estimating the electrical conductivity of the melt phase of a partially molten asthenosphere from seafloor magnetotelluric sounding data seafloor magnetotelluric soundings provide models of electrical conductivity distributions in the earth s oceanic mantle by inverting the sounding results a high conductivity typically 0 01 0 1 s m layer is often obtained in the oceanic upper mantle which is referred to as the electrical asthenosphere the obtained high conductivity is then interpreted in terms of the amount of additional conduction that accounts for the conductivity value based on a physical model of the asthenosphere there are two major candidates that are considered as the cause of the asthenosphere the effect of water and partial melting in this paper we consider the partial melting hypothesis we propose a method to estimate the electrical conductivity of the melt phase that is responsible for high conductivity by assuming the melt fraction distribution in the asthenosphere we applied this method to one dimensional conductivity profiles recently obtained from three regions of different seafloor age and the results indicate that the proposed approach combined with other approaches such as seismology and mineral physics will provide useful information in testing a partial melting hypothesis for the cause of the asthenosphere

coal facies studies in spain this work is a synthesis of the distribution of the main coal basins and sub basins in spain as well as the research carried out on their coal facies the coal fields are distributed through the paleozoic mainly pennsylvanian mesozoic cretaceous and cenozoic times peats also exist in the southeast spain granada area although these types of deposits are not included in this review spanish coal basins are both of a paralic and intramontane type and the coal rank is highly variable from lignite in the case of the younger coal seams to anthracite for those of carboniferous age

electrical image of passive mantle upwelling beneath the northern east pacific rise sea floor magnetotelluric soundings along a portion of the east pacific rise reveal a symmetric high conductivity triangular region at depths of 20 90 kilometres that is consistent with partial melting of passively upwelling mantle the east pacific rise is a fast spreading mid ocean ridge where sea floor volcanoes and hydrothermal vents result from a robust mantle melt supply to explore how this magma is supplied to the surface kerry key and colleagues use sea floor magnetotelluric soundings to image mantle electrical structure to a depth of about 160 km along the northern east pacific rise the images reveal a symmetrical high conductivity anomaly beneath the ridge consistent with partial melting of passively upwelling mantle they explain a deeper conductor observed east of the ridge by asymmetric upwelling due to viscous coupling across two nearby transform faults these findings suggest that plate driven passive upwelling dominates this ridge segment while dynamic forces are negligible melt generated by mantle upwelling is fundamental to the production of new oceanic crust at mid ocean ridges yet the forces controlling this process are debated1 2 passive flow models predict symmetric upwelling due to viscous drag from the diverging tectonic plates but have been challenged by geophysical observations of asymmetric upwelling3 4 5 that suggest anomalous mantle pressure and temperature gradients2 6 7 and by observations of concentrated upwelling centres8 consistent with active models where buoyancy forces give rise to focused convective flow2 here we use sea floor magnetotelluric soundings at the fast spreading northern east pacific rise to image mantle electrical structure to a depth of about 160 kilometres our data reveal a symmetric high conductivity region at depths of 20 90 kilometres that is consistent with partial melting of passively upwelling mantle9 10 11 the triangular region of conductive partial melt matches passive flow predictions suggesting that melt focusing to the ridge occurs in the porous melting region rather than along the shallower base of the thermal lithosphere a deeper conductor observed east of the ridge at a depth of more than 100 kilometres is explained by asymmetric upwelling due to viscous coupling across two nearby transform faults significant electrical anisotropy occurs only in the shallowest mantle east of the ridge axis where high vertical conductivity at depths of 10 20 kilometres indicates localized porous conduits this suggests that a coincident seismic velocity anomaly12 is evidence of shallow magma transport channels13 14 rather than deeper off axis upwelling we interpret the mantle electrical structure as evidence that plate driven passive upwelling dominates this ridge segment with dynamic forces being negligible

