discrete plio pleistocene phases of tilting and counterclockwise rotation in the southeastern aegean arc rhodos greece early pliocene formation of the south aegean left lateral strike slip system the island of rhodos represents an uplifted block in the largely submerged southeastern aegean forearc it has a complex history of subsidence uplift and counterclockwise rotation during the plio pleistocene in response to the interplay between large scale geodynamic processes in this paper we present a new chronostratigraphic framework for the continental pliocene apolakkia basin of southwestern rhodos we combine these time constraints with recently published chronostratigraphic data from the marine plio pleistocene basins of northeastern rhodos to reconstruct rotational and vertical motions our palaeomagnetic results identify two rotation phases for rhodos c 10 9 6 counterclockwise ccw rotation between 3 8 and 3 6 ma and c 17 6 ccw rotation since 0 8 ma between these phases rhodos tilted to the se drowning the southeastern coast to a depth of 500 600 m between 2 5 and 1 8 ma then to the nw which resulted in the re emergence of the drowned relief between 1 5 and 1 1 ma we relate the rotations of rhodos to incipient formation of the south aegean sinistral strike slip system and the foundering of the rhodos basin the previously shown absence of messinian evaporites in the deep marine rhodos basin in combination with the 3 8 ma onset of ccw rotation of rhodos constrains the onset of the formation of the south aegean strike slip system between 5 3 and 3 8 ma the formation of this strike slip system is probably related to the interplay of oblique collision between the southeastern aegean region and the northward moving african plate the westward motion of anatolia gravitational spreading of the overthickened aegean lithosphere and the recently postulated southwestward retreat of the african subducted slab along a subduction transform edge propagator fault

pedogenic modification of loess significance for palaeoclimatic reconstructions abstract this review considers the role of pedogenic processes in modifying wind blown dust loess concentrating particularly on the ways that resulting properties may be interpreted as indicators of past climatic conditions and changes emphasis is placed on the sequences of palaeosols developed within loess deposits that are frequently regarded as some of the best terrestrial equivalents of marine sediment records of long term global climatic change a palaeosol is generally interpreted in terms of the broad pedogenic processes and environments assumed to be currently responsible for that type of soil forming at the present surface even the very presence of a palaeosol may have palaeoclimatic significance however in that it is often taken to indicate a period of relative land surface stability and warmer and or moister conditions between cold and or arid phases of loess accumulation in reality it may be more useful to consider many loess palaeosol sequences in terms of changing balances between pedogenesis and loess accumulation over geological time in most regions it seems that the balance swings towards pedogenesis during interglacials or interstadials when sediment supply and transport are limited and the climate is warmer and or wetter where accumulation rates are still appreciable during these soil forming intervals however the soils and palaeosols may be accretionary with surface build up keeping pace with pedogenesis welding may also occur where covering sediments are insufficiently thick to isolate an underlying palaeosol from the effects of pedogenesis active at a new land surface further complications occur due to reworking of palaeosols and syndepositional pedogenic alteration of loess units generally such pedocomplexes can only be deciphered if the different pedogenic geomorphic and sedimentary processes are identified and ordered within a pedosedimentary reconstruction a recent trend has been to treat some loess palaeosol sequences as quasi continuous time series particularly when comparing depth functions of climatic proxy properties such as magnetic susceptibility and grain size with marine and ice core isotope curves

variation of seismic coupling with slab detachment and upper plate structure along the western hellenic subduction zone abstract the western hellenic subduction zone is characterized by a trenchward velocity of the upper plate in the ionian islands segment complete seismic coupling is achieved as is predicted by standard plate tectonic models in which there is no slab pull force because the slab has broken off the moderate local seismic moment rate relates to a shallow downdip limit for the seismogenic interface this characteristic may be attributed to the ductility of the lower crust of the upper plate which allows a decollement between the upper crust of the overriding plate and the subducting plate farther south a deeper downdip limit of the seismogenic interface is indicated by thrust faulting earthquakes which persist much deeper in western crete a correspondingly larger downdip width of this seismogenic zone is consistent with the suggested larger maximum magnitude of earthquakes here however since the seismic moment release rate seems to be moderate in the peloponnese and western crete like in in the ionian islands this seismically active interface cannot maintain complete seismic coupling across its larger downdip width a cause may be the lateral addition of overweight to the part of the slab still attached in crete by the free fall of its part that has broken off from the surface further north this increased slab pull reduces the compressive normal stress across the seismogenic interface and thus causes partial seismic coupling in its shallower part however the width of this part may provide an additional area contributing to slip in large earthquakes which may nucleate deeper on stick slip parts of the interface hints at anomalies in structure and seismicity which need to be resolved may relate to the present location of the edge of the tear in the slab

reconciling regional continuity with local variability in structure uplift and exhumation of the timor orogen abstract along strike variations in orogenic development can be difficult to constrain resulting assumptions projecting similarity or variability along strike can lead to erroneous conclusions at the orogen scale young orogens provide opportunities to document limits of along strike projection and test factors that may control lateral variability here we present new constraints on the history of uplift exhumation and shortening in the timor orogen from west timor indonesia structural mapping documents a foreland thrust stack of jurassic miocene australian margin strata and a hinterland antiformal stack of permo triassic australian continental units duplexed below banda arc lithosphere biostratigraphy within the piggyback central basin reveals earliest deepwater synorogenic deposition at 5 57 5 53 ma uplift from lower to middle bathyal depths at 3 35 2 58 ma and uplift from middle to upper bathyal depths at 2 58 1 30 ma hinterland permo triassic strata yield apatite u th he ages of 0 33 2 76 ma apatite fission track ages of 2 19 3 53 ma and partially reset zircon u th he ages these thermochronology ages are youngest or most strongly reset in the center of the antiformal stack and yield modeled exhumation rates of 0 45 3 31 km myr a balanced cross section reveals a minimum of 300 km of shortening including 210 km of australian continental subduction below the banda forearc when compared to published results from timor leste these data show that the timing of initial collision synorogenic basin uplift and total shortening amount were broadly similar across the island therefore despite along strike changes in orogen morphology and significant small scale spatial variability in deformation first order structural similarity dominates at large scales we suggest that along strike variations in orogen morphology are due to changes in the distribution of deformation within the orogen driven by differences in backstop strength internal wedge strength and basal decollement friction as well as the presence of the wedge top central basin in west timor

segmentation and configuration of subducted lithosphere in italy an important control on thrust belt and foredeep basin evolution the apennine foredeep basin system located on continental crust consists of four roughly parallel basin segments each containing a flexural outer rise and an inner trough that deepens continuously toward the thrust belt flexural modeling of subsidence data across the basin indicates that this foredeep basin results mainly from deep subsurface loads acting on the subducted slab from within the subduction zone rather than from the topographic load of the apennine mountains the geometry of the four basin segments observed within the apennine foredeep is thus inferred to reflect subduction of segmented lithosphere where each lithospheric segment corresponds to a segment of the foredeep basin beneath the basin and in the foreland the lithosphere is continuous segmentation occurs only at depth beneath the thrust belt this pattern olf segmentation of the subducted lithosphere at depth is reflected in the large scale geometry of the outer part of the apennine thrust belt and appears to control it similarly the pattern of segmentation also appears to control the position of the eastern limit of back arc type extension in western italy these relations strongly suggest a genetic relation between subduction zone processes foredeep basin geometry and thrust belt evolution in which the configuration of the subducted lithosphere largely controls the large scale surface deformation observed in the apennine system

