lithospheric structure in central eurasia derived from elevation geoid anomaly and thermal analysis we present new crustal and lithospheric thickness maps for central eurasia from the combination of elevation and geoid anomaly data and thermal analysis the results are strongly constrained by numerous previous data based on seismological and seismic experiments tomographic imaging and integrated geophysical studies our results indicate that high topography regions are associated with crustal thickening that is at a maximum below the zagros himalaya tien shan and the tibetan plateau the stiffer continental blocks that remain undeformed within the continental collision areas are characterized by a slightly thickened crust and flat topography lithospheric thickness and crustal thickness show different patterns that highlight an important strain partitioning within the lithosphere the arabia eurasia collision zone is characterized by a thick lithosphere underneath the zagros belt whereas a thin to non existent lithospheric mantle is observed beneath the iranian and anatolian plateaus conversely the india eurasia collision zone is characterized by a very thick lithosphere below its southern part as a consequence of the underplating of the cold and stiff indian lithosphere our new model presents great improvements compared to previous global models available for the region and allows us to discuss major aspects related to the lithospheric structure and acting geodynamic processes in central eurasia

the strain path and kinematics of lava domes an example from lipari aeolian islands southern tyrrhenian sea italy 1 a circular dome from lipari island consists of latitic enclaves hosted in a rhyolitic magma a strain analysis of the enclaves has been carried out and the pure shear and simple shear deformation the vorticity number wk and flow kinematics are determined the axial ratio rf of the enclaves and the angle between the long axis of the enclaves and the transport direction are measured in 131 sites concentrated in the axial zone z1 upper distal zone z2 and basal zone z3 of the flow the values depict a pattern suggesting endogenous growth in z1 1 in z2 1 0 8 lateral stretching due to the upward motion of magma from the conduit prevails in z1 here the increase of pure shear strain from the bottom to the top reflects strain accumulation due to endogenous growth z2 and z3 suffer simple shear deformation in z3 the sense of shear is consistent with the transport direction an opposite sense of shear characterizes z2 this is due to velocity gradients located in the lower and upper portions of the flow the kinematics is viscous spreading in z1 and viscous gliding hyperbolic flow in z2 z3 possible rupturing of the exterior may be important in z1 where lateral stretching occurs and in z3 where is at a maximum the effusion rate is 1 93 m3 s strain rates calculated using structural data span a range from 1 9 to 5 8 10 6 s 1

exchange through the bab el mandab during the last 10 years there have been a number of important developments in the understanding of the exchange flow in the bab el mandab new and improved estimates of the fluxes of mass heat and salt through the strait have been made directly from oceanographic measurements and indirectly from air sea flux data hydraulic theory has been applied to explain the seasonal variations in the exchange flow and in particular the three layer summer circulation the effects of wind stress friction and seasonal sea level variability on hydraulic control are addressed in this paper analyses of oceanographic data have failed to provide direct evidence of hydraulic control but they have highlighted the importance of tidal scale variability and differences between real continuously stratified fluids and idealised layer flows often used in hydraulic theory other studies have investigated the coupling between the flow in the strait and the circulation within the red sea

troposphere planetary boundary layer interactions and the evolution of ocean surface density lessons from red sea corals a time series of oxygen isotope d18o measurements of a coral from the northern red sea rs is presented and used as a direct proxy for water surface density rs with a relatively constant subsurface density the generated surface density time series closely tracks water mass formation variability two positive and two negative high amplitude rs anomalies are studied and associated atmospheric and oceanic data are analyzed to understand large scale ocean atmosphere processes the dominant process is lower tropospheric subsidence it dries the boundary layer bl increases surface evaporation and rs and ultimately drives water mass formation the main cause of the subsidence is a temperature increase along the principal axis of the rs from the eastern mediterranean to the convergence zone cz 188 228n the increase entails isentropes sloping down to the southeast crossing pressure surfaces due to their tilt with nearly adiabatic flow along the principal axis air parcels move roughly along the sloped isentropes toward ever increasing pressure that is they subside the subsidence supplies the northern rs bl with upstream air from higher altitudes where humidity is low thus drying the bl the resultant high evaporation north of 258n with low evaporation minus precipitation south of 228n depresses sea levels in the northern rs and thus drives the rs thermohaline circulation and controls water mass formation excluded from the presented picture but probably very important is mixing with the hot dry air of the surrounding deserts

insolation values for the climate of the last 10 million years new values for the astronomical parameters of the earth s orbit and rotation eccentricity obliquity and precession are proposed for paleoclimatic research related to the late miocene the pliocene and the quaternary they have been obtained from a numerical solution of the lagrangian system of the planetary point masses and from an analytical solution of the poisson equations of the earth moon system the analytical expansion allows the direct determination of the main frequencies with their phase and amplitude numerical and analytical comparisons with the former astronomical solution ber78 are performed so that the accuracy and the interval of time over which the new solution is valid can be estimated the corresponding insolation values have also been computed this analysis leads to the conclusion that the new values are expected to be reliable over the last 5 ma in the time domain and at least over the last 10 ma in the frequency domain

inhomogeneous structure of the voronezh shield lithosphere from explosion seismology data abstract this paper presents the results of a seismological investigation of the voronezh shield the use of industrial quarry blasts as the most economic seismic energy source and telemetric arrays of the taiga type for deep seismic sounding observations has enabled the geophysical research group of the voronezh state university to obtain complete and valid information concerning the deep structure of the shield seismic records of refracted and reflected p and s phases from the intracrustal and subcrustal discontinuities allow the determination of independent and compatible velocity models v p z and v s z analysis of the travel time and amplitude curves derived from the deep seismic sounding data reveals a complex and inhomogeneous structure of the voronezh shield lithosphere the major discontinuities are found in the middle part of the consolidated crust several rather thick layers can be resolved which are separated by first order seismic boundaries in the consolidated crust beneath the southeastern part of the shield at depths from 6 7 to 11 13 km a low velocity layer is clearly established from the compressional wave data within the low velocity channel v p appears to decrease by 5 6 the low velocity channel in the uppermost consolidated crust is assumed to be due to metamorphogeneous granitization this is revealed by the precambrian basement structure poisson s ratio calculated from the compatible velocity models v p z and v s z shows a systematic increase down to the crustal basement and becomes discontinuous only in the low velocity channel at the top of the mantle poisson s ratio decreases on all the deep seismic sounding profiles the systematic variation of poisson s ratio is related to changes in the composition and mineralogy of the voronezh shield lithosphere

seismic study of upper mantle and transition zone beneath hotspots abstract we compute receiver functions for 18 permanent seismic stations on oceanic islands after selecting earthquake records with high signal to noise ratio p to s conversions from the 660 km discontinuity are well observed at all except one station the 410 km discontinuity is in some cases not equally well observed all measured 410 conversion times are close to or later than predicted by iasp91 some are as late as to 6 s this extreme case corresponds to averaged velocities in the upper mantle down to 410 km depth that are 15 lower than in the iasp91 reference model the transition zone thickness derived from differential times of the p s conversions from the 410 and 660 km discontinuities is similar or up to 15 4 s in time thinner than predicted by the iasp91 reference model we found no case of an oceanic station with 410 arrival times earlier and only one station with transition zone thickness larger than predicted by iasp91 we have also identified measurable topography of the transition zone underneath a few stations

distribution of crenarchaeota tetraether membrane lipids in surface sediments from the red sea abstract the red sea represents an extreme marine environment with high salinity high temperature and low level of nutrients complicating the application of standard geochemical palaeotemperature proxies in order to investigate the applicability of the tex 86 tetraether index of gdgts with 86 carbons proxy for sea surface temperature sst in the red sea the distribution of glycerol dialkyl glycerol tetraether membrane lipids gdgts in sediments from the red sea and the gulf of aden were examined against expectations tex 86 values for the red sea do not show a simple linear relationship with sst and deviate from the global core top calibration in the northern red sea at temperatures between 25 and 28 c the values increase linearly with sst whereas in the southern red sea at temperatures above 28 c tex 86 decreases with increasing temperature factors like seasonality and depth of production salinity and nutrient availability as well as diagenetic overprint or influence of allochtonous terrestrial lipids cannot explain this pattern however the observed tex 86 relationship with sst could be explained by the presence of a hypothetical endemic crenarchaeota population in the red sea with a specific tex 86 vs sst relationship in the southern red sea a two component mixing model implies an exponential decrease in the endemic population towards the gulf of aden thus the application of the tex 86 as a palaeotemperature proxy in the red sea is likely only possible for the northern red sea area with the specific sst vs tex 86 relationship determined in this study and potentially for the whole red sea basin during glacials when water exchange with the indian ocean was more restricted than today and the endemic archaeal lipid distribution was not affected by transport from the indian ocean our results suggest that distinct populations of crenarchaeota in extreme environments such as evaporitic basins may have different membrane composition necessitating application of another calibration than the global core top calibration for tex 86 palaeothermometry

an example of two dimensional synthetic seismogram modeling abstract synthetic seismograms for laterally inhomogeneous velocity and q structures can be calculated by the disk ray theory drt method ray tracing through the model provides travel time distance slowness and ray amplitude data which are combined to synthesize seismic record sections by drt the amplitude factors include geometrical spreading attenuation due to q 1 reflection and transmission coefficients and the free surface conversion coefficient comparison of drt synthetic seismograms with those calculated by the reflectivity method for a layer over a half space model shows excellent agreement in both amplitude and waveform character of all arrivals direct reflected p to s converted multiply reflected and head waves may be synthesized by the drt method in an application of two dimensional synthetic seismogram modeling using the drt method synthetic seismogram record sections were calculated for a complicated geological model of the crust in the eastern snake river plain idaho and compared with observed seismic data in this application we find that a small modification of the snake river plain velocity model which was interpreted from travel time data produces drt synthetic seismograms which compare well with the amplitude and waveform character of the observed seismograms

