deep seated gravitational slope deformations related landslides and tectonics abstract deep seated gravitational slope deformations and their relationships with tectonic deformation of rocks is considered to examine the viewpoint of tectonics as a causative factor in slope deformation first a distinction is made between the different types of deep seated gravitational slope deformation then the geomorphological and structural effects of the different macrostructural deformations induced by tectonics on the scale of the whole deforming ridge is briefly discussed finally some case studies that represent either verified or possible cases of gravity deformation in response to tectonic activity are used as illustration

landslides and climate change in the italian dolomites since the late glacial abstract the paper deals with the relationship between the temporal occurrence of landslides and climatic changes in the italian dolomites since the late glacial after an introduction on the state of the art with particular reference to the alpine region the results of recent investigations in the two study sites are illustrated at cortina d ampezzo several landslides were dated mainly by the radiocarbon method the most ancient landslide event there involved large rock slides which affected the dolomitic slopes following the withdrawal of glaciers after the last glacial maximum lgm and also slides and flows mainly occurring in pelitic materials of the valley floors from 13 000 to 10 000 cal bp a later series of flows occurred between 5500 and 2500 cal bp in the upper badia valley alta badia the most ancient events go back to 10 000 and 9000 cal bp and correspond with earth flows that followed vast rotational slides affecting the bedrock up to a depth of about 50 m more recent earth flows involving more modest amounts of material took place between 6500 and 2300 cal bp by analysing the dates from the two study areas it was possible to correlate the recorded increase of landslide activity with the climatic changes occurring at the boundary between the late glacial and the holocene and between the atlantic and the subboreal and to compare the results with those derived from other european regions the types and causes of landslides taking place in these two periods were substantially different reflecting the different morphoclimatic conditions that existed in the two areas when these mass movements were triggered finally notwithstanding the importance of non climatic causes such as geological structural factors and possible human influences it is concluded that many of the dated landslides can be considered as indicators of climatic change

a new model for the emplacement of columbia river basalts as large inflated pahoehoe lava flow fields extensive flows of the columbia river basalt crb group in washington oregon and idaho are dominantly inflated compound pahoehoe sheet lavas early studies recognized that crb lavas are compound pahoehoe flows with textures suggesting low flow velocities but it was thought that the great thickness and extent of the major flows required very rapid emplacement as turbulent floods of lava over a period of days or weeks however small volume 1 km compound pahoehoe flows on kilauea hawai i demonstrate that such flows can thicken by at least an order of magnitude through gradual inflation and the same mechanism has been proposed for larger 10 20 km3 pahoehoe flows in iceland the vertical distribution of vesicles and other morphologic features within crb lava flows indicate that they grew similarly by inflation small pahoehoe lobes at the base and top of many crb pahoehoe lava flows indicate emplacement in a gradual piecemeal manner rather than as a single flood we propose that each thick crb sheet flow was active for months to years and that each group of flows produced by a single eruption a flow field was emplaced slowly over many years

isotopically depleted late pleistocene groundwater in columbia river basalt aquifers evidence for recharge of glacial lake missoula floodwaters 1 late pleistocene outburst flooding of ice dammed glacial lake missoula and possible discharge from the cordilleran ice sheet cis catastrophically altered the northwestern united states landscape yet little is known about potential infiltration of flood waters into the subsurface this study provides compelling evidence for the presence of late pleistocene cis related recharge waters in the columbia river basalt aquifers crbas in central washington crba groundwaters with corrected 14c ages from 15 7 and 33 3 k yrs bp during periods of flood events have anomalously low 18o values 18 9 to 17 6 compared to late pleistocene soil waters 16 1 to 13 4 and modern precipitation in the region average 15 9 consistent with cis related meltwater recharge these results have implications for our understanding of megaflood phenomena on earth and mars

geomagnetic fluctuations during a polarity transition the extensive roza member of the columbia river basalt group washington state has intermediate paleomagnetic directions bracketed by underlying normal and overlying reverse polarity flows a consistent paleomagnetic direction was measured at 11 widely distributed outcrops the average direction has a declination of 189 and an inclination of 5 with greater variation in the inclination rietman 1966 in this study the roza member was sampled in two pasco basin drillcores where it is a single cooling unit and its thickness exceeds 50 m excellent core recovery allowed uniform and dense sampling of the drillcores during its protracted cooling the roza flow in the drillcores recorded part of a 15 5 ma geomagnetic polarity transition the inclination has symmetric quasicyclic intraflow variation while the declination is nearly constant consistent with the results from the outcrops thermal models of the cooling flow provide the timing for remanence acquisition the inclination is inferred to have progressed from 0 to 15 and back to 3 over a period of 15 to 60 years at rates of 1 6 to 0 5 yr because the geomagnetic intensity was probably weak during the transition these apparently high rates of change are not significantly different from present day secular variation these results agree with the hypothesis that normal secular variation persists through geomagnetic transitions the iow amplitude quasicyclical fluctuations of the field over tens of years recorded by roza suggest that the geomagnetic field reverses in discrete steps and that more than 15 60 years were required to complete this reversal

preeruption history of the grande ronde formation lavas columbia river basalt group american northwest evidence from phenocrysts basaltic andesite lavas belonging to the grande ronde formation constitute 87 of the columbia river basalt group although these lavas are chemically evolved they generally contain 5 phenocrysts two hypotheses have been proposed to explain this observation the first hypothesis suggests that grande ronde lavas were near primary melts generated by large scale melting of eclogite from the inferred yellowstone plume the alternative hypothesis proposes that grande ronde magmas were extremely hydrous and rose rapidly from the mantle such that the dissolved water kept the magmas close to their liquidi we present new information on textures and mineral chemistry of phenocrysts in two well characterized field sections through the grande ronde formation the new data lead us to conclude that at least some of the grande ronde primary magmas were highly hydrous however they all underwent extensive fractionation magma mixing and degassing in a shallow intrusive network prior to eruption as lava

