constraints on the lateral strength of slabs from three dimensional dynamic flow models if the viscosity of subducted lithosphere is described purely by temperature and pressure it should remain considerably more viscous than the surrounding material as it descends through the upper mantle many dynamic models of the long wavelength geoid associated with slabs require an increase in viscosity from the upper to the lower mantle but assume the perturbation to the lateral viscosity structure arising from the slabs themselves can be ignored previous studies indicate that strong and localized viscosity variations should have a dramatic influence on the geoid we present 3d finite element models of the regional geoid of the western pacific subduction zones slab buoyancies and viscosities are defined using the distribution of seismicity the geoid is very sensitive to the lateral strength of the slab very viscous slabs penetrating a low viscosity mantle generate significant 10 50 m long wavelength geoid lows opposite to the geoid high which is observed over slabs to obtain a geoid high comparable to that observed the lower mantle viscosity must be 60 200 times greater than the upper mantle viscosity and the slab must be in contact with the lower mantle these strict requirements suggest that slabs have been weakened and cannot act as stress guides from the deep mantle to the surface

formation of diamond with mineral inclusions of mixed eclogite and peridotite paragenesis two unusual diamonds were studied from kimberlites from china which contain both ultramafic and eclogitic mineral inclusions in the same diamond hosts diamond l32 contains seven fe rich garnets four omphacites and one olivine inclusion four olivine one sanidine and one coesite were recovered from diamond s32 both garnet and omphacite inclusions have similar compositions as those from other localities of the world and show basaltic bulk composition all the garnet and omphacite inclusions in diamond l32 have positive eu anomalies eu eu 1 64 1 79 these observations support the proposal that mantle eclogite is the metamorphic product of subducted ancient oceanic crust the mg mg fe ratio of the olivine inclusions from the two diamonds 91 92 are evidently lower than the normal olivine inclusions in diamonds from the same kimberlite pipe 92 95 the following model is proposed for the formation of diamonds with mixed mineral inclusions ascending diamond bearing eclogite recycled oceanic crust entrained in mantle plumes may experience extensive partial melting whereas the ambient peridotite matrix remains subsolidus in the diamond stable field this provides a mechanism for the transport of diamond from its original eclogitic host to an ultramafic one subsequent re growth of diamond in the new environment makes it possible to capture mineral inclusions of different lithological suites partial melts of basaltic sources may interact with the surrounding peridotite resulting in the relatively lower mg mg fe ratios of the coexisting olivine inclusions from the studied diamonds diamonds with mixed mineral inclusions demonstrate that plume activity also occurred in the archean cratons

viscosity in transition zone and lower mantle implications for slab penetration 1 the evolution of a subducting slab is strongly influenced by the viscosity of the mantle which it overlies however there is still no consensus about the viscosity in the transition zone and shallower lower mantle we use a numerical self consistent subduction model and run a set of experiments in order to find critical patterns of viscosity that would allow the evolution of the different subduction styles that can actually be found in nature our results show that a jump in viscosity of 5 times from transition zone to lower mantle gives the most reasonable results optimal values of viscosity in the transition zone are in the range of 3 1020 1021 pa s higher values would produce piling up of the slab and later sinking or even slab flattening lower viscosities result in velocities 30 cm yr that are too high while the new slab subducts through the upper mantle and transition zone a phenomenon that is rarely seen in nature reduction of the clapeyron slope related to the spinel perovskite transition variations in oceanic crustal thickness and in the age of the slab do not influence much the style of subduction when overriding velocity is applied to the upper plate the previously penetrating slab tends to lay at the 660 km boundary but does not substantially change the subduction velocity

a numerical study of the interaction between the mantle wedge subducting slab and overriding plate abstract we have formulated a numerical model with strongly temperature dependent viscosity to calculate thermal structure and flow field in subduction zones one important particularity of the model is that the overriding plate is not fixed over its whole thickness in order to allow material exchange between the wedge and the upper lithosphere numerical problems due to very high viscosity contrasts are avoided by coupling a finite difference method and a finite element method for solving the energy conservation equation and the stockes equation respectively in this model a temperature decrease from 1400 to 1300 c increases the viscosity by an order of magnitude we study the temperature structure and the velocity field of the subducting slab and mantle wedge surface heat flow velocity anomalies and geometry of the partial melting zone are also calculated to study the effect that boundary conditions play on the interaction between the mantle wedge overriding plate and subducting plate we examine models with both fixed and free slip conditions applied to the overriding plate when the overriding plate is allowed to move laterally free slip the subducting slab is thick and both the temperature field and the convective motions in the mantle wedge are similar to those observed when using constant viscosity numerical models or analytical corner flow models if the surface of the overriding plate is fixed the subducting slab is thin and the mantle wedge impinges upon the overriding plate forming a high temperature nose between the overriding plate and subducting lithosphere furthermore viscous decoupling occurs implicitly at shallow depth between the slab and the wedge because hot material from the wedge is entrained close to the trench in that case the subducting slab tectonically erodes the lower lithosphere of the overriding plate leading to high temperatures low seismic velocities high attenuation and high heat flow beneath volcanic arc in agreement with geophysical observations

stress distribution within subducting slabs and their deformation in the transition zone abstract the mechanical behavior of slabs in the mantle transition zone is a poorly understood phenomenon to obtain a better understanding of the stress and deformation pattern inside subducting slabs we performed 2d numerical simulations of the subduction process in a purely viscous non linear rheological model including diffusion creep dislocation creep and a stress limiting mechanism the model calculations are used to investigate the effects of yield stress plate age and surface boundary condition free slip versus given plate velocity on the stress development in and around a subducting slab and on the deformation of the subducting plate in the transition zone the deformation and morphology of subducted slabs may differ between free slip and kinematic boundary condition models in some cases especially for young and relatively weak slabs even though kinematically driven subduction morphology may look realistic in most cases our results show that stress distributions can differ significantly if the discrepancy between free slip and kinematic subduction velocity is large and in some model cases even influence the ability of the plate to penetrate into the lower mantle stress distributions such as the ones presented in this study can be a valuable tool in understanding the complex and enigmatic interaction between subducting slabs and the transition zone

thermoelastic properties of eclogitic garnets and omphacites implications for deep subduction of oceanic crust and density anomalies in the upper mantle

debris flow deposits in an alluvial plain succession the upper triassic callide coal measures of queensland australia the carnian rhaetian callide coal measures are preserved in a small 22 5 km by 8 km partially fault bounded basin remnant in east central queensland australia the 150 m thick coal measure succession is interpreted to have accumulated during a phase of mild crustal extension that formed a series of discrete intermontane basins in eastern australia the succession fines upward from a conglomerate rich lower part into a finer grained and coal bearing upper section including coal seams 34 m thick and is interpreted as the deposits of an alluvial plain environment anomalous matrix rich diamictites breccias and conglomerates have been recognized within the succession at several localities in many cases interbedded with coals these are interpreted as the product of debris flows two debris flow lithofacies are recognized 1 mixtures of fine carbonaceous material clay silt sand gravel and volcaniclastic debris and 2 breccias consisting principally of coal clasts in a coaly matrix with minor clastic and volcaniclastic debris facies 1 is found in sharp based simple or composite bodies 15 m thick that are elongate to lobate in plan with some multi lobate and as much as at least 1500 m long and 600 m wide facies 2 is less common and occurs in sharp based units as much as 1 5 m thick at least 200 m in length and 60 m in width both facies are characterized by abundant fine matrix and a very poorly sorted clast population and show little internal organization or sedimentary structure other than variably developed imbrication of coarse clasts parts of some bodies show an erosional base with up to several meters of coal removed although a flat apparently non erosional contact is more common the distribution of debris flows in the callide coal measures shows a coincidence with mapped faults and interpreted structural lineaments the debris flows may have been triggered by fault movements which formed rupture topography on the flat alluvial plain and caused destabilization of water saturated clastic and organic sediments some debris flow bodies may have been mounded such that subsequent peat formation was restricted until those bodies were buried the preservation of debris flow units at different stratigraphic levels along mapped structures suggests multiple paleoseismic events or multiple debris flow events along those structures the mixing of volcaniclastic debris into debris flow facies suggests that seismic events were coincident with or perhaps caused by nearby explosive volcanic activity the close relationship between debris flow deposits and thick coal bodies on the inferred downthrown sides of faults at callide further suggests that periodic tectonic subsidence may have facilitated thick coal accumulation

controls of the structure of subducted slabs numerical simulations of subducting slabs are formulated in which the shape and dip of the slab are determined by the dynamics of the flow rather than imposed a priori the dip of slabs is a function of the time since the initiation of subduction slabs fold develop a kink in dip and thicken on entry into a high viscosity lower mantle comparison of the simulations with seismic observations suggest that the lower mantle is at least 10 30 times more viscous than the upper mantle

