curie isotherm depth from aeromagnetic data constraining shallow heat source depths in the central aeolian ridge southern tyrrhenian sea italy the salina lipari and vulcano volcanic ridge and the surrounding sea sectors aeolian archipelago southern tyrrhenian sea italy are characterized by vents responsible for a recent 40 ka 1889 1890 ad effusive and explosive subareal activity and repeated 56 to 7 ka in age submarine explosive eruptions from source areas located between lipari and vulcano a spectral depth estimation of the magnetic bottom using a fractal method on aeromagnetic data from vulcano lipari and salina volcanic ridge allows us to constrain the curie isotherm depth the elevated portion of the isotherm is between 2 and 3 km below salina and vulcano and about 1 km below lipari the curie depth results in the context of other geological and geophysical evidence suggest that the rise of the curie isotherm is mainly due to the occurrence of shallow heat sources such as magma ponds and associated hydrothermal systems the short wavelength magnetic anomaly field reflects magnetic contrasts from highly magnetized volcanic bodies low magnetization sediments and hydrothermally altered rocks borehole temperature data verify the curie temperature derived from the magnetic methods on the island of vulcano we conclude that the whole vulcano lipari and salina volcanic ridge is active and should be monitored

sand dune patterns on titan controlled by long term climate cycles linear sand dunes on equatorial titan are shaped by winds the morphologies of smaller dunes that have been reoriented with respect to the linear dune crests suggest that winds shift with long term orbitally driven climate cycles on titan

a recent tectonic reorganization in the south central mediterranean abstract new geodetic data combined with seismicity geologic and geochemical information document a major tectonic reorganization in the central mediterranean around 0 8 0 5 ma when rapid trench migration and consequent tyrrhenian back arc extension which dominated the region s evolution since the tortonian 10 8 ma essentially stopped in response the african convergence in sicily was transferred to a back thrust in the southern tyrrhenian characterized by frequent m5 6 earthquakes in the last 20 years a diffuse transform boundary formed across northeastern sicily to connect the sicilian and calabrian plate boundaries causing opening of the messina straits home to large historical earthquakes and unusual volcanism in the aeolian island arc and the intraplate mount etna a divergence of the ionian region from the main part of africa with northeastward motions that reflect the joint influence of african push and hellenic slab pull and are transmitted to calabria and adria could explain motions observed in the sicily channel calabria and apulia as well as the high level of southeastern sicilian seismic activity

cosmic ray labeling of erosion surfaces in situ nuclide production rates and erosion models a number of in situ cosmogenic radionuclides and stable nuclides have been measured in natural exposed rock surfaces with a view to study their in situ production and rock erosion rates 1 the in situ radionuclides can be used for a high resolution tomography of the erosional history of an exposed surface two stable nuclides 3he 21ne and five radionuclides 10be 26al 36cl 14c 39ar having half lives in the range of 300 1 5 106 yr half life are measurable in many rock types a prerequisite for the application of the in situ nuclides for the study of erosional histories of surfaces is a knowledge of their production rates under different irradiation conditions altitude latitude irradiation geometry and shielding relative nuclide production rates can be determined fairly accurately using the extensive available data on cosmic ray neutrons 2 absolute nuclide production rates cannot generally be predicted with any accuracy because of lack of data on excitation functions of nuclides unless some normalization is possible as was done in the case of several cosmic ray produced isotopes in the atmosphere 3 based on a recent natural calibration experiment in which erosion free surfaces exposed to cosmic radiation for 11 000 yrs were sampled the absolute production rates of 10be and 26al in quartz have been accurately estimated for mountain altitudes in sierra nevada 4 the absolute production rates of 10be and 26al in quartz can therefore be estimated fairly accurately for any given latitude and altitude some measurements of 14c in rocks of low erosion rate 5 similarly allow an estimate of its production rate attempts made to measure the in situ production rates of 3he in rocks have not yet led to a convergent production rate in view of the importance of knowing the production rates of isotopes of he ne and ar i present here theoretical estimates of their production rates based on available cross section data i discuss the information that can be extracted from the study of the in situ nuclides in rocks useful parameters characterizing the exposure history of a rock surface are 1 the effective surface exposure age and 2 the time averaged erosion rate the implications of these parameters for single and multiple nuclide studies are discussed in terms of the erosion models considered

cosmogenic 3 he in hematite and goethite from brazilian canga duricrust demonstrates the extreme stability of these surfaces helium isotopes were measured in hematite and goethite samples from several lateritiric duricrusts canga developed on banded iron formations these samples uniformly have high 3 he concentrations which must arise from long periods of cosmic ray exposure from coexisting phases from the quadrilatero ferrifero in east central brazil we determined the ratio of cosmogenic 3 he in hematite to that of 21 ne in quartz to be 3 96 0 19 combined with best current estimates of the 21 ne production rate in quartz this ratio implies a sea level high latitude slhl 3 he production rate in hematite of 68 1 8 1 atoms g yr from the chemical composition we estimate the 3 he production rate in goethite to be 5 higher we use these production rate estimates to interpret 3 he concentrations measured in goethite and hematite from a 10 m depth profile collected from a surface canga in carajas in the amazon basin of brazil we find that the carajas canga has experienced a very low rate of surface erosion 0 16 0 54 m myr over at least the last few millions of years this iron rich canga surface is remarkably resistant to erosion despite its location in a wet tropical environment details of the depth profile suggest that despite its stability the canga has also been internally dynamic translocation of material solution and reprecipitation over million year timescales

new 26al 10be and u th he constraints on the age of the upland complex central mississippi river valley abstract the upland complex is a widespread terrace of the ancestral mississippi river it has played a central role in studies of the pliocene mississippi river drainage as well as uplift and seismicity in the central mississippi river valley previous efforts to date the upland complex have yielded a range of age estimates spanning the miocene through pleistocene we dated gravels and fe oxide cements from quarries of the upland complex in arkansas kentucky mississippi and tennessee using 26al 10be burial dating and u th he geochronology our 26al 10be burial dates revealed possible pliocene to pleistocene depositional ages while u th he dating showed that the onset of weathering dates to at least the pliocene taken together the 26al 10be and u th he age constraints demonstrate that the upland complex is at least pliocene in age and likely formed during a prolonged period of base level stability that preceded pleistocene glaciations

fractal analysis of mingled mixed magmas an example from the upper pollara eruption salina island southern tyrrhenian sea italy abstract upper pollara eruption products 13 ka salina island italy include both homogeneous and heterogeneous pumices resulting from mixing mingling processes between an hk andesite and a high sio2 rhyolite representative samples of heterogeneous pumices are collected and analyzed in order to check the correspondence between glass composition and morphological features of the mingling mixing structures image analysis techniques are applied and eight grey color ranges classes are extracted from high resolution scans of pumice class 1 lighter colors and class 8 darker colors show end member glass compositions i e hk andesite and high sio2 rhyolite respectively these two classes show spot to cluster like morphological structures intermediate classes show an hk dacitic to rhyolitic composition and a banding to fold like morphology fractal analysis by box counting of the boundary pattern of eight grey classified images is performed over a length scale of 0 028 1 8 cm fractal dimension d is between 1 01 and 1 84 coupled fractal analysis and geochemical data reveal that d increases as the degree of magma interaction homogenization increases this feature well fits the results from numerical models on the convective mixing of fluids driven by thermal convection we conclude that the increase of d observed in the upper pollara samples reflects the transition from fractal mixing to homogenization end member magmas hk andesite and high sio2 rhyolite represent isolated mixing regions while homogenized magmas represent active mixing regions in the analyzed pumices isolated and active mixing regions coexist at scales between 10 4 and 10 2 m morphological and compositional features of the upper pollara pumices result from turbulence

near bed mass flux profiles in aeolian sand transport high resolution measurements in a wind tunnel vertical profiles of the streamwise mass flux of blown sand in the near bed 17 mm region are analysed from high resolution measurements made using an optical sensor in a wind tunnel this analysis is complemented by detailed measurements of mass flux and mean velocity profiles throughout the boundary layer depth 0 17 m using passive chambered sand traps of small dimensions and armoured thermal anemometers respectively the data permit a preliminary analysis of the relations between the observed forms of the profiles of near bed fluid stress and horizontal mass flux within a carefully conditioned boundary layer profiles of mass flux density are found to be characterized by three regions of differing gradient with transitions at about 2 mm and 19 mm above the bed the exponential decay of mass flux with height is confirmed for elevations above 19 mm and when plotted as a function of u 2 g a parameter of mean vertical trajectory height in saltation the gradient of mass flux in this region scales with the wake corrected friction velocity u where u 0 30 m s 1 a separate near bed region of more intense transport below 19 mm is identified which carries 80 per cent of the total mass flux this region is evident in some previous field and wind tunnel data but not in profiles simulated by numerical models ventilated passive sand traps underestimate mass flux in this region by 37 per cent at slow or moderate wind speeds a third significant region below 2 mm is observed these regions are likely to be related to grain populations in successive saltation low energy ejections and intermittent bed contact respectively optical measurements reveal locally high grain concentrations at some elevations below 5 mm these heights scale with transport rate mass flux gradient and wind speed copyright 1999 john wiley sons ltd

analysis and modelling of the aeromagnetic anomalies of gran canaria canary islands abstract in this paper we present a crustal magnetic model of the volcanic island of gran canaria based on aeromagnetic data this magnetic study has made it possible to constrain the location and geometry of 1 the mafic core of gran canaria built as the result of the crystallization of magmas which rose from the mantle during the submarine and shield basaltic stages of its evolution the most intense magnetic high displayed over the nw part of the island likely shows the main feeding system of the shield volcano 2 the residual syenitic shallow magma chamber which fed the salic volcanic activity in the center of the island linked to the formation of the tejeda caldera and to the intrusion of felsic rocks which made up a cone sheet 3 a reversely magnetized linear intrusion located in the marine area to the nw of the island which could be related to the magmatic source of the submarine volcanism between gran canaria and tenerife most of these magnetic sources show a linear pattern with trends that are in close agreement with the orientations of previously identified fractures the magmatic intrusion to the nw of the island could be related with a wsw ene active fault between gran canaria and tenerife while the main trend and location of the mafic core agree with a nw se fault suggested by geological studies this means that these magnetic sources are the result of the ascent and intrusion of magma along regional fractures therefore this study provides fresh data which demonstrate the influence of regional tectonics on the growth of gran canaria during its entire evolution finally the spectral analysis of the magnetic anomaly map suggests that it is possible that rocks located at mantle like depths from the moho to about 23 km behave as magnetic sources a fact that can be related with the magmatic underplating detected by other geophysical techniques