the genesis of coal from the viewpoint of coal petrology abstract the genesis of the microscopic constituents of coal macerals and of maceral associations microlithotypes representing various coal facies is discussed in the light of recent advances that have been made in the study of coals and modern peats peat microscopy especially promoted the understanding of humification and biological gelification both of which are decisive for the genesis of huminites vitrinites in brown coals and hard coals respectively microbial activity during peatification has been documented by chemists microbiologists and petrologists and recently by electron microscopical observations in coals this activity leads to the incorporation of lipid substances into the humic matter and later influences the chemical physical and technological properties of vitrinites geochemical gelification transforms the huminites of brown coals into the vitrinites of bituminous coals and is probably caused by the onset of bitumen generation in coal in this process the hydrogel brown coal is transformed to the bitumogel bituminous coal coal as a source rock for oil has become an important research subject for coal petrologists and oil exploration the formation of more or less liquid bitumen and its later cracking to gaseous hydrocarbons leads to the coalification jumps of the macerals especially liptinites and vitrinites and to the generation of secondary macerals like exsudatinite bitumen and micrinite dead carbon bituminization in coal has been revealed by the use of fluorescence microscopy which also found the presence of new liptinite macerals bituminite fluorinite and exsudatinite and suggests a higher proportion of algal material in coals than was thought earlier the genesis of various types of inertinite macerals will probably become an increasingly important subject of research especially with regard to rank inertinites that seem to attain their high inertinitic reflectance initially during coalification besides the origin of macerals the origin of various coal facies in terms of maceral associations is considered in relation to the palaeogeographic depositional milieu the peat forming vegetation palaeoclimate water and nutrient supply acidity marine and calcareous influence and fire with examples from euramerican carboniferous coals gondwana coals and tertiary brown coals vegetation water and oxygen supply eh conditions are most important for the generation of coal facies vegetation has been reconstructed with the help of palaeobotany including palynology cuticular analysis and wood anatomy in brown coals and with the study of petrified permineralized peats preserved in coal balls the microscopical investigations of botanically recognizable plant remains isolated from coals or accompanying rocks has been especially informative however the results of palynological and cuticular analyses should be evaluated with caution considering the varying resistance of palynomorphs and cuticles and in the case of palynomorphs their possible extrapaludal origin microscopical studies of modern peats that were derived from different types of vegetation growing in different hydrological environments have been very helpful in interpreting coal facies especially in brown coals the much disputed origin of brown coal lithotypes is considered in detail for hard coals there seems to be agreement that coal layers rich in vitrites and liptinite poor clarite were deposited in wet forest swamps that microlayered liptinite rich clarites are sub aquatic humic muds and that inertinite rich durites represent oxidized peats the origin of liptinite rich durites is controversial either subaquatic muds or oxidized peats the latter perhaps from raised bogs a recent trend in the literature is the assumption that many if not all mineable coal seams have been deposited in raised bogs under ombrogenous oligotrophic conditions although raised bogs with a dense arborescent vegetation are known from borneo it seems not probable that most seams which were deposited in foredeeps or steadily sinking graben zones are of ombrogenous origin although a succession from relatively wet and eutrophic to relatively dry and oligotrophic conditions may be true for occasional seams but as in modern peats striking changes of coal facies are commonly caused by hydrological events e g inundations as a consequences of crevasses or of fires that burned the peat the origin of the inertinite rich gondwana coals is discussed in relation to their specific climatic conditions and a comparison with sub arctic peats is recommended coals influenced by marine and calcareous conditions are characterized by high contents of sulfur and pyrite as well as by hydrogen rich vitrinites with a relatively low reflectance and high fluorescence all due to a strong bacterial activity in peats of low acidity proposals for further research are made in the conclusions

organic petrology and clastic depositional environments with special reference to australian coal basins abstract two questions are addressed in this paper 1 what are the types of organic matter that accumulate as coal seams or are dispersed in shaly sediments to form potential petroleum source rocks in clastic fluvial lacustrine deltaic and nearshore marine environments and 2 what are the systematic variations that exist between the petrographic compositions of related coals and dispersed organic matter dom irrespective of environment as few published studies combine sedimentology and quantitative organic petrology most of the data considered especially for dom are from australian occurences tectonic setting geological age and flora appear to be the major determinants of organic matter type but atypical occurrences of coals and dom suggest that their influence can be overridden by unique events or the depositional conditions from the small amount of information available no particular coal type was found to be overwhelmingly associated with a specific paleodepositional environment systematic and thus predictable relationships between coals and related dom of permian and jurassic ages are 1 vitrinite dom vitrinite coal 20 1 2 inertinite dom inertinite coal 25 5 2 3 inertinite coal inertite durite 0 5 intermediates 3 4 inertinite dom inertite durite intermediates 4 5 vitrinite dom 0 6 vitrite clarite 5 relationships 1 and 2 do not hold for some jurassic data and 4 and 5 do not apply to the permian restricted sea environment where inertinite dom inertinite coal 40

