low heat flux and large variations of lithospheric thickness in the canadian shield 1 ten new heat flux determinations have been made using measurements in 22 mining exploration boreholes located at latitudes higher than 51 n in the canadian shield they provide data in poorly sampled regions near the core of the north american craton where one expects the lithosphere to be thickest the new heat flux values are all smaller than 34 mw m 2 and are among the lowest recorded so far in the shield for all the new sites there is no relationship between heat flux and heat production in surface rocks in the canadian shield heat flux variations occur at wavelengths 100 km and are mostly of crustal origin local averages in two 250 250 km windows located on archean areas at high latitudes on either side of james bay are 29 mw m 2 and 31 mw m 2 the lowest values found so far at this scale in the canadian shield s wave traveltime delays derived from tomographic models provide the additional constraints needed to resolve differences of deep lithospheric thermal structure there is no significant correlation between average surface heat flux and traveltime delays within the canadian shield confirming that variations of the surface heat flux are mostly of crustal origin traveltime delays cannot be explained by variations in crustal heat production only and require variations of heat supply to the lithosphere and or radiogenic heat production in the lithospheric mantle these variations are associated with changes of lithospheric thickness that may be as large as 80 km the heat flux at the base of the superior lithosphere is constrained to be 11 2 mw m 2

thermal structure and seismicity of subducting lithosphere it has recently been suggested that the mechanical behaviour of the oceanic and continental uppermost mantle depends on temperature alone and that there is no strong evidence for compositional effects it seems in the majority of cases that if uppermost mantle temperatures exceed 600 c any deformation that occurs does so in the absence of significant seismicity this observation apparently applies irrespective of whether that mantle material underlies an ocean or a continent this paper investigates whether the same behaviour exists for earthquakes occurring in descending lithospheric slabs namely whether there is some limiting temperature above which deformation occurs without significant seismicity and whether that limiting temperature is consistent with the behaviour seen in the uppermost mantle beneath oceans and continents by re examining the thermal structure in subducting slabs accounting for the temperature dependence of the relevant physical parameters teleseismically recorded seismicity is shown to be limited to material having potential temperatures less than not vert similar570 600 c or homologous temperatures less than not vert similar0 42 the exceptions to this pattern occur in the subhorizontally subducting regions of the nazca plate in which temperatures are probably affected by the relatively cold overriding plate

differential contraction of subducted lithosphere layers generates deep earthquakes abstract the origin of forces for generating deep earthquakes remains elusive we propose a new mechanical model that involves constant release of shear strain accumulated between the crust and mantle lithosphere caused by differential volume changes during phase transformations as a slab sinks this generates increasing down dip compression inside the slab with depth consistent with the global distribution of deep earthquake focal mechanisms using experimentally calibrated slab rheology we show that the estimated distribution of slab internal stress agrees well with the depth frequency relationship of deep earthquakes in both cold and warm slabs with the peak in seismicity at 600 km depth corresponding to an induced stress maximum this mechanism of residual stress within a cold slab also provides a solution to deep earthquakes occurring beneath former subduction zones such as western tonga and spain we further suggest that this model may reconcile existing geodynamic paradoxes concerning the absolute strength of slabs discrepancies on mantle rock strength between laboratory and geophysical inversions as well as the competition between earthquake generating stresses and slab pull forces

crystallization of interstitial liquid and latent heat buffering in solidifying gabbros skaergaard intrusion greenland new compositional profiles across plagioclase grains from the layered series ls marginal border series mbs and upper border series ubs of the skaergaard intrusion are used to understand the mechanisms of cumulate rock solidification and the fate of the interstitial liquid the data show that plagioclase crystals display three types of compositional profile over the whole intrusion as follows 1 grains with normal zoning which dominate the mbs and ubs these are interpreted as having formed at the top of a crystal mush and then buried in the cumulate pile crystallization of the interstitial melt resulted in liquid differentiation and produced normally zoned rims on plagioclase cores 2 unzoned crystals which dominate the upper part of the ls also crystallized at the top of the mush and were then buried in mush with a low interstitial liquid fraction or one experiencing convective movements that kept the liquid to a constant composition 3 crystals with a mantle of decreasing an content followed by a rim of constant composition grains showing this complex zoning mostly occur in the lower parts of the ls depending on the stratigraphic position within the intrusion the composition of the rim can be an56 an51 or an40 in the main magma body these compositions an contents correspond to those of plagioclase primocrysts e g cores at the appearance of cumulus clinopyroxene an56 fe ti oxides an51 and apatite an40 compositional buffering of plagioclase rims is interpreted as being a consequence of enhanced release of latent heat of crystallization at the appearance of new interstitial phases in the crystal mush when a new phase saturates the latent heat contribution to the global enthalpy budget of the system becomes sufficiently high to keep the interstitial melt at its liquidus temperature for a period of time that could exceed thousands of years under these conditions equilibrium adcumulus growth together with diffusion and possibly advection of chemical components result in the formation of plagioclase rims of constant composition an content efficient thermal buffering of the mush liquid depends on the porosity i e fraction of liquid within the mush and the degree of compositional homogeneity of the mush in a heterogeneous and highly porous mush saturation of the new phase occurs in the coldest part of the mush and the enhanced latent heat release at the saturation of this phase is quickly dissipated to the whole volume of liquid including the warmest part that is not yet saturated in a new phase as a consequence no thermal buffering occurs and interstitial crystallization produces grains with normal zoning the distribution of the various types of plagioclase grains throughout the skaergaard intrusion can therefore be used to infer the spatial variability in the physical properties of the crystal mush such as the residual porosity both at an intrusion wide scale and at a millimetre to centimetre scale

a new self organizing mechanism for deep focus earthquakes the mechanism of deep focus earthquakes has been a puzzle since their discovery almost 70 years ago1 2 because brittle fracture and frictional sliding at depths in excess of 100 200 km would require unrealistic rock strengths3 4 rock strength does increase with pressure but a few hundred mpa equivalent to 10 20 km depth suffices to inhibit most fracture and elevated temperature activates ductile mechanisms that operate at stresses less than the fracture stength a range of mechanisms has been proposed for deep earthquakes including plastic instabilities5 7 shear induced melting8 11 and instabilities accompanying recrystallization12 13 or polymorphic phase transformation14 23 each of these proposed mechanisms has exhibited certain inherent weaknesses see kirby22 for review and discussion here we report experimental observations of high pressure faulting of metastable mg2geo4 olivine as it undergoes incipient transformation to a spinel 24 25 structure we present a model in which this faulting arises from the generation propagation and linking up of spinel filled anticracks26 when applied to the olivine spinel transformation in the earth s mantle the anticrack model27 satisfactorily accounts for the similarities and differences between shallow and deep earthquakes and removes the problems associated with frictional sliding

thermal conductivities under high pressure in core samples from iodp nantroseize drilling site c0001 we examined the effects of high pressure on thermal conductivity in core samples from the slope apron facies and the upper part of the accretionary prism at site c0001 of the nantroseize drilling program and in other samples of five terrestrial rock types thermal conductivity clearly increased with increasing pressure for both wet water saturated and dry samples we determined the rate of thermal conductivity change of the nantroseize sediments to be 0 014 wm 1k 1 mpa when pressure was increased and 0 01 wm 1k 1 mpa when pressure was decreased using the rate determined for decreasing pressure we estimated that thermal conductivities measured at atmospheric pressure rather than at in situ pressure may be underestimated by 7 for a core sample from around 1 km depth and by 20 for a core sample from around 3 km depth in general the rate of thermal conductivity change with pressure showed a positive correlation with porosity however the relationship of the rate of thermal conductivity change to porosity is also dependent on the fabric mineral composition and pore structure of the sediments and rocks furthermore for two sandstones we tested the effect of pressure on thermal conductivity for dry samples was greater than that for wet samples