multi spatial analysis of aeolian dune field patterns abstract aeolian dune fields are composed of different spatial scales of bedform patterns that respond to changes in environmental boundary conditions over a wide range of time scales this study examines how variations in spatial scales of dune and ripple patterns found within dune fields are used in environmental reconstructions on earth mars and titan within a single bedform type different spatial scales of bedforms emerge as a pattern evolves from an initial state into a well organized pattern such as with the transition from protodunes to dunes additionally different types of bedforms such as ripples coarse grained ripples and dunes coexist at different spatial scales within a dune field analysis of dune field patterns at the intersection of different scales and types of bedforms at different stages of development provides a more comprehensive record of sediment supply and wind regime than analysis of a single scale and type of bedform interpretations of environmental conditions from any scale of bedform however are limited to environmental signals associated with the response time of that bedform large scale dune field patterns integrate signals over long term climate cycles and reveal little about short term variations in wind or sediment supply wind ripples respond instantly to changing conditions but reveal little about longer term variations in wind or sediment supply recognizing the response time scales across different spatial scales of bedforms maximizes environmental interpretations from dune field patterns

comparative tertiary stratigraphy of the rhine graben bresse graben and molasse basin correlation of alpine foreland events abstract comparative tectonostratigraphic analysis of the tertiary middle eocene pliocene of the rhine bresse graben system and the western molasse basin demonstrates the occurrence of eleven correlative sequences crf i xi these show a close relationship between intra basinal tectonics and depositional history their punctuated sediment accumulation can be related to phases of extra alpine taphrogenesis and alpine orogenesis and to coeval eustatic changes in sea level apparent simultaneity in rift and foredeep sequence development structural deformation and global change in sea level suggests a common causal control in which the development of the alps played an important role

new unspiked k ar ages of volcanic rocks of the central and western sector of the aeolian islands reconstruction of the volcanic stages abstract a geochronological study of the filicudi salina lipari and vulcano islands aeolian archipelago using the unspiked potassium argon technique provides new age data which combined with stratigraphic correlation better constrain the temporal evolution of volcanism the unspiked k ar age of the oldest exposed lavas on filicudi 219 5 ka is significantly younger than the previous estimation of 1 02 ma in the general context of aeolian volcanism this new date suggests that the volcanism of the western sector of the aeolian archipelago is younger than previously thought geochronological data point out on the rapid transition from calc alkaline to potassic volcanism the distribution of the k ar ages within the salina lipari vulcano group shows that the volcanism started on lipari and propagated over time northward on salina and southward on vulcano geochronological and geophysical data suggest that the onset of volcanism in the central sector of the aeolian arc may be due to a mantle upwelling structure located below lipari a change in the style of the eruptions occurred in the salina lipari vulcano system at about 100 ka from the present low energy magmatic eruptions occurred between 188 and about 100 ka from about 100 ka to the present higher energy eruptions and low energy events due to magma water interaction also occurred this change in the style of activity together with the appearance of evolved products i e rhyolites during the last 50 ka is consistent with the formation of magmatic reservoirs located at shallower depth with respect to those of the 188 100 ka period the new geochronological data and available petrological models reveal that a change in the deep source of the primary magmas occurred in a relatively short time interval

well preserved late precambrian paleosols from northwest scotland abstract two paleosol profiles were developed side by side on gneiss sheigra clay paleosol and amphibolite staca clay paleosol along the same unconformable contact of lewisian metamorphic rocks 2 7 1 7 ga overlain by torridonian sandstones 0 8 ga in northwestern scotland although altered during burial by compaction and illitization these profiles are well preserved compared with most other precambrian paleosols that are metamorphosed to at least greenschist facies in addition deformation of pegmatite veins in a manner similar to soil creep can be taken as an indication that upper horizons of these paleosols have been preserved soil development in both profiles was characterized by the oxidation of iron in biotite and magnetite and by hydrolysis of plagioclase orthoclase and hornblende clay skins soil like microfabrics and pedogenic smectite have been preserved in the profiles alteration of silicate grains other than quartz microcline and biotite has been intense but chemical analyses failed to show dramatic removal of alkalis and alkaline earths from the profiles microscopic concretions similar to pedogenic carbonate were found in subsurface horizons of the staca clay rare earth elements are more abundant within the paleosols than in their parent materials these paleosols developed on a well drained landscape that was buried by torridonian alluvial fans atmospheric oxidation was greater than revealed by studies of archean paleosols but probably still short of modern levels paleoclimate was subhumid and probably seasonal organic carbon and its light isotopic composition in the paleosol is evidence for photosynthetic microbial crusts paleosols of such great antiquity do not fit comfortably within modern soil taxonomies and are for the moment assigned to the informal category of green clays

regolith residence time and the concept of surface age of the piedmont peneplain the common upland weathering profile on foliated metamorphic rocks on the appalachian piedmont between alabama and maryland includes a 50 cm 1 m thick clay rich soil b horizon over 10 20 m of saprolite the saprolite retains the volume fabric and structure of the underlying parent rock but has lost about one third of the mass of the parent rock where the saprolite is thickest beneath upland drainage divides those divides are of loow slope and relief the flatness of the piedmont drainage divides provides the appearance of a planation surface of accordant summits or peneplain i interpret this flatness to be the result of three active processes volume reduction during compaction of saprolite into soil loss of mass in dissolved solids draining the soil b horizon and loss of mass from the soil surface by erosion of clay size particles the cumulative effects of these upland processes are to convert saprolite into soil to limit soil thickness and residence time and to limit the age of the oldest residual soils on the surface this results in a continual lowering of the piedmont peneplain surface this interpretation is corroborated by evidence of topographic inversion of fluvial gravels since the miocene near the fall line study of baseflow dissolved solids draining piedmont basins indicates a minimum rate of saprolite production of about 4 m ma 1 this minimum rate of production near the fall line is less than the estimated rate of surface lowering and saprolite consumption during the late tertiary and quaternary periods of topographic inversion measurement of cosmogenic 10be inventories in two 15 20 mores of piedmont upland regolith indicate a minimum residence time of residual soil and saprolite of about 1 ma this indicates a possible maximum rate of saprolite production and erosion of about 20 m ma 1 using the best available evidence therefore the typical piedmont upland regolith has a residence time of between 1 and 5 ma residence times may not be the same everywhere and ages may vary systematically across the surface the geomorphic evidence of topographic inversion and similar regolith profiles in other humid temperate and tropical regions strongly suggests that production and removal of piedmont saprolite has been an ongoing quaternary process and that most of the piedmont regolith is significantly younger than 5 ma independent geophysical evidence suggests that the rate of uplift probably involving tilting of parts of the piedmont blue ridge and valley and ridge has averaged between 5 and 20 m ma 1 through the cenozoic

environmental memory and a possible seasonal bias in the stable isotope composition of u th he dated goethite from the canadian arctic abstract goethite ax 2 from axel heiberg island 80 n on the margin of the arctic ocean is the dominant mineral in a sample of petrified eocene wood but u th and he measurements suggest that the goethite feooh crystallized in the latest miocene pliocene ca 5 5 to 2 8 ma measured d and 18 o values of ax 2 are 221 6 and 9 6 0 5 respectively the inferred d and 18 o values of the ancient water were about 139 and 18 6 respectively with a calculated temperature of crystallization of 3 5 c which compares with the modern summer j j a temperature of 3 c and contrasts with a modern mat of 19 c published results from various biological proxies on nearby ellesmere island indicate a pliocene 4 ma mat of either 6 or 0 4 c and corresponding seasonal amplitudes of about 18 or 13 c a conductive heat flow model suggests that a temperature of 3 c could represent goethite crystallization at depths of 100 200 cm for mat 6 c or 250 450 cm for mat 0 4 c over seasonally restricted intervals of time the 18 o value of the ax 2 water 18 6 is more positive than the modern j j a precipitation 22 in combination the paleotemperatures and 18 o values of ancient waters from ax 2 and published results from three eocene or pliocene proxy sites on axel heiberg and ellesmere islands are consistent with a warm season bias in those isotopic proxies the results are also consistent with higher proportions of j j a precipitation in the annual total if so this emphasizes the importance of seasonality at high latitudes even in times of warmer global climates and suggests that the arctic hydrologic cycle as expressed in the seasonal distribution and isotopic composition of precipitation perhaps modified by a warmer arctic ocean differed from modern the 13 c value of the fe co 3 oh component in the ax 2 goethite is 6 6 which is much more positive than expected if crystallizing goethite incorporated co 2 derived primarily from oxidation of relict eocene wood with 13 c values of about 24 this apparent paradox may be resolved if the goethite is a product of oxidation of 13 c rich siderite which had previously replaced wood in an eocene methanogenic burial environment thus the goethite retains a carbon isotope memory of a diagenetic eocene event but a d and 18 o record of the latest miocene pliocene arctic climate

u loss associated with laser heating of hematite and goethite in vacuum during u th he dating and prevention using high o2 partial pressure abstract single aliquot u th he dating of hematite has been used to study iron oxide precipitation in various environments but we show there is an important challenge to the method highly retentive hematite samples require temperatures of 1000 c to be completely degassed whereas the temperature for major u loss is 980 c this leads to erroneously high u th he ages through the analysis of u th and sm of hematite and goethite samples we establish the degree of u loss at this temperature and demonstrate that prolonged heating at temperatures of 950 c can lead to u loss we show that loss of u in goethite and hematite samples is associated with phase change from hematite to magnetite as fe is reduced the onset temperature of vacuum reduction of hematite can be increased from about 800 900 c in vacuum to approximately 1250 c in an oxygen partial pressure of 100 mbar we demonstrate that samples can be outgassed to extract helium at 1150 c without u loss in an o2 rich atmosphere during heating which does not increase the analytical blanks we describe our implementation and automation of the procedure an average age calculated on a reference hematite sample from replicate aliquots n 12 which were analyzed using this procedure has a relative uncertainty of 2 1 and is within uncertainty of the previously measured two aliquot age we suggest this o2 degassing procedure as a way to precisely and reproducibly determine single aliquot hematite and goethite u th he ages