phyterals of humic coals in the u s s r abstract the results of a study of plant remains found in coals of devonian to neogene age which were studied mainly by the method of phyteral analysis are presented most of phyterals discussed and illustrated in this paper are from coal basins in the u s s r however a discussion of occurrences of phyterals in coal basins worldwide is also included middle devonian coals contain fungal remains and phyterals of the enigmatic vascular plant orestovia the most characteristic phyterals of euramerican carboniferous coals are the following periderm of stems and rhizomes of lepidophytes wood and cortex of gymnosperms of uncertain systematic position rachides of pteridosperms and fructifications of spore bearing plants vitrinized phyterals predominate over fusinized phyterals in carboniferous coals in permian coals of gondwana and angarida vitrinized and fusinized woods bark tissues and leaves of pycnoxylic gymnosperms are characteristic phyterals differences in phyteral composition of early and late permian coals indicate that phyterals from vitrinized leaves were more dominant in late permian coals triassic coals rarely contain phyterals of known affinity jurassic and early cretaceous coals are similar in phyteral composition periderm and cork of conifers and ginkgoaceous plants are typical phyterals phyterals of vitrinized and fusinized gymnospermous wood played a significant role in these coals as well leaf phyterals usually compose layers of the paper and fall of leaves coals distinctive characteristics of phyteral composition of cenozoic coals are 1 wide distribution of lignitized woods 2 constant presence of well identified and very specific root remains 3 high content of plant attritus 4 commonly occurring and distinctive fungal phyterals further study of coal phyterals is suggested for correlation of coal seams and coal bearing strata and for the prediction of coal quality

palaoecologic trends and petroleum potential of upper carboniferous coal seams of western germany as revealed by their petrographic and organic geochemical characteristics abstract petrographic compositions of microscopically homogeneous vertical sections in coal profiles from the ruhr basin northwestern germany are reported the studied coal seams of late westphalian age are between 0 4 and 2 4 m thick mean vitrinite reflectivities in the range of 0 1 0 thus indicating high volatile a bituminous coal changes in the organic facies within the coal profiles are common and can be linked to changes of plant communities and preservation conditions in the depositional environments also associated variations in mineral content are usually found although patterns of changes in maceral and mineral contents are complex some general trends have been observed continuous development from seat earth to coal with vitrinitic roots and detritic liptinites and inertinites representing the initial stage of peat and coal evolution just above the base thick vitrinite rich sections with abundant mudstone layers are overlain by inertinite rich sections with low mineral and high sporinite contents the latter may represent highly degraded oxidized peats that accumulated at morphologically elevated areas deposition of clastic roof strata had only a minor influence on organic facies coals and dispersed organic matter in these clastic rocks are in the main similar in maceral group composition organic geochemical characterization of selected lithotypes revealed significant differences between coals and dispersed organic matter this can be explained by trapping of generated hydrocarbons in the coals differences in elemental compositions of coals of the same organic facies at different ranks vitrinite reflectance of 0 70 and 0 92 respectively reflect a loss of about 20 wt co 2 bitumen water during this maturation stage gas chromatographic mass spectrometric analyses of the saturated hydrocarbon fraction in solvent extracts separated from selected samples reveal that all samples contain the same classes of compounds namely straight chain alkanes hopanoids and isoprenoids but that there is a significant difference in the relative abundance of these classes of compounds in the different coals

maceral distribution in garumnian coals and palaeoenvironmental implications in the central pyrenees spain abstract the organic content of garumnian coals in the central pyrenees of spain is heterogeneous and is formed of plant fragments with the fossil remains of botanic structures and secondary products resulting from thermal and biochemical transformation of macerals the maceral composition of the three areas studied berga tremp and ager is similar the berga and tremp zones include an upward decrease in organic materials and the top sequence is significantly richer in inorganic sediments in contrast in the ager zone only one level with organic matter is present the organic matter of the tremp formation is humic and five resinite groups have also been characterized the mineral phases determined mainly carbonates appear closely associated with macerals infilling cell lumens or replacing cell walls and in layers within the organic matter the maturity and source rock potential of the organic rich beds were investigated using reflected light and fluorescence microscopy the results are compared with other maturity parameters rock eval calorific value and diagenetic mineral matter the vitrinite reflectance r o 0 35 0 45 and the maximum temperature 430 c are low and homogeneous in the different areas these values indicate that the rank of the samples corresponds to an immature diagenetic state close to the lower oil window and allows classification of this coal as subbituminous the relationship between inorganic and organic phases indicates low grade transformation as a consequence of a low lithostatic pressure the macerals indicate that the coal forming peat was deposited in a predominantly forest moor swamp environment the liptinite assemblage suggests a subtropical and damp dlimate during peat deposition the amount of organic matter decreases upwards within the sedimentary sequences analyzed palaeoenvironments were similar in the three areas which could originally have been part of the same basin