long term gravitational deformation of rocks by mass rock creep abstract subsurface rocks beneath slopes are deformed to various degrees in various ways by mass rock creep mrc when they are subjected to a gravitationally unstable state for a long period mrc forms folds faults and numerous kinds of fractures such deformation is one of the main factors for deteriorating rock masses on slopes and also precursors of many landslides mrc deformations which have often been ascribed to tectonic origins can be distinguished from tectonic ones by their deformational features landforms and relationships between slope morphology and subsurface structures mrc folds are flexural slip folds that have the following mesoscopic to microscopic characteristics their axial surfaces are not smooth but are jagged and many visible openings or open fractures develop in association with the folds the jagged axial surfaces become smoother at depth and openings decrease in width with increasing overburden at the deformation site macroscopic types of mrc folds change according to the relationship between foliations and slopes buckling folds form in consequent slopes drag folds form in a deeper part of obsequent slopes and bending folds form in slopes with steep dipping foliations consequent or obsequent by downslope bowing of foliations shear fractures and tension fractures are the main deformational structures formed by mrc in massive rocks among shear fractures those of listric origin are remarkable tension fractures in general occur either in networks dividing rocks into fragments that slip and rotate irregularly in relation to each other or in parallel arrays of steeply dipping fractures an mrc fault has a shear zone consisting of a pulverized zone with gouge and a phyllitic or brecciated zone in a densely foliated rock the phyllitic zone is formed by microscopic slip along foliations in a sparsely foliated rock the brecciated zone is formed by random crushing except for the faults made through the shear fractures in massive rocks landforms due to mrc are gentle slopes bounded by horseshoe knicklines upslope convex slopes ridge top depressions multiple ridges uphill facing scarps and ridge crossing depressions

the roza member columbia river basalt group a gigantic pahoehoe lava flow field formed by endogenous processes we present studies on the physical volcanology of the 15 ma roza member of the wanapum formation in the columbia river basalt group the roza member represents a compound pahoehoe flood basalt lava flow field with an area of 40 300 km 2 and a volume of 1300 km 3 it consists of 4 major lava flows each composed of numerous decimeter to kilometer long pahoehoe lobes roza lavas feature a wide range of pahoehoe surface structures such as lava rise plateaus tumuli and surface breakouts and we illustrate that the lava morphology is inconsistent with previous proposals of rapid emplacement for these lavas an integral component of the roza flow field is the sheet lobe with internal structures identical to those of inflated pahoehoe sheet lobes from hawaii and iceland both at the same scale and at much larger scales we identify a three part division of the sheet lobes into basal crust lava core and lava crust which are interpreted as the equivalent to the bottom crust the liquid lava core and the surface crust of an active inflating pahoehoe lobe the upper lava crust grows continuously during lava emplacement and its growth rate can be approximated by conductive cooling this relationship is used to calculate the emplacement time for individual roza sheet lobes and to derive a first order estimate on the duration of the roza eruption the results indicate that the emplacement of individual roza lobes lasted for months to years and that the lava flow field was constructed over a period of at least 14 years we propose that the roza flows achieved great areal dimensions and thicknesses by inflation and endogenous growth as the lava flowed from vent to flow front it traveled under an insulating crust which maintained cooling rates of 0 1 c km and allowed for efficient transport of lava over distances up to 300 km

the eruption environment of multi tiered columnar basalt lava flows field studies on the eruption environment and prevailing cooling conditions of multi tiered lava flows of the type exemplified by the giant s causeway were carried out at localities on the columbia river plateau southern iceland on the islands of mull and staffa and around the giant s causeway ne ireland common features can be recognized in the volcanology of such flows in all the localities examined these include palaeotopographic evidence of river valleys giving conditions conducive to the ponding of flows and the damming of existing drainage evidence of high rainfall regimes or abundant surface water association of interlava lacustrine and fluviatile sediments association of hyaloclastite flow foot breccias within multi tiered basalt lava successions and evidence of large volume lava flows and high eruption rates examination of the petrography of the upper curvi columnar parts of the lava the entablature shows textural signs of quenching compared with the lower more regular columnar zone the colonnade these common field and petrographic features confirm the model of multi tiered flow formation by modification of the cooling regime in the upper part of the flow following inundation of the hot lava surface by displaced river drainage

sequence response to syndepositional regional uplift insights from high resolution sequence stratigraphy of late early pleistocene strata periadriatic basin central italy abstract this paper deals with the depositional sequences that occur within the uppermost part of the plio pleistocene periadriatic basin fill in the southern marche region central italy the succession is an early pleistocene easterly dipping clastic wedge showing an overall shallowing trend from slope clays to shallow marine and non marine deposits comprising two major sequences namely qmb and qmc analysis has provided new insights into i the nature of sedimentary facies and facies associations occurring within the upper part of qmb and qmc ii the gradual contact within qmb between regressive littoral deposits rld and underlying deep marine blue clays iii the composite origin of the emilian surface which is a widespread erosional unconformity separating qmb from qmc iv the cyclothemic pattern of qmc composed of downstepping small scale depositional sequences v the role played by synsedimentary uplift on the stacking pattern of small scale sequences and their internal architecture up to three small scale depositional sequences have been recognised within qmc qmc1 qmc2 and qmc3 they are up to 50 m thick and defined by previously unrecorded lower rank regionally extensive surfaces facies organization indicates that as a rule in ascending stratigraphic order each small scale sequence may includes a distinctive basal unconformity surface that can be traced from incised valleys to associated interfluves an incised valley fill a transgressive surface of marine erosion a transgressive systems tract a highstand systems tract a regressive surface of marine erosion and an attached falling stage systems tract in proximal positions the small scale sequences are dominated by transgressive and highstand systems tracts with incised valley fills and falling stage systems tracts absent or volumetrically much less significant in relatively basinward locations where the regressive surfaces of marine erosion converge with the lower sequence boundary the falling stage systems tract may represent the entire depositional sequence high frequency sequences display a distinctive stacking pattern and form a tectonically induced forced regressive sequence set underlain by a composite tectonically enhanced regressive surface of marine erosion formed by the lateral connection of lower rank sequence boundaries