enclaves provide new insights on the dynamics of magma mingling a case study from salina island southern tyrrhenian sea italy abstract three lava flows hereafter flows a b and c from salina island italy consist of basaltic andesitic enclaves dispersed in a dacitic matrix enclaves represent 8 12 vol of the erupted magma the number of enclaves and the surface covered by the enclaves at each outcrop do not vary significantly with the distance from the vent in the flows a and b these feature reflect the dynamics of magma mingling within the reservoir and not the kinematics of the lava flow in the flow c these parameters vary irregularly the statistical entropy s t of the enclaves which is a measure of their spatial distribution dispersion is estimated in outcrops located at different distance from the vent the kolmogorov sinai entropy rate k which describes the variations of s t with time is also determined in the lava flow a s t increases linearly with time t for 0 0 5 s t attains its maximum value and maintains constant with increasing t in the lava flow b s t linearly increases with t and k is 0 01 in the lava flow c there is not correlation between s t and t the comparison between the results from the analysis of the porri enclaves and those from numerical experiments on the variation of s t in chaotic advective mixing systems and from previous experimental models on magma mixing allow us to draw some conclusions on dynamics of the basaltic andesite dacite mingling in the magma chamber fully chaotic magma mingling systems show three evolution stages an initial stage which is unknown because of the disruption of the initial configuration of the interacting magmas a second stage characterized by a linear increase of the statistical entropy with time and a third stage in which the uniformity of the system is reached and the entropy does not vary with increasing time a system in which the uniformity is never attained is characterized by irregular variations of s t with time in the flows a and b the relations between s t and t are consistent with those of a fully chaotic dynamics possibly associated to convection the basaltic andesite was uniformly distributed in the dacitic host due to the occurrence of convective movements driven by the injection of the basaltic andesite within the dacitic chamber the mingling system recorded by the lava flow a evolved with a higher rate with respect to that of the flow b this suggests that chaotic advection stirring and folding is more efficient in the magmatic system a than in b on the contrary the mingling system c is characterized by a non uniform distribution of the basaltic andesite within dacite this reflects the occurrence of a dynamics in which stirring and folding processes do not operate efficiently and are unable to uniformly distribute the dispersed phase within the continuous one the decrease of k from a to b and the lack of a measurable k in c along with the observation that a and b were emitted before c indicate that the efficiency of advective movements within the porri magma chamber declined with decreasing time mingled magmas characterized by a homogeneous spatial distribution of enclaves or an initially inhomogeneous distribution evolving towards a homogeneous one are indicative of efficient advection processes that may favor magma mixing mingled magmas characterized by an inhomogeneous distribution of enclaves suggest low dynamical interaction between the two end members magma mixing is not allowed

the viscosity of latitic melts from lipari aeolian islands italy inference on mixing mingling processes in magmas abstract the viscosity of latitic melts occurring as enclaves in the rhyolitic lava flow of rocche rosse rr lipari aeolian islands italy has been measured in the high t range 1323 1473 k for a dissolved water content varying from 1 23 to 4 39 wt measurements were performed by the falling sphere method in an internally heated gas pressure vessel as expected the viscosity of latite decreases with increasing water content and temperature no pressure effect was detected between 200 and 500 mpa combining the new viscosity data for hydrous melts with data for dry latite of similar base composition giordano d mangiacapra a potuzak m russell j k romano c dingwell d b di muro a 2006 an expanded non arrhenian model for silicate melt viscosity a treatment for metaluminous peraluminous and peralkaline liquids chemical geology 229 42 56 we propose an empirical equation to estimate the viscosity of latitic melts as a function of temperature and water content over the range 101 to 1012 pa s the obtained relationship reproduces the experimental data with a 1 standard deviation of 0 22 log units however the empirical model is not constrained by data for hydrous melts at high viscosity and therefore it can only be used at low temperatures for water poor melts the viscosity data were used to model mixing mingling processes between latitic and rhyolitic magmas at conditions relevant for the rocche rosse rr lipari aeolian islands and la fossa cone 1888 1890 lfc vulcano aeolian islands eruptions the results demonstrate that the ratio between mafic and silicic end members is the main parameter governing mixing mingling interactions between magmas this study suggests a faster ascent of magma underneath vulcano compared to lipari which may be taken into account in hazard forecasting

crustal structure of central saudi arabia determined from seismic refraction profiling abstract based on a two dimensional ray path interpretation of travel time and wave amplitude ratios a detailed crustal velocity structure of central saudi arabia has been derived using the deep seismic refraction profile of saudi arabia the crustal model derived significantly differs from previous interpretations carried out on the same data set since more energetic crustal phases were considered in this analysis the two dimensional crustal model derived shows that the crust consists of four distinct layers it is approximately 42 km thick under the arabian platform and thins gradually in a southwest direction to about 38 km under the shield the upper crust consists of two layers the first one has a p wave velocity of about 6 1 km s and is about 3 km thick thinning to about 1 km under the platform the second layer has a p wave velocity of about 6 2 km s and is about 14 km thick but thins to about 7 km under the platform the intermediate crustal layer has a p wave velocity of about 6 4 km s is about 7 5 km thick under the shield under the platform it is about 16 km thick with a velocity of about 6 3 km s the lower crust has a p wave velocity of about 6 9 km s and is about 15 km thick a decrease in the upper mantle pn velocity from 8 2 to 8 1 km s seems to accompany the crustal thinning the moho discontinuity is sharply defined beneath the shield and gently dips towards the northeast a significant crustal inhomogeneity in the region separating the afif terrane from the ar rayn terrane is interpreted as a thrusting system rather than a distinct vertical discontinuity in the crustal structure as previously interpreted this region between the two terranes which is of different crustal composition is probably the result of thrusting and emplacement of nappes of upper crustal materials of the afif terrane onto the ar rayn foreland the nature and location of this zone were constrained by travel time and wave amplitude ratio measurements the detailed velocity crustal model derived in this study is of significant importance in earthquake studies tectonics and determining the evolution of the arabian plate

non linear deformation and break up of enclaves in a rhyolitic magma a case study from lipari island southern italy 1 a dome from lipari island southern italy consists of 12 vol of circular elongated and folded latitic enclaves hosted in a rhyolitic matrix the dm to cm scale enclaves are more deformed than the mm scale blobs the critical value of the ratio between the viscous forces which allow deformation and eventually break up blobs of latitic magma and the interfacial tension forces is larger than 0 29 the reynolds number is 5 3 the equivalent radius and the axial ratio of the enclaves follow power law distributions this feature suggests that the break up and stretching of magmas are non linear scale invariant probably cyclic processes the coexistence of enclaves of different shape and the self similar size distributions suggest that chaotic advection plays a major role in the formation of mingled magmas caution must be used when measuring the finite strain from enclave shapes because they may break apart during the deformation

glacial conditions in the red sea in this paper results from previous studies on planktonic foraminifera 6 o and global sea level are combined to discuss climatic conditions in the red sea during the last glacial maximum 18 000 b p first the influence of 120 m sea level lowering on the exchange transport through the strait of bab el mandab is considered this strait is the only natural connection of the red sea to the open ocean next glacial red sea outflow salinity is estimated about 48 parts per thousand from the foraminiferal record combined these results yield an estimate of the glacial net water deficit which appears to have been quite similar to the present about 2 rn yf finally budget calculation of 6 o fluxes suggests that the glacial 6 o value of evaporation was about 50 of the present value this is considered to have resulted from substantially increased mean wind speeds over the glacial red sea which would have caused a rapid drop in the kinematic fractionation factor foro the sensitivity of the calculated values for water deficit and isotopic fractionation to the various assumptions and estimates is evaluated in the discussion improvents are to be expected especially through research on the glacial salinity contrast between the red sea and gulf of aden it is argued however that such future improvement will likely result in a worsening of the isotopic discrepancy thus increasing the need for an additional mechanism that influenced fractionation such as mean wind speed this study demonstrates the need for caution when calculating pal osaliniti s from 5 so records under the assumption that the modem s 5 so relation has remained constant through time previously overlooked factors such as mean wind speed may have significantly altered that relation in the past

fractals in geology and geophysics the definition of a fractal distribution is that the number of objectsn with a characteristic size greater thanr scales with the relationn r d the frequency size distributions for islands earthquakes fragments ore deposits and oil fields often satisfy this relation fractals were originally introduced by mandelbrot to relate the length of a coastline to the length of the measuring stick this application illustrates a fundamental aspect of fractal distributions scale invariance the requirement of an object to define a scale in photographs of many geological features is one indication of the wide applicability of scale invariance to geological problems scale invariance can lead to fractal clustering geophysical spectra can also be related to fractals these are self affine fractals rather than self similar fractals examples include the earth s topography and geoid

methods of determining the rheological properties of magmas at sub liquidus temperatures non vesicular basaltic melts behave as newtonian fluids at temperatures above their liquidus and their viscosities can be calculated using a method developed by shaw 1972 and bottinga and weill 1972 because many igneous processes involve the flow of silicates at sub liquidus temperatures numerous attempts have been made to calculate the interactive effects of the crystal phase however current methods are appropriate only for relatively low crystal concentrations and they assume newtonian behaviour we argue that this assumption is invalid when bubble or crystal concentrations exceed 30 at higher concentrations factors other than concentration become increasingly important these include particle shape and size distribution a method which takes these factors into account is tested on a range of suspensions including magmas at sub liquidus temperatures and rheological properties calculated using this method agree closely with the measured values we also demonstrate that an equation which was introduced to explain large differences in measured apparent viscosities during the cooling and crystallisation of mount st helens dacite murase et al 1985 and which is currently used to calculate the rheological properties of crystallising lavas generates viscosities which may be in error by several orders of magnitude this difference is argued to be caused by a combination of factors including the ten orders of magnitude range in the strain rates utilised during the mount st helens measurements causing orders of magnitude difference in the resulting apparent viscosities rheological data on crystallising silicic melts are reinterpreted taking into account the non newtonian rheology of the magmas and changes in activation energy of flow during crystallisation

