influences of quaternary climatic changes on processes of soil development on desert loess deposits of the cima volcanic field california summary soils formed in loess are evidence of both relict and buried landscapes developed on pliocene to latest pleistocene basalt flows of the cima volcanic field in the eastern mojave desert california the characteristics of these soils change systematically and as functions of the age and surface morphology of the lava flow four distinct phases of soil development are recognized phase 1 weakly developed soils on flows less than 0 18 m y old phase 2 strongly developed soils with thick argillic horizons on 0 18 0 7 m y old flows phase 3 strongly developed soils with truncated argillic horizons massively impregnated by carbonate on 0 7 to 1 1 m y old flows and phase 4 degraded soils with petrocalcic rubble on pliocene flows a critical aspect of the development of stage 1 soils is the evolution of a vesicular a horizon which profoundly affects the infiltration characteristics of the loess parent materials laboratory studies show that secondary gypsum and possibly other salt accumulation probably occurred during the period of phase 1 soil development slight reddening of the interiors of peds from vesicular a horizons of phase 1 soils and presence of weakly developed b horizons indicates a slight degree of in situ chemical alteration however clay and fe oxide contents of these soils show that these constituents as well as carbonates and soluble salts are incorporated as eolian dust in contrast to phase 1 soils chemical and mineralogical analysis of argillic horizons of phase 2 soils indicate proportionally greater degrees of in situ chemical alteration these data the abundant clay films and the strong reddening in the thick argillic horizons suggest that phase 2 and phase 3 soils formed during long periods of time and periodically were subjected to leaching regimes more intense than those that now exist flow age data and soil stratigraphic evidence also indicate that several major loess deposition events occurred during the past 1 0 m y loess events are attributed to past changes in climate such as the pleistocene to holocene climatic change that periodically caused regional desiccation of pluvial lakes reduction of vegetational density and exposure of loose unconsolidated fine materials during times of warmer interglacial climates precipitation infiltrates to shallower depths than during glacial periods extensive saline playas which developed in the mojave desert during the holocene are a likely source of much of the carbonates and soluble salts that are accumulating at shallow depths both in phase 1 soils and in the formerly noncalcareous nongypsiferous argillic horizons of phase 2 and 3 soils

similarities and dissimilarities between the dynamics of sand and dust during wind erosion of loamy sandy soil abstract aeolian dynamics were measured during a wind erosion event on an agricultural field in northern germany because the topsoil was loamy sand particle flow behaved as a sand dust mixture and not as pure sand 63 m or pure dust

two dimensional strain determination by the inverse surfor wheel abstract a simple method of two dimensional strain determination from the preferred orientation of deformed lines is presented it is based on the change of probability of intersecting lines on a given traverse as a function of traverse orientation the method can be applied to real lines such as grain boundary outlines or to virtual lines such as the tie lines between centre points of neighbouring grains in this manner estimates for the strain of surfaces i e of the particles enclosed by the surfaces and of bulk strain can be obtained

influence of late quaternary climatic changes on geomorphic and pedogenic processes on a desert piedmont eastern mojave desert california radiocarbon dating of late quaternary deposits and shorelines of lake mojave and cation ratio numerical age dating of stone pavements dorn 1984 on the adjacent soda mountains piedmont provide age constraints for alluvial and eolian deposits these deposits are associated with climatically controlled stands of lake mojave during the past 15 000 yr six alluvial fan units and three eolian stratigraphic units were assigned ages based on field relations with dated shorelines and piedmont surfaces as well as on soil geomorphic data all but one of these stratigraphic units were deposited in response to time transgressive climatic changes beginning approximately 10 000 yr ago increased eolian flux rates occurred in response to the lowering of lake mojave and a consequent increase in fine sediment availability increased rates of deposition of eolian fines and associated salts influenced pedogenesis stone pavement development and runoff infiltration relations by 1 enhancing mechanical weathering of fan surfaces and hillslopes and 2 forming clay and silt rich surface horizons which decrease infiltration changes in alluvial fan source areas from hillslopes to piedmonts during the holocene reflect runoff reduction on hillslopes caused by colluvial mantle development and runoff enhancement on piedmonts caused by the development of less permeable soils inferred increased in early to middle holocene monsoonal activity resulted in high magnitude paleo sheetflood events on older fan pavements this runoff triggered piedmont dissection which in turn caused increased sediment availability along channel walls thus runoff infiltration changes during the late quaternary have occurred in response to eolian deposition of fines pedogenesis increased sheetflood activity in the holocene and vegetational changes which are related to many complicated linkages among climatic change lake fluctuations and eolian hillslope and alluvial fan processes

a climatic trigger for the giant troll pockmark field in the northern north sea abstract pockmarks are seafloor craters usually formed during methane release on continental margins however the mechanisms behind their formation and dynamics remain elusive here we report detailed investigations on one of the world s largest pockmark fields located in the troll region in the northern north sea seafloor investigations show that 7000 pockmarks are present in a 600 km2 area a similar density of pockmarks is likely present over a 15 000 km2 region outside our study area based on extensive monitoring coring geophysical and geochemical analyses no indications of active gas seepage were found still geochemical data from carbonate blocks collected from these pockmarks indicate a methanogenic origin linked to gas hydrate dissociation and past fluid venting at the seafloor we have dated the carbonates using the u th method in order to constrain the pockmark formation the carbonates gave an isochron age of 9 59 1 38 ka i e belonging to the initial holocene moreover radiocarbon dating of microfossils in the sediments inside the pockmarks is consistent with the ages derived from the carbonates based on pressure and temperature modelling we show that the last deglaciation could have triggered dissociation of gas hydrates present in the region of the northern part of the norwegian channel causing degassing of 0 26 mtch4 km2 at the seafloor our results stress the importance of external climatic forcing of the dynamics of the seafloor and the role of the rapid warming following the younger dryas in pacing the marine gas hydrate reservoir