volcanic geomorphology and tectonics of the aeolian archipelago southern italy based on integrated dem data the geomorphological and morphometric analysis of the sea floor topography surrounding the aeolian islands south tyrrhenian sea italy provides insights into the relationships between the volcanological evolution of the islands and their tectonic features we constructed geomorphological maps of the submarine portions of the seven large edifices constituting the islands on the basis of a dem with a 5 m resolution step these maps include constructional and destructional landforms such as submarine volcanic vents located west of lipari and north of alicudi and hummocky surfaces recognised north of lipari and salina the latter landforms together with the occurrence of large scars affecting the main edifices on land suggest that sector collapses affected some islands geomorphological data indicate that the location of subaerial and submarine vents is strongly controlled by local tectonic structures striking wnw ese alicudi filicudi sector nnw sse salina lipari vulcano sector and ne sw panarea stromboli sector the islands can be divided into two groups on the basis of some morphometric parameters a first group with a pancake like shape dp d abrasion platform diameter basal diameter higher than 0 40 and h d total height basal diameter lower than 0 13 and a second group with a conical shape characterised by dp d lower than 0 34 and h d higher than 0 14 these ratios and other morphometric parameters reflect the different volcanological and structural evolution of the aeolian islands the pancake like shaped complexes have been created in addition to their submarine stage by extrusive and highly explosive activity whereas the cone shaped edifices have been characterised by effusive or moderate explosive activity

enclaves provide new insights on the dynamics of magma mingling a case study from salina island southern tyrrhenian sea italy abstract three lava flows hereafter flows a b and c from salina island italy consist of basaltic andesitic enclaves dispersed in a dacitic matrix enclaves represent 8 12 vol of the erupted magma the number of enclaves and the surface covered by the enclaves at each outcrop do not vary significantly with the distance from the vent in the flows a and b these feature reflect the dynamics of magma mingling within the reservoir and not the kinematics of the lava flow in the flow c these parameters vary irregularly the statistical entropy s t of the enclaves which is a measure of their spatial distribution dispersion is estimated in outcrops located at different distance from the vent the kolmogorov sinai entropy rate k which describes the variations of s t with time is also determined in the lava flow a s t increases linearly with time t for 0 0 5 s t attains its maximum value and maintains constant with increasing t in the lava flow b s t linearly increases with t and k is 0 01 in the lava flow c there is not correlation between s t and t the comparison between the results from the analysis of the porri enclaves and those from numerical experiments on the variation of s t in chaotic advective mixing systems and from previous experimental models on magma mixing allow us to draw some conclusions on dynamics of the basaltic andesite dacite mingling in the magma chamber fully chaotic magma mingling systems show three evolution stages an initial stage which is unknown because of the disruption of the initial configuration of the interacting magmas a second stage characterized by a linear increase of the statistical entropy with time and a third stage in which the uniformity of the system is reached and the entropy does not vary with increasing time a system in which the uniformity is never attained is characterized by irregular variations of s t with time in the flows a and b the relations between s t and t are consistent with those of a fully chaotic dynamics possibly associated to convection the basaltic andesite was uniformly distributed in the dacitic host due to the occurrence of convective movements driven by the injection of the basaltic andesite within the dacitic chamber the mingling system recorded by the lava flow a evolved with a higher rate with respect to that of the flow b this suggests that chaotic advection stirring and folding is more efficient in the magmatic system a than in b on the contrary the mingling system c is characterized by a non uniform distribution of the basaltic andesite within dacite this reflects the occurrence of a dynamics in which stirring and folding processes do not operate efficiently and are unable to uniformly distribute the dispersed phase within the continuous one the decrease of k from a to b and the lack of a measurable k in c along with the observation that a and b were emitted before c indicate that the efficiency of advective movements within the porri magma chamber declined with decreasing time mingled magmas characterized by a homogeneous spatial distribution of enclaves or an initially inhomogeneous distribution evolving towards a homogeneous one are indicative of efficient advection processes that may favor magma mixing mingled magmas characterized by an inhomogeneous distribution of enclaves suggest low dynamical interaction between the two end members magma mixing is not allowed

relationships among crustal structure volcanism and strike slip tectonics in the lipari vulcano volcanic complex aeolian islands southern tyrrhenian sea italy abstract the lipari vulcano volcanic complex lvvc aeolian arc southern tyrrhenian sea italy develops along a strike slip fault system that bisects the aeolian arc the lvvc crustal structure is investigated by applying seismic methods to two data sets p wavefronts generated by local and distant events constrain the shallow velocity structure dss data provide shape and depth of the main crustal discontinuities the obtained velocity model shows that the lvvc shallow structure is characterized by the presence of two sharp lateral discontinuities the northern discontinuity bounds a low velocity basin like structure including the la fossa caldera and mt guardia caldera depressions the southern discontinuity coincides with the southern boundary of a high velocity diffractor located beneath the la fossa cone direct modeling of dss data define three crustal discontinuities showing a complex geometry the intra crustal interfaces and the moho discontinuity show an upheaval beneath the lvvc central sector the estimated crustal velocities are lower than those generally reported for the continental crust this feature is due to the high heat flux and fluid circulation affecting the lvvc area the ratio between the thickness of the upper and lower crust and the presence of the moho upheaval are consistent with that reported for continental areas affected by extensional strain the collected geophysical data combined with volcanological and structural information indicate that a the mt guardia and la fossa caldera depressions represent the surface expression of a single structure whose formation is mainly due to tectonic processes b the lvvc crustal structure and the evolution of the volcanism are consistent with those recognized in zones of transition from arc related to rift volcanism in addition results of a preliminary mechanical analysis based on the available structural data indicate low values of the ratio between magmatic overpressure and tectonic stress this suggests a passive mechanism of mantle upwelling the mantle upwelling is due the post collisional normal strike slip tectonics affecting the aeolian arc

rifted margin formation in the south tyrrhenian sea a high resolution seismic profile across the north sicily passive continental margin a new 150 km long seismic line across the continental margin of north sicily has been acquired and interpreted the overall structure of the margin is controlled by extension which caused crustal thinning and widespread normal faulting two main thinned zones are observed in the south in correspondence with the cefalu basin and farther to the north at the continent ocean transition zones of thinned crust coincide with zones of intense normal faulting extension began in late tortonian times and caused the opening of the cefalu basin controlled by a northward dipping listric fault messinian stretching affected most of the future margin and provoked a widening of the cefalu basin and normal faulting in the north following a phase of relative quiescence in the early pliocene renewed extension determined further opening of the cefalu basin and subordinate normal faulting in the north here however the record is unclear because of the emplacement of the calc alkaline sisifo volcano with associated volcanoclastic deposits breakup took place in the late pliocene and was followed by the deposition of postrift pleistocene sediments at the lithospheric scale the sites of extension thinning did not migrate during rifting on the smaller scale on the contrary the cefalu basin displays a remarkably systematic pattern of migration toward the foot wall of the listric fault which controlled the opening of the basin the spacing of 4 6 km between faults is also quite systematic elongation experienced by the continental part of the margin presently 97 km has been derived by comparing the present day and the preextensional lengths and is 10 km the corresponding strain rate is 5 10 16 s 1

quantifying the diffusion kinetics and spatial distributions of radiogenic 4he in minerals containing proton induced 3he apatite titanite and olivine samples were bombarded with a 150 mev proton beam to produce 10 8 atoms mg of spallation 3he high precision stepped heating experiments were then performed in which the artificial 3he and for apatite and titanite the natural radiogenic 4he were measured to characterize the diffusive behavior of each isotope helium 3 diffusion coefficients are in excellent agreement with concurrently and or previously determined he diffusion coefficients for each mineral our results indicate that proton induced 3he is uniformly distributed and that radiation damage associated with a proton fluence of 5 x 10 14 protons cm 2 does not cause noticeable changes in 4he diffusion behavior in at least apatite and titanite proton induced 3he can therefore be used to establish he diffusion coefficients in minerals with insufficient natural helium for analysis or those in which the natural 4he distribution is inhomogeneous in addition step heating 4he 3he analysis of a mineral with a uniform synthetic 3he concentration provides a means by which a natural 4he distribution can be determined

measurement of ancient cosmogenic 21ne in quartz from the 28 ma fish canyon tuff colorado abstract measurement of 21 ne in quartz from the 28 ma buried fish canyon tuff of colorado yielded a maximum of 2 75 0 57 10 6 21 ne atoms g sio 2 1 above nucleogenic and modern concentrations this quantity represents cosmogenic 21 ne produced on the fish canyon tuff surface prior to the deposition of the overlying carpenter ridge tuff ancient 21 ne was isolated through the analysis and identification of 1 background 21 ne produced from particle interactions or inherited and 2 cosmogenic 21 ne produced from modern radiation multiple samples of fish canyon tuff shielded during both exposure periods 28 ma ago and in modern time yielded the background that was then subtracted from all samples likewise samples of fish canyon exposed today but well below the fish canyon carpenter ridge contact and therefore shielded 28 ma ago yielded a modern component that was also removed from all sample concentrations the presence of an ancient cosmogenic isotope in a buried surface has several potential applications including the quantification of paleoelevation paleolatitude and pre quaternary erosion rates

inverse modelling of the reversely magnetized shallow plumbing system hosting oil reservoirs of the auca mahuida volcano payeina retroarc neuquen basin argentina