on the sources formation and circulation of red sea deep water red sea deep water is renewed from sources in the far north of the red sea upwelling of deep water throughout the basin maintains the sharp pycnocline with its base near the depth of the sill at bab el mandeb before now deep water renewal was thought to occur mainly by means of convective deep water formation in the north which renews the bottom water and gives rise to a southward flowing bottom current carbon 14 and 3he data from the geosecs indian ocean expedition lead to the identification of an additional volumetrically larger mode of northern deep water formation in which new deep water is injected immediately beneath the pycnocline this mode of deep water formation to be called the isopycnal mode also gives rise to a southward flowing current in this case at the top of the deep water mass geosecs data also demonstrate the existence at intermediate depths in the deep water of a return flow to the north the surface history in the nuclear era of the 14c in the deep water source region was reconstructed by direct radiocarbon measurements on annual growth bands of corals calculation then shows that new deep water forms in the convective mode at a rate of 0 05 0 01 sverdrup sv expressed as if the flow were continuous and is due principally to processes occurring in the mouth of the gulf of suez the injection beneath the pycnocline of new deep water formed in the isopycnal mode is 0 11 0 02 sv this new deep water appears to originate mainly in the extreme open northern red sea the gulf of aqaba makes a modest but significant contribution to both modes the total deep water renewal rate is about 0 16 sv yielding a bulk deep water residence time of about 36 years oxygen consumption in the deep water shows approximately exponential decrease of consumption rate with depth as expected on geological and geophysical grounds hydrographically significant fluxes of heat and salt from the sea floor into the red sea deep water are discernible in the hydrography helium 3 flux from the sea floor into the deep water is about 69 1 stp year

crustal structure along mehmadabad billimora profile in the cambay basin india from deep seismic soundings abstract deep seismic sounding dss investigations were carried out along a 220 km long n s profile from mehmadabad 22 50 n 72 46 e to billimora 20 46 n 72 58 e in the cambay basin india for studying the detailed crustal structure in the region seismic refraction as well as narrow and wide angle reflection travel time data were obtained for various crustal boundaries starting from the sedimentary section down to the moho by continuous profiling analysis of reversed reflection and refraction travel time data has yielded crustal velocity depth functions for the mehmadabad broach and broach navsari sections along the profile which are significantly different from each other the average velocities at depths in the magmadabad broach section have been found to be considerably lower than those in the broach navsari section by about 25 at 5 km 17 at 10 km 7 at 20 km and 2 at the moho depth and even deeper down in the upper mantle the presence of a relatively thicker sedimentary section especially in the jambusar broach area as revealed by the reversed refraction data analysis is responsible for this gross difference in the average velocity functions for the two parts of the profile and the same have therefore been used for obtaining the detailed crustal depth along the profile the cambay basin which is well known to be bounded by step faults on the eastern and western margins is also dissected into seven major crustal blocks in the n s direction from mehmadabad to billimora the various crustal blocks identified are from the north 1 i mehmadabad block 2 ii tarapur block 3 iii petlad katana block 4 iv jambusar broach block 5 v kosamba block 6 vi surat block and 7 vii navsari billimora block these blocks are displaced up or down relative to the adjacent blocks due to movements along the faults bounding them most of the faults have been found to extend quite deep and to affect the moho boundary considerably as is quite evident from the relief of the moho found along the profile further the seismic activity observed in the region during historical as well as modern times suggests that these deep faults may even be currently active the jambusar broach block which is well known as a broad regional syncline with the maximum thickness of cenozoic sediments has been found to be a major graben revealing a maximum crustal thickness of 38 40 km the granitic basement in this graben is also the deepest at 6 0 6 5 km depth towards the north and south of this major graben the moho as well as the granitic basement are found to be at relatively shallower depths in various crustal blocks the boundary velocity at the moho has been found to be 8 1 8 2 km sec whereas at the granitic basement level there seems to be a lateral velocity variation from 5 7 to 6 3 km sec the crustal depth section obtained in the present study reveals a close relationship between the deep and shallow structural features in this region the deccan traps which form the basement of the overlying tertiary sediments over most part of the profile vary in thickness from 1 0 to 1 8 km however the trap surface rises to very shallow depths on the southern part of the profile the boundary velocity in the deccan traps has been found to vary between 4 8 and 5 2 km sec in the anklesvar kosamba area there is also evidence for the presence of a 1 2 km thick layer of mesozoic sediments with a velocity of about 4 0 km sec underlying the 1 1 km thick deccan traps layer

improved statistical processing for common conversion point stacked receiver functions the interpretation of teleseismic receiver functions rfs is typically limited by poor constraints on the uncertainty of amplitudes of converted phases in continental regions these problems are overcome by stacking large amounts of data in oceanic regions however data quality is notoriously noisy and the number of events are often limited by significantly shorter station deployment times estimates of rf pulse amplitude uncertainty are therefore necessary to allow an analyst to differentiate between real structure in the earth and random correlations in ambient noise here we combine a common conversion point stacking technique with multiple taper correlation rf estimates which allow frequency domain weighting we then compute jackknife statistics to estimate local uncertainties in rf amplitude we apply this technique to a continental station in arabia rayn and to the ocean island station at raratonga cook islands rar in order to compare our method to results obtained via other techniques the structure we recover matches previous crustal studies at both stations and provides new interpretations of conversions in the upper mantle at single stations this technique works well to resolve crust and mantle structure up to a depth of 100 km geographical dispersion of ray paths at greater depths decreases the number of events per bin and therefore increases the uncertainty in converted amplitude the ability to stack crossing ray paths implies that this method will be well suited to the analysis of data from seismic arrays

seismic crustal structure of the proterozoic north australian craton between tennant creek and mount isa seismic recording along a 600 km traverse across the southern part of the north australian craton indicates that lateral velocity variations exist in the middle lower crust taken together with other data from the craton there is evidence for midcrustal velocities increasing from east to west and from south to north these trends could result from a greater proportion of high velocity granulites being emplaced at higher levels in the crust between tennant creek and mount isa the velocity structures near the surface are compatible with an assemblage of younger and older metamorphic rocks intruded by granites near surface 0 5 km p wave velocities on the tennant creek inlier increase from 5 47 km s at the surface to about 6 2 km s at 6 km depth and correspond with low grade metamorphics of the warramunga group interspersed with weathered granites overlying amphibolite facies rocks of older metamorphic domains in the mount isa geosyncline velocities of 6 03 6 15 km s correspond to the leichhart metamorphics interspersed with granites in the middle crust p wave velocities of 6 85 km s occur at a depth of 26 km near tennant creek whereas such velocities are not evident until depths of about 37 km near mount isa there is therefore a trend for midcrust velocities to increase from east to west the lower crust is characterized by velocities of 7 3 7 5 km s and the upper mantle velocities of 8 16 8 20 km s are reached at depths of 51 54 km exposed granulite facies rocks in central australia are low in heat producing elements and are compatible with the low surface heat flow generally measured in precambrian australia these data taken together with laboratory velocity measurements on worldwide samples reported elsewhere indicate that middle to lower crustal rocks could be an assemblage of granulite facies rocks varying from pyroxene granulite in the middle crust through hornblende granulite to garnet granulite in the lower crust

crustal anisotropy beneath pacific ocean islands from harmonic decomposition of receiver functions crustal anisotropy beneath ocean islands can be attributed to preferentially aligned minerals cracks or dike structures stacked with harmonic weighting receiver functions from permanent ocean island stations display evidence of strong and distinct anisotropy parameters in the underlying crust and underplated layer we analyze data for 11 iris gsn stations in the pacific ocean we observe the prevalence of two lobed receiver function rf amplitude variations with back azimuth consistent with slow tilted axis anisotropy in most cases the anisotropy is accommodated in the underplated crust synthetic modeling of a representative station indicates that the strength of anisotropy of vp 10 and vs 5 is possible the strike direction of the inferred symmetry axis tends to align with plate motion with some scatter at stations in the northwest pacific i e kwaj tara and wake the strike direction of the symmetry axis aligns with plate motion at the time of volcano emplacement beneath station poha and the closest stations to the present day hawaiian hotspot alignment of the symmetry axis is almost orthogonal to the plate motion we attribute the crustal anisotropy to the preferred alignment of dike structures that transported asthenospheric magma toward the seafloor volcanic edifice our results suggest that the thermal plume origin for ocean islands must be supplemented by tectonic stress heterogeneities that allow magma to penetrate the lithosphere via fractures magma transport fractures should align normal to the least compressive direction which are predicted by theoretical models to align approximately with plate motion at the time of emplacement

linking enclave formation to magma rheology 1 magmatic enclaves record the history of deformation and disaggregation i e fragmentation of relatively hot compositionally more mafic magmas injected into actively convecting silicic magma chambers through dikes enclave size distributions may provide crucial clues for understanding the nature of this mechanical mixing process accordingly we conduct a comprehensive field study to measure enclave size distributions in six cascade lava flows using results from recent fluid dynamics experiments along with thermodynamic and modeling constraints on key physical properties of the injected and host magmas i e temperature density and effective viscosity we use the size distributions of enclaves to characterize the magmatic flow regime governing enclave formation scaling arguments suggest that the viscous stresses related to magma chamber flow acting against the yield strength of a crystallizing injected magma control the breakup of 1 m wide mafic dikes into millimeter to centimeter scale enclaves our data analysis identifies a characteristic length scale of breakup that constrains the yield strength of the injected magmas in a more restrictive way than existing empirical models for yield strength based on crystal content in all six lava flows we show that the progressive fragmentation of the injected magma is self similar and characterized by a fractal dimensiondf 2 which is comparable to previous studies on enclaves we also find a small but statistically significant dependence of df on the effective viscosity ratio between host and enclave magmas such that large variations in effective viscosity enhance breakup this work demonstrates that field observations of enclave size distributions can reliably constrain the rheological and flow conditions in which enclaves form

the monte guardia eruption lipari aeolian islands an example of a reversely zoned magma mixing sequence the monte guardia rhyolitic eruption 22 ka lipari aeolian islands italy produced a sequence of pyroclastic deposits followed by the emplacement of lava domes the total volume of dense magma erupted was nearly 0 5 km3 the juvenile clasts in the pyroclastic deposits display a variety of magma mixing evidence mafic magmatic enclaves streaky pumices mineral disequilibria and heterogeneous glass composition petrographic mineralogical and geochemical investigations and melt inclusion studies were carried out on the juvenile clasts in order to reconstruct the mixing process and to assess the pre eruptive chemico physical magmatic conditions the results suggest that the different mingling and mixing textures were generated during a single mixing event between a latitic and a rhyolitic end member a denser mixed magma was first erupted followed by a larger volume of an unmixed lighter rhyolitic one this compositional sequence is the reverse of what would be expected from the tapping of a zoned magma chamber the monte guardia rhyolitic magma stored below 200 mpa was volatile rich and fluid saturated or very close to this despite its relatively low explosivity in contrast to previous interpretations there exists the possibility that the rhyolite could rise and erupt without the trigger of a mafic input the entire data collected are compatible with two possible mechanisms that would generate a reversely zoned sequence 1 the occurrence of thermal instabilities in a density stratified salic to mafic magma chamber and 2 the intrusion of rising rhyolite into a shallower mafic sill dike

