new evidence of a herd of titanosauriform sauropods from the lower berriasian of the iberian range spain abstract a study of the undescribed part of the las cerradicas tracksite in galve teruel spain has revealed 6 trackways made by small sauropods showing gregarious behaviour parallel trackways las cerradicas is located towards the top of the villar del arzobispo formation early berriasian the wide gauge condition the manus pes distance the kidney shaped morphology of the manus and the subtriangular morphology of the pes with a big digit i that swells medially and a narrow heel oriented posterolaterally suggest that the sauropods in question are more similar to sauropodichnus giganteus than to any other sauropod ichnotaxa some of the features point to the titanosauriforms as the best candidates to be the trackmakers recent work in bone histology the differences with respect to other iberian tracksites of similar age and the differences with respect to other sauropod herds of the track record do not allow us to establish whether the sauropods were juvenile or dwarfs the sauropod skeletal record and other large sauropod footprints in the villar del arzobispo formation could tip the scales in favour of the first hypothesis

sub volcanic crystallization at stromboli aeolian islands southern italy preceding the sciara del fuoco sector collapse evidence from monzonite lithic suite we describe texture mineralogy and whole rock composition of cognate monzonite sub volcanic clasts within debris flow deposits related to the 5000 years catastrophic phreatomagmatic eruption probably linked to the sciara del fuoco sector collapse the debris flows are at the top of accretionary lapilli rich ash deposits overlying potassic ks shoshonites lavas of the neostromboli period the monzonites are inferred to be crystallized in situ at low p at the side walls and or roof margins of a shallow magma chamber and to be cogenetic with the ks neostromboli extrusives they can be considered ideal orthocumulates since they approximately retain a bulk liquid composition and possibly represent slowly cooled equivalents of their ks shoshonite host rock the closure temperature of final solidification of the monzonite lithic suite was estimated through ternary feldspar geothermobarometry plagioclase k feldspar and k feldspar biotite equilibria and is in the range of 750 790 c with a maximum logfo2 around 15 1 15 3 the estimated pressure of crystallization is 0 5 kbar potassic lavas and dikes previously emplaced during the neostromboli period also resemble the monzonites in both major trace elements and mineral chemistry the cogenetic relationship between ks neostromboli extrusives and the monzonite host rock magma from which the sub volcanic clasts were derived is clear evidence that a shallow magma chamber existed between the caldera collapse of the vancori period and the sciara del fuoco sector collapse i e between 13 000 and 5000 years the monzonite clasts were derived from crystallization at very shallow depth ca 1 km and strongly support the hypothesis of violent decompression of the shallow magmatic plumbing system during the sciara del fuoco sector collapse climax of the regressive landslide event with maximum disruption of the chamber walls took place during emplacement of the debris flows i e during the late stage of the neostromboli phreatomagmatic eruption

high precision u pb geochronology and a new chronostratigraphy for the canadon asfalto basin chubut central patagonia implications for terrestrial faunal and floral evolution in jurassic abstract the fluvial lacustrine and tuffaceous sedimentary succession of the canadon asfalto continental basin exposed in the argentinean chubut province of central patagonia preserves an extraordinary record of jurassic fauna and flora that marks key events in the evolution of dinosauria early mammals and major south american plant groups however basin wide correlation of the fossiliferous units is complicated by fault displacements unconformities and repetitive lithofacies new u pb analyses of zircon ca tims method from five primary tuff beds interstratified with the lacustrine strata establish a new chronostratigraphic framework for the sedimentary and volcanic units of canadon asfalto basin constraining ca 33 m y of depositional history and biotic evolution that spans nearly all three epochs of the jurassic five major vertebrate and plant rich stratigraphic intervals have been identified and are being actively investigated that range in age from pliensbachian to kimmeridgian or younger our combined biostratigraphic and high precision geochronologic results indicate that the major faunal turnover of the sauropodomorph dinosaurs which led to the rise of the eusauropods took place in the early jurassic earlier than previously recognized similarly the first successful radiation of the ornithischian dinosaurs heterodontosaurids as well as the evolutionary diversifications of the araucarian conifers and the osmundaceous ferns all occurred before the end of the early jurassic the diverse palynofloral assemblage of the canadon calcareo formation that was once considered to be early cretaceous in age is now entirely constrained to the late jurassic

the oldest evidence for birds in northern gondwana small tridactyl footprints from the middle jurassic of msemrir morocco we revise a famous set of fossil footprints that were described in the mid 1980s from the middle jurassic bathonian of morocco and that have often been considered to be an early record for mesozoic birds if correct these tracks are the oldest records of birds from gondwana and would have critical biogeographic and palaeobiological implications the oldest skeletal fossils of avians are from the late jurassic of germany laurasia thus these important historical footprints are re described and re examined and new analyses are carried out on the additional tracks that also occur on the surface but that have never been described before all the tracks on the surface show the same morphological characteristics though their size is variable and are compared here to known dinosaur and bird ichnotaxa we used a laser scanner to generate a 3d digital model of the slab this new approach allowed detailed descriptions of the specimens the identification of new footprints on the surface and the conclusion that they were likely left by non avian dinosaurs rather than birds we show the potential of this new approach to the study of fossil footprints and trackways high resolution imaging and laser scanning add new information fundamental for a revision of the criteria for distinguishing between closely related vertebrate groups in this case dinosaurs and birds

pacific subduction coeval with the karoo mantle plume the early jurasssic subcordilleran belt of northwestern patagonia the early mesozoic magmatism of southwestern gondwana is reviewed in the light of new u pb shrimp zircon ages 181 2 ma 181 3 ma 185 2 ma and 182 2 ma that establish an early jurassic age for the granites of the subcordilleran plutonic belt in northwestern argentine patagonia new geochemical and isotopic data confirm that this belt represents an early subduction related magmatic arc along the proto pacific margin of gondwana thus subduction was synchronous with the initial phase of chon aike rhyolite volcanism ascribed to the thermal effects of the karoo mantle plume and heralding rifting of this part of the supercontinent overall there is clear evidence that successive episodes of calc alkaline arc magmatism from late triassic times until establishment of the andean patagonian batholith in the late jurassic involved westerly migration and clockwise rotation of the arc this indicates a changing geodynamic regime during gondwana break up and suggests differential rollback of the subducted slab with accretion of new crustal material and or asymmetrical scissor like opening of back arc basins this almost certainly entailed dextral displacement of continental domains in patagonia

flattened fossil footprints implications for paleobiology abstract studies of natural casts of dinosaur footprints associated with very thin mudstone and siltstone intervals in thick sand dominated sequences often reveal casts that are significantly flattened due to the differential effects of overburden pressures on different lithologies they are in effect squeezed vise like between two thick non compactable sand layers thus the sand filled tracks casts are flattened or widened as the ductile layers are compressed such flattening here described from five localities is a previously unreported phenomenon with implications for vertebrate ichnology present evidence suggest that significant flattening is not evident in most sequences in which mudstone and siltstone intervals are thicker even though overburden pressures may have been comparable examples from the jurassic of north america and the cretaceous of china show that the flattening widening of tridactyl theropod tracks leads to predictable changes in track cast morphology which may influence interpretations of track maker identity and ichnotaxonomy in the theropod dominated samples described here such extramorphological changes differentially affect the shape of the whole cast and individual digit trace casts making them appear more fleshy and sometimes deceptively convergent with ornithopod tracks

anisotropy beneath hawaii from surface wave particle motion observations observed polarization ellipses for fundamental mode surface waves observed at a digital station in hawaii deviate from those expected for isotropic models of crust and mantle structure for that region the anomalous motion occurs as rotations of the ellipse about all three axes in a cartesian corrdinate system the largest and most consistent deviations occur as anomalous slopes of the ellipse about the horizontal axis transverse to the direction of propagation

