the european african collision and its effects on the lithosphere asthenosphere system abstract in the european area lateral changes in the shear wave velocities of the lithosphere asthenosphere system are quite pronounced gravity data imply a positive density contrast 0 03 0 07 g cm 3 in the upper mantle related to almost aseismic lithospheric roots which seem to characterize many orogenic belts the analysis of a transect along the longitudinal axis of the alps seems to indicate that relevant lateral variations in density are also present in the lithospheric part of the mantle

application of multi element statistical analysis for regional geochemical mapping in central japan abstract some 434 stream sediment samples were collected in central japan for a nationwide geochemical mapping project the resulting geochemical maps are compared with geological mineral resource and land use maps spatial distribution patterns of elemental concentrations in stream sediments are determined mainly by surface geology elevated elemental concentrations of alkali elements be ga y cs ba lanthanide ln tl th and u are consistent with outcrop areas of granite felsic volcanic rock and accretionary complexes high concentrations of mgo al 2 o 3 p 2 o 5 cao 3d transition metals zn and sr are present in sediments supplied from mafic volcanic rock high pressure metamorphic rocks and mafic ultramafic rocks in accretionary complexes a procedure is established and guidelines are set for a statistical test suite for geochemical mapping analysis of variance anova and multiple comparison tests are effective for comparing means among the data subsets that are classified by parent lithological materials among the many procedures that have been proposed for multiple comparison tests the holm procedure was selected for this study multiple comparison statistically confirmed the correspondence of elemental abundance in stream sediments with surface geologies however visual interpretation of some elements is inconsistent with results of multiple comparison according to the holm procedure the u content in stream sediments is affected not by granite but by felsic volcanic rock the holm procedure clarifies that as sb and bi that are not explained by the presence of mineral deposits are enriched significantly in samples derived from accretionary complexes hydrothermal activity on the ocean floor might affect their levels of enrichment significant enrichment of cu zn cd sn sb hg and pb observed in urban areas are also supported by the holm procedure the authors inferred that these sediment samples had been contaminated

geochemical mapping in northern honshu japan abstract geochemical mapping of northern honshu in the northeast japan arc was carried out using stream sediments at a sampling density of one sample per 130 km 2 more than 50 elements were determined in 395 stream sediment samples

regional spatial distribution of multiple elements in the surface sediments of the eastern tsushima strait southwestern sea of japan abstract a total of 402 coastal sea sediment samples were collected from the continental shelf slope and basin off tsushima island in the western sea of japan and were analyzed for 51 elements as part of a nationwide marine geochemical mapping project the samples were compared to potentially related sample sets and the results were considered from the viewpoint of the origin of marine surface sediments in the western sea of japan the spatial distribution of elemental concentrations in the coastal sea sediments correspond to texture grain size the presence of shells and foraminifera and the mud content of surface marine sediments most elemental concentrations increased with increasing mud content some samples located in littoral areas included sediment particles apparently supplied from nearby rivers but their contribution was limited overall the mean chemical compositions of clastic material in coastal sea sediments appear to differ from those of stream sediments in adjacent terrestrial areas in addition the geochemistry of the coastal sea sediments cannot be fully explained by the mixing of the material supplied from korean and chinese stream sediments which are the most feasible sources coastal sea sediments in the study area are well mixed by transportation processes therefore elemental abundances in these marine sediments may be homogenized to such an extent that it is not possible to determine their origin alternatively most of the clastics in the sediment may actually represent relict reworked material originally formed in the yellow sea and tsushima strait during the last glacial stage and subsequent transgression

subduction zones and back arc basins a review in the framework of plate tectonics the basic mechanism operating in the trencharc back arc systems is believed to be the subduction of oceanic lithosphere this model however was developed more or less as a logical consequence of sea floor spreading the question then is whether or not the subduction model can explain all the major features of the trench arc back arc systems many features such as thrust type inter plate earthquakes and deep earthquakes along wadati benioff zones are readily explained but the occurrences of extentional spreading and high heat flow in the back arc region and arc volcanism are difficult to explain an approach to solve these problems may be found in what may be called comparative subductology there seem to exist two basically different modes of subduction one chilean type causing compressional stress regime in the arc and back arc regions the other mariana type causing tensional world s subduction zones are classified in terms of the postulated two modes and some tectonic implications and causes of the two modes are discussed