quantitative estimates of pedogenic ferromagnetic mineral formation in chinese loess and palaeoclimatic implications abstract the quasi continuously deposited loess sediments of the central chinese loess plateau constitute one of the most complete and long lasting records of quaternary palaeoclimate on land much of this record has been uncovered by measurement and interpretation of the magnetic properties of the loess the polarity of natural remanent magnetization has provided absolute age dates by correlation with the geomagnetic polarity time scale magnetic low field susceptibility has been used to reconstruct the cyclic changes of pleistocene palaeoclimates although the origin of the signal is still poorly understood from comparison with the 10 be concentration throughout the sequence we are able to determine the contributions to susceptibility from inherited and authigenic sources for the last 130 ky since the production of authigenic magnetite is directly related to regional precipitation annual palaeoprecipitation rates can be calculated palaeoprecipitation rates similar to present day rates are derived for oxygen isotope stage 5 including the last interglacial in contrast cold periods corresponding to oxygen isotope stages 2 and 4 experienced negligible precipitation the beginning and end of the time interval represented by oxygen isotope stage 3 however was characterized by short episodes when precipitation exceeded the holocene average

chemistry and microstructures of clay particles in smectite rich shelf sediments south shetland islands antarctica the clay mineralogy of a holocene sediment core from the shelf of livingston island south shetland islands antarctica has been investigated by x ray diffraction xrd lattice imaging bulk chemical analysis of fine clay fractions and analytical transmission electron microscopy atem the clay minerals identified by xrd of 2 m fraction are smectite 63 chlorite 25 and illite 12 with little downcore variation lattice imaging of clay particles has confirmed the presence of interstratified illite smectite and interstratified chlorite smectite atem of ca saturated samples showed that the smectitic clay particles are rich in k fe and mg k in the smectitic particles is mostly present as a fixed cation in the interlayer confirming the presence of interstratified illite a comparison of the mineralogy of the bedrock soils in the probable source area and the core sediment strongly supports the view that the clay minerals must have originated by glacial erosion physical weathering and reworking of hydrothermally altered volcanic bedrock and tephra of the south shetland islands

the ionian and alfeo etna fault zones new segments of an evolving plate boundary in the central mediterranean sea highlights plate boundary re organization in the central mediterranean sea segmentation of the subduction complex along lithospheric transverse faults step faults in the ionian sea pleistocene active faulting and mt etna formation abstract the calabrian arc is a narrow subduction rollback system resulting from africa eurasia plate convergence while crustal shortening is taken up in the accretionary wedge transtensive deformation accounts for margin segmentation along transverse lithospheric faults one of these structures is the nnw sse transtensive fault system connecting the alfeo seamount and the etna volcano alfeo etna fault aef a second nw se crustal discontinuity the ionian fault if separates two lobes of the ca subduction complex western and eastern lobes and impinges on the sicilian coasts south of the messina straits analysis of multichannel seismic reflection profiles shows that 1 the if and the aef are transfer crustal tectonic features bounding a complex deformation zone which produces the downthrown of the western lobe along a set of transtensive fault strands 2 during pleistocene times transtensive faulting reactivated structural boundaries inherited from the mesozoic tethyan domain which acted as thrust faults during the messinian and pliocene 3 the if and the aef and locally the malta escarpment accommodate a recent tectonic event coeval and possibly linked to the mt etna formation regional geodynamic models show that whereas aef and if are neighboring fault systems their individual roles are different faulting primarily resulting from the ese retreat of the ionian slab is expressed in the northwestern part of the if the aef on the other hand is part of the overall dextral shear deformation resulting from differences in africa eurasia motion between the western and eastern sectors of the tyrrhenian margin of northern sicily and accommodating diverging motions in the adjacent compartments which results in rifting processes within the western lobe of the calabrian arc accretionary wedge as such it is primarily associated with africa eurasia relative motion

paleorainfall reconstructions from pedogenic magnetic susceptibility variations in the chinese loess and paleosols the rock magnetic properties of the chinese loess and paleosols constitute a unique and sensitive record of east asian paleoclimate through the quaternary period systematic variations in the concentration and grain size of the magnetic minerals in these sediments have produced systematic variations in the magnetic susceptibility signal which can be easily and rapidly measured at many sites across the loess plateau variations in many other rock magnetic properties can be used to identify the key shifts in ferrimagnetic grain size but magnetic susceptibility alone is sufficiently sensitive to record stadial and interstadial climate stages as well as glaciations and interglaciations past changes in rainfall and monsoon activity for this region are reconstructed from the susceptibility variations the susceptibility record is calibrated using the modern relationship between rainfall and pedogenic susceptibility on the loess plateau our rainfall reconstructions identify enhanced summer monsoonal activity in the chinese loess plateau region in the early holocene and the last interglaciation in the presently semiarid western area of the plateau annual precipitation in interglacial times was up to 80 higher than at present in the more humid southern and eastern areas values were up to 20 higher than today s levels during the last glaciation precipitation decreased across the entire plateau typically by 25 the relationship between pedogenic susceptibility climate and weathering age was examined over the northern hemisphere temperate zone and the observed positive correlation between rainfall and susceptibility indicates that climate rather than soil age is the predominant factor that controls pedogenic susceptibility enhancement in loess soils

loess stratigraphy in central china abstract loess sequences in central china provide a detailed record of climate changes during the last 2 5 million years at least 44 major shifts from glacial to interglacial conditions occurred during this time in china prolonged loess deposition lasting more than 40 millennia occurred eleven times with only four of these intervals in brunhes chron the climate oscillations took place with increased frequency between 2 4 and 0 5 ma compared to the last half million years major shifts toward cooler and drier climates occurred at about 2 4 ma 1 2 ma and 0 5 ma while less pronounced shifts are dated to 1 65 ma 0 8 ma and 0 2 ma three of the last four reversals of the earth s magnetic field whose lithostratigraphic position has been detail are recorded in a glacial deposit the low field magnetic susceptibility of loess and soils which reflects the concentration of ultrafine magnetite is related to the degree of pedogenesis and serves as a proxy measure of climate the accumulation rate of the magnetite was fairly constant throughout the last 1 2 million years and can serve as a measure of time susceptibility records from localities near xifeng and luochuan located 160 km apart are compared and used to define informal lithostratigraphic units in the loess plateau of china

lateral shifts of apenninic foredeep depocentres reflecting detachment of subducted lithosphere abstract the hypothesis of lateral migration of slab detachment was formulated on the basis of seismic tomography results on the 3 d structure of subduction zones in the mediterranean region m j r wortel and w spakman structure and dynamics of subducted lithosphere in the mediterranenan region proc k ned akad wet 95 1992 325 347 the redistribution of slab pull forces associated with the tearing process is taken to affect foredeep development by adding a lateral component to internal external depocentre migrations in the case of the apenninic arc the direction of detachment and associated depocentre migration is expected to be southeast this prediction has been confronted with the tectonostratigraphy of oligocene to recent apenninic foredeeps results show there are two episodes marked by important lateral shifts of foredeep depocentres during the early late miocene tortonian the depocentre of the northern apennines foredeep shifted towards the southeast this is evidenced by the relative positions of the depocenters of the burdigalian serravallian marnoso arenacea and the tortonian umbrian marchean and lazian minor basins a further stepwise southeastward migration can be inferred from the plio pleistocene records of the central and southern apennines in a more general sense our results indicate that slab detachment may play a significant role in the evolution of foredeeps along convergent plate boundaries