diagenesis and organic maturation of sedimentary rocks under volcanic strata oregon 1 in the pacific northwest diagenesis of cretaceous strata mantled by extrusive volcanic rocks occurred at temperatures of 150 200 degrees c due to heat conducted downward from a perched confined geothermal aquifer this aquifer produced a homogeneous temperature field within the underlying sedimentary rock authigenic minerals such as sphene chlorite illite and quartz developed throughout a vertical section composed of andesites basalts and both silicic and mafic sedimentary rocks the geologically rapid heating also resulted in nearly constant organic maturation profiles within the sedimentary rock and produced unknown quantities of hydrocarbons the contemporaneous diagenesis and maturation took place before extrusion of the columbia river basalt group and was p rhaps associated with earlier intrusive activity such hydrothermal maturation accounts for both local diagenesis and other organic maturation anomalies in the pacific northwest the mechanism has ramifications for the petroleum potential of geologically active basins because it provides a means by which volcanism and associated geothermal activity can increase maturation and generate hydrocarbons

crystal mush compaction in the cohassett flood basalt flow hanford washington abstract the 40 m thick central part of the cohassett flow which was probably emplaced by inflation of an earlier more ti rich flow exhibits textural evidence of crystal mush compaction during solidification although most of the crystallization started in the roof zone as water circulated through fractures in the crust plumes of dense crystal mush must have dripped from the roof to the floor of the sheet thus displacing upward the colonnade entablature boundary the mush initially consisted of loosely stacked plagioclase crystals and liquid surrounding rapidly grown pyroxene oikocrysts containing radial chadacrysts of plagioclase upon compaction in the floor zone the liquid between the loosely stacked plagioclase crystals was expelled as the crystals packed tightly together to form sub parallel grains wrapped around the pyroxene oikocrysts which recrystallized into granular aggregates of augite and pigeonite stacks of sinking plagioclase crystals and rising liquid accumulated on the upper and lower sides respectively of horizontal plagioclase phenocrysts this asymmetric texture clearly indicates the relative motion of solids and liquid the degree of compaction as determined from variations in the amount of interstitial liquid and quantitative measures of textural anisotropy accounts for the chemical variation through the central part of the flow with compatible elements being concentrated in the lower part of the flow and incompatible elements concentrated in the upper part modeling of the compaction process using the iridium melt infiltration and reaction program of boudreau a 2003 iridium a program to model reaction of silicate liquid infiltrating a porous solid assemblage computers and geosciences 29 423 429 shows that the observed chemical and compaction dilation profiles are to be expected in a 40 m thick sheet of basaltic magma solidifying on the earth s surface compaction of crystal mush should be even more likely in slowly cooled intrusive bodies

volcanological and tectonic control of stratigraphy and structure in the western deccan traps many of the world s flood basalt provinces form elevated plateaux at the margins of continents although in most cases their present large elevation is not the result of mountain building processes several explanations have recently been put forward to explain such occurrences of epeirogeny the deccan trap basalt province forms one such elevated plateau and results are presented here showing how the epeirogenic uplift in this region combined with crustal subsidence probably associated with the rifting of the indian continental margin has affected the structure of the basalt sequence trace element analytical data are used for samples from numerous vertical sections through the deccan traps lava series along and around the western ghats ridge in india the results reinforce the previously defined stratigraphy of the mahabaleshwar area and extend it over a region covering some 36 000 km2 reaching as far south as belgaum and the trap basement contact these results show that the lava pile is not flat lying but forms a very low amplitude anticlinal fold structure plunging southwards by up to 0 3 over most of the area although in the south there is evidence of a reversal of this plunge the fold is interpreted as being the result of two tilting processes 1 westward tilting near the coast due to the foundering of the passive continental margin and 2 epeirogenic uplift along the whole west coast of india producing the observed topography and the peninsula wide drainage patterns and also the easterly component of dip variations in the magnitude of the latter effect along the western continental margin may also be important in generating the plunge of the fold although the possibility of some component of depositional dip may also be important this latter possibility can be modelled using a simple computer program the results of this modelling show that a migrating linear volcanic edifice fits the observations best

evolution of eureka flat a dust producing engine of the palouse loess usa sedimentologic stratigraphic and pedologic evidence demonstrates that eureka flat ef a narrow 80 km long deflation plain in south central washington usa is the source for the thick and widespread loess of the palouse region located in the southern columbia plateau ef has been a depocenter for abundant clay to sand sized sediment derived from repeated glacial outburst floods that swept through the area during the pleistocene prevailing sw winds that were funneled across ef remobilized flood sediment into sand dunes sand sheets and loess an eolian sand sheet buried beneath 1 8 m of loess at the downwind end of ef attests to bioclimatically driven changes in the style of eolian deposition the depositional transition from sand sheet to loess is characterized by a change from wind rippled strata to structureless bimodal sand and silt with insect burrows and rhizoliths to unimodal sandy loess soil moisture and density of dust trapping vegetation control where sand dunes and loess accumulate up to 4 5 m of post lgm loess mantles the landscape adjacent to and downwind from ef some of the thickest loess deposits owe their origins to the sequestering of eolian sand particles by topographic traps such as the touchet river and its tributary valleys the removal of saltating sand from the eolian system promotes thick accumulation of loess downwind of topographic traps patterns of loess accumulation across the columbia plateau are identified on isopach maps of major pre and post lgm loess units and show that ef has been the major engine for the production of atmospheric dust and loess during both times