rheological stratification of the lithosphere abstract the rheology of the lithosphere is estimated on the basis of pore pressure dependent frictional failure in the brittle regime and power law steady state creep in the ductile regime different petrological models of the continental and oceanic lithosphere combined with different geotherms and thicknesses are used to generate models covering a variety of geodynamic situations results show that the depth dependence of lithospheric rheology varies with the tectonic province and that in many instances the continental lithosphere has one at the bottom of the crust or two the previous one plus another at mid crustal levels soft ductile layers sandwiched between brittle layers the depth distribution of geophysical parameters seismicity seismic wave velocity and electrical conductivity matches the theological predictions well the lithospheric rheological profiles are used to analyze observed variations in the structural style of deformed continental margin and oceanic terranes in the southeastern canadian cordillera the large scale characteristics of the system show a satisfactory agreement with the inferred rheological structure sub horizontal decollements should be the rule rather than the exception where the lithospheric rheology is strongly stratified

on a tectonic mechanism for regional sealevel variations abstract no satisfactory tectonic explanations have yet been offered for the apparent sealevel fluctuations of about 1 cm 1000 years and a magnitude of up to a few hundred meters that have been proposed by vail et al 1 we propose a mechanism that does appear to be able to explain these changes if horizontal stresses of the order of a few kilobars occur in the lithosphere and if changes in these stress fields occur on geological time scales the proposed model is one of an interaction between these stresses and the deflections of the lithosphere caused by sedimentary loading apparent sealevel changes of up to 100 m can be produced at the flanks of the sedimentary basins by this interaction the mechanism is most effective for young margins that are subject to rapid sediment loading by its nature the tectonic model can explain contemporaneous fluctuations in apparent sealevel in neighbouring depositional environments in principle it implies the possibility of regional correlations in different basinal settings

factors controlling regional spatial distribution of 53 elements in coastal sea sediments in northern japan comparison of geochemical data derived from stream and marine sediments abstract in all 53 elements were analyzed in 1406 coastal sea sediment samples collected from an area off hokkaido and the tohoku region of japan during a nationwide marine geochemical mapping project the spatial distribution patterns of the elemental concentrations in coastal seas along with the existing geochemical maps in terrestrial areas were used to define natural geochemical background variation and mass transport processes the terrestrial area is covered by mafic volcanic rocks and accretionary complexes associated with ophiolite which has small amounts of felsic volcanic rocks and granite the spatial distribution patterns of elements enriched in mafic lithologies such as fe total fe 2 o 3 and sc in marine environments are influenced by adjoining terrestrial materials the spatial distribution patterns of cr and ni concentrations which are highly abundant in ultramafic rocks on land are used to evaluate the mass transport from land to the sea and the dispersive processes caused by oceanic currents the scale of mass transport by oceanic currents occurs up to a distance of 100 200 km from the coast along the coastal areas the regional differences of elements rich in felsic lithologies such as k k 2 o nb and la in marine sediments are determined mainly by the relative proportion of minerals and lithic fragments enriching felsic materials to those associated with mafic materials the spatial distribution of elemental concentration is not always continuous between the land areas and coastal sea areas that difference is interpreted as resulting from 1 transportation of marine sediments by oceanic currents and storm waves 2 contribution of volcanic materials such as tephra 3 occurrence of shell fragments and foraminifera tests and 4 distribution of relict sediments of the last glacial age and early transgression age contamination with cu zn cd as mo sn sb hg pb and bi was not observed in marine environments because the study area has little anthropogenic activity terrestrial materials are the dominant source for these metals the mo cd sn sb hg pb and bi are abundant in silty and clayey sediments locally because of early diagenetic processes authigenic precipitation and organic substances associated with these elements the spatial distribution of as concentration shows exceptions it is concentrated in some coarse and fine sands on the shelf the enrichment is explained by adsorption of as sourced from a coal field to fe hydroxide