pathways of dust input to the chinese loess plateau during the last glacial and interglacial periods abstract it has been established that loess deposited on the chinese loess plateau was derived from arid and semi arid regions in north and northwest china but the specific pathways of dust transport are still not proved in this study 32 loess palaeosol profiles of the last glacial and interglacial periods were measured for magnetic susceptibility in order to investigate the dust transport pathways of dust input to the loess plateau the magnetic susceptibility variations of the loess palaeosol deposits within the last glacial cycle can be correlated with marine oxygen isotope variations to estimate the ages of boundaries of the loess units and intercalated palaeosols the sedimentation rate of each depositional unit can be obtained by dividing the thickness by the time that it represents because sedimentation rates decrease downwind from the dust source the spatial distribution of dust sedimentation rates shows that northwest and west winds were the two most important agents for transport of dust to the loess plateau during the last glacial cycle the north and northeast winds played an almost negligible role in addition topography and dust from local sources strongly affected the dust accumulation rates at some measured sites

late miocene uplift in the romagnan apennines and the detachment of subducted lithosphere abstract we report part of a test of the hypothesis that detachment of subducted lithosphere may be a process of lateral propagation of a horizontal tear wortel and spakman proc kon ned akad wetensch 95 1992 325 347 we have used the apennines as a test area the test procedure consists of the comparison of hypothetical vertical motions predicted from the expected redistribution of slab pull forces with observed vertical motions we demonstrate that a late miocene depocentre migration from the northern towards the central apennines is associated with uplift of the fore arc of the northern apennines such a combination of a depocentre shift and uplift is thought to be diagnostic for lateral migration of slab detachment the depocentre migration was identified in earlier work van der meulen et al earth planet sci lett 154 1998 203 219 this contribution focuses on uplift which has primarily been identified through the geohistory analysis of the monte del casino section romagnan apennines northern italy owing to methodological problems the start and duration of the uplift phase could not be constrained and only a minimum estimate of the total amount of uplift 483 180 m is obtained the data do allow for an estimate of the uplift rate 163 61 cm ky a review of regional data results in better constraints on the timing of the above lateral reorganisation of the fore arc and on the spatial extent of the uplifted area depocentre development in the central apennines began between 8 6 and 8 3 ma b p uplift started between 9 and 8 ma b p and affected the entire northernmost apennines

variation of rb sr ratios in the loess paleosol sequences of central china during the last 130 000 years and their implications for monsoon paleoclimatology abstract rb sr and magnetic susceptibility have been measured in the last interglacial glacial loess profiles at luochuan and huanxian central china a high degree of similarity between the parameters in both profiles suggests that variations of rb sr ratios in the sequence can be regarded as an indicator of east asian summer monsoon strength matching the rb sr record with the specmap 18o curve suggests that the rb sr ratio responds sensitively to changes of the east asian monsoon induced by global ice volume variation

distribution and genesis of calcitic pedofeatures within a rapidly aggrading loess paleosol sequence in china abstract the distribution of calcitic pedofeatures within part of a buried paleosol complex on gaolanshan mountain near lanzhou in the western semi arid part of the loess plateau of china is interpreted in terms of a pedosedimentary model controlled by changes in dominance of regional climatic monsoonal forces during periods of moderate loess accumulation rates and moisture availability accretionary pedogenesis was characterised by localised dissolution and redistribution of calcite and development of compound calcitic depletion concentration pedofeatures these took one of two forms i equigranular hypidiotopic calcitic coatings or infillings 100 350 m and calcitic depletion hypocoatings the reconstruction provides the basis for explaining the ubiquitous occurrence of high concentrations of sand size grains and nodules of calcite within weakly leached horizons of other paleosols in the western part of the loess plateau of china their presence reflects not only the influence of semi arid conditions prevailing during the main stable soil forming intervals but also preceding drier periods of accretionary pedogenesis associated with transitional changes in relative dominance of dry northwesterly winter monsoons responsible for the transport of the dust to that of moist southwesterly and southeasterly monsoons the study emphasises the general need for a pedosedimentary approach when attempting to interpret loess paleosol sequences

paleobathymetry in the backstripping procedure correction for oxygenation effects on depth estimates abstract this paper aims to provide a straightforward and easily applicable method for estimating the depositional depth evolution of marine basins vertical movements of the basin floor can be reconstructed from the sedimentary record and more accurately constrained when information from the sedimentary history is combined with palaeodepth estimates derived from fauna to this end we propose to extend an existing method based on the percentage of planktonic foraminifera with respect to the total planktonic and benthic foraminiferal association which is expressed as the percentage planktonics p the ratio between planktonic and benthic foraminifera is related to water depth and the p generally increases with increasing distance to shore however next to water depth the oxygen level of bottom waters has a profound effect on the abundance of benthic foraminifera and as such influences the p depending on basin configuration the oxygen level at the sea floor can vary on milankovitch time scales and is reflected by the fraction of benthic foraminiferal species that indicate an effect of oxygen stress on the biotic system these species can be used as stress markers and their percentage with respect to the total benthic population is here expressed as s to assess whether the effect of sea floor oxygenation impairs depth reconstructions we studied the percentage of planktonic foraminifera p in five well dated sedimentary successions from the lower pliocene of crete corfu and milos in greece additionally we assessed whether different foraminiferal size fractions and counting methods affect the determination of the percentage of planktonic foraminifera the palaeobathymetric evolution calculated for each basin was confirmed for all successions by an independent check on depth related occurrences of benthic foraminifera after correction for bathymetry changes of the basin due to sedimentation compaction and eustatic sea level variations the vertical movement history of the basin floor was inferred we propose a standard methodology for reconstructions of palaeobathymetry of marine sedimentary successions from foraminiferal associations

two dimensional simulations of surface deformation caused by slab detachment detachment of the deeper part of subducted lithosphere causes changes in a subduction zone system which may be observed on the earth s surface constraints on the expected magnitudes of these surface effects can aid in the interpretation of geological observations near convergent plate margins where detachment is expected in this study we quantify surface deformation caused by detachment of subducted lithosphere we determine the range of displacement magnitudes which can be associated with slab detachment using numerical models the lithospheric plates in our models have an effective elastic thickness which provides an upper bound for rapid processes like slab detachment to the surface deformation of lithosphere with a more realistic rheology the surface topography which develops during subduction is compared with the topography shortly after detachment is imposed subduction with a non migrating trench system followed by detachment leads to a maximum surface uplift of 2 6 km while this may be higher for the case of roll back preceding detachment in the latter situation the back arc basin may experience a phase of compression after detachment within the context of our elastic model the surface uplift resulting from slab detachment is sensitive to the depth of detachment a change in friction on the subduction fault during detachment and viscous stresses generated by sinking of the detached part of the slab overall surface uplift of these magnitudes is not diagnostic of slab detachment since variations during ongoing subduction may result in similar vertical surface displacements d 2002 elsevier science b v all rights reserved

magnetic susceptibility evidence of monsoon variation on the loess plateau of central china during the last 130 000 years the magnetic susceptibility of loess and paleosols in central china represents a proxy climate index closely related to past changes of precipitation and vegetation and thus to summer monsoon intensity time series of magnetic susceptibility constructed for three loess paleosol sequences in the southern part of the chinese loess plateau document the history of summer monsoon variation during the last 130 000 yr they correlate closely with the oxygen isotope record of stages 1 to 5 in deep sea sediments soils were forming during intervals of strong summer monsoon whereas loess units were deposited at times of reduced monsoon intensity the chinese loess paleosol sequence can thus be viewed as a proxy record of asian monsoon variability extending over the last 2 5 myr