effect of rock fragment eccentricity on eolian deposition of atmospheric dust abstract the effect of rock fragment eccentricity on the deposition of airborne dust was examined in a wind tunnel eccentricity was defined as the ratioa b wherea is the longest andb the intermediate axis of the rock fragments the effect of eccentricity on the deposition of dust on the pebbles on the deposition of dust between and underneath the pebbles and on total dust deposition pebbles interpebble space was measured separately and this for different values of pebble size pebble flattening cover density and wind speed the more pebbles are elongated the larger dust deposition on them will be this effect is more pronounced as pebbles become larger as they become less flattened and as wind speed increases but no correlation is observed with cover density it also holds that the more pebbles are elongated the less dust settles between and underneath them this effect is more pronounced as pebbles become smaller and cover density becomes larger but there is no relationship with pebble flattening whether or not there is a relationship with wind speed is unclear pebble eccentricity indirectly influences total dust deposition on a pebble field since it determines whether or not and to what extent total dust deposition will be a function of pebble size for circular pebbles total dust deposition is independent of pebble size but once pebbles become elongated total dust deposition will be smaller on pebble fields composed of small pebbles than on pebble fields composed of large pebbles it was also demonstrated that the more pebbles are elongated the more the dust will tend to settle on the pebbles rather than between or underneath them air flow separation plays a primary role in the deposition of dust on a rock fragment field since it determines the location and size of the low sedimentation areas that are connected to the air flow separation bubbles highly elongated pebbles oriented parallel to the wind catch much more dust also per unit surface than circular pebbles the surface of which is largely located in a zone of very low deposition dust deposition density on highly elongated pebbles normal to the wind on the contrary is equal to dust deposition on circular pebbles it should be noted that all data in this study refer to initial dust deposition not accumulation since only wind velocities below the dust deflation threshold were tested

a comment on in situ zircon u pb dating and o isotopes of the neoarchean hongtoushan vms cu zn deposit in the north china craton implication for the ore genesis by ming tian zhu et al ore geol rev 67 2015 354 367

the effect of surface curvature on the deposition of loess a physical model summary a physical model for the deposition of fine dusty material loess on curved surfaces is presented the model is tested in a sedimentation experiment with a symmetrical hill with length axis perpendicular to the flow direction in a wind tunnel it appears both from the model and the experiment that loess deposition will occur preferably on windward slopes and not on leeward ones in contrast to the widespread wind shadow concept below the deflation threshold loess deposition increases as wind speed increases above the deflation threshold an effective accumulation of the loess layer on the surface will occur within a well defined wind speed interval the loess layer on the surface will erode away only if wind speed has exceeded this interval for flat and dry surfaces free of roughness elements the upper limit of the interval is 7 m s free stream velocity for wet surfaces however it may be considerably higher 15 m s and more

trace element geochemistry and petrogenesis of felsic volcanic rocks associated with volcanogenic massive cu zn pb sulfide deposits volcanogenic massive cu zn pb sulfide vms deposits occur primarily in subaqueous rift related environments e g oceanic fore arc arc back arc continental margin or continental are hosted primarily by bimodal mafic felsic volcanic successions and are typically associated with felsic volcanic rocks with specific geochemical characteristics fi alkalic dacites and rhyodacites despite being abundant in the rock record are typically barren some fii calc alkalic rhyodacites and rhyolites host vms deposits but most are barren fiii tholeiitic and fiv depleted rhyolites and high silica rhyolites are much less abundant in the rock record but commonly host vms deposits regardless of age and fiii rhyolites appear to host the largest deposits most petrogenetic models proposed for the formation of fii and fiii fiv felsic volcanic rocks link felsic magma genesis to fractionation processes in high level magma chambers now represented by associated subvolcanic intrusions where the magma is also interpreted to have supplied the heat and or metals required to generate and sustain the vms forming convective hydrothermal system however the relatively constant compositions of fii and fiii fiv felsic volcanic rocks within individual areas the high eruptive temperatures at or above liquidus of fiii rhyolites and the bimodality of vms hosting volcanic successions indicate that fractional crystallization within subvolcanic intrusions could not have generated or significantly modified the compositions of fii and fiii fiv magmas this coupled with detailed geological geochemical and geochronological studies indicates that many of these subvolcanic intrusions were emplaced in multiple phases and that the later most voluminous phases often cut ore associated hydrothermally altered rocks a reassessment of the physical conditions responsible for producing the geochemistry of ore associated fii and fiii fiv felsic volcanic rocks and a review of the compositions of felsic volcanic rocks associated with vms deposits that range in age from mesoarchean to cenozoic provide important constraints on models for vms associated felsic volcanic rocks and their relationship to mineralization the compositions of felsic volcanic rocks may be explained by low to moderate degrees of partial melting of mafic sources at a range of depths within rift environments where the mineralogy and composition of the source regions modes and degrees of partial melting pressure and temperature of melting and to a lesser extent subsequent fractionation processes account for the compositional variations from fi through fii to fiii fiv long lived enhanced heat flow and structural permeability of rift environments that allows partial melting to form some fii rhyolites at midcrustal levels 10 15 km and fiii fiv rhyolites at shallow crustal levels 10 km both within the zone of brittle fracture permeability are essential to sustain the high temperature convective hydrothermal systems that are required to form large vms deposits and camps rift environments contain long lived thermal magmatic and structural corridors that focus magma ascent heat flow high temperature convective hydrothermal systems and emplacement of subvolcanic intrusions that are favorable environments for the formation of vms deposits and fii and fiii fiv felsic volcanic rocks