the viscosity of earth s lower mantle inferred from sinking speed of subducted lithosphere abstract the viscosity of the mantle is indispensable for predicting earth s mechanical behavior at scales ranging from deep mantle material flow to local stress accumulation in earthquakes zones but mantle viscosity is not well determined for the lower mantle particularly only few constraints result from elaborate high pressure experiments karato 2008 and a variety of viscosity depth profiles result from joint inversion of the geoid and postglacial rebound data forte and mitrovica 1996 kaufmann and lambeck 2000 mitrovica and forte 2004 here we use inferred lower mantle sinking speed of lithosphere subduction remnants as a unique internal constraint on modeling the viscosity profile this entails a series of elaborate dynamic subduction calculations spanning a range of viscosity profiles from which we select profiles that predict the inferred sinking speed of 12 3 mm yr van der meer et al 2010 our modeling shows that sinking speed is very sensitive to lower mantle viscosity good predictions of sinking speed are obtained for nearly constant lower mantle viscosity of about 3 4 1022 pa s viscosity profiles incorporating a viscosity maximum in the deep lower mantle as proposed in numerous studies only lead to a good prediction in combination with a weak postperovskite layer at the bottom of the lower mantle and only for a depth average viscosity of 5 1022 pa s

rheology of the upper mantle a synthesis rheological properties of the upper mantle of the earth play an important role in the dynamics of the lithosphere and asthenosphere however such fundamental issues as the dominant mechanisms of flow have not been well resolved a synthesis of laboratory studies and geophysical and geological observations shows that transitions between diffusion and dislocation creep likely occur in the earth s upper mantle the hot and shallow upper mantle flows by dislocation creep whereas cold and shallow or deep upper mantle may flow by diffusion creep when the stress increases grain size is reduced and the upper mantle near the transition between these two regimes is weakened consequently deformation is localized and the upper mantle is decoupled mechanically near these depths

effects of slab mineralogy on subduction rates although velocities of subducting slabs should be controlled primarily by their negative thermal buoyan cies their mineralogy can also have signicant eects we explore this by using thermo kinetic modeling to predict mineralogy and compare the resultant buoyant driving force to the opposing viscous drag phase transitions of mg fe 2sio4 in subducting slabs depend on thermal struc ture in two ways first equilibrium phase boundaries should be deflected causing local buoyancy anomalies whose sign depends upon that of the clapeyron slope as slabs rst enter the transition zone negative anomalies should acceler ate them but positive anomalies that arise when they fully penetrate the transition zone should slow them such ef fects may induce geologically abrupt changes in plate mo tions second olivine that persists metastably in slabs will form regions of positive buoyancy which should reduce slab velocities the coldest and fastest slabs should be slowed more greatly thus narrowing the range of feasible subduc tion rates decreased descent rates however allow slabs to warm and metastable wedges to thermally erode such neg ative feedback mechanisms may serve to regulate subduction rates

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

slab dynamics in the transition zone abstract seismic images of horizontal slab segments in across or below the transition zone invoke scenarios in which slabs are laid down in the mantle through progressive trench retreat however observations of subduction characteristics do not exhibit a clear correlation between trench retreat and slab dip in the transition zone instead analysis of a range of subduction characteristics demonstrates that while transition zone slabs include slabs of many ages and subduction velocities with both retreating and advancing trench motion they also have several enigmatic characteristics such as faster sinking rates and a larger range in slab dip than slabs that extend to either shallower or deeper depths comparison of subduction characteristics with several analytical and numerical models of subduction dynamics suggests that many of the possible mechanisms for trapping slabs in the transition zone e g positive buoyancy sources viscous resistance slab weakening are only viable if the slab is already shallow dipping two scenarios for the formation of stagnant slabs are proposed 1 trench retreat prior to slabs entering the transition zone or caused by the negative buoyancy forces associated with the wadsleyite and ringwoodite phase transitions and 2 slow lateral migration of slabs in stable subduction zones

layered convection induced by phase transitions we report a systematic study on the conditions under which an endothermic phase transition can enforce layered convection two dimensional numerical calculations of convection in a domain containing a divariant phase change were performed in the framework of the extended boussinesq approximation i e considering the effects of adiabatic gradient latent heat and frictional heating in the energy equation we find that the critical value of the negative clapeyron slope which must be surpassed in order to induce layered convection decreases in magnitude with increasing rayleigh number ra in the range 104 ra 2 106 near the critical clapeyron slope vacillations between double and single layer convection or strongly leaking double layer convection are possible the breakdown into layers is influenced very little by the latent heat release but depends solely on the phase boundary deflection caused by lateral temperature differences the value of the critical clapeyron slope also seems little affected by the width of the transition zone or by its depth a possible superplastic rheology within the transition zone would tend to favor layered convection scaling the model results to the 670 km discontinuity in the earth s mantle as a possible endothermic phase boundary we estimate the critical clapeyron slope to be in the range of 4 to 8 mpa k 40 to 80 bar k the possibility that the spinel perovskite periclase transition is within this range appears to be remote but certainly cannot be neglected

initiation of gravitational collapse of an evaporite basin margin the messinian saline giant levant basin eastern mediterranean regional 2d and 3d seismic data from the levant basin reveal the updip extensional component of thin skinned gravity tectonics on this continental margin because of its youth 5 7 ma the earliest stages of deformation of this salt basin are preserved without the severe structural overprinting common on more mature giant salt tectonic systems extension detaches onto and within messinian evaporites up to 1800 m thick by structural restoration we reconstruct the tectonic evolution of the messinian evaporites using paleobathymetric constraints from wells and seismic profiles this analysis suggests that the mediterranean drawdown during the messinian salinity crisis was 800 m the 10 to 15 km wide extensional domain tracks the landward pinch out of the mobile messinian evaporites against an older late miocene scarp diachronous extension began in the center of the margin in the mid pliocene then spread northward in the late pliocene then finally southward in the early pleistocene extension continues today on many of the most landward faults extensional strain varies greatly along strike from 1 km to as much as 12 15 km comparing observations with four end member conceptual models we infer that both extension and seaward salt flow thinned the evaporite margin and its overburden both processes were triggered by a combination of uplift of the continental shoulder of the dead sea rift and subsidence in the mediterranean basin at least three factors controlled variations in extension 1 degree of tilting of the salt wedge related to the interplay of coastal uplift and basin subsidence 2 presence of pre messinian canyons overlain by landward salients of salt and 3 variations in evaporite facies and the proportion of siliciclastic admixture

eclogitic inclusions in diamonds evidence of complex mantle processes over time the first ion probe trace element analyses of clinopyroxene garnet pairs both included within diamonds and from the eclogite host xenoliths are reported these diamondiferous eclogites are from the udachnaya and mir kimberlite pipes yakutia russia the major and trace element analyses of these diamond inclusion and host rock pairs are compared in order to determine the relative ages of the diamonds confirm or deny genetic relationships between the diamonds and the eclogites evaluate models of eclogite petrogenesis and model igneous processes in the mantle before during and after diamond formation the most striking aspect of the chemical compositions of the diamond inclusions is the diversity of relationships with their eclogite hosts no single distinct pattern of variation from diamond inclusion minerals to host minerals is found for all four samples garnet and clinopyroxene inclusions in the diamonds from two samples u 65 3 and u 66 3 have lower mg s lower mg and higher fe contents and lower lree than those in the host eclogite we interpret such variations as due to metasomatism of the host eclogite after diamond formation one sample u 41 3 shows enrichment in diamond inclusion mree enrichment relative to the eclogite host and may indicate a metasomatic event prior to or during diamond formation bulanova 2 found striking differences between inclusions taken from within different portions of the very same diamond clinopyroxene inclusions taken from the central early portions of yakutian diamonds were lower in mg and mg contents by up to 25 than those later inclusions at the rims of diamonds these trends are parallel to those between diamond inclusions and host eclogites determined for four of the five samples from the present study and may merely represent changing magmatic and or p t conditions in the mantle garnet trace element compositions are similar in relative proportions but variable in abundances between diamond inclusions and host eclogites this is probably due to the rapid diffusion of trace elements in garnet under mantle temperatures and consequent alteration of the garnet and not due to juvenile diamonds locking in source heterogeneities c f 3 trace element compositions of clinopyroxenes included in diamonds are generally similar to those in the host eclogite however one host clinopyroxene does show enrichment in the lree compared to that in the inclusion and may be attributed to mantle metasomatism not related to kimberlite transport in another eclogite m 46 the host clinopyroxene is depleted in the lree and fe and enriched in the hree and mg relative to the inclusion and is consistent with partial melting of the eclogite subsequent to diamond formation smnd ratios in clinopyroxenes appear to be little affected by these processes for most samples allowing sm nd isotopic studies to yield important information about ancient protoliths eclogitic mineral inclusions in yakutian diamonds appear consanguineous with the diamonds a contention supported by the observations of bulanova 2 therefore re os whole rock and smnd clinopyroxene age determinations of the udachnaya eclogites also yield the time of diamond formation approximately 2 9 ga 32 33