the opening processes in the deep tyrrhenian basins of marsili and vavilov as deduced from magnetic and chronological evidence of their igneous crust abstract shapes and chronology of magnetic anomalies of the mafic crust flooring the marsili and vavilov abyssal plains in the central tyrrhenian sea are discussed in the marsili deep basin the possible 3 phase evolution of a magmatic tectonic process of spreading is considered the early magmatic phase apparently took place at the time of the olduvai magnetic event 1 87 to 1 67 ma b p site 650 of the ocean drilling project leg 107 it appears to consist of spreading manifestations of a low magnetic intensity and a round shape forming the igneous basement around the marsili volcano the late phase was characterized by a spreading process exhibiting a linear configuration and high intensity of the magnetic anomalies organized spreading this phase of the brunhes epoch has given rise to the great marsili volcano emplaced in the basin s central part the intermediate phase shows reversed magnetic polarity and slightly elongated shapes it appears to have developed in late matuyama times from 1 67 to 0 73 ma ago the intensities of the magnetic anomalies in the basin of vavilov are on the whole lower than those present in the magnetic field of the marsili also in the vavilov deep basin the magnetic anomalies associated with the early volcanic manifestations which are of late miocene age about 7 5 ma are characterized by low intensity and a round shape whereas those associated with the effusions on the vavilov volcano whose age ranges from late pliocene to late quaternary from 2 4 to less than 0 12 ma exhibit a high intensity and a linear shape the two bathyal plains have inter arc structural settings from west to east the vavilov bathyal plain is bordered by the orogenic volcanic belt of the island of sardinia and maybe a central tyrrhenian arc the latter and the arc of the eolie which is active in the present time border the marsili plain the ages of the early spreading processes in the bathyal plains respectively from about 10 to 6 ma and from 1 9 to 1 3 ma appear to represent distinctive temporal markers in fact they may be coincident with the periods of quiescence of the volcanic activity that affected the adjoining arcs

delay time tomography of the upper mantle below europe the mediterranean and asia minor summary the method of linearized delay time tomography is applied to retrieve the p velocity heterogeneity of the upper mantle in central europe the mediterranean and asia minor the upper mantle is parametrized in slowness cell functions with lateral dimensions of 1 the model parametrization includes event mislocation vectors and station delay time corrections in all 20 000 parameters describe the model delay time data selected from the isc data base 1964 1982 from regional events and from stations up to 90 of epicentral distance are used about 18 000 events and 937 stations contributed nearly 500 000 delay times we discuss the tomographic method the data processing the cell model employed the computation of the ray geometry the use of composite rays in tomography and the cell hit count the inversions are performed with two different iterative row action methods lsqr and sirt results obtained with the lsqr method will be shown only the spatial resolution is investigated with sensitivity analyses using two different synthetic velocity models a spike model and a model with harmonically varying velocity anomalies the spatial resolution is estimated to be high on the order of the cell size in the mantle below central and southeastern europe the mapped velocity heterogeneity exhibits primarily low velocities around a depth of 200 km and just above the transition from upper to lower mantle this indicates a systematic deviation of the reference model jeffreys bullen from the radially averaged earth structure which may violate the basic assumptions underlying the linearized approach a posteriori investigation of the data also indicates the presence of a low velocity zone and the existence of strong velocity depth gradients

a mineral tracer toward high resolution dust provenance on the chinese loess plateau sem tem and sulfur isotopes of sulfate inclusions in biotite the most important terrestrial archive of the quaternary climate is the chinese loess plateau clp distributed over a vast region peripheral to the deserts of inner asia numerous paleoclimatic studies have examined magnetic chemical and isotopic proxies from deep loess paleosol sections however the highly uniform mineralogy of the clp has made it difficult to track the provenance transportation and deposition of dust particles here we report that the micrometer scale mineralogical heterogeneity of the loess particles has a significant potential in determining high resolution loess provenance scanning and transmission electron microscopy of the chinese loess reveals that biotite particles commonly have microinclusions of ba sr sulfates displacing the micaceous layers along cleavages chemical compositions varied widely from barite to celestine within the same biotite grain the ba rich sulfates precipitated first followed by an overgrowth of sr rich sulfates the frequency of sulfate bearing biotite varied greatly over several loess sections implying a specific source and sedimentation process their abundance on the western clp and sulfur isotopic composition support their derivation from porous sedimentary sequences reacted with hypersaline solutions e g arkosic sandstone probably located west of the clp covering the qilian mountains qaidam basin and surrounding mountains of the tibetan qinghai plateau the sulfate bearing biotite is the first microscopic mineral tracer in the clp provoking further search for other microscopic heterogeneities of the chinese loess and their equivalents in the source regions

plio quaternary vertical motion of the northern apennines insights from dynamic modeling we test the effects of different geodynamic mechanisms on the pliocene to present day dynamics and in particular on the vertical motions of the northern apennines system by means of two dimensional finite element models we show that the pliocene features of the northern apennines exhumation of deep rocks in western italy and fast subsidence rates in the adriatic foredeep can be adequately reproduced by a model slab characterized by the passive sinking of a negatively buoyant adriatic slab and by the upwelling of buoyant asthenosphere beneath western italy model slab is however not able to account for the quaternary and present day pattern of vertical motion of eastern italy and of the adriatic basin a deep configuration of the system characterized by a detached slab model detach may explain the vertical motions of these areas constrained by uplift of the eastern portions of the apenninic chain by an eastward shift of the foredeep depocenter and by lower subsidence rates in the adriatic basin the tectonic and stratigraphic data showing major differences between the tertiary and the quaternary evolution of the northern apennines are discussed

changes in mineralogy of loess paleosol sections across the chinese loess plateau quantitative mineralogical analysis of bulk samples and single particles was carried out on three loess sections of different local climate settings on the chinese loess plateau clp mineralogy geochemistry and single particle petrography of loess and paleosols are relatively uniform over the clp however in detail there are mineralogical changes related to eolian process and chemical weathering particle size sorting eastward from western sources led to an eastward increase of the total phyllosilicate contents enriched in fine illitic clay minerals after deposition detrital minerals susceptible to chemical weathering were sequentially altered in a progressive fashion with increasing precipitation in the order of calcite dolomite biotite illite chlorite amphibole and plagioclase the weathering of biotite chlorite and illite resulted in a significant increase of expandable phyllosilicate contents the sequential weathering of the minerals is reflected chemically in the decrease of na and mg and the increase of iron oxidation mineralogy of the chinese loess at individual sites reflects the effects of size fractionation during eolian transportation and progressive sequential weathering along the climatic gradient and it is essential to consider both effects when using mineralogical and dependent chemical data in the paleoclimatic reconstruction of the clp

pedosedimentary development and palaeoenvironmental significance of the s1 palaeosol on the northeastern margin of the qinghai xizang tibetan plateau the s1 pedocomplex correlated to oxygen isotope stage 5 of the ocean cores has been traced west of the loess plateau on to the extreme northeastern margin of the qinghai xizang tibetan plateau in china detailed micromorphological analysis of closely spaced thinsections from the pedocomplex at this site provides the basis for reconstruction of the sequence of pedosedimentary processes and associated palaeoenvironmental changes occurring during this time interval the six pedosedimentary stages identified are interpreted in terms of temporal variations in depositional rates size of particles transported and availability of moisture for pedogenic alteration as determined by changing balances in dominance of winter and summer monsoonal forces two main soil forming intervals are identified the more extensive of the two in terms of resultant pedological features reflects pedogenic alteration at a relatively stable land surface under a semi arid climate during the later part of pedosedimentary stage 2 the other main period corresponds to pedosedimentary stages 4 and 5 when leaching and bioturbation processes were active at aggrading surfaces leading to development of an accretionary unit without clear differentiation of horizons pedosedimentary stages 1 3 and 6 were characterised mainly by rapid rates of coarse loess accumulation with synsedimentary modification restricted to surface slaking and crust formation and minor localised redistribution of calcite