effects of latent heat release at phase boundaries on flow in the earth s mantle phase boundary topography and dynamic topography at the earth s surface abstract mantle flow models that do not consider the effects of latent heat on phase boundaries typically predict dynamic surface topography too large to be compatible with observations here these effects were implemented in a mantle flow model and resulting changes in dynamic topography and topography of phase boundaries were computed inclusion of these effects was found to reduce the rms amplitude of dynamic topography by about 50 60 m still leaving a substantial misfit from observations in most cases considered generally it also leads to a slight improvement of correlation with dynamic surface and phase boundary topography constrained by observations results thus indicate that the model implemented here is applicable to the earth but that other effects need to be considered as well in order to fully explain phase boundary and dynamic surface topographies

effects of variable thermal conductivity on the mineralogy of subducting slabs and implications for mechanisms of deep earthquakes abstract thermal and thermo kinetic models of subduction zones have been based in general on a constant value of thermal conductivity e g 3 138 w m k for solving the conservation of energy equation in order to make such models more realistic we have used variable thermal conductivities k that depend on pressure temperature and mineralogy olivine wadsleyite or ringwoodite as determined recently by xu et al xu y shankland t j linhardt s rubie d c langenhorst f klasinski k 2004 thermal diffusivity and conductivity of olivine wadsleyite and ringwoodite to 20 gpa and 1373 k phys earth planet inter 143 144 321 336 we have used these variable conductivities to model a variety of slabs with thermal parameters vertical subduction rate age of lithosphere at the trench ranging between 3500 and 17 000 km our models show that when radiative transfer is included k could plausibly be increased by as much as 2 w m k relative to a standard constant lithospheric value 3 138 w m k stein c a stein s 1992 a model for the global variation in oceanic depth and heat flow with lithospheric age nature 359 123 129 causing temperatures in the interiors of the slabs to increase by 50 100 c in turn the volume of metastable olivine in the slabs is reduced by as much as 20 30 with the maximum depth of olivine metastability decreasing by 30 50 km in general the maximum depths of olivine metastability are 160 230 km less than the depths of the deepest seismicity even in the extreme case of tonga metastable olivine falls short of the deepest earthquakes by 140 km in our model even taking the various uncertainties into account these results indicate that deep focus earthquakes occur in regions already transformed to wadsleyite or ringwoodite and must therefore be caused by a mechanism other than transformational faulting

coherent and subsequent incoherent ringwoodite growth in olivine of shocked l6 chondrites abstract pervasive replacement of original olivine grains by ringwoodite adjacent to a shock melt vein of yamato 791384 l6 chondrite was observed with a feg sem in these olivines we observed three distinct olivine ringwoodite textures arranged in a spatially successive arrangement from the wall of the shock melt vein into the olivine grains 1 polycrystalline ringwoodite 2 oriented several sets of ringwoodite lamellae and 3 oriented single lamellae tem images show that the polycrystalline and oriented several sets of lamellae parts consist of polycrystalline ringwoodite indicating that phase transformation from olivine to ringwoodite is controlled by incoherent growth mechanism on the other hand the set of oriented single lamellae consists of thin ringwoodite platelets

controls on the location of compressional deformation on the nw european margin the distribution of cenozoic compressional structures along the nw european margin has been compared with maps of the thickness of the crystalline crust derived from a compilation of seismic refraction interpretations and gravity modelling and with the distribution of high velocity lower crust and or partially serpentinized upper mantle detected by seismic experiments only a subset of the mapped compressional structures coincide with areas susceptible to lithospheric weakening as a result of crustal hyperextension and partial serpentinization of the upper mantle notably partially serpentinized upper mantle is well documented beneath the central part of the southern rockall basin but compressional features are sparse in that area where compressional structures have formed but the upper mantle is not serpentinized simple rheological modelling suggests an alternative weakening mechanism involving ductile lower crust and lithospheric decoupling the presence of pre existing weak zones associated with the properties of the gouge and overpressure in fault zones and local stress magnitude and orientation are important contributing factors

earth mineralogical model gibbs free energy minimization computation in the system mgofeosio2 abstract a thermodynamic database which is consistent with most available phase equilibrium experiments and calorimetric and physical measurements on the solids in the system mgo feo sio 2 is established for the phases with the compositions mg fe sio 3 garnet perovskite pyroxene and ilmenite mg fe 2 sio 4 olivine and phases sio 2 stishovite and coesite and mg fe o periclase and wustite the data are systematized by using the high temperature birch murnaghan equation of state which includes the pressure and temperature dependent bulk modulus k and temperature dependent thermal expansion of the solids the systematized thermodynamic data contains heat capacity c p data which is internally consistent with the data on k volume and temperature such a systematized database is used to calculate by the method of minimization of gibbs free energy the mineralogical composition of the peridotitic pyrolitic and chondritic mgo feo sio 2 mantles the model corresponds closely to the seismological prem preliminary earth reference model in predicting the major seismic discontinuities however such discontinuities resulting from reactions or phase transformation are not as sharp as the seismic ones calculated adiabatic geothermal gradient starting at 6 gpa and 1500 k reaches a temperature of 2046 k at the core mantle pressure 135 gpa in a pyrolite mantle the model earth parameters in the lower mantle are prem parameters in bracket k s 308 306 to 687 656 gpa 70 69 to 121 118 km 2 s 2

why intracontinental basins subside longer 3 d feedback effects of lithospheric cooling and sedimentation on the flexural strength of the lithosphere

origin of azimuthal seismic anisotropy in oceanic plates and mantle abstract seismic anisotropy is ubiquitous in the earth s mantle but strongest in its thermo mechanical boundary layers azimuthal anisotropy in the oceanic lithosphere and asthenosphere can be imaged by surface waves and should be particularly straightforward to relate to well understood plate kinematics and large scale mantle flow however previous studies have come to mixed conclusions as to the depth extent of the applicability of paleo spreading and mantle flow models of anisotropy and no simple globally valid relationships exist here we show that lattice preferred orientation lpo inferred from mantle flow computations produces a plausible global background model for asthenospheric anisotropy underneath oceanic lithosphere the same is not true for absolute plate motion apm models a 200 km thick layer where the flow model lpo matches observations from tomography lies just below the 1200 c isotherm of a half space cooling model indicating strong temperature dependence of the processes that control the development of azimuthal anisotropy we infer that the depth extent of shear and hence the thickness of a relatively strong oceanic lithosphere can be mapped this way these findings for the background model and ocean basin specific deviations from the half space cooling pattern are found in all of the three recent and independent tomographic models considered further exploration of deviations from the background model may be useful for general studies of oceanic plate formation and dynamics as well as regional scale tectonic analyses

frozen melt rock reaction in a peridotite xenolith from sub arc mantle recorded by diffusion of trace elements and water in olivine this research was supported by natural environment research council algorithm doctoral studentship nerc 10 000497448 to pete tollan