paleobotanical and paleoecological constraints on models of peat formation in the late carboniferous of euramerica abstract the dominant plants of the late carboniferous lowland tropics were taxonomically and structurally distinct from those of any later time periods dominance was distributed among lycopsids ferns sphenopsids pteridosperms and cordaites and each of these groups had distinctive and different ecological preferences and amplitudes peat forming habitats were dominated by lycopsids throughout the westphalian with a significant cordaitean element in the middle westphalian during the stephanian tree ferns were dominant following major extinctions near the westphalian stephanian transition each of the major plant groups had distinctive architectures and tissue composition trees contributed up to 95 of the peat biomass and tree forms of lycopsids psaronius and medullosa lack good modern analogues the cordaites were the only woody plant group to contribute significantly to peat and then only during the mid westphalian structurally wood like lycopsid bark is the major woody tissue encountered in most westphalian coals tree ferns and pteridosperms were largely parenchymatous in construction the stigmarian root systems of lycopsids also were largely parenchymatous the tissue structure of these dominant plant suggests the need for extreme caution in the inference of mire ecological conditions or vegetational structure from coal petrographic data peat formed under arborescent ferns or pteridosperms or peat repeatedly exposed to decay and rerooting by stigmarian root systems of lycopsids would have a distinctly non woody signature and yet would have formed in a forested environment a summary is presented of the autecology and synecology of mire plants emphazing the structural framework provided by lycopsids during the westphalian certain constraints in the links between peat biomass and miospore palynology are discussed in terms of over representation under representation and non representation the formulation of smith s four phase hydroseral model is discussed and compared with more recent data available from plant paleoecology the current debate over an ombrotrophic vs rheotrophic origin of late carboniferous peats relies in large part on paleobotanical data almost entirely palynological in combination with petrographic analyses ecological studies of miospores and of coal ball and compression macrofossils and the linkage of miospores to source plants permit the re evaluation of mire successional models evidence for tree lycopsids sphenopsids pteridosperms and cordaites suggests growth mainly in rheotrophic mires tree ferns are likely candidates for growth in domed mires although evidence is ambiguous and some tree ferns clearly grew under rheotrophic conditions densospores produced by at least sporangiostrobus lycopsid subtrees have been considered diagnostic of ombrotrophic conditions abundant evidence refutes this simplistic interpretation and suggests broad ecological amplitudes for densospore producers including growth under rheotrophic conditions although plant fossils alone can not resolve most of the major debates in modern coal geology paleobotany does contribute significantly to our understanding of ancient mires an approach combining paleobotanical data with petrography sedimentology and geochemistry on a case by case basis is most likely to produce a clear picture

coal facies studies in the eastern united states coals in the eastern united states east of the mississippi river have been the subject of a number of coal facies studies going back to the 19th century such studies would not necessarily fall within a strict modern classification of coal facies studies but if a study encompassed some aspects of paleobotany palynology petrology geochemistry or sedimentology we assumed that some data and interpretations may be of use in evaluations of the facies references are presented as a guide for further research with annotation in the tables

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

origin of discontinuities in coal bearing strata at roaring creek basal pennsylvanian of indiana abstract basal pennsylvanian coal bearing strata exposed along roaring creek west central indiana exhibit extreme lateral discontinuity coal seams abruptly change in thickness and elevation they split grade into shale are cut out by channels and disrupted by soft sediment deformational structures initial sediments were laid down by a network of southwest flowing streams that traversed a deeply channelized upland surface of mississippian carbonate rocks channels aggraded rapidly as uplands were worn down so the region changed through time from uplands to upper deltaic plain local environments included channels localized point bars small natural levees and crevasse splays overbank deposits and swamps differential compaction and subsidence slumping stream banks and possibly collapsing sinkholes influenced sedimentation as a consequence coals are too discontinuous for economical mining although they are locally thick and high in quality

channel fill coal beds along the western margin of the eastern kentucky coal field abstract four channel filling coal beds from the lower part of the breathitt formation lower middle pennsylvanian late westphalian a were examined palynologically petrographically and geochemically to determine the paleoenvironmental conditions under which these peats accumulated these results were then compared with detailed sedimentological analyses of the strata overlying the coal in the channels to see if any genetic relationship between coal composition and the origin of the overburden could be drawn all four of the coal beds used in this study are located in the western most part of the eastern kentucky coal field and occur at or near the early pennsylvanian unconformity 0 30 m lycospora and densosporites and related crassicingulate taxa e g cristatisporites cingulizonates and radiizonates dominate the studied assemblages with granulatisporites and related trilete sphaerotriangular genera e g leiotriletes and lophotriletes laevigatosporites and schulzospora being common accessory genera petrographically all four coals contain high percentages of vitrinite macerals avg 78 6 mineral matter free moderate amounts of liptinite or exinite macerals avg 14 9 mmf and low percentages of inertinite macerals avg 6 5 mmf strata above the coals consist of dark carbonaceous shales and heterolithic strata that exhibit varying degrees of bioturbation commonly occurring trace fossils include arenicolites monocraterion planolites and skolithos although marine influenced strata as determined from detailed sedimentology and ichnology the study of trace fossils covers all four coal beds they are not uniformly high in total total sulfur content as might be expected rather they are extremely variable ranging from 1 9 dry basis total sulfur ash yields are also variable ranging from 6 2 54 3 dry basis it is probable that the origin of the very first sediments covering the peat as well as the amount of brackish water influence during peat accumulation were important factors in determining the total sulfur content of the resultant coal initial sedimentation of fresh water clays and silts may have acted as a barrier to downward percolation diffusion of sulfate bearing waters or may have served as a site for sulfide formation thereby keeping the total sulfur content of the underlying coal low if initial sedimentation was of brackish or marine origin as indicated by bioturbated laminae directly above the coal or if the peat was subject to frequent brackish or marine water influence during accumulation then sulfide generation might proceed unchecked resulting in high sulfur coal

elasticity of single crystal iron bearing pyrope up to 20 gpa and 750 k abstract elastic properties of the major constituent minerals in the earth s upper mantle at relevant high pressure temperature p t conditions are crucial for understanding the composition and seismic velocity structures of this region in this study for the first time we have measured the single crystal elasticity of natural fe bearing pyrope mg 2 04 fe 0 74 ca 0 16 mn 0 05 al 2 si 3 o 12 using in situ brillouin spectroscopy and x ray diffraction at simultaneous high p t conditions up to 20 gpa and 750 k in an externally heated diamond anvil cell the derived aggregate adiabatic bulk and shear moduli k s 0 g 0 at ambient conditions are 168 2 1 8 gpa the value in parentheses represents propagated uncertainties 1 and 92 1 1 1 gpa respectively consistent with literature results using the third order eulerian finite strain equation to model the high p t data the derived pressure derivatives of the bulk and shear moduli at constant temperature are k s p t 4 4 0 1 and g p t 1 2 0 1 respectively whereas the temperature derivatives of these moduli at constant pressure are k s t p 16 8 1 3 mpa k and g t p 5 1 1 1 mpa k respectively compared to literature values our results show that addition of 25 mol fe in pyrope increases the pressure derivative of the bulk modulus by 7 but has a negligible effect on other elastic parameters extrapolation of our results shows that fe bearing pyrope remains almost elastically isotropic at relevant p t conditions of the upper mantle indicating that it may not have a significant contribution to seismic v p and v s anisotropy in the upper mantle together with the elasticity of olivine and pyroxene minerals in the upper mantle we have constructed new velocity profiles for two representative compositional models pyrolite and piclogite along a representative geotherm of the earth s upper mantle these velocity models show v s profiles consistent with seismic observations although v p profiles are slightly lower than global seismic observations our analyses also show that approximately 30 garnet in a mineralogical model is needed to best match both seismic v p and v s profiles of the region although such high garnet content needs to be reconciled with our current geochemical understanding our results here provide new insights into seismic profiles and mineralogical models of the upper mantle region

metastable olivine wedge and deep dry cold slab beneath southwest japan abstract oceanic plates subducted at trenches penetrate into the deep mantle and encounter a structural boundary at a depth of 410 km where olivine the dominant element of mantle rocks transforms into a higher density form wadsleyite this transformation may be delayed within the coldest core of subducting plates slabs due to kinetic effects and it has been suggested that metastable olivine may persist deeper than 410 km using high density seismic array data in japan we show the direct image of the structure corresponding to this metastable olivine wedge mow beneath southwest japan numerical simulation of a subducting slab including the kinetic effect of water h 2 o on the olivine wadsleyite transformation indicates that the presence of the imaged mow requires an insignificant amount of water less than 100 wt ppm be present in the slab mantle thus a deep dry cold slab we infer that the transportation of water into the deep mantle occurs along the top surface of the subducting slab but no significant amount within the slab itself we also demonstrate that a numerical simulation including the kinetics of 660 km phase transformation can reconcile the observed deep depression of the 660 km discontinuity with a gentle clapeyron slope

the geology and palynology of lower and middle pennsylvanian strata in the western kentucky coal field abstract the western kentucky coal field is the southern tip of the eastern interior or illinois basin pennsylvanian rocks in this area which include conglomerate sandstone siltstone shale limestone and coal were deposited primarily in coastal deltaic settings at a time when western kentucky was located close to the equator this paper discusses temporal changes in regional sedimentation patterns and coal forming floras of lower and middle pennsylvanian strata in the western kentucky coal field lower pennsylvanian strata of the caseyville formation are characterized by paleovalley filling sedimentation patterns and extabasinal quartz pebbles caseyville formation coals are characteristically thin and discontinuous and were strongly influenced by subsidence within underlying paleovalleys and the dissected lower pennsylvanian paleotopography caseyville coals are commonly dominated by lycospora but can also have variable palynofloras which probably reflects variable edaphic conditions and edge effects within small patchy paleomires tradewater formation strata show increased marine influences and tidal estuarine sedimentation especially in the middle and upper parts coal beds in the lower part of the tradewater typically are thin and discontinuous although some economically important beds are present coals become thicker more abundant and more laterally persistent towards the top of the formation palynologically lower and middle tradewater formation coals are dominated by lycospora but begin to show increased amounts of tree fern spores middle and upper tradewater coals are thicker and more continuous and contain high percentages of tree fern spores in addition cordaite pollen is locally abundant in this interval carbondale and shelburn desmoinesian strata are much more laterally continuous and occur within classic cyclothems that can be traced across the coal field cyclothems have long been interpreted as being eustatically driven and glacio eustacy controlled not only sedimentation but also the formation of desmoinesian paleomires palynologically carbondale and shelburn coals are either dominated by lycospora or have heterogeneous palynofloras palynologic and coal quality data suggest that hydrologic base level may have been the primary control on desmoinesian paleomires rather than paleoclimate as the coals display rheotrophic rather than ombrotrophic characteristics