time domain pure state polarization analysis of surface waves traversing california a time domain pure state polarization analysis method is used to characterize surface waves traversing california parallel to the plate boundary the method is applied to data recorded at four broadband stations in california from twenty six large shallow earthquakes which occurred since 1988 yielding polarization parameters such as the ellipticity euler angles instantaneous periods and wave incident azimuths the earthquakes are located along the circum pacific margin and the ray paths cluster into two groups with great circle paths connecting stations mhc and pas or cmb and gsc the first path mhc pas is in the vicinity of the san andreas fault system safs and the second cmb gsc traverses the sierra nevada batholith parallel to and east of the safs both rayleigh and love wave data show refractions due to lateral velocity heterogeneities under the path indicating that accurate phase velocity and attenuation analysis requires array measurements t he rayleigh waves are strongly affected by low velocity anomalies beneath central california with ray paths bending eastward as waves travel toward the south while love waves are less affected providing observables to constrain the depth extent of anomalies strong lateral gradients in the lithospheric structure between the continent and the ocean are the likely cause of the path deflections

dinosaur footprints in the early jurassic of patagonia marifil volcanic complex argentina biochronological and palaeobiogeographical inferences a new dinosaurian track bearing site with tridactyl footprints from the lower jurassic pre middle pliensbachian volcanogenic and epiclastic rocks of the marifil volcanic complex patagonia argentina is presented and described the best preserved footprint classified as cf anomoepus confirms the utility of the anomoepus like tracks for the early jurassic biochronology palaeobiogeographically this record supports the idea that the south american early jurassic dinosaur fauna presents elements of pangaean distribution and others with gondwanan relationships with prevalent southern african affinities dinosaur records from south america between the rhaetian and the pliensbachian are very scarce and this find contributes to the knowledge of early radiation and evolution of dinosauria

gregarious behaviour among non avian theropods inferred from trackways a case study from the cretaceous cenomanian candeleros formation of patagonia argentina abstract gregarious behaviour among dinosaurs has been inferred from several lines of evidence monospecific bonebeds skeletal morphology phylogenetic inferences comparison with modern ecosystems and parallel trackways with particular characteristics but is relatively poorly documented for non avian theropods here we report five parallel theropod trackways of large track size average length of 28 cm in the cretaceous cenomanian candeleros formation from northwestern patagonia argentina the tracks are provisionally assigned to aff asianopodus pulvinicalx and considering the autopod morphology of the theropod taxa documented in the candeleros formation abelisaurid theropods are suggested as trackmakers the trackways possess similar stride speed estimation direction and preservational features and track show uniform depth and do not overlap physical barriers i e large fluvial channels or perennial lake that could influence the direction of the theropod trackmaker gaits were not recognized in the section taking into account these considerations a gregarious behaviour for the abelisaurid theropod trackmakers is proposed the tracks are preserved as shallow undertracks in a medium grained sandstone bed deposited in a floodplain setting the tracking surface is interpreted as the overlaying layer of muddy siltstone the occurrence of swelling clays and microbial mats in the track bearing level could have contributed to the substrate stabilization and their role in the preservation is discussed

plesiosaurian fossils from baltic glacial erratics evidence of early jurassic marine amniotes from the southwestern margin of fennoscandia early jurassic plesiosaurian fossils are rare in the scandinavian region with a few isolated bones and teeth known from bornholm and anecdotal finds from east greenland the only other identifiab

melting dehydration and the dynamics of off axis plume ridge interaction 1 we present results from a series of two dimensional numerical experiments in which a thermally buoyant off axis mantle plume interacts with a nearby ridge axis these experiments incorporate melting and a number of related dynamical feedbacks including energy loss to latent heating and fe depletion buoyancy as well as viscosity increases due to dehydration during melting results indicate that dehydration which acts to increase the viscosity of the residual mantle during melting profoundly impacts the morphology of flow between plume and ridge axis as upwelling plume material begins to melt it becomes significantly more viscous and readily accretes to the overlying lithosphere this creates a viscous plug that grows downward from the base of the lithosphere directly above the plume conduit plume material traveling to the ridge axis is then deflected horizontally at subsolidus depths by this plug allowing pristine unmelted plume material to reach the ridge axis experiments without dehydration show that the loss of thermal energy to latent heating during melting marginally decreases the flow of plume material along the base of the lithosphere to the ridge axis alternatively extraction of fe from the solid during melting slightly increases plume flow to the ridge these results also demonstrate that the flow of plume material to the ridge axis is sensitive to the slope of the base of the rheological lithosphere consistent with previous studies of off axis plume ridge interaction

late triassic and early jurassic palaeogeography of the world abstract a new version of global and regional palaeogeographic maps is presented for two time intervals these maps depict the plate tectonic configuration palaeoenvironment and lithofacies during the late triassic carnian norian and early jurassic hettangian toarcian time the individual maps illustrate the general conditions present during the maximum marine transgressions of higher frequency cyclicity within the absaroka sequence of sloss during triassic time pangaea began to stretch initiating the rifting and future break up of the supercontinent the continued northward drift of the cimmerian continent corresponded with the progressive closure and consumption of palaeotethys oceanic crust and the opening of the neotethys ocean the most significant late triassic convergent event was the indosinian orogeny occurring as a result of the consolidation of south china and north china blocks also indochina and indonesia were sutured to south china at the same time the qiangtang block approached the eurasian margin the consolidation of the north chinese and amurian blocks left open a large embayment of panthalassa between amuria and laurasia the so called mongol okhotsk ocean active subduction existed along the margin of this ocean dipping cratonwards towards east siberia the last collisional events of the uralian orogeny took place during the triassic and early jurassic time the conclusion of the uralian orogeny was accompanied by uplift of the adjacent areas of eastern europe and western siberia during the early jurassic the palaeotethys ocean was finally closed and the cimmerian continent collided with asia causing the cimmerian orogeny the time around the triassic jurassic boundary marked an important biotic extinction event plate tectonic activity caused palaeogeographic and palaeoclimatic change which may have contributed to the mass extinction from the plate tectonic and palaeogeographic point of view the following events could have influenced the extinction 1 the closure of palaeotethys and assembly of the asian part of pangaea 2 the break up of pangaea in the future central atlantic area and transition from rifting to drifting and 3 the very extensive basaltic volcanism of the central atlantic magmatic province

dinosaur trackways from the upper cretaceous oldman and dinosaur park formations belly river group of southern alberta canada reveal novel ichnofossil preservation style1 dinosaur tracksites recently discovered in exposures of the belly river group in the milk river natural area mrna and dinosaur provincial park dpp of southern alberta represent a novel type of

terrane processes at the margins of gondwana the process of terrane accretion is vital to the understanding of the formation of continental crust accretionary orogens affect over half of the globe and have a distinctively different evolution to wilson type orogens it is increasingly evident that accretionary orogenesis has played a significant role in the formation of the continents the pacific margin of gondwana preserves a major orogenic belt termed here the australides which was an active site of terrane accretion from neoproterozoic to late mesozoic times and comparable in scale to the rockies from mexico to alaska or the variscan appalachian orogeny the new zealand sector of this orogenic belt was one of the birthplaces of terrane theory and the australide orogeny overall continues to be an important testing ground for terrane studies this volume summarizes the history and principles of terrane theory and presents 16 new works that review and synthesize the current state of knowledge for the gondwana margin from australia through new zealand and antarctica to south america examining the evolution of the whole gondwana margin through time