dependence of near surface magnetic susceptibility on dust accumulation rate and precipitation on the chinese loess plateau magnetic susceptibility ms of surface sediment varies systematically across the loess plateau in central china decreasing exponentially from 200 10 8 m3 kg at the northern margin of the qinling shan to 30 10 8 m3 kg near the southern margin of the mu us desert ms correlates highly with loess median grain size r2 0 79 which decreases south southeastward across the plateau it also correlates with mean annual temperature mat and mean annual precipitation map r2 0 58 and 0 60 respectively and with their product mat map r2 0 83 which is considered a measure of potential pedogenic activity because regional isopleths depicting grain size and the primary meteorological parameters are nearly parallel it is difficult to determine their relative influence on ms a simple ms model based on the observed spatial variation in loess thickness permits quantitative assessment of the effect of the dust accumulation rate on the ms signal of surface sediment and isolates the likely role of climate in the production of magnetic minerals the model suggests that 84 of the loess ms variance is dictated by the diluting effect of dust and 10 11 is associated with meteorological factors primarily precipitation the observed and modeled relationships support hypotheses that attribute variations in ms in the loess paleosol succession to varying rates of dust deposition and in situ production of magnetic minerals in the accretionary soils both of which are controlled by monsoon climate

rb sr and k ar systems of biotite in surface environments regulated by weathering processes with implications for isotopic dating and hydrological cycles of sr isotopes abstract biotite is widely used for rb sr and k ar isotopic dating and influences sr isotope geochemistry of hydrological regimes the isotopic system of biotite behaves diversely in response to surface weathering i e the complete preservation of original rb sr and k ar isotopic ages or dramatic reduction in this study we have explored the relation between the behavior of isotopic systems and complex weathering processes of biotites in the weathering profiles distributed on the mesozoic granitoids in south korea in the lower parts of the profiles biotite in the early stages of weathering was transformed into either oxidized biotite or hydrobiotite with a mass release of 87 sr and 40 ar forced by the rapid oxidation of ferrous iron during the transformation to oxidized biotite 87 sr and 40 ar were preferentially released relative to rb and k respectively via solid state diffusion through the biotite lattice resulting in a drastic reduction of original isotopic age the reduction of rb sr age was greater than that of k ar age because k was preferentially released over rb whereas 87 sr and 40 ar were released proportionally to each other however during the transformation of biotite to hydrobiotite i e to regularly interstratified biotite vermiculite 87 sr rb 40 ar and k were completely retained in the alternating biotite interlayer and thus the original isotopic age can be preserved in the upper parts of the profiles where iron oxidation was almost completed 87 sr rb 40 ar and k were gradually and proportionally released with no further significant change in isotopic age during the gradual transformation of the early formed oxidized biotite into hydrobiotite and vermiculite or during their final decomposition to kaolinite the ratios and amounts of isotopes released from weathered biotites are dependent upon the degree of iron oxidation and the pathways of mineralogical transformation regional and local variations in isotopic systems affected by particular weathering processes should be considered when dating biotite or biotite bearing rocks in weathering environments modeling the transfer of sr isotopes to hydrologic regimes and tracking the provenance of sediments

the nature origin and accumulation of loess abstract loess can be defined simply as a terrestrial clastic sediment composed predominantly of silt size particles which is formed essentially by the accumulation of wind blown dust there are three fundamental requirements for its formation 1 a sustained source of dust 2 adequate wind energy to transport the dust and 3 a suitable accumulation site most loess has been modified to some degree by local reworking bioturbation and syn depositional weathering but a process of loessification is not necessary for a dust deposit to qualify as loess the terms primary loess and secondary loess have previously been used to described wind deposited loess and redeposited loess respectively but it is more accurate to describe material reworked and redeposited by non aeolian processes as loess derived colluvium or loess derived alluvium during the quaternary loess formed in three main situations 1 mid continental shield areas beyond the limits of ice sheets periglacial loess 2 on the margins of high mountain ranges perimontane loess and 3 on the semi arid margins of some lowland deserts peridesert loess peridesert loess is relatively poorly developed partly due to the limited efficiency of silt generating mechanisms in low land deserts compared with glaciation but also important is the tendency in arid areas for dust to be dispersed over a wide area and to be rapidly reworked after deposition particularly in areas which experience frequent climatic changes the remarkably thick loess of china and central asia results from an unusual combination of conditions which has persisted for much of the last 2 3 million years namely rapid uplift of the tibetan plateau and surrounding mountain ranges high rates of sediment production and supply to adjacent basins a strong northwesterly and westerly wind regime and the existence of effective dust traps downwind of the source regions

the origin of rhythmic bedding in the pliocene trubi formation of sicily southern italy abstract foraminiferal palynological stable isotope geochemical clay mineralogical and granulometric data have been gathered for the successive layers of four rhythmic alterations of relatively carbonate poor and carbonate rich beds in the early pliocene trubi formation of sicily southern italy the marly rhythmites consist of a grey layer and a white more indurated layer in which an additional beige less indurated layer is intercalated they are therefore more complex than the well known marl limestone couples elsewhere these rhythmites probably originate from the alternate predominance of increased dilution of river supplied terrigenous material grey and decreased carbonate production in the surface waters beige the grey layers are considered to correspond to periods of increased local run off and higher surface water temperatures and productivity the beige layers signal more arid and cooler climatic conditions lower surface water productivity and stronger or more frequent dust loaded southern winds the white layers apparently reflect intermediate climatic and environmental conditions these periodical changes probably brought about by astronomical precession appear to have occurred not only during the pliocene but also during the late miocene

three dimensional numerical modeling of detachment of subducted lithosphere recent seismological studies suggest that slab detachment has occurred in the mediterranean and the new hebrides subduction zones subducted slabs in these regions are recognized to be torn at depths ranging from 100 to 300 km presumably caused by the lateral migration of the tear along the strike of the slab to investigate the physical mechanism of the slab detachment and in particular its migration we constructed a viscoelastic three dimensional finite element model and introduced a small initial tear from one side of the slab we investigated spatio temporal variations in the state of stress within the slab as a function of tear length rheology and a variety of force distribution our results show that an area of high shear stress concentration of the order of several hundred megapascals forms near the tip of the tear inside the slab which is probably sufficient to cause further lateral migration of the tear the stress concentration increases with the length of the tear and lower viscosity values of the surrounding mantle and increases with downdip tension from our modeling we conclude that favorable conditions for slab detachment are characterized by a high interplate frictional force at a subduction zone and a low convergence rate forming in plate tensional stress at intermediate depths such a condition is indeed observed in the dinarides hellenic and the new hebrides subduction zone

grain size of quartz as an indicator of winter monsoon strength on the loess plateau of central china during the last 130 000 yr the chinese loess paleosol sequence constitutes an important record of variations in asian monsoon climate over the past 2 4 myr magnetic susceptibility of loess and paleosols has been used as a proxy for summer monsoon intensity while median grain size has been regarded as a measure of the strength of winter monsoon winds that were responsible for most of the dust transport however median grain size is only an approximate index of winter monsoon strength because both paleosols and loess have been modified to various degrees by weathering processes that have produced pedogenic clay the quartz component of loess and paleosols is largely unaffected by weathering processes and therefore constitutes a more reliable proxy index of monsoon wind strength median grain size qmd and maximum grain size qmax values of monomineralic quartz isolated from the loess paleosol section at luochuan in the central loess plateau are characterized by two main intervals during the last ca 130 000 yr when these parameters were significantly greater than 9 and 85 m respectively and three main intervals when they were lower the data imply that the winter monsoon weakened during the intervals with low qmd and qmax values which coincide with marine oxygen isotope stages 5 3 and 1 and was strongest ca 67 000 and 20 000 yr ago during isotope stages 4 and 2 however both quartz grainsize records display second order high frequency high amplitude variations which are lacking in the magnetic susceptibility record that imply rapid and significant changes in atmospheric conditions that affect dust transport and deposition