elasticity of diopside to 8 gpa and 1073 k and implications for the upper mantle abstract simultaneous measurements of elastic wave velocities and density have been conducted on diopside by a combined ultrasonic interferometry and x ray diffraction methods at pressure and temperature conditions relevant to the earth s upper mantle the current study not only yielded the first direct measurement of the shear modulus at high pressures but also enabled a simultaneous determination of the bulk and shear properties and their pressure and temperature derivatives from the measured density and velocities finite strain analysis of the experimental data results in ks0 116 4 7 gpa k s 0 4 9 1 ks t p 0 012 1 gpa gpa g 0 1 6 1 and g t p 0 011 1 gpa k with these results and the same finite strain equations the p and s wave velocities of diopsidic mantle clinopyroxene were calculated along a 1600 k adiabatic geotherm in comparison with other mantle minerals the seismic velocities of diopsidic clinopyroxene at upper mantle depths are 1 3 higher than those of orthopyroxene 1 2 and 6 8 lower than those of olivine and majoritic garnet respectively

a numerical evaluation on the effects of impermeable faults on degasification efficiency and methane emissions during underground coal mining abstract impermeable geologic faults in the coal seam can cause intermittent production problems or can cause unexpected amounts of water or gas to issue from degasification boreholes these faults also can impact methane emissions into the mine workings especially if they hinder proper and effective degasification of the coal bed they may also act as barriers for methane flow in the coal seam although this might seem beneficial for advancing mine workings faulting may also cause gas pressure buildups and result in compartmentalization of the gassy regions from which large quantities of water and methane may rush into mine workings this study uses reservoir simulations to illustrate the effects of impermeable faults with and without throws on the production performance of vertical and horizontal degasification boreholes these boreholes were drilled from the surface to intercept the coal layer and fault and were assumed to produce methane two years prior to mining of the coal seam longwall advances and face position related emissions and reservoir properties were characterized using sector definitions along the path of the panel grids this work numerically evaluates water and gas productions of each borehole and presents the effects and the impacts of impermeable faults on methane emissions due to an advancing coal face the results can be used to understand the effects of impermeable faults on borehole productions and face emissions due to these coal seam anomalies

observations on the palynology petrography and geochemistry of the western kentucky number 4 coal bed abstract eight bench column samples of the western kentucky number 4 coal bed collected from an area along the southern margin of the western kentucky coal field were analyzed palynologically petrographically and geochemically to document both temporal and spatial variability among these parameters the western kentucky number 4 coal occurs near the top of the tradewater formation is of early desmoinesian age and is correlative with the lower part of the allegheny formation of the appalachian basin and late bolsovian strata of western europe palynologically the coal is co dominated by spores that were produced by lycopod trees lycospora and granasporites medius and tree ferns thin walled tree fern spores punctatisporites minutus p minutus p rotundus are more abundant than thick walled forms laevigatosporites globosus p granifer calamitean spores calamospora and laevigatosporites spp are locally abundant as is cordaitean pollen florinites small fern granulatisporites and small lycopod spores densosporites cirratriradites endosporites and anacanthotriletes spinosus are present but occur in minor amounts temporal changes in palynomorph composition occur but are not uniform between columns spatial variability among columns is also evident petrographically the coal is dominated by vitrinite macerals with telinite and telocollinite generally occurring more commonly than desmocollinite and gelocollinite basal benches typically contain high percentages of vitrinite middle benches usually contain higher percentages of liptinite and inertinite in about half the studied columns the terminal coal benches show a slight increase in vitrinite in the study area the petrography of the western kentucky number 4 coal is more uniform than the palynology ash yields and total sulfur contents are temporally uniform in some columns but variable in others in the latter case higher percentages of ash and sulfur occur at the base of the bed and decrease up to the middle of the bed the terminal benches of these columns often but not always show slight increases in ash or sulfur both syngenetic and epigenetic forms of sulfur are present in the western kentucky number 4 coal the high vitrinite contents and moderate to high sulfur contents suggest that the western kentucky number 4 paleomire was mainly planar and rheotrophic throughout its developmental history groundwaters carrying dissolved solutes may have helped neutralize the normally acidic interstitial peat waters allowing for the production of sulfide minerals several of the columns with high sulfur contents at the base of the bed occur in faulted areas the faults could have promoted the flow of groundwaters through the peat providing an increased dissolved load for acid mitigation and sulfide formation the concentration of sulfur at the base of the bed may be a function of the peat underclay contact enhancing sulfide formation the clay layer may also have acted as an impermeable boundary for downward moving groundwaters causing mainly lateral rather than vertical movement along the base of the coal bed

rifted margins ductile deformation boudinage continentward dipping normal faults and the role of the weak lower crust the stunningly increased resolution of the deep crustal levels in recent industrial seismic profiles acquired along most of the world s rifted margins leads to the unraveling of an unexpected variety of structures it provides unprecedented access to the processes occurring in the middle and lower continental crust we present a series of so far unreleased profiles that allows the identification of various rift related geological processes such as crustal boudinage ductile shear and low angle detachment faulting and a rifting history that differs from the classical models of oceanward dipping normal faults the lower crust in rifted margins appears much more intensely deformed than usually represented at the foot of both magma rich and magma poor margins we observe clear indications of ductile deformation of the deep continental crust along large scale shallow dipping shear zones these shear zones generally show a top to the continent sense of shear consistent with the activity of continentward dipping normal faults cdnf observed in the upper crust this pattern is responsible for a migration of the deformation and associated sedimentation and or volcanic activity toward the ocean we discuss the origin of these cdnf and investigate their implications and the effect of sediment thermal blanketing on crustal rheology in some cases low angle shear zones define an anastomosed pattern that delineates boudin like structures the maximum deformation is localized in the inter boudin areas the upper crust is intensely boudinaged and the highly deformed lower crust fills the inter boudins underneath the boudinage pattern controls the position and dip of upper crustal normal faults we present some of the most striking examples from the margins of uruguay west africa south china sea and barents sea and discuss their implications for the time temperature history of the margins

diamond garnet geobarometry the role of garnet compressibility and expansivity abstract we report p v and t v equations of state eos for synthetic single crystal pyrope py mg3al2si3o12 and the p v eos for synthetic single crystals of almandine alm fe3al2si3o12 as well as an intermediate composition py60alm40 as measured by in situ high pressure and high temperature x ray diffraction experiments the unit cell volumes of the three samples were measured at room temperature and different pressures and up to about 8 gpa in a diamond anvil cell the high temperature experiment was carried out using a micro furnace the pressure volume data were fitted to a third order birch murnaghan eos giving the following coefficients v0 1506 15 16 a3 kt0 163 7 1 7 gpa and k 6 4 4 for pyrope v0 1533 52 10 a3 kt0 172 6 1 5 gpa and k 5 8 5 for almandine and v0 1516 32 13 a3 kt0 167 2 1 7 gpa and k 5 6 5 for the intermediate py60alm40 composition the unit cell volume along the pyrope almandine join changes linearly within the error of measurement indicating ideality in the volume of mixing behaviour for the solid solution the first pressure derivative k for all three garnets is similar within experimental uncertainty with an average value of k 6 0 4 the thermal expansion parameters for end member pyrope as described using to the kroll type eos with the einstein temperature e fixed to 320 k are 303 k 1 bar 2 543 5 10 5 k 1 and v0 1504 64 4 a3 the determined thermoelastic parameters were combined in a thermal pressure type eos thermal p type eos to calculate the entrapment pressures pe for natural garnet inclusions in diamonds at mantle temperatures a calculated pressure of 5 8 gpa at t 1500 k using our newly determined thermoelastic parameters appears to be more consistent with diamond forming conditions compared to the higher pressures that range up to 6 8 gpa at t 1500 k which are obtained using thermoelastic data in the literature