localized polymorphic phase transformations in high pressure faults and applications to the physical mechanism of deep earthquakes earthquake mechanisms based on frictional instabilities are widely accepted for relatively shallow earthquakes such mechanisms in unmodified form are highly unlikely for deep earthquakes because of the expected high frictional shear stresses at depths of 300 700 km several alternative mechanisms have been proposed here i discuss a new type of shear instability observed in experiments on ordinary polycrystalline ice and polycrystalline tremolite by my colleagues and me these shear instabilities lead to rapid stress drops and sound emissions and have the following characteristics 1 a single sharp shear zone forms in the maximum shear stress orientation 2 confining pressure does not suppress the instability and under some conditions raising confining pressure pc lowers the differential stress at which it occurs 3 stress drops can occur repeatedly after reloading at about the same differential stress 4 the mean stress vs temperature conditions at which the instabilities occur in ice and tremolite place them in the fields of thermodynamic stability of ice ii and diopside talc respectively although i have not as yet confirmed the existence of these high pressure phases in the shear zones transformation in the shear zone is implicated because such shear instabilities do not occur in similar materials in which polymorphic phase changes do not occur reconstructive polymorphic phase changes localized along shear zones may be a general phenomenon in crystalline materials stressed non hydrostatically near transition boundaries moreover by analogy the reconstructive phase transformations that are thought to occur in deeply subducted lithosphere may lead to localized shear instabilities manifested by deep earthquakes and produce the observed double couple first motion distribution finally if this is the earthquake source mechanism in deeply subducted lithosphere then earthquakes should shut off when all of the polymorphic phase changes have occurred this may explain the maximum depth of earthquakes at about 680 km

thermal diffusivity and conductivity of olivine wadsleyite and ringwoodite to 20 gpa and 1373 k abstract we present results of lattice thermal diffusivity measurements on mg0 9fe0 1 2sio4 olivine and its high pressure polymorphs wadsleyite and ringwoodite under mantle conditions we used the angstrom method on cylindrical samples in multianvil apparatus at pressures up to 20 gpa and temperatures up to 1373 k because of the fine polycrystallinity of the specimens 30 40 m or less there is strong scattering absorption of light and suppression of radiative transport so that the lattice vibrational component is the dominant heat transfer mode lattice thermal conductivities were calculated from the thermal diffusivity results using heat capacity and equation of state data olivine thermal conductivities are consistent with previous results obtained at 1 atm e g j am ceramic soc 38 1954 107 j geophys res 77 1972 6966 science 283 1999 1699 thermal conductivity increases by approximately 30 at the transition from olivine to wadsleyite corresponding to the 410 km discontinuity and a further but smaller increase may occur at the transition from wadsleyite to ringwoodite for each of these phases lattice conductivity closely follows a t 1 2 dependence on temperature t phys rev 119 1960 507 j geophys res 79 1974 703 brown 2002 if such a dependence applies to other silicates and complex crystals there should be a useful way to estimate conductivities at high temperatures from room temperature measurements

reduced lattice thermal conductivity of fe bearing bridgmanite in earth s deep mantle complex seismic thermal and chemical features have been reported in earth s lowermost mantle in particular possible iron enrichments in the large low shear wave velocity provinces llsvps could influence thermal transport properties of the constituting minerals in this region altering the lower mantle dynamics and heat flux across core mantle boundary cmb thermal conductivity of bridgmanite is expected to partially control the thermal evolution and dynamics of earth s lower mantle importantly the pressure induced lattice distortion and iron spin and valence states in bridgmanite could affect its lattice thermal conductivity but these effects remain largely unknown here we precisely measured the lattice thermal conductivity of fe bearing bridgmanite to 120 gigapascals using optical pump probe spectroscopy the conductivity of fe bearing bridgmanite increases monotonically with pressure but drops significantly around 45 gigapascals due to pressure induced lattice distortion on iron sites our findings indicate that lattice thermal conductivity at lowermost mantle conditions is twice smaller than previously thought the decrease in the thermal conductivity of bridgmanite in mid lower mantle and below would promote mantle flow against a potential viscosity barrier facilitating slabs crossing over the 1000 km depth modeling of our results applied to llsvps shows that variations in iron and bridgmanite fractions induce a significant thermal conductivity decrease which would enhance internal convective flow our cmb heat flux modeling indicates that while heat flux variations are dominated by thermal effects variations in thermal conductivity also play a significant role the cmb heat flux map we obtained is substantially different from those assumed so far which may influence our understanding of the geodynamo

hydration reduced lattice thermal conductivity of olivine in earth s upper mantle earth s water cycle enables the incorporation of water hydration in mantle minerals that can influence the physical properties of the mantle lattice thermal conductivity of mantle minerals is critical for controlling the temperature profile and dynamics of the mantle and subducting slabs however the effect of hydration on lattice thermal conductivity remains poorly understood and has often been assumed to be negligible here we have precisely measured the lattice thermal conductivity of hydrous san carlos olivine mg0 9fe0 1 2sio4 fo90 up to 15 gigapascals using an ultrafast optical pump probe technique the thermal conductivity of hydrous fo90 with 7 000 wt ppm water is significantly suppressed at pressures above 5 gigapascals and is approximately 2 times smaller than the nominally anhydrous fo90 at mantle transition zone pressures demonstrating the critical influence of hydration on the lattice thermal conductivity of olivine in this region modeling the thermal structure of a subducting slab with our results shows that the hydration reduced thermal conductivity in hydrated oceanic crust further decreases the temperature at the cold dry center of the subducting slab therefore the olivine wadsleyite transformation rate in the slab with hydrated oceanic crust is much slower than that with dry oceanic crust after the slab sinks into the transition zone extending the metastable olivine to a greater depth the hydration reduced thermal conductivity could enable hydrous minerals to survive in deeper mantle and enhance water transportation to the transition zone

radiative heat transfer in a hydrous mantle transition zone abstract the structure and dynamics of earth s interior depend crucially upon heat flow and thus upon the thermal conductivity of its constituents we measured optical absorbance spectra of hydrous wadsleyite and hydrous ringwoodite at simultaneous high pressure and high temperature conditions up to 26 gpa and 823 k in order to determine their radiative conductivities and to study the potential influence of hydration in the transition zone on thermal conductivity of the mantle we report radiative thermal conductivities of 1 5 0 2 wm 1 k 1 for hydrous wadsleyite and 1 2 0 1 wm 1 k 1 for hydrous ringwoodite at transition zone conditions the analytically derived radiative thermal conductivities of anhydrous wadsleyite and ringwoodite are 40 and 33 higher respectively the total thermal conductivities calculated from temperature and pressure dependent optical absorption measurements maintain an energy transmission window in the infrared and visible spectral range at high pressures and temperatures the results indicate that the mantle transition zone may contribute significantly to heat transfer in the mantle and demonstrate the importance of radiative heat transfer in controlling geodynamic processes in earth s mantle

operational prediction of ash concentrations in the distal volcanic cloud from the 2010 eyjafjallajokull eruption 1 during the 2010 eruption of eyjafjallajokull improvements were made to the modeling procedure at the met office uk enabling peak ash concentrations within the volcanic cloud to be estimated in this paper we describe the ash concentration forecasting method its rationale and how it evolved over time in response to new information and user requirements the change from solely forecasting regions of ash to also estimating peak ash concentrations required consideration of volcanic ash emission rates the fraction of ash surviving near source fall out and the relationship between predicted mean and local peak ash concentrations unresolved by the model to validate the modeling procedure predicted peak ash concentrations are compared against observations obtained by ground based and research aircraft instrumentation this comparison between modeled and observed peak concentrations highlights the many sources of error and the uncertainties involved despite the challenges of predicting ash concentrations the ash forecasting method employed here is found to give useful guidance on likely ash concentrations predicted peak ash concentrations lie within about one and a half orders of magnitude of the observed peak concentrations a significant improvement in the agreement between modeled and observed values is seen if a buffer zone accounting for positional errors in the predicted ash cloud is used sensitivity of the predicted ash concentrations to the source properties e g the plume height and the vertical distribution of ash at the source is assessed and in some cases seemingly minor uncertainties in the source specification have a large effect on predicted ash concentrations