aeromagnetic anomalies reveal hidden tectonic and volcanic structures in the central sector of the aeolian islands southern tyrrhenian sea italy 1 salina island italy in the central aeolian chain is the northernmost volcanic structure of an elongated ridge on a regional shear zone with nnw sse strike slip faults and second order n s and ne sw faults modeling of high resolution low altitude aeromagnetic data collected in 2003 and 2005 using volcanological data constraints reveals the inner structure of the salina volcanoes and surrounding marine regions regional negative anomalies overlie e w elongated sedimentary basins related to the early pliocene pleistocene opening of the southern tyrrhenian sea these negative anomalies flank positively magnetized crust of salina and seamounts off its eastern coast where the shorter wavelength anomalies map late pleistocene holocene volcanic conduits dikes and faults the magnetic and volcanological data indicate that the early circa 168 100 ka basaltic to andesitic salina volcanism developed along n s and ne sw tectonic faults whereas the more recent andesitic lavas and rhyolitic pyroclastics circa 100 13 ka were emitted by vents related to the main nw se faults the tectonic structures also controlled the location of the seamounts around the island and the geometry of the volcano tectonic collapses salina volcanism was emplaced on a nnw sse tear fault of the presently developing roll back slab in the southern tyrrhenian sea

comparing dune migration measured from remote sensing with sand flux prediction based on weather data and model a test case in qatar this study explores validating and calibrating the wind regime predicted by global circulation models gcm on earth and other planets using optical remote sensing of dune dynamics we use spot 5 images to track the migration of 64 barchan dunes in qatar using the cosi corr technique we estimate the volume of the dunes using a scaling law calibrated from one particular dune which was surveyed in the field using volume and migration rate we determine the sand flux from a single dune q dunes and scale this estimate to the whole dune field we compare the measured sand flux with those derived from wind velocity measurements at a local meteorological station as well as with those predicted from era interim a global circulation model the comparison revealed that the wind velocity predicted by era interim is inappropriate to calculate the sand flux this is due to the 6 h sampling rate and to systematic bias revealed by a comparison with the local wind data we describe a simple procedure to correct for these effects with the proposed correction similar sand flux are predicted using the local and era interim data independently of the value of the value of the shear velocity threshold u t the predicted sand flux is about 65 of q dunes the agreement is best assuming the value u t 0 244 m s which is only slightly larger than the value of u t 0 2612 m s estimated based in the sand granulometry measured from field samples the influence of the dune topography on the wind velocity field could explain the underestimation in any case the study demonstrates the possibility of validating gcm model and calibrating aeolian sand transport laws using remote sensing measurements of dune dynamics and highlights the caveats associated to such an approach

seepage induced penetration of water vapor and dust beneath ripples and dunes 1 we present stratigraphic measurements of humidity and bulk density beneath the surface of a barchan dune obtained with a capacitance probe a model shows that air seeping through the sand bed in response to spatial variations of static pressure along the ripple surface guides water vapor through ripple crests and gradually stores dust beneath troughs the accumulated dust remains trapped beneath the relatively compact trough surface until wind is violent enough to mobilize sand deeply

the role of slab detachment processes in the opening of the western central mediterranean basins some geological and geophysical evidence abstract a review of the geological and geophysical data from the central and western mediterranean region and the present day upper mantle structure derived from tomographic studies are utilized in order to define the oligocene recent geodynamic evolution for the area in line with previous work we suggest that the miocene quaternary opening of the western and central mediterranean basins is the result of back arc extension due to the roll back toward the southeast of a northwestward subducting african slab in a geodynamic setting pinned between the alpine and betic collisional zones we find however that this general pattern is complicated by four different detachment events which occurred beneath the alps early oligocene the betic chain aquitanian northern africa langhian and the apennines late miocene pliocene we show that each of these events determines a major tectonic reorganization within the european plate

assessing the martian surface distribution of aeolian sand using a mars general circulation model a sand transport model using white s 1979 sand flux equation and the mars general circulation model pollack et al 1990 was developed to understand the erosional sources transport pathways and depositional sinks of windblown sand on mars an initially uniform distribution of sand 4 mm over the entire surface is regionally transported based on wind stress saltation threshold and percentage of topographic trapping results are consistent with the observed polar and hellespontus dunes and christensen s 1986 modeled block size distribution but only for an extremely low saltation threshold 0 024 n m 2 low thresholds generally result in transport of sand sized particles originating in the northern mid latitudes to the north pole and transport from the northern lower latitudes to the southern hemisphere our results indicate that the polar dune fields could form in 50 000 years consistent with the active polar dunes and lack of longitudinal dunes observed on the surface of mars

eocene pliocene time scale and stratigraphy of the upper rhine graben urg and the swiss molasse basin smb we present a general stratigraphic synthesis for the upper rhine graben urg and the swiss molasse basin smb from eocene to pliocene times the stratigraphic data were compiled both from literature and from research carried out by the authors during the past 6 years an index of the stratigraphically most important localitites is provided we distinguish 14 geographical areas from the helvetic domain in the south to the hanau basin in the north for each geographical area we give a synthesis of the biostratigraphy lithofacies and chronostratigraphic ranges the relationships between this stratigraphic record and the global sea level changes are generally disturbed by the geodynamic e g subsidence evolution of the basins however global sea level changes probably affected the dynamic of transgression regression in the urg e g middle pechelbronn beds and serie grise corresponding with sea level rise between ru1 ru2 and ru2 ru3 sequences respectively as well as in the molasse basin regression of the umm corresponding with the sea level drop at the ch1 sequence the urgent project upper rhine graben evolution and neotectonics provided an unique opportunity to carry out and present this synthesis discussions with scientists addressing sedimentology tectonics geophysics and geochemistry permitted the comparison of the sedimentary history and stratigraphy of the basin with processes controlling its geodynamic evolution data presented here back up the palaeogeographic reconstructions presented in a companion paper by the same authors see berger et al in int j earth sci 2005

fossil cosmogenic 3 he record from k ar dated basaltic flows of mount etna volcano sicily 38 n evaluation of a new paleoaltimeter this study investigates the reliability of a paleoaltimeter based on the elevation dependency of the cosmogenic nuclides production rate the proposed method relies on fossil cosmogenic record indeed measuring the cosmogenic nuclide concentration in an exposed and then buried lava flow combined with an independent estimate by k ar or 40ar 39ar dating of the past exposure duration theoretically allows recording fossil cosmogenic production rates which can thus be converted in paleoelevations this approach was tested by measuring cosmogenic 3he 3hec in olivines and clinopyroxenes of quaternary k ar dated basaltic flows of mount etna volcano sicily 38 n the agreement within uncertainties 1 500 m between current and cosmogenic derived elevations demonstrates the paleoaltimeter reliability however dating imprecision earth s paleomagnetic fluctuations and erosion contemporary to the flow exposure are parameters that may affect the accuracy and the precision of the method on older geological scales their respective influences were thus carefully evaluated and discussed to conclude that the paleoaltimeter can potentially reach resolutions better than 1000 m even for cenozoic records

basaltic sand ripples at eagle crater as indirect evidence for the hysteresis effect in martian saltation abstract the rover opportunity documented small basaltic sand ripples at the bottom of eagle crater meridiani planum on mars these ripples are composed of fine basaltic sand 100 m diameter and their average wavelength and height are 10 cm and 1 cm respectively present theories on the transition between saltation and suspension predict that such light particles are suspended by turbulence at the fluid threshold which is the minimum wind speed required to initiate saltation consequently the existence of these 100 m ripples on mars indicates that either current suspension theories are incorrect or that saltation can take place at wind speeds substantially below the fluid threshold indeed recent studies point to the occurrence of hysteresis in martian saltation that is once initiated hysteresis can be maintained at much lower wind speeds than the fluid threshold we investigated the possible role of hysteresis in the formation of fine grained ripples on mars by coupling for the first time a detailed numerical saltation model comsalt with a dynamic model for sand ripple formation the results from the coupled model indicate that ripples with properties similar to those observed at eagle crater can be developed by the impact mechanism at shear velocities far below the fluid threshold these findings are consistent with the occurrence of hysteresis in martian saltation and support the hypothesis that hysteresis plays a role in the surprisingly large sand mobility observed at several locations on mars

paleogeography of the upper rhine graben urg and the swiss molasse basin smb from eocene to pliocene twenty paleogeographic maps are presented for middle eocene lutetian to late pliocene times according to the stratigraphical data given in the companion paper by berger et al this volume following a first lacustrine continental sedimentation during the middle eocene two and locally three rupelian transgressive events were identified with the first corresponding with the early rupelian middle pechelbronn beds and the second and third with the late rupelian serie grise fischschiefer and equivalents during the early rupelian middle pechelbronn beds a connection between north sea and urg is clearly demonstrated but a general connection between north sea urg and paratethys via the alpine sea is proposed but not proved during the late rupelian whereas in the southern urg a major hiatus spans early aquitanian to pliocene times early and middle miocene marine brackish and freshwater facies occur in the northern urg and in the molasse basin omm osm however no marine connections between these basins could be demonstrated during this time after the deposition of the molasse series a very complex drainage pattern developed during the late miocene and pliocene with a clear connection to the bresse graben during the piacenzian sundgau gravels during the late miocene pliocene and quaternary sedimentation persisted in the northern urg with hardly any interruptions the present drainage pattern of the rhine river from alpine area to the lower rhine embayment was not established before the early pleistocene

intracrystalline site preference of oxygen isotopes in goethite a single mineral paleothermometer abstract the crystal structure of goethite feo oh has two distinct oxygen sites one with exclusively fe o bonds the other with bonds to both iron and hydrogen we developed a method to assess the oxygen isotope contrast between these sites by measuring both the bulk goethite and the oxygen released in the conversion of goethite to hematite the method involves collecting the water released by dehydroxylation fluorinating that population of extracted atoms and measuring the resulting oxygen isotope composition extracted o 18 then on a separate aliquot all structural oxygen is fluorinated and measured bulk o 18 using synthetic goethite precipitates grown under controlled environmental conditions we found significant temperature dependent fractionation e bulk extracted 5 51 0 26 10 6 t 2 44 5 2 8 t in kelvin this intracrystalline fractionation forms the basis of a single phase paleothermometer with an estimated uncertainty of 2 3 c the temperature dependence appears to be independent of the isotopic composition of the parent fluid from which the goethite formed and the ph of that fluid this intracrystalline thermometer can be used to simultaneously determine the formation temperature of a goethite and the isotopic composition of the water from which it formed natural goethites analyzed with this technique yield geologically reasonable formation temperatures of between 15 and 41 c