chinese loess record of monsoon climate during the last glacial interglacial cycle the thick loess paleosol succession of central china contains a detailed record of changes in east asian monsoon climate since the late miocene epoch the alternating loess paleosol stratigraphy closely resembles the marine oxygen isotope record implying that episodic dust deposition and pedogenesis are in phase with global ice volume fluctuations and controlled by variations in solar radiation reaching the land surface deposits equivalent to marine isotope stages mis 5 through 1 have been dated by 14c 10be luminescence and magnetic susceptibility and grain size models malan loess mis 4 2 decreases in thickness southeastward from 30 m in the western loess plateau to 5 m east of xi an downwind asian dust is found in japan the north pacific ocean and the greenland ice sheet where it has a chemical signature that points to a primary source in western china during glacial times the mean dust flux in the central loess plateau reached 0 35 mm year whereas in interglacial times it fell to 0 1 mm year times of high dust influx and reduced soil development coincided with strengthened winter monsoon conditions which are inferred from variations in loess grain size times of decreased dust accumulation and strong pedogenesis marked by high values of magnetic susceptibility represent times of strengthened summer monsoon conditions high frequency fluctuations in dust influx during deposition of the malan loess include peaks that likely correlate with north atlantic heinrich events the younger dryas oscillation is recorded in chinese eolian and organic deposits by a shift from cool humid late glacial conditions to cold and dry conditions followed by a return to milder humid climate at the beginning of the holocene warm moist climate associated with a strong summer monsoon characterized the first half of the holocene epoch when a widespread paleosol complex developed on the loess plateau increased dust deposition during the middle to late holocene marked a shift to cooler drier conditions

geochemistry of the xining xifeng and jixian sections loess plateau of china eolian dust provenance and paleosol evolution during the last 140 ka abstract loess and paleosol samples from three distant sections xining xifeng jixian of the chinese loess plateau were analyzed for chemical and nd sr isotopic compositions in order to obtain information about the paleoclimatic variation during the last 140 ka these three sections represent three different climatic conditions from arid in the west xining to more humid in the east jixian across the loess plateau isotopic analyses show that all the three sections display a restricted range of 143 nd 144 nd ratios or e nd 10 0 5 indicating the dominance of relatively young and uniform upper crustal sources for the eolian dust the loess and paleosol samples have typical upper crustal 87 sr 86 sr ratios 0 714 0 718 and their variation can partly be attributed to different carbonate silicate ratios in the samples ree data from the three sections are indistinguishable from each other they show typical upper crust patterns characterized by la yb n 10 and eu eu 0 65 the high degree of chemical and isotopic homogeneity suggests that the dust source region must have undergone multiple recycling and thorough sedimentary mixing processes various chemical indicators have been used to monitor the pedogenetic intensity in these sections although results for the jixian section agree reasonably well with the known climatic conditions on the loess plateau the other two sections yield results not in agreement with some well accepted proxies like magnetic susceptibility or grain size distribution some chemical proxy indicators established in our previous work on the luochuan section such as the systematic u depletion and negative ce anomalies in ree patterns in soils are not clearly recorded in the present case the discrepancy between different climatic proxies could be related to the effective soil water budget temperature as well as the rate of development of each proxy

an early pliocene uplift of the central apenninic foredeep and its geodynamic significance van der meulen et al 1998 identified a pattern of lateral shifts of apenninic foredeep depocenters which was interpreted as the regional expression of lateral migration of slab detachment in the sense of wortel and spakman 1992 in addition to being expressed in such a pattern of lateral reorganisations slab detachment is expected to result in rebound this study focuses on plio pleistocene vertical motions of the central apenninic inner forearc here a major late early pliocene phase of uplift is identified by means of 1 micropaleontology based paleobathymetry 2 analysis of the compaction history and 3 numerical modeling of the flexural response of the underlying lithosphere to sediment loading the timing of the uplift event is consistent with that of the regional reorganizations on the basis of this consistency and the fact that it can be demonstrated that the uplift is not related to accretionary processes we interpret this event as rebound after slab detachment

paleoproductivity the benthic planktonic ratio in foraminifera as a productivity index abstract when the effects of differential dissolution are excluded the benthic to planktonic ratio in deep sea foraminifera can be read as a productivity index for pelagic conditions we use the bz index which is the product of the benthic planktonic ratio in percent and the depth of deposition which controls supply of organic matter for hemipelagic conditions we use bz d which is the product of the bz value and a factor for proximity to the shore square root of distance from land which controls coastal productivity anomalous values readily stand out from the normal populations which cluster around typical values of bz or bz d off northwest africa wherever calcite dissolution can be excluded as a factor because of presence of aragonite these anomalies are due to lateral supply of redeposited organic matter

exploratory models of long term crustal flow and resulting seismicity across the alpine aegean orogen 1 long term crustal flow is computed with a kinematic finite element model based on iterated weighted least squares fits to data and prior constraints data include 773 fault traces 106 fault offset rates 510 geodetic velocities 2566 principal stress azimuths and velocity boundary conditions representing the rigid parts of the eurasia africa and anatolia plates model predictions include long term velocities fault slip rates and distributed permanent strain rates between faults one model assumes that geodetic velocities measured adjacent to the aegean trench reflect a temporarily locked subduction zone in this case long term subduction velocity averages 45 mm yr and rapid crustal extension is predicted in the southern aegean sea another model assumes steady creeping subduction in this case subduction velocity averages only 29 mm yr and the eastern aegean seafloor is predicted to be more nearly rigid long term seismicity maps are computed for each model on the basis of the shift hypotheses and previous global calibrations of plate boundary earthquake production retrospective comparisons to seismic catalogs are encouraging map patterns spatial distribution functions and total earthquake counts are all comparable while neither model accurately predicts earthquake rates at all magnitudes the creeping subduction model is more accurate for strong m6 events which dominate the seismic hazard

recent and modern marine erosion on the new jersey outer shelf abstract recent chirp seismic reflection data combined with multibeam bathymetry backscatter and analysis of grab samples and short cores provide evidence of significant recent erosion on the outer new jersey shelf the timing of erosion is constrained by two factors 1 truncation at the seafloor of what is interpreted to be the transgressive ravinement surface at the base of the surficial sand sheet and 2 truncation of apparently moribund sand ridges along erosional swales oriented parallel to the primary direction of modern bottom flow and oblique to the strike of the sand ridges these observations place the erosion in a marine setting post dating the passage of the shoreface ravinement and the evolution of sand ridges that form initially in the near shore environment also truncated by marine erosion are shallowly buried fluvial channel systems formed during the last glacial maximum and filled during the transgression and a regional reflector r that is 40 kyr depths of erosion range from a few meters to 10 m the seafloor within eroded areas is often marked by ribbon morphology seen primarily in the backscatter data as areas of alternating high and low backscatter elongated in the direction of primary bottom flow ribbons are more occasionally observed in the bathymetry where observed crests exhibit low backscatter and troughs exhibit high backscatter sampling reveals that the high backscatter areas of the ribbons consist of a trimodal admixture of mud sand and shell hash with a bimodal distribution of abraded and unabraded sand grains and microfauna the shell hash is interpreted to be an erosional lag while the muds and unabraded grains are in this non depositional environment evidence of recent erosion at the seafloor of previously undisturbed strata the lower backscatter areas of the ribbon morphology were found to be a well sorted medium sand unit only a few 10 s of cm thick overlying the shelly muddy sandy material concentrations of well rounded gravels and cobbles were also found in eroded areas with very high backscatter and at least one of these appears to be derived from the base of an eroded fluvial channel seafloor reworking over the transgressive evolution of the shelf appears to have switched from sand ridge evolution which is documented to 40 m water depth to more strictly erosional modification at greater water depths we suggest that this change may be related to the reduction with water depth in the effectiveness of sediment resuspension by waves resuspension is a critical factor in the grain size sorting during transport by bottom currents over large bedforms like sand ridges otherwise we speculate displacement of sand by unidirectional currents will erode the seafloor

