paleoclimatic significance of magnetic properties on the red clay underlying the loess and paleosols in china abstract the red clay unit of northern china is a widespread miocene pliocene 7 2 2 5 ma aeolian deposit that underlies much of the quaternary loess paleosol sequence in the central loess plateau it comprises a sequence of highly developed soils and interbedded layers of less weathered loess like material here referred to as reddish loess in common with the loess paleosol alternations of the overlying quaternary deposits the soil reddish loess alternations are interpreted to represent climatic fluctuations in this case between warm humid and relatively dry cool conditions however while magnetic susceptibility variations in the quaternary deposits provide a good proxy for pedogenic intensity in the red clay the relationship is less clear and magnetic susceptibility data are in conflict with other measures of pedogenesis in an attempt to resolve this issue we have investigated a red clay section and overlying loess paleosol sequence at xifeng and have supplemented these data with samples from the red clay at lingtai our study indicates that the red clay and loess paleosol sequence have a common magnetic mineralogy comprising magnetite maghemite and hematite and possibly goethite and that both sequences show a good correlation between magnetic susceptibility and the magnitude of the superparamagnetic sp component this implies that susceptibility enhancement in the red clay is strongly related to the magnitude of the sp content a component that is widely recognised as having a pedogenic origin in quaternary deposits further support for a correlation between pedogenesis and magnetic susceptibility in the red clay is provided by a good correlation between magnetic susceptibility and the rb sr ratio an independent weathering index however differences in the magnetic mineralogy of the two units are also evident the minimum magnetic susceptibility of the red clay is less than half the value of the overlying quaternary deposits at locations such as xifeng and lingtai while the maximum sp content is relatively larger than for the quaternary deposits while we cannot discount the possibility that the former difference is a reflection of different parent materials for the two units climate may also be a contributory factor in explaining these differences precipitation is a major control on magnetic enhancement in paleosols maher and thompson 1995 quat res 44 383 391 liu et al 1995 palaeogeogr palaeoclimatol palaeoecol 113 243 248 but soil anoxia and iron oxide dissolution occur if moisture exceeds some critical level soil moisture is therefore a critical factor in determining whether the correlation between pedogenesis and magnetic susceptibility in loess deposits is positive central loess plateau china magnetic enhancement negative alaska siberia magnetic destruction or uncertain pakistan argentina new zealand cycles of enhancement and destruction while our results indicate a generally positive correlation between pedogenesis and magnetic susceptibility in the red clay they also imply that a more thorough paleoclimatic interpretation can only be achieved using complementary but independent techniques more work is required to deconvolve the climatic record of the red clay but the reward may be the extension of the record of paleomonsoon evolution back into the pliocene and late miocene

extrusion tectonics of the okhotsk plate northeast asia based on focal mechanism geologic and lineament data faulting in the chersky range northeast asia changes from right lateral transpression between north america and eurasia to left lateral strike slip between north america and the okhotsk plate the location of the okhotsk eurasia boundary is poorly constrained available data suggest this boundary is right lateral the okhotsk plate is being compressed and extruded from between north america and eurasia resulting in high levels of microseismic activity along the southern flanks of the chersky range

vertical averages of rheology of the continental lithosphere relation to thin sheet parameters abstract we calculate vertically averaged rheologies for continental lithosphere subject to biaxial states of stress corresponding to extensional compressional and strike slip regimes we assume that brittle deformation occurs by byerlee s law and that ductile deformation occurs by steady state creep mechanisms under these conditions the vertically averaged rheology may be approximated by a single power law over the range of strain rates from 10 13 to 10 17 s 1 this is true not only when either brittle or ductile behavior dominates the strength of the lithospere but also when the contributions of brittle and ductile behavior are comparable the value of the power law exponent n and the strength of the lithosphere depend on the depth and stress difference at the brittle ductile transition the temperature at the moho and the geothermal gradient in the range of vertically integrated stress between 1012 and 1013 n m 1n reaches a minimum of between 5 and 10 under other circumstancesn increases rapidly as brittle behavior dominates over ductile behavior the strength of the lithosphere depends most strongly on the thermal state of the upper mantle but also is influenced by the stress supported in brittle portions of the lithosphere

thermal structure beneath tohoku northeast japan combined with geophysical observations and petrological considerations we have studied the thermal models of the tohoku northeast japan subduction zone the temperature of the deeper part of the mantle wedge is constrained by the petrological requirements that demand a high temperature region 1400 c beneath the volcanic zone to satisfy this condition namely to explain the arc volcanism in the tohoku subduction zone a high temperature upper mantle beneath the japan sea possibly 1400 c at the depth shallower than 100 km is required heat flow distribution which constrains the temperature structure at shallower depth shows that low heat flow values ranging from 20 to 50 mw m2 are distributed between the trench and aseismic front and consistently high heat flow values 80 120 mw m2 prevail in the area landward of the volcanic front including the japan sea recent heat flow measurements indicate that the transition from low to high heat flow occurs between the aseismic front and volcanic front this heat flow distribution restricts the form of the flow in the mantle wedge and shear stress acting at the plate boundary a rigid non moving triangular region bounded by the subducting slab and the vertical plane beneath the aseismic front is necessary to explain the low heat flow zone between the trench and aseismic front shear stress of about 500 to 1000 bar is supposed to act at the interface between the subducting slab and rigid triangular mantle we also suggest that to explain the peak of heat flow near the volcanic front 120 mw m2 magma migration rate of about 0 05 cm3 cm 2 year 1 is necessary a comparison of the thermal structure of the tohoku subduction zone with that of the central south america which was preliminary calculated by the similar scheme shows that the temperature in the mantle wedge of the central south america is probably lower than that of the tohoku subduction zone this difference may result in that of the nature of volcanic rocks

the evolution of forearc structures along an oblique convergent margin central aleutian arc multichannel seismic reflection data were used to determine the evolutionary history of the forearc region of the central aleutian ridge since at least late miocene time this sector of the ridge has been obliquely underthrust 30 west of orthogonal convergence by the northwestward converging pacific plate at a rate of 80 90 km m y our data indicate that prior to late eocene time the forearc region was composed of rocks of the arc massif thinly mantled by slope deposits the forearc region probably lacked both major depositional basins and a tectonically attached accretionary prism of offscraped oceanic deposits beginning in latest miocene or earliest pliocene time a zone of outer arc structural highs and a forearc basin began to form formation of these companion intraarc structures may be linked to the late neogene growth of an accretionary wedge that formed as the result of the deposition of a thick turbidite wedge in the aleutian trench initial structures of the zone of outer arc highs formed as the thickening wedge underran compressively deformed and uplifted the seaward edge of the arc massif above a landward dipping backstop thrust forearc basin strata ponded arcward of the elevating zone of outer arc highs however most younger structures of the zone of outer arc highs cannot be ascribed simply to the orthogonal effects of an underrunning wedge oblique convergence created a major right lateral shear zone the hawley ridge shear zone that longitudinally disrupted the zone of outer arc highs truncating the seaward flank of the forearc basin and shearing the southern limb of hawley ridge an exceptionally large antiformal outer arc high structure slivers of forearc basement rocks and overlying strata have been transported along the shear zone that is flanked by differentially elevated structures attributed to localized transpressive and transtensional processes uplift of hawley ridge may be related to the thickening of the arc massif by westward directed basement duplexes in addition the forearc is disrupted by structures transverse to the margin that occur where unusually high stress accumulations have resulted in the rupture of repeated great earthquakes it is likely that many ancient active margins evolved in tectonic and depositional settings similar to those of the central aleutian ridge great structural complexity including the close juxtaposition of coeval structures recording compression extension differential vertical movements and strike slip displacement should be expected even within areas of generally kindred tectonostratigraphic terranes