history of subduction and back arc extension in the central mediterranean summary geological and geophysical constraints to reconstruct the evolution of the central mediterranean subduction zone are presented geological observations such as upper plate stratigraphy hp lt metamorphic assemblages foredeep trench stratigraphy arc volcanism and the back arc extension process are used to define the infant stage of the subduction zone and its latest back arc phase based on this data set the time dependence of the amount of subducted material in comparison with the tomographic images of the upper mantle along two cross sections from the northern apennines and from calabria to the gulf of lyon can be derived further the reconstruction is used to unravel the main evolutionary trends of the subduction process results of this analysis indicate that 1 subduction in the central mediterranean is as old as 80 myr 2 the slab descended slowly into the mantle during the first 20 30 myr subduction speeds were probably less than 1 cm year x1 3 subduction accelerated afterwards producing arc volcanism and back arc extension and 4 the slab reached the 660 km transition zone after 60 70 myr this time dependent scenario where a slow initiation is followed by a roughly exponential increase in the subduction speed can be modelled by equating the viscous dissipation per unit length due to the bending of oceanic lithosphere to the rate of change of potential energy by slab pull finally the third stage is controlled by the interaction between the slab and the 660 km transition zone in the southern region this results in an important re shaping of the slab and intermittent pulses of back arc extension in the northern region the decrease in the trench retreat can be explained by the entrance of light continental material at the trench

evolution of the magmatic plumbing system at mt etna new evidence from gravity and magnetic data new gravity and aeromagnetic data from mt etna volcano are presented which provide evidence for and constraints on relatively dense high magnetization bodies at shallow levels below the summit craters these are modelled and interpreted in terms of dyke sill complexes which may be the sites of short term magma storage a similar but larger body with high density and high magnetization is modelled below the southern wall of the valle de bove and may be the remnant of a prehistoric storage system this body is close to the valle del bove a major collapse feature and may have influenced its geometry by buttressing and or focusing zones of weakness

chemical and physical erosion rhythms of the west african cenozoic morphogenesis the 39 ar 40 ar dating of supergene k mn oxides chemical weathering and mechanical erosion are first order processes of long term tropical morphogenesis which is still poorly deciphered for lack of time constraints we address this issue by laser probe 39ar 40ar dating of generations of cryptomelane k1 2mn8o16 nh2o from the manganese ore deposit of tambao in northern burkina faso this mn deposit results from the supergene weathering of carbonate and silicate mn protores underneath lateritic palaeolandsurfaces it consists of an upper cryptomelane rich domain and a lower domain where pyrolusite b mno2 is the dominant mn oxide the oldest 39ar 40ar ages 59 45 ma are obtained on surface outcrops while the youngest ones characterize deep oxidation fronts 3 4 2 9 ma apparent correlations of 39ar 40ar age groups with d18o and eustatic curves allow definition of the different stages of morphogenesis paleocene eocene ages 59 45 ma bracket a greenhouse period propitious to bauxitic weathering the lack of significant ages between 45 and 29 ma characterizes a period dominated by mechanical erosion during which detrital sediments including lateritic materials were accumulated in intracratonic basins allowing the exhumation of a new lateritic landsurface two major weathering periods separated by a second erosion episode 24 18 ma are also depicted at the end of oligocene 29 24 ma and lower to mid miocene 18 11 5 ma in the upper domain during which newly shaped land surfaces conspicuously weathered the shorter weathering and erosion episodes recorded in the lower domain from 18 to 2 9 ma led to the final geomorphic changes that were conducive to the formation of glacis the preservation of old cryptomelane 59 45 ma in the upper part of the ore deposit indicates a cenozoic denudation limited to the erosion of previous bauxites and partly of ferricretes

from basalt to dacite origin and evolution of the calc alkaline series of salina aeolian arc italy the island of salina comprises one of the most distinct calc alkaline series of the aeolian arc italy in which calc alkaline high k calc alkaline shoshonitic and leucite shoshonitic magma series are developed detailed petrological geochemical and isotopic sr nd pb o data are reported for a stratigraphically well established sequence of lavas and pyroclastic rocks from the middle pleistocene volcanic cycle 430 127 ka of salina which is characterized by an early period of basaltic volcanism corvo capo rivi fossa delle felci group 1 and a sequence of basaltic andesites and andesites and dacites in the final stages of activity fossa delle felci groups 2 8 major and trace element compositional trends rare earth element ree abundances and mineralogy reveal the importance of crystal fractionation of plagioclase clinopyroxene olivine orthopyroxene titanomagnetite amphibole apatite in generating the more evolved magma types from parental basaltic magmas and plagioclase accumulation in producing the high al2o3 contents of some of the more evolved basalts sr isotope ratios range from 0 70410 to 0 70463 throughout the suite and show a well defined negative correlation with 143nd 144nd 0 51275 0 51279 pb isotope compositions are distinctly radiogenic with relatively large variations in 206pb 204pb 19 30 19 66 fairly constant 207pb 204pb 15 68 15 76 and minor variations in 208pb 204pb ratios 39 15 39 51 whole rock 18o values range from 6 4 to 8 5 and correlate positively with sr isotope ratios overall the isotopic variations are correlated with the degree of differentiation of the rocks indicating that only small degrees of crustal assimilation are overprinting the dominant evolution by crystal liquid fractionation afc type processes the radiogenic and oxygen isotope composition of the salina basalts suggests derivation from primary magmas from a depleted mantle source contaminated by slab derived fluids and subducted sediments with an isotopic signature of typical upper continental crust these magmas then evolved further to andesitic and dacitic compositions through the prevailing process of low pressure fractional crystallization in a shallow magma reservoir accompanied by minor assimilation of crustal lithologies similar to those of the calabrian lower crust

4he 3he thermochronometry using classical diffusion theory we present a mathematical technique for the determination of 4he concentration profiles in minerals this approach should prove useful for constraining the low temperature cooling histories of individual samples and for correcting u th he ages for partial diffusive loss the calculation assumes that the mineral of interest contains an artificially produced and uniform distribution of 3he obtained by proton irradiation shuster et al earth planet sci lett 217 2004 19 32 in minerals devoid of natural helium this isotope allows measurement of he diffusion coefficients in minerals with measurable radiogenic he it permits determination of 4he profiles arising during ingrowth and diffusion in nature the 4he profile can be extracted from stepwise degassing experiments in which the 4he 3he ratio is measured the evolution of the 4he 3he ratio as a function of cumulative 3he released can be compared with forward models to constrain the shape of the profile alternatively we present a linear inversion that can be used to directly solve for the unknown 4he distribution the inversion incorporates a standard regularization technique to filter the influence of random measurement errors on the solution using either approach we show that stepwise degassing data can yield robust and high resolution information on the 4he profile profiles of radiogenic he are a sensitive function of the time temperate t t path that a cooling sample experienced thus by step heating a proton irradiated sample it is possible to restrict the sample s acceptable t t paths the sensitivity of this approach was explored by forward modeling 4he profiles resulting from a range of realistic t t paths using apatite as an example results indicate that 4he profiles provide rich information on t t paths especially when the profiles are coupled with u th he cooling ages on the same sample samples that experienced only moderate diffusive loss have 4he concentration profiles that are rounded at the edge but uniform in the core of the diffusion domain such profiles can be identified by nearly invariant 4he 3he ratios after the first few to few tens of percent of 3he have been extracted by step heating we show how such data can be used to correct u th he ages for partial diffusive loss

evidence for 5 ma paleo exposure of an eocene miocene paleosol of the bohnerz formation switzerland we obtained u th he formation ages and cosmogenic 3he concentrations for pisoliths from a paleosol of the bohnerz formation siderolithic of central europe the paleosol is exposed in the almenbuhl quarry near lohn canton schaffhausen switzerland the paleosol consists of red clay of 3 4 m thickness developed on deeply weathered jurassic limestone and overlain by early miocene conglomerates the u th he formation ages of the pisoliths are between 50 ma and 8 ma with most ages being older than 17 ma there is a sharp decline in the frequency of ages at the time of burial of the paleosol at 17 ma these ages are inconsistent with the previous assumption that the bohnerz formation formed in a cretaceous to early eocene laterite in a tropical climate we propose that the bohnerz formation more closely resembles terra rossa soils which do not require a tropical climate to form the 3he concentration in the pisoliths is roughly constant with depth throughout the paleosol at 300 matoms g we interpret this as the result of soil convection during cosmic ray exposure the minimum exposure duration at the surface of the paleosol is 5 ma a simple model of soil convection shows that the true exposure duration of the paleosol is approximately 10 20 ma these results indicate that the clay soils of the bohnerz formation were continuously exposed at the surface for millions of years since the paleosol was covered by conglomerate since 17 ma the 3he measured here was produced by cosmic ray exposure before burial cosmogenic 3he concentrations measured in fine grained soil iron oxides 1 m are similar to those measured in pisoliths this might indicate that fine grained iron oxides are retentive to helium and might be used for studying the formation and cosmic ray exposure of modern soils and paleosols

magmatic control along a strike slip volcanic arc the central aeolian arc italy the regional stress field in volcanic areas may be overprinted by that produced by magmatic activity promoting volcanism and faulting in particular in strike slip settings the definition of the relationships between the regional stress field and magmatic activity remains elusive to better understand these relationships we collected stratigraphic volcanic and structural field data along the strike slip central aeolian arc italy here the islands of lipari and vulcano separate the extensional portion of the arc to the east from the contractional one to the west we collected 500 measurements of faults extension fractures and dikes at 40 sites most structures are nne ssw to nnw sse oriented eastward dipping and show almost pure dip slip motion consistent with an e w extension direction with minor dextral and sinistral shear our data highlight six eruptive periods during the last 55 ka which allow considering both islands as a single magmatic system in which tectonic and magmatic activities steadily migrated eastward and currently focus on a 10 km long 2 km wide active segment faulting appears to mostly occur in temporal and spatial relation with magmatic events supporting that most of the observable deformation derives from transient magmatic activity shorter term days to months rather than from steady longer term regional tectonics 102 104 years more in general the central aeolian case shows how magmatic activity may affect the structure and evolution of volcanic arcs overprinting any strike slip motion with magma induced extension at the surface