first evidence of the cretaceous decapod crustacean protocallianassa from sweden an assemblage of the burrowing ghost shrimp protocallianassa faujasi is described providing the first evidence of this decapod species from sweden the fossils occur in successions of the informal earliest late campanian belemnellocamax balsvikensis zone at asen and the latest early campanian b mammillatus zone at ivo klack both in the kristianstad basin of ne skane numerous heavily calcified chelipeds were found within a restricted bed at a sen that was rich in carbonate cemented nodules based on the burrowing lifestyle of modern mud shrimps we interpret these nodules as infilled burrow chambers the low abundance of molluscs within the protocallianassa beds is also consistent with analogous extant communities indicating that a similar ecologically exclusive relationship ruled within the late cretaceous shallowmarine ecosystems less

surface wave tomography of the gulf of california 1 we measured interstation fundamental mode rayleigh wave phase velocities using data from the nars baja seismic network located around the gulf of california a region average shear velocity model and a set of azimuthally anisotropic phase velocity maps are obtained from these data the average shear velocity structure shows a strong low velocity zone underlying a thin lid and the data are suggestive of low velocities down into the transition zone the phase velocity maps display signatures of sedimentary layers crustal thickness variations upwelling under the plate boundary and the presence of the subducted farallon microplate remnants beneath the gulf the upper mantle features inferred from this study provide new seismic evidence on the tectonic evolution of the region

ichnological evidence for small quadrupedal ornithischians from the basal cretaceous of se asia and north america implications for a global radiation

magma evolution of the sete cidades volcano sao miguel azores the sete cidades volcano sao miguel azores is situated at the eastern end of the ultraslow spreading terceira rift axis the volcano comprises several dominantly basaltic pre caldera eruptions a trachytic caldera forming stage and a post caldera stage consisting of alternating trachytic and basaltic eruptions the post caldera flank lavas are more primitive 5 wt mgo than the pre caldera lavas implying extended fractional crystallization and longer crustal residence times for the pre caldera shield building lavas thermobarometric estimates show that the ascending alkali basaltic magmas stagnated and crystallized at the crust mantle boundary similar to 15 km depth whereas the more evolved magmas mainly fractionated in the upper crust similar to 3 km depth the caldera forming eruption was triggered by a basaltic injection into a shallow trachytic magma chamber lavas from all stages follow a single continuous liquid line of descent from alkali basalt to trachyte although slight differences in incompatible element e g ba nb la nb and sr isotope ratios imply some heterogeneity of the mantle source major and trace element data suggest similar partial melting processes throughout the evolution of the volcano slight geochemical differences between post and pre caldera stage lavas from the sete cidades volcanic system indicate a variation in the mantle source composition with time the oxygen fugacity increased from the pre caldera to the post caldera stage lavas probably as a result of the assimilation of crustal rocks this is supported by the presence of crustal xenoliths in the lavas of the flank vents the lavas from the sete cidades volcano generally have low sr isotope ratios however rocks from one post caldera vent on the western flank indicate mixing with magmas resembling the lavas from the neighbouring agua de pau volcano having higher sr isotope ratios the different magma sources at sete cidades and the adjacent agua de pau volcano imply that despite their close proximity there is only limited interaction between them

partial melting and upwelling rates beneath the azores from a u series isotope perspective we report u series systematics 238u 230th 231pa 226ra for basalts from the azores islands and the nearby mid atlantic ridge with the aim of constraining melting processes in this region of plume ridge interaction both 230th and 231pa excess show rough negative trends with indices of source enrichment sr nd and pb isotopes which cannot be explained by melting of a source variably enriched by mafic components e g pyroxenite however there is evidence for a distinct source component possibly sediment beneath sao miguel which may give rise to these trends 231pa excess and sm nd fractionation are positively and negatively correlated respectively with distance from the centre of the plume while 230th excesses show no clear trend this suggests that mantle upwelling velocity exerts a strong control on u pa fractionation and that melting is initiated deeper in the centre of the plume these observations are used to infer melting conditions beneath the mid atlantic ridge and azores islands the mantle upwelling velocity is constrained to be 3 4 cm a which is smaller than that inferred for hawaii or iceland predicted 226ra excesses are similar to or lower than those measured suggesting high velocity melt ascent in channels and rapid differentiation prior to eruption the effect of the presence of volatiles in the source is also investigated and we show that the presence of water could explain the 230th and 231pa trends as a function of distance across the plume a 3 d model for the azores plume can reproduce the u series isotope observations

first report of protoceratopsians neoceratopsia from the late cretaceous judith river group alberta canada protoceratopsians are best known in north america from associated skeletal material of montanoceratops from the early maastrichtian of montana and campanian of alberta and leptoceratops from the la

complex polarization analysis of particle motion knowledge of particle motion polarization aids in identifying phases on three component seismograms the scheme of montalbetti and kanasewich 1970 is extended to analytic three component seismograms where the imaginary part of the signal is the hilbert transform of the real part this scheme has only one free parameter the length of the time window over which the polarization parameters are estimated so it can be applied in a routine way to three component data the azimuth and dip of the direction of maximum polarization and the degree of elliptical polarization as a function of time for the seismograms are obtained polarization analysis of strong motion data from the 1971 san fernando earthquake aids in the discrimination between wave types which is important for the understanding of the complicated earthquake induced shaking observed in basins most arrivals are incident on the receivers in the direction of the back azimuth to the epicenter which suggests that despite the complicated motions two dimensional finite difference methods are sufficient to understand the effect on seismic waves of the los angeles and san fernando basins vidale and helmberger 1986b

discovery of moissanite in a peralkaline syenite from the azores islands abstract our discovery of moissanite grains in a peralkaline syenite from the agua de pau volcano sao miguel azores islands portugal represents the first report of this mineral in present day oceanic geodynamic settings raman spectroscopy and single crystal x ray diffraction show the presence of both the 6h and 4h polytypes with the predominance of the first one the distribution of trace elements is homogeneous except for al and v azorean moissanite often hosts rounded inclusions of metallic si and other not yet identified metallic alloys a process involving a flushing of ch4 h2 ultra reducing fluids in the alkaline melts might be considered as a possible mechanism leading to the formation of natural sic thus calling for strongly reducing conditions that were locally met in the crust mantle beneath the sao miguel island

quantitative measurements of shear wave polarizations at the anza seismic network southern california implications for shear wave splitting and earthquake prediction we analyze shear wave polarizations from local earthquakes recorded by the anza network in southern california using an automated method which provides unbiased and quantitative measurements of the polarization and the duration of linear motion following the shear wave arrival the linearity interval initial shear wave particle motions are strongly aligned at four stations a feature that is not predicted by focal mechanisms the particle motion alignment is most likely caused by shear wave splitting due to anisotropy beneath these stations a result supported by the clear shear wave splitting seen in a borehole recording near one of the anza stations these results are consistent with an earlier analysis of these data by peacock et al 1988 however our analysis does not support claims by crampin et al 1990 that shear wave splitting delay times at station knw exhibit temporal variations which can be correlated with the occurrence of the north palm springs earthquake ml 5 6 of july 8 1986 automatically determined linearity intervals scatter widely from 0 02 to 0 15 s and exhibit no clear temporal trends we find a correlation between earthquake moment and the linearity interval possibly a result of longer effective source time functions for the larger events the inability to identify a distinct slow quasi shear wave pulse for the vast majority of these events indicates that scattering strongly affects the particle motion even in the very early shear wave coda analysis of earthquake clusters with similar waveforms recorded at knw shows that seismic green functions are stable throughout the observational period and that most linearity interval variation is due to source and ray path differences between events if shear wave splitting is causing the observed delay times between horizontal components the waveform stability for events in these clusters restricts any temporal changes in shear wave splitting delay times to less than 5 10

late cretaceous campanian leaf and palynoflora from southern skane sweden a late cretaceous campanian leaf megaflora from the vomb trough in southern skane sweden has been investigated on the basis of collections held at the swedish museum of natural history the mai