tomographic images of the upper mantle below central europe and the mediterranean results from delay time tomography of the european mediterranean upper mantle are discussed and where possible interpreted in terms of geodynamic processes slab like positive velocity anomalies of which the locations correlate well with deeper seismicity are found beneath spain the tyrrhenian basin and the aegean these structures are interpreted as images of subducted slabs large aseismic regions with positive velocity anomalies are found beneath the western mediterranean italy the alps dinarides the pannonian basin northern greece and the aegean these anomalies can also be linked to subducted lithosphere from the anomaly patterns it is deduced that subduction occurred below the western mediterranean and along both sides of the adriatic micro plate beneath the dinarides and northern greece the velocity structures suggest detachment of the slab from the surface

the depth dependency of planktonic benthic foraminiferal ratios constraints and applications abstract study of the ratio between planktonic and benthic foraminifera in a great number of areas shows that variation of this ratio with depth can be described using organic matter flux equations essentially the share of benthic foraminifera in the total association is inversely proportional to depth as is the amount of organic matter resulting from primary productivity reaching the sea bottom variation in the p b ratio from area to area appears to be strongly dependent on the amount of inbenthic living foraminifera if the ratios are corrected for this the regressions between the proportion of planktonic foraminifera p and depth appear to be near identical in the gulf of mexico the gulf of california the west coast of the usa and the adriatic sea this regression can be described by depth e 3 58718 0 03534 p a study of the behaviour of this function in nine cores from the adriatic upper quaternary reveals that the palaeodepth reconstructions are not influenced by fluctuations in productivity and temperature but that they are significantly influenced by redeposition of fine grained deposits

interfering paths of deformation and development of arcs in the fold and thrust belt of the central apennines italy in the foreland fold and thrust belt of the central apennines the major thrust sheets design systems of arcs interfering with noncoaxial trends localization of shortening by thrusting and shearing appears to be controlled by the squeezing of low competence basinal units marche gran sasso monte picca and monte genzana in between the rigid blocks of the lazio abruzzi and adriatic carbonate platforms the geometrical interlocking has been resolved by differential rotations of the superposed thrust sheets as also substantiated by paleomagnetic data the structural analysis and the age of the syntectonic siliciclastic deposits suggest an irregular sequencing of superposed contractional and extensional events during late miocene middle pliocene times interfering kinematic paths characterize the arcuate belts where slip partitioning has adjusted the coeval deformation of the noncoaxially arranged tectonic units in the arcuate gran sasso monte picca thrust belt out of sequence thrusting displacement transfer on high angle strike slip faults and growth of high angle normal faults behind the most rotated blocks have resulted in the back and forth superposition of contractional and extensional structures in adjacent domains our kinematic reconstruction of the central apennines indicates that it is impossible to perform the retrodeformation of tectonic events by assuming a regular outward progression of deformation pulses in such a strongly arcuate belt the irregular trajectories of the displacement field and the complex overprinting relations between different sets of structures reflect the kinematic accommodation of blocks with contrasting rigidity and are not fitted easily within a regionally smoothed stress field

iron geochemistry of loess and red clay deposits in the chinese loess plateau and implications for long term asian monsoon evolution in the last 7 0 ma abstract recently some groups of authors have demonstrated that the tertiary red clay deposits underlying the pleistocene loess paleosol sequence in the chinese loess plateau are wind blown in origin thus extending the eolian record in the plateau from 2 6 ma back to about 7 0 ma and providing a good opportunity to reconstruct long term monsoon changes as magnetic susceptibility the widely used paleomonsoon proxy of loess deposits is problematic in reconstructing the monsoon history recorded in the red clay the development of other proxies is urgently needed in this study we analyzed the ratios of citrate bicarbonate dithionite cbd extractable fe2o3 to total fe2o3 concentrations in four loess sections along a north south transect of the loess plateau and in the lingtai loess red clay sequence of 305 m thick the fe2o3 ratio in the loess sections clearly shows higher values in soil units than in loess horizons and a southward increase in this ratio is also remarkable along the transect these are in good agreement with the temporal spatial variations in the east asia summer monsoon intensity identified by other monsoon proxies and soil development observations the fe2o3 ratio thus attests to being a good proxy indicator of the summer monsoon evolution the lingtai fe2o3 ratio record shows high values over three time intervals 4 8 4 1 ma 3 4 2 6 ma and during the interglacial periods of the past 0 8 ma the increase in summer monsoon intensity over the three intervals also coincides with the well developed soil characteristics it is therefore concluded that the east asia summer monsoon has experienced a non linear evolution since the late miocene the occurrence of a monsoon prime at about 4 8 4 1 ma implies that the tibetan plateau one of the most important boundary conditions in maintaining the monsoon circulation must have been uplifted to a critical height at that time

mechanisms of thrust faulting in the gran sasso chain central apennines italy abstract the gran sasso chain in central italy is made up of an imbricate stack of eight thrust sheets which were emplaced over the upper miocene lower pliocene laga flysch the thrust sheets are numbered from 1 to 8 in order of their decreasing elevation in the tectonic stack and their basal thrusts are numbered from t 1 to t 8 accordingly on the basis of their different deformation features the major thrust faults fall into three groups 1 thrust faults marked by thick belts of incoherent gouges and breccia zones t 1 t 2 t 3 2 thrust faults characterized by a sharp plane which truncates folds that had developed in the footwall rocks t 5 t 6 and 3 thrust faults truncating folds developed in both the hangingwall and footwall units and bordered by foliated fault rocks t 7 the deformation features observed for the different faults seem to vary because of two combined factors 1 lithologic changes in the footwall and hangingwall units separated by the thrust faults and 2 increasing amounts of deformation in the deepest portions of the imbricate stack the upper thrust sheets from 1 to 6 are characterized by massive calcareous and dolomitic rocks they maintain a homoclinal setting and are truncated up section by the cataclastic thrust faults the lowermost thrust sheets 7 and 8 are characterized by a multilayer with competence contrasts which undergoes shear induced folding prior to the final emplacement of the thrust sheets bedding and axial planes of folds rotate progressively towards the t 5 t 6 t 7 and t 8 thrust boundaries and are subsequently truncated by propagation of the brittle thrust faults the maximum deformation is observed along the t 7 thrust fault consistent with horizontal displacement that increases progressively from the uppermost to the lowermost thrust sheet in the tectonic stack the axial planes of the folds developed in the hangingwall and footwall units are parallel to the t 7 thrust fault and foliated fault rocks have developed field data and petrographic analysis indicate that cleavage fabrics in the fault rocks form by a combination of cataclasis cataclastic flow and pressure solution slip associated with pervasive shearing along subtly distributed slip zones parallel to the t 7 thrust fault the development of such fabrics at upper crustal levels creates easy slip conditions in progressively thinner domains which are regions of localized flow during the thrust sheet emplacement