iron oxide mineralogy of terra rossa and its genetic implications abstract fe d fe d fe t hematite geothite ratios and al substitution in hematite and goethite were found to vary to a rather limited extent in 48 terra rossa samples from various locations around the world this seems to indicate a rather specific pedoenvironment in which terra rossa is formed it is suggested that this pedoenvironment is characterized by an association of mediterranean climate high internal drainage due to the karstic nature of a hard limestone and neutral ph conditions under those conditions relatively high amounts of fe are released fe d fe t ca 0 7 from autochthonous and or allochthonous primary fe sources followed by preferential formation of hematite over goethite both having a medium level of al substitution the close association between terra rossa and the underlying limestone must therefore be seen in the role the rock plays for the water and air regimes of the soil rather than in its material characteristics except for soil ph neither an fe content in the limestone insufficient to explain the fe content of the solum nor the addition of eolian or alluvial material can therefore be used as an argument against a genetic relationship between terra rossa and its underlying limestone

weathering geochronology by u th he dating of goethite nine samples of supergene goethite feooh from brazil and australia were selected to test the suitability of this mineral for u th he dating measured he ages ranged from 61 to 8 ma and were reproducible to better than a few percent despite very large variations in u and th in all samples with internal stratigraphy or independent age constraints the he ages corroborated the expected relationships these data demonstrate that internally consistent he ages can be obtained on goethite but do not prove quantitative 4he retention to assess possible diffusive he loss stepped heating experiments were performed on two goethite samples that were subjected to proton irradiation to produce a homogeneous distribution of spallogenic 3he the 3he release pattern indicates the presence of at least two diffusion domains one with high helium retentivity and the other with very low retentivity at earth surface conditions the low retentivity domain which accounts for 5 of 3he contains no natural 4he and may represent poorly crystalline or intergranular material which has lost all radiogenic 4he by diffusion in nature diffusive loss of 3he from the high retentivity domain is independent of the macroscopic dimensions of the analyzed polycrystalline aggregate so probably represents diffusion from individual micrometer size goethite crystals the 4he 3he evolution during the incremental heating experiments shows that the high retentivity domain has retained 90 95 of its radiogenic helium this degree of retentivity is in excellent agreement with that independently predicted from the helium diffusion coefficients extrapolated to earth surface temperature and held for the appropriate duration considering both the high and low retentivity domains these data indicate that one of the samples retained 90 of its radiogenic 4he over 47 5 ma and the other retained 86 over 12 3 ma thus while diffusive loss corrections to supergene goethite he ages are required these initial results indicate that the corrections are not extremely large and can be rigorously quantified using the proton irradiation 4he 3he method

timescale dependence of aeolian sand flux observations under atmospheric turbulence 1 the transport of sand in saltation is driven by the persistently unsteady stresses exerted by turbulent winds based on coupled high frequency observations of wind velocity and sand flux on a desert dune during intermittent saltation we show here how observations of saltation by natural winds depend significantly on the timescale and method used for determining shear stress and sand flux the correlation between sand flux and excess shear stress stress above a threshold value systematically improves for longer averaging timescale t and is better for stress determined by the law of the wall versus the reynolds stress method fitting parameters for the stress flux relationship do not converge with increasing t which may be explained by the nonstationary nature of wind velocity statistics we show how it may be possible based on the scale dependent statistics of stress fluctuations to rescale saltation flux predictions for wind observations made at different timescales however our observations indicate hysteresis and time lags in thresholds for initiation and cessation of saltation which complicate threshold based approaches to predicting sediment transport at different timescales

a new model for the evolution of the volcanic island of reunion indian ocean the island of reunion has been studied using data from airborne and shipborne magnetic surveys the subaerial history of reunion spans the last 2 1 million years the brunhes matuyama geomagnetic reversal enables differentiation of volcanic rocks older and younger than 0 78 ma the lower submarine flanks are poorly magnetized and are interpreted as landslide deposits the core of the island is composed of highly magnetized rocks piton des neiges volcano is composed mostly of rocks older than 0 78 ma only its western flank and central area include thick piles of younger rocks piton de la fournaise is a highly and normally magnetized edifice but its northern and eastern flanks are underlain at shallow depth by reversely magnetized formations the latter are regarded as remnants of les alizes volcano associated with the grand brule hypovolcanic complex at the matuyama brunhes transition the island was composed of at least two main volcanoes piton des neiges and les alizes and perhaps also of a third old volcano takamaka at the center north of the island piton de la fournaise grows on the flank of les alizes and is a relatively young focus of volcanism these volcanoes have had successive phases of construction and destruction the analysis of magnetic anomalies over reunion was decisive in defining a new coherent model for the evolution of the island

variability of the apparent von karman parameter during aeolian saltation 1 the variability of the apparent von karman parameter a during aeolian saltation was evaluated in a field experiment at jericoacoara brazil to test this variability velocity profiles reynolds stress and sand transport data were gathered and analyzed we used 15 data sets with sand laden airflow and 2 runs with clear airflow results indicated an inverse linear relationship between a and bulk gravimetric sand concentration r2 0 746 and sand transport rate r2 0 577 we found values of a as low as 0 26 this means that using the von karman constant 0 40 rather than the variable a to estimate shear velocity based on the slope of the velocity profile will lead to over estimation of shear velocity averaging about 20 in this study this in turn produces an over estimation of wind blown sand transport rates based on models that have terms with shear velocity cubed

an isochron method for cosmogenic nuclide dating of buried soils and sediments we describe an improved method for dating buried paleosols using measurements of the cosmic ray produced radionuclides 10be and 26al in quartz grains and apply it to a sequence of intercalated tills and paleosols in central missouri usa that record plio pleistocene advances of the laurentide ice sheet a buried paleosol implies a period of surface exposure and nuclide accumulation followed by burial and a halt to nuclide production if the paleosol is formed in a sedimentary unit such as till this unit may also have been emplaced with unknown 26al and 10be concentrations inherited from past surface exposure if the inherited nuclide concentrations are the same at all depths in the soil as is true for well mixed sediments such as till then the 26al and 10be concentrations at different depths in the paleosol will show a linear relationship the slope of this line depends on the duration of burial of the paleosol but not on the inherited nuclide concentrations or on the sample depths thus one can date strata overlying buried paleosols by measuring 26al and 10be at multiple depths in the paleosol and calculating the burial age of the paleosol from the resulting isochron we focus on applying this approach to till paleosol sequences but the basic idea of forming an 26al 10be burial isochron with a set of samples that share the same burial age but differ in other aspects of their exposure history applies to other stratigraphic settings as well the method yields ages for four tills in missouri that are stratigraphically consistent agree with paleomagnetic age constraints and show that ice advanced into missouri near 1 25 ma near 0 8 ma and twice between ca 0 4 and 0 2 ma

a buried volcano in the calabrian arc italy revealed by high resolution aeromagnetic data 1 aeromagnetic data collected between the aeolian volcanoes southern tyrrhenian sea and the calabrian arc italy highlight a wnw ese elongated positive magnetic anomaly centered on the capo vaticano morphological ridge tyrrhenian coast of calabria characterized by an apical subcircular flat surface results of forward and inverse modeling of the magnetic data show a 20 km long and 3 5 km wide magnetized body that extends from sea floor to about 3 km below sea level the magnetic properties of this body are consistent with those of the medium to highly evolved volcanic rocks of the aeolian arc i e dacites and rhyolites in the calabria mainland widespread dacitic to rhyolitic pumices with calc alkaline affinity of pleistocene age 1 0 7 ma are exposed the tephra falls are related to explosive activity and show a decreasing thickness from the capo vaticano area southeastward the presence of lithics indicates a provenance from a source located not far from capo vaticano the combined interpretation of the magnetic and available geological data reveal that 1 the capo vaticano wnw ese elongated positive magnetic anomaly is due to the occurrence of a wnw ese elongated sill 2 such a sill represents the remnant of the plumbing system of a pleistocene volcano that erupted explosively producing the pumice tephra exposed in calabria and 3 the volcanism is consistent with the aeolian products in terms of age magnetic signature and geochemical affinity of the erupted products the results indicate that such volcanism developed along seismically active faults transversal to the general trend of the aeolian arc and calabria block in an area where uplift is maximized 4 mm yr such uplift could also be responsible for fragmentation of the upper crust and formation of transversal faults along which seismic activity and volcanism occur

multiple hazards and paths to eruptions a review of the volcanic system of vulcano aeolian islands italy abstract vulcano is one of the 7 volcanic islands and 6 seamounts forming the aeolian volcanic district italy vulcano has a long eruptive record and its last eruption 1888 90 originated the definition of the vulcanian eruptive style like most volcanic islands vulcano generates many potentially interconnected hazards determining a potentially high risk here we review the state of knowledge on its geology eruptive activity historical accounts structural setting geophysical and geochemical surveillance and available hazard quantifications in order to have an updated picture of the state knowledge on volcanic hazard we follow a prototypal reviewing scheme based on three standardized steps i review of the volcanic system ii review of available eruptive and non eruptive hazard quantifications iii development of a conceptual interpretative model we find that while a rather vast literature is dedicated to the volcanic system of vulcano and the reconstruction of past events few quantitative hazard assessments exist in addition the range of natural variability considered for each hazard is potentially underestimated e g limited range of considered eruption magnitude and style and of vent position as it is the potential effect of multi hazard impact the developed conceptual model for the feeding system provides a synthetic picture of the present knowledge about the system as emerged from the review in addition it allows for the identification of potential paths to eruption and provides a first order link among the main hazards this review provides an up to date snapshot of existing knowledge on volcanic hazard at vulcano on which to build future hazard quantifications as well as to support present and future decision making