shear and compressional mode measurements with ghz ultrasonic interferometry and velocity composition systematics for the pyrope almandine solid solution series abstract successful fabrication of a high frequency up to 600 mhz shear transducer enables us to determine the complete sets of sound velocities for single crystal samples using ghz ultrasonic interferometry sound velocities for a natural pyrope and a natural almandine were measured re examining the existing database we found that velocities for the pyrope almandine solid solution series can be modeled quantitatively with linear relationships v p 100 0 0067 x alm 9 08 km s 1 v s 100 0 0041 x alm 5 08 km s 1 v p 110 0 0074 x alm 9 10 km s 1 where x alm is the fe mg fe ratio in the garnet samples maximum deviation of the measurement data from these linear relationships is 1 for every 10 increase in the fe mg fe ratio almandine the velocities decrease by about 1 published density data for this garnet solid solution series fit to a straight line with a maximum deviation of 1 thus the velocities follow linear laws with the density and such velocity density systematics acquire the form of the birch s law using these relationships velocities of an arbitrary composition in this garnet solid solution series can be predicted at present measurement precision of existing data does not warrant an examination of whether bulk modulus is linear with composition the suggested values for the p and s velocities for the pyrope end member and the almandine end member are km s 1 v p 100 v s 100 v p 110 pyrope mg 3 al 2 si 3 o 12 9 08 5 08 9 10 almandine fe 3 al 2 si 3 o 12 8 42 4 68 8 34 the technique used in monitoring the thickness of the linbo 3 crystal during the fabrication of the shear transducer illustrates the feasibility of using samples as thin as a few micrometers in the ghz ultrasonic interferometric measurements

geochemistry of the blue gem coal bed knox county kentucky abstract the blue gem coal bed middle pennsylvanian westphalian b breathitt formation has low ash with some sample sites having less than 1 ash and low sulfur contents through parts of knox county kentucky most collection sites exhibit similar vertical elemental trends in ash geochemistry the relatively high ash 1 ash lower part of the bed displays enrichment in tio2 zr cr v and ni co zn rb and mn show enrichment at some sites a low ash 1 ash and a relative enrichment in sio2 k2o and rb and a relative decrease in cu ni co ba and mn when compared to the middle part of the bed principal components analysis indicates that the samples with an ash content 0 63 1 0 show associations for ni cu cr and co samples with between 1 01 2 0 ash display strong element associations that suggest increased clastic sediment contributions tio2 zr k2o rb sio2 the low ash content and the upwards decrease in trace concentrations both suggest that the blue gem peat swamp was ombrotrophic through at least a part of its geologic history

time dependent interaction between subduction dynamics and phase transition kinetics summary numerical subduction models are presented that account for the kinetics of the olivine spinel transformation and the equilibrium transformation of spinel into perovskite and magnesiowustite temperature depth and stress dependent rheology is used buoyancy due to temperature and the olivine spinel and magnesiowustite perovskite phases leads to free subduction into the transition zone and retarded penetration into the lower mantle a dynamic feed back mechanism is found between the different buoyancy forces the kinetics of the phase transition and the release of latent heat this mechanism modulates the parachute effect of the metastable olivine mo in a subducting slab and leads to characteristic temporal variations of the depth of mo and with a time delay variations of the subduction velocity time periods are of the order of 3 4 myr this mechanism allows to explain variations of the depths of the deepest earthquakes in otherwise similar subduction zones further conclusions are as follows the maximum depth of mo increases roughly linearly with lithospheric thickness and the maximum depth may reach as deep as 720 750 km different subduction zones may represent different stages of velocity depth phase loops of mo

in situ x ray diffraction study of post spinel transformation in a peridotite mantle implication for the 660 km discontinuity abstract we present the phase relations in anhydrous cao mgo feo al2o3 sio2 pyrolite to examine the influence of compositional difference between pyrolite and mg2sio4 on the post spinel phase transformation it is shown that in the pyrolite system the transformation occurs at about 0 5 gpa lower pressure relative to mg2sio4 we have carried out several in situ x ray diffraction experiments on ringwoodite to mg perovskite ferropericlase and backward transformations and found that post spinel transformation boundary can be expressed as p gpa 0 0005 t k 23 54 using the gold equation of state by tsuchiya t tsuchiya first principles prediction of the p v t equation of state of gold and the 660 km discontinuity in earth s mantle j geophys res 108 2003 doi 10 1029 2003jb002446 the interval for coexisting ringwoodite and mg perovskite was found to be 0 1 0 5 gpa the discrepancy between our data and the depth of the seismic discontinuity global average 654 km is about 20 km at 1850 k based on the results of in situ measurements we confirmed that the difference in chemical composition between pyrolite and mg2sio4 cannot modify the clapeyron slope of the post spinel transformation using experimental data and assuming the average mantle temperature 1850 k at 660 km we can account for only a half of variations in the depth of the 660 km discontinuity in subduction zones and at hot spots an additional explanation for the observed seismological variations at the 660 km discontinuity is required and may reflect influence of other minor components or volatiles

interaction of subducted slabs with the mantle transition zone a regime diagram from 2 d thermo mechanical models with a mobile trench and an overriding plate transition zone slab deformation influences earth s thermal chemical and tectonic evolution however the mechanisms responsible for the wide range of imaged slab morphologies remain debated here we use 2 d thermo mechanical models with a mobile trench an overriding plate a temperature and stress dependent rheology and a 10 30 or 100 fold increase in lower mantle viscosity to investigate the effect of initial subducting and overriding plate ages on slab transition zone interaction four subduction styles emerge i a vertical folding mode with a quasi stationary trench near vertical subduction and buckling folding at depth vf ii slabs that induce mild trench retreat which are flattened horizontally deflected and stagnate at the upper lower mantle interface hd iii inclined slabs which result from rapid sinking and strong trench retreat isr iv a two stage mode displaying backward bent and subsequently inclined slabs with late trench retreat bir transitions from regime i to iii occur with increasing subducting plate age i e buoyancy and strength regime iv develops for old strong subducting and overriding plates we find that the interplay between trench motion and slab deformation at depth dictate the subduction style both being controlled by slab strength which is consistent with predictions from previous compositional subduction models however due to feedbacks between deformation sinking rate temperature and slab strength the subducting plate buoyancy overriding plate strength and upper lower mantle viscosity jump are also important controls in thermo mechanical subduction for intermediate upper lower mantle viscosity jumps 30 our regimes reproduce the diverse range of seismically imaged slab morphologies

dynamics of subduction and plate motion in laboratory experiments insights into the plate tectonics behavior of the earth 1 three dimensional laboratory experiments have been designed to investigate the way slab bearing plates move during subduction inside the mantle in our experiments a viscous plate of silicone lithosphere subducts under its negative buoyancy in a viscous layer of pure honey mantle varying thickness width viscosity and density of the plate and mantle three characteristic modes of subduction are observed a retreating trench mode mode i a retreating trench mode following a transient period of advancing trench mode ii and an advancing trench mode mode iii these modes are characterized by different partitioning of the amount of subduction into plate and trench motion our experiments show that the velocity of subduction can be modeled by the dynamic interaction between acting and resisting forces where lithospheric bending represents 75 95 of the total resisting forces however our experimental results also show the impossibility to predict a priori the plate velocity only from the velocity of subduction without considering trench migrations we find experimentally that the lithospheric radius of curvature which depends upon plate characteristics stiffness and thickness and the mantle thickness exerts a primary control on the trench behavior our results suggest that the complexity of the style of subduction could be controlled by geometrical rules of a plate bending inside a stratified mantle the earth system is in the crucial range for the interplay between the rigidity of the plate and the mantle stratification this setting may be the responsible for the complexity of the past and present tectonic styles

mining geology of the pond creek seam pikeville formation middle pennsylvanian in part of the eastern kentucky coal field usa abstract the pond creek seam is one of the leading producers of coal in the eastern kentucky coal field the geologic factors that affect mining were investigated in several underground mines and categorized in terms of coal thickness coal quality and roof control the limits of mining and thick coal are defined by splitting along the margin of the coal body within the coal body local thickness variation occurs because of 1 leader coal benches filling narrow elongated depressions 2 rider coal benches coming near to or merging with the main bench 3 overthrust coal benches being included along paleochannel margins 4 cutouts occurring beneath paleochannels and 5 very hard and unusual rock partings occurring along narrow elongated trends in the study area the coal is mostly mined as a compliance product sulfur contents are less than 1 and ash yields are less than 10 local increases in sulfur occur beneath sandstones and are inferred to represent post depositional migration of fluids through porous sands into the coal run of mine quality is also affected by several mine roof conditions and trends of densely concentrated rock partings which lead to increased in and out of seam dilution and overall ash content of the mined coal roof control is largely a function of a heterolithic facies mosaic of coastal estuarine origin regional fracture trends and unloading stress related to varying mine depth beneath the surface lateral variability of roof facies is the rule in most mines the largest falls occur beneath modern valleys and parallel fractures along paleochannel margins within tidally affected stackrock and beneath rider coals shale spalling kettlebottoms and falls within other more isolated facies also occur many of the lithofacies and falls related to bedding weaknesses within or between lithofacies occur along northeast southwest trends which can be projected in advance of mining fracture related falls occur independently of lithofacies trends along northwest southeast trends especially beneath modern valleys where overburden thickness decreases sharply differentiating roof falls related to these trends can aid in predicting roof quality in advance of mining

new evidence for dislocation creep from 3 d geodynamic modeling of the pacific upper mantle structure laboratory studies on deformation of olivine in response to applied stress suggest two distinct deformation mechanisms in the earth s upper mantle diffusion creep through diffusion of atoms along grain boundaries and dislocation creep by slipping along crystallographic glide planes each mechanism has very different and important consequences on the dynamical evolution of the mantle and the development of mantle fabric due to the lack of in situ observations it is unclear which deformation mechanism dominates in the upper mantle although observed seismic anisotropy in the upper mantle suggests the presence of dislocation creep we examined the thermo mechanical erosion of the lithosphere by thermal boundary layer instabilities in 3 d dynamical models this study demonstrates that the seismically derived thermal structure of the pacific lithosphere and upper mantle imposes an important constraint on the upper mantle deformation mechanism the predominant deformation mechanism in the upper mantle is dislocation creep consistent with observed seismic anisotropy the acceptable activation energy range of 360 540 kj mol is consistent with although at the lower end of those determined from laboratory studies