trace element geochemistry of ore associated and barren felsic metavolcanic rocks in the superior province canada reply archaean felsic metavolcanic rocks in the superior province of the canadian shield may be divided into three major groups on the basis of trace element abundances and ratios 1 fi felsic metavolcanic rocks are dacites and rhyodacites characterized by steep ree patterns with weakly negative to moderately positive eu anomalies high zr y low abundances of high field strength elements e g hree y zr hf and high abundances of sr examples occur in the bowman subgroup and skead group in the abitibi belt in the kakagi lake lake of the woods shoal lake and sturgeon lake areas of the wabigoon belt and in the confederation lake area of the uchi belt none of these horizons as known hosts base metal sulphide deposits 2 fii felsic metavolcanic rocks are rhyodacites and rhyolites characterized by gently sloping ree patterns with variable eu anomalies moderate zr y and intermediate abundances of hfs elements and sr examples occur in the misema subgroup of the abitibi belt in the wabigoon lake a

the structural evolution of the english channel area the structural evolution of the english channel area is controlled by structure and particularly by the pre existing cadomian and variscan crustal discontinuities which have been reactivated repeatedly in post variscan times they controlled the crustal subsidence that produced basin development in the mesozoic prior to the sea floor spreading in the north atlantic region they were then reactivated during the cenozoic compression and basin inversion the english channel development is ascribed to mid tertiary differential uplift oligocene to miocene during late tertiary to quaternary times the channel displays characteristics of a tectonically controlled fluvial basin periodically invaded by the sea at the lithospheric scale the channel can be considered as an active intraplate area influenced by the nw se alpine push the nw se atlantic ridge push and glacial rebound stresses copyright 2003 john wiley sons ltd

the application of zircon cathodoluminescence imaging th u pb chemistry and u pb ages in interpreting discrete magmatic and high grade metamorphic events in the north china craton at the archean proterozoic boundary abstract two distinct late neoarchean to early paleoproterozoic magmatic events are recognized at the northern margin of the eastern block of the north china craton based on interpretation of zircon structure cathodoluminescence signature th u pb chemistry and age the first event is represented by emplacement of the chaihe trondhjemite and xianjinchang tonalite with magmatic zircon core ages ranging from 2559 2553 7 ma respectively these rocks experienced a subsequent high grade metamorphic event constrained by partial recrystallization of primary magmatic zircon and growth of new zircon rims between 2517 and 2490 ma a second magmatic episode generated by partial melting of crustal rocks during this metamorphic event is represented by the hongshilazi syenogranite with an age of 2502 11 ma the short time interval between initial magmatism and high grade regional metamorphism signifies they were related to the same major tectonothermal event when considered along with evidence of a similar sequence of events at this time 800 km to the south in eastern hebei and the previously established 2500 ma age of granulite facies metamorphism in mafic rocks across the craton it is proposed that a large mantle plume developed beneath the north china craton at the close of the archean

structural control of igneous complexes and kimberlites a new statistical method abstract the spatial distribution of magmatic activity may provide important information about magma formation magma transport through the lithosphere and the mechanical properties of the lithosphere zones of weakness in the crust tentatively associated with deep crustal fractures have been hypothesized to control the locations of magmatic centers a connection between some lineaments and large scale crustal structures suggests that magma emplacement could be controlled by sets of fractures with linear outcrop patterns in this case the locations of magmatic centers would not be distributed randomly but would have an anisotropic component thus identification and characterization of such anisotropic control is a valuable exercise previous attempts to derive information about anisotropies from the locations of magmatic centers have been flawed or have provided only an estimate of the directions of anisotropy in this paper we extend concepts presented previously lutz 1986 to derive estimates of the locations as well as the trends of the features that could control magmatism monte carlo simulations of random point patterns are used to provide a null model relative to which the characteristics of actual patterns can be evaluated on a statistical basis tests on simulated anisotropic patterns show that the method can successfully reveal underlying anisotropies even if a substantial proportion of the magmatic centers are located randomly applications to central magmatic complexes in nigeria and to kimberlites in south africa reveal control by anisotropies in both areas however the trends and locations are not apparently related to prominent geologic features previously suggested to have played a role thus the anisotropies are imposed either by structures at depth or by structures that appear at the surface as minor fractures and joints shallow igneous complexes are often associated with potentially valuable economic deposits therefore this method provides a means to predict the locations of resources however the method can be applied to the analysis of anisotropy in any features that can be approximated by points lying within a plane thus earthquake epicenters might be analyzed to determine locations to be avoided to reduce seismic risk