the 1989 1990 eruption of redoubt volcano alaska impacts on aircraft operations abstract the december 1989 june 1990 eruption of redoubt volcano affected commercial and military air operations in the vicinity of anchorage alaska these effects were due to the direct impact of volcanic ash on jet aircraft as well as to the rerouting and cancellations of flight operations owing to eruptive activity between december and february five commercial jetliners were damaged from ash encounters the most serious incident took place on december 15 1989 when a boeing 747 400 aircraft temporarily lost power of all four engines after encountering an ash cloud as the airplane descended for a landing in anchorage while there were no injuries to passengers the damage to engines avionics and aircraft structure from this encounter is estimated at 80 million four additional encounters between jet aircraft and redoubt ash clouds occurred in the anchorage area on december 15 and 16 1989 and february 21 1990 none resulted in engine failure two additional encounters took place on december 17 1989 when jet airliners encountered the redoubt cloud over west texas at the time of these encounters the cloud was up to 55 hours old and had traveled in excess of 2 900 nautical miles 5 300 km following the december 15 encounters anchorage international airport remained open however most airline companies canceled operations for up to several days as communications between federal agencies and airlines improved and as a better understanding of the nature and behavior of ash rich eruption clouds was achieved most airlines resumed normal service by early january 1990 the resulting loss of revenue at anchorage international airport during several months following the eruption is estimated to total 2 6 million the impact on general aviation and military operations consisted mostly of cancellation and rerouting of flights

improving volcanic ash cloud detection by a robust satellite technique abstract automated and reliable satellite based techniques are strongly required for volcanic ash cloud detection and tracking in fact volcanic ash clouds pose a serious hazard for air traffic and the synoptic and possibly frequent coverage offered by satellites can provide exciting opportunities for monitoring activities as well as for risk mitigation purposes a new avhrr based technique for improved automatic detection of volcanic clouds by means of multi temporal analysis of historical long term satellite records has been recently proposed the technique basically rests on the robust avhrr techniques rat approach which is an innovative strategy of satellite data analysis devoted to a former characterisation of the measured signal in terms of expected value and natural variability and a further recognition of signal anomalies by an automatic unsupervised change detection step in this work an extension of this method to nighttime observations is presented by using thermal infrared information coming from avhrr bands centred approximately at 3 5 11 0 and 12 0 m results achieved for two recent eruptive events of mount etna occurred in may 2000 and in july 2001 seem to be encouraging showing clear improvements in terms of ash detection sensitivity as well as in terms of false alarms reduction the technique performance is also evaluated by comparison with the traditional split window brightness temperature difference method this exercise revealed a general improvement obtained by the proposed approach even though some common problems still remain unsolved the main merits of such an approach are its intrinsic self adaptability to different environmental natural observational conditions and its natural exportability also to different satellite sensors the results here presented show the benefits of such a technique especially when different observational conditions time of pass seasonal period atmospheric moisture solar illumination volcanic cloud composition satellite angles of view etc are considered the future prospects also in terms of possible operational scenarios coming from the implementation of such an approach on the new generation of satellite sensors like for example seviri aboard meteosat second generation platform are also discussed

experimental constraints on the depth of olivine metastability in subducting lithosphere the hypothesis that metastable olivine persists in some subducting slabs into the transition zone has wide implications for mantle dynamics and rheology in order to evaluate this possibility we derive new thermo kinetic subduction zone models to predict the extent of olivine metastability within the stability fields of its high pressure polymorphs wadsleyite and ringwoodite our updated models improve on previous work by incorporating experimental kinetic data on realistic mantle compositions mg fe 2sio4 rather than analogue systems furthermore latent heat due to the transformation is fed back into both the kinetics and the thermal model we also consider the effects of transformation stress on growth kinetics and the possibility of an intracrystalline transformation mechanism previously thought to be important only at high shear stresses our models predict significantly smaller wedges of metastable olivine than previous work in the case of tonga for example where high values of lithospheric age 100 140 million years and convergence rate 14 cm per year are most favorable for metastability models considering only grain boundary nucleation and interface controlled growth predict olivine metastability to 600 km depth in contrast to 660 km predicted previously by kirby et al rev geophys 34 1996 261 when intracrystalline transformation is considered the depth of metastability is further reduced by as much as 100 km due to the large increase in the density of nucleation sites inhibition of growth by transformation stress can increase the depth interval over which the transformation takes place but is unlikely to be a dominant factor especially if the intracrystalline mechanism operates these results indicate that the existence of metastable olivine at depths corresponding to those of the deepest earthquakes 680 km requires subduction of old lithosphere 100 million years and a high vertical subduction velocity 15 cm per year such conditions currently may only be achieved in the very northern part of the tonga subduction zone yet earthquakes occur at depths down to 680 km in other subduction zones in which lithospheric age and or subduction velocity are relatively low e g indonesia and the marianas therefore mechanisms other than transformational faulting in metastable olivine must operate to cause the deepest earthquakes

new views on the structure and rheology of the lithosphere over the last 10 years a series of developments have led to a new understanding of what controls the variations in lithosphere strength structure and evolution that produce dramatic contrasts between the geological histories of oceans ancient shields and young orogenic belts those developments involve a wide range of observations from a great diversity of geological geophysical and geochemical disciplines that none the less provide a mutually consistent and coherent overall picture this paper summarizes in one place the essential stages in the evolution of the relevant ideas and observations that have led to this situation

caliop observations of the transport of ash from the eyjafjallajokull volcano in april 2010 1 the cloud aerosol lidar with orthogonal polarization caliop is an elastic backscatter lidar carried on the calipso satellite caliop observations between 15 and 20 april 2010 of volcanic ash plumes following the eruption of the icelandic eyjafjallajokull volcano are reported here while caliop has limited spatial coverage due to nadir only sampling ash plumes were observed by caliop over a wide region from the north atlantic ocean to eastern europe during both day and night due to its nadir only view however caliop did not sample the densest ash plumes which were observed by passive satellite sensors and ground based lidar lidar depolarization and spectral backscatter signatures are used to discriminate ash layers from clouds most ash was observed in thin layers of laminar appearance with thicknesses ranging from 0 4 km to a little more than 1 km and at relatively low altitudes between 1 and 7 km most layers reported here produced strong lidar depolarization indicating a predominance of ash over sulfate aerosol in the plumes estimates of lidar extinction to backscatter ratio allow the retrieval of profiles of ash optical properties layers were observed with mean optical extinction ranging from 0 03 km 1 to nearly 1 km 1 combined with an estimate of mass extinction efficiency mass concentration profiles can also be estimated these observations of the three dimensional dispersion of the plume are complementary to observations from passive satellite instruments and ground based lidars and can be useful for verification of dispersion models such as those used by the volcanic ash advisory centers

