bioturbation and the upward movement of sediment particles and archaeological materials comments on bueno et al the literature on bioturbation both from the biological and archaeological points of view is growing steadily available data suggests that ants and termites are responsible for the upward movement of soil sediment particles and archaeological materials it is argued that this could be the most parsimonious explanation for the stratigraphic data presented by bueno et al 2013 given the size range of displaced materials and the environmental setting composed of a sandy soil in a savannah region

structure and seismic response of extended continental crust stochastic analysis of the strona ceneri and ivrea zones italy a two dimensional stochastic seismic model of the crustal cross section exposed in the strona ceneri and ivrea zones northern italy was derived from geologic maps and petrophysical data with techniques used in microfabric analysis the model has a layered self affine structure which agrees with the intrinsic scale independence of geologic phenomena synthetic seismograms from this model replicate many pertinent features observed in deep seismic reflection data and allow insight into crustal structure 1 reflectivity depends on the lithological populations present and their distribution within a crustal unit 2 transparent zones within the reflective lower crust can arise from metamorphic reactions 3 the transition from upper to lower crust may be a change in small scale seismic fabric rather than a first order seismic discontinuity

enstatite jadeite join and its role in the earth s mantle phase relations on the enstatite jadeite join were experimentally determined at solidus temperatures and 90 152 kb and at 1400 2050 c 175 219 kb with a split sphere anvil apparatus ussa 2000 new findings include immiscibility in garnet and determination of the stability of naalsio4 calcium ferrite structure with stishovite a thermodynamic model for the enstatite jadeite join was developed to calculate a complete phase diagram for the join at 500 2500 c and 0 270 kb the results indicate that the two major discontinuities in the earth s mantle at 400 and 670 km depths could correspond respectively to the formation and the breakdown of garnet with a pyroxene composition a model for a chondritic upper mantle is proposed in which large scale chemical and mineral layering was produced by fractionation of liquidus phases in a magma ocean solidification was completed at 400 km depth by crystallization of sodium enriched residual melts which produced a pyroxene layer at 300 400 km depths

mineral inclusions in diamonds associations and chemical distinctions around the 670 km discontinuity three new mineral associations have been discovered within diamonds from the juina district of brazil these include a previously unrecorded na al mg fe sio3 phase associated with ferropericlase and the tetragonal almandine pyrope phase tapp also reported are an association of corundum with aluminous pyroxene and an olivine composition phase associated with ferropericlase the minerals in each association often occurred within the same diamonds in addition to being recovered from individual diamonds in different combinations high pressure experimental data indicate that these associations formed at different depths within a region ca 60 km on either side of the upper mantle lower mantle boundary mineral compositions show that for the regions sampled the deep transition zone and lower mantle are chemically distinct and inhomogeneous importantly in the shallow lower mantle al is not solely accommodated within perovskite structured mg fe sio3 as some recent experimental studies have suggested

a seismic geotraverse across the iberian variscides orogenic shortening collisional magmatism and orocline development 1 a crustal geotraverse through the iberian variscides is presented by integrating the available geological and seismic profiling data different modes of orogenic shortening are identified with varying degrees of coupling between upper and lower crust in northern and southern regions of the geotraverse a decoupling in the middle crust permits the lower crust to subduct underthrust thus compensating for strong upper crustal shortening this behavior does not result in great crustal thickening except in sectors of crustal underthrusting in southern central iberia moderate upper crustal shortening is due to a mechanically strong lower crust impeded to subduct underthrust in this region shortening is partitioned between upper and lower crust deformation being distributed in the upper crust while localized at major fault zones in the lower crust finally the central region of the geotraverse northern central iberia shows a coupled crustal deformation having given way to the largest orogenic thickening in the iberian variscides the thermal maturity of this much thickened crust originated voluminous crustal melting and concomitant normal fault detachments developed while shortening dominated in other regions theoretical models suggest that compressive stresses may prevail in the lower crust beneath the extending upper crust thus explaining the efficient syncollisional exhumation in this part of the orogen a particular feature of the iberian variscan geotraverse is the great importance of out of section mass movements mainly left lateral shear zones concentrated in two suture boundaries which displaced to the nw present coordinates central and northern iberia with respect to southern iberia