effect of rock fragments on eolian deposition of atmospheric dust abstract the effect of rock fragments and rock fragment cover on the deposition of airborne dust was examined in a wind tunnel four parameters were studied pebble size pebble flattening cover density and wind speed the effect of these parameters on the deposition of dust on the pebbles on the deposition of dust bewween and underneath the pebbles and on total dust deposition pebbles interpebble space was measured separately deposition on the pebbles increased with pebble size pebble flattening and wind speed deposition between and underneath the pebbles increased with increasing wind speed and with decreasing pebble flattening but there was no consistent relationship with pebble size total dust deposition was not influenced by pebble size pebble flattening and cover density but it increased linearly with wind speed it was also demonstrated that the larger and the flatter the pebbles and the higher cover density the more the dust will tend to settle on the pebbles rather than between or underneath them air flow separation seems to play a primary role in the spatial distribution of dust deposition within a rock fragment field as it determines the location and size of the low sedimentation areas that are connected to the air flow separation bubbles it should be noted that all data in this study refer to dust deposition not accumulation since only wind velocities below the dust deflation threshold were used

regional orientation of tectonic stress and the stress expressed by post subduction high magnesium volcanism in northern baja california mexico tectonics and volcanism of san borja volcanic field abstract because of its long lived late miocene to pleistocene post subduction volcanic activity and location the san borja volcanic field sbvf is a key area for understanding the physical mechanisms controlling the spatial distribution of post subduction volcanism on the peninsula of baja california in this paper we study the distribution and general characteristics of individual eruptive centers in the sbvf aiming to provide insight into the changing physical nature of post subduction magmatism and the control on vent location in a very unique tectonic setting volcanic activity has built more than 227 high magnesium andesites hma monogenetic scoria cones and thick lava flows capping large mesas during the last 12 5 ma the average mean eruptive center in the sbvf has a height of 85 m a basal diameter of 452 m and a slope angle of 30 our volcanic alignment analysis of this field is based on field data satellite images and a quantitative method for detecting volcanic center alignments the morphologic data together with new 40ar 39ar geochronology data have been used to refine our alignment analysis and to better delineate the temporal evolution of post subduction volcanic activity in this field the available ages vary from 3 53 0 18 to 10 0 23 ma suggesting that the long lived hma volcanism occurred almost continuously with some concentration of pulses throughout late miocene and extending to the pleistocene and even into the quaternary replacing the arc related activity of the comondu arc which vanished in this area around 12 5 ma alignment analysis confirms a nw se direction as the preferred orientation of volcanic alignments and shows that vent elongations do not display a strong parallelism in any particular direction marking the absence of matches between lineaments defined by multiple vents and orientations of vent elongation the results of the volcanic alignment analysis allowed us to infer the direction of the maximum instantaneous extension s1 local at sbvf from late miocene to quaternary we compared this value to the direction of maximum instantaneous extension for the baja california peninsula at a regional scale s1 regional which can be estimated from regional tectonic reconstruction the comparison of s1 regional and s1 local allows us to quantify the influence of tectonic stresses in controlling the localization of monogenetic volcanism at the sbvf

effect of rock fragment embedding on the aeolian deposition of dust on stone covered surfaces many stone covered surfaces on earth are subject to aeolian deposition of atmospheric dust this study investigates how the deposition of dust is affected when rock fragments become gradually more embedded in the ground or inversely become more concentrated on the surface experiments were executed in an aeolian dust wind tunnel with eight different types of pebbles the following parameters were measured dust deposition on the pebbles dust deposition between and underneath pebbles total dust deposition pebbles inter pebble space and the fraction of total deposition of dust caught by the pebbles alone the absolute amount of dust deposition and the dust deposition density dust deposition per unit surface were studied for each parameter the effects exerted by pebble size pebble flattening pebble elongation and wind speed were also investigated dust patterns on and around pebbles were also studied via flow visualization the absolute amount of dust settling on pebbles decreases the more that the pebbles become embedded dust deposition density on pebbles on the other hand increases with embedding the more pebbles become embedded in the soil the more efficient the process of dust deposition on pebbles becomes dust deposition between and underneath pebbles increases with pebble embedding dust deposition density between and underneath pebbles is maximum at 50 per cent embedding showing that in this area dust deposition is most efficient when pebbles are halfway embedded total deposition slightly decreases the more pebbles become embedded but total dust deposition density increases with embedding aerodynamic flow separation and diverging and converging airflow play an important role in the process of dust deposition on stone covered surfaces the more pebbles protrude above the soil the more they act as an obstacle and the more they disturb the air and dust flow creating scouring zones flow separation bubbles and shelter areas for the dust all these effects diminish as pebbles become more embedded in the soil however perturbations in dust patterns remain visible until pebbles have disappeared entirely

desert pavement dynamics numerical modeling and field based calibration desert pavements are widely used as a relative surface dating tool because they are progressively better developed on surfaces ranging from thousands to hundreds of thousands of years in age recent work however has highlighted the dynamic nature of pavements and undermined their use as surface age indicators quade 2001 proposed that latest pleistocene vegetation advances destroyed all mojave desert pavements above 400 m elevation making all such pavements holocene in age in an effort to reconcile young pavement evidence with their widespread use as pleistocene surface age indicators we developed a numerical model based on the classic conceptual model in which pavements co evolve with their underlying eolian epipedons over millennial timescales in this co evolutionary process fine grained eolian deposition and av horizon development within the eolian epipedon promotes surface clast motion and pavement development enhancing the eolian sediment trapping ability of the pavement in a positive feedback model results illustrate the multi scale nature of pavement dynamics pavements may require tens of thousands of years to fully develop from a newly abandoned alluvial surface but may heal over timescales of decades to centuries if a mature eolian epipedon is present as such there is no inconsistency between rapid pavement healing and a pleistocene age for the underlying alluvial surface to calibrate the model we conducted surficial geologic mapping and pavement sedimentological analysis on two desert piedmonts our study areas include both proximal and distal fan environments illustrating the role of parent material texture in controlling the mode of pavement formation using available geochronology our work provides a rigorous calibration of pavement formation rates in our study areas and provides evidence supporting the use of pavements as local relative surface age indicators over holocene to late pleistocene timescales copyright 2007 john wiley sons ltd