231pa and230th chronology of mid ocean ridge basalts mass spectrometric measurements of235u231pa and238u230th disequilibria are used to further constrain processes producing u series disequilibria in young mid ocean ridge basalts morb and to determine eruption ages for samples from 9 10 n east pacific rise and juan de fuca gorda ridges 231pa 235u activity ratios for axial basalts are large and relatively uniform within ridge segments the systematically large231pa 235u 230th 238u and226ra 230th activity ratios in morb are inconsistent with simple equilibrium melting models and crustal contamination or seawater alteration processes more complicated melting processes involving disequilibrium or heterogeneous melting of mantle sources and disequilibrium transport of melts to the crust could produce the large u series disequilibria in morb 231pa and230th model ages were determined by estimating initial231pa 235u and230th 232th ratios from axial samples and by assuming constancy of these ratios over time all231pa and230th ages agree to 0 7 ka for samples with ages of 0 130 ka these concordant ages validate the model assumptions of the two dating methods and suggest that mantle sources and melt generation processes have been uniform for these areas during the past 130 ka consequently 231pa and230th age dates can be used to quantify the temporal and spatial dependence of volcanism at oceanic spreading centers during the past 375 ka

an introduction to the mesozoic biotas of scandinavia and its arctic territories the mesozoic biotas of scandinavia have been studied for nearly two centuries however the last 15 years have witnessed an explosive advance in research most notably on the richly fossiliferous t

rayleigh wave multipathing along the west coast of north america we have created a movie of surface ground motion for the 3 november 2002 denali fault earthquake based on spectral element simulations using crustal model crust2 0 mantle model s20rts topography and bathymetry model etopo5 and a finite fault slip model the movie features two anomalous wave packets that travel along the west coast of the north american plate following off great circle paths these wave packets are rayleigh waves with dominant periods around 20 sec which are also found in seismograms recorded by the southern cali fornia seismic network one of these packets is the direct surface wave whose group arrival time changes laterally as dictated by the shape of the oregon coast the other packet is a surface wave reflected by a lateral interface underneath the rocky moun tains a linear reflector parallel to the canadian coast offsetting it by a few hundred kilometers can explain its arrival time but the offsetting distance derived from the synthetic seismograms puts the reflector 350 km northeast of the result obtained from the data indicating a need to update the crustal and mantle models in this area online material animation of normalized simulated vertical displacement for the 2002 denali earthquake

peculiarities of surface wave propagation across central eurasia abstract the recent installation of six broadband digital iris ida seismic stations in the ussr has provided new opportunities for studying surface wave propagation across eurasia group velocities of fundamental rayleigh and love modes between epicenters and these stations were determined for 35 events that occurred since april 1989 to the middle of july 1990 near eurasia differential phase velocities were found for the same arrivals along paths between several pairs of stations group and phase velocities were obtained in the period range from 15 to 300 sec frequency time polarization analysis was used for studying polarization properties of surface waves in some cases significant anomalies in the particle motion for periods up to 100 sec were observed they are attributed to surface wave refraction and scattering due to lateral inhomogeneities at the boundaries and inside the eurasia continent

inversion of surface wave spectra for source parameters of large earthquakes using aspherical earth models abstract amplitude and phase spectra of rayleigh and love waves of periods of 150 to 300 s from eight large earthquakes which occurred between 1990 and 1993 are corrected for wave propagation and then inverted for the source duration rupture directivity and moment tensor of the earthquake source for various propagation anomalies predicted by models of the earth s aspherical elastic and anelastic structure the application of corrections for the focusing and take off azimuth anomaly in addition to conventional corrections for the phase anomaly improves inversions of surface waves rayleigh waves provide better constraints than love waves in the determination of source parameters the data consist of either only rayleigh waves or both love and rayleigh waves whenever the full moment tensor is involved for several earthquakes there is clear discrepancy between source parameters determined from different data sets particularly from rayleigh or love waves the moment tensor solution tends to underpredict observed amplitude spectra for data sets with large amplitude anomalies especially for love waves this study shows that 1 the 1990 sudan earthquake is anomalous for its unusually large non double couple component of the moment tensor 2 the 1990 iran earthquake has a strike slip mechanism with a subvertical nw striking nodal plane which is the fault plane inferred from surface ruptures 3 the 1991 costa rica earthquake may have a seismic moment larger than previously determined from long period surface waves 4 the 1992 nicaragua earthquake involves a predominant rupture parallel to the trench and a large centroid offset up dip to the trench axis and the latter process may be responsible for large tsunami generation 5 the 1993 hokkaido earthquake has a shallow dipping and west plunging nodal plane which is consistent with the p wave first motions but differs from the centroid moment tensor solutions

carl wiman and the foundation of mesozoic vertebrate palaeontology in sweden in 1908 carl wiman of uppsala university sweden discovered rich horizons with triassic vertebrate remains in spitsbergen on svalbard norway this marked the beginning of vertebrate palaeontolog

volcanic geology of furnas volcano sao miguel azores abstract furnas is the easternmost of the three active central volcanoes on the island of sao miguel in the azores unlike the other two central volcanoes sete cidades and fogo furnas does not have a well developed edifice but consists of a steep sided caldera complex 8 5 km across it is built on the outer flanks of the povoacao nordeste lava complex that forms the eastern end of sao miguel constructive flanks to the volcano exist on the southern side where they form the coastal cliffs and to the west the caldera margins tend to reflect the regional local tectonic pattern which has also controlled the distribution of vents within the caldera and areas of thermal springs activity at furnas has been essentially explosive erupting materials of trachytic composition products associated with the volcano include plinian and sub plinian pumice deposits ignimbrites and surge deposits phreatomagmatic ashes block and ash deposits and dome materials most of the activity has occurred from vents within the caldera or on the caldera margin although strombolian eruptions with aa flows of ankaramite and hawaiite have occurred outside the caldera the eruptive history consists of at least two major caldera collapses followed by caldera infilling based on 14 c dates it appears that the youngest major collapse occurred about 12 000 10 000 years bp new 14 c dates for a densely welded ignimbrite suggest that a potential caldera forming eruption occurred at about 30 000 years bp recent eruptions

anisotropic models of the upper mantle long period rayleigh wave and love wave dispersion data particularly for oceanic areas have not been simultaneously satisfied by an isotropic structure in this paper available phase and group velocity data are inverted by a procedure which includes the effects of transverse anisotropy anelastic dispersion sphericity and gravity we assume that the surface wave data represents an azimuthal average of actual velocities thus we can treat the mantle as transversely isotropic the resulting models for average earth average ocean and oceanic regions divided according to the age of the ocean floor are quite different from previous results which ignore the above effects the models show a low velocity zone with age dependent anisotropy and velocities higher than derived in previous surface wave studies the correspondence between the anisotropy variation with age and a physical model based on flow aligned olivine is suggestive for most of the earth sh sv in the vicinity of the low velocity zone neat the east pacific rise however sv sh at depth consistent with ascending flow anisotropy is as important as temperature in causing radial and lateral variations in velocity the models have a high velocity nearly isotropic layer at the top of the mantle that thickens with age this layer defines the lid or seismic lithosphere in the pacific the lid thickens with age to a maximum thickness of 50 km this thickness is comparable to the thickness of the elastic lithosphere the lid thickness is thinner than derived using isotropic or pseudo isotropic procedures a new model for average earth is obtained which includes a thin lid this model extends the fit of a prem type model to shorter period surface waves