the strain path and emplacement mechanism of lava flows an example from salina southern tyrrhenian sea italy abstract a lava flow from salina southern tyrrhenian sea consists of subcircular to ellipsoidal basaltic enclaves dispersed in a dacitic host a 2d strain and kinematic analysis of the enclaves has been performed in order to determine a the relative contribution of the coaxial and non coaxial components to the bulk flow deformation b the flow vorticity wk c the strain path and d the mechanism of flow emplacement the axial ratio r f and the angle f between the long axis of the enclaves and the transport direction have been measured in 196 sites located at different distances from the vent in the near vent zone whereas further from the vent values were always larger than 1 ranging from 1 6 in the near vent zone to 1 at the front values were between 0 2 at the back and 2 6 at the front wk was between 0 13 and 1 and increased from the back to the front the enclaves result from the injection of basalt into dacite most of the deformation was acquired during the lava flow emplacement and not during the rise in the conduit plug flow the strain path depicted by the enclaves is consistent with that resulting from experimental analogue models and reveals that the lava suffers lateral extension near the vent further from the vent the lava deforms according to an ideal non coaxial model the lava emplacement is mainly controlled by the gravity evidence of deformation induced by the magma pressure is lacking near the vent the lava behaves as a hyperbolic flow whereas at the front it behaves as a simple shear flow the mechanism of flow emplacement is consistent with a mixed viscous gliding spreading transport model at the back and with a viscous gliding model at the front

microgranitic enclave shapes and magmatic strain histories constraints from drop deformation theory microgranitic mafic enclaves are common components of plutonic bodies and may represent the result of mingling of mafic and felsic magmas these enclaves are often ellipsoidal or elongate in shape in order to constrain the conditions under which such enclaves were generated and deformed by their host pluton we apply drop deformation theory to model their distortion our model takes into account the change in viscosity of both the host and enclave with temperature composition and the amount of suspended solids in enclave host systems and it assumes that simple shear flow predominates in the plutonic system we focus on the deformational history of enclaves over the time period in which they remain liquid and are either more or less viscous than their granitic host we find that the most stable enclaves with respect to being broken up by their entraining flow are generally the most mafic enclaves those with silica contents near those of the host granite are highly unstable this is in reasonable accord with field observations of the abundance of enclaves of different chemistry most deformation of microgranitic enclaves is likely to occur at relatively high temperatures probably between 950 c and 1050 c and therefore the enclaves record magmatic strain of the host over only a limited temperature time range in the host s cooling history furthermore the observation of apparent deformation of these enclaves in a liquid regime coupled with our calculated dependences of enclave deformation on flow velocity implies that magmatic flow velocities are likely to be below 10 m yr in enclave bearing plutonic systems

the dimensions of magmatic inclusions as a constraint on the physical mechanism of mixing abstract silicic lavas often bear inclusions of more mafic lava several physical processes have been proposed by which these magmas may become mixed measurements of the sizes of mafic inclusions in lavas of two calc alkaline volcanoes are used here to obtain a characteristic length scale for this type of mixing and provide a means to discriminate between different mixing processes we quantitatively assess the proposal that in a stratified reservoir dynamic interactions of rising gas bubbles with the interface between a lower layer of mafic magma and an upper layer of silicic magma lead to the formation of vesiculated blobs of the lower magma in the upper one this is due to gravitational instability of a foam layer growing at the interface between the two magmas our theoretical calculations of this instability predict both the correct order of magnitude for the characteristic size of inclusions and the way in which inclusion size varies with the physical properties of the magmas this fluid dynamic framework is used to map out different possible flow regimes and place constraints on the fraction of gas in these systems

area perimeter relation for rain and cloud areas following mandelbrot9s theory of fractals the area perimeter relation is used to investigate the geometry of satellite and radar determined cloud and rain areas between 1 and 1 2 x 106square kilometers the data are well fit by a formula in which the perimeter is given approximately by the square root of the area raised to the power d see equation in the pdf where d is interpreted as the fractal dimension of the perimeter it is concluded that rain and cloud perimeters are fractals they have no characteristic horizontal length scale between 1 and 1000 kilometers

seismic velocity and q model for the shallow structure of the arabian shield from short period rayleigh waves the shear velocity and q sub beta structure for the upper 1 km in different tectonic regions of the arabian shield have been investigated using high frequency vertical component records of rayleigh waves 1 20 hz which were recorded at source to receiver separations 55 80 km during a deep seismic refraction survey group and phase velocities of the fundamental and first higher modes were inverted for the shear wave velocity structure rayleigh wave attenuation coefficients were determined from the decay of the amplitude spectrum of the fundamental mode and used to invert for the q sub beta structure models derived from the data were tested by calculating synthetic seismograms for the fundamental and the first higher modes from surface wave theory with a center of compression used to represent the source both band pass filtered step and dirac delta source time functions were tested modeling indicates that the shear wave velocity of the shield increases from 2 6 km s to 3 4 km s in the upper 400 m of the crust q sub beta increases from 30 in the upper 50 m to 150 at 500 m depth the underlying material has a q sub beta of 400 500 for the outcropping igneous rocks such as granite and may reach values higher than 700 for the metamorphic green schist rock a band pass filtered dirac delta source time function produces the synthetic that is the best fit with observations

glacio eustatic sea level control on red sea salinity previous studies of the red sea demonstrated that glacial surface and bottom water salinities in the basin were significantly higher than at present the very low abundance of planktonic foraminifera the so called aplanktonic zone during the last glacial indicates that surface water conditions approached or exceeded the tolerance limits of this plankton group1 2 glacial sediments are also characterized by high concentrations of magnesian calcite3 4 dolomite3 inorganically precipitated aragonite4 5 and benthic foraminifera typical of hypersaline environments3 6 additional evidence from oxygen isotope records of planktonic2 7 and benthic foraminifera8 9 as well as pteropods2 demonstrate that glacial interglacial contrasts in the red sea have an amplitude much larger than typically observed in open ocean records here we use both oxygen isotope data and a fractional overmixing model to estimate the impact of the most recent 18 000 yr bp pleistocene glacio eustatic sea level lowering on red sea salinity we estimate that during the last glacial maximum surface salinities in the central red sea were more than 10 0 higher than at present deep water salinities were also higher during the last glaciation and remained unusually high through deglaciation the combination of very high bottom salinities and the onset of pluvial conditions during deglaciation in the red sea region prevented ventilation of red sea bottom waters and resulted in the accumulation of organic rich sediments

transition to chaos and implications for time scales of magma hybridization during mixing processes in magma chambers abstract in this contribution numerical simulations of magma mixing are carried out with the aim of understanding the physico chemical conditions that trigger the development of chaotic mixing dynamics in detail the mixing process is simulated in a magma chamber where a less evolved magma underplates a more evolved magma the chaoticity of this system is quantitatively estimated via computed finite time lyapunov exponents it is shown that magma chamber dynamics are strongly controlled by the rayleigh number ra whereas other parameters such as buoyancy ratio and viscosity ratio play a subordinate role results indicate that magma chambers with ra of the order of 10 6 are dominated by non chaotic behaviour increasing ra shifts the system towards an increasing chaotic state and in particular above ra 10 7 chaotic dynamics are fully developed in the magma chamber estimates of possible time scales of hybridization of magmas during chaotic mixing suggest for example that a blob of mafic magma with an initial diameter of 100 m within a magma chamber with a width of 1000 m is stretched to a filament like structure with a thickness of 15 m after 320 years and after 1900 years its thickness is reduced to 4 0 mm using typical chemical diffusion coefficients for magmas of the order of 10 14 m 2 s it can be calculated that a 4 0 mm thick filament would homogenize by diffusion in 10 years such homogenization time scales are orders of magnitude lower that typical life times estimated for magma chambers even in the volcanic environment indicating that fast hybridization of magmas can be rapidly achieved when chaotic dynamics govern the evolution of the magmatic system

insights into magma chamber processes from the analysis of size distribution of enclaves in lava flows a case study from vulcano island southern italy the size distribution of latitic enclaves dispersed in a rhyolitic lava flow is studied enclave size distribution is self similar a feature that can be explained by a fractal fragmentation process and estimated fractal dimension of fragmentation is 2 50 fragment size distribution of enclaves generated by disruption of viscous fingering structures in granitoid rocks is analyzed it is shown that this distribution is fractal with a value of fractal dimension of fragmentation of 2 55 in close agreement with the value estimated for enclaves in the lava flow it is suggested that the fragmentation process producing the size distribution of enclaves in the lava flow may have occurred in response to the disruption of viscous fingering morphologies generated by the injection of the more mafic magma into the felsic one accordingly the size distribution of enclaves dispersed in the lava flow is considered a feature inherited from deep magma chamber processes and gives insights into magma chamber dynamics

high rates of sea level rise during the last interglacial period sea level during the last interglacial stood at least 4 m higher than at present with evidence of short term fluctuations of up to 10 m a new continuous sea level record from the red sea and coral ages suggest that during these fluctuations sea level changes were on the order of 1 6 m per century

numerical modeling of the development of small scale magmatic emulsions by korteweg stress driven flow abstract the occurrence of micron to millimeter size globular heterogeneities in igneous rocks is frequently explained by processes of liquid immiscibility however such textures have also been documented in miscible magmatic pairs in this study the ability of miscible magmas to develop transient surface tensions and mimic the behavior of immiscible liquids is tested for the whole spectrum of magmatic compositions we implemented a numerical model that includes the effect of gradient stresses namely korteweg stress in order to investigate the role of such stresses in the evolution of diffusive interfaces the results show that an initially elongated heterogeneity surrounded by a miscible and compositionally diverse magma will tend to minimize its contact surface by relaxing to a spherical shape advected by a korteweg stress driven flow if the initial aspect ratio of the heterogeneity exceeds a critical value surface minimization may be achieved by drop breakup in addition it is shown that two neighboring heterogeneities may coalesce to a single spherical drop these results imply that even for fully miscible magmas rheological barriers may prevent efficient mechanical intermingling and induce the formation of small scale globular textures analogous to those commonly observed in immiscible liquids a better understanding of the role of korteweg stress may be of the utmost importance for deciphering the textures generated by the interaction of compositionally diverse magmas