cenozoic continental climatic evolution of central europe continental climate evolution of central europe has been reconstructed quantitatively for the last 45 million years providing inferred data on mean annual temperature and precipitation and winter and summer temperatures although some regional effects occur the european cenozoic continental climate record correlates well with the global oxygen isotope record from marine environments during the last 45 million years continental cooling is especially pronounced for inferred winter temperatures but hardly observable from summer temperatures correspondingly cenozoic cooling in central europe is directly associated with an increase of seasonality in contrast inferred cenozoic mean annual precipitation remained relatively stable indicating the importance of latent heat transport throughout the cenozoic moreover our data support the concept that changes in atmospheric co2 concentrations although linked to climate changes were not the major driving force of cenozoic cooling

u th he geochronology of goethite and the origin and evolution of cangas abstract u th he geochronology of 147 grains of goethite cements extracted from ferruginous duricrusts cangas developed on banded iron formations from the quadrilatero ferrifero region minas gerais brazil records a history of protracted mineral dissolution reprecipitation that started at ca 48 1 4 8 ma and continues intermittently until the present a large majority of the samples more than 30 are younger than 2 ma revealing active mineral dissolution reprecipitation in the recent past within cangas goethite cements are younger near the surface and become progressively older towards the bottom of the weathering profile indicating that iron is more effectively cycled in the parts of the weathering profile more strongly affected by biogenic activity u th he geochronology of 14 goethite grains from saprolites in the same profiles yield results ranging from 55 3 5 5 to 25 7 2 6 ma for a single weathering profile goethite cements from cangas are invariably younger than goethite grains from the underlying saprolite indicating that the duricrust and the saprolite behave as independent and separate systems responding to different environmental controls thorium shows conservative behaviour during goethite dissolution reprecipitation and it is enriched towards the surface of the weathering profile uranium on the other hand is preferentially leached from the surface into the saprolite or out of the weathering profile recurrent goethite dissolution reprecipitation lends great textural complexities to cangas but it is also responsible for its capacity to reheal when physically disrupted this self healing property accounts for canga s role in armoring banded iron formation landscapes

oblique rifting in salina lipari and vulcano islands aeolian islands southern italy a structural analysis carried out on the volcanic products of the islands of salina lipari and vulcano aeolian archipelago points out that the large scale tectonic setting is dominated by nw se trending right lateral extensional strike slip faults and by n s to ne sw trending normal faults and fractures this fault pattern generates pull apart type structures developing between different right hand overlapping fault segments and a characteristic extensional imbricate fan geometry at the tip of the major strike slip faults all the structures representing the surface expression of an active crustal discontinuity which controls the evolutionary history of the magmatism of the three islands are kinematically compatible with a n100 e extension related to a rifting process affecting southern italy

morpho bathymetric and seismo stratigraphic analysis of the insular shelf of salina aeolian archipelago to unveil its late quaternary geological evolution abstract the distribution and morphological characteristics of the shelves around salina island have been analyzed and integrated with observations from onshore geological field studies in order to improve knowledge about its evolution and to demonstrate how shelf width depth can be used as proxies for reconstructing the development of the volcanic edifice insular shelves form essentially through marine erosion of volcanic centres during stages of reduced or inactive volcanism and are representative of their original extension shelves having larger widths commonly 1000 m and deeper edges over 125 m depth experienced wave erosion during successive cycles of sea level fluctuations and subsidence after their formation thus being indicative of a relatively older age of the eroded volcanic centres accordingly we document offshore salina the occurrence of presently submerged and largely dismantled volcanic centres namely pizzo capo north and fossa delle felci south predating the oldest subaerial products exposed on the adjacent coastal sectors these offshore centres have subsided after their erosion and are no more documented on land furthermore the finding of the largest and deepest shelf around the subaerial remnants of pizzo di corvo volcanic edifice allows relating it to an earlier stage of evolution of salina shedding light on contradictory radiometric ages on land narrower shelves commonly on the whole our results show the importance of integrated field and marine studies to unravel the geological evolution of insular volcanoes and to obtain inferences on their vertical mobility

residual topography lithospheric structure and sunken slabs in the central mediterranean abstract the central mediterranean comprises subduction collision and backarc extension all in a relatively small area in this paper we analyze the topography of this region examining the influence of subducting slabs on overriding plates we take the observed surface elevation remove the contribution of the crust to it and use the residual topography to identify regions that are unusually low unusually high or normal then we calculate lithospheric thickness where local isostasy applies the results provide information about the structure of the lithosphere in this complex region and about the vertical tectonics in particular we found a difference between the south tyrrhenian subduction zone and the apennines consistent with the processes of slab rollback and slab break off respectively in the south tyrrhenian the edge of the oceanic plate is strongly pulled down whereas the edge of the overriding plate the calabrian peninsula is uplifted this opposite trend indicates weak plate coupling that is the subducting slab which is rapidly rolling back hangs almost entirely on the oceanic plate and the overriding plate is free in contrast in the apennines high residual topography and uplifting are detected on both sides of the mountain belt consistent with complete break off of the subducted lithosphere

direct dating of weathering phenomena by 40ar39ar and k ar analysis of supergene k mn oxides abstract potassium bearing manganese oxides cryptomelane k1 2 mn3 mn4 8 o16 xh2oand hollandite k ba 1 2 mn3 mn4 8 o16 xh2o are often authigenically precipitated in weathering profiles the presence of structural potassium in manganese oxides makes these minerals datable by the k ar and 40 ar 39 ar methods dating of these phases allows us to time the progression of oxidation fronts during weathering and pedogenic processes detailed age resolution of the weathering history allows us to use deep weathering profiles as land based stratigraphic records of past climatic and geomorphic events complementing evidence from the marine sedimentary and paleontological record potential problems in manganese oxide dating such as ar and or k losses excess argon 39ar loss by recoil during neutron irradiation contamination by primary minerals resistant to weathering the presence of multiple generations of manganese oxides and proportionately low radiogenic ar yield due to adsorbed atmospheric gases are addressed the k ar and 40 ar 39 ar analytical results indicate that ar and or k losses excess 40ar and 39ar recoil seem not to pose problems in manganese oxide dating this investigation suggests that fine scale laser probe 40 ar 39 ar technique is most appropriate for dating of weathering phenomena because this technique permits us to identify contaminating phases and the presence of multiple generations of weathering minerals in the inherently complex mineral assemblage characteristic of weathering profiles k ar and 40 ar 39 ar dating of supergene k bearing manganese oxides formed during lateritization of archean and proterozoic bedrocks in the caraj s region amazonia brazil indicates that weathering started before 72 6 ma petrographic electron microscope and electron microprobe investigation reveal multiple generations of manganese oxide precipitation k ar and 40 ar 39 ar laser probe step heating results independently confirm the presence of these various generations of manganese oxides age clusters at 65 69 51 56 40 43 33 35 20 24 12 17 ma and zero age 0 2 0 2 ma suggest episodic precipitation of k mn oxides resulting from changing weathering conditions in the amazon throughout the cenozoic k ar and 40 ar 39 ar dating of supergene cryptomelane from weathering profiles in eastern minas gerais southeastern brazil suggests continuous weathering from 10 to 5 6 ma ago possibly reflecting local climatic conditions due to the proximity with the atlantic ocean

volcanological evolution of the rivi capo volcanic complex at salina aeolian islands magma storage processes and ascent dynamics lava flows and pyroclastic deposits from strombolian fallout related to the activity of the rivi and capo volcanoes which are representative of early subaerial volcanoes on salina aeolian islands have been investigated through a geological petrological approach our geological field survey shows that rivi and capo volcanoes are part of a single n50 e aligned volcanic complex here named rivi capo volcanic complex rcvc stratigraphically specific rock sampling has allowed reconstruction of the magma feeding processes through time whole rock major element compositions together with core to rim profiles of plagioclase and clinopyroxene crystals show a general evolution toward more basic compositions through the three formations constituting the capo volcano and within the rivi center melts simulations and mass balance modeling suggest that the rcvc rocks are the result of fractional crystallization of plagioclase clinopyroxene and olivine ca 45 of solid removed from a primary magma in addition to fractional crystallization continuous recharge and mixing with more basic magma coming from deeper parts of the magmatic plumbing system contributed to the final volcanic rock compositions our textural and microanalytical data on plagioclase and clinopyroxene crystals allow the definition of a multilevel magmatic storage system with reservoirs at 20 and 3 km below sea level when processes of magma differentiation ascent and storage are considered together with the stratigraphic position of each sample a history of continuous modification of the rcvc plumbing system can be constructed volcanism may have been characterized by fissure type eruptions during the early stages lower capo lower rivi and middle capo formations gradually changing later to central type volcanism upper capo and upper rivi formations

the 10th generation international geomagnetic reference field abstract the international association of geomagnetism and aeronomy iaga on 12 december 2004 released the 10th generation international geomagnetic reference field igrf the latest version of a standard mathematical description of the earth s main magnetic field and used widely in studies of the earth s deep interior its crust ionosphere and magnetosphere the coefficients were finalised by a task force of iaga the igrf is the product of a large collaborative effort between magnetic field modellers and the institutes involved in collecting and disseminating magnetic field data from satellites and observatories around the world

a continuous model for sand dunes review new developments and application to barchan dunes and barchan dune fields basically sand dunes are patterns resulting from the coupling of hydrodynamic and sediment transport once grains move they modify the surface topography which in turns modifies the flow this important feedback mechanism lies at the core of continuous dune modelling here we present an updated review of such a model for aeolian dunes including important modifications to improve its predicting power for instance we add a more realistic wind model and provide a self consistent set of parameters independently validated as an example we are able to simulate realistic barchan dunes which are the basic solution of the model in the condition of unidirectional flow and scarce sediments from the simulation we extract new relations describing the morphology and dynamics of barchans that compare very well with existing field data next we revisit the problem of the stability of barchan dunes and argue that they are intrinsically unstable bed forms finally we perform more complex simulations first a barchan dune under variable wind strength and second barchan dune fields under different boundary conditions the latter has important implications for the problem of the genesis of barchan dunes copyright 2010 john wiley sons ltd