emplacement of the youngest flood lava on mars a short turbulent story abstract recently acquired data from the high resolution imaging science experiment hirise context ctx imager and compact reconnaissance imaging spectrometer for mars crism onboard the mars reconnaissance orbiter mro spacecraft were used to investigate the emplacement of the youngest flood lava flow on mars careful mapping finds that the athabasca valles flood lava is the product of a single eruption and it covers 250 000 km 2 of western elysium planitia with an estimated 5000 7500 km 3 of mafic or ultramafic lava calculations utilizing topographic data enhanced with mro observations to refine the dimensions of the channel system show that this flood lava was emplaced turbulently over a period of only a few to several weeks this is the first well documented example of a turbulently emplaced flood lava anywhere in the solar system however mro data suggest that this same process may have operated in a number of martian channel systems the magnitude and dynamics of these lava floods are similar to the aqueous floods that are generally believed to have eroded the channels raising the intriguing possibility that mechanical erosion by lava could have played a role in their incision

geochemistry and petrogenesis of mashhad granitoids an insight into the geodynamic history of the paleo tethys in northeast of iran mashhad granitoids in northeast iran are part of the so called silk road arc that extended for 8300 km along the entire southern margin of eurasia from north china to europe and formed as the result of a north dipping subduction of the paleo tethys the exact timing of the final coalescence of the iran and turan plates in the silk road arc is poorly constrained and thus the study of the mashhad granitoids provides valuable information on the geodynamic history of the paleo tethys three distinct granitoid suites are developed in space and time ca 217 200 ma during evolution of the paleo tethys in the mashhad area they are 1 the quartz diorite tonalite granodiorite 2 the granodiorite and 3 the monzogranite quartz diorite tonalite granodiorite stock from dehnow vakilabad 217 4 215 4 ma intruded the pre late triassic metamorphosed rocks large granodiorite and monzogranite intrusions comprising the mashhad batholith were emplaced at 212 5 2 ma and 199 8 3 7 ma respectively the high initial 87 sr 86 sr ratios 0 708042 0 708368 low initial 143 nd 144 nd ratios 0 512044 0 51078 and low e nd t values 5 5 to 6 1 of quartz diorite tonalite granodiorite stock along with its metaluminous to mildly peraluminous character al 2o 3 cao na 2o k 2o mol 0 94 1 15 is consistent with geochemical features of i type granitoid magma this magma was derived from a mafic mantle source that was enriched by subducted slab materials the granodiorite suite has low contents of y 18 ppm and heavy ree hree yb 594 ppm and high ratio of sr y 35 that resemble geochemical characteristics of adakite intrusions the metaluminous to mildly peraluminous nature of granodiorite from mashhad batholiths as well as its initial 87 sr 86 sr ratios 0 705469 0 706356 initial 143 nd 144 nd ratios 0 512204 0 512225 and e nd t values 2 7 to 3 2 are typical of adakitic magmas generated by partial melting of a subducted slab these magmas were then hybridized in the mantle wedge with peridotite melt the quartz diorite tonalite granodiorite stock and granodiorite batholith could be considered as arc related granitoid intrusions which were emplaced during the northward subduction of paleo tethys ocean crust beneath the turan micro continent the monzogranite is strongly peraluminous al 2o 3 cao na 2o k 2o mol 1 07 1 17 alkali rich with normative corundum ranging between 1 19 and 2 37 has high initial 87 sr 86 sr ratios 0 707457 0 709710 and low initial 143 nd 144 nd ratios 0 512042 0 512111 and e nd t values 5 3 to 6 6 that substantiate with geochemical attributes of s type granites formed by dehydration melting of heterogeneous metasedimentary assemblages in thickened lower continental crust the monzogranite was emplaced as a consequence of high temperature metamorphism during the final integration of turan and iran plates the ages found in the mashhad granites show that the subduction of paleo tethys under the turan plate that led to the generation of arc related mashhad granites in late triassic finally ceased due to the collision of iran and turan micro plates in early jurassic

structural constraints on deep seated slope deformation kinematics abstract a significant sackung type deep seated slope gravitational deformation dsgsd was recognised for the first time by the authors in the middle part of valfurva east of bormio rhaetian alps italy the reconstruction of its kinematics age and state of activity is presented through a detailed description of its morphological geomechanical and structural features an integrated multi disciplinary approach was performed to achieve a clear comprehension of the phenomenon field surveys and aero photo interpretation were carried out in order to clarify the structural geological and geomorphological setting in which the dsgsd developed a kinematic conceptual model of the slope deformation was developed through the analysis of morpho structures of their significance and relationships with lithological markers and quaternary deposits after a geomechanical characterisation of the rock mass involved in the slope deformation numerical modelling was performed to verify the hypotheses made on kinematics and driving factors of the phenomenon the sackung affects pre permian metapelites metabasites and marbles belonging to the upper austroalpine basement of the campo nappe as well as late pleistocene and holocene glacial and rock glacier deposits the deformation started after the late wurmian age 15 000 11 000 years b p and continued until few centuries ago not excluding a present day low rate activity deformation consists in a large oblique sagging along a deep confined sliding surface associated with gravitational reactivation of pre existing late alpine and recent tectonic brittle structures leading to the formation of n s and wnw ese trending gravitational morpho structures the evolution of the wnw ese trending system resulting in asymmetric trenches led to progressive failure of the lower part of the slope during the last 10 000 years as testified by large paleo landslide accumulations and it is still in progress numerical modelling indicates post glacial unloading as the main triggering factor of the slope deformation the importance of this deep seated slope deformation is enhanced by the occurrence of the 30 mm 3 active ruinon landslide in the lower part of the slope such landslide is subjected to rapid evolution and threatens the valley floor establishing an important risk factor connected to human lives and socio economic activities

geologic and geochemical evidence for the nature and development of the middle proterozoic keweenawan midcontinent rift of north america abstract general models of active continental rifting must take into account the large plateau basalt provinces many of which have been precursors of or associated with continental breakup the keweenawan middle proterozoic midcontinent rift mcr of north america 2300 km long is one such major continental rift but it aborted before significant crustal separation was achieved these plateau basalt rifts including the mcr differ from the east african type in being dominated by broad subsidence rather than rift valleys tholeiitic flood basalts rather than alkalic central volcanoes and large positive gravity anomalies geologic and geophysical evidence is reviewed which contradicts some recent models which have been proposed for the development of the mcr the basic causes of the pre rift subsidence the u shaped nature of the structure and the abrupt termination of its activity are obscure a triple junction in the usual sense does not appear to have been formed