3d modelling of electrical anisotropy from electromagnetic array data hypothesis testing for different upper mantle conduction mechanisms abstract upper mantle electrical conductivities provide besides seismic velocities or thermal diffusivities another source of information on upper mantle structure and composition we present the results of a long period magnetotelluric dataset consisting of 64 sites covering an area of 300 km 400 km in central germany mapping electrical conductivities at the base of the lithosphere to seperate the effect of crustal and upper mantle structures we interprete the obtained dataset by 3d conductivity modelling we observe high conductivities and anisotropies at asthenospheric upper mantle depth with main bulk conductivities of 1 2 s m in west east and 4 1 0 3 s m in north south direction differing by about two orders of magnitude in comparing with results from laboratory measurements on electrical conductivites for various conduction mechanisms we are able to confine the conduction mechanisms possibly dominating at these depths with melt volume fractions of 1 only partial melt can be excluded as origin of the high upper mantle conductivities instead conductivity enhancement due to hydrogen diffusion along the olivine 1 0 0 axis is favoured as the dominant conduction mechanism at the base of the lithosphere

an appraisal of coal petrographic facies in lower gondwana permian coal seams of india abstract petrographic facies in lower gondwana coals of india are characterized by coal types that depend upon the paleogeographic and tectonic framework of the coal basins paleoclimate the flora and fauna of the coal forming swamps and coal constituent characteristics an appraisal of coal petrographic facies of these coals was made using these parameters with time permian coal peat seams were deposited in india over a wide range of structural and sedimentary settings and formed suites of composite genetic coal types or in other words petrographic facies controlled mainly by temporal climatic and floristic differences at the first level of resolution of petrographic facies variation the composite genetic coal types were controlled by stratigraphic sequences namely karharbari barakar and raniganj formations then within the coal of each stratigraphic units further differentiation in coal facies are discernible based on petrographic types in terms of restricted paleoenvironmental and structural setting the coal seams of the karharbari formation are mainly characterized by high inertinite content although several local seams with high vitrinite content are present in contrast barakar and raniganj coal seams are generally characterized by high vitrinite content although some coal seams are rich in inertinite content the four main petrographic coal facies found in permian strata are 1 fusic rich in inertinite group macerals over vitrinite 2 trimaceric rich in vitrinite group macerals over inertinite macerals vitro fusic 3 trimaceric rich in inertinite group macerals over vitrinite and liptinite fuso vitric and 4 vitric rich in vitrinite group macerals the succession of these four main petrographic facies with time was governed mainly by changes in climate and peat forming floras and paleoenvironmental conditions in the coal swamp petrographic composition differs within a restricted period of time as illustrated in the model given for the bokaro coal basin such petrographic coal types forming coal facies character are mainly controlled by the regional tectonic and sedimentary framework a considerable diversity and overlapping of coal petrographic facies is discernible with most of the coal measures of india yet the main petrographic facies or composite genetic coal types were controlled by evolving flora and changing paleoclimatic patterns the delimitation of various petrographic facies of the indian coal seams has implications for understanding the origin and evolution of gondwana coals

new insights into crustal and mantle flow beneath the red river fault zone and adjacent areas on the southern margin of the tibetan plateau revealed by a 3 d magnetotelluric study

brine mineral reactions in evaporite basins implications for the composition of ancient oceans the chemical evolution of several european mesozoic and tertiary evaporite basins was reconstructed by using mineral associations primary fluid inclusion analyses and numerical simulations of evaporation scenarios the solute proportion recorded in the fluid inclusions can be explained by the evaporation of present day seawater as a major recharge the sulfate depletion in the brines is responsible for the type of potash deposit formed potassium magnessium sulfates or sylvite this sulfate depletion can be due either to dolomitization or to the addition of a cacl 2 rich solution to the basin the sulfate depletion occurred in varying intensity in basins of the same age as well as throughout the evolution of the same basin therefore changes in potash mineralogy and sulfate depletion in fluid inclusions are not conclusive arguments in favor of secular variations in the composition of the ocean as recently proposed by several authors