jurassic and cretaceous paleomagnetic data from the southern alps italy jurassic and cretaceous paleomagnetic data from 46 sites in the venetian alps trento plateau and se lombardian basin have been compiled nine of these site mean directions have been previously published the sites can be divided into four age groups senonian hauterivian barremian kimmeridgian tithonian and callovian oxfordian for three of the age groups positive regional fold tests indicate at the 99 confidence level that the characteristic magnetization components predate the deformation structural mapping in the venetian alps allowed us to assign sites to individual thrust sheets and we observe no significant relative rotation of thrust sheets in the nappe pile indeed we observe remarkable consistency in mean direction throughout the entire sampling area for each of the four age groups the senonian and hauterivian barremian pole positions lie close to coeval poles on african apparent polar wander paths apwps this result is consistent with previous analyses of middle and late cretaceous data from the venetian alps the new jurassic poles deviate significantly from recently published african apwps reflecting either the poor definition of the african apwp in the late jurassic or about 20 anticlockwise rotation of the southern alps relative to africa during early cretaceous time the former of the two possibilities is favored by a new late jurassic early cretaceous pole from north america and by early permian paleomagnetic data from the southern alps which are consistent with coeval african data implying that the movement of the southern alps was similar to that of africa since early permian

biot gardner theory of extensional waves in porous rods many measurements have been made on fluid saturated porous rods executing extensional flexural and torsional motion measurements for extensional and flexural motion yield a loss parameter for young s modulus waves qy and the measurement for torsional motion yields qs for shear waves qp has then been calculated for compressional waves in bulk rock on the assumption that the fluid saturated rock is an isotropic solid i point out the fallacy of computing qp from these measurements and also urge workers to recognize the losses due to simple fluid viscosity in interpreting their data on extensional waves in rods by application of published theory i show that peaks in attenuation of extensional waves are to be expected at frequencies of several hertz to several kilohertz depending upon rod radius computed curves are compared with published measurements on navajo sandstone saturated with water ethanol and n decane in each case computed peak frequency agrees with published measurements shift of th

elemental distribution of coastal sea and stream sediments in the island arc region of japan and mass transfer processes from terrestrial to marine environments abstract a total of 49 elements have been identified in 338 coastal sea sediment samples collected from an area situated off the ise tokai region of japan for a nationwide marine geochemical mapping project the spatial distribution patterns of the elemental concentrations in coastal seas along with the existing geochemical maps in terrestrial areas were used to define the natural geochemical background variation mass transport and contamination processes the elemental concentrations of coastal sea sediments are determined primarily by particle size and regional differences most elemental concentrations increase with a decrease in particle size some elements such as ca mn and yb are found to exist in large quantities in coarse particles containing calcareous shells fe mn oxides and felsic volcanic sediments regional differences reflect the mass transfer process from terrestrial areas to coastal seas and the influence of the local marine geology an analysis of variance anova reveals that for many elements the particle size effect is predominant over regional difference the mean chemical compositions of coastal sea sediments are similar to those of stream sediments in adjacent terrestrial areas and in the upper crust of japan this observation supports the fact that coastal sea sediments have certainly originated from terrestrial materials however the spatial distributions of elemental concentrations are not always continuous between the land and coastal seas the scale of mass movement observed in marine geochemical maps occurs at a distance of 20 km from the river mouth a detailed examination of the spatial distribution patterns of k k2o and cr concentrations suggests that terrestrial materials supplied through rivers are deposited near the shore initially and then gravity driven processes shift the sediments deeper into the basin contamination with heavy metals such as zn cd and pb was observed in coastal bays surrounded by urban and industrial areas it is noteworthy that the areas with the highest concentration of these elements usually do not occur near the shore not near the contamination source but at the center of the bay unexpected low concentrations of zn cd and pb near shore may either be due to a decreased anthropogenic load in the most recent sediments or to dilution by unpolluted flood sediments