the crustal and upper mantle structure of the interior arabian platform summary the crustal and upper mantle velocity structure of the interior arabian platform is derived using the spectral analysis of long period p wave amplitude ratios the ratio of the vertical to the horizontal component is utilized to obtain crustal transfer functions using the thomson haskell matrix formulation for horizontally layered crustal models 20 earthquakes recorded at the long period station ryd between azimuths n20 w and n150 e were selected for the analysis based on the following criteria focal depths in the range 5 to 215 km body wave magnitudes greater than 5 0 and epicentral distances in the range 7 to 97 a careful quality check of the data left us with six events out of 29 that had short epicentral distances 20 to be analysed the selection criterion for the final model in the forward modelling process was based on the correlation coeycient between observed and theoretical transfer function the model suggested that the crust consists of five distinct layers the upper crustal layer has a p wave velocity of about 5 6 km s 1 and is about 3 km thick the second layer has a velocity of about 6 3 km s 1 and is 10 km thick the third layer has a velocity of 6 6 km s 1 and is 8 km thick the fourth layer has a velocity of 6 9 km s 1 and is 15 km thick the lower layer has a velocity of about 7 6 km s 1 and is 10 km thick for the mohorovicic discontinuity a velocity of 8 3 km s 1 for the upper mantle and 46 km depth are indicated

distribution of oceanic and continental leads in the arabian nubian shield new common lead data for feldspar whole rock and galena samples from the arabian nubian shield together with data from previous work can be divided into two main groups group i leads have oceanic mantle characteristics whereas group ii leads have incorporated a continental crustal component of at least early proterozoic age the group i leads are found in rocks from the red sea hills of egypt and the western and southern parts of the arabian shield group ii leads are found in rocks from the northeastern and eastern parts of the arabian shield as well as from the southeastern shield near najran they are also found in rocks to the south in yemen to the east in oman and to the west at aswan egypt this distribution of data suggests that the arabian nubian shield has an oceanic core flanked by rocks that have developed at least in part from older continental material two mechanisms are suggested by which this older lead component could have been incorporated into the late proterozoic rocks and each may have operated in different parts of the shield the older lead component either was derived directly from an underlying early proterozoic basement or was incorporated from subducted pelagic sediments or sediments derived from an adjacent continent

imaging the shallow crust with teleseismic receiver functions summary teleseismic receiver functions rfs represent an estimate of the site response to incoming seismic energy this technique has long been a staple of the global earthquake community as rfs are sensitive to impedance contrasts associated with major discontinuities in the crust and upper mantle however there is substantial debate in the community concerning the lateral and vertical resolution limits possible using these methods due to limitations resulting from ambient noise and non uniform spatial sampling of finite frequency wave kernels here we take advantage of data from the labarge passive seismic experiment to examine these questions in more detail we find 1 that rfs can provide a robust image of the near surface 5 km structure 2 that vertical resolution may exceed 500 m and 3 that our results compare favourably to nearby wells these results indicate that rf analysis can provide high resolution images of the shallow crust which has potential value for hydrocarbon exploration

climatological coastal jet collision intermediate water formation and the general circulation of the red sea the authors present climatologies of a numerical model of the red sea focusing on the dynamics of winter intermediate water formation northward flowing boundary currents are identified as the major dynamical elements at the northern boundary the eastern current follows the geometry eventually turning back to the south at 268n and the western wall the two boundary currents collide at the collision site the denser eastern current subducts under the western boundary current the subduction forces the western boundary current eastward into the interior convection communicates the surface fluxes to the downwelled plume and intermediate water forms the estimated rate 0 11 sv sv 106 m3 s21 agrees with previous estimates the authors identify basin scale sea surface tilt to the north due to variable thermohaline forcings as the key dynamical variable the resultant geostrophic eastward cross channel flow interacts with the boundaries and creates upwelling and surface topography spatial patterns that drive the coastal jets upwelling induced vortex stretching dominates the vorticity balance and governs the separation of the western boundary current from the western wall the process ceases in the summer

constraining the recent plumbing system of vulcano aeolian arc italy by textural petrological and fractal analysis the 1739 a d pietre cotte lava flow 1 the 1739 a d pietre cotte lava flow is part of a sequence of low explosive to weak effusion events occurred at la fossa cone the active vent on vulcano island aeolian arc italy this lava is rhyolitic texturally heterogeneous and contains lati trachytic enclaves these compositions are recurrent in the la fossa volcanic products and are representative of the recent vulcano plumbing system the host lava is vesicular relatively phenocryst free and locally contains microlites and millimeter sized spherulites the enclaves are up to 10 cm in size display angular to spherical shapes and can form the core of spherulites enclaves mostly consist of plagioclase and augitic phenocrysts set in a weakly vesicular groundmass characterized by variable abundance of glass and feldspar microlites field textural and fractal data allow us to constrain the rheological features of the rhyolitic and lati trachytic magmas in situ major trace and volatile element analyses provide evidence for heterogeneities in the glassy matrix and zoning of phenocrysts processes of magma evolution have been quantitatively constrained by using the apparent distribution ratios of trace elements measured between mineral phases and glassy matrices the collected data in combination with petrological and fluid inclusion data from the literature provides evidence for 1 a genetic relationship between the two magmas through assimilation fractional crystallization process 2 a mingling mechanism between an uprising rhyolitic magma and a shallower partly crystallized lati trachytic magma plug 3 the desegregation enclaves at variable scales of the lati trachyte within the rhyolite and 4 the possible eruptive scenarios consequent to a future magmatic unrest

intermittent generation of mafic enclaves in the 1991 1995 dacite of unzen volcano recorded in mineral chemistry mafic enclaves in the 1991 1995 dacite of unzen volcano show chemical and textural variability such as bulk sio2 contents ranging from 52 to 62 wt and fine to coarse grained microlite textures in this paper we investigated the mineral chemistry of plagioclase and hornblende microlites and distinguished three enclave types type i mafic enclaves contain high mg plagioclase and low cl hornblende as microlites whereas type iii enclaves include low mg plagioclase and high cl hornblende type ii enclaves have an intermediate mineral chemistry type i mafic enclaves tend to show a finer grained matrix have slightly higher bulk rock sio2 contents 56 60 wt when compared with the type iii mafic enclaves sio2 53 59 wt but the overall bulk enclave compositions are within the trend of the basalt dacite eruptive products of quaternary monogenetic volcanoes around unzen volcano the origin of the variation of mineral chemistry in mafic enclaves is interpreted to reflect different degree of diffusion controlled re equilibration of minerals in a low temperature mushy dacitic magma reservoir mafic enclaves with a long residence time in the dacitic magma reservoir whose constituent minerals were annealed at low temperature to be in equililbrium with the rhyolitic melt represent type iii enclaves in contrast type i mafic enclaves result from recent mafic injections with a mineral assemblage that still retains the high temperature mineral chemistry taking temperature ca ca na ratio of plagioclase and water activity of the hydrous unzen magma into account the mg contents of plagioclase indicate that plagioclase microlites in type iii enclaves initially crystallized at high temperature and were subsequently re equilibrated at low temperature conditions compositional profiles of mg in plagioclase suggest that older mafic enclaves type iii had a residence time of 100 years at 800 c in a stagnant magma reservoir before their incorporation into the mixed dacite of the 1991 1995 unzen eruption presence of different types of mafic enclaves suggests that the 1991 1995 dacite of unzen volcano tapped mushy magma reservoir intermittently replenished by high temperature mafic magmas

particle size distributions of some soils from the umbria region italy fractal analysis and numerical modelling abstract application of principles of fractal geometry has had a strong influence on the understanding of many geological processes one of the research fields which has benefited of the development of fractal methods is soil science in this field fractal geometry techniques mainly applied to the study of particle size distributions psd contributed to shed new light on the complex dynamics involved in soil forming processes in this contribution we present new data of psd of a number of soil samples from the umbria region italy particle size distributions are analysed by applying fractal geometry methods and results indicate that they display a fractal behaviour in addition two fractal scaling domains are identified characterizing different ranges of particle sizes to understand the basic mechanisms responsible for the production of fractal features observed in studied soil samples numerical models based on computer automata are presented it is shown that the numerical simulations are in good conceptual agreement with natural data and give the opportunity to explain the basic features observed in the psd of studied soil samples

ray path interpretation of the crustal structure beneath saudi arabia abstract interpretation of a long range seismic refraction line in saudi arabia has shown that beneath the arabian shield velocity generally increases with depth from about 6 km s 1 at the surface to about 7 km s 1 at the top of the crust mantle transition zone the base of this transition zone moho occurs at 37 44 km in depth intracrustal discontinuities can also be recognized the most important being in the 10 20 km depth range and separating the upper from the lower crust laterally the variations in the intracrustal discontinuities and the total crustal thickness can be correlated with previously defined tectonic regions beneath the red sea shelf and coastal plain the crust including 4 km of sediments is only 15 17 5 km thick with the aid of both seismic and gravity data an abrupt steeply dipping transition from the crust of the red sea shelf and coastal plain to that of the arabian shield has been derived with a jump of more than 20 km in moho depth this appears to be the major discontinuity between the red sea depression and the arabian continental shield