upper limits of power law creep of rocks at depths below a few kilometers most rocks probably flow in the steady state dominantly by diffusion assisted dislocation creep mechanisms whereby strain rate is proportional to a low power of deviatoric stress at high stress levels for metals ceramics and rocks the power law breaks down plb to some other strain rate stress functional relationship and this paper explores four methods by which the breakdown stress b may be estimated for metals alloys and ceramics b 10 3 for non silicate rocks b 5 10 3 and for silicates b 10 2 for silicates the low stress exponent power law breaks down at high stresses to an exponential dependence of strain rate upon stress or to a dorn law the governing flow mechanisms generally being lattice resistance controlled dislocation glide and mechanical twinning plb breakdown stresses for silicates are nearly strain rate insensitive and extrapolated values of b are so high as to suggest that low temperature high stress plasticity may be suppressed entirely in geological deformations plb for olivine rich rocks is discussed in some detail and new three dimensional deformation mechanism surfaces for wet and dry olivine polycrystals are presented

on the choice of boundary conditions in continuum models of continental deformation recent studies of continental deformation have treated the lithosphere as a viscous media and investigated the time evolution of the deformation caused by tectonic and buoyancy forces we examine the differences between continuum models that keep velocity boundary conditions b c constant with time and models that keep stress b c constant with time and demonstrate these differences by using a simple example of a continental lithosphere that is subjected to horizontal compression our results show that in the case of constant stress b c the indentation velocity decreases with time while in the case of constant velocity b c the indentation velocity remains constant with time observations from the tibetan plateau and from the andes indicate that the rate of indentation decreases with time this suggests that when buoyancy forces are comparable in magnitude to tectonic forces constant stress b c are more appropriate for time evolutionary models of continental lithosphere we propose a simple procedure that translates velocity b c which are easy to estimate into stress b c at the initial stage and keep the stress b c constant along the time progression of the calculations

structure of an island arc wide angle seismic studies in the eastern aleutian islands alaska new seismic wide angle data from the eastern aleutian islands show a mafic composition and a 30 km thick island arc crust traveltimes of p and s refracted arrivals and prominent crustal and mantle reflectors observed to offsets of over 300 km were used to derive velocity models for the eastern aleutian arc between the islands of atka and unimak using a three dimensional finite difference modeling and tomography code we interpret the highest crustal p wave velocities of 7 2 7 4 km s between about 12 and about 22 km depth to the south and north of the main volcanic line as remainders of preexisting oceanic crust into which arc magma is intruded apart from the pieces of oceanic crust the velocities suggest an overall mafic composition for the arc composed mainly of metabasalts diorite and diabase in the upper crust and garnet granulite or amphibolite to hornblendite in the lower crust reflected arrivals from the subducting pacific plate at depths of 45 55 km beneath the fore arc together with pn show a mantle wedge with p wave velocities as low as 7 4 km s increasing with depth to about 8 1 km s with an average of about 7 7 km s a mantle composition that grades from mainly pyroxenite probably ultramafic cumulates near the moho to dunite at greater depths best explains these observed velocities

seismicity of the forearc marginal wedge accretionary prism three different types of seismic data have been examined for seismic events occurring within the zone called the accreted wedge or forearc marginal wedge that underlies the inner trench wall of some arcs these types of data are 1 teleseismically recorded earthquakes that have been reported in the literature as occurring in major arc trench regions these events fail to demonstrate that earthquakes occur within the accreted wedge because the uncertainty of focal depth usually exceeds the depth dimension of the accreted wedge these data include many tsunamigenic earthquakes 2 local earthquakes located by combined ocean bottom seismograph and land networks in the arc trench region in the new hebrides and the central and eastern aleutian trench none of the more reliable of these hypocenters lies within the accreted wedge 3 s p intervals measured at stations on islands located on the outer ridge or at ocean bottom seismograph stations on the forearc marginal wedge these data do not show the existence of events occurring within the accreted wedge e g from 18 ocean bottom seismograph stations with a cumulative operation time of about 1 year the smallest s p time is about 2 5 s for events in the new hebrides and about 4 s for events in the adak and kodiak regions we found no s p time smaller than 2 s from 6 years of seismograms recorded at middleton island alaska and no s p time smaller than 4 s from 25 years of seismograms recorded on barbados all of the events could have occurred outside the forearc marginal wedge although we have located no events with hypocenters which are situated unambiguously within the accreted wedge we have located many events which occurred in the vicinity of the accreted wedge some occur in the upper portion of the benioff zone shallower than about 40 km and others occur in the leading edge of the overriding plate these locations reported in this paper which are within or close to the seismic networks comprise some of the most reliably located shallow events ever reported in convergent margins of island arcs the absence of seismic activity within the accreted wedge in any island arc that we studied suggests that the deformation evident in this region occurs aseismically

the role of a heterogeneous inclusion during continental collision abstract we study a simple model of the deformation due to collision between two continental plates the model is patterned after the geometry of the india asia collision but it may be applicable to more general situations the collision is modelled by the indentation of a viscoplastic plate asia by a rigid punch india a finite element approach capable of dealing with finite deformation heterogeneity and non linear rheologies is used to study the role of an inclusion of increased rigidity on the viscoplastic flow of the plate the heterogeneous zone was chosen to approximate the shape and position of the tarim basin behind tibet the lateral boundaries of the plate were defined so as to approximate those that are believed to apply for the asian plate i e fixed boundaries to the west and north free boundaries to the west and south several geometries and contrasts of rheology were analyzed to verify the general validity of our results the purpose was to determine the main kinematic features of the flow not to model the particular case of tarim it is found that the heterogeneity affects the flow in a drastic way even for small contrasts of rigidity and for small size heterogeneities the main effect of the heterogeneity is to create two important shear zones or internal boundary layers the most important is in front of the inclusion separating the main flow from the inclusion as the flow proceeds the inclusion rotates and the shear zone progressively bends in qualitative agreement with the bending of the large strike slip faults like the altyn tagh that separates the tarim from tiber our model of continuous deformation does not allow for the formation of faults or fractures but the shear zones may be understood as the initial stages for the generation of fractures or velocity discontinuities another shear zone develops to the left of the inhomogeneity near the fixed boundary and in the wake of the punch the role of these shear zones is to isolate the heterogeneity from the main flow to facilitate its rigid rotation inside the flow of the softer plate a final observation is that in the presence of the heterogeneity the lower left hand corner rotates almost like a rigid block producing a sharp bend on the left hand side of the plate as the inclusion rotates pushed by the punch this rigid block rotates clockwise to open up the space necessary for the homogeneity

roughness at the base of the seismogenic zone contributing factors the cutout depth of microseismic activity in continental fault zones appears to correspond to the onset of greenschist metamorphic conditions at about 300 c it can generally be modeled as the transition from frictional to quasi plastic behavior in quartzofeldspathic crust shear resistance increases with depth through the frictional regime to peak at the transition beneath which it falls off exponentially with increasing temperature larger earthquake ruptures ml 5 5 nucleate around this transition depth where the highest concentrations of strain energy may accumulate varying depth and amplitude of the peak shear resistance along strike induce fluctuations in strain energy concentration at the base of the seismogenic zone factors affecting the depth of the transition include crustal composition geometry and mode of faulting fluid pressure levels in the frictional regime and water content in the quasi plastic regime quasi plastic strain rate and geothermal gradient evaluation of their relative importance is complicated because several are interdependent however compositional change may cause abrupt irregularities in seismogenic depth and peak shear resistance while regional variations in heat flow look to be particularly effective in creating long wavelength heterogeneities in strain energy concentration affecting faulting style