flexural behavior of the continental lithosphere in italy constraints imposed by gravity and deflection data a procedure is developed that systematically matches observations of plate flexure and gravity anomalies at simple convergent boundaries to the bestfitting two dimensional flexural geometry obtained by a thin elastic sheet of specified elastic strength the procedure allows analytical solution for three independent variables one of which is the initial preflexure elevation of the reference surface and two of which are related to the vertical forces and bending moments that act on the plate application to four profiles constructed across the apennine convergent system in italy shows that the observed depth of the basal pliocene surface which marks the base of the foredeep basin and the observed bouguer gravity anomalies can be fit by a two dimensional elastic plate model with an effective elastic thickness of about 20 km on three profiles and about 10 km on the fourth profile the initial elevation prior to flexure is determined to have been about 1000 m below sealevel on all profiles large bending moments and or vertical shear forces are required to act at the effective plate ends in order to maintain the observed deflection moments between 0 5 1017 and 3 1017 n and shear forces between 3 1012 and 3 1012 n m gravity modelling indicates that on the two northernmost profiles these terminal forces can not be supplied by a static mass at crustal depths and suggests that on all four profiles the terminal forces are supplied by anomalously dense material present at depths of 75 150 km beneath and west of the west coast of italy this dense material probably corresponds to westward subducted lithosphere of the adriatic plate extending from the northern apennines to the southern apennines and calabria this study suggests that in subduction systems like the apennines that are characterized by backarc extension forces acting on subducted lithosphere at depth can be expressed at the surface in the geometry of the foredeep basin that forms adjacent to the subduction zone

bulk and single particle mineralogy of asian dust and a comparison with its source soils 1 the mineralogical properties of asian dust have been examined in detail and the results have been compared with the chinese source soils using high resolution scanning electron microscopy transmission electron microscopy x ray diffraction and chemical analysis mineralogical classification of asian dust particles showed that the most common single particles were clay aggregates 48 that were often mixed with nanosized calcite followed by particles of quartz 22 plagioclase 11 coarse calcite 6 k feldspar 5 muscovite chlorite kaolinite amphibole gypsum fe and ti oxides which were either partly or entirely attached with clay size mineral grains the clay minerals in asian dust were mostly illite and interstratified illite smectite the average mineral composition of the bulk dust samples by x ray diffraction was quartz 28 plagioclase 11 k feldspar 8 calcite 8 illite 19 interstratified illite smectite 22 chlorite 2 smectite 1 and kaolinite 1 in the silty soils from the source regions the clay minerals and nanosized pedogenic calcite aggregated and covered silt size minerals while the sands were mostly composed of quartz and feldspars and were lined with clay minerals the mineralogy of asian dust was similar to that of the silty soil from the loess plateau but the total phyllosilicate content increased from desert sands 7 silty soil 23 to asian dust 45 fining eastward the optical properties of asian dust and its interaction with atmospheric gases and cloud are probably affected by the clay rich mineral composition the aggregation and attachment of the clay minerals on the coarser minerals and the nanosized calcite

variations in loess and palaeosol properties as indicators of palaeoclimatic gradients across the loess plateau of north china abstract new data are presented on micromorphology magnetic susceptibility and particle size characteristics of three soil sediment units at four locations along a wnw ese transect across the loess plateau of north china differences and spatial trends are used to assess the sensitivity of such data as proxies of regional palaeoclimatic gradients the steepest climatic gradient suggested by the magnetic susceptibility for the s1 palaeosol is at the eastern humid end of the traverse micromorphology and particle size analysis show that the loess units in the east are richer in clay than the best developed palaeosols in the semi arid west and that particle size in the west appears to provide a more sensitive record of climatically driven changes than magnetic susceptibility the use of surface and near surface soils as a datum for inferring palaeoprecipitation values is reviewed in the light of recent evidence of substantial degradation of such soils micromorphological and particle size analysis of closely spaced samples from loess palaeosol sequences is a sensitive addition to magnetic susceptibility stratigraphy and correlation

variations in 87sr 86sr ratios of calcites in chinese loess a proxy for chemical weathering associated with the east asian summer monsoon abstract 87sr 86sr ratios of loess paleosol calcites of luochuan in china over the past 130 ka display a regular change with increasing trend of 87sr 86sr ratios in the following order loess calcite weakly pedogenetic paleosol calcite paleosol calcite pure secondary calcite the observed variations in the 87sr 86sr record of loess paleosol calcites correlate closely with the records of the magnetic susceptibility coarse grain fraction content in the same profile an et al chin sci bull 39 1994 182 184 and the specmap stacked 18o record of global ice volume imbrie et al in berger et al eds milankovitch and climate part i reidel boston 1984 pp 269 305 strata from the last glacial consist mostly of loesses and weakly developed paleosols and have lower 87sr 86sr ratios averaging 0 71079 paleosols which developed during the last interglacial have higher 87sr 86sr ratios averaging 0 71131 the four periods ca 125 110 98 90 80 75 and 9 5 ka b p of increased summer monsoonal rainfall coincide with the four peaks in 87sr 86sr values a series of 87sr 86sr high frequency high amplitude fluctuations is superimposed on the last glacial interglacial cycle over the past 130 ka occurring on millennium timescales with an average time span of about 3 ka during the last glacial the fluctuations of the 87sr 86sr ratios of the luochuan loess paleosol calcites lie in the range 0 71036 0 71176 for the past 130 ka the study shows that the sr isotopic system in loess paleosol calcites may therefore be an excellent proxy of chemical weathering on continents associated with the east asian summer monsoon

travel time tomography of the european mediterranean mantle down to 1400 km abstract the 3 d p wave velocity structure of the mantle below europe the mediterranean region and a part of asia minor is investigated this study is a considerable extension of an earlier tomographic experiment that was limited to imaging upper mantle structure only here the earth s volume under study encompasses the mantle to a depth of 1400 km and we increase the number of international seismological centre isc data for inversion by a factor of four by taking more years of observation and by including data from teleseismic events the most important departure from the earlier study is that we do not use the jeffreys bullen model as a reference model but an improved radially symmetric velocity model the pm2 model which is appropriate for the european mediterranean mantle our inversion procedure consists of two steps first the radial model pm2 is determined from the isc delay times by a nonlinear trial and error inversion of the data as opposed to the jeffreys bullen model the new reference model has a high velocity lithosphere a low velocity zone and seismic discontinuities at depths of 400 and 670 km next the isc data are corrected for effects related to the change in reference model and inverted for 3 d heterogeneity relative to the pm2 model we follow this two step approach to attain a better linearizable tomographic problem in which ray paths computed in the pm2 model provide a better approximation of the actual ray paths than those computed from the jeffreys bullen model hence the two step scheme leads to a more credible application of fermat s principle in linearizing the tomographic equations inversion results for the 3 d heterogeneity are computed for both the uncorrected isc data and for the pm2 data the data fit obtained in the two step approach is slightly better than in the inversion of isc data using the jeffreys bullen reference model a comparison of the tomographic results demonstrates that the pm2 data inversion is to be preferred to assess the spatial resolution an analysis is given of hit count patterns sampling of the mantle by ray paths and results of sensitivity tests with 3 d synthetic velocity models the spatial resolution obtained varies with position in the mantle and is studied both in map view and in cross section in the well sampled regions of the mantle the spatial resolution for larger scale structure can qualitatively be denoted as reasonable to good and at least sufficient to allow interpretation of larger scale anomalies a comparison is made of the results of this study with independent models of s velocity heterogeneity obtained in a number of investigations and with a prediction of the seismic velocity structure of the mantle computed from tectonic reconstructions of the mediterranean region in the context of this comparison interpretations of large scale positive anomalies found in the mediterranean upper mantle in terms of subducted lithosphere are given specifically addressed are subduction below southern spain below the western mediterranean and italy and below the aegean in the last region a slab anomaly is mapped down to depths of 800 km