kinematic significance of morphological structures generated by mixing of magmas a case study from salina island southern italy morphological features of mixing mingling structures of heterogeneous juveniles from the 13 ka old upper pollara eruption salina island southern italy are studied these heterogeneous rocks result from the mixing between an andesitic and a rhyolitic magma concentration patterns generated by magma mixing are analyzed on digital images and results have been compared with those obtained from numerical simulations of mixing processes coupling chaotic advection and chemical diffusion results show that the upper pollara rocks were produced by mixing 24 49 of andesite and 76 51 of rhyolite multifractal analysis of the mixing structures is performed and the mixing intensity i e the degree of interaction between the two end member magmas has been deduced from the analysis of the singularity spectrum results show that narrower is the multifractal spectrum the higher is the degree of homogenization of magmas reynolds number re during mixing has been estimated from the geometrical analysis of mixing structures by using experimentally defined relationships between shape parameters and re results show that re is between ca 500 and 7000 there is a positive correlation between the estimated initial percentage of mafic magma in the different analyzed samples and re in agreement with the observation that the higher is the percentage of the mafic lower viscosity magma the higher is the turbulence of the mixing system in addition our analysis reveals an unexpected inverse relationship between the calculated re and the degree of magma homogeneity suggesting that energy dissipation may have had a major role in the controlling mixing process because dissipation is inversely proportional to the mixing efficiency results suggest that mixing processes between the andesitic and rhyolitic magmas mainly developed in the conduit it is also suggested that mixing occurred in a shear layer type or pipe type flow

unravelling the complex interaction between mantle and crustal magmas encoded in the lavas of san vincenzo tuscany italy part ii geochemical overview and modelling abstract this work reports a geochemical overview and modelling of the lavas erupted 4 4 ma ago at san vincenzo tuscan magmatic province tmp although these lavas cover a relatively small area 10 km2 they show very large geochemical variations caused by the interaction of mantle derived and crustal anatectic magmas the lavas consist of peraluminous rhyolites 87sr 86sr i up to 0 726 hosting primarily variably sized magmatic enclaves with shoshonite latite compositions 87sr 86sr i down to 0 708 new whole rock data for a large shoshonite enclave show high concentrations of lree lile and tetravalent hfse coupled with pentavalent hfse depletions and enrichments in compatible elements such as cr and co the chondrite normalised ree pattern is strongly fractionated and characterised by a negative eu anomaly eu eu 0 79 hybridisation and afc models suggest that the shoshonite enclave is the result of 12 rhyolite contamination of a mantle derived magma akin to the potassic trachybasalt shoshonite lavas of capraia island 4 6 ma tmp following an 18 5 assimilation of late triassic metasediments 13 evaporite and 5 5 carbonate and 56 fractionation of clinopyroxene 39 plagioclase 10 and biotite 7 each rhyolite sample is characterised by mineral scale isotopic disequilibria e g 87sr 86sr i 0 711 0 726 glass inclusions with large k2o na2o variations 1 1 3 4 and a poli thermobarometric history of crustal melt production at eutectic conditions a multi parametric approach accounting for k2o na2o 1 3 2 2 87sr 86sr i 0 713 0 725 sr 104 311 ppm and rb 294 403 ppm whole rock variations allowed us to divide the anatectic a rhyolites into five groups a1 a2 1 a2 2 a2 3 a3 group a1 shows the highest 87sr 86sr i ratios and the lowest values of sr k2o na2o and rb it is related to a2 1 and a3 rhyolites by positive k2o na2o rb and k2o na2o feo correlations these three rhyolite groups crop out in the south of san vincenzo and are interpreted to derive from mixing and ascent of peraluminous magma batches locally extracted at progressively higher temperatures from the heterogeneous paleozoic metamorphic basement the a2 3 rhyolites show the highest rb concentrations up to 403 ppm and inverse sr rb and k2o feo correlations suggesting reactions involving the incongruent melting of a biotite bearing crustal source which was previously depleted in low temperature melting components such as muscovite and albite most of the a2 3 rhyolites crop out in the northern svvc area and appear spatially and geochemically related to the a2 2 rhyolites by similarly low 87sr 86sr i ratios however a2 2 rhyolites show lower rb contents 296 316 ppm and geochemical correlations e g 87sr 86sr i rb sr rb mgo feo clearly indicating hybridisation mixing with the shoshonite mantle derived magma rb 109 122 ppm finally we propose a four stage model for the magma plumbing system of san vincenzo produced by the uprising of a mantle derived magma in a normally faulted and doubled crustal basement characterised by two sections of paleozoic siliciclastic rocks separated by late triassic evaporite carbonate sequences

saudi arabian seismic refraction profile a traveltime interpretation of crustal and upper mantle structure abstract the crustal and upper mantle compressional wave velocity structure across the southwestern arabian shield has been investigated by a 1000 km long seismic refraction profile the profile begins in mesozoic cover rocks near riyadh on the arabian platform trends southwesterly across three major precambrian tectonic provinces traverses cenozoic rocks of the coastal plain near jizan and terminates at the outer edge of the farasan bank in the southern red sea more than 500 surveyed recording sites were occupied and six shot points were used including one in the red sea two dimensional ray tracing techniques used to analyze amplitude normalized record sections indicate that the arabian shield is composed to first order of two layers each about 20 km thick with average velocities of about 6 3 km s and 7 0 km s respectively west of the shield red sea margin the crust thins to a total thickness of less than 20 km beyond which the red sea shelf and coastal plain are interpreted to be underlain by oceanic crust a major crustal inhomogeneity at the northeast end of the profile probably represents the suture zone between two crustal blocks of different composition elsewhere along the profile several high velocity anomalies in the upper crust correlate with mapped gneiss domes the most prominent of which is the khamis mushayt gneiss based on their velocities these domes may constitute areas where lower crustal rocks have been raised some 20 km two intracrustal reflectors in the center of the shield at 13 km depth probably represent the tops of mafic intrusives the mohorovicic discontinuity beneath the shield varies from a depth of 43 km and mantle velocity of 8 2 km s in the northeast to a depth of 38 km and mantle velocity of 8 0 km s depth in the southwest near the shield red sea transition two velocity discontinuities occur in the upper mantle at 59 and 70 km depth the crustal and upper mantle velocity structure of the arabian shield is interpreted as revealing a complex crust derived from the suturing of island arcs in the precarnbrian the shield is currently flanked by the active spreading boundary in the red sea

magnetically inferred basement structure in central saudi arabia abstract a compilation of magnetic data acquired during the past three decades for a region in central saudi arabia where precambrian basement is partly exposed on the arabian shield and partly concealed by overlying phanerozoic strata shows a central sector of conspicuous n s trending anomalies a heterogeneous western sector of short wavelength high intensity anomalies and an eastern sector of low to moderate intensity broad wavelength anomalies anomalies in the western and central sectors correlate with neoproterozoic metavolcanic metasedimentary and intrusive rocks of the arabian shield and are interpreted as delineating extensions of shield type rocks down dip beneath phanerozoic cover these rocks constitute terranes making up part of a neoproterozoic orogenic belt that underlies northeast africa and western arabia and it is proposed that their magnetically indicated easternmost extent marks the concealed eastern edge of the orogenic belt in central arabia the flat magnetic signature of the eastern sector not entirely accounted for as an effect of deep burial may reflect the presence of a crustal block different in character to the terranes of the orogenic belt and speculatively may outline a continental block that according to some tectonic models of the region collided with the neoproterozoic terranes and thereby caused their deformation and tectonic accretion

surface waveform tomography of the turkish iranian plateau summary the middle east is a tectonically complex region consisting of terrains as diverse as precam brian shields and young orogens the dominant tectonic feature is the turkish iranian plateau a recently elevated seismically active region along the zagros bitlis suture which results from the collision of the arabian plate with eurasia in this study we use surface waveform tomography to elucidate the upper mantle shear wave velocity structure beneath the turkish iranian plateau and adjacent regions the main large scale feature in the tomographic model is a low shear wave velocity anomaly in the uppermost mantle beneath the plateau this low velocity feature correlates with a long wavelength free air gravity anomaly and with recent volcanism whose geochemistry has a lower lithospheric mantle signature seismology gravity and volcanism all suggest the presence of a thin lithosphere and warm upper mantle beneath the turkish iranian plateau the upper mantle low shear wave velocity zone the high free air gravity and the deep lithospheric source depth for the basaltic volcanism are all consistent with a partial delamination of the lithosphere as a result of earlier lithospheric thickening resulting from the continental collision

reply to comment by kawakatsu and abe on nature of the seismic lithosphere asthenosphere boundary within normal oceanic mantle from high resolution receiver functions kawakatsu and abe 2016 have highlighted the potential complicating effect of sediment reverberations on the analysis and interpretation of crust and mantle phases inferred from receiver functions analyzed from ocean bottom seismograms in their comment they identify resonant peaks in the power spectrum at one of the stations t06 in the analysis of olugboji et al 2016 and demonstrate with synthetic modeling how sediment induced resonances can cause instability in the recovered receiver function rf traces they also request a detailed explanation of how lqt rotation is conducted and why its use leads to stable receiver functions in the analysis of olugboji et al 2016 we welcome this query as an opportunity to highlight certain technical aspects of the data analysis procedures used in olugboji et al 2016 our methods derive partly from methods recommended by previous studies of receiver functions estimated from seismic seafloor data bostock and trehu 2012 janiszewski and abers 2015 audet 2016 particularly the use of the modal wavefield decomposition e g reading et al 2003 which we approximated by the lqt rotation to suppress reverberation signals in the overlying water column bostock and trehu 2012 this article is protected by copyright all rights reserved

temporal evolution of a three component system the island of lipari aeolian arc southern italy the volcanic products from lipari define an evolutionary trend with a high gradient of k enrichment similar to the calc alkaline to potassic volcanism of other islands in the aeolian arc stratigraphic reconstruction of the island based on field and geochronological data indicate that the volcanic activity can be subdivided in two stages the first stage from 223 to 42 ka consists of six eruptive cycles and is characterized by basalts and basalt andesites showing progressive increase in both sio2 and k2o contents with time the second stage consists of four cycles erupted since 42 ka and is marked by an apparent rejuvenation of the geochemical system with the appearance of the first rhyolitic products fractional crystallization assimilation and mixing models suggest that the geochemistry of lipari volcanism evolved with time by a complex interplay between two mantle derived components one sub alkaline and the other alkaline in addition to crustal melts and or crustally derived materials a petrogenetic model in which fractional crystallization was subordinate to mixing best fits the geochemical data and petrographic observations of macro and microscopic features melts from the crustal and mantle end members are almost always present in the system but the relative proportions appear to vary with time the sub alkaline mantle component source of tyrrhenian tholeiites is an important contributor to the early evolution of the volcanism in lipari input from the alkaline mantle component source of the roman comagmatic province increases with time and the crustal component becomes dominant in the later activity the preferred petrogenetic model for the temporal evolution of the volcanic system in lipari involves melting initially caused by an increase in the thermal input related to the opening of the tyrrhenian sea and or to subduction processes the quick rise of the isotherms and almost contemporaneous melting of source materials with different compositions favored complex mixing during ascent of the melts