middle holocene sea level rise and highstand at 2 m central texas coast new data suggest a revised picture of middle holocene sea level change for the texas gulf of mexico coast and suggest reevaluation of coastal evolution first brackish marsh facies with calibrated radiocarbon ages of 7 7 to 7 8 ka have been recovered from depths of 8 5 to 9 m in a core from the ancestral colorado river delta and are interpreted to represent a sea level pinning point second a series of ridges along the copano bay margin farther south consist of shelly mud and fine sand with subtidal foram assemblages occur at elevations of 1 95 m above the modern intertidal zone and have produced calibrated radiocarbon ages on foram tests of ca 6 8 to 4 8 ka these ridges are interpreted to represent relict shallow subtidal to intertidal spits that provide minimum sea level positions for the middle holocene and are now emergent because of later sea level fall in aggregate these data show rates of sea level rise during this time period that are very comparable to or even lower than published eustatic rates and suggest a middle holocene sea level highstand for this non uplifting non rebounding and very slowly subsiding part of the north american coastline

the komandorsky basin as a product of spreading behind a transform plate boundary abstract a long term study of the komandorsky basin in particular by the cruises of r vvulkanolog and r vdmitry mendeleev in the summer of 1988 made it possible to describe in detail the main structural features of this marginal basin several ne and n s trending spreading axes were detected in the basin in the rear of the transform sector of the aleutian arc spreading axes are shifted relative to each other along nw striking transform faults there is variation in style from north to south along the strike of the spreading axes and a less well defined symmetry compared to that typical of mid oceanic ridges the tectonic pattern and heat flow reflect several stages starting from the eocene in the history of the opening of the basin caused by the changes in the velocity and direction of the relative motion between the pacific and north american plates

new finite element techniques for modeling deformation histories of continents with stratified temperature dependent rheology previous techniques for modeling anelastic deformation of the lithosphere have included plane strain models restricted to two dimensional problems and quasi three dimensional plane stress or thin plate models that did not accurately include the effects of the shallow frictional layer or of kinematic detachment of crust from mantle this paper presents techniques to remedy these deficiencies of thin plate models an iteration strategy in which the rheology is linearized using artificial prestress and a particular effective viscosity tensor causes the calculation of horizontal velocities to converge monotonically even with a frictional layer at the top of the lithosphere a technique using two planar grids allows deformation and displacement to be different at the crust and mantle levels at far less cost than that of a three dimensional grid a finite element technique is developed for computing the changes in thickness of these layers caused by pure shear simple shear and pressure gradients a technique based on relaxation of perturbation eigenfunctions solves the heat equation in the lithosphere during deformation accuracy of component numerical methods is good for simple test problems but in realistic nonlinear problems utilizing all components only the precision can be determined because of the lack of analytic solutions precision of the combined program is tested with a realistic sample problem and presented as a function of the number of iterations in each velocity solution convergence factor 0 73 to 0 88 size of time step in the predictor corrector time integration convergence as t0 8 and number of degrees of freedom in the finite element grid convergence as n 0 5 to 0 8 for most variables overall cost of a simulation varies with the fractional precision as 3 3 a new consequence of kinematic detachment a moving wave of crustal thickness is found unfortunately the form of the wave depends on the finite element size this means that element size must be chosen to approximate the smoothing by flexural rigidity effects that were neglected because of cost

geotechnical properties of expansive clay shale in tabuk saudi arabia abstract expansive soils prevail in several parts of saudi arabia tabuk city in the northwest is underlain by a shale formation of ordovician to devonian age arid climate accelerates the development of expansive clays through desiccation and weathering of the shale the expansion of the city limits extends to potential areas of swelling and urbanization increases the clay moisture content which leads to soil volume change this causes significant damage to low rise buildings and pavements in this paper the subsurface conditions and geotechnical properties of the expansive soils in tabuk are presented the clay type was identified and its degree of expansion was determined the swelling parameters were measured utilizing the standard oedometer test and modeled by multiple linear regression the effect of geological and environmental conditions on the swelling behavior of expansive soils in tabuk were considered the modeled swelling values are in good agreement with the measured values

anisotropy and large scale lateral inhomogeneity of the upper mantle abstract an investigation of travel time residuals of p waves as compared to an average global travel time curve with a base line determined shows that about 400 500 km of the upper mantle at the boundary with the crust and a similar thickness of the lower mantle at the boundary with the core are laterally inhomogeneous the upper mantle both under continents and under oceans consists of crust mantle blocks distinguished by longitudinal wave velocity surface tectonics and intensity of the heat flow it has been revealed that within individual crust mantle blocks there is an azimuthal relationship of p wave travel time indicative of possible anisotropy of upper mantle elastic properties down to depths of the order of several hundred kilometers

terrestrial heat flow in the northwestern pacific abstract on the basis of 150 new heat flow measurements the thermal structure of the uppermost layer of the earth in the transition zone of the northwestern pacific and relation of heat flow values to the age of tectonic magmatic activity have been established an analysis was made of the main factors distorting the geothermal field in the region under study and a map of measured and background heat flow values was constructed calculations were made to determine the temperatures in the deep crust and upper mantle along the dss profiles in the northwestern pacific and a map was constructed showing the depth of the zone of fractional melting 1200 c isotherm identified with the upper boundary of the asthenospheric layer

on the possibility of newtonian flow in the upper mantle abstract the possibility of a linear creep newtonian viscosity upper mantle is reexamined on the basis of present knowledge on flow mechanisms in olivine including differences between activation parameters for creep and for diffusion and revised estimates of grain boundary width results of the comparison between linear superplastic creep and power law creep are presented as crossover temperature between lattice and grain boundary diffusion and crossover stress between non linear and linear creep as a function of temperature depth grain size grain boundary width grain boundary diffusion activation energy and rate controlling species silicon or oxygen for the most realistic values of the parameters linear creep is well within the range of possibilities there is no major objection from rheology to the idea of a newtonian viscosity upper mantle viscosities for the two kinds of creep are compared for laboratory upper mantle and tentatively lower mantle conditions this results in a prediction of the grain size at which coble creep could be observed in olivine polycrystals in the laboratory 10 m or less the upper mantle viscosity is in the 1020 1021 pa s range minimum estimates for the viscosity of the lower mantle are of the same order the pictures of the rheology of the mantle derived from microphysical models of flow and from geophysical observation can therefore be made compatible

terrestrial heat flow estimation of deep temperature and seismicity of the kamchatka region abstract the results of heat flow measurements in the kamchatka region are discussed in this paper on the basis of more than 60 continental measurements and a number of heat flow measurements made at sea a schematic heat flow map has been compiled an interpretation of the anomalous fraction of heat flow is made and a likely temperature distribution in the lithosphere of kamchatka was calculated based on 3 d modelling of the thermal field an analysis is made of the geothermal regime of the kamchatka sector of the focal zone temperature is shown to be the controlling factor for the maximum depth of occurrence of seismic events the majority of earthquakes occur in a layer 0 100 km thick where the temperature does not exceed 700 c