petrological evolution of the crust and mantle in its simplest form crust mantle evolution can be thought of as a study of the processes by which material is lost from the mantle and forms new crust the overall goal is achievement of mass balance between the average composition of material known to have been added to the crust and the estimated average composition of the entire crust attainment of this goal for the earth has been elusive primarily because the materials available for study have generally been involved in several stages of evolution including fractionation within both the crust and mantle and recycling of material from crust to mantle thereby complicating the interpretation of available data although the overall composition of the continental crust generally has been modelled as andesitic taylor and mclennan 1981a the present upper continental crust is granodioritic and requires a more mafic lower crust it has been proposed taylor and mclennan 1981a that originally the archean crust had an andesitic composition throughout its volume and that partial melting in the lower crust developed more felsic melts that rose to enrich the upper crust leaving a more mafic residuum of lower crust this concept has been challenged by weaver and tarney 1981a who argue that the granulites of presumed lower crustal origin do not have the correct compositions for this model if one considers more recent additions to the crust from the mantle over the past several hundred million years it appears that these latest additions are basaltic with very little if any granitic additions in fact barker 1981 in his introduction to a special issue of jgr on granites and rhyolites states to date no one has demonstrated that such magmas may form in the mantle indeed much experimental and geochemical work indicates that such siliceous liquids cannot originate there therefore such magmas must be generated in the crust in island arc environments where the average composition of added material normally is thought to be andesitic a anderson 1982 has shown that the parent melt is basaltic not andesitic in addition kay 1980 has shown that the k content of the newly added material is less than the average k content of the previously existing crust in the oceanic crust the additions from the mantle are basaltic and according to o hara 1982 probably are derived from very mafic picritic melts as parents continental flood basalts which have also added material from mantle to crust also are clearly derived from basaltic parental melts basaltic volcanism study project 1981 thus the evidence for the nature of material subtracted from the mantle and added to the crust for the past several hundred million or perhaps a billion years points to very mafic melts this contrasts significantly with the overall andesitic composition of continental crust it implies furthermore that if the overall archean crustal composition was andesitic as estimated by taylor and mclennan 1981a then additions to the crust have become more mafic with time a concept in direct conflict with most models in which secular trends are from mafic to felsic with time veizer and jansen 1979 and mclennan et al 198o a question which is beginning to appear either explicitly or implicitly is whether crustal volcanic rocks or the crust as a whole really represents the parent melt that formed in the mantle a anderson 1982 o hara 1982 and nisbet and walker 1982

failure and flow development of a complex slide the 1993 sesa landslide abstract large landslides are often characterised by complex activity resulting from their ability to suddenly change behaviour in fact these landslides can pass from a slump to a flow characterised by relatively high mobility this characteristic is a cause of extremely high severity and hazard in areas affected by such phenomena an interesting case of a large slide in glacial deposits which occurred in 1993 in the valcamonica of the italian alps is presented different approaches both to characterise the coarse frictional materials involved in the slide and to model the slide initiation and its evolution are adopted the initial slide mass had a volume of almost 2 mm 3 and after its initial sliding motion along the slope flowed for about 7 km down the main valley stream voight s method has been used to analyse measured slope displacements recorded for a few years before the slope failure this analysis provided evidence that different times of failure could have been predicted beforehand by rigorous examination of the available data laboratory tests and image processing techniques have been performed to characterise the landslide material as resembling a bimrock block in matrix material slope stability analyses have been performed and a dynamic modelling method has been tested on the flow by comparing its results to those obtained by analysis of eyewitness statements and field observations on the mudline left by the flow finally existing empirical approaches for hazard assessment on an alluvial fan have been applied and modified to produce a hazard zonation map for the alluvial fan area by considering maximum expected discharge local geometry of the channel and the possibility of channel occlusion and subsequent avulsion

rock physics modeling of a dispersed clay sandstone and dispersed quartz shale sequence abstract the elastic and petrophysical properties of the fluvial rocks of the miocene in the western basin of the gulf of thailand display typical signatures of dispersed clay sandstones and dispersed quartz shales that is the relationships between various properties exhibit two strong trends associated with a grain supported domain and a matrix supported domain the minimum porosity and maximum p velocity occur at the transition between these domains at a clay volume of approximately 40 50 this means that the hardest rocks occur at this transition a simple rock physics model has been developed that quantifies the elastic properties over a large depth range but does not explicitly account for the dispersed nature of the clay and quartz it employs a single aspect ratio at each depth within an inclusion based modeling scheme the required aspect ratio at each depth can be estimated from the depth the porosity and the clay volume of the rock

geomorphological evidence for anti apennine faults in the umbro marchean apennines and in the peri adriatic basin italy abstract the apennines are a relatively recent mountain chain which has been affected by uplift movements since the upper pliocene in fact the remnants of an erosional surface reduced close to base level is preserved at the top of the relief there is no general agreement on the geodynamic stress field and mechanisms which are creating the chain however it is largely accepted that uplift occurred together with the activation on the western side of the chain of extensive faults oriented in the apennine direction nw se which have been linked to the opening of the tyrrhenian sea a great debate is going on about the presence and significance of anti apennine faults ne sw which have been observed by some authors but completely denied by others the main evidence is represented by 1 block faulting of the remnants of the erosional surface along the marchean ridge more elevated relief delimiting relatively depressed areas was created in correspondence with the sibillini mts and mt s vicino similar evidence has been found in the umbro marchean ridge locally more than 1500 metres of displacement have been observed between more and less uplifted remnants 2 block faulting of fan deltas and related beaches of sicilian to crotonian age with more elevated sediments preserved between the tronto and tenna rivers and between the musone and esino rivers maximum displacement along a transect parallel to the coast is 200 metres 3 fault scarps affecting the middle pleistocene river terraces as observed along the esino the tronto the chienti and the tenna river valleys maximum displacements are in the order of 50 metres 4 faulting of horizontal karst galleries and reorientation of the cave network as in the frasassi gorge maximum displacements are about 100 metres 5 captures and alignments in the drainage network of the main river courses 6 large scale gravitational movements as in the ancona landslide and along the chienti and esino rivers their activation occurred in most cases after the lower pleistocene and although their displacements may be of relatively limited extent dispite their recent activity they played a major role in the modelling of the landscape these faults display transtensive extensional and trascurrent movements apart from the controversial geodynamic significance of these faults from a geomorphological point of view they must be considered transverse elements of the stress field from blocks more or less uplifted along the apennine chain the importance and timing of activity of these faults in the quaternary geomorphological evolution of the umbria marchean apennines is demonstrated using evidence usually underestimated by structural geologists which can contribute to a debate based on a multidisciplinary approach