the structure and sharpness of mg fe 2sio4 phase transformations in the transition zone abstract to calculate accurately the pressure interval and mineral proportions i e yields across the olivine to wadsleyite and wadsleyite to ringwoodite transformations requires a detailed knowledge of the non ideality of fe mg mixing in these mg fe 2 sio 4 solid solutions in order to constrain the activity composition relations that describe non ideal mixing fe mg partitioning experiments have been conducted between magnesiowustite and mg fe 2 sio 4 olivine wadsleyite and ringwoodite as a function of pressure at 1400 c using known activity composition relations for magnesiowustite the corresponding relations for the three polymorphs were determined from the partitioning data in all experiments the presence of metallic iron ensured redox conditions compatible with the earth s transition zone the non ideality of the mg fe 2 sio 4 solid solutions was found to decrease in the order w wadsleyite femg w ringwoodite femg w olivine femg these partitioning data were used along with published phase equilibria measurements for the mg 2 sio 4 and fe 2 sio 4 end member transformations to produce an internally consistent thermodynamic model for the mg 2 sio 4 fe 2 sio 4 system at 1400 c using this model the pressure interval of the olivine to wadsleyite transformation is calculated to be significantly smaller than previous determinations by combining these results with fe mg partitioning data for garnet the widths of transition zone phase transformations in a peridotite composition were calculated the olivine to wadsleyite transformation at 1400 c in dry peridotite was found to occur over a pressure interval equivalent to approximately 6 km depth and the mineral yields were found to vary almost linearly with depth across the transformation this transformation is likely to be even sharper at higher temperatures or could be significantly broader in wet mantle or in regions with a significant vertical component of mantle flow the entire range of estimated widths for the 410 km discontinuity 4 35 km could therefore be explained by the olivine to wadsleyite transformation in a peridotite composition over a range of quite plausible mantle temperatures and h 2 o contents the wadsleyite to ringwoodite transformation in peridotite mantle was calculated to take place over an interval of 20 km at 1400 c this transformation yield was also found to be near linear

effect of iron content on thermal conductivity of olivine with implications for cooling history of rocky planets abstract the influence of fe concentration on heat transport properties of olivine was investigated to understand the cooling history of rocky planets such as mercury mars and asteroids thermal conductivity and thermal diffusivity were measured simultaneously for olivine polycrystal with different fe contents fo fo90 fo70 fo50 fo31 and fo0 up to 10 gpa and 1100 k by a pulse heating method with increasing fe in olivine thermal conductivity of olivine first decreases and then slightly increases the minimum was found to be at composition near fo31 the absolute value of fo31 is about 65 lower than that of fo small amounts of fe in olivine can strongly reduce the thermal conductivity at low temperature value of fo90 is about 50 of fo at room temperature thermal conductivities of polycrystalline olivine have smaller absolute values and weaker pressure and temperature dependences compared with those of natural single crystal olivine determined by previous studies heat capacity of fo70 and fo50 calculated from and is independent of pressure and is controlled by nearly constant thermal expansion coefficient with increasing temperature smaller of olivine aggregate with high fe content would produce a warmer mantle and in turn possibly a thicker crust in the fe rich mars while heat in the fe poor mercury can escape faster than the other terrestrial planets olivine dominant asteroids with high fe concentration could have longer cooling history and lower thermal inertia on the surface

thermal diffusivity of olivine under upper mantle conditions summary thermal diffusivity of olivine with mg xsfeo i 2si04 composition is measured at pressures up to 9 gpa and temperatures up to 1700 k using the angstrom method in a cylindrical geometry the experimental results demonstrate that lattice thermal diffusivity increases with increasing pressure at a small rate 46 per cent increase over 10 gpa the experimental data also suggest that radiative thermal diffusivity may decrease with increasing pressure thermal diffusivity in the upper mantle has almost constant values of 7 8 x

on the seasonal sea ice cover of the sea of okhotsk free of ice 4 months of the year the sea of okhotsk begins to freeze over in a few coastal locations in november attains its maximum ice coverage usually in mid march and by june retains ice in only a few coastal regions this sequence is well recorded by satellite imagery from the electrically scanning microwave radiometer esmr on board nimbus 5 four years of esmr data reveal significant interannual variations in the maximum ice cover and in the smoothness of the growth and retreat periods of the years 1973 1976 the heaviest ice cover occurred in 1973 and the growth period most interrupted by temporary ice edge retreats was in 1974 comparison of the general features of the cycle of sea ice distribution with basic oceanographic factors shows that ice forms first in cold shallow low salinity waters and then seems to drift in a direction approximating the okhotsk kuril current system two basic patterns of ice edge positioning which occur frequently in the esmr data are identified as a rectangular structure and a wedge structure each of these is strongly correlated with the bathymetry of the region and with the known current system suggesting that convective depth and ocean currents play an important role in determining ice patterns certain major interannual variations in the ice extents are accounted for by interannual contrasts in the atmospheric pressure fields

a case study of observations of volcanic ash from the eyjafjallajokull eruption 1 in situ airborne observations on 17 may 2010 the faam bae 146 aircraft made remote and in situ measurements of the volcanic ash cloud from eyjafjallaja kull over the southern north sea the falcon 20e aircraft operated by deutsches zentrum fa r luft und raumfahrt dlr also sampled the ash cloud on the same day while no a wingtip to wingtipa co ordination was performed the proximity of the two aircraft allows worthwhile comparisons despite the high degree of inhomogeneity e g column ash loadings varied by a factor of three over 100 km the range of ash mass concentrations and the ratios between volcanic ash mass and concentrations of so2 o3 and co were consistent between the two aircraft and within expected instrumental uncertainties the data show strong correlations between ash mass so2 concentration and aerosol scattering with the faam bae 146 data providing a specific extinction coefficient of 0 6a 0 8 m2 g 1 there were significant differences in the observed ash size distribution with faam bae 146 data showing a peak in the mass at 3 5 mm volume equivalent diameter and dlr data peaking at 10 mm differences could not be accounted for by refractive index and shape assumptions alone the aircraft in situ and lidar data suggest peak ash concentrations of 500a 800 mg m 3 with a factor of two uncertainty comparing the location of ash observations with the ash dispersion model output highlights differences that demonstrate the difficulties in forecasting such events and the essential nature of validating models using high quality observational data from platforms such as the faam bae 146 and the dlr falcon

semi brittle behavior of wet olivine aggregates the role of aqueous fluid in faulting at upper mantle pressures the role of aqueous fluid in fracturing in subducting slabs was investigated through a series of deformation experiments on dunite that was undersaturated i e fluid free or saturated with water i e aqueous fluid bearing at pressures of 1 0 1 8 gpa and temperatures of 670 1250 k corresponding to the conditions of the shallower regions of the double seismic zone in slabs in situ x ray diffraction radiography and acoustic emissions aes monitoring demonstrated that semi brittle flow associated with aes was dominant and the creep failure strength of dunite was insensitive to the dissolved water content in olivine in contrast aqueous fluid drastically decreased the creep failure strength of dunite up to 1 gpa of weakening over a wide range of temperatures in the semi brittle regime weakening of the dunite by the aqueous fluid resulted in the reduction of the number of ae events i e suppression of microcracking and shortening of time to failure the ae hypocenters were located at the margin of the deforming sample while the interior of the faulted sample was aseismic i e aseismic semi brittle flow under water saturated conditions a faulting slip rate of 10 3 to 10 4 s 1 associated with a large drop of stress 0 5 to 1 gpa and or pressure p 0 5 gpa was dominant in fluid free dunite while a slow faulting slip rate 8 10 5 s 1 without any stress pressure drop was common in water saturated dunite aseismic semi brittle flow may mimic silent ductile flow under water saturated conditions in subducting slabs