oblique plate convergence slip vectors and forearc deformation slip vectors from thrust earthquakes at subduction zones where convergence is oblique to the trench often point between the directions of relative plate convergence and normal to the trench axis suggesting that oblique convergence is taken up by partial decoupling decoupling means that a component of arc parallel motion of the leading edge of the upper plate results in less oblique thrusting at the trench partial decoupling is modeled by partitioning of oblique convergence into slip on thrust and strike slip faults that are parallel to the trench and to each other and starting with a force equilibrium condition a relationship between the obliquity and the earthquake slip vector orientation is derived assuming that either fault slips when shear stress on it reaches a yield stress oblique slip parallel to the plate vector should occur on the thrust fault when obliquity is smaller than a critical angle for obliquity at or greater than this angle the stress on the strike slip fault is large enough to start it slipping and when both faults are active the arc parallel motion of the forearc deflects the slip vector back toward the trench normal if we assume that continued slip on either fault occurs at constant stress but the two faults can be at different stresses the slip vector will maintain a constant angle relative to the trench normal even when obliquity is larger than the critical angle this limiting angle of the slip vector called max measured relative to the trench normal is simply the arcsine of the ratio of the shear forces resisting slip on the strike slip and thrust faults a consequence is that when the obliquity exceeds max the slip vectors on the thrust fault are sensitive only to the thrust fault orientation and contain no information about the convergence direction between the plates slip vectors at the java trench southwest of sumatra show the relationship clearly with max 20 5 while slip vectors at the aleutian trench show the relationship less clearly with max 25 to 45 the greater angle at the aleutian trench suggests that the upper plate is stronger in the aleutian arc relative to the thrust fault than in the sumatran arc consistent with the sumatran arc being continental and having a well developed strike slip fault while the aleutian arc is oceanic and without a clear transcurrent fault slip vectors at the philippine trench which like sumatra has a large strike slip fault inboard of it tend to stay within 25 of the trench normal when obliquity is as large as 50 if obliquity exceeds max and continues to increase along a subduction zone the rate of motion of the forearc relative to the upper plate will vary with obliquity in which case the forearc sliver should extend or contract parallel to the arc from the geometry of modern island arcs arc parallel extension should be the more common and has been hypothesized for both sumatra and the aleutians on the basis of earthquake slip vectors and for these and other arcs from geological observations from estimates of max and the arc parallel gradients in obliquity arc parallel strain rates are estimated to be 1 to 3 10 8 yr for the sumatran forearc 2 to 6 10 8 yr for the aleutian forearc and 0 3 to 3 10 8 yr for the philippine forearc oblique convergence and subsequent arc parallel extension if accompanied by crustal thinning may provide an important yet little appreciated mechanism for bringing high grade metamorphic rocks to the surface of subduction complexes

massive sediment bypassing on the lower shoreface offshore of a wide tidal inlet cat island pass louisiana abstract analysis of a series of historical bathymetric and shoreline surveys along the louisiana coast west of the mississippi river mouth detected a large area of deposition in water depths of 2 0 8 5 m offshore of a 9 km wide tidal inlet the cat island pass wine island pass system a 59 9 106 m3 sandy deposit formed from the 1930s 1980s spanning 27 km in the alongshore direction delineating the transport pathway for sediment bypassing offshore of the inlet on the shoreface bypassing connected the shorefaces of two barrier island systems the isles dernieres and the bayou lafourche the processes responsible for formation of this deposit are not well understood but sediment transport modeling suggests that sediment is transported primarily by wind driven coastal currents during large storms and hurricanes deposition appears to be related to changes in shoreline orientation closing of transport pathways into a large bay to the east and the presence of tidal inlets this newly documented type of bypassing an offshore bypassing of the inlet system naturally nourished the immediate downdrift area the eastern isles dernieres where shoreface and shoreline erosion rates are about half of pre bypassing rates erosion rates remained the same farther downdrift where bypassing has not yet reached as this offshore bypassing continues the destruction of the isles dernieres will be slowed

the depositional environment of the late pliocene red clay jing le basin shanxi province china abstract red silty clays of late pliocene age are widely distributed in northern china at the type section in the jing le basin in shanxi province they overlie alluvial and lacustrine sands and gravels and underlie loess new data on grain size grain shape fabric chemistry floral pollen content and previously catalogued faunal evidence suggest sedimentation of the silty clays in a warm temperate and sub humid environment as a weathered mantle transported down gentle slopes by creep and rainwash the jing le formation represents a transition from dominantly alluvial deposition in the upper pliocene to dominantly aeolian deposition in the lower pleistocene

mantle heterogeneities within active margins of the world oceans and their seismological characteristics abstract the principal geotectonic element of active marginal areas is represented by arcuate structures characterized by two mantle volumes in contact containing materials with different properties the rigid high density and comparatively cold region with concentrated earthquake hypocentres is accompanied by an aseismic mantle where a low velocity layer at depths from 150 to 250 km and a low velocity zone under the present volcanoes form a specific volume p wave velocity of the latter is nearly 15 below the standard values and nearly 20 lower than that in the adjacent seismically active blocks as a result of these lateral changes in the physical properties there appears to exist a considerable gradient of lithostatic pressure whose maximum occurs in the focal zone and its resulting forces point to the arc centre thus determining the horizontal displacement of sinking high density matter with the focal zone velocity changes of the aseismic mantle block along the geostructure are determined by the geological evolution of the region and reflected in its morphostructure in shallow parts of the northern sea of okhotsk and western kamchatka with continenetal type of crust developed on the bottom of the pre mesozoic platform the p wave velocities in the upper mantle are 0 5 0 6 km s smaller than those under the kuril abyssal plain with suboceanic crust small scale mantle inhomogeneities of the focal zone manifest themselves in a seismic anisotropy which changes both in magnitude and direction it reflects a reaction of the medium to the shearing stresses and is controlled by strength anisotropy distribution of seismic parameters velocity and attenuation of elastic waves in the mantle of active margins is represented by alternating areas of high and low strength weaker areas coincide both in setting and trend with deep seated faults which cut across the arcuate geofeatures this combination of arcuate and orthogonal tectonic systems in the northwestern pacific under the conditions of tensile stresses which act along the island arc favours a displacement of the central portion of the island arc toward the ocean

centroid moment tensor solutions for october december 1991 centroid moment tensor solutions are presented for 160 earthquakes that occurred during the fourth quarter of 1991 the solutions are obtained using corrections for aspherical earth structure represented by a whole mantle shear velocity model sh8 u4l8

large scale deformation related to the collision of the aleutian arc with kamchatka the far western aleutian island arc is actively colliding with kamchatka westward motion of the aleutian arc is brought about by the tangential relative motion of the pacific plate transferred to major right lateral shear zones north and south of the arc early geologic mapping of cape kamchatka a promontory of kamchatka along strike with the aleutian arc revealed many similarities to the geology of the aleutian islands later studies support the notion that cape kamchatka is the farthest west aleutian island and that il has been accreted to kamchatka by the process of arc continent collision deformation associated with the collision onshore kamchatka includes gravimetrically determined crustal thickening and formation of a narrow thrust belt of intensely deformed rucks directly west of cape kamchatka the trend of the thrust faults is concave toward the collision zone indicating a radial distribution of maximum horizontal compressive stress offshore major crustal faults trend either oblique to the kamchatka margin or parallel to major aleutian shear zones these offshore faults are complex accommodating both strike slip and thrust displacements as documented by focal mechtmisms and seismic reflection data earthquake activity is much higher in the offshore region within a zone bounded to the north by the northernmost aleutian shear zone and to the west by an apparent aseismic front analysis of focal mechanisms in the region indicate that the present day arc continent contact zone is located directly east of cape kamchatka in modeling the dynamics of the coiiision zone using thin viscous sheet theory the rhealogical parameters are only partially constrained to values of n the effective power law exponent 2 3 and ar the argand number s 30 these values are consistent with a fnrcarc thermal profile of kamchatka previously determined from heat flow modeling the thin viscous sheet modeling also indicates that onshore thrust faulting is a consequence not only of compressive stresses resulting from the west directed collision but also of sediment induced coupling of the subducting pacific plate