the eclogite garnetite transformation at high pressure and some geophysical implications mineral assemblages displayed by morb and alkali poor olivine tholeiites have been investigated over the pressure interval 4 6 18 gpa at 1200 c both compositions crystallize to form normal eclogites between 4 6 and 10 gpa and there is little change in the relative proportions of garnet and pyroxene over this range however the proportion of garnet increases rapidly above 10 gpa as pyroxene dissolves in the garnet structure and pyroxene free garnetites stishovite are produced by 14 15 gpa dependent upon composition the garnetite facies for both compositions possess zero pressure densities of 3 75 g cm3 implying that subducted oceanic crust remains appreciably denser than surrounding mantle to depths exceeding 600 km it is demonstrated that the seismic velocity distributions in the mantle between 400 and 650 km are inconsistent with anderson s hypothesis that this region is of eclogitic composition

survival of pyropic garnet in subducting plates abstract an experimental study has been conducted to clarify the conditions and kinetic aspects of the pyroxene garnet transformation by using synthetic polycrystals two pyroxenes garnet in the cao mgo al 2 o 3 sio 2 system the run products recovered from the in situ x ray diffraction experiments in a double stage multi anvil system at 15 5 20 4 gpa and 800 1600 c were carefully analyzed by scanning electron microscopy our results show that the pyroxene garnet transformation proceeds by overgrowth of garnet absorbing the surrounding pyroxene components above 1550 c at 18 4 gpa and 1320 c pyroxenes enstatite diopside directly decomposed to the assemblages wadsleyite stishovite ca perovskite without dissolving in garnet the pyroxene garnet transformation requires much higher temperatures than those needed for transformation of olivine to wadsleyite 1000 c and of pyroxenes to their high pressure phases 1300 c in laboratory time 10 3 s and grain 10 5 m scales therefore the pyroxene garnet transformation is likely to be kinetically inhibited at low temperatures in the subducting plate and the pyropic garnet could survive in the transition zone instead of equilibrium majoritic garnet

sound velocities of fe3al2si3o12 almandine up to 19 gpa and 1700 k abstract elastic wave velocities of synthetic fe 3 al 2 si 3 o 12 almandine have been determined at simultaneous high pressure and temperature up to 19 gpa and 1700 k by the ultrasonic technique in conjunction with in situ synchrotron x ray diffraction in a multi anvil apparatus velocities of almandine are found substantially lower than those of other major end member garnets such as pyrope grossular and mgsio 3 majorite while their pressure and temperature derivatives are comparable to those of the latter garnets the observed density and compressional v p and shear v s velocities were combined and fitted to functions of the eulerian strain eos yielding a adiabatic bulk modulus k s 0 174 2 12 gpa and a shear modulus g 0 94 9 7 gpa and their pressure and temperature derivatives k s p 4 61 14 g p 1 06 6 k s t 2 67 7 10 2 gpa k 1 and g t 1 31 8 10 2 gpa k 1 the pressure derivative of the bulk modulus of almandine is similar to those of other garnet end members which is in contrast to the substantially higher value k s p 6 2 5 reported for pure almandine in an earlier study based on experiments up to 3 gpa the present new results combined with those of pyrope grossular and mgsio 3 majorite are successfully used to reproduce the sound velocities of majoritic garnet in the pyrolite composition

thermodynamic and elastic properties of pyrope at high pressure and high temperature by first principles calculations pyrope is an mg end member garnet which constitutes up to 15 of the upper mantle thermodynamic and thermoelastic properties of garnet at high pressure and high temperature are important for understanding the composition and structure of the earth here we report the first principles calculations of vibrational properties thermodynamic properties and elasticity of pyrope over a wide pressure and temperature range the calculated results exhibit good consistency with the available experimental results and provide values up to the pressure and temperature range that are challenging for experiments to achieve and measure pyrope is almost isotropic at high pressure the elastic moduli especially the shear modulus of pyrope exhibit nonlinear pressure and temperature dependences density and seismic velocities of pyrope along with piclogite pyrolite and eclogite are compared with seismic models along the normal upper mantle and the cold subducting lithospheric plate geotherms pyrope has the highest density and seismic velocities among the major minerals of the upper mantle along these geotherms eclogite with 30 pyrope and 70 clinopyroxene is denser than the surrounding mantle even along the normal upper mantle geotherm and becomes still denser along the cold slab geotherm seismic velocities of eclogite with 30 pyrope along the normal upper mantle geotherm are slower than the surrounding mantle but along the cold slab geotherm are faster than the surrounding mantle

on the fundamental difference between coal rank and coal type abstract this article addresses the fundamental difference between coal rank and coal type while theoretically settled long ago as being different aspects of coal systems science the two concepts are still often confounded in recent years this has resulted in the publication of several works stating that coal type changes with coal rank coal type refers solely to coals depositional origin and the maceral mineral admixture resulting from that origin coal types typically fall in to two categories humic coals developed from peat and sapropelic coals developed from organic mud either type may be allocthonous or autochthonous and within types further refinement of depositional environment can be made coal rank refers to the changes in geochemistry and resultant changes in reflectance caused by increasing thermal maturity of the coal thus it provides an overprint of maturity on existing coal types with proper techniques such as use of crossed polars and etching maceral forms can be differentiated even at high ranks and the original coal type determined

comparison of the eastern and western kentucky coal fields pennsylvanian usa why are coal distribution patterns and sulfur contents so different in these coal fields abstract more than 130 mt of pennsylvanian coal is produced annually from two coal fields in kentucky the western kentucky coal field occurs in part of the illinois basin an intercratonic basin and the eastern kentucky coal field occurs in the central appalachian basin a foreland basin the basins are only separated by 140 km but mined western kentucky coal beds exhibit significantly higher sulfur values than eastern kentucky coals higher sulfur coal beds in western kentucky have generally been inferred to be caused by more marine influences than for eastern kentucky coals comparison of strata in the two coal fields shows that more strata and more coal beds accumulated in the eastern than western kentucky coal field in the early and middle pennsylvanian inferred to represent greater generation of tectonic accommodation in the foreland basin eastern kentucky coal beds exhibit a greater tendency toward splitting and occurring in zones than time equivalent western kentucky coal beds which is also inferred to represent foreland accommodation influences overprinted by autogenic sedimentation effects western kentucky coal beds exhibit higher sulfur values than their eastern counterparts but western kentucky coals occurring in langsettian through bolsovian strata can be low in sulfur content eastern kentucky coal beds may increase in sulfur content beneath marine zones but generally are still lower in sulfur than mined western kentucky coal beds indicating that controls other than purely marine influences must have influenced coal quality the bulk of production in the eastern kentucky coal field is from duckmantian and bolsovian coal beds whereas production in the western kentucky coal field is from westphalian d coals langsettian through bolsovian paleoclimates in eastern kentucky were favorable for peat doming so numerous low sulfur coals accumulated these coals tend to occur in zones and are prone to lateral splitting because of foreland tectonic and sedimentation influences in contrast westphalian d coal beds of western kentucky accumulated during low differential tectonic accommodation and therefore tend to be widespread and uniform in characteristics but exhibit higher sulfur values because they accumulated in seasonally drier paleoclimates that were unfavorable for peat doming hence basin analyses indicate that many differences between the mined coals of kentucky s two coal fields are related to temporal changes in paleoclimate and tectonic accommodation rather than solely being a function of marine influences

pennsylvanian fossil forests in growth position t0 assemblages origin taphonomic bias and palaeoecological insights abstract fossil forests buried in growth position in a geological instant t 0 assemblages are far more abundant in pennsylvanian successions than in any other part of the geological record in this review paper we evaluate the fundamental controls on the origin of these phenomena investigate the taphonomic biases that influence their composition and summarize their palaeoecological significance following earlier workers we highlight that high rates of burial and accommodation are essential for the formation and preservation of t 0 assemblages contexts especially favourable for their origin include ashfalls proximal to volcanic centres coastal plains drowned by relative sea level rise and fluvial environments such as channel bars crevasse splays and distributary lobes long term preservation requires high rates of subsidence consequently the vast majority of palaeozoic t 0 assemblages are confined to wetland settings at or close to sea level whereas drylands are poorly represented and uplands rarely sampled if ever however this is not the only major bias in the fossil record taphonomic processes selectively preserve plants dependent on their anatomy and stature and on groundwater chemistry thus although t 0 assemblages offer unrivalled insights into the nature of ancient forests whole plant reconstructions tree density canopy height productivity plant hydraulics cohort dynamics spatial heterogeneity ecological gradients tree sediment interactions and animal plant interactions to name but a few it is naive to believe they provide photographic snapshots9 of palaeoecosystems none the less careful taphonomic analysis of t 0 assemblages offers the potential for a nuanced understanding of these evocative phenomena and much remains to be learned from these important palaeoecological resources