conduit diameter and buoyant rising speed of mantle plumes implications for the motion of hot spots and shape of plume conduits 1 mantle plumes are expected to be affected by large scale flow in the earth s mantle related to plate motions subducted slabs and possibly large scale upwellings motion of plume conduits will depend on both large scale flow and buoyant rising speed of the conduit through the mantle here we present a model of depth dependent plume conduit temperature viscosity radius and buoyant rising speed and use it to compute plume and hot spot motion results support a temperature anomaly of about 500 k at the plume base in this case sublithospheric temperature anomaly is about 150 k for the iceland plume transition zone anomaly is between 150 and 200 k for iceland about 250 k for samoa and about 300 k for hawaii thermal plume radii are about 100 km in the upper mantle increasing to about 200 km in the lower mantle beneath the lithosphere viscosity in the vicinity of plumes is substantially reduced compared to the underlying mantle and fast moving plates deflect plumes by 200 km or less corresponding to a plume conduit buoyant rise time of about 3 myr between 400 and 100 km depth where most of the shear flow due to plate motions occurs during 100 myr plume conduits rise buoyantly from about 1500 2000 km depth in many cases computed hot spot motion agrees with previous computations south southeastward motion of the hawaiian hot spot during the past 100 myr louisville hot spot motion in a similar direction but at slower speed during the past 50 myr and westward motion of the easter hot spot relative to hawaii and louisville however the previously computed substantial southward motion of the kerguelen hot spot is not confirmed if plume sources in the lowermost mantle are assumed to move with large scale flow they are predicted to be displaced toward the two large scale upwellings beneath africa and the pacific relative to hot spot surface locations for fixed sources predicted tilts of the lower part of conduits tend to be opposite to that

so2 as a possible proxy for volcanic ash in aviation hazard avoidance 1 airborne volcanic ash poses a significant danger to aircraft but is difficult to quantify accurately using satellite data while sulphur dioxide is much easier to detect accurately but is much less of a direct hazard to aviation this paper investigates the reliability of using so2 as a proxy for the location of volcanic ash using an so2 retrieval from the infrared atmospheric sounding interferometer iasi and ash detections from iasi and the advanced along track scanning radiometer aatsr using a numerical missed ash fraction applied to the eruptions of eyjafjallajokull in 2010 and puyehue cordon caulle in 2011 reveals that the so2 flag typically misses 30 of the detectable ash furthermore the missed ash fraction is found to be highly variable both between the two eruptions and over the course of each eruption with values of over 80 found on some days the detection threshold of the aatsr ash flag is also investigated using radiative transfer calculations allowing the threshold of the iasi flag to be inferred and these are related to the ash contamination levels

variable conductivity effects on the thermal structure of subducting slabs understanding the thermal structure of the lithosphere in subduction zone environments is a key element in the realization of the source of deep focus earthquakes and other geodynamic processes model predictions of the thermal structure of subducting slabs are dependent upon a priori knowledge of how thermal conductivity varies within the slab using recent results for the variation of thermal conductivity as a function of temperature pressure and gross mineralogy we investigate how models that utilize a realistic model for variable conductivity compare with canonical models for constant conductivity results suggest that jumps in thermal conductivity across the phase boundaries that arise due to transformations to and spinel phases lead to old fast steeply dipping slabs being considerably warmer than previously thought although these results do not rule out the possibility of a metastable wedge source of deep focus earthquakes they do imply the likelihood of metastable olivine being found at depth is less than once thought

delayed cooling of the earth s mantle due to variable thermal conductivity and the formation of a low conductivity zone abstract the thermal conductivity of mantle materials decreases with higher temperatures and increases with greater pressure due to phonon mechanism but increases with temperature for radiative transfer this trade off attribute allows for the formation of a low conductivity zone lcz within the top thermal boundary layer in mantle convection we have studied with a two dimensional 2 d cartesian model the potential of this low conductivity zone in retarding secular cooling of the mantle for a longer period of time than models with constant thermal conductivity using a recently proposed model for thermal conductivity and an adiabatic boundary condition for the bottom of the mantle we have carried out a set of numerical experiments within the framework of the extended boussinesq approximation for constant viscosity depth dependent thermal expansivity and variable thermal conductivity with surface rayleigh numbers between around 106 and around 107 we have employed internal heating between two and four times the chondritic level and half life time values of 2 5 ga and 5 ga the cooling rate of the mantle can be decreased by the feedback interaction between mantle conductivity and internal heating which gives rise to slower sinking cold currents the retardation time increases with the strength of radiogenic heating and can be as long as a couple of billion years for high initial heating rates four times the chondritic value however increasing the radiative contribution of the conductivity speeds up the cooling process the less the radiative contribution is the more mantle cooling would be retarded in the course of adiabatic cooling we find the paradoxical situation in which the effective rayleigh number of the mantle can actually increase with time we suggest then that because of the possibilities for the formation of low conductivity zones adjacent to the thermal boundary layers which bring forth unexpected consequences mantle thermal conductivity should be considered as a fundamentally important factor in constraining the thermal evolution of both the core and mantle

supercritical fluid in the mantle transition zone deduced from h d interdiffusion of wadsleyite abstract knowledge of the distribution of water in the earth s mantle is key to understanding the mantle convection and geochemical evolution of the earth as wadsleyite and ringwoodite can incorporate large amounts of water in their crystal structures proton conduction has been invoked to account for the widespread conductive anomalies observed in the mantle wedge where descending slab stagnates at the transition zone however there is a lot of controversy on whether proton conduction by itself is able to explain such anomalies because of large discrepancy in the extent of the water effect deduced from previous electrical conductivity measurements on hydrous polycrystalline wadsleyite and ringwoodite here we report the hydrogen self diffusion coefficient obtained from h d interdiffusion experiments in wadsleyite single crystal couples our results demonstrate that the effect of water on the electrical conductivity of wadsleyite is limited and hydrous wadsleyite by itself is unable to explain conductive anomalies in the transition zone in contrast the expected hydrogen effective diffusion does not allow the wide propagation of water between the stagnant slab and surrounding mantle probably leading to persistence of local water saturation and continuous release of supercritical fluids at the stagnant slab roof on geological time scales this phenomenon provides an alternative explanation for both the high conductivity and seismic velocity anomalies observed in the mantle wedge at the transition zone depth

thermal conductivity profile in the nankai accretionary prism at iodp nantroseize site c0002 estimations from high pressure experiments using input site sediments

early evolution of a stratospheric volcanic eruption cloud as observed with toms and avhrr this paper is a detailed study of remote sensing data from the total ozone mapping spectrometer toms and the advanced very high resolution radiometer avhrr satellite detectors of the 1982 eruption of el chichon mexico the volcanic cloud atmosphere interactions in the first four days of this eruption were investigated by combining ultraviolet retrievals to estimate the mass of sulfur dioxide in the volcanic cloud krueger et al 1995 with thermal infrared retrievals of the size optical depth and mass of fine grained 1 10 m radius volcanic ash wen and rose 1994 our study provides the first direct evidence of gravitational separation of ash from a stratospheric gas rich plinian eruption column and documents the marked differences in residence times of volcanic ash and sulfur dioxide in volcanic clouds the eruption column reached as high as 32 km carey and sigurdsson 1986 and was injected into an atmosphere with a strong wind shear which allowed for an observation of the separation of sulfur dioxide and volcanic ash the upper more sulfur dioxide rich part of the cloud was transported to the west in the stratosphere while the fine grained ash traveled to the south in the troposphere the mass of sulfur dioxide released was estimated at 7 1 109 kg with the mass decreasing by approximately 4 1 day after the peak the mass of fine grained volcanic ash detected was estimated at 6 5 109 kg amounting to about 0 7 of the estimated mass of the ash which fell out in the mapped ash blanket close to the volcano over the following days 98 of this remaining fine ash was removed from the volcanic cloud and the effective radius of ash in the volcanic cloud decreased from about 8 m to about 4 m