elasticity of a majorite pyrope solid solution the elastic properties of a solid solution consisting of 59 mole percent pyropic garnet and 41 mg sub 4 si sub 4 o sub 12 majorite a high pressure form of pyroxene have been measured by brillouin spectroscopy under ambient conditions values of the adiabatic bulk modulus k sub s 164 plus minus 15 gpa and shear modulus g 89 4 plus minus 3 7 gpa are similar to those for low pressure aluminosilicate garnets the enstatite majorite reaction is characterized by a large 49 increase in k sub s and a much smaller 13 increase in g the properties of low pressure garnets suggest that the contrast in shear moduli for this reaction is probably larger in ca rich systems taken at face value the stp properties of these phases imply that large quantities of ca rich clinopyroxene are needed in order to satisfy seismologically determined shear modulus gradients in the transition zone this suggestion is however subject to considerable uncertainties in the pressure and temperature derivatives of elastic properties for mantle minerals and the velocity structure of the transition zone

imaging the crustal structure of the central iberian zone variscan belt the alcudia deep seismic reflection transect alcudia is a 230 km long vertical incidence deep seismic reflection transect acquired in spring 2007 across the southern central iberian zone part of the pre mesozoic gondwana paleocontinent of the variscan orogen of spain the carefully designed acquisition parameters resulted in a 20 s twtt deep 60 90 fold high resolution seismic reflection transect the processed image shows a weakly reflective upper crust the scarce reflectivity matching structures identified at surface a thick highly reflective and laminated lower crust and a flat moho located at 10 s twtt 30 km depth the transect can be divided into three segments with different structural styles in the lower crust in the central segment the lower crust is imaged by regular horizontal and parallel reflectors whereas in the northern and southern segments it displays oblique reflectors interpreted as an important thrust north and tectonic wedging involving the mantle south the alcudia seismic image shows that in an intracontinental orogenic crust far from the suture zones the upper and lower crust may react differently to shortening in different sectors which is taken as evidence for decoupling the interpreted structures as deduced from surface geology and the seismic image show that deformation was distributed homogeneously in the upper crust whereas it was concentrated in wedge thrust structures at specific sectors in the lower crust the seismic image also shows the location of late variscan faults in spatial association with the lower crustal thickened areas

lithospheric structure in northwestern canada from lithoprobe seismic refraction and related studies a synthesis the snorcle refraction wide angle reflection r war experiment snore 97 included four individual lines along the three transect corridors a combination of snore 97 results with those from earlier studies permits generation of a 2000 km long lithospheric velocity model that extends from the archean slave craton to the present pacific basin using this model and coincident near vertical incidence nvi reflection data and geological information an interpreted cross section that exemplifies 4 ga of lithospheric development is generated the velocity structural models correlate well with the reflection sections and provide additional structural compositional and thermal constraints geological structures and some faults are defined in the upper crust at a larger scale the seismic data identify a variety of orogenic styles ranging from thin to thick skinned accretion in the cordillera and crustal scale tectonic wedging associated with both paleoproterozoic and mesozoic collisions models of poisson