buoyancy bending and seismic visibility in deep slab stagnation abstract the petrological consequences of deep subhorizontal deflection stagnation of subducting slabs should affect both apparent seismic velocity structures and slab morphology we construct kinematic thermal models of stagnant slabs and perform thermodynamic modeling of the consequent perturbation of high pressure phase transitions in mantle minerals focusing upon japan as our study area we calculate associated thermo petrological buoyancy forces and bending moments which along with other factors such as viscosity variations and rollback dynamics may contribute to slab deformation we consider effects of variations in depth of stagnation post stagnation dip angle phase transition sharpness transition triplication due to multiple intersection of geotherms with phase boundaries and potential persistence of metastable phases due to kinetic hindrance we also estimate seismic velocity anomalies as might be imaged by seismic tomography and corresponding seismic velocity gradients as might be imaged by receiver function analysis we find that buoyant bending moment gradients of petrological origin at the base of the transition zone may contribute to slab stagnation such buoyancy forces vary with the depth at which stagnation occurs so that slabs may seek an equilibrium slab stagnation depth metastable phase bending moment gradients further enhance slab stagnation but they thermally decay after 4600 700 km of horizontal travel potentially allowing stagnant slabs to descend into the lower mantle stagnant slabs superimpose zones of negative velocity gradient onto a depressed 660 km seismic discontinuity affecting the seismological visibility of such features seismologically resolvable details should depend upon both stagnation depth and the nature of the imaging technique travel time tomography vs boundary interaction phases while seismic tomography appears to yield images of stagnant slabs discontinuity topography beneath japan resolved by migrated receiver functions appears to be consistent with slab penetration of the transition zone however model slabs which bottom around 4780 810 km and then bend upwards by a few degrees can match both the tomographic and receiver function images

cretaceous mantle of the congo craton evidence from mineral and fluid inclusions in kasai alluvial diamonds abstract alluvial diamonds from the kasai river democratic republic of the congo drc are sourced from cretaceous kimberlites of the lucapa graben in angola analysis of 40 inclusion bearing diamonds provides new insights into the characteristics and evolution of ancient lithospheric mantle of the congo craton silicate inclusions permitted us to classify diamonds as peridotitic containing fo 91 95 and en 92 94 23 diamonds 70 of the suite and eclogitic containing cr poor pyrope and omphacite with 11 27 jadeite 6 diamonds 18 of the suite fluid inclusion compositions of fibrous diamonds are moderately to highly silicic matching compositions of diamond forming fluids from other drc diamonds regional homogeneity of congo fibrous diamond fluid inclusion compositions suggests spatially extensive homogenization of cretaceous diamond forming fluids within the congo lithospheric mantle in situ cathodoluminescence secondary ion mass spectrometry and fourier transform infrared spectroscopy reveal large heterogeneities in n n aggregation into b centers n b and 13 c indicating that diamonds grew episodically from fluids of distinct sources peridotitic diamonds contain up to 2962 ppm n show 0 88 n b and have 13 c isotopic compositions from 12 5 to 1 9 with a mode near mantle like values eclogitic diamonds contain 14 1432 ppm n n b spanning 29 68 and wider and lighter 13 c isotopic compositions of 17 8 to 3 4 fibrous diamonds on average contain more n up to 2976 ppm and are restricted in 13 c from 4 1 to 9 4 clinopyroxene garnet thermobarometry suggests diamond formation at 1350 1375 c at 5 8 to 6 3 gpa whereas n aggregation thermometry yields diamond residence temperatures between 1000 and 1280 c if the assumed mantle residence time is 0 9 3 3 ga integrated geothermobaromtery indicates heat fluxes of 41 44 mw m 2 during diamond formation and a lithosphere asthenosphere boundary lab at 190 210 km the hotter than average cratonic mantle may be attributable to contemporaneous rifting of the southern atlantic multiple post archean reactivations of the craton and or proximal cretaceous plumes

density of morb eclogite in the upper mantle in order to study the role of eclogite subducted oceanic crust in geodynamics we carried out high pressure experiments on natural mid oceanic ridge basalt morb using a multi anvil apparatus we determined phase relations of morb as a function of pressure and temperature in the temperature range of 1200 1700 c and pressures from 5 to 14 gpa the present results differ from a previous high pressure study of morb earth planet sci lett 77 1986 245 conducted at 1200 c as follows 1 coesite coe or stishovite st appears throughout the studied pressure range and 2 the clinopyroxene garnet cpx gar ratio is smaller particularly in the low pressure range 12 gpa our results show that the calculated bulk density of subducted oceanic crust increases discontinuously at around 9 gpa due to the coesite stishovite phase transition the density is considerably higher than estimates based on the previous experiments at pressures less than 12 gpa thus the role of eclogite in driving subduction should be more important than previously thought on the other hand the density difference between peridotite and eclogite in ascending mantle plumes becomes smaller as temperature increases a result of the increase in clinopyroxene garnet sio2 ratio in eclogite with increasing temperature as eclogite is still denser than peridotite even under subsolidus conditions recycled oceanic crust entrained in ascending plumes must be sustained by the upward flow of ambient peridotite in mantle plumes

mineralogy garnet goes hungry sinking slabs of oceanic lithosphere often stagnate in earth s mantle experiments show that common slab minerals transform to their high pressure high density counterparts at very slow rates thus keeping the slabs buoyant and impeding subduction

metastability of enstatite in deep subducting lithosphere olivine and mg fe sio3 pyroxene the most abundant minerals in the earth s upper mantle are believed to transform to high pressure phases at 400 km depth1 5 the possible metastable persistence of olivine to greater depths in some subduction zones with consequences for the origin of deep focus earthquakes and the dynamics of subduction has been discussed extensively6 14 but the role of other mantle minerals has not been considered we report here an experimental study of the kinetic behaviour of the magnesian pyroxene enstatite mgsio3 at upper mantle conditions we find that whereas forsterite mg olivine mg2sio4 transforms rapidly to phase at 1 200 c and 16 gpa the transformation of enstatite to phase plus stishovite on the same timescale requires much higher temperatures at lower temperatures enstatite transforms directly to the ilmenite structure but only at pressures greater than 20 gpa enstatite should therefore persist metastably to greater depths than olivine in subduction zones transforming directly to the ilmenite structure the enstatite ilmenite transformation is accompanied by a large decrease in volume which should increase the stresses in subducting slabs change the buoyancy forces that drive subduction and might also contribute to the origin of deep focus earthquakes

elasticity of pyrope and majorite pyrope solid solutions to high temperatures abstract majorite garnet solid solutions are major mineral phases in the earth s upper mantle and transition zone here we present the first brillouin scattering measurements of the elasticity of majorite mj mg 4 si 4 o 12 pyrope py mg 3 al 2 si 3 o 12 solid solutions mj 50 py 50 and mj 80 py 20 and single crystal elasticity of pure synthetic pyrope at temperatures up to 800 c the temperature derivatives of the adiabatic bulk k s and shear moduli for all compositions along the mj py join are the same within the experimental uncertainties k s t 14 0 14 5 20 mpa k t 8 3 9 2 10 mpa k the temperature dependence of the acoustic velocities for mj py solid solutions is about half that of other major transition zone minerals this implies that temperature variations in the transition zone inferred from lateral velocity heterogeneity can be significantly underestimated if the properties of majoritic garnet are not taken into account

the effect of metastable pyroxene on the slab dynamics seismic studies show that some subducting slabs penetrate straight into the lower mantle whereas others seem to flatten near the base of the mantle transition zone slab stagnation is often attributed to an increase in viscosity and phase transformations in the olivine system however recent mineral physics studies showed that due to extremely low transformational diffusion rates low density metastable pyroxene may persist into the transition zone in cool slabs here we use a dynamically fully self consistent subduction model to investigate the influence of metastable pyroxene on the dynamics of subducting oceanic lithosphere our results show that metastable pyroxene affects slab buoyancy at least as much as olivine metastability however unlike metastable olivine which can inhibit slab penetration in the lower mantle only for cold old and fast slabs metastable pyroxene is likely to also affect sinking of relatively young and slow slabs

evolution of the cretaceous astrid thrust belt in the ultradeep water lower congo basin gabon the lower congo basin contains the greatest salt based fold and thrust belt off africa s atlantic margin our study area in the anton marin and astrid marin exploration blocks is in the northern part of the basin gravity driven tectonic shortening began soon after the aptian salt deposition forming gentle west trending salt cored anticlines which together with salt diapirs created a template for later thrusting in the late cretaceous a thrust front propagated landward into the study area and thrusts formed above salt anticlines and diapirs formation of a hanging wall wedge of growth strata was recorded when each thrust fault ruptured the seabed thrusting began after widespread salt thinning as autochthonous salt was expelled into older passive diapirs thinning stiffened the detachment so that thrusts verge strongly seaward structural restorations dip corrected isochron maps and fault activity graphs all show that the landward edge of the thrust belt propagated landward three main pulses of shortening episodically reactivated thrust faults as the thrust front broke landward as thrusting culminated precursor passive diapirs were squeezed and extruded small allochthonous sheets translation culminated in major erosional scouring from which we infer epeirogenic slope steepening in the late cretaceous as shortening spread updip into the previously extensional domain during the late cretaceous to paleogene older extensional faults were inverted and new extensional faults formed orthogonally parallel to the regional paleoslope the structural pattern created in the late cretaceous when the paleoslope dipped southward remains recognizable in the little deformed neogene strata although the present continental slope dips westward