three component analysis of regional seismograms abstract both phased array techniques for single component sensors and vectorial analysis of three component recordings can provide estimates of the azimuth and slowness of seismic phases however a combination of these approaches provides a more powerful tool to estimate the propagation characteristics of different seismic phases at regional distances conventional approaches to the analysis of three component seismic records endeavor to exploit the apparent angles of propagation in horizontal and vertical planes as well as the polarization of the waves the basic assumption is that for a given time window there is a dominant wavetype e g a p wave traveling in a particular direction arriving at the seismic station by testing a range of characteristics of the three component records a set of rules can be established for classifying much of the seismogram in terms of wavetype and direction it is however difficult to recognize sh waves in the presence of other wavetypes problems also arise when more than one signal in either wavetype or direction arrive in the same window the stability and robustness of the classification scheme is much improved when records from an array of three component sensors are combined for a set of three component instruments forming part of a larger array it is possible to estimate the slowness and azimuth of arrivals from the main array and then extract the relative proportions of the current p sv and sh wave contributions to the seismogram this form of wavetype decomposition depends on a model of near surface propagation a convenient choice for hard rock sites is to include just the effect of the free surface which generates a frequency independent operation on the three component seismograms and which is not very sensitive to surface velocities this approach generates good estimates of the character of the s wavefield because the phase distortion of sv induced by the free surface can be removed the method has been successfully applied to regional seismograms recorded at the medium aperture warramunga array in northern australia and the two small arrays noress and arcess in norway which were designed for studies of regional phases the new wavefield decomposition scheme provides results in which the relative proportions of p sv and sh waves as a function of time can be compared without the distortion imposed by free surface amplification such information can provide a useful adjunct to existing measures of signal character used in source discrimination

north america s largest dinosaur trackway site implications for morrison formation paleoecology little known exposures of the upper jurassic morrison formation from the purgatoire valley of southeastern colorado have yielded the world s largest continuously mapped assemblage of dinosaur trackways body fossils include plant invertebrate and vertebrate remains indicative of predominantly fresh water conditions the tracks occur in a lacustrine sequence characterized by 1 shallow water shales 2 micritic shoreface limestones with ooids intraclasts ripple marks mud cracks and 3 minor quartzose sandstone with salt crystal casts analysis of these sedimentary facies suggests that in southeastern colorado lakes were larger and longer lived than in other morrison paleoenvironments trackway orientations and footprint depth contours pinpoint the location of the paleoshoreline at successive levels in the section detailed mapping of 1 300 footprints in bed 2 has revealed more than 100 trackways which testify to the activity of both quadrupedal and bipedal dinosaurs the respective ratio based on trackway counts is 40 60 the quadrupedal tracks are attributed to sauropods and represent the first ever discovered in north america they also exhibit the first known manus claw impressions and are in need of formal description more than 90 of the bipedal tridactyl prints lack claw impressions and are tentatively therefore referred to the ornithopoda cf gypsichnites possibly a camptosaurus the small proportion with distinct claw impressions may represent allosaurus resulting estimates of species diversity 5 and predator prey ratio 1 30 are in general agreement with the estimates of other authors based on skeletal remains and they suggest that the purgatoire river tracks may accurately reflect the composition of the dinosaur fauna distinctive groupings of parallel non overlapping trackways suggest gregarious behavior among sauropods and tridactylous forms

surface wave propagation in an ocean basin with an anisotropic upper mantle observations of polarization anomalies summary observations of surface waves crossing ocean basins indicate that at least in some cases a better interpretation of what was previously considered to be the simultaneous arrival of fundamental love and second rayleigh modes with similar group velocities is the coupled motion of the second generalized mode surface wave propagating in an anisotropic upper mantle this mode displays the polarization anomalies expected from anisotropic alignments caused by syntectonic recrystallization of olivine in a zone of horizontal shear the polarity of the pattern of anomalies found in waves crossing the pacific basin suggests that the lithosphere is dragging the asthenosphere

some observations on trackway evidence for gregarious behavior among small bipedal dinosaurs abstract although trackway evidence for social behavior herding or gregariousness has been demonstrated for large mainly quadrupedal dinosaurs until recently footprint evidence for herding among small bipedal dinosaurs has been sparse recent reports now increase the number of sites suggestive of social behavior to nine found in strata of early jurassic through mid cretaceous age in europe north america and east asia present evidence suggests that small gregarious dinosaurian bipeds included both theropod and ornithopod species

late cretaceous dinosaurian remains from the kristianstad basin of southern sweden mesozoic dinosaur fossils are exceptionally rare in scandinavia the swedish record is typically depauperate with the kristianstad basin of skane scania yielding all of the known fossils from swedish cretaceous strata although highly fragmentary these body remnants are important because they provide evidence of a relatively diverse fauna including previously recognized hesperornithiform birds and leptoceratopsid ceratopsians as well as indeterminate ornithopods that are confirmed here for the first time in this paper we describe three phalanges from asen and an incomplete right tibia from ugnsmunnarna from the kristianstad basin one of the phalanges appears to pertain to a leptoceratopsid ceratopsian providing further evidence of these small ornithischians in the cretaceous sediments of sweden the other two phalanges are interpreted as deriving from small ornithopods similar to thescelosaurus and parksosaurus the tibia appears to represent the first evidence of a non avian theropod dinosaur in the cretaceous of sweden with a previous report of theropod remains based on fish teeth having been corrected by other authors the remains described herein provide important additions to the enigmatic dinosaurian fauna that inhabited the fennoscandian archipelago during the latest cretaceous less

geometric effects of global lateral heterogeneity on long period surface wave propagation long period rayleigh waves from iranian earthquakes have large amplitude asymmetries between minor arc and major arc arrivals e g r 2 and r 3 at digital stations in the azimuth range n20 w to n60 e these asymmetries are as large as a factor of 2 at a period of 256 s and persist to periods greater than 300 s in some cases the entire rayleigh wave group arrival spanning periods from 100 to 300 s is either uniformly enhanced in amplitude or diminished to such a degree that the group arrival appears to be missing the amplitude anomalies are generally not accompanied by significant phase anomalies the irregular azimuthal distribution of the amplitude asymmetries and their occurrence for events with different focal mechanisms and epicentral separations of several hundred kilometers preclude an explanation of these observations by source complexity events in the mediterranean and nepal do not produce similar amplitude asymmetries at the same stations the anomalies are thus most likely due to focusing and defocusing propagation effects as a preliminary investigation of the effects of lateral heterogeneity of upper mantle velocity structure on long period surface wave amplitudes surface wave ray tracing calculations are performed using recently proposed global phase velocity distributions dramatic deviations from great circle paths are predicted for long propagation paths e g r 3 the particular spatial distribution of lateral velocity gradients around a given source location determines whether substantial amplitude asymmetries will be observed between minor arc and major arc arrivals and whether these will persist for sequential great circle orbits the 200 s period amplitude asymmetry observed at kip for the iranian source region r 2 4 r 3 is well predicted by the ray tracing results the absence of this anomaly for the other source regions is also predicted other observed anomalies are not all well predicted but it is clear that geometric effects can contribute significantly to the observed variations of rayleigh and love wave amplitudes this is the probable explanation for the instability of q estimates made from surface waves other source regions producing large surface wave amplitude anomalies include japan and southeastern alaska