hunting for oceanic island moho summary the structure of the oceanic crust conforms in general to a very simple model however fine scale variations of this structure in anomalous regions such as beneath oceanic islands remain poorly resolved here we examine teleseismic receiver functions rfs computed at four permanent broadband seismic stations on islands in the pacific region the rf method is ideal for examining the fine structure of the crust because it is sensitive to the interfaces between layers though less sensitive to average wave speed rfs at these oceanic island stations are characterized by a train of ps conversions from shallow depths rather than the isolated moho conversion typically seen at continental stations we find that a simple three layer structure the old oceanic crust sandwiched between an extruded volcanic layer and an underplated layer explains the main features of the rfs our data indicate that oceanic islands share a common structure a principal feature of which is crustal underplating with a total crustal thickness of 11 20 km

seismic evidence for water deep in earth s upper mantle water in the deep upper mantle can influence the properties of seismic discontinuities in the mantle transition zone observations of converted seismic waves provide evidence of a 20 to 35 kilometer thick discontinuity near a depth of 410 kilometers most likely explained by as much as 700 parts per million of water by weight

shear wave velocity structures of the arabian peninsula abstract the shear velocity structures of the different tectonic provinces of the arabian peninsula has been studied using surface wave data recorded by the ryd riyadh station the inversion of rayleigh wave group velocities indicates that the arabian shield can be modeled by two layers each of which is 20 km thick with a shear velocity of 3 61 km s in the upper crust and 3 88 km s in the lower crust the underlying upper mantle velocity is 4 61 km s inversion of both love and rayleigh waves group velocities shows that the arabian platform upper and lower crusts are comparable in their thicknesses to those of the shield but with shear velocities of 3 4 and 4 km s respectively the upper mantle velocity beneath the platform is 4 4 km s and the average total thickness of the crust is 45 km

surface wave velocities across arabia the group velocity distribution beneath the arabian plate is investigated using love and rayleigh waves we obtained a balanced path coverage using seismograms generated by earthquakes located along the plate boundaries we measured love and rayleigh wave group velocity dispersion using multiple filter analysis and then performed a tomographic inversion using these observations to estimate lateral group velocity variations in the period range of 5 60 s the love and rayleigh wave results are consistent and show that the average group velocity across arabia increases with increasing period the tomographic results also delineate first order regional structure heterogeneity as well as the sharp transition between the arabian shield and the arabian platform systematic differences are observed in the distribution of the short period group velocities across the two provinces which are consistent with surface geology the slower velocities in the platform reveal the imprint of its thick sedimentary section while faster velocities correlate well with the exposed volcanic flows in the shield shear wave velocity models for the two regions obtained from the inversion of the group velocities confirm results from previous studies of higher s wave velocity in the upper crust beneath the shield this may be due to the present remnants of the oceanic crust ophiolite belts associated with the island arcs evolutionary model of the arabian shield

interpretation of a seismic refraction survey across the arabian shield in western saudi arabia abstract in february 1978 seismic refraction profiles were recorded by the u s geological survey along a 1000 km line across the arabian shield in western saudi arabia this report presents a traveltime and relative amplitude study in the form of velocity depth functions for each individual profile assuming horizontally flat layering the corresponding cross section of the lithosphere showing lines of equal velocity reaches to a depth of 60 80 km the crust thickens abruptly from 15 km beneath the red sea rift to about 40 km beneath the arabian shield the upper crust of the western arabian shield yields relatively high velocity material at about 10 km depth underlain by velocity inversions while the upper crust of the eastern shield is relatively uniform the lower crust with a velocity of about 7 km s is underlain by a transitional crust mantle boundary for the lower lithosphere beneath 40 km depth the data indicate the existence of a laterally discontinuous lamellar structure where high velocity zones are intermixed with zones of lower velocities beneath the crust mantle boundary of the red sea rift most probably strong velocity inversions exist here the data do not allow a detailed modelling velocities as low as 6 0 km s seem to be encountered between 25 and 44 km depth

climatological evaporation seasonality in the northern red sea 1 the dynamic and thermodynamic processes that underlie the exceptionally high evaporation over the northern red sea are examined through a combination of data analysis and a simple numerical model we show that the key boundary layer dehumidifier is ageostrophic cross channel sea breezes this circulation develops semidiurnally in response to thermal gradients across the red sea s coasts because of disparate land ocean heat capacities during the summer day the thermally induced high pressure center over the red sea axis results in near surface flows from the red sea toward the neighboring deserts the strong divergence associated with these flows is maximized along the red sea axis and is accompanied by strong subsidence that suppresses boundary layer relative humidity by both reducing specific humidity and increasing temperatures because the summer nighttime reversed thermal gradients are smaller in magnitude the daytime circulation dominates over the nighttime in summer and thus dominates over the daily and seasonal means following similar reasoning we also devise a winter dehumidifier we conclude by advancing a simple means of estimating red sea evaporation under diverse paleoinsolation regimes and we show small but clear evaporation changes during the course of the holocene our estimates represent lower bounds and we plan to refine them in follow up work

bomb radiocarbon in the red sea a medium scale gas exchange experiment the history of bomb produced radiocarbon in the surface waters of the red sea and the western gulf of aden was reconstructed from annual growth bands of corals gulf of aden surface water entering the red sea and flowing to the north at the surface of the red sea becomes progressively enriched in bomb sup 14 c by air sea exchange of carbon dioxide with physical oceanographic observations and analysis as the basis of a simple model this progressive northward enrichment can be used to calculate a mean invasionn flux for co sub 2 across the red sea surface the co sub 2 invasion flux so calculated is 8 mol m sup 2 yr with an uncertainty of approximately 2 mol m sup 2 yr when combined with the extensive historical observations of wind speeds in the red sea the calculated co sub 2 invasion flux supports the empirical relationship between co sub 2 invasion and wind speed proposed by other workers sea surface pco sub 2 was measured at seven stations along the length of the red sea in january 1985 these pco sub 2 data show that in midwinter the net flux of co sub 2 across the red sea surface i e the difference between the invasion and evasion fluxes is approximately zero formore the red sea as a whole copyright american geophysical union 1989 less

influence of northern hemisphere climate and global sea level rise on the restricted red sea marine environment during termination i 1 we present high resolution paleoceanographic records of surface and deep water conditions within the northern red sea covering the last glacial maximum and termination i using alkenone paleothermometry stable oxygen isotopes and sediment compositional data paleoceanographic records in the restricted desert surrounded northern red sea are strongly affected by the stepwise sea level rise and appear to record and amplify well known millennial scale climate events from the north atlantic realm during the last glacial maximum lgm sea surface temperatures were about 4 c cooler than the late holocene pronounced coolings associated with heinrich event 1 2 c below the lgm level and the younger dryas imply strong atmospheric teleconnections to the north atlantic owing to the restricted exchange with the indian ocean red sea salinity is particularly sensitive to changes in global sea level paleosalinities exceeded 50 psu during the lgm a pronounced freshening of the surface waters is associated with the meltwater peaks mwp1a and mwp1b owing to an increased surface near inflow of normal saline water from the indian ocean vertical 18o gradients are also increased during these phases indicating stronger surface water stratification the combined effect of deglacial changes in sea surface temperature and salinity on water column stratification initiated the formation of two sapropel layers which were deposited under almost anoxic condition in a stagnant water body

on the deformation and freezing of enclaves during magma mixing abstract mixing of an enclave of hot mafic magma into cooler silicic magma involves the competing effects of heat transfer acting to rigidify the enclave and viscous shearing imposed by a flowing host magma acting to deform and disperse the enclave we model the time required to grow a rigid chilled margin and compare this with the time required to deform the initially hot enclave whether an enclave will deform before it freezes depends on the ratio of the thermal and deformation timescales pe app 3 a 2 s r 2 and the dimensionless rigidification temperature t r t s t m t s where app is the applied shear stress a is the enclave radius is the thermal diffusivity s is the viscosity of the host r is the strength of the chilled rind t r is the temperature at which the enclave attains strength r and t m and t s are the initial temperatures of the mafic enclave and silicic host according to the model small values of pe and large values of promote rapid rigidification the model is verified by laboratory experiments on the flow and freezing of polyglycol wax droplets in cold water geological observations show that correlations between enclave size degree of deformation and local shear stress match the model s predictions studies of enclave size and shape as functions of eruption rate and position within lava flows and minor intrusions offer a new technique for studying magma flow processes during eruptions

seismological structure of the upper mantle a regional comparison of seismic layering abstract we investigate seismic layering i e discontinuities regions of anomalous velocity gradients and anisotropy and its lateral variability in the upper mantle by comparing seismic models from three tectonic regions old 100 ma pacific plate younger 40 ma philippine sea plate and precambrian western australia these models were constructed by combining two data sets scs reflectivity profiles which provide travel times and impedance contrasts across mantle discontinuities and observations of frequency dependent travel times of three component turning s ss ss sss sss sa and surface r1 g1 waves which constrain the anisotropic velocity structure between discontinuities the models provide a better fit to observed seismograms from these regions than the current generation of global tomographic models the australian model is characterized by high shear velocities throughout the upper 350 km of the mantle with no low velocity zone lvz in the isotropically averaged shear velocities in contrast the oceanic models are characterized by a thin high velocity seismic lid underlain by a distinct lvz with a sharp boundary the g discontinuity separating them the g is significantly deeper beneath the western philippine sea plate than beneath the older pacific 89 and 68 km respectively implying that thermal cooling alone does not control the thickness of the lid we interpret this discontinuity as a compositional boundary marking the fossilized base of the melt separation zone msz active during sea floor spreading no discontinuity is detected at the base of the lvz in the oceanic models the s velocity gradient between 200 and 410 km depth is much steeper in the oceans than beneath australia this high oceanic gradient is probably controlled by a decrease in the homologous temperature over this depth interval the relative depths of the transition zone tz discontinuities are consistent with clapeyron slopes expected for an olivine dominated mineralogy the 660 km discontinuity displays variability in its amplitude that appears to correlate with its depth shallow and bright beneath the pacific deep and dim beneath australia and the philippine sea such behavior is possibly caused by the juxtaposition of the olivine and garnet components of the phase transition radial anisotropy extends through the upper 250 km of the mantle in the australia model and through the upper 160 km of the two oceanic models the magnitude of anisotropy is consistent with that expected for models of horizontally oriented olivine and the localization of anisotropy in the shallowest upper mantle implies that it reflects strain associated with past or present tectonic events