thermal regime of the lithosphere in the canadian shieldthis article is one of a series of papers published in this special issue on the theme lithoprobe parameters processes and the evolution of a continent geothermal studies were conducted within the framework of lithoprobe to systematically document variations of heat flow and surface heat production in the major geological provinces of the canadian shield one of the main conclusions is that in the shield the variations in surface heat flow are dominated by the crustal heat generation horizontal variations in mantle heat flow are too small to be resolved by heat flow measurements different methods constrain the mantle heat flow to be in the range of 12 18 mw m 2 most of the heat flow anomalies high and low are due to variations in crustal composition and structure the vertical distribution of radioelements is characterized by a differentiation index di that measures the ratio of the surface to the average crustal heat generation in a province determination of mantle temperatures requires the knowledge of both the surface heat flow and di mantle temperatures increase with an increase in surface heat flow but decrease with an increase in di stabi

dynamical consequences in the lower mantle with the post perovskite phase change and strongly depth dependent thermodynamic and transport properties article i nfo we have carried out numerical simulations of large aspect ratio 2 d mantle convection with the deep phase change from perovskite pv to post perovskite ppv using the extended boussinesq approximation for a fluid with temperature and pressure dependent viscosity we have investigated the effects of various ppv phase parameters on the convective planform heat transport and mean temperature and viscosity profiles since ppv is expected to have a relatively weak rheology with respect to pv and a large thermal conductivity we have assumed that the transition from pv to ppv is accompanied by both a reduction in viscosity by 1 to 2 orders of magnitude and by an increase in thermal conductivity by a factor of 2 furthermore we have analyzed the combined effects of a strongly decreasing thermal expansivity in pv and steeply increasing thermal conductivity according to recent evidence from high pressure experiments and first principle calculations as long as the thermal expansivity and conductivity are constant ppv exerts a small but noticeable effect on mantle convection it destabilizes the d layer causes focusing of the heat flux peaks and an increase of the average mantle temperature and of the temporal and spatial frequency of upwellings when the latest depth dependent thermal expansivity and conductivity models are introduced the effects of ppv are dramatic on the one hand without ppv we obtain a very sluggish convective regime characterized by a relatively cool mantle dominated by large downwellings that tend to stagnate beneath the transition zone with ppv on the other hand we observe an extremely significant increase of the average mantle temperature due to the formation of large sized and vigorous upwellings that in some cases tend to cluster thus forming superplumes if a very large thermal conductivity at the core mantle boundary is assumed k 20 wk 1 m 1 we obtain a quasi steady state regime characterized by large and stable plumes with long lifetimes the combination of strongly depth dependent expansivity and conductivity is a viable mechanism for the formation of long wavelength long lived thermal anomalies in the deep mantle even if a low viscosity ppv atop the core mantle boundary is included

intermediate depth earthquakes linked to localized heating in dunite and harzburgite earthquakes can occur at great depths in the earth within subducting tectonic plates deformation experiments suggest these deep earthquakes can be triggered by localized heating of the slabs under high pressures

the effect of variable thermal diffusivity on kinematic models of subduction 1 we examine the influence of variable thermal properties on the thermal state of a subducting slab in the upper mantle and the transition zone by combining a kinematic slab model with models of thermal conductivity thermal diffusivity and conductivity models for major mantle minerals in the mgo sio2 system are developed based on experimental measurements on these minerals at high pressure and temperature the models show significantly higher thermal conductivity for stishovite and clinopyroxene compared to the mg2sio4 polymorphs and majorite garnet in our subduction model we consider scenarios with a differentiated slab basalt harzburgite pyrolite in a pyrolite mantle and uniform composition for both the slab and the mantle pyrolite or a pure mg2sio4 based system the role of highly conductive pyroxene is examined by taking it into account in some models and replacing it in others with majorite garnet this choice has a strong influence on the thermal state of the slab shifting the depth of the 1000 k temperature anomaly by as much as 100 km this is caused by faster cooling of the plate at the surface and thermal insulating effects once subducted temperature differences between models with variable thermal diffusivity and those with constant parameters can reach 125 k i e 10 of total thermal anomalies of the slab relative to an average geotherm taking into account the stable mineral phases we evaluate density variations between different models and find that variable thermal diffusivity results in a modest increase of negative buoyancy of the slab

on the increase in thermal diffusivity caused by the perovskite to post perovskite phase transition and its implications for mantle dynamics the thermal diffusivity of perovskite and post perovskite cairo3 has been measured at elevated pressure and temperatures up to 600 c using the x radiographic angstrom method at high temperatures we find that the thermal diffusivity of post perovskite is slightly below twice that of isochemical perovskite over the temperature range investigated assuming a similar effect occurs in mgsio3 post perovskite the effect of the contrasting thermal transport properties between perovskite and post perovskite on mantle dynamics has been investigated using simple two dimensional convection models these show a reduction in extent and increase in depth of post perovskite lenses as well as increased core mantle boundary heat flux broader upwellings and more vigorous downwellings when compared to the reference constant a case

measurement of thermal conductivity of omphacite jadeite and diopside up to 14 gpa and 1000 k implication for the role of eclogite in subduction slab thermal conductivity and diffusivity for three pyroxenes omphacite jadeite and diopside were determined up to 14 gpa and 1000 k in the kawai type multianvil apparatus via the pulse heating method measurements for omphacite are characterized by much lower thermal conductivity and thermal diffusivity than those of its two end members of jadeite and diopside presumably because of the complex substitution of four cations na 1 ca 2 al 3 and mg 2 in omphacite therefore simple arithmetic averaging is unsuitable for estimating thermal conductivity and diffusivity of the jadeite diopside solid solution system the thermal property of eclogite was estimated from those of garnet and omphacite the thermal conductivity of eclogite is much smaller than that of harzburgite which is assumed to compose of 80 olivine and 20 enstatite implying that subducted oceanic crust impedes thermal conduction from the hotter wedge mantle to the subducting slab thermal structure simulation results show that temperature of the subduction zone is about 50 c decreased when the effect of oceanic crust is included

computation of seismic profiles from mineral physics the importance of the non olivine components for explaining the 660 km depth discontinuity the recent increasing number of experimental works leads us to review the elastic properties and mineralogical transformations of mantle minerals the updated data set is used to compute seismic profiles for two petrological models along three adiabatic temperature profiles these profiles are chosen to stress out the influence of non olivine minerals on seismic parameters and to represent cold and horizontally averaged temperature profiles of the earth s mantle in a first part starting compositions of pyrolite and piclogite and a single layer convection are assumed the results clearly point out the importance of the non olivine part of the mineralogy two scenarios are found to explain the 660 km depth discontinuity