new dinosaur ichnotaxa from the early jurassic of the holy cross mountains poland abstract the numerous ornithopod tracks discovered during the last four years in the holy cross mts allow the identification of two new ichnospecies anomoepus pienkovskii ichnosp nov and moyenisauropus karaszevskii ichnosp nov the moyenisauropodid structure indicates that the trackmakers may well have been hitherto unknown forms of the earliest iguanodontids newly discovered theropod footprints grallator grallator zvierzi ichnosp nov and grallator eubrontes soltykovensis ichnosp nov supplement knowledge of the early jurassic terrestrial fauna of poland the majority of the tracks occurring in the gliniany las exposure upper hettangian were left by dinosaurs which occupied the margins of a lagoonal environment the other footprints discovered in the soltykow lower hettangian outcrop were left by carnosaurs walking across the fluvial plain

temporal changes in shear wave splitting during an earthquake swarm in arkansas shear wave splitting has been observed in seismograms of two aftershock and one foreshock sequence recorded over 12 days by a local network of nine three component digital seismometers during the 1982 enola arkansas earthquake swarm polarizations of the faster split shear wave show alignments within the shear wave window which correlate with the regional stress field the time delay between split shear waves appears to increase before and to decrease at or after the time of each main shock this behavior is similar to observations before and after a m 6 0 event near the anza seismic gap southern california and may correspond to variations in crack geometry caused by changes in the stress field before and after the earthquakes there are indications that the decrease in delay may occur a few hours before the main shock and could be a possible precursor for earthquake prediction

coal deposits in the front ranges and foothills of the canadian rocky mountains southern canadian cordillera abstract canada has the fifth largest inventory of coal resources in the world more than one third of canada s resources currently favourable for exploitation occur in the southern canadian rocky mountains with major deposits in the front ranges inner foothills and outer foothills physiographic provinces in the front ranges major deposits of metallurgical and thermal high volatile bituminous to semi anthracite coal occur in the late jurassic early cretaceous mist mountain formation in the inner foothills of northeastern british columbia and west central alberta significant resources of metallurgical and thermal medium and low volatile bituminous coal occur in early cretaceous strata of the gething aptian and gates albian formations in the outer foothills resources of thermal high volatile bituminous coal occur in late cretaceous and paleocene strata of the belly river campanian coalspur maastrichtian paleocene and paskapoo paleocene formations the major coal deposits of the front ranges and inner foothills accumulated within the coastal plains of the fernie and moosebar clearwater seas respectively shorelines prograded to the north and northeast into a foreland basin that evolved in advance of and in response to the evolving columbian orogen in the outer foothills coal deposits of the belly river formation originated within prograding coastal plains during the withdrawal of the pakowki sea the major coal deposits of the coalspur and paskapoo formations accumulated in the alluvial plain environments of the foreland basin during the laramide orogeny coal measures of the southern canadian rocky mountains were variably folded and faulted during the laramide orogeny late cretaceous eocene structural deformation has significantly affected the mineability and quality of the coals many of the coal seams are sheared structurally thickened or thinned and repeated by thrust faults or truncated by normal faults shearing of the seams in adjacent hanging and footwall strata has led locally to pronounced oxidation resulting in weak coal pillars and roofs in underground mines faulting and folding has partitioned many coal deposits into discrete structural domains of varying style and complexity each of which can present a unique challenge in designing optimum coal extraction methods the variation in coal rank in the southern canadian rocky mountains mainly reflects the preorogenic pre laramide depth of burial in some areas however there is evidence for syn and post orogenic coalification resulting from the emplacement of thick overthrust sheets and or deposition of thick tertiary molasse most of which has been subsequently eroded with few exceptions coals of the southern canadian rocky mountains are characterized by low sulphur contents

late cretaceous campanian actinopterygian fishes from the kristianstad basin of southern sweden although a diverse range of aquatic vertebrates are documented from the upper cretaceous mid campanian marine strata of the kristianstad basin in southern sweden only chondrichthyans and marine amniotes have been described in detail to date in contrast coeval actinopterygians are virtually unreported yet their remains are extremely abundant at most sampled localities a comprehensive assessment of these fossils has identified the first late cretaceous actinopterygian fauna from the fennoscandian shield incorporating indeterminate lepisosteids the durophagous pycnodontid anomoeodus subclavatus the predatory pachycormid protosphyraena sp a large ichthyodectid pachyrhizodontids resembling pachyrhizodus the enchodontid enchodus cf gladiolus and indeterminate small teleosts these taxa are diagnosed mainly from isolated teeth and scales implying substantial taphonomic loss prior to burial moreover the prolific recovery of actinopterygian skeletal remnants in recent excavations suggests that historical collecting biases rather than ecological paucity have contributed to their under representation in the swedish cretaceous record palaeobiogeographically the kristianstad basin actinopterygians show compositional resemblance to assemblages from the northern european platform and the western interior seaway of north america advocating distributional communication across the boreal proto atlantic ocean

age distribution of cinder cones within the bandas del sur formation southern tenerife canary islands the quaternary bandas del sur formation in the south of tenerife comprises a complex sequence of pyroclastic rocks and lavas in contrast to the nw and ne rift zone on tenerife the s rift zone comprises a number of characteristics with respect to the morphological features eruption cyclicity and the geochemistry of the volcanic deposits various flank eruptions of the las canadas volcano associated with basaltic lavas and the formation of cinder cones within the bandas del sur are important volcanic units for understanding the explosive volcanic cycles during the pleistocene on tenerife a number of palaeomagnetic studies as well as major and trace element geochemistry and two radio isotope dates k ar have been carried out on prominent cinder cones in order to discover their stratigraphic position combining our results with previous k ar data the cones and lavas can be subdivided into three stratigraphic units the first unit contains cinder cones with reverse magnetization and y nb ratios between 0 37 and 0 41 cinder cones which belong to the second unit show normal magnetization and y nb ratios of c 0 948 0 779 ma and 0 323 0 300 ma these units define volcanic cycles ending in violent plinian eruptions the third and youngest unit possibly marks the beginning of a further volcanic cycle that started c 0 095 ma ago

the dynamical and thermal structure of deep mantle plumes abstract if the interpretation of the d layer at the base of the mantle as a thermal boundary layer with a temperature increment in the order of 800 k is correct then the formation of deep mantle plumes to vent material from it appears inevitable we demonstrate quantitatively that the strong temperature dependence of viscosity guides the upward flow into long lived chimneys that are 20 km in diameter near the base of the mantle and decrease in width with progressive upward softening and partial melting of plume material the speed of flow up the axis of the plume is correspondingly fast 1 6 m y 1 at the base and 4 8 m y 1 at 670 km depth thermal diffusive spreading of a heated plume is compensated by a slow horizontal convergence of mantle material toward the chimney in response to the lower pressure there this convergence which contributes only a small increment to the flux of material up the plume also serves to throttle the flow in the chimney the global plume mass flux necessary to transport 1 6 10 12 w of core heat upward through the mantle is 1 8 10 6 kg s 1 at its base plume material is probably still significantly below its solidus or eutectic temperature but substantial partial melting is very likely as it rises we speculate that a small fraction of this fluid component eventually emerges at the surface in hot spots with the fate of the remainder being unknown the behaviour and properties of d and of plumes are closely coupled not only are plumes a necessary consequence of a thermal boundary layer but their existence is impossible without that layer