could plate tectonics on venus be concealed by volcanic deposits the low upper limit on heat removal by plate tectonics inferred by kaula and phillips 1981 has been questioned on the grounds that volcanic deposits may conceal the characteristic shape of topography arising from plate tectonic spreading but a quantitative analysis indicates that volcanism sufficient for concealment must bring a major part of the heat to the surface thus making plate tectonics the secondary process for heat removal this inference is reinforced by consideration of the topographic structure and thickness of lava flows necessary it thus appears that the principal process bringing heat to the surface of venus is either lithospheric conduction or lava flows

interactions between mantle upwelling drainage evolution and active normal faulting an example from the central apennines italy summary in this paper we show that the processes that have shaped the quaternary surface development of the apennines in central italy are all consequences of a single subcrustal process the upwelling of the mantle the relationship between gravity and topography shows that mantle convection is responsible for a long wavelength 150 200 km topographic bulge over the central apennines and stratigraphic evidence suggests this bulge developed in the quaternary active normal faulting is localized at the crest of this bulge and produces internally draining fault bounded basins these basins have been progressively captured by the aggressive headward erosion of major streams that cut down to the sea on the flanks of the regional bulge the only surviving closed basins are those on the apennine watershed most distant from the marine base level where continued normal faulting is still able to provide local subsidence that defeats their capture by the regional drainage network understanding the competition between regional capture and local fault related subsidence of intermontane basins is crucial for recognizing potentially hazardous active faults in the landscape and also for interpreting the sediment supply to adjacent offshore regions central italy provides a good modern analogue for processes that are probably common in the geological record particularly on rifted margins and intracontinental rifts but may not have been fully appreciated

keweenaw hot spot geophysical evidence for a 1 1 ga mantle plume beneath the midcontinent rift system the proterozoic midcontinent rift system of north america is remarkably similar to phanerozoic rifted continental margins and flood basalt provinces like the younger analogues the volcanism within this older rift can be explained by decompression melting and rapid extrusion of igneous material during lithospheric extension above a broad asthenospheric thermal anomaly which the authors call the keweenaw hot spot great lakes international multidisciplinary program on crustal evolution seismic reflection profiles constrain end member models of melt thickness and stretching factors which yield an inferred mantle potential temperature of 1 500 1 570c during rifting combined gravity modeling and subsidence calculations are consistent with stretching factors that reached 3 or 4 before rifting ceased and much of the lower crust beneath the rift consists of relatively high density intruded or underplated synrift igneous material the isotopic signature of keweenawan volcanic rocks presented in a companion paper by nicholson and shirey this issue is consistent with the model of passive rifting above an asthenospheric mantle plume

the columbia river basalts between 17 million and 6 million years ago 200 000 square kilometers of the american northwest were flooded by basaltic lava that erupted through fissures in the crust up to 150 kilometers long larger individual eruptions covered over a third of the columbia plateau in a few days the lavas represent partial melts of the earth s mantle that were only slightly modified by near surface upper crustal processes the abundant chemical and mineralogical data now available offer an opportunity to study mantle composition and the processes involved in the evolution of the earth s crust

electromagnetic sounding in the columbia basin yakima washington a controlled source electromagnetic csem survey was conducted near yakima washington to map the thickness and resistivity of a thick volcanic sequence overlying a sedimentary section and to infer structure in the sediments the survey was conducted with a frequency domain system employing loop transmitters 400 500 m on a side and three component squid magnetometer receivers separated from the loop by 1 to 5 km data collected along a 30 km profile orthogonal to regional strike were interpreted initially with 1 d layered models which were then pieced together to make a geoelectric section induction logs in a 5000 m exploration hole at one end of the profile agree very well with the csem soundings made around the hole the geoelectric section reveals a smoothly varying thickness of volcanics with a pronounced anticlinal structure approximately concordant with a surface topographic ridge to assess the validity of inferring lateral structure from 1 d interpretations we made scale models of an anticlinal structure and of a surface inhomogeneity and conducted csem measurements over the scale models layered model inversions of these data show that the anticlinal structure and its location are very well determined by 1 d inversion but its height and width are not accurately determined csem sounding over the surface inhomogeneity model shows that this feature does not significantly degrade the interpretation of a deep target layer in this setting a geoelectric section made up from 1 d interpretations provides good qualitative measures of subsurface structure and also provides excellent starting models for detailed 2 d or 3 d modeling

geomorphological features and 3d modelling of montelparo mass movement central italy abstract the ancient village of montelparo marche region central italy is affected by a large translational mass movement the relief is modeled on arenaceous and arenaceous pelitic units overlying pelitic arenaceous terrains the bedding strata form a gently dipping monocline the translational slide is about 1100 m long and 500 700 m wide the upper boundary between the stable area and the sliding mass is marked by a large active trench near the hilltop the main sliding surface is located at a depth ranging between 65 and 100 m in the politic arenaceous unit we studied the mechanism of the slope instability along the stratigraphic contact between a rigid arenaceous unit and an underlying ductile pelitic unit the uncovering of the contact caused by the intense downcutting processes of the river at the hill foot during the holocene favoured the onset of the movement this was enhanced by the fractured bedrock and especially by the jointing we created a numerical model based on the finite differences code flac 3d by using a specific approach for mesh generation the model suggests a further enlargement and deepening of the trench and a sliding direction not aligned with the slope dip direction failure in the model concentrates at and around the main trench all the other elements staying in an elastic state and inducing a rigid sliding the model shows that both the failure onset and the current evolutionary state can be explained by the geological and static conditions of the slope