rock fragments in top soils significance and processes this introductory paper reviews various aspects of rock fragments in top soils such information is required for various reasons and in particular for predicting the impact of climatic or landuse changes on the response of these soils particular attention is paid to the definition and measurement of rock fragment content in top soils the density of soils containing rock fragments the spatial distribution and movement of rock fragments in top soils the effects of rock fragments on some key hydrological processes thermal properties of top soils physical soil degradation soil erosion and soil productivity

the vesicular layer and carbonate collars of desert soils and pavements formation age and relation to climate change abstract the vesicular fine grained a horizon av is the widespread ubiquitous surficial horizon of desert soils in diverse landforms and parent materials of varying ages now known to form mostly through accumulation of eolian dust recent studies show that dust accumulation and concomitant soil development are genetically linked to stone pavement formation changes in the magnitude of eolian activity and effective leaching related to quaternary climatic changes are also hypothesized to have influenced the evolution of the av horizon numerical modeling geochronologic and field laboratory studies elucidate the nature of pedogenic processes controlling compositional evolution of av how the changing av horizon increasingly influences soil infiltration and carbonate translocation and accumulation and the control that clasts of the evolving pavement exert on pedogenic processes results of a model that determines soil bulk chemical composition based on mixing of estimated proportions of externally derived eolian material and parent materials imply that the evolution of the soil bulk composition is strongly influenced by av horizon formation the early development of a weakly to moderately developed av horizon directly over gravelly parent material in late and middle holocene soils moderately influences soil infiltration but significant leaching of very soluble materials and some carbonate in dust are permitted in older pleistocene soils however the texturally more mature av and underlying cumulic nongravelly horizons more strongly limit the rate and depth of leaching and soil bulk composition therefore more closely approximates a simple mixture of dust and parent material other aspects of av horizon development and its relations to the pavement are evaluated through studies of pavement clasts with coatings of soil carbonate referred to as carbonate collars development of a numerical model that integrates soil hydrology a co2 production diffusion model calcite kinetics and thermodynamic considerations composition and thermal characteristics of pavement clasts and the textural and structural properties of the surface horizon provides the basis for testing a hypothesis of collar formation model results combined with results of 13c and 18o analyses of collar carbonate demonstrate how precipitation of calcite on pavement clasts and within the av is favored at a depth much shallower than that indicated by the classic carbonate depth climate relationship of jenny and leonard jenny h j leonard c d 1935 functional relationships between soil properties and rainfall soil science 38 363 381 and arkley arkley r j 1963 calculations of carbonate and water movement in soil from climatic data soil science 96 239 248 or simulated by numerical models of carbonate accumulation simultaneous development of thick carbonate collars and the av horizon requires the sustained pavement clast av horizon coupling for at least centuries to possibly millennia new thermoluminescence ages also indicate that much of the av horizon formed in the holocene and that it is certainly much younger than the older pleistocene pavements this supports the previously proposed hypothesis that increased dust flux during the pleistocene to holocene transition triggered and or greatly accelerated av horizon development an understanding of the genesis of collars provides not just an understanding of how carbonate can accumulate in surface environments but it also provides important clues into processes of pavement evolution and preservation of av horizons during long glacial periods the av horizon is not merely an insignificant surficial zone of recent dust accretion instead its development profoundly influences the genesis of desert soils and pavements

intraplate seismicity new seismotectonic data in western europe abstract fault plane solutions for 128 earthquakes which occurred in france and neighbouring areas have been determined stress field information given by these data are discussed in relation to previous tectonic knowledge the western alps are characterized by a compressional regime with a fan shaped distribution of p axes which might be related to the interaction mechanism between europe and the adriatic plate the pyrenean region is mainly submitted to a south north compression tectonic activity in this area seems to be determined by the presence of two subduction zones with reverse dips in the south bay of biscay and in the central pyrenees the transition zone between these two active belts is characterized by significant seismicity with a transpression regime

trapping of airborne dust by mosses in the negev desert israel airborne silt and clay containing calcium carbonate quartz clays marine nannoplankton and aquatic diatoms are trapped among stems of mosses in the negev highlands desert the mosses were studied in an area with 70 mm mean annual rainfall they grow over the particles covering them and trap additional dust as it comes resulting in the accumulation of loess sediments the mosses protect the accumulated soil from erosion by wind or water remnants of the moss leaves and stems were found at a depth of 15 mm and more no particles or minerals typical to basalt were found in the moss trapped soil the function of cushiony mosses may be used to explain the processes of loess trapping and protection in larger areas in moister areas such as the northern negev microscopic fossils in the dust may be used as guides to the origin of the aeolian sediments