238u 230th 226ra fractionation in historical lavas from the azores long lived source heterogeneity vs metasomatism fingerprints abstract this study reports 238u 230th 226ra nuclides measured by mass spectrometry trace elements and 87sr 86sr isotopes on historical alkali basalts from the azores region the 230th 232th activity in the alkali basalts spans a range from 0 897 in sao miguel to 1 382 in terceira island that is almost as large as the global variation of mid ocean ridge basalts morb and oceanic island basalts oib the 230th 238u activity 10 40 th u 2 92 3 74 and the 87sr 86sr 0 70354 0 70467 also display large variations the 226ra 230th activity varies from 0 84 in sao miguel to 1 60 in pico island samples from pico faial and terceira islands are found to plot on the negative 230th 238u vs 226ra 230th correlation defined by the 1730 1736 eruption of lanzarote canary islands sigmarsson et al earth planet sci lett 162 1998 137 except for the sample from sao miguel island we propose that the negative correlation reflects a mixing between two end member melts one displaying a low 230th 238u and a high 226ra 230th and the other end member displaying a high 230th 238u and a low 226ra 230th numerical model suggests that the high 226ra low 230th excesses end member represented by samples from pico island can be explained by partial melting of a garnet lherzolite the other end member represented by the terceira lava is shown to result from the interaction of low degree melts with the metasomatized mantle containing phlogopite phlogopite crystals in contact with a melt enriched in 226ra and ba have a 226ra 230th 1 and high ba th because of crystal affinities for ra and ba relative to th and u after 8000 years however the unsupported 226ra excess will have decreased down to 0 as phlogopite displays little amount of u and th so during the process of interaction with phlogopite crystals low degree melts formed in the garnet stability field that are characterized by high 230th 238u 226ra 230th and ba th will loose the 226ra excess scavenged by phlogopite while the 230th 238u and ba th will remain unaffected one finds that this process may be valid over 250 years maximum so that only the first interacting melts may preserve a high 230th 238u low 226ra 230th activity on sao miguel island it is shown that the low 230th 238u while the source is clearly enriched in th cannot be explained by a lack of garnet in the mantle neither by a higher degree of melting the 226ra deficit 15 and low ba th and sr th are explained by partial melting of an enriched mantle in the presence of phlogopite

azimuthal anisotropy in the earth from observations of sks at geoscope and nars broadband stations abstract we have analyzed observations of low frequency sks waves recorded on horizontal components at several broadband stations of the geoscope and nars arrays splitting of sks is consistently observed and in good agreement with a hypothesis of azimuthal anisotropy due to transverse anisotropy with a horizontal axis in the upper mantle beneath the receivers we have designed an inversion method which takes advantage of observations made simultaneously at different azimuths and which permits us to obtain estimates of the direction of fast axis of anisotropy as well as the time delay between the orthogonal quasi shear waves in general the directions of fast velocity obtained both for stations around the atlantic and around the pacific appear to be related to directions of past and present plate motions

the dynamics of plume ridge interaction 2 off ridge plumes a variety of geophysical and geochemical evidence indicates that ascending mantle plumes can interact with ocean ridges located up to 1400 km away i investigate the dynamics of this interaction using a simple model in which a point source with volume flux q analogous to a plume stem releases buoyant fluid into a viscous corner flow driven by the divergence of rigid surface plates with thickness kx u 1 2 where u is the half spreading rate the point source is located at a distance xp from the ridge and ridge migration is neglected the buoyant fluid forms a thin sublithospheric layer whose thickness s x y satisfies a nonlinear advection diffusion equation describing the balance of advection by the corner flow buoyancy driven self spreading flow toward the ridge along the sloping base of the lithosphere and continuous accretion into the lithosphere numerical solutions of this equation yield scaling laws for the lateral extent w waist width of plume material along the ridge the fraction r of the plume flux that crosses the ridge and the maximum value of xp beyond which interaction ceases the sloping base of the lithosphere has only a minor few tens of percent influence on these quantities which are determined principally by the balance of advection and self spreading an extension of the model to include plume induced lithospheric thinning shows that this process increases the waist width by an amount of order 10 finally the model provides a new explanation for the observation that plumes interact primarily with ridges that are migrating away from them rather than toward them

splendid and seldom isolated the paleobiogeography of patagonia the idea that south america was an island continent over most of the cenozoic during which its unusual mammalian faunas evolved in isolation is outstandingly influential in biogeography although large numbers of recent fossil discoveries and related advances require that the original isolation concept be significantly modified it is still repeated in much current literature the persistence of the idea inspired us to present here an integrated paleobiogeographic account of mammals reptiles and plants from the jurassic to the paleogene of patagonia which has by far the richest fossil record on the continent all three groups show distribution patterns that are broadly consistent with south america s long separation history first from laurasia by the late jurassic then from africa and india madagascar during the late early cretaceous and finally from antarctica and australia during the early middle eocene after which isolation finally commenced we highlight areas of promising future research a

the terceira rift as hyper slow hotspot dominated oblique spreading axis a comparison with other slow spreading plate boundaries abstract we suggest the 550 km long terceira rift tr azores plateau is the world s slowest spreading hyper slow 4 mm a plate separation 2 3 3 8 mm a perpendicular to oblique axial segments organized accreting plate boundary in its slightly sinuous ca 300 km radius of curvature axial trace its oblique spreading angles ca 40 65 and in frequency and first motions of earthquakes the tr resembles better known ultra or super slow spreading ridges e g gakkel and southwest indian ridges interpreted simply as volcanically unfilled rift valley segments the inter island basins e g the 3200 m deep hirondelle basin are slightly wider 30 60 km but not significantly deeper 1000 2200 m than the mid atlantic ridge mar median valley 20 28 mm a 10 n 53 n however along axis segmentation wavelengths ca 100 km are double those along the central mar but make tr comparable to the ultra slow 15 16 mm a southwest indian and gakkel 7 13 mm a ridges if this segmentation wavelength reflects rayleigh taylor instabilities the viscosity contrast between the overlying axial lithosphere and the partial melt zones is about an order of magnitude greater at ca 4 16 mm a than at 20 30 mm a the tr differs dramatically from ultra slow ridges only in the large amplitude of along strike topography 2000 4000 m 4200 m total variation owing perhaps to a copious melt flux from the azores hotspot combined with a spreading rate determined greater axial flexural strength and plate thickness and slower export of volcanics from the rift axis the probable tr youth ca 1 ma requiring less than 4 km new oceanic crust suggests lack of steady state spreading conditions which may explain the published gravity evidence against tr spreading absolute plate motions support the creation of the azores plateau by successive ne jumps of the rift axis to maintain its position over a fixed hotspot

production of jurassic rhyolite by anatexis of the lower crust of patagonia abstract the mid jurassic marifil and chon aike volcanic rocks of eastern patagonia are part of one of the largest silicic igneous provinces known rb sr geochronology indicates eruptive ages of 175 190 ma for the marifil complex mostly toarcian aalenian the majority of the rocks are isotopically uniform with initial 87sr 86sr 0 7067 0 0003 and endt 4 2 primary magmas of andesitic composition were generated by partial melting of mafic grenvillian lower crust indentified by depleted mantle model ages of 1150 1600 ma lower crustal pyroxene granulite xenoliths can be modelled as residual jurassic source although they may alternatively be co genetic cumulates the dacite rhyolite suite formed by crystal liquid fractionation processes from the primary andesites involving multistage crystallization and re melting during magma ascent with the later stages of evolution being explicable by fractional crystallization of plagioclase amphibole and accessory minerals the province represents large scale lower crustal reworking associated with the unique tectonic and igneous environment of gondwana break up