elasticity of majorite and a majorite pyrope solid solution to high pressure implications for the transition zone 1 high seismic velocity gradients in the transition zone have been attributed to large pressure derivatives of the elastic moduli of transition zone minerals such as majorite garnet here we present brillouin scattering measurements of the elasticity of polycrystalline mg majorite mj100 mg4si4o12 and a mj50py50 majorite pyrope solid solution to pressures similar to those at the top of the transition zone 15 1 1 gpa and 12 8 1 gpa respectively the pressure derivatives of the adiabatic bulk ks and shear moduli of both mj50py50 and mj100 are 4 2 3 and 1 4 2 respectively and are equal to those of pyrope within the experimental uncertainties we conclude that neither the adiabatic compression of majorite garnet nor any other likely transition zone phase is able to produce the high velocity gradients observed seismically high velocity gradients are consistent with gradual transformations between minerals with very different elastic properties the transformation of 25 or more of clinopyroxene into majorite above 520 km and the formation of ca silicate perovskite below 520 km could produce the observed seismic gradients

elastic moduli of jadeite enstatite majorite 1 the adiabatic bulk ks and shear g moduli of a polycrystalline majorite garnet solid solution with composition na0 92mg2 08 mg0 02al1 06si0 92 si3o12 were measured at ambient conditions by brillouin spectroscopy ks and g were found to be 171 6 3 5 gpa and 103 5 2 0 gpa respectively assuming a linear dependence of the elastic moduli on composition for the mg2si2o6 enstatite majorite en mj naalsi2o6 jadeite majorite jd mj join the calculated ks and g of the fictive jd mj end member are 178 and 125 gpa respectively at ambient conditions the shear velocity change associated with the pyroxene to majorite transition increases dramatically with increasing na content in the system in contrast there is virtually no shear velocity increase associated with the pyroxene to majorite transition in mgsio3 if this relationship holds at high pressures and temperatures it suggests that for mineral assemblages containing an abundance of large radius cations such as ca and na the pyroxene garnet reaction will produce higher shear velocity gradients than assemblages that are relatively deficient in these elements such chemical effects could play a significant role in explaining high seismic velocity gradients in the transition zone

sound velocities and elastic properties of fe bearing wadsleyite and ringwoodite the sound velocities and single crystal elastic moduli of phase wadsleyite and phase ringwoodite of mg fe 2sio4 with fe fe mg ratios of 0 075 and 0 09 respectively have been determined at ambient conditions by brillouin spectroscopy both compressional and shear wave aggregate velocities decrease with increasing fe content in both phases but the magnitude of this decrease is different for the two phases the adiabatic bulk modulus ks of fe bearing mg2sio4 ks 170 2 gpa is indistinguishable from that of the mg end member within experimental uncertainty whereas ks of mg fe 2sio4 increases rapidly with increasing iron content the shear moduli of both phases decrease with increasing fe content our measurements indicate that the velocity and impedance contrasts between olivine and mg fe 2sio4 are independent of fe content for mg rich compositions but the contrast for the mg fe 2sio4 transition increases significantly with increasing fe content the new data support a previous estimate of 40 10 for the olivine content of the upper mantle and suggest that less than 50 mg fe 2sio4 is sufficient to account for the observed impedance contrasts at depths of both 410 km and 520 km unless the effect of fe on elastic properties is accounted for it is difficult to account for both the 410 and 520 km discontinuities with a single olivine content

seismic velocity gradients in the upper mantle the radial velocity gradients for p and s waves in the upper mantle are of considerable interest for petrological studies of the upper mantle but are difficult to constrain directly comparison of three different styles of velocity model constructed within a common parametrisation to give a good fit to the travel times of p and s waves to 30 provide a useful framework for constructing bounds on the radial gradients for depths from 250 1000km a somewhat subjective set of bounds are suggested for the velocity gradients and velocity contrasts at the major discontinuities in an average mantle one of the most significant factors affecting the estimation of radial gradients is the presence of small scale heterogeneity in the mantle modest heterogeneity around 1 percent perturbations on scale lengths of about 300km can give rise to horizontal velocity gradients which can overwhelm the radial gradients in the shallower parts of the mantle and still be a quarter of the size of the radial gradients at greater depths however such scales of heterogeneity are unlikely to simulate the presence of additional upper mantle discontinuities for ray paths travelling near vertical