toroidal poloidal energy partitioning and global lithospheric rotation during cenozoic time the motion of surficial plates can be split into two terms the toroidal field related to shear between plates or to spin around their centres and the poloidal field associated with horizontal divergence at ridges and subductions recent papers have suggested that the present day plate motion minimizes the ratio of toroidal to poloidal energies 1 and that the existence of a global lithospheric rotation results from viscosity variations between oceans and continents 2 this paper tests and confirms these two hypotheses using plate reconstructions during cenozoic time the partition of energy between the two modes always favours the poloidal velocities the global rotation computed using a viscosity one order of magnitude lower below oceans than below continents agrees with observations the existence of a non linear rheology in a uniform asthenosphere leads to a satisfactory location of the global lithospheric rotation but with too small an amplitude

sea level cycles during the growth of atlantic type oceans abstract first order changes in global sea level are commonly thought to be the result of short term fluctuations in oceanic spreading rate however eustatic high stands have occurred only twice in phanerozoic time and in both cases have followed supercontinent break up by a lag period of 50 100 ma therefore if pulses in spreading rate were the primary control of eustasy then for some reason rate increases would have had to have occurred with predictable periodicity with respect to major rifting events alternatively we propose that the major control on first order sea level cycles is the formation of atlantic type oceans with its attendant changes in the area age distribution of the global ocean floor and the formation of extensional passive margins our calculations indicate that both the approximate magnitude and relative timing of sea level highstands relative to supercontinent break up are predicted by this mechanism thus the importance of short term spreading rate variations in eustatic cycles becomes secondary

some remarks on the origin of foredeeps abstract geological observations show that there are two main types of foredeep basins on the base of their subsidence rate and their relationship with the associated orogen or accretionary wedge high rates of subsidence up to 1600 m myr and a ratio lower than 1 between the area of the elevated belt and the area of the basin characterize the foredeeps associated with w dipping subduction low rates of subsidence up to 300 m myr and a ratio higher than 1 between the area of the orogen and the area of the basin characterize the foredeeps associated with e or ne dipping subductions this observation enables us to interpret the slow filling of foredeeps of the first type and the much faster filling of foredeeps of the second type moreover w dipping subductions have a steeper and faster monocline bounding the base of the deep foredeep in contrast to e or ne dipping subductions which have a shallower monocline this differentiation supports the notion of the eastward mantle flow with respect to the lithosphere detected in the hot spot reference frame in this view the foredeep depth in w dipping subductions is mainly controlled by the roll back of the subduction hinge pushed by the relative eastward mantle flow while foredeep depth in e or ne dipping subductions is instead mainly generated by the load of the thrust sheets and by the roll back of the subduction hinge due to the advancing upper plate contrasting the upward push of the mantle the shape of the foredeeps is regularly arcuate in case of w dipping subduction while is linear or following the shape of the inherited continental margin in case of e or ne dipping subduction fold development in the two opposite foredeeps is significantly different in w dipping subduction the folds are transported down in subduction while they are forming and consequently they are poorly eroded syntectonic sediments drape a preserved fold in the e ne dipping subduction folds and thrust sheets are instead uplifted and deeply eroded this is also predicted by the envelope of the crests in the two distinct accretionary wedges in the w dipping case the envelope may dip toward the subduction while it is rising toward the hinterland in the other cases this approach may explain the differences in terms of geometries amount and rates of subsidence between the foredeeps around the adriatic plate for instance the foredeep of the southern alps back thrust belt foredeep is deformed in the western part by the later apenninic foredeep development associated with the sinistral oblique ramp of the w dipping adriatic plate subduction the relationship in the frontal parts of a thrust belt between accretion and eustacy has to be analyzed in terms of when where and how fast thrusts propagation took place with respect to the randomly distributed sea level third order fluctuations and by the type of subduction which is connected to the foredeep and thrust belt or accretionary wedge therefore the stratigraphic patterns in foredeep basins are peculiar and casual successions that record the combination of regional tectonic evolution with independent wider scale sea level changes