application of fractal fragmentation theory to natural pyroclastic deposits insights into volcanic explosivity of the valentano scoria cone italy abstract the extent of fragmentation triggered by basaltic volcanic eruptions has been studied by analyzing the grain size distribution of natural pyroclastic deposits and applying the fractal fragmentation theory for this purpose 75 samples have been collected from individual layers along horizontal section of the well exposed valentano scoria cone italy the cone is constituted by well defined layers of fall deposits of up to 180 cm in thickness an important feature of the stratigraphic sequence is the occurrence of several intercalated layers called breccias with clasts of different characteristics angular shape low porosity and high crystallinity in respect to the normal layers results indicate that all achieved grain size distributions show fractal behavior and can be clearly correlated with a single fragmentation event namely the magmatic fragmentation during the eruption the fractal dimension of fragmentation d increases as fragmentation efficiency increases values of d are found to vary significantly along the pyroclastic sequence defining two major trends 1 a general long range increase of d during the course of the eruption and 2 a superimposed high frequency oscillating variation of fragmentation efficiency noteworthy is the fact that the highest values of d are measured for pyroclastic deposits following breccia deposits application of a conceptual model of fractal fragmentation as claimed by natural data indicates that larger values of d have to be associated with a higher probability of fragmentation thus suggesting that the d value can be used as a proxy for the fragility i e ability to fragment of samples fractal dimension of fragmentation of single layers is positively correlated with the vesicularity of clasts this indicates that the bubble content in the ascending magma prior to and at fragmentation likely was the key factor modulating the variable fragmentation efficiency observed in the studied pyroclastic sequence we hypothesize that the long range variation of d may be associated with magma fragmentation triggered by expansion of gas bubbles progressively coalescing below solid plugs during later stages of eruptive activity whereas high frequency variations of d are interpreted as due to magma fragmentation during the slug flow regime characterizing the strombolian activity of the scoria cone

experimental and textural constraints on mafic enclave formation in volcanic rocks abstract we have used experiments and textural analysis to investigate the process of enclave formation during magma mixing at southwest trident volcano alaska andesite enclaves are present throughout the four dacite lava flows produced by the eruption and resemble mafic enclaves commonly found in other volcanic rocks our experiments replicate the pressure temperature time path taken by enclave forming andesite magma as it is engulfed in dacite during magma mixing pressure and temperature information for the andesite and dacite are from coombs et al contrib mineral petrol 140 2000 99 118 the andesite was annealed at 1000 c and then cooled to 890 c at rates of 110 c h 1 10 c h 1 and 2 c h 1 once cooled to 890 c andesite was held at this lower temperature from times ranging from 1 to 40 h the andesite that was cooled at the slower rates of 2 c h 1 and 10 c h 1 most resembles enclave groundmass texturally and compositionally based on simple thermal calculations these rates are more consistent with cooling of the andesite groundmass below an andesite dacite interface than with cooling of enclave sized spheres if enclaves do crystallize as spheres post crystallization disaggregation must occur calculations using the melts algorithm ghiorso and sack contrib mineral petrol 119 1995 197 212 show that for incoming andesite to become less dense than the dacite 34 volume of its groundmass must crystallize to undergo 18 volume vesiculation these values are similar to those determined for southwest trident enclaves thus such crystallization may lead to flotation of enclaves and be a viable mechanism for enclave formation and dispersal the residual melt in the cooling experiments did not evolve to rhyolitic compositions such as seen in natural enclaves due to a lack of a decompression step in the experiments decompression experiments on southwest trident dacite suggest an average ascent rate for the eruption of 2 3 mpa h 1 an andesite experiment that was cooled and then decompressed at this rate contains melt that matches that of the natural enclaves it is apparent that decompression ascent induced crystallization occurs in enclaves but not in the form of microlites as happens in the dacite host due either to insufficient residence time at chamber temperatures or to the pre existing microphenocrysts which act as sites for new growth

receiver functions from regional p waves summary p waves from regional distance earthquakes are complex and reverberatory as would be expected from a combination of head waves post critical crustal reflections and shallow incident p waves from the upper mantle although designed for steeply incident teleseismic p waves receiver functions rfs can also retrieve information about crustal structure from regional p using a new computation method based on multiple taper spectral analysis regional distance rfs for gsn stations rayn and anto show broad agreement with teleseismic rfs at rayn the moveout of the moho converted ps phase relative to direct p follows the predictions of the iasp91 earth model well the moho converted ps phase shows complexity associated with the transition zone triplications near 20 and constant delay zero moveout as 0 consistent with conversion from pn similar behaviour is seen for anto for events that arrive from the west for eastern backazimuths the anto rfs show features whose moveout is negative as 0 this moveout is poorly fit by reverberations in flat layers or by direct scattering from a dipping interface but is consistent with a topographic scatterer 20 30 km eastward of the anto site regional receiver functions may therefore be useful in judging whether teleseismic rfs at a particular station are suitable candidates for a 1 d velocity structure inversion synthetic seismograms of regional p phases computed with a locked mode reflectivity approach in a 1 d structure confirm several gross features of the rayn and anto regional receiver functions

the significance of microgranitoid enclave shapes and orientations abstract enclaves are often incorrectly used to measure magmatic strains in plutons we emphasize that microgranitoid enclaves are not like other ellipsoidal markers used to determine strain for the following reasons 1 adjacent enclaves may form at different times and different places and initially have non spherical shapes with axial ratios up to 2 7 2 the final shapes and orientations of enclaves are a complex function of a initial shape and temperature of enclaves b subtle changes in composition melt percents volatiles grain sizes and thus temporally variable viscosity contrasts between the enclave and magma c a competition between strain and interfacial energies and d deformation path which may include internal strain and rigid rotations caused by magma flow during ascent convection expansion chamber boundary processes and tectonism 3 enclaves spend much of their time in magma as relatively rigid objects and thus rigidly rotate and potentially break apart rather than strain at matrix strain rates 4 in some instances enclaves do not record or track finite strain because of the above final enclave populations are heterogeneous and the use of single enclaves or enclave populations as strain markers violates many assumptions needed to complete strain analyses on the other hand a comparison of the preserved characteristics of igneous layering mineral fabrics and carefully evaluated enclave fabrics including internal mineral alignment in enclaves may provide qualitative data on the changing magnitude and kinematics of magmatic strains

dominant northern hemisphere climate control over millennial scale glacial sea level variability abstract based on a radiocarbon and paleomagnetically dated sediment record from the northern red sea and the exceptional sensitivity of the regional changes in the oxygen isotope composition of sea water to the sea level dependent water exchange with the indian ocean we provide a new global sea level reconstruction spanning the last glacial period the sea level record has been extracted from the temperature corrected benthic stable oxygen isotopes using coral based sea level data as constraints for the sea level oxygen isotope relationship although the general features of this millennial scale sea level records have strong similarities to the rather symmetric and gradual southern hemisphere climate patterns we observe in constrast to previous findings pronounced sea level rises of up to 25 m to generally correspond with northern hemisphere warmings as recorded in greenland ice core interstadial intervals whereas sea level lowstands mostly occur during cold phases corroborated by climber 2 model results the close connection of millennial scale sea level changes to northern hemisphere temperature variations indicates a primary climatic control on the mass balance of the major northern hemisphere ice sheets and does not require a considerable antarctic contribution

african climate change and faunal evolution during the pliocene pleistocene abstract environmental theories of african faunal evolution state that important evolutionary changes during the pliocene pleistocene interval the last ca 5 3 million years were mediated by changes in african climate or shifts in climate variability marine sediment sequences demonstrate that subtropical african climate periodically oscillated between markedly wetter and drier conditions paced by earth orbital variations with evidence for step like 0 2 ma increases in african climate variability and aridity near 2 8 ma 1 7 ma and 1 0 ma coincident with the onset and intensification of high latitude glacial cycles analysis of the best dated and most complete african mammal fossil databases indicates african faunal assemblage and perhaps speciation changes during the pliocene pleistocene suggesting more varied and open habitats at 2 9 2 4 ma and after 1 8 ma these intervals correspond to key junctures in early hominid evolution including the emergence of our genus homo pliocene pleistocene shifts in african climate vegetation and faunal assemblages thus appear to be roughly contemporary although detailed comparisons are hampered by sampling gaps dating uncertainties and preservational biases in the fossil record further study of possible relations between african faunal and climatic change will benefit from the accelerating pace of important new fossil discoveries emerging molecular biomarker methods for reconstructing african paleovegetation changes tephra correlations between terrestrial and marine sequences as well as continuing collaborations between the paleoclimatic and paleoanthropological communities

lithospheric structure of the arabian shield from the joint inversion of receiver functions and surface wave group velocities abstract we estimate lithospheric velocity structure for the arabian shield by jointly modeling receiver functions and fundamental mode group velocities from events recorded by the 1995 1997 saudi arabian portable broadband deployment receiver functions are primarily sensitive to shear wave velocity contrasts and vertical travel times and surface wave dispersion measurements are sensitive to vertical shear wave velocity averages so that their combination bridge resolution gaps associated with each individual data set our resulting models correlate well with the observed surface geology the asir terrane to the west consists of a 10 km thick upper crust of 3 3 km s overlying a lower crust of 3 7 3 8 km s in the afif terrane to the east the upper crust is 20 km thick and has an average velocity of 3 6 km s and the lower crust is about 3 8 km s separating the terranes the nabitah mobile belt is made of a gradational upper crust up to 3 6 km s at 15 km overlying an also gradational lower crust up to 4 0 km s the crust mantle transition is found to be sharp in terranes of continental affinity east and gradual in terranes of oceanic affinity west the upper mantle shear velocities range from 4 3 to 4 6 km s temperatures around 1000 c are obtained from our velocity models for a thin upper mantle lid observed beneath station taif and suggest that the lithosphere could be as thin as 50 60 km under this station