the portland hills fault uncovering a hidden fault in portland oregon using high resolution geophysical methods abstract the portland metropolitan area historically is the most seismically active region in oregon at least three potentially active faults are located in the immediate vicinity of downtown portland with the portland hills fault phf extending directly beneath downtown portland the faults are poorly understood and the surface geologic record does not provide the information required to assess the seismic hazards associated with them the limited geologic information stems from a surface topography that has not maintained a cumulative geologic record of faulting in part due to rapid erosion and deposition from late pleistocene catastrophic flood events and a possible strike slip component of the faults we integrated multiple high resolution geophysical techniques including seismic reflection ground penetrating radar gpr and magnetic methods with regional geological and geophysical surveys to determine that the portland hills fault is presently active with a zone of deformation that extends at least 400 m the style of deformation is consistent with at least two major earthquakes in the last 12 15 ka as confirmed by a sidehill excavation trench high resolution geophysical methods provide detailed images of the upper 100 m across the active fault zone the geophysical images are critical to characterizing the structural style within the zone of deformation and when integrated with a paleoseismic trench can accurately record the seismic history of a region with little surface geologic exposure

stability analysis of three dimensional seismic landslides using the rigorous limit equilibrium method abstract in this paper a new method combining the rigorous limit equilibrium method and the pseudo dynamic method is proposed to investigate stability of 3d seismic landslides in which the force equilibrium conditions along three coordinate axes and the overall moment equilibrium conditions around three coordinate axes are all strictly satisfied moreover sinusoidal cosinusoidal wave is applied to simulate earthquake displacement and an amplification factor of peak seismic acceleration is referred to as the amplification of seismic wave when it propagates from the bottom to the top of landslides the pseudo dynamic factor of safety of 3d seismic landslides is determined using trust region reflective iterative algorithm the effects of the parameters of the seismic landslides on the stability are analyzed by the bp neural network algorithm in which a database to investigate the stability of 3d seismic landslides is established in addition the stability of donghekou landslide is studied to verify the accuracy and precision of the present method

the interaction of plume heads with compositional discontinuities in the earth s mantle the effects of compositional discontinuities of density and viscosity in the earth s mantle on the ascent of mantle plume heads is studied using a boundary integral numerical technique three specific problems are considered 1 a plume head rising away from a deformable interface 2 a plume head passing through an interface and 3 a plume head approaching the surface of the earth for the case of a plume attached to a free surface the calculated time dependent plume shapes are compared with experimental results two principal modes of plume head deformation are observed plume head elongation or the formation of a cavity inside the plume head the inferred structure of mantle plumes namely a large plume head with a long tail is characteristic of plumes attached to their source region and also of buoyant material moving away from an interface and of buoyant material moving through an interface from a high to low viscosity region as a rising plume head approaches the upper mantle most of the lower mantle will quickly drain from the gap between the plume head and the upper mantle if the plume head enters the upper mantle if the plume head moves from a high to low viscosity region the plume head becomes significantly elongated and for the viscosity contrasts thought to exist in the earth could extend from the 670 km discontinuity to the surface plume heads that are extended owing to a viscosity decrease in the upper mantle have a cylindrical geometry the dynamic surface topography induced by plume heads is bell shaped when the top of the plume head is at depths greater than about 0 1 plume head radii as the plume head approaches the surface and spreads the dynamic topography becomes plateau shaped the largest stresses are produced in the early stages of plume spreading when the plume head is still nearly spherical and the surface expression of these stresses is likely to be dominated by radial extension as the plume spreads compressional stresses on the surface are produced beyond the edges of the plume consequently extensional features will be produced above the plume head and may be surrounded by a ring of compressional features

celadonite in continental flood basalts of the columbia river basalt group celadonite is a common alteration product of basalts in marine environments it has been argued that marine fluids are necessary for celadonite formation possibly by providing a source of k and other dissolved cations laterally extensive deposits of celadonite occur in basalts of the grande ronde basalt of the columbia river basalt group the celadonite is found in scoriaceous flow tops of layered basalt flows where it fills vesicles and replaces the surrounding groundmass evolved interstitial glasses are present in the basalts and dissolution of these glasses may provide sufficient k for celadonite formation whereas dissolution of groundmass augite provides a source of mg and fe these observations show that alteration by seawater or any other external source of dissolved ions is not necessarily required for celadonite formation

late archaean crustal extension sedimentary basin formation flood basalt volcanism and continental rifting the nullagine and mount jope supersequences western australia abstract the mount bruce megasequence set formerly the mount bruce supergroup is a succession of volcanic and sedimentary rocks that was deposited on the pilbara craton of western australia in the late archaean to early proterozoic its history can be described and explained in terms of modern style sequence stratigraphy and of phanerozoic style plate tectonics the megasequence set comprises the chichester range megasequence that was deposited on a rifted to divergent continental margin and the overlying hamersley range megasequence that was deposited on a convergent continental margin the chichester range megasequence comprises in order of superposition the nullagine and mount jope supersequences and the marra mamba supersequence package the nullagine and mount jope supersequences are each the rock record of one phase of a protracted two phase late archaean 2770 2700 ma continental break up the nullagine supersequence consists of the mount roe sequence which comprises mostly subaerial basalt and the overlying hardey sequence package which comprises mostly terrigenous sedimentary rocks that were deposited in extensional sedimentary basins the mount jope supersequence consists of in order of superposition the kylena sequence which comprises mostly basalt the tumbiana sequence which comprises mostly tuff and tuffaceous rocks and the maddina sequence package which comprises mostly basalt the nullagine supersequence was deposited during an episode of wnw ese directed crustal extension that possibly led to the development of a rift to the west of the present pilbara craton the mount jope supersequence was deposited during the subsequent development of a wnw ese trending rift the position of which approximates the present southern craton margin regional scale uplift was associated with the development of both supersequences particularly with the nullagine supersequence basement strike slip faults were reactivated as dip slip structures during crustal extension and controlled the locations of some hardey sequence package extensional sedimentary basins nullagine supersequence and mount jope supersequence rifting led to a divergent continental margin bordering an ocean along the south and probably the far west of the craton post rift thermal subsidence was accompanied by the accumulation of mudrock carbonate sedimentary rock and iron formation of the marra mamba supersequence package in a shelf setting the implications of these interpretations are that at 2800 ma the pilbara craton was significantly larger than at present and that it had a sufficiently thick subcontinental lithosphere that divided it in a manner analogous to the break up of phanerozoic continents the nullagine and mount jope supersequences contain three stacked flood basalt successions which were erupted over a time period of between of 55 and 80 m y stacked flood basalt successions covering such a long time period are not known in the phanerozoic and are tangible evidence of a hotter late archaean mantle