lithospheric dismemberment and magmatic processes of the great basin colorado plateau transition utah implied from magnetotellurics 1 to illuminate rifting processes across the transition zone between the extensional great basin and stable colorado plateau interior we collected an east west profile of 117 wideband and 30 long period magnetotelluric mt soundings along latitude 38 5 n from southeastern nevada across utah to the colorado border regularized two dimensional inversion shows a strong lower crustal conductor below the great basin and its transition zone in the 15 35 km depth range interpreted as reflecting modern basaltic underplating hybridization and hydrothermal fluid release this structure explains most of the geomagnetic variation anomaly in the region first measured in the late 1960s hence the transition zone while historically included with the colorado plateau physiographically possesses a deep thermal regime and tectonic activity like that of the great basin the deep crustal conductor is consistent with a rheological profile of a brittle upper crust over a weak lower crust in turn on a stronger upper mantle jelly sandwich model under the incipiently faulted transition zone the conductor implies a vertically nonuniform mode of extension resembling early stages of continental margin formation colorado plateau lithosphere begins sharply below the western boundary of capitol reef national park as a resistive keel in the deep crust and upper mantle with only a thin and weak moho level crustal conductor near 45 km depth several narrow steep conductors connect conductive lower crust with major surface faulting some including modern geothermal systems and in the context of other great basin mt surveying suggest connections between deep magma sourced fluids and the upper crustal meteoric regime the mt data also suggest anisotropically interconnected melt over a broad zone in the upper mantle of the eastern great basin which has supplied magma to the lower crust consistent with extensional mantle melting models and local shear wave splitting observations we support a hypothesis that the transition zone location and geometry ultimately reflect the middle proterozoic suturing between the stronger yavapai lithosphere to the east and the somewhat weaker mojave terrane to the west we conclude that strength heterogeneity is the primary control on locus of deformation across the transition zone with modulating force components

a joint interpretation of electromagnetic and seismic tomography models suggests the mantle transition zone below europe is dry abstract the three dimensional 3d electrical conductivity distribution in the mantle transition zone mtz below europe is resolved by directly inverting geomagnetic response functions from 12 selected european observatories comparison of the conductivity image with the results of global seismic tomography reveals a good correlation between low conductivity and high velocity anomalies at depths of 400 700 km beneath the mediterranean subduction zone in central europe interpretation of the 3d conductivity model combined with seismic tomography indicates that the european mtz is drier than the mtz beneath the western pacific subduction zone even though the subducted slab material is stagnating similarly in both regions

constraints on the fe s melt connectivity in mantle silicates from electrical impedance measurements the connectivity of fes melts in olivine and in a fertile peridotite matrix has been addressed through in situ electric impedance spectroscopy is measurements at 1 gpa a first series of experiments used sintered powder samples of a fertile peridotite xenolith mixed with 5 15 vol fe70s30 of eutectic composition the sheared high t garnet peridotite with mg 0 90 is composed of 60 vol olivine 15 orthopyroxene 5 3 clinopyroxene and 19 garnet the powder grain size was 20 30m similar to the one employed by yoshino et al 2003 for a second series san carlos olivine aggregates were used as solid matrix and 10 20 vol of eutectic fe70s30 were added for these the average grain size was 3m much smaller than in the experiments by yoshino et al 2003 the powder mixtures of peridotite fe70s30 and olivine aggregates fe70s30 were first annealed for 2 5 days in a conventional piston cylinder at 1 gpa and

seo3 a new model of olivine electrical conductivity summary standard electrical olivine 3 seo3 is a new model of electrical conductivity for olivine as a function of temperature and oxygen fugacity and is based on a previous study of point defect behaviour in a dunite that study produced quantitative estimates of mobility and concentration for small polarons and magnesium vacancies as a function of temperature and oxygen fucacity unlike earlier so1 and so2 models of olivine conductivity the dunite sample was buffered by pyroxene and avoided alteration at high temperature the low temperature extrapolation produced by seo3 is in good agreement with so2 while the high temperature extrapolation is significantly more conductive which is in general agreement with many field studies that show the earth s upper mantle to be more conductive than predicted by so2 for reasonable temperatures plausible variations in mantle oxygen fugacity correspond to about half an order of magnitude variation in electrical conductivity equivalent to about 100 degrees in temperature

ocean bottom geophysical array studies may reveal the cause of seafloor flattening abstract flattening of old seafloor as a result of the time evolution of oceanic lithosphere and asthenosphere has been studied for several decades and remains one of the unresolved fundamental problems of geodynamics the phenomenon of seafloor flattening at ages greater than 70 80 ma can be explained by a simple model of a cooling plate with a fixed thickness but the physical cause of flattening is not fully understood here a simple model of lithosphere rejuvenation is considered as an alternative mechanism and is also shown to represent similar features of seafloor flattening we suggest that constraints on mantle structure from use of data such as variations of seafloor depth and heat flow are weak but that first order differences in mantle thermal structure are introduced by these two models this suggests that probing of the mantle by geophysical arrays on the seafloor particularly those sensitive to mantle temperature such as magnetotelluric imaging should be able to constrain the cause of seafloor flattening in the present study recent results of seafloor electromagnetic explorations are compiled and estimated depths to the high conductivity layer hcl are used as a proxy for 1 300 c isotherm depths for the data obtained at sites well away from plate boundaries in the pacific ocean a model of lithosphere rejuvenation was found to better explain the correlation between hcl depths and seafloor depths than a standard plate cooling model