spatial prediction of landslide susceptibility using an adaptive neuro fuzzy inference system combined with frequency ratio generalized additive model and support vector machine techniques abstract the spatial prediction of landslide susceptibility is an important prerequisite for the analysis of landslide hazards and risks in any area this research uses three data mining techniques such as an adaptive neuro fuzzy inference system combined with frequency ratio anfis fr a generalized additive model gam and a support vector machine svm for landslide susceptibility mapping in hanyuan county china in the first step in accordance with a review of the previous literature twelve conditioning factors including slope aspect altitude slope angle topographic wetness index twi plan curvature profile curvature distance to rivers distance to faults distance to roads land use normalized difference vegetation index ndvi and lithology were selected in the second step a collinearity test and correlation analysis between the conditioning factors and landslides were applied in the third step we used three advanced methods namely anfis fr gam and svm for landslide susceptibility modeling subsequently the results of their accuracy were validated using a receiver operating characteristic curve the results showed that all three models have good prediction capabilities while the svm model has the highest prediction rate of 0 875 followed by the anfis fr and gam models with prediction rates of 0 851 and 0 846 respectively thus the landslide susceptibility maps produced in the study area can be applied for management of hazards and risks in landslide prone hanyuan county

double seismic zone beneath the mariana island arc a double zone of seismicity has been found beneath the northern marianas in the depth range 80 120 km the benioff zone undergoes a pronounced bend with radius of curvature about 200 km before straightening and descending nearly vertically to a depth of more than 600 km thus this is an ideal area in which to search for evidence of stresses associated with unbending of the subducted oceanic plate we relocated all teleseismic events from 1963 through 1975 by using a regional composite master event technique which significantly decreased the scatter of the hypocenters the three events of the lower seismic zone are separated from the upper zone by about 30 35 km the true thickness of the upper seismic zone is probably 20 km or less the limited focal mechanism data indicate that there is downdip tension in the lower zone and downdip compression in the upper zone the seismicity patterns could be generated either by thermal stresses or by unbending a plate which was originally deformed anelastically we show that an elastic perfectly plastic model of the rheology of the plate can account for the separation of the two seismic zones the focal mechanisms and the greater activity of the upper seismic zone

the relationship between strain rates crustal thickening palaeomagnetism finite strain and fault movements within a deforming zone the deformation of continental lithosphere generally does not occur on a single fault but is distributed over a zone up to a few hundred kilometers wide if the deformation rate is constant throughout the zone and if the velocity is continuous everywhere and does not change with time the deformation gradient tensor can be obtained analytically this tensor directly determines the amount of crustal thickening and is related in a complicated manner to the finite strain tensor the declination of remnant magnetization measured within the zone can also be rotated by the deformation because palaeomagnetic measurements are generally made on rigid blocks which have not been deformed there is no simple relationship between such rotations and the finite strain expressions for all these quantities are obtained in terms of the velocity gradients which are taken to be constant the history of western north america is used to illustrate the relationship between the present deformation by strike slip and thrust motions the rotations of the remnant magnetization vectors and the shape of accreted terranes at the surface distributed deformation is taken up by motion on faults which separate the zone into blocks the displacement rate on the faults their strike and the finite rotations of the blocks are all controlled by the velocity gradients analytic expressions relating these quantities are obtained a deforming zone containing normal faults which crosses central greece takes up both strike slip and extension and illustrates the relationship between the structures within and the motion across the zone a similar but more complicated zone in northeastern iran involves both strike slip and shortening

the refinement of hypocenter parameters on the basis of three dimensional velocity models of focal zones abstract a complex approach to the processing of seismological data to determine hypocenter coordinates and to construct three dimensional velocity fields of focal zones is considered the iterative process includes the determination of focal coordinates under the assumption of a laterally homogeneous medium the construction of a three dimensional velocity model and subsequent redefinition of the focal coordinates taking into account the inhomogeneous structure of the medium the principal results of calculations of three dimensional velocity fields and refined earthquake hypocenters are presented for focal zones in vrancea carpathians the caucasus and kamchatka

a new depositional model for the buried 4000 yr bp new orleans barrier implications for sea level fluctuations and onshore transport from a nearshore shelf source abstract the holocene new orleans barrier complex now buried by the st bernard delta of the mississippi river provides an excellent example of barrier deposition fed by a nearshore sediment source this reworking and onshore transport was initiated by a sudden change in the shelf equilibrium profile caused by a sea level fall about 4100 yr bp here we present a new model of barrier formation which does not invoke an shepard type holocene sea level curve nor the supply of sediment from a longshore source the holocene new orleans barrier complex consists of fine grained locally cross bedded quartz sand that contains ophiomorpha nodosa burrows and disarticulated mollusks primarily marine buried beneath up to 4 m of silty mud of the st bernard lobe this barrier island and shoal deposit overlies interbedded fine grained sand and mud containing marine mollusks some articulated that is interpreted to be a nearshore shelf deposit its deposition took place between 5500 and 4200 yr bp 14c based on individual dates on seven articulated and seven disarticulated shells the barrier formation is effectively limited to a several hundred year window approximately 4000 yr bp by the 3800 yr bp rangia sp shells from the immediately overlying st bernard lobe delta plain deposits and the buried 3900 3500 yr bp linsley archeological site situated on a more gulfward distributary levee in this paper we present a new depositional model on the new orleans barrier the barrier complex contains an abundance of large mollusk shells that have been reworked to the extent that 14 individual shells yield a 2500 year range 6000 3500 yr bp an older nearby source is required the current model of a spit shoal complex migrating westward from an eroding eastern pleistocene headland probably cannot account for the deposition of large reworked shells given the effects of abrasion and selective size sorting over approximately 50 km of longshore transport furthermore this model demands transport rates of millions of cubic meters per year for the present northern gulf coast which are at least an order of magnitude higher than its highest known rates we postulate a nearby shell and sand source that is subjacent and offshore rather than adjacent and littoral we propose it to be the underlying nearshore shelf deposit that could be mobilized by a brief fall of sea level and carried landward the barrier complex and the uppermost nearshore shelf deposit have markedly different net deposition rates the upper 25 cm of the nearshore shelf deposit were deposited over 800 years based on ages of articulated marine pelecypods a 20 km long 3 km wide and 4 m thick segment of the barrier complex was deposited in less than 300 years a 10 cm thick lag pavement of bryozoan and oyster encrusted mollusk shells that comprises the nearshore shelf deposit beneath the northern edge of the barrier complex is evidence for an essentially zero net deposition rate the current interpretation of a conformable progradational relationship between these two units is rejected in favor of a disconformable contact the hiatus across this disconformity must be less than the several hundred year duration of barrier complex deposition the positioning of the shallower water barrier complex disconformably over the deeper water nearshore shelf deposits indicates a sea level fall

mineralogy geochemistry and petrogenesis of kurile island arc basalts whole rock major and trace element and mineral chemical data are presented for basaltic rocks from the main evolutionary stages of the kurile island arc nw pacific an outer inactive arc contains a cretaceous lower tertiary sequence of tholeiitic calcalkaline and shoshonitic basalts the main arc miocene quaternary is dominated by weakly tholeiitic with lesser alkalic basalts the mineralogy of kuriles basalts is characterised by an rich plagioclases a continuous transition from chromites to titanomagnetites pyroxenes with low fe3 contents and without strong fe enrichment abundance of groundmass pigeonites and the absence of amphiboles there is an increase in k2o contents both along arc northwards and towards the reararc side the basalts show an exceptionally wide but continuous range of k2o contents 0 1 4 7 which correlate with other lil element contents tholeiitic basalts with low lil element contents la yb and th u but high k rb p2o5 la and zr nb were derived from depleted lherzolitic mantle which had suffered fluid metasomatism by k rb cs sr ba pb and h2o only alkali basalts are also thought to be derived from depleted mantle but melt metasomatism involved addition of all lil elements to a garnet lherzolite mantle the kuriles basalts and their mantle sources range continuously between these two end member compositions the metasomatic fluids melts were probably released by early dehydration and later melting within subducted oceanic lithosphere though the process is not adequately constrained

