface evolution the clouds migrate by season moving poleward from 71 s at l s 200 until l s 318 when the last cloud is detected our atmospheric simulations find that the fastest winds on the pole are found roughly near the external boundary of the seasonal co 2 ice cap thus we find that the migration of clouds and katabatic jumps corresponds spatially to the retreat of the co 2 seasonal ice as detected by titus 2005 and that trough morphology through recent accumulation is integrally related to this seasonal retreat