pressure effect on electrical conductivity of mantle olivine abstract we report new measurements of electrical conductivity of olivine that were made in a multi anvil press using solid buffers mo moo2 to stabilize oxygen partial pressure the temperature range was 1000 c 1400 c and the pressure range was 4 10 gpa when pressure effects are interpreted as activation volumes in the arrhenius equation they yield values of order 0 6 0 6 cm3 mole values of the pre exponential factor 0 are of the order of hundreds of s m and the zero pressure activation energy is about 1 5 ev in agreement with laboratory measurements at lower pressure conditions in addition we analyzed older literature data which produced a similar result but with larger variation the common practice of assuming that the pressure effect on electrical conductivity of olivine in the earth s upper mantle depends weakly on pressure has rested on uncertain grounds these new observations suggest that for upper mantle conditions depths of 80 200 km neglecting pressure effects on olivine conductivity is justified a weak pressure effect also supports the small polaron fe3 model as the dominant conduction mechanism although the mainly positive activation volumes argue for a component of lattice deformation when applied to the depth range 200 400 km in the earth the laboratory data yield conductivities of order 10 2 s m slightly lower than the range of geophysical conductivity profiles but well within this range after allowing for probable effects of oxygen activity and temperature uncertainty

velocity conductivity relationships for mantle mineral assemblages in archean cratonic lithosphere based on a review of laboratory data and hashin shtrikman extremal bounds article i nfo can mineral physics and mixing theories explain field observations of seismic velocity and electrical conductivity and is there an advantage to combining seismological and electromagnetic techniques these two questions are at the heart of this paper using phenomenologically derived state equations for individual minerals coupled with multi phase hashin shtrikman extremal bound theory we derive the likely shear and compressional velocities and electrical conductivity at three depths 100 km 150 km and 200 km beneath the central part of the slave craton and beneath the kimberley region of the kaapvaal craton based on known petrologically observed mineral abundances and magnesium numbers combined with estimates of temperatures and pressures we demonstrate that there are measurable differences between the physical properties of the two lithospheres for the upper depths primarily due to the different ambient temperature but that differences in velocity are negligibly small at 200 km we also show that there is an advantage to combining seismic and electromagnetic data given that conductivity is exponentially dependent on temperature whereas the shear and bulk moduli have only a linear dependence in cratonic lithospheric rocks focussing on a known discontinuity between harzburgite dominated and lherzolitic mantle in the slave craton at a

europe from the bottom up a statistical examination of the central and northern european lithosphere asthenosphere boundary from comparing seismological and electromagnetic observations abstract the lithosphere asthenosphere boundary lab is a fundamental boundary in the plate tectonic paradigm it is the most pervasive on the planet yet comparatively it is one we know little about defined initially on the basis of the mechanical response of the earth to loading its usage has become ubiquitous across the geosciences but the natural differences in its definition due to differences in thermal physical and chemical parameters cause confusion to advance this debate comparisons are made both qualitatively and quantitatively between the delineation of the lab for europe based on seismological and electromagnetic observations we examine statistically using robust methods the labs derived from independent datasets and methods essentially all definitions of the lab as an impedance contrast from receiver functions slabrf a seismic anisotropy change slaba and an increase in conductivity from magnetotellurics elab are consistent with a deeper lab beneath precambrian europe and a shallower lab beneath phanerozoic europe with some exceptionally deep regions in phanerozoic europe such as the alps all three labs increase in depth significantly and rapidly at a location consistent with the surface expression of the trans european suture zone tesz which separates precambrian europe to the north and east from phanerozoic europe in the centre two of the definitions slabrf and elab are consistent for phanerozoic europe with mean values of 90 100 km compared to an average slabrf of 135 km a different two slaba and slabrf are consistent for precambrian europe with mean values of 170 180 km compared to an elab mean of 250 km the deeper elab depths for precambrian europe are more consistent with body wave and surface wave tomography models than are the slaba and slabrf ones suggesting that the lower lithosphere beneath precambrian europe between 170 to 250 km is responding to shearing on the base of the lithosphere from plate driving forces taken together the definitions provide strong constraints on the nature of the lab for example the electrical elab beneath the tesz is anomalously thick to possibly the transition zone whereas slaba and slabrf seismological definitions would place it at far shallower depths given the sensitivity of electrical conductivity to partial melt and water content the thick elab beneath the tesz excludes interpretation of the seismic lab in that location in terms of a thermal structure that would induce partial melting or of hydration