a large shock vein in l chondrite roosevelt county 106 evidence for a long duration shock pulse on the l chondrite parent body a large shock induced melt vein in l6 ordinary chondrite roosevelt county 106 contains abundant high pressure minerals including olivine enstatite and plagioclase fragments that have been transformed to polycrystalline ringwoodite majorite lingunite and jadeite the host chondrite at the melt vein margins contains olivines that are partially transformed to ringwoodite the quenched silicate melt in the shock veins consists of majoritic garnets up to 25 m in size magnetite maghemite and phyllosilicates the magnetite maghemite and phyllosilicates are the terrestrial alteration products of magnesiowustite and quenched glass this assemblage indicates crystallization of the silicate melt at approximately 20 25 gpa and 2000 c coarse majorite garnets in the centers of shock veins grade into increasingly finer grained dendritic garnets toward the vein margins indicating increasing quench rates toward the margins as a result of thermal conduction to the surrounding chondrite host nanocrystalline boundary zones that contain wadsleyite ringwoodite majorite and magnesiowustite occur along shock vein margins these zones represent rapid quench of a boundary melt that contains less metal sulfide than the bulk shock vein one dimensional finite element heat flow calculations were performed to estimate a quench time of 750 1900 ms for a 1 6 mm thick shock vein because the vein crystallized as a single high pressure assemblage the shock pulse duration was at least as long as the quench time and therefore the sample remained at 20 25 gpa for at least 750 ms this relatively long shock pulse combined with a modest shock pressure implies that this sample came from deep in the l chondrite parent body during a collision with a large impacting body such as the impact event that disrupted the l chondrite parent body 470 myr ago

metastable mantle phase transformations and deep earthquakes in subducting oceanic lithosphere earth s deepest earthquakes occur as a population in subducting or previously subducted lithosphere at depths ranging from about 325 to 690 km this depth interval closely brackets the mantle transition zone characterized by rapid seismic velocity increases resulting from the transformation of upper mantle minerals to higher pressure phases deep earthquakes thus provide the primary direct evidence for subduction of the lithosphere to these depths and allow us to investigate the deep thermal thermodynamic and mechanical ferment inside slabs numerical simulations of reaction rates show that the olivine spinel transformation should be kinetically hindered in old cold slabs descending into the transition zone thus wedge shaped zones of metastable peridotite probably persist to depths of more than 600 km laboratory deformation experiments on some metastable minerals display a shear instability called transformational faulting this instability involves sudden failure by localized superplasticity in thin shear zones where the metastable host mineral transforms to a denser finer grained phase hence in cold slabs such faulting is expected for the polymorphic reactions in which olivine transforms to the spinel structure and clinoenstatite transforms to ilmenite it is thus natural to hypothesize that deep earthquakes result from transformational faulting in metastable peridotite wedges within cold slabs this consideration of the mineralogical states of slabs augments the traditional largely thermal view of slab processes and explains some previously enigmatic slab features it explains why deep seismicity occurs only in the approximate depth range of the mantle transition zone where minerals in downgoing slabs should transform to spinel and ilmenite structures the onset of deep shocks at about 325 km is consistent with the onset of metastability near the equilibrium phase boundary in the slab even if a slab penetrates into the lower mantle earthquakes should cease at depths near 700 km because the seismogenic phase transformations in the slab are completed or can no longer occur substantial metastability is expected only in old cold slabs consistent with the observed restriction of deep earthquakes to those settings earthquakes should be restricted to the cold cores of slabs as in any model in which the seismicity is temperature controlled via the distribution of metastability however the geometries of recent large deep earthquakes pose a challenge for any such models transformational faulting may give insight into why deep shocks lack appreciable aftershocks and why their source characteristics including focal mechanisms indicating localized shear failure rather than implosive deformation are so similar to those of shallow earthquakes finally metastable phase changes in slabs would produce an internal source of stress in addition to those due to the weight of the sinking slab such internal stresses may explain the occurrence of earthquakes in portions of lithosphere which have foundered to the bottom of the transition zone and or are detached from subducting slabs metastability in downgoing slabs could have considerable geodynamic significance metastable wedges would reduce the negative buoyancy of slabs decrease the driving force for subduction and influence the state of stress in slabs heat released by metastable phase changes would raise temperatures within slabs and facilitate the transformation of spinel to the lower mantle mineral assemblage causing slabs to equilibrate more rapidly with the ambient mantle and thus contribute to the cessation of deep seismicity because wedge formation should occur only for fast subducting slabs it may act as a parachute and contribute to regulating plate speeds wedge formation would also have consequences for mantle evolution because the density of a slab stagnated near the bottom of the transition zone would increase as it heats up and the wedge transforms to denser spinel favoring the subsequent sinking of the slab into the lower mantle

seismicity structure and rheology of the lithosphere in the lake baikal region this paper combines observations of seismicity gravity topography and thermal and velocity structures to investigate the rheological properties of the lithosphere in the lake baikal region we examine the seismogenic thickness ts using 25 earthquakes of mw 5 1 7 1 whose full source parameters have been determined by inversion of teleseismic waveforms 13 of which are presented here for the first time these 25 events plus six others mw 5 0 5 8 whose depths are well constrained show that moderate earthquakes occur at depths up to 30 km in the northeast baikal rift based on the teleseismic waveform modelling results and published relocations of microearthquakes using regional networks we conclude that the mantle is not a significant source of seismicity in the baikal region using the admittance between free air gravity and topography we estimate the effective elastic thickness te in the region to be between 5 and 20 km nowhere do the data require that te ts consistent with the simple interpretation that the long term strength of the lithosphere resides in its seismogenic layer a weak mantle in the baikal region can be explained by its high temperature which we estimate by combining local geotherm estimates with the regional upper mantle velocity structure obtained from fundamental and higher mode surface waves geotherms are fitted to pressure and temperature estimates from mantle nodules at four sites both within and outside the siberian shield in order to constrain the temperatures at the moho we estimated crustal thicknesses using teleseismic receiver functions moho temperatures are estimated to exceed 550 c beneath the siberian shield and are higher in the more recently deformed mountain belts to the south based on a reassessment of oceanic geotherms and seismicity it seems likely therefore that the mantle in the baikal region is too hot to be a source of long term strength this is consistent with the recent suggestion that the distribution of mantle seismicity in both the oceans and the continents is dependent on temperature alone finally we note that results from s wave tomography studies combined with the observed locations of rift related earthquakes lead us to suspect that the frequently published position of the edge to the siberian shield at the surface provides a poor description of that same boundary at depth

thermal evolution model for the h chondrite asteroid instantaneous formation versus protracted accretion abstract we present a model of the thermal evolution of asteroids assuming an onion shell model for the h chondrite parent body we obtain constraints for the h chondrite asteroid parameters by fitting empirical h chondrite cooling ages of estacado guarena kernouve mt browne richardton allegan nadiabondi ste marguerite and forest vale by using a genetic algorithm for parameter optimisation the model improves previous calculations on the thermal history calculated in the instantaneous accretion approximation considering sintering and porosity dependent heat conduction the model is extended to include a finite growth time of the parent body to study whether the meteoritic record constrains the duration of the growth phase of the parent body where it assembles most of its mass it is found that only short accretion times of up to 0 1 ma are compatible with the empirical data on h chondrite cooling histories best fit models yield excellent agreement with the cooling age data particularly they indicate that i 26 al was the major heat source driving metamorphism while 60 fe contributed rather marginally ii maximum temperatures remained below partial melting temperatures throughout the body indicating that no partial differentiation occurred on the h chondrite parent asteroid iii the h chondrite asteroid formed 2 ma after cais briefly after most ordinary chondrite chondrules formed if 26 al abundance defines a chronological sequence