a simple model of the 1982 83 californian el nino steric height steric height anomaly sea level and sea level anomaly show that the 1940 41 and the 1982 83 californian el nino events were resonant responses of the california current to the expansion and intensification of the aleutian low and decrease in strength of the north pacific high in both cases the subsurface anomalies were dynamically produced by onshore transport of subarctic water and a downward tilt of the inshore thermocline sea surface temperature anomalies however resulted from thermodynamic as well as dynamic processes most previous californian el nino or anti el nino events probably were resonant or anti resonant responses of the seasonal cycle of the california current to anomalous large scale atmospheric forcing

composition of the upper mantle geophysical tests of two petrological models the elastic properties of candidate mantle phases are used to test the viability of olivine rich pyrolitic and cao al 2o 3 rich eclogitic assemblages for the mantle high temperature adiabats for each phase of interest are constructed and compared to mantle seismic properties both pyrolitic and eclogitic assemblages satisfy the seismic properties between 200 and 400 km between 400 and 670 km depth an eclogitic assemblage yields a superior match to velocities and velocity gradients the 400 km seismic discontinuity may represent a chemical boundary between pyrolite and picritic eclogite piclogite or phase transformations in the olivine orthopyroxene components of a piclogitic assemblage containing about 16 olivine high velocity gradients in the transition zone may be explained by the transformation of ca rich cpx to majorite garnet seismic properties at the top of the lower mantle are consistent with pyrolite piclogite or perovskite implying that the 670 km discontinuity may be a chemical boundary

how the crust meets the mantle lithoprobe perspectives on the mohorovicic discontinuity and crust mantle transition application of regional geophysical and geological methods throughout two decades of canada s lithoprobe project provides new opportunities to analyze the mohorovicic discontinuity moho and crust mantle transition the transect format employed during lithoprobe in which 10 specified regions of canada were targeted for approximately a decade each between 1984 and 2003 permitted teams of scientists to focus on geological geophysical and tectonic issues for each transect as a primary objective was to enhance knowledge of the structure of the crust and lithosphere an obvious target in each transect was the nature and origin of the moho and crust mantle transition accordingly the combined results provide new perspectives on the moho and the relationship of the moho to the crust mantle transition perhaps the most important result is that the continental geophysical moho is a deceptively simple feature it has a variety of signatures at different scales that preclude a single universally applicable interpretation in methods that provide large scale information such as regional seismic studies it is a relatively abrupt refraction velocity contrast that often displays a dramatic downward decrease in seismic reflectivity however its origin in a geological or tectonic sense is perhaps best determined by careful analyses of structural details near the geophysical moho which are complex and varied in some areas within canada it appears that the geophysical moho may be old and perhaps remains from the time the crust formed in other areas it appears to be a relatively young feature that was superimposed onto older crustal fabrics

transformation of enstatite diopside jadeite pyroxenes to garnet the high pressure stability of enstatite en diopside di jadeite jd pyroxenes has been investigated experimentally with a split sphere anvil apparatus ussa 2000 on the enstatite pyrope join the compositions of garnet coexisting with enstatite were determined at 100 165 kbar and 1450 1850 c the results indicate complete solubility between enstatite and pyrope in the system cao mgo al2o3 sio2 cmas the compositions of coexisting pyroxenes and garnet were determined at 100 165 kbar and 1250 1750 c at 157 kbar 1650 c garnet with the composition en79di21 mol forms on the en di join in the system na2o mgo al2o3 sio2 nmas the compositions of coexisting pyroxenes and garnet were determined at 60 160 kbar and 1200 1850 c on the en jd join the first garnet has the composition en48jd52 at 135 kbar 1650 c and en53jd47 at 140 kbar 1500 c on the di jd join the first garnet with the composition di63jd37 forms around 170 kbar 1650 c in the en di jd system the first appearance of garnet with the composition en42di9jd49 is estimated at 133 kbar 1650 c the new pyroxene with the composition namg0 5si2 5o6 napx transforms to garnet at 154 kbar 1650 c the experimental results indicate that the transformation of a twopyroxene assemblage to garnet and residual pyroxene in the en di jd system could occur at pressures consistent with the 400 km seismic discontinuity and in a pressure interval of 0 3 kbar