cinder cone clustering in the transmexican volcanic belt implications for structural and petrologic models cinder cone distributions have most often been characterized using univariate statistics here a new technique to volcano distribution studies cluster analysis is applied to cinder cone distribution in the central transmexican volcanic belt tmvb a total of 1016 cinder cones are identified over an area of approximately 60 000 km2 application of cluster analysis reveals structure in cinder cone distribution using a search radius parameter of 16 km 75 of the cinder cones within the central tmvb are found within eight clusters of 45 159 cones each these clusters are each 2000 to 5000 km2 in area only 22 cones are found within clusters of three or fewer cinder cones indicating that clustering is a pervasive phenomenon some petrologic variation is evident among clusters low mg alkaline cinder cones are found within a single cluster 360 400 km from the trench application of alignment analysis techniques including the two point azimuth method the hough transform and two dimensional fourier analysis demonstrates that cinder cone alignments have common orientations on a regional scale within three clusters all located in the southernmost part of the michoacan guanajuato volcanic field in the western portion of the study area these alignments consist of tens of cinder cones are 20 50 km long and are all oriented with azimuths of 020 040 parallel to the direction of plate convergence high mg lavas which last fractionated at pressures in excess of 8 kbar are only found associated with these alignments indicating that magma transport is significantly enhanced in these areas although local alignments of three to six cinder cones occur within mapped fault zones that transect the area regional cinder cone alignment patterns and the distribution of clusters themselves do not appear to be affected by the presence of these fault zones the cluster analysis the alignment analysis and some petrologic data support the hypothesis that the tmvb is segmented near 101 w

a point pattern analysis of the distribution of earthquakes in normandy france abstract a new mathematical method has been developed to guide the interpretation of sparse epicenter distributions the aim of the technique is the assessment of the significance of epicenter alignments this assessment is connected to the detection of seismic faults the method has been tested on synthetic data sets and on seismicity from the san francisco bay area these tests show high detection capabilities when the method is applied to actual data in order to discard artificial lines the interpreter must check the results using geological information the method is applied to epicenters in western normandy the main structural directions of normandy are tracked by sparse epicenters

the aeolian dust accumulation curve this article presents a simple physical concept of aeolian dust accumulation based on the behaviour of the subprocesses of dust deposition and dust erosion the concept is tested in an aeolian dust wind tunnel the agreement between the accumulation curve predicted by the model and the accumulation curve obtained in the experiments is close to perfect and shows that it is necessary to discriminate between the processes of aeolian dust deposition and aeolian dust accumulation two important thresholds determine the accumulation process for wind speeds below the deflation threshold the aeolian accumulation of dust increases linearly with the wind speed for wind velocities between the deflation threshold and the accumulation limit the sedimentation balance is above unity and there is still accumulation though it rapidly drops once the deflation threshold has been exceeded at wind speeds beyond the accumulation limit the sedimentation balance is below unity and there will no longer be an accumulation of dust the thresholds have been determined in a wind tunnel test at friction velocity u 0 34 m s 1 deflation threshold and u 0 43 m s 1 accumulation limit but these values are only indicative since they depend heavily on the characteristics of the accumulation surface and of the airborne grains

influences of eolian and pedogenic processes on the origin and evolution of desert pavements well developed desert pavements are present above eolian deposits that mantle flows of the cima volcanic field located in the mojave desert california soil stratigraphic data and geochemical data demonstrate that eolian and pedogenic processes play major roles in the evolution of these pavements eolian dust 1 accelerates mechanical fragmentation of flow rock providing the source material for pavements and 2 accumulates slowly below basaltic colluvium in flow depressions eventually promoting development of cumulate soils below the evolving stone pavement an increase in dust flux during the holocene has raised ancient pleistocene pavements as much as 20 cm above the former land surface the results of our studies demonstrate for the first time that most desert pavements do not form by deflation by overland flow or by upward migration of stones through a slowly formed clayey argillic horizon desert pavements are born and maintained at the surface

scale model simulations of the deposition of loess in hilly terrain the sedimentation of loess in a 40 km2 area on the northern border of the belgian loess belt is investigated by means of wind tunnel experiments loess deposition is simulated on a relief scale model for different wind directions it appears that simulation with northeast winds produces a loess deposition pattern that coincides closely to the field pattern which may be an indication that the loess bearing winds at the end of the weichselian came from the northeast loess deposition occurs preferably on windward slopes and not on leeward ones the wind shadow concept which is important in the case of sand deposition may therefore not necessarily apply to fine materials such as fine silt and clay

geophysical exploration on the subsurface geology of la garrotxa monogenetic volcanic field ne iberian peninsula we applied self potential sp and electrical resistivity tomography ert to the exploration of the uppermost part of the substrate geology and shallow structure of la garrotxa monogenetic volcanic field part of the european neogene quaternary volcanic province the aim of the study was to improve knowledge of the shallowest part of the feeding system of these monogenetic volcanoes and of its relationship with the subsurface geology this study complements previous geophysical studies carried out at a less detailed scale and aimed at identifying deeper structures and together will constitute the basis to establish volcanic susceptibility in la garrotxa sp study complemented previous smaller scale studies and targeted key areas where ert could be conducted the main new results include the generation of resistivity models identifying dykes and faults associated with several monogenetic cones the combined results confirm that shallow tectonics controlling the distribution of the foci of eruptive activity in this volcanic zone mainly correspond to nnw sse and accessorily by nne ssw neogene extensional fissures and faults and concretely show the associated magmatic intrusions these structures coincide with the deeper ones identified in previous studies and show that previous alpine tectonic structures played no apparent role in controlling the loci of this volcanism moreover the results obtained show that the changes in eruption dynamics occurring at different vents located at relatively short distances in this volcanic area are controlled by shallow stratigraphical structural and hydrogeological differences underneath these monogenetic volcanoes