an upper bound on the electrical conductivity of hydrated oceanic mantle at the onset of dehydration melting abstract electrical conductivity soundings provide important constraints on the thermal and hydration state of the mantle recent seafloor magnetotelluric surveys have imaged the electrical conductivity structure of the oceanic upper mantle over a variety of plate ages all regions show high conductivity 0 02 to 0 2 s m at 50 to 150 km depths that cannot be explained with a sub solidus dry mantle regime without unrealistic temperature gradients instead the conductivity observations require either a small amount of water stored in nominally anhydrous minerals or the presence of interconnected partial melts this ambiguity leads to dramatically different interpretations on the origin of the asthenosphere here i apply the damp peridotite solidus together with plate cooling models to determine the amount of h2o needed to induce dehydration melting as a function of depth and plate age then i use the temperature and water content estimates to calculate the electrical conductivity of the oceanic mantle with a two phase mixture of olivine and pyroxene from several competing empirical conductivity models this represents the maximum potential conductivity of sub solidus oceanic mantle at the limit of hydration the results show that partial melt is required to explain the subset of the high conductivity observations beneath young seafloor irrespective of which empirical model is applied in contrast the end member empirical models predict either nearly dry

lithospheric structure evolution and diamond prospectivity of the rehoboth terrane and western kaapvaal craton southern africa constraints from broadband magnetotellurics abstract a 1400 km long 2 d magnetotelluric mt profile consisting of 69 sites at 20 km intervals across the western part of the archaean kaapvaal craton the proterozoic rehoboth terrane and the late proterozoic early phanerozoic ghanzi chobe damara belt reveals significant lateral heterogeneity in the electrical resistivity structure of the southern african lithosphere the lithospheric structures of the rehoboth terrane and ghanzi chobe damara belt have not been imaged previously by geophysical methods temperature is the primary control on the resistivity of mantle minerals and the mt derived lithospheric thicknesses therefore provide a very reasonable proxy for the thermal thickness of the lithosphere i e the thickness defined by the intersection of a conductive geotherm with the mantle adiabat allowing approximate present day geotherms to be calculated the work indicates the following present day average lithospheric thicknesses to a precision of about 20 km for each of the terranes traversed inferred geotherms in brackets eastern kimberley block of the kaapvaal craton 220 km 41 mw m 2 western kimberley block 190 km 44 mw m 2 rehoboth terrane 180 km 45 mw m 2 and ghanzi chobe damara belt 160 km 48 mw m 2 a clear relationship between the electrical resistivity structure of the lithosphere and the tectonic stabilisation age of the terrane is evident good agreement between the inferred present day lithospheric geotherms and surface heat flow measurements indicate the latter are strongly controlled by variations in lithospheric thickness a significant difference in lithospheric thickness is observed between the eastern and western kimberley blocks and is consistent with previous seismic tomography images of the kaapvaal craton the present day lithospheric thickness and reduced depth extent into the diamond stability field accounts for the absence of diamondiferous kimberlites in the gibeon and gordonia kimberlite fields in the rehoboth terrane previously published mantle xenolith p t arrays from the gibeon gordonia and kimberley fields however suggest that the rehoboth terrane had equilibrated to a cooler conductive palaeo geotherm 40 42 mw m 2 very similar to that of eastern kimberley block of the kaapvaal craton at some time prior to the mesozoic eruption of the kimberlites the timing and nature of both the thermal equilibration of the rehoboth terrane and the subsequent lithospheric heating thinning event required to account for its present day lithospheric structure are not well constrained a model consisting of the penetration of heat transporting magmas into the lithosphere with associated chemical refertilisation at an early stage of mesozoic thermalism appears to be the most plausible model at present to account for both the present day lithospheric structure of the rehoboth terrane and an earlier cooler palaeo geotherm some problems however remain unresolved in terms of the isostatic response of the model based on a compilation of xenocryst cr ca in pyrope barometry observations the extent of depleted mantle in the rehoboth terrane is found to be significantly reduced with respect to the eastern kimberley block 117 km versus 138 167 km it appears most likely that the depletion depth in both terranes at least in the vicinity of kimberlite eruption is explained by refertilisation of the lower lithospheric mantle