cool climate or warm spike lateritic bauxites at high latitudes abstractlaterites and bauxites and their associated ultisols and oxisols are widespread in warm wet climates today and their spread to high latitudes has been attributed to episodes of past global warming bauxitic paleosols from the early eocene monaro volcanics of southeastern australia have been claimed as exceptions formed in a cool wet climate reexamination and chemical analysis of a sequence of intrabasaltic paleosols in the bega no 7 core of radiometrically dated monaro volcanics now show highly variable paleotemperature and precipitation the core includes 53 successive paleosols mostly nonbauxitic but bauxitic paleosols reveal local spikes in warmth and precipitation coincident with early eocene 55 52 51 and 48 ma global spikes of warmth precipitation and high atmospheric co2 these bauxitic paleosols thus formed in warm wet not cool dry climates and their poleward spread coincided with global greenhouse spikes

magma storage conditions and differentiation of the mafic lower pollara volcanics salina island aeolian islands italy implications for the formation conditions of shoshonites and potassic rocks crystallization experiments of basaltic andesite mafic endmember from the 24 ka lower pollara eruption salina aeolian islands italy were investigated at 200 mpa 950 1100 c in the h2o activity ah2o range 0 3 to 1 and at two ranges of oxygen fugacity fo2 between fmq to fmq 1 and fmq 2 to fmq 3 3 log bars fmq is fayalite magnetite quartz comparison of the produced phase assemblages and phase compositions with the natural sample reveals that the storage conditions were 1050 c 2 8 wt h2o in the melt ah2o 0 5 and relatively oxidizing fmq 2 5 the composition of plagioclase in the groundmass indicates a period of cooling to 950 c the overall differentiation trends of the salina volcanics can be explained by fractional crystallization close to h2o saturated conditions 5 wt h2o in the melt at 200 mpa and most likely by accumulation of plagioclase i e in basaltic andesites and by various degree of mixing mingling between the corresponding differentiates the slightly elevated k2o contents of the most mafic basaltic andesites that can be found in the lowermost unit of the lower pollara pyroclastics reveal earlier processes of moderately hydrous fractional crystallization at higher temperature 1050 c fractional crystallization with decreasing influence of h2o causes a moderate decrease of mgo and a significant increase of k2o relative to sio2 in the residual liquids it is exemplarily shown that the crystallization of sio2 rich phases at high temperature and low ah2o of only moderately k2o rich calc alkaline basalts can produce shoshonitic and high potassic rocks similar to those of stromboli and volcano this suggests that the observed transition from calc alkaline to shoshonitic and high potassic volcanism at the aeolian arc over time can be initiated by a general increase of magmatic temperatures and a decrease of ah2o in response to the extensional tectonics and related increase of heat flow and declining influence of slab derived fluids

the deep structure of the eolian arc filicudi panarea vulcano sector in light of gravity magnetic and volcanological data abstract the magnetic and gravimetric methods of investigation have been applied to the central sector of the eolian arc combined with geovolcanological data for the purpose of defining the structural framework in which the volcanism developed the processing of the magnetic and gravimetric data involved 3d modeling of the volcanic bodies and the application of a depth separation filter in order to subtract from the measured field the effect caused by the subaerial and submarine volcanic edifices and by all surface inhomogeneities magnetic and gravimetric 2 5d modeling on selected profiles has also been done in a joint interpretation of the magnetic and gravimetric data constrained by volcanological knowledge the interpretation of the final maps and profiles has demonstrated the existence of extensional tectonics resulting in the development of horst and graben volcanism occurs in the graben areas in particular the salina lipari vulcano magmatic axis has developed in a very deep articulated graben of lithospheric importance and completely filled by volcanic deposits and intrusive bodies the origin of this structure and of the associated igneous activity is suggested to be related to trans tensional tectonics along a plio pleistocene regional strike slip fault system

magnetic models of crystalline terrane accounting for the effect of topography igneous rocks commonly have large magnetic susceptibilities so that high topographic relief in crystalline terrane can produce significant anomalies in aeromagnetic surveys topographic anomalies are particularly significant in relatively undeformed volcanic terrane because young volcanic rocks generally have large natural remanent magnetizations as well as large susceptibilities these anomalies commonly appear in aeromagnetic surveys as a complex pattern of high amplitude short wavelength magnetic features that tend to obscure anomalies caused by deeper geologic sources we have facilitated geologic interpretation of an aeromagnetic survey of the oregon cascade range by calculating the magnetic field caused by a three dimensional 3 d topographic model maps of the calculated field are compared with observed aeromagnetic data both visually and with a numerical technique that produces a contour map of correlation coefficients for the model these comparisons allow quick recognition of anomalies caused

aeromagnetic data provide new insights on the volcanism and tectonics of vulcano island and offshore areas southern tyrrhenian sea italy 1 the active vulcano island southern tyrrhenian sea represents the southernmost portion of a nw se elongated volcanic ridge that includes also lipari and salina islands the ridge is affected by a regional nw se to n s striking fault system the elaboration and analysis of data from three high resolution aeromagnetic surveys carried out between 1999 and 2004 on vulcano and offshore allow us to recognize high intensity magnetic anomalies related to volcanic centers conduits or shallow intrusions previously unreported offshore submarine vents have been also recognized some of them may correspond with source areas of outcropping exotic pyroclastics on vulcano the spatial analysis of the recognized magnetic anomalies and volcanic structures shows that they are preferably aligned along the strikes of the main regional faults that affect the volcanic ridge submarine volcanic conduits revealed by the aeromagnetic survey might represent potential sources for future submarine effusive or explosive activity

a two species model of aeolian sand transport the transport of sand by wind results from the equilibrium between the erosion of grains dragged by the flow and the resulting slow down of the wind velocity the dynamical mechanisms governing the saturation of the sand flux are investigated theoretically we first demonstrate that previous models based on the assumption that all the grains have the same trajectory are either not self consistent or lead to unstable solutions a model based on a discrete number of states is derived which solves these problems two well defined species of grain appear which correspond to saltons high energy grains and reptons grains ejected from the sand bed by the impact of saltons they play specific roles the negative feedback of the transport on the wind is limited to the reptation layer while most of the transport is due to saltation the model is further simplified benefiting from the existence of these two species and the dependencies of the threshold velocity the saturated flux the aerodynamic roughness and the saturation length are derived and compared to experimental measurements

earth like sand fluxes on mars strong and sustained winds on mars have been considered rare on the basis of surface meteorology measurements and global circulation models raising the question of whether the abundant dunes and evidence for wind erosion seen on the planet are a current process recent studies showed sand activity but could not determine whether entire dunes were moving implying large sand fluxes or whether more localized and surficial changes had occurred here we present measurements of the migration rate of sand ripples and dune lee fronts at the nili patera dune field we show that the dunes are near steady state with their entire volumes composed of mobile sand the dunes have unexpectedly high sand fluxes similar for example to those in victoria valley antarctica implying that rates of landscape modification on mars and earth are similar

lateritization and bauxitization events laterites and bauxites are produced in tropical soils by weathering which enriches iron of laterites and alu mina of bauxites as well as trace elements such as nickel gold phosphorus and niobium to ore grade la terites and bauxites can be redeposited into sedimentary sequences and remain as ores if not transported far and diluted with other materials the age of redeposited laterites and bauxites and of bauxitic and lateritic pa leosols can be established from the geologic age of overlying rocks an approach especially effective in pale osols within sequences of isotopically datable volcanic rocks lateritic profiles can also be dated by paleomag netic inclination in special cases in which land masses such as in australia and india drifted long distances northward during cenozoic time in addition cryptomelane and other k mn oxides can be dated by k ar and 40ar 39ar techniques to obtain multiple ages from different crystals in a single relict paleosol compilation of new and more accurate laterite and bauxite ages reveals unusually widespread and intense laterite and bauxite formation during events of less than 100 k y duration at 2 12 16 35 48 55 65 and 100 ma such events can also be inferred at times older than 100 ma from paleolatitudinal distribution of laterites and bauxites but these are poorly sampled laterite and bauxite peaks were coeval with times of global high warmth and pre cipitation elevated atmospheric carbon dioxide oceanic anoxia exceptional fossil preservation and mass ex tinction these co2 greenhouse events and attendant titration of carbonic acid with soils are interpreted as transient fluctuations in the atmosphere produced by meteorite impact flood basalt volcanism and methane outbursts concentration of bauxite and laterite resources in particular stratigraphic horizons formed during greenhouse crises suggests the usefulness of an event stratigraphic approach to exploration and exploitation of these and related ores

cosmogenic and nucleogenic 3he in apatite titanite and zircon cosmogenic 3he was measured in apatite titanite and zircon and cosmogenic 21 ne in quartz at 13 depth intervals in a 2 7 m long drill core in a miocene ignimbrite from the altiplano of bolivia all three 3he depth profiles as well as the 21 ne profile attenuate exponentially with depth indicating that both of these isotopes are cosmogenic in origin with no significant contribution from other sources the attenuation lengthscale for 3he production of 180 11 g cm 2 is consistent with expectations for neutron spallation and is identical to that found for the cosmogenic 21 ne in quartz by normalizing the measured 3he concentrations to 21 ne and using the independently known cosmogenic 21 ne production rate the apparent cosmogenic 3he production rates in apatite titanite and zircon were respectively found to be 112 97 and 87 atoms g yr at sea level and high latitude the formal uncertainty on these estimates is 20 2 and arises in equal parts from uncertainties in the measured 3he 21 ne ratios and the uncertainty in the 21 ne production rate however an additional factor affecting the apparent 3he production rate in these phases arises from the long stopping range of spalled 3he and tritium which decays to 3he because all three accessory phases have higher mean atomic number than major rock forming minerals they will have lower 3he production rates than their surroundings as a consequence the long stopping ranges will cause a net implantation of 3he and therefore higher apparent production rates than would apply for purely in situ production thus these apparent production rates apply only to the specific grain sizes analyzed analysis of sieved zircon aliquots suggests that a factor of 2 increase in grain size from 50 to 100 m cross section yields a 10 decrease in apparent production rate while this effect warrants further study the grain sizes analyzed here are typical of the accessory phases commonly encountered so the apparent rates provide an appropriate starting place for surface exposure dating using 3he in these minerals