defining the morphological quality of fossil footprints problems and principles of preservation in tetrapod ichnology with examples from the palaeozoic to the present abstract the morphology of fossil footprints is the basis of vertebrate footprint ichnology however the processes acting during and after trace fossil registration which are responsible for the final morphology have never been precisely defined resulting in a dearth of nomenclature therefore we discuss the concepts of ichnotaphonomy ichnostratinomy taphonomy biostratinomy registration and diagenesis and describe the processes acting on footprint morphology in order to evaluate the morphological quality of tetrapod footprints we introduce the concept of morphological preservation which is related to the morphological quality of footprints m preservation acronym mp and distinguish it from physical preservation p preservation acronym pp which characterizes whether or not a track is eliminated by taphonomic and diagenetic processes m preservation includes all the morphological features produced during and after track registration prior to its study and may be divided into substages ichnostratinomic registrational taphonomic stratinomic diagenetic moreover we propose an updated numerical preservation scale for m preservation it ranges from 0 0 worst preservation to 3 0 best preservation intermediate values may be used and specific features may be indicated by letters in vertebrate footprint ichnotaxonomy we regard the anatomy consistent morphology and to a lesser extent the trackway pattern as the only acceptable ichnotaxobases only footprints showing a good morphological preservation grade 2 0 3 0 are useful in ichnotaxonomy whereas ichnotaxa based on poor morphological preservation grade 0 0 1 5 are considered ichnotaphotaxa nomina dubia characterized by extramorphologies we applied the preservation scale on examples from the palaeozoic to the present time including three ichnotaphotaxa and 18 anatomy consistent ichnotaxa morphotypes attributed to several vertebrate footprint producers results indicate the utility feasibility and suitability of this method for the entire vertebrate footprint record in any lithofacies strongly recommending its use in future ichnotaxonomic studies

seismic determination of elastic anisotropy and mantle flow when deformed many rocks develop anisotropic elastic properties on many seismic records a long period 100 to 250 seconds quasi love wave with elliptical polarization arrives slightly after the love wave but before the rayleigh wave mantle anisotropy is sufficient to explain these observations qualitatively as long as the fast axis of symmetry is approximately horizontal quasi love observations for several propagation paths near pacific ocean subduction zones are consistent with either flow variations in the mantle within or beneath subducting plates or variations in the direction of fossil spreading in older parts of the pacific plate

the chon aike province of patagonia and related rocks in west antarctica a silicic large igneous province the field occurrence age classification and geochemistry of the mesozoic volcanic rocks of patagonia and west antarctica are reviewed using published and new information dominated by rhyolitic ignimbrites which form a bimodal association with minor mafic and intermediate lavas these constitute one of the largest silicic igneous provinces known equivalent in size to many mafic lips diachronism is recognized between the early middle jurassic volcanism of eastern patagonia marifil and chon aike formations and the middle jurassic earliest cretaceous volcanism of the andean cordillera el quemado ibanez and tobifera formations this is accompanied by a change in geochemical characteristics from relatively high zr and nb types in the east to subalkaline arc related rocks in the west although the predominance of rhyolites remains a constant factor all of the associated mafic rocks are well fractionated compared to direct mantle derivatives petrogenetic models favour partial melting of immature lower crust as a result of the intrusion of basaltic magmas possibly with some hybridisation of the liquids and subsequent fractionation by crystal settling or solidification and remelting the formation of large amounts of intracrustal silicic melt acted as a density barrier against the further rise of mafic magmas which are thus rare in the province

the origin and early radiation of dinosaurs abstract dinosaurs were remarkably successful during the mesozoic and one subgroup birds remain an important component of modern ecosystems although the extinction of non avian dinosaurs at the end of the cretaceous has been the subject of intense debate comparatively little attention has been given to the origin and early evolution of dinosaurs during the late triassic and early jurassic one of the most important evolutionary radiations in earth history our understanding of this keystone event has dramatically changed over the past 25 years thanks to an influx of new fossil discoveries reinterpretations of long ignored specimens and quantitative macroevolutionary analyses that synthesize anatomical and geological data here we provide an overview of the first 50 million years of dinosaur history with a focus on the large scale patterns that characterize the ascent of dinosaurs from a small almost marginal group of reptiles in the late triassic to the preeminent terrestrial vertebrates of the jurassic and cretaceous we provide both a biological and geological background for early dinosaur history dinosaurs are deeply nested among the archosaurian reptiles diagnosed by only a small number of characters and are subdivided into a number of major lineages the first unequivocal dinosaurs are known from the late carnian of south america but the presence of their sister group in the middle triassic implies that dinosaurs possibly originated much earlier the three major dinosaur lineages theropods sauropodomorphs and ornithischians are all known from the triassic when continents were joined into the supercontinent pangaea and global climates were hot and arid although many researchers have long suggested that dinosaurs outcompeted other reptile groups during the triassic we argue that the ascent of dinosaurs was more of a matter of contingency and opportunism dinosaurs were overshadowed in most late triassic ecosystems by crocodile line archosaurs and showed no signs of outcompeting their rivals instead the rise of dinosaurs was a two stage process as dinosaurs expanded in taxonomic diversity morphological disparity and absolute faunal abundance only after the extinction of most crocodile line reptiles and other groups

hunting for azimuthal anisotropy beneath the pacific ocean region lateral variations in azimuthal anisotropy cause significant waveform anomalies in long period surface waves 8 mhz suggesting lateral variations with wavelength twice the spacing of fracture zones in the north central pacific

plutonic processes in transitional oceanic plateau crust structure age and emplacement of the south rallier du baty laccolith kerguelen islands

40ar 39ar dating of the jurassic volcanic province of patagonia migrating magmatism related to gondwana break up and subduction abstract the mesozoic large igneous province lip of patagonia southern south america which is one of the largest silicic provinces on earth has been investigated by the 40ar 39ar method twenty seven ages considered as valid including twenty plateau ages show that the volcanic activity ranging from 187 to 144 ma occurred between and contemporaneously with the initial break up of gondwana starting with the karoo antarctic tasmanian kat flood basalt province in the east and a subduction in the west the data display a regular decreasing of ages from the ene 187 ma to the wsw 144 ma along about 650 km apparently related to the tectonic structure in half grabens oriented nnw sse the good fitting of this trend with the opening of the rocas verdes sarmiento marginal basin favors a space time evolution of this continental volcanism culminating towards the ssw in a continental disruption behind the magmatic arc the observed age progression of volcanism may be the result of the variations of the physical characteristics of the subduction the spreading and thermal effect of the kat plume may have an additional effect and also could account for the unusually large volume of magma

changes in shear wave splitting at anza near the time of the north palm springs earthquake changes in shear wave splitting are observed at knw before and after the m 6 north palm springs earthquake of july 8 1986 knw is a station of the anza seismic network monitoring the anza seismic gap on the san jacinto fault southern california the gradual increase in the delays between the split shear waves over 3 years at knw reported by peacock et al 1988 ended in june 1986 the further 2 years of observations analyzed here show that the behavior of the delays changed abruptly near the time of the north palm springs earthquake 33 km north of knw peacock et al demonstrated that the increase in delays could be simulated by increasing the aspect ratio of stress aligned fluid filled inclusions and speculated that this increase might be the result of a buildup of stress before an impending earthquake the new data appear to confirm this speculation but the temporal variations require a more complex interpretation although they still suggest that the changes in shear wave splitting are caused by earthquake induced stress changes to the fluid filled inclusions throughout the rockmass central to interpretation of temporal changes in shear wave splitting is the well established existence throughout at leastmore the uppermost 10 to 20 km of the crust of small fluid filled cracks microcracks and pores the existence of such inclusions introduces a compliant quality to otherwise stiff crustal rock the authors term these distributions of inclusions extensive dilatancy anisotropy or eda and the individual inclusions eda cracks because although they may include a wide range of shapes many of the seismic properties can be simulated by distributions of thin parallel cracks less