2d modelling of large scale platform margin collapses along an ancient carbonate platform edge maiella mt central apennines italy geological model and conceptual framework abstract results of numerical simulations of large scale platform margin collapses along the edge of the cretaceous platform of the maiella central apennines are presented adding a new contribution to the understanding of the role and quantification of the various factors that control triggering of these phenomena and the production of breccias and megabreccias for this purpose a sophisticated numerical code widely used in recent contexts to simulate overall mass movements and deep gravity driven deformation is applied for the first time to an ancient system on a scale of several kilometres the modelling carried out is a simplified attempt to understand a very complex phenomenon produced over a very long time span it tests whether the perturbing causes in the model acting together or separately are able to activate such large scale collapse and helps to understand the effects of perturbing causes and their variations in particular modelling was carried out considering both static variations in sea level and dynamic seismic events without and with fault formation conditions and combinations of them variations in sea level alone do not produce all the effects observed but may certainly be a predisposing element seismic shock simulations show that fracturing and shear stresses are concentrated on the platform margin representing the most sensitive and vulnerable area earthquake swarms associated with an active fault are the most likely means of triggering large scale platform margin collapses such as those occurring during the early cretaceous in the maiella

formation of the ferruginous smectite swa 1 by alteration of soil clays clay minerals found in and near the surface of mars contain unique information about the geochemical environment in the martian near surface in the ancient past to interpret this information it is necessary to fully understand the environments in which different clay minerals form studies of terrestrial analog materials and environments are a useful way to address such questions and some terrestrial materials are also important standards for remote sensing and in situ chemical and mineralogical analyses this study presents new information on the formation environment of an unusual standard clay the clay minerals society source clay swa 1 ferruginous smectite of grant county the swa 1 collection locality is in the columbia river basalts crb at the contact between a paleosol and a capping basalt flow features at the contact indicate the paleosol soil was wet when the capping flow was emplaced that lava sediment mixing occurred and that both the soil and the capping lava were hydrothermally altered the soil was hydrothermally enriched in fe mn and si the swa 1 sample was collected from within the altered zone suggesting it formed through alteration of paleosol clays by addition of fe similar environments are widespread in the crb particularly at the plateau margins suggesting that altered clays may occur frequently at lava sediment contacts such environments are likely to occur wherever basalt flows are emplaced under warm wet conditions promoting weathering such as mars 3 5 ga before the present when clay minerals were forming at its surface this information has important implications for the use of clay compositions to inform clay formation environments on mars

lunar and terrestrial crust formation planetary crusts may be accreted produced in primordial differentiation or built up piecemeal by serial magmatism the existence of old polygenetic laterally heterogeneous partial melt rocks in the lunar highlands suggests that the moon produced its early crust by serial magmatism this view can be reconciled with lunar eu anomalies previously thought to support the magma ocean model of crust formation if complications in the fractionation of mare basalts are recognized phase equilibrium and magmatic density information for mare basalts suggest a model in which plagioclase fractionation can occur even though plagioclase is not a near liquidus phase the cryptic fractionation of clinopyroxene in morb provides a precedent for this model the necessity for a lunar magma ocean is questioned but a role for a terrestrial magma ocean of sorts at depth is suggested

petrology of the lower tertiary clarno formation in north central oregon the importance of magma mixing predominantly eocene rocks of the clarno formation in north central oregon consist of lava flows volcaniclastic rocks and tuffaceous sedimentary rocks lying between cretaceous shallow marine deltaic sedimentary rocks and younger volcanic rocks whole rock rb and sr isotopic data yield a poor isochron with an age of 47 5 ma clarno rocks are broadly calc alkaline range from basalt to rhyolite and show complex textural and compositional properties plagioclase and clinopyroxene phenocrysts are present in most lavas with olivine in mafic rocks and orthopyroxene quartz and subordinate biotite and hornblende in intermediate rocks spongy sieve textured plagioclase and glass bearing plagioclase are both common many quartz grains are resorbed and some pyroxene grains are spongy some samples contain quartz in which plagioclase inclusions have undergone partial melting along the plagioclase quartz boundaries plagioclase inclusions in these rocks are more calcic an54 66 than the cores of their companion xenocrysts an41 suggesting digestion of earlier mafic rocks mafic cumulates have high mgo cr and ni values some oxide and element sio2 diagrams show linear trends but scatter from the trends is large plots of sio2 versus al2o3 sr y and possibly other components show inflections in trends in the range of 55 60 sio2 the abundance of disequilibrium textures shows that the dominant process in the evolution of the clarno suite was mixing of magmas with liquid and partly solid sources probably including earlier crystallized clarno magmatic rocks cumulate textures and compositions however indicate that clarno magmas were modified by crystal fractionation which also may have contributed to the scatter from linear trends on composition diagrams initial 87sr 86sr ratios corrected for a model age of 50 ma range from 0 70350 to 0 70397 consistent with mantle source s or with contamination by young mafic material but not with interaction with old upper continental crust