lithospheric folding in iberia integration of stress indicator data gravity data crustal kinematics data and analysis of topography and recent vertical motions demonstrates the occurrence of consistently oriented spatial patterns of large scale alpine to recent intraplate deformation in iberia the inferred upper crustal and lithospheric deformation patterns and the timing of the associated expressions at or near the surface support the existence of a close coupling with plate boundary processes operating at the margins of iberia patterns of lithosphere and upper crustal folds are oriented perpendicular to the main axis of present day intraplate compression in iberia inferred from structural analysis of stress indicator data and focal mechanism solutions these findings suggest the presence of lithospheric folds with wavelengths compatible with theoretical predictions of folding wavelengths of variscan lithosphere stress induced intraplate deformation set up by plate interactions is compatible with indications for the absence of present day deep mantle lithosphere interactions inferred from seismic tomography

the eclogite garnetite transformation in the morb h2o system abstract to decipher phase relations of oceanic crust in the coldest slab at the mantle transition zone multi anvil experiments were conducted in the morb h 2 o system at pressures of 10 19 gpa and temperatures of 700 1500 c garnet and stishovite were recognized in all run charges above 15 gpa garnet drastically increases nasi na 2 msi 5 o 12 component m ca mg fe 2 jadeite occurs instead of omphacite na k hollandite containing 7 mol naalsi 3 o 8 and ca perovskite with 60 mol catio 3 were observed at p 17 gpa with decomposition of omphacite and increase of modal ratio of garnet there is a sharp increase of density at 440 km the density increase due to appearance of ca perovskite at 570 km is estimated approximately 100 km shallower than that of previous estimation

upper crustal seismic velocity heterogeneity as derived from a variety of p wave sonic logs sonic log measurements provide detailed 1 d information on the distribution of elastic properties within the upper crystalline crust at scales from about one metre to several kilometres 10 p wave sonic logs from six upper crustal drill sites in europe and north america have been analysed for their second order statistics the penetrated lithological sequences comprise archean volcanic sequences proterozoic mafic layered intrusions and precambrian to phanerozoic gneisses and granites despite this variability in geological setting tectonic history and petrological composition there are notable similarities between the various data sets after removing a large scale deterministic component from the observed velocity depth function the residual velocity fluctuations of all data sets can be described by autocovariance functions corresponding to band limited self affine stochastic processes with quasi gaussian probability density functions depending on the maximum spatial wavelength present in the stochastic part of the data the deterministic trend can be approximated either by a low order polynomial best fit or by a moving average of the original sonic log data the choice of the trend has a significant impact on the correlation length and on the standard deviation of the residual stochastic component but does not affect the hurst number for trends defined by low order polynomial best fits correlation lengths were found to range from 60 to 160 m whereas for trends defined by a moving average the correlation lengths are dominated by the upper cut off wavenumber of the corresponding filter regardless of the trend removed the autocovariance functions of all data sets are characterised by low hurst numbers of around 0 1 0 2 or equivalently by power spectra decaying as 1 k a possible explanation of this statistical uniformity is that sonic log fluctuations are more sensitive to the physical state in particular to the distribution of cracks than to the petrological composition of the probed rocks