a method for determining significant structures in a cloud of earthquakes the interpretation of a cloud of earthquake hypocenters in terms of causative structures is not a simple task locations are subject to uncertainties which will not be the same for every earthquake the data should therefore not be interpreted simply by inspection which is difficult in the case of three dimensional data anyway instead we propose using the location uncertainties as a guide in processing the data earthquake locations are moved inside their uncertainty or confidence ellipsoids until a simplified picture of the earthquake cloud is obtained which can then be interpreted in terms of some simplified structure such as faults the aim of the approach is to give the simplest possible structure that is consistent with all the location and confidence ellipsoid data the method is applied to three synthetic sets of data these illustrate the potential and limitations of the method application to a real earthquake data set from rabaul caldera in papua new guinea gives an image of the caldera ring fault that suggests departures from the simple ring fault structure previously assumed sensitivity analysis on the rabaul data shows that the method is not unduly sensitive to the assumptions that have to be made in applying it

active tectonics seismicity and geomorphology with special reference to normandy france integrated studies based on tectonic seismotectonic and geomorphological analyses indicate that normandy northwest france has been an active area during the quaternary topography and landform discontinuities reflect the dislocation and differential uplift of a late cenozoic platform the tectonic activity is represented by i active faults indicated by linear scarps and seismic activity ii offsetting of pre existing surfaces iii plio pleistocene sedimen tation restricted within narrow subsiding zones and iv morphometric properties of drainage basins that indicate zones of differential uplift the inferred strain pattern involves i a shortening direction that strikes nw se as expected in the european context of alpine compression and ii a ne sw trending extension accommodated by nw se normal faults the geomorphological systems encountered in normandy preferentially record differential vertical displacements copy right 2000 john wiley sons ltd

the mechanics and geological implications of dust transport and deposition in deserts with particular reference to loess formation and dune sand diagenesis in the northern negev israel

in situ zircon u pb dating and o isotopes of the neoarchean hongtoushan vms cu zn deposit in the north china craton implication for the ore genesis abstract the hongtoushan volcanogenic massive sulfide vms deposit is the largest archean cu zn deposit in china located in the qingyuan greenstone belt on the northern margin of the north china craton the cu zn mineralization was stratigraphically controlled by the interbeds 100 m in thickness of mafic felsic volcanic sets and overlain by banded iron layers however the relationship between vms deposits and associated volcanics has not been examined this study ultimately clarifies the times and sources of the volcanics and mineralization based on in situ zircon u pb and o isotope on vms hosting mafic felsic volcanic rocks banded and massive sulfide ores and postmineralization pegmatite vein we considered that there were two main formation stages for the qingyuan cu zn deposits one was exhalative hydrothermal sedimentation and another was further cu zn enriched by later hydrothermal processes the timing of the first stage occurred at 2571 6 ma based on the magmatic zircons in the vms hosting mafic volcanic rocks from which the inherited zircons also indicate the existence of 2 65 3 12 ga ancient supercrustal rocks in the qingyuan district a modern mantle like 18 o zircon value of 5 5 0 1 2sd for this volcanism was well preserved in the inherited core domains of ore samples it suggests that the mafic volcanics was most likely sourced from partial melting of juvenile crust e g ttg granites a large scale metamorphic or hydrothermal event is documented by the recrystallized zircons in sulfide ores the timing is tightly constrained by the hydrothermal zircon u pb ages they are 2508 4 ma for the banded ore 2507 4 ma for the massive ore and 2508 2 ma for the postmineralization pegmatite vein these indistinguishable ages indicate that the 2507 ma hydrothermal systems played a significant role in the upgrading of the vms cu zn orebodies the weighted 18 o values of hydrothermal zircons show a successively increasing trend from 6 0 0 1 2 for the banded ore 6 6 0 2 2 for the massive ore to 7 3 0 2 2 for the later pegmatite vein this variation might be induced by gradual inputting of the 18 o rich oceanic crust and or oceanic sediment during the hydrothermal cycling system considering its modern mantle like oxygen isotope composition of 2571 ma volcanism a submarine volcanic hydrothermal system involving mantle plumes is a preferred setting for the neoarchean vms cu zn deposits in the qingyuan greenstone belt

a wind tunnel simulation and field verification of desert dust deposition avdat experimental station negev desert the deposition of natural dust in an area of 53 ha situated in the northern negev desert is investigated in detail both in the wind tunnel dust storm simulations over a topographic scale model and in the field the wind tunnel results and the field results show a high degree of agreement indicating that scale model simulation may be considered an important technique for future loess and desert research more dust settles on windward slopes than on leeward slopes which is in contradistinction with the widespread wind shadow concept air flow separation zones immediately downwind of steep windward slopes have an important impact on dust deposition too in the case of dust deposition on topographic scale models a restricted height distortion of the model will not necessarily lead to serious problems in addition wind tunnel blockage percentages up to 13 may be allowed in order to obtain acceptable dust deposition patterns for the scale model a mean gross dust deposition of about 200 250 g m 2 year 1 is calculated for the northern negev desert for 1987 thus if the settled dust can be protected against erosion in the cultivated areas in the negev the dust content of the top soil will markedly increase with time however it has to be borne in mind that cultivation activities themselves may also contribute to a higher soil erosion and hence to a higher dust content in the atmosphere at any rate a higher dust content in the top soil will unquestionably have an important positive effect on agricultural yields from the air dust concentration data and the dust deposition data a deposition velocity of 4 7cms 1 can be calculated for avdat dust