a continuum model of continental deformation above subduction zones application to the andes and the aegean large scale continental tectonics of back arc extensional and andean type compressional environments are investigated by using the thin viscous sheet model to calculate the deformation within continental lithosphere that is subjected to horizontal forces on its plate boundaries and to basal drag from the asthenospheric flow beneath the shear tractions acting on the base of a deformable lithosphere are derived from a corner flow model that assumes a rigid subducting plate and a deformable overlying plate because the calculated shear tractions and the deformation within the overlying plate are interdependent the corner flow and the thin viscous sheet models are solved simultaneously we use a perturbation method to obtain analytical solutions for the velocity and strain rate fields within the overlying continental lithosphere the solutions depend on the angle of subduction the dimensionless thickness of the lithosphere and the ratio of asthenospheric to lithospheric viscosities which governs the viscous coupling between the asthenosphere and the lithosphere calculations are compared with observations from the andes and the aegean our results explain some of the features of the deformation in these regions that have heretofore not been explained by other models our model predicts that in a compressional environment a broad region of uplifted topography will tend to develop above a more steeply dipping slab 30o rather than above a shallower slab 10o 15o this is in accord with observations in the various segments of the central andes for an extensional environment the model predicts that a zone of compression can develop near the trench and that extensional strain rate can increase with distance from the trench as is observed in the aegean we also estimate the effective viscosities of 102o pa s for the asthenosphere 2x 1021 pa s for the aegean lithosphere and 1022 pa s for the andean lithosphere

considerations on the global seismic sequences the second and the third largest aftershocks summary statistical considerations on the occurrence of the second largest aftershock of an earthquake sequence have been developed using global data the time distribution of the second m and the third m3 largest aftershocks are studied here as well the probability that these two aftershocks would occur in the first 24 hr after the main shock is more than 50 per cent it was found that the second and the third largest aftershocks are distributed like the first largest aftershock the difference d2 is determined between the magnitudes of the main shock m and the second largest aftershock m2 of an earthquake sequence using a complete data set it was found that the difference d2 has a mean of about 2 0 two distinct cases of the m2 occurrence are observed the first case case 1 corresponds to normal aftershock sequence evolution where m2 follows mi which is the largest aftershock of a sequence while in the second one case 2 m2 precedes mi the values of the time distribution are totally different between case 1 and case 2 an attempt is made to interpret the temporal occurrence of the aftershocks with respect to the surface terrestrial heat flow the mean heat flow value for case 1 is qa 1 61 f 0 86 while for case 2 this is qb 1 38 f 0 82 it is shown that when the heat flow is high the three largest aftershocks m m2 and m3 temporally occur closer to the main shock

geological and geotechnical characteristics of n2 laterite in northwestern china abstract the neogene pliocene series n2 laterite is a special zonal soil widely distributed in northwestern china however given that it is largely covered by loess and other quaternary deposits there has been a lack of in depth studies on its engineering geological characteristics in recent years with the development of resources and the construction of grand scale industrialization in northwest china many projects slope tunnel mining etc have encountered geological engineering problems due to the n2 laterite investigating the engineering geological characteristics of the n2 laterite provides the key to solving these problems using n2 laterite samples from typical regions in northwestern china and conducting laboratory tests this paper analyzes the mineralogical composition particle size distribution clay mineral content and microstructure characteristics of the n2 laterite it discusses its origin and depositional environment characteristics and probes into its physical hydrological and mechanical properties finally the engineering environmental effect of the n2 laterite is summarized according to the results the n2 laterite composition is dominated by quartz followed by feldspar interstitial materials mainly consist of fine grained microcrystalline calcite and clay minerals particle size distribution mainly covers clay and silt with relatively uniform particle sizes in clay minerals the contents of hydrophilic minerals montmorillonite and illite montmorillonite mixed layer are fairly high n2 laterite is mainly an aeolian deposit with medium water holding capacity and plastic hard plastic or hard in its natural state and as a medium swelling soil it is relatively impermeable under natural moisture content conditions the n2 laterite has a relatively high strength but when subjected to long term groundwater its strength decreases rapidly in addition the n2 laterite is a medium high compressibility soil

multiple sediment sources and a cellular non integrated longshore drift system northwest florida and southeast alabama coast usa abstract the morphosedimentary maintenance of a 225 km stretch of coast along the northeast gulf of mexico from grayton beach florida to morgan point alabama has been interpreted previously within the framework of a unidirectional integrated monotonic longshore drift model with a single headland source of sediment located east of grayton beach net longshore transport and the granulometry and composition of some 2000 foredune beach and step samples indicate a cellular net drift system supplied by three independent sources of sediment one source is provided by the pleistocene barrier island complex along grayton mirimar beach the second at pensacola beach on santa rosa island and the third is onshore transport across the inner shelf between pensacola florida and morgan point alabama the pleistocene headland and pensacola beach supply two cells along santa rosa island whereas onshore transport from the low gradient inner shelf supplies sediment to three cells along the largely accretional beach ridge dominated coast from pensacola pass to morgan point drift cells along this coast experience negligible net sediment exchange these findings have significant implications for both the late holocene evolution and the morphodynamic maintenance of this coast

thermal modeling of subducted plates tear and hotspot at the kamchatka corner pacific plate subduction at the aleutian kamchatka juncture or corner could be accommodated by either a large bend or a tear in the oceanic lithosphere in this paper we describe a number of observations which suggest that the pacific plate terminates abruptly at the bering transform zone tz seismicity shoals along the subduction zone from southern kamchatka 600 km to relatively shallow depths near the kamchatka bering fault intersection 100 200 km this seismicity shoaling is accompanied by an increase in the heat flow values measured on the pacific plate moreover unusual volcanic products related to adakites are erupted on kamchatka peninsula at the juncture simple thermal modeling shows that a slab torn and thinner along the northern edge of the pacific plate would be compatible with the observations delayed thickening of the lithosphere due to the meiji hawaiian hotspot may be responsible for the required thinning d 2004 published by elsevier b v

orogeny in arc continent collision the banda arc and western new guinea eastern indonesia contains a modern continent island arc collision that demonstrates how a complex juxtaposition of continental and oceanic elements can occur in an orogenic belt shallow earthquakes show that strike slip faulting transports large crustal blocks into out of and along the collision zone while crustal shortening and thickening occur by steep angle thrust faulting near the strike slip faulting whereas strike slip faulting is paramount in positioning australian continental rocks so as to enclose the oceanic and island arc rocks of eastern indonesia its role may be overshadowed by the contemporaneous thrusting and may confuse geologic interpretations of the resulting orogenic belt

initial rupture and the main fault of earthquakes a comparison of the body wave first arrivals and cmt data for the kamchatka commander region abstract centroid moment tensor cmt data by dziewonski and coworkers and body wave first arrival earthquake parameters obtained from local networks were simultaneously investigated for 55 earthquakes in the kamchatka commander region which occurred from 1977 to 1986 the magnitude range considered was 4 5 7 5 the focal depths were 0 190 km the following parameters were studied origin time hypocenter coordinates focal mechanism and seismic moment the first arrival data were referred to the initial rupture in the earthquake focus and cmt estimates to the main earthquake fault the principal results obtained are as follows shifts of the centroid location with respect to initial hypocenters and the change or stability of the type of faulting from the initial rupture to the main fault depend on the tectonic position of the hypocentral area the character of the source time function depends on the sign of the main fault propagation i e downwards upwards horizontally