the structure and nature of the moho beneath central iberia abstract the moho is the most conspicuous feature in the alcudia deep normal incidence and wide angle seismic reflection datasets acquired across the central iberia zone this discontinuity appears to be sub horizontal with a slight dip toward the center of the iberian peninsula beneath the tajo basin densely spaced wide angle seismic reflection data reveal conspicuous pmp and sms reflections in the shot records these reflections arriving over a 1 5 s time window and characterized by a relatively low frequency content are used to infer the internal structure and characteristics of this crustal boundary in an effort to place constraints on its nature beneath the studied area the wide angle shot records were processed in order to generate low fold stacks that reveal gradual deepening of moho pmp phases from 10 2 s twt 31 km in the central iberian zone to 11 8 s twt 36 km beneath the tajo basin the moho seismic signature was the main objective of a series of 1 d and 2 d synthetic modeling simulations reflectivity modeling was used as the 1 d modeling approach and an elastic finite difference scheme was used for the 2 d modeling the moho can be considered to be a self similar fractal heterogeneous media with a bimodal velocity distribution alternating crustal and mantle values with horizontal correlation lengths that range between 1 and 4 km and vertical correlation lengths that range from 0 2 to 1 km the depth of this boundary is most probably the result of late to post variscan re equilibration processes affecting a previously deformed and laminated lower crust the mechanisms that took part in this process might have differed to the north and south of the sampled central iberian zone being more thermally induced to the north near the central system processes leading to the layered structure of the moho boundary either tectonic or magmatic should be further investigated

shear wave modeling and poisson s ratio in the variscan belt of sw iberia in 2003 two wide angle reflection refraction seismic transects were acquired in the variscan belt of sw iberia the approximately 250 and 300 km long dense trace spacing transects revealed clear s wave arrivals in the shot gathers recorded by vertical component sensors in both transects first s wave arrivals sg and moho reflections sms are the most prominent phases that can be correlated from shot to shot sg is observed up to relatively large offsets and constrains the upper and middle crust s wave velocities the sms is seen from offset 0 18 s twtt to 150 km offset where it intercepts first s wave arrivals sg the upper mantle refracted phase sn is difficult to recognize although pms smp converted phases can be identified using a 2 d ray tracing approach two s wave velocity models for the crust of sw iberia were obtained these s wave velocity models complement the previous p wave velocity models and provide us with relatively well resolved poisson s ratio crustal sections for sw iberia the resulting poisson s ratio models present differences between tectonic zones at upper and middle crustal depths thus supporting the existence of different tectonic zones prior to the variscan collision the most noteworthy feature is the high poisson s ratio value over 0 28 coincident with high p wave velocity areas over 6 8 km s at midcrustal depths in order to constrain the possible crustal composition p wave velocities and poisson s ratios have been compared with published laboratory measurements on different crustal rock types this comparison indicates that the high p wave velocity and poisson s ratios are compatible with a mixture of mafic to ultramafic rock types alternating with felsic ones this result is consistent with the existence of mafic layered bodies in the middle crust in the same way that has been suggested by previous works in this area

experimental evidence for the origin of two kinds of inclusions in diamonds from the deep mantle abstract the conditions of origin for the type iii inclusions in diamonds from brazil hutchison thesis 1997 and the napx en inclusion from china wang and sueno miner j 18 1996 9 16 were experimentally determined using a split sphere anvil apparatus ussa 2000 the type iii inclusions formed at a minimum pressure and temperature of 25 gpa and 2000 c while the origin of the napx en inclusion was close to 23 gpa and 1900 c both determinations suggest that the temperature at the corresponding depths is about 300 c higher than predicted by most geotherms for a convecting mantle without a thermal boundary layer at 660 km both kinds of inclusions required rapid single stage transport by carbonate melt to the earth s surface which is consistent with the depths of origin for this melt greater than 660 km the unusual composition of the napx en inclusion is the result of metasomatism by carbonate melt enriched in na k and mg and depleted in si and al since this melt is not kimberlitic in composition exchange of material between the melt and the mantle was necessary for the melt to become kimberlitic by the time it reached the surface the resulting metasomatism taking place over a long period of time could cause major changes in the mineral and chemical composition and the structure of the earth s mantle and thus play an important role in its evolution