seismic images of modern convergent margin tectonic structure in 1980 a w bally assembled and edited an innovative three volume picture and work atlas of seismic reflection record sections this compilation of more than 130 excellent seismic section reproductions provided much new data from the earth s subsurface for petroleum geologists academic scientists and students it is the field geologist s counterpart of outcrops and type sections the smaller collection of seismic sections presented in this studies 26 publication was inspired by bally s atlas and follows his general format and philosophy the objective is to provide a reference series of sections for the earth sciences and a vehicle for continuing scientific dialogue relating to modern convergent margins this publication s assembled sections represent a single facet of that dialogue by bringing together a series of exceptional seismic sections from the fronts of presently active convergent margins around the pacific

paleomagnetically determined rotations in the western sicilian fold and thrust belt new paleomagnetic data from the west sicilian fold and thrust belt indicate large scale clockwise rotations during tectonic transport for the platform and seamount paleogeographic units of the fold and thrust belt panormide and trapanese units there is a general consistency in the magnitude of rotation along strike suggesting the existence of large coherent structural units for the panormide platform clockwise rotations in the range of 90 to 140 relative to the underlying iblean parautochthon are recorded along 125 km of outcrop strike in the case of the trapanese unit clockwise rotations in the range of 47 to 70 relative to iblei are recorded along about 90 km of outcrop strike intervening basinal paleogeographic units imerese and sicanian units show clockwise rotations of similar magnitude although few reliable data are available from these units palinspastic reconstruction of the thrust belt incorporating the rotations and arguments for the present orientation of the margins of the paleogeographic units implies that the panormide platform and trapanese seamounts were originally elongated more or less north south relative to the present orientation of iblei the two units apparently coalesced to the south and were discontinuous to the north they and their intervening basins were part of a passive continental margin which occupied a large part of the area that was subsequently rifted to form the tyrrhenian sea

geochemical mapping in hokuriku japan influence of surface geology mineral occurrences and mass movement from terrestrial to marine environments abstract the authors have created terrestrial and marine geochemical maps of the hokuriku region japan and examined the background distribution of elemental concentrations the terrestrial geochemical maps strongly reflect the surface geology and mineral occurrences an analysis of variance anova reveals the relationships between the distribution of surface geology and geochemical maps granite metamorphic and felsic volcanic rocks and sedimentary rock in accretionary complexes give rise to high concentrations of alkali metal be y ba ree except eu tl th and u the distributions of mgo al 2 o 3 p 2 o 5 cao 3d transition metals except cu ga sr and eu are controlled by mafic volcanic and ultramafic rocks the watersheds with above threshold levels for cu zn as cd mo sn sb hg pb and bi strongly relate to the mineral occurrences but anova demonstrated that they are partly affected by surface geology the marine geochemical maps exhibit control by 3 factors calcareous sediments on the continental shelf clay minerals on the continental slope and ocean floor and sediments supplied from rivers many elemental concentrations are quite low in continental shelf sediment because of dilution by calcareous materials the continental slope and deep valley sediments are rich in most elements except for mgo cao and sr coarse sediments supplied from large rivers contribute to local enrichments of several elements such as k 2 o cr and zn the spatial distribution patterns of cr and zn concentrations show that gravity moves the river sediments over 60 km offshore along a deep valley

exhumation of high pressure metamorphic rocks the exhumation of high pressure metamorphic minerals necessitates the removal of overburden which was present at the time of metamorphism assuming metamorphism during an orogenic phase and exhumation during an uplift phase the model presented here is based on postulating continuous deformation at the active margin of an ocean continent interaction accepting the conclusion that coesite bearing eclogites and other high pressure minerals were formed when a sliver of continental crust was subducted down to 100 km i propose that their uplift was caused by a shift of the beniofff zone the high pressure slab now accreted to the continental lithosphere was lifted up the ramp of a benioff zone when ocean lithosphere was thrust under the continent the geology of the western alps illustrates this model