fluorescence spectral analysis of resinite macerals from coals of the hanna formation wyoming u s a abstract flourescence spectral analysis indicates that resinite macerals from tertiary hanna formation coals hanna coal field southcentral wyoming u s a can be separated into five distinct groups the first resinite group fluoresces a a medium green in blue light its average spectral maximum occurs at or below 440 mm with a red green quotient of 0 22 the second resinite group fluoresces yellow green with an average spectral maximum of 500 nm and a red green quotient of 0 53 the third resinite group displays a yellow fluorescence having an average spectral maximum of 580 nm and a red green quotient of 0 86 the fourth resinite group fluorescence orange brown having an average spectral maximum of 610 nm and a red green quotient of 1 20 these four groups mostly occur as primary globular resinites exhibiting scratches and fractures indicating that they are brittle solid substances primary cell filling and secondary fracture filling resinites also occur in these four groups the fifth group only occurs as a secondary void filling material and lacks evidence of br of brittle properties it fluoresces a reddish brown has a spectral maximum at 690 nm and a red green quotient of 1 54 the fifth group has properties resembling exsudatinite the five resinite groups can be separated on the basis of their nine spectral properties alone without qualitative petrographic interpretation the relative quantities of the five resinite groups vary among hanna formation coals the origins of these five resinite groups are probably related to their botanical properties and pre and post depossitional conditions overall hanna formation resinites have petrographic characteristics similar to other north american resinites however only four resinite groups have been distinguished in in certain coals from utah and new mexico u s a and western canada

electrical conductivity anisotropy of dry and hydrous olivine at 8 gpa the effects of dissolved h2o on the electrical conductivity and its anisotropy in olivine fo90 at 8 gpa were investigated by complex impedance spectroscopy at nominally anhydrous conditions conduction along 1 0 0 and 0 0 1 is slightly higher than along 0 1 0 in contrast to observations made at lower pressures in earlier studies increasing h2o content increases conductivities but activation energies are lower and h2o concentration dependent the use of polarized ftir spectroscopy to determine h2o concentrations reveals a weaker than expected effect that water has on olivine conductivity and distinguishes our results from earlier studies based on analyses using non polarized infrared spectroscopy we show that at h2o concentrations of a few hundred wt ppm or less that the dominant conduction mechanism at mantle temperatures continues via small polarons such as that observed for anhydrous olivine our results also suggest that at depths greater than 200 km the presence of h2o may not be necessary to explain regions in the upper mantle where both electrical and seismic anisotropy are observed this can be explained by differences in the pressure dependence of the activation energy for conduction along each of the three crystallographic axes however while electrical anisotropy of anhydrous olivine remains weak at 8 gpa it is nevertheless enhanced by elevated concentrations several hundred wt ppm of dissolved h2o at these conditions dominated by proton hopping conductivity along 0 1 0 is highest approximately an order of magnitude greater than along 1 0 0 additionally at 1000 wt ppm and 1500 c an isotropic conductivity derived from the data is about 1 order of magnitude higher than that for nominally anhydrous olivine thus in regions of the mantle characterized by anomalously high conductivities and both electrical and seismic anisotropy significant amounts of dissolved hydrogen can be expected

electrical conductivity of san carlos olivine along 100 under oxygen and pyroxene buffered conditions and implications for defect equilibria the electrical conductivity along 100 of single crystal san carlos olivine was measured as a function of temperature between 1100 and 1200 c and oxygen fugacity between 10 6 and 10 0 5 pa at 1200 c and either with pyroxene buffered or without self buffered an added natural pyroxene buffer from a san carlos lherzolite under these temperature and o2 conditions electrical conduction in the self buffered sample is attributed to polarons fe and electrons e and in the pyroxene buffered sample is attributed to polarons fe and magnesium vacancies v mg over the range of temperature and o2 investigated the electrical conductivity of the self buffered sample is given by sb 100 2 27 s m e 0 55 ev kt o20 18 306 3 s m e 2 25 ev kt o2 0 18 and for the pyroxene buffered sample by pb 100 0 18 s m e 0 34 ev kt o20 17 15 2 s m e 1 3 ev kt where k is boltzmann s constant t is in kelvin and o2 is in atmospheres the conductivity of the pyroxene buffered sample is lower than that of the self buffered sample primarily as a result of a decrease in the polaron concentration the electrical conductivity of both samples was found to decrease irreversibly once the samples experienced an oxygen fugacity more reducing than approximately the wustite magnetite buffer electron microprobe analyses indicate that this effect results from loss of iron from the olivine samples to the iridium electrodes a series conduction model based on the observed compositional gradient adequately accounts for the magnitude of the irreversible conductivity decrease and limits the thickness of any surficial pyroxene phase to 0 1 m mantle temperature profiles based on laboratory measurements of self buffered samples predict temperatures of the order of between 25 and 150 c colder depending on the ambient oxygen fugacity than those based on measurements of pyroxene buffered samples