constraints on extension of continental lithosphere the extension of the continental lithosphere is considered in terms of the deformation of a thin viscous sheet with a temperature dependent rheology which is governed primarily by the strength of the upper mantle the lithosphere is subjected either to a constant strain rate or to a strain rate decreasing with time corresponding to the stretching of a region of fixed volume with a constant velocity boundary condition the progress of the extension is influenced by the decrease in strength of the lithosphere owing to its attenuation and by an increase in strength resulting from cooling the relative importance of these two effects depends on two parameters a dimensionless strain rate and the total strain for a given strain rate the extending lithosphere goes through two phases as the strain increases in the first the effect of thinning the lithosphere is predominant and the average strength of the lithosphere remains close to and perhaps slightly below its original strength in the second the effect of cooling of the lithosphere leads to very rapid increase in strength as a function of strain resulting presumably in an effective limit on the degree of stretching that the lithosphere experiences for the case of strain rate decreasing with time when the initial strain rates are of order 10 15s 1 this maximum extension is between 100 and 150 for a strain rate of 10 l4 s 1 the maximum lies around 400 to 500 at higher strain rates than this very large extension may occur before cooling significantly affects the strength of the lithosphere this model accords well with the constraints available from the continental margins of the north atlantic

cold moho boundary beneath island arc systems an example from the north kamchatka arc a suite of amphibole bearing ultramafic and mafic xenoliths representing the crust mantle boundary was sampled in the northern segment of the kamchatka arc these nodules exhibit low equilibration temperatures at elevated pressures suggesting relatively cold conditions at moho depths which are uncommon in modern island arcs a model including successive stages of subduction initiation subduction cessation resulting in cooling of the lithospheric wedge followed by intra arc rifting due to upwelling of astenospheric diapirs is proposed to explain the observed textural petrologic and chemical characteristics of sampled rock assemblage

pedostratigraphy and paleomagnetism of a 7 0 ma eolian loess red clay sequence at lingtai loess plateau north central china and the implications for paleomonsoon evolution abstract a 305 m thick loess red clay sequence was discovered recently at lingtai which is located in the middle part of the chinese loess plateau it consists of a complete pleistocene loess soil sequence with a thickness of about 175 m and 130 m of tertiary red clay deposits the red clay sequence at lingtai is the thickest one presently known in the loess plateau field observations show that the lingtai red clay contains over 110 couplets of pedogenic b horizons and horizontal carbonate nodule horizons and that it can be regarded as an extremely thick soil complex paleomagnetic studies of 680 samples suggest that the basal age of the lingtai loess red clay sequence is about 7 05 ma grain size analysis of samples taken at 3 3 cm intervals indicates that the red clay has the same sedimentological characteristics as those observed in the loess thus suggesting a wind blown origin of the tertiary red clay and continuous atmospheric dust deposition in the loess plateau during the last 7 05 ma the pedogenic characteristics of the paleosols within the pleistocene loess and the b horizons in the red clay suggest that the east asia summer monsoon in the latest miocene may have already been slightly stronger than that during the holocene this implies that at about 7 5 ma bp the tibetan plateau could have been uplifted to a critical height in maintaining the east asia summer monsoon system observations of the loess red clay sequence also suggest that the long term changes in the east asia summer monsoon strength have been nonlinear since the latest miocene

a new magnetostratigraphic framework for late neogene hipparion red clay in the eastern loess plateau of china abstract mammalian fossils especially the hipparion fauna found in the red clay of the loess plateau are of immense value for reconstructing late neogene paleoecology and paleoclimatology in northern china the lack of a precise chronological framework for these fossil sites has impeded our understanding of the evolution of the chinese mammalian fauna their correlation with european mammalian units and the retrieval of paleoclimatic information in this study a field survey of regional stratigraphy in the baode area of shanxi was carried out and three profiles tanyugou yangjiagou i and yangjiagou ii of late neogene deposits were selected for detailed investigation a new chronological framework of the late neogene sequences in the baode area is established by means of paleomagnetism our results show that the red clay accumulation in the baode area began at least 7 23 ma ago deposition continued to the superposed jingle formation the most continuous and complete exposure of the jingle formation known to date was identified and dated to 2 72 5 34 ma a lithological distinction between the jingle formation and the underlying baode formation forms a clear boundary in the red clay that is not coincident with the miocene pliocene boundary documented elsewhere three rich fossil layers are found in the yangjiagou ii profile and dated to 6 43 6 54 ma 6 83 6 86 ma and 7 15 7 18 ma respectively with the application of three different demagnetization techniques the matuyama gauss geomagnetic reversal boundary was identified in a transitional unit between loess and typical red clay deposits a lock in depth of as large as 6 8 m corresponding to ca 65 ka was inferred but remains unexplained

origin transport and emplacement of an exotic island arc terrane exposed in eastern kamchatka russia the regional stratigraphy of eastern kamchatka includes an exotic early late cretaceous ophiolite and late cretaceous island arc volcanic sequence integrating the existing geologic and geophysical data we examine the origin transport emplacement and postemplacement deformation of the island arc terrane which is named the olyutorsky island arc results from several paleomagnetic studies consistently indicate that the island arc terrane originated 1000 km to the south of where it is presently exposed although the formative paleolatitudes of the island arc rocks approximately correspond to the location of the izanagi farallon subduction zone the age of the volcanic rocks postdates the cessation of izanagi farallon convergence thus indicating that an unnamed plate or back arc basin existed in the northwest pacific during late cretaceous time we examine two possible models for northward transport of the island arc terrane to kamchatka 1 infra oceanic transport with the pacific or kula plates and 2 coastwise translation of the island arc terrane after accretion to the eurasian margin far to the south of kamchatka for both models the dominant eocene and miocene deformation ages observed in eastern kamchatka are used as two possible age limits for the cessation of northward transport although the observed paleolatitudes from paleomagnetic data correspond best with the infra oceanic transport model the provenance of the paleogene transport stratigraphy indicates a near shore sediment supply our preferred interpretation is that the island arc terrane 1 accreted onto the eurasian margin concurrent with cessation of island arc volcanism maastrichtian danian and 2 underwent northward coastwise translation along a major strike slip fault zone ending by middle late eocene time 43 50 ma it is unclear whether the ophiolite was exposed during arc continent collision or whether the ophiolite was obducted onto the island arc prior to collision a consequence of either infra oceanic transport or coastwise translation is that an open corridor between the western terminus of the aleutian arc and kamchatka must have existed until middle to late eocene time spreading within the komandorsky basin subduction of sea mounts and collision of the aleutian arc with kamchatka are proposed to have instigated the second miocene phase of deformation which uplifted and reexposed the island arc terrane

validity of sea level indicators a comment on a new depositional model for the buried 4000 yr bp new orleans barrier implications for sea level fluctuations and onshore transport from a nearshore shelf source by f w stapor and g w stone marine geology 204 2004 215 234 the holocene history of the se louisiana mississippi coast and a recently revised regional sea level curve fail to support the concept of an abrupt gulf wide decline from 2 0 m to 1 5 m and regression with barrier aggradation between 4 1 and 3 9 14c ka bp triggered by massive onshore sediment transport a subsequent rapid rise followed by minor oscillations are equally unsubstantiated suggestions for an overwhelming role of onshore transport during the assumed regression or otherwise may not be justified a small hardcrust lens in the continuous subaqueous barrier sequence does not prove major fall in sea level regional regression and subaerial exposure elevation and lithofacies of florida shore scarps and radiocarbon dated beach ridges fail to support sea level fluctuations the presented paleogeographic and sea level models indicate continuous shoal and associated island formation between ca 5 2 and 4 0 14c ka bp uninterrupted by sea level decline rapid progradation of a mississippi river st bernard delta lobe terminated barrier development