field experiments of aeolian dust accumulation on rock fragment substrata the effect of rock fragments and rock fragment cover on the accumulation of airborne dust was examined in a long term field experiment in the negev desert of israel four parameters were studied pebble eccentricity pebble size pebble flattening and cover density the effect of these parameters on the accumulation of dust on the pebbles on the accumulation of dust between and underneath the pebbles and on total dust accumulation pebbles interpebble space was measured separately accumulation on the pebbles increased as the pebbles became larger less flattened and more elongated and as cover density increased accumulation between and underneath the pebbles increased as the pebbles became smaller more flattened and more elongated and as cover density increased although the accumulation area available became smaller total dust accumulation increased as the pebbles became smaller more flattened and more elongated and as cover density increased rock fragments act as a dust trap as dust accumulation on pebble covered surfaces is several tens of times larger than dust accumulation on similar but pebble free surfaces however less than 20 of the initially settled dust is protected from further erosion in the negev desert dust erosion by wind is of the order of 10 times larger than dust erosion by water the rate of long term dust accumulation in the negev is of the order of 15 30 g m 2 yr 1 this is considerably lower than the rates proposed elsewhere in the literature which are based upon over optimistic dust retainment percentages

numerical recognition of alignments in monogenetic volcanic areas examples from the michoacan guanajuato volcanic field in mexico and calatrava in spain abstract identification of geological lineaments using numerical methods is a useful tool to reveal structures that may not be evident to the naked eye in this sense monogenetic volcanic fields represent an especially suitable case for the application of such techniques since eruptive vents can be considered as point like features application of a two point azimuth method to the michoacan guanajuato volcanic field mexico and the calatrava volcanic province spain demonstrates that the main lineaments controlling the distributions of volcanic vents 322 in calatrava and 30 in michoacan approach the respective main compressional axes that dominate in the area i e the cocos north america plates convergence and the main betics compressional direction respectively considering the stress fields that are present in each volcanic area and their respective geodynamic history it seems that although volcanism may be a consequence of contemporaneous extensional regimes the distribution of the volcanic vents in these kinds of monogenetic fields is actually controlled by reactivation of older fractures which then become more favourable for producing space for magma ascent at near surface levels

spatial distribution and alignments of volcanic centers clues to the formation of monogenetic volcanic fields monogenetic basaltic volcanic fields occur worldwide in tectonic environments ranging from extensional to convergent understanding similarities and differences between these fields may help to characterize key controls on their generation such volcanic fields consist of numerous volcanic centers each of which represents a pathway of magma from its source to the surface we analyzed the spatial distribution of volcanic centers in 37 monogenetic volcanic fields and assuming that the distribution of volcanic centers relative to each other is matched by a similar source pattern within the mantle applied the following methods for each 1 the poisson nearest neighbor pnn analysis representing the degree to which the distribution of the volcanic centers departs from a predicted poisson distribution and 2 a volcanic alignment analysis to ascertain the preferential pathways if any used by the magma to reach the surface this is the first comprehensive global comparison of such analyses magma pathways within the brittle upper crust are influenced to various degrees by two end member situations 1 formation of new extension fractures perpendicular to the least compressive stress 3 and 2 re activation of pre existing fractures that are near parallel to the maximum principal stress 1 the results of the pnn analysis show that independently of the tectonic environment most volcanic fields display a clustered distribution of their volcanic centers alignment analysis shows that either the ambient tectonic environment exerts a strong influence on the preferential orientations of the volcanic alignments or that it is in competition with other factors e g pre existing structures local stress changes due to older intrusions overall these results indicate that the propagation of the magma and therefore the spatial distribution of the volcanic centers within volcanic fields is the product of an interplay between deep level influences i e nature of the magma source and shallow level influences i e stress field pre existing crustal structures of the lithosphere

zircon thermometry of high temperature rhyolites near volcanic associated massive sulfide deposits abitibi subprovince canada high temperature high silica rhyolites are commonly found near cu zn volcanic associated massive sulfide vms deposits in the archean abitibi subprovince they are characterized by anhydrous phenocrysts feldspar quartz in concentrations of generally 73 sio 2 high incompatible element contents rb sr 1 zr y

oxygen isotope ratios of archean plutonic zircons from granite greenstone belts of the superior province indicator of magmatic source zircons commonly preserve primary magmatic oxygen isotope ratios even through high grade metamorphic events unlike quartz which more readily loses its primary 18o value by subsolidus exchange intrusive bodies from the superior province canada have an average 18o zircon of 5 8 0 6 n 59 rocks those from granite greenstone belts have an average 18o zrc 5 8 0 6 n 55 in contrast to those from metasedimentary belts that average 18o zrc 6 7 0 2 n 4 the 18o zircon values from granite greenstone belts indicate a maximum allowable input of 14 supracrustal high 18o material into archean magmas of the superior province relative to mantle 18o values igneous bodies of the superior province have been separated into two groups based on geochemistry unenriched plutons and sanukitoids magmatic oxygen isotope ratios inferred from these zircons indicate up to a subtle but significant division of 1 between the two geochemical sets of rocks this distinction is apparent only in the 18o zrc and not in more commonly analyzed less refractory minerals such as quartz and feldspar oxygen isotope data correlate with geochemical modeling of sanukitoids the average 18o zrc for sanukitoids is 6 4 0 2 in comparison to 5 5 0 4 for unenriched plutons there is almost no overlap in values the elevation of sanukitoid 18o zrc indicates input from a high 18o source such as fluids from the subducting oceanic crust melts of subducted sediments or continental crust all of the plutons analyzed in this study have been dated by u pb zircon techniques and the combination of u pb ages and 18o zrc indicates little variability of 18o versus age during archean plutonism in the superior province therefore recycling of sediments and other high 18o sources was not a dominant process during crustal growth from 3003 to 2670 ma in the superior province