a new approach for predicting bedding separation of roof strata in underground coalmines abstract in order to avoid the influence of monitoring location to measured vertical bedding separation a new estimating approach for vertical bedding separation which uses the ratio between current and average vertical bedding separation k has been proposed in situ investigations showed there exists a threshold value of k t for any kind of roof stratum and the sedimentation has a great influence on it in the eastern deep coal mines which are subjected to intense sedimentation in shandong province china k t ranges from 1 48 to 1 73 in the western shallow coalmines which are subjected to weak sedimentation inner mongolia china k t ranges from 1 32 to 1 37 k t is related to t the lower layer thickness and separation position when separation occurs in the anchored range k t increases with t but in a downward gradient and slightly decreases with the lower layer thickness when separation occurs outside the anchored range k t increases with t in an upward gradient and increases with the lower layer thickness to combine monitoring the technique for k and the borehole camera scanning technique is a more reliable for estimating roof safety in a roadway

paleomagnetism of paleogene rocks of the central east kamchatka and komanorsky islands tectonic implications abstract paleomagnetic investigation of paleocene eocene to miocene rocks has been carried out at five localities in the eastern kamchatka and komandorsky islands after thermal and af cleanings consistent paleomagnetic directions were isolated for a number of formations data from the kronotsky peninsula and medny island passed both the fold and reversal tests and thus can be considered as reliable other results are of lower quality all the results were derived from sedimentary rocks and thus the corresponding paleolatitudes may be biased due to inclination errors a limited collection of basalts yielded inclination values systematically lower than those in sediments this anomaly was tentatively explained by shape anisotropy the correctness of paleolatitude estimations was thus left unproved several models of the northern pacific tectonic evolution were suggested and analyzed but the authors failed to find a model that was fully compatible with paleomagnetic kinematic and geological data

magma in forearcs implication for ophiolite generation abstract forearc areas non volcanic arcs of contemporary island arcs at convergent plate boundaries contain magmatic rocks geological evidence seismic profiles heat flow data density considerations and petrological and geochemical arguments suggest that a forearc tholeiitic association fat containing high mg calc alkaline andesites is present in non volcanic arcs at some stage of island arc development the fractionated as well as primitive magma is unable to penetrate low density sediments and underplates thick piles of unconsolidated accreting rocks the underplating causes upwelling the occurrence of magma in forearcs provides an alternative interpretation for the tectonic setting of some ophiolitic masses rather than ocean ridge formation and later obduction it offers an autochthonous island arc bound and geologically substantiated interpretation for the ophiolite suite

deformation of the central andes 15 27 s derived from a flow model of subduction zones a simple viscous flow model of a subduction zone is used to calculate the deformation within continental lithosphere above a subducting slab our formulation accounts for two forces that dominate the deformation in the overriding lithosphere tectonic forces and buoyancy forces the tectonic forces arise from the subduction of oceanic lithosphere and produce minor extension in the lithosphere near the trench and compression farther inland buoyancy forces can induce horizontal pressure gradients due to variations in crustal thickness which cause lithospheric extension where the crust is thick numerical solutions obtained by using a finite element technique are compared with observations from the central andes 15 27 s the model predicts the observed deformation pattern of extension in the forearc compression in the western monocline corresponding to magmatic activity extension in the altiplano compression in the eastern monocline and subandes and no deformation in the brazilian shield by comparing the calculated solutions with the large scale tectonic observations we are able to evaluate the forces that govern the deformation in the central andes the approximately constant subduction velocity in the past 26 m y suggests that the rate of crustal shortening in the andes has decreased with time due to the thickening of the crust

formation of the rocky mountains western united states a continuum computer model one hypothesis for the information of the rocky mountain structures in late cretaceous through eocene time is that plate of oceanic lithosphere was underthrust horizontally along the base of the north american lithosphere the horizontal components of the motion of this plate are known from paleomagnetism and the edge of the region of flat slab can estimated from reconstructed patterns of volcanism new techniques of finite element modeling allow prediction of the thermal and mechanical effects of horizontal subduction on the north american plate a model that has a realistic temperature dependent rheology and a simple plane layered initial condition is used to compute the consequences of horizontal underthrusting in the time interval 75 million to 30 million years before present successful prediction of this model include i the location amount and direction of horizontal shortening that has been inferred from laramide structures ii massive transport of lower crust from southwest to northeast iii the location and timing of the subsequent extension in metamorphic core complexes and the rio grande rift and iv the total area eventually involved in basin and range style extension in a broad sense this model has predicted the belt of laramide structures the transport of crust from the coastal region to the continental interior the subsequent extension in metamorphic core complexes and the rio grande rift and the geographic region of late tertiary basin and range extension its principal defects are that i many events are predicted about 5 million to 10 million years too late and ii the wave of crustal thickening does not travel far enough to the east reasonable modifications to the oceanic plate kinematics and rheologies that were assumed may correct these defects the correspondence of model predictions to actual geology is already sufficiently close to show that the hypothesis that horizontal subduction caused the laramide orogeny is probably correct the rocky mountain thrust and reverse faults formed in an environment of east west to northeast southwest compressive stress that was caused by the viscous coupling between the oceanic plate and the base of the north american crust nonuniform crustal thickening by simple shear transport also caused relative uplifts therefore this model is consistent with both of the range forming mechanisms that have been inferred 1 a new proposal that arises from this simulation is that horizontal subduction also caused the subsequent extensional basin and range taphrogeny by stripping away the mantle lithosphere so that the crust was exposed to hot asthenosphere after the oceanic slab dropped away

a test of present day plate geometries for northeast asia and japan alternative geometries for the present day configuration of plate boundaries in northeast asia and japan are tested using nuvel 1 and 256 horizontal earthquake slip vectors from the japan and northern kuril trenches statistical analysis of the slip vectors is used to determine whether the north american eurasian or okhotsk plate overlies the trench along the northern kuril trench sup vectors are well fit by the nuvel 1 pacific north america euler pole but are poorly fit by the pacific eurasia euler pole results for the japan trench are less conclusive but suggest that much of honshu and hokkaido are also part of the north american plate the simplest geometry consistent with the trench slip vectors is a geometry in which the north american plate extends south to 41 n and possibly includes northern honshu and southern hokkaido although these results imply that the diffuse seismicity that connects the lena river delta to sakhalin island and the eastern sea of japan records motion between eurasia and north america onshore geologic and seismic data define an additional belt of seismicity in siberia that cannot be explained with this geometry assuming that these two seismic belts constitute evidence for an okhotsk block two published kinematic models for motion of the okhotsk block are tested the first model which predicts motion of up to 15 mm yr 1 relative to north america is rejected because kuril and japan trench slip vectors are fit more poorly than for the simpler geometry described above the second model gives a good fit to the trench slip vectors but only if okhotsk north america motion is slower than 5 mm yr 1

preliminary magnetostratigraphy of the red clay underlying the loess sequence at baoji china magnetic remanence and bulk susceptibility measurements are reported from 93 samples spanning the uppermost 27m of the red clay underlying the loess sequence at baoji shaanxi province china if a new previously undetected short about 20ka excursion or reversed interval near 3 3ma be accepted then a reasonable fit to the standard time scale emerges a linear accumulation rate of 1 5cm ka is implied and the correlation coefficient is 0 992 no significant hiatus occurs between the red clay and the overlying loess so the 27m investigated reach back to about 4 3ma fourier analysis of the bulk susceptibility data yields a strong peak near 400ka in agreement with astronomical calculations of the orbital parameters responsible for climatic forcing