dips ramps and rolls evidence for paleotopographic and syn depositional fault control on the western kentucky no 4 coal bed tradewater formation bolsovian illinois basin abstract the western kentucky no 4 coal is a high volatile b to high volatile c bituminous coal that has been heavily mined along the southern margin of the western kentucky coal field the seam has a reputation for rolling floor elevation elongate trends of floor depressions are referred to as dips and rolls by miners some are relatively narrow and straight to slightly curvilinear in plan view with generally symmetric to slightly asymmetric cross sections others are broader and asymmetric in section with sharp dips on one limb and gradual ramp like dips on the other some limbs change laterally from gradual dip to sharp dip to offset of the coal lateral changes in the rate of floor elevation dip are often associated with changes in coal thickness and in underground mines changes in floor elevation are sometimes associated with roof falls and haulage problems in order to test if coal thickness changes within floor depressions were associated with changes in palynology petrography and coal quality the coal was sampled at a surface mine across a broad ramp like depression that showed down dip coal thickening increment samples of coal from a thick 150 cm down ramp and thinner 127 cm up ramp position at one surface mine correlate well between sample sites a distance of 60 m except for a single increment the anomalous increment 31 cm in the lower middle part of the thick coal bed contained 20 more lycospora orbicula spores the rolling floor elevations noted in the study mines are inferred to have been formed as a result of pre peat paleotopographic depressions syn depositional faulting fault controlled pre peat paleotopography and from compaction beneath post depositional channels and slumps although the association of thick coal with linear trends and inferred faults has been used in other basins to infer syn depositional faulting changes in palynology within increment samples of the seam along a structural ramp in this study provide subtle evidence of faulting within a specific increment of the coal itself the sudden increase in l orbicula produced by paralycopodites in a single increment of a down ramp sample of the western kentucky no 4 coal records the reestablishment of a rheotrophic mire following a sudden change in edaphic conditions paralycopodites was a colonizing lycopod which in this case became locally abundant after the peat was well established along a fault with obvious growth during peat accumulation because many coal mire plants were susceptible to sudden edaphic changes as might accompany faulting or flooding changes in palynology would be expected in coals affected by syn depositional faulting

sound velocities of majorite garnet and the composition of the mantle transition region the composition of the mantle transition region characterized by anomalous seismic wave velocity and density changes at depths of approximately 400 to 700 km has remained controversial some have proposed that the mantle transition region has an olivine rich pyrolite composition whereas others have inferred that it is characterized by pyroxene and garnet rich compositions piclogite because the sound velocities in pyrolite estimated from laboratory data are substantially higher than those seismologically observed although the velocities of the olivine polymorphs at these pressures wadsleyite and ringwoodite have been well documented those of majorite another significant high pressure phase in the mantle transition region with realistic mantle compositions have never been measured here we use combined in situ x ray and ultrasonic measurements under the pressure and temperature conditions of the mantle transition region to show that majorite in a pyrolite composition has sound velocities substantially lower than those of earlier estimates owing to strong nonlinear decreases at high temperature particularly for shear wave velocity we found that pyrolite yields seismic velocities more consistent with typical seismological models than those of piclogite in the upper to middle parts of the region except for the potentially larger velocity jumps in pyrolite relative to those observed at a depth of 410 km in contrast both of these compositions lead to significantly low shear wave velocities in the lower part of the region suggesting possible subadiabatic temperatures or the existence of a layer of harzburgite rich material supplied by the subducted slabs stagnant at these depths

syntectonic sedimentation rigs and fault reactivation in the coal measures of britain rigs are sediment bodies that occupy linear arcuate and ringed depressions in coal seam roofs and are interpreted as the sites of pools that formed on a peat surface the form of the rigs indicates that their origin is due to contemporary tilting of the peat surface during movement attributed to activity of a nearby contemporary fault subsequent movement ultimately led to the formation of a coal seam split at a later date the fault was reactivated but with a different sense of movement

iron partitioning in a pyrolite mantle and the nature of the 410 km seismic discontinuity pyrolite1 is a hypothetical mixture of distinct minerals which iswidely believed to represent the composition of the earth s mantle the main pressure induced phase transformations of the olivine component of pyrolite occur at about 13 5 gpa to and 24 gpa to mgsio3 rich perovskite magnesiowustite 2 3 which are thought to be responsible for the seismic discontinuities at 410 and 660 km depths in the mantle recent seismological studies however have demonstrated that the 410 km seismic discontinuity is sharper in some areas than that expected from the to transformation in mantle olivine with a fixed composition4 5 6 7 moreover some mineral physics studies suggest that the seismic velocity jump at the 410 km discontinuity is inconsistent with that associated with the to transformation in olivine8 9 here we present a phase equilibria study of a material having pyrolite composition at pressures of 6 16 gpa we found that the iron content in olivine changes significantly with increasing pressure as a result of the formation of a relatively iron rich majorite phase at these pressures this variation in iron content can overcome or at least reduce both of the above difficulties encountered with the pyrolite model of mantle composition by showing that the component mineral systems cannot be treated as separate

petrology and palynology of the middle pennsylvanian leatherwood coal bed eastern kentucky indications for depositional environments abstract the eastern kentucky coal field is located in the central portion of the appalachian basin the pennsylvanian breathitt formation in this region is characterized by numerous sequences of bituminous coal bearing sedimentary rocks these coals have distinct maceral compositions due to variations in depositional environments coal characterization is an important method for determining conditions that influenced peat accumulation and overall depositional settings of mires this study focuses on the characterization of the maceral composition of the middle pennsylvanian age leatherwood coal bed it utilizes petrographical palynological and geochemical analyses to describe specific depositional environments and associated peat accumulation conditions petrographic analyses indicate that these coals have relatively high liptinite and varying inertinite content along with trace amounts of mineral matter vitrinite mainly in the form of collotelinite is the most dominant maceral group geochemical data reveals low ash and sulfur content ancillary palynological data shows the palynomorph assemblage to be dominated by tree fern and large lycopod tree spores with lesser amounts of small lycopod tree small fern and cordaites and calamites spores the petrographic geochemical and palynological data indicate that both domed ombrotrophic and planar rheotrophic mire conditions with limited local detrital influx contributed to the formation of the leatherwood coal

the crystal structure of diopside at pressure to 10 gpa the crystal structure of diopside has been determined at various pressures to 10 16 gpa the results to 5 gpa are consistent with levien and prewitt 1981 the crystal structures have been analyzed using the geometric pyroxene model of thompson and downs 2004 the anion packing algorithm of thompson and downs 2001 and a new algorithm that quantifies the distortion of observed pyroxenes from their geometric model equivalents diopside is shown to compress via three main mechanisms isotropic scaling kinking of the tetrahedral chains and collapse of the m1 chain toward its axis the kinking of the chains accounts for most of the anisotropy of compression observed in the a c plane and the collapse of the m1 chain explains the anisotropy seen in the b c plane model behavior is shown to reproduce many of the observations of previous workers anion anion interactions are shown to be important in the distortion of observed diopside from its geometric model equivalent

lacustrine delta deposits and their effects on coal mining in a surface mine in derbyshire england abstract five late carboniferous pennsylvanian coal seams and associated inter seam strata have been examined at lodge house surface mine in the east midlands coalfield of england deposition of these coal seams and their accompanying inter seam intervals occurred in an equatorial fluvio lacustrine environment in an area approximately halfway between the depocentre and the southern margins of the pennine basin controls on the onset of inter seam sedimentation and cessation of peat formation appear to have operated at two scales fourth order glacio eustatic rises exerted the dominant control over formation of peats in laterally extensive mires however fifth order and smaller scale autocyclic mechanisms specifically avulsion are believed to have accompanied splitting of other seams close to but beyond the confines of the mine a study of contrasting lacustrine delta deposits occupying two of the inter seam intervals has enabled proximal distal wave dominated and delta distributary channel sub facies to be recognised the lacustrine deltas prograded rapidly into shallow but extensive freshwater lakes and both delta lobe switching and avulsion of delta distributary channels were important mechanisms the lower lacustrine delta sequence is characterised by mud filled delta distributary channels near the top of the interval the upper sequence is dominated by wave formed structures and massive sandstone delta distributary channels which formed during a period of episodic floods and strong winds lacustrine delta deposits generally create good mining conditions but delta distributary channels can present difficulties in underground mines mud filled delta distributary channels subject to early compaction can give rise to swilleys elongate depressions resulting in thickness changes and undulation of the overlying seam when filled with strong well cemented abrasive sandstone delta distributary channel deposits can be hard to excavate at lodge house the narrow width of the delta distributary channels meant that they were not detected by drilling prior to mining thus outcrop studies should be used to complement subsurface data as they can significantly enhance our understanding of small scale features

physical conditions producing slab stagnation constraints of the clapeyron slope mantle viscosity trench retreat and dip angles abstract recent seismic tomography has revealed various morphologies in the subducted lithosphere in particular significant flattening and stagnation of slabs around the 660 km boundary are seen in some areas beneath the northwestern pacific subduction zones we examined the cause of slab stagnation in terms of the clapeyron slope of the phase transformation from ringwoodite to perovskite magnesiowustite trench retreat velocity dip angles and high viscosity of the lower mantle based on two dimensional 2 d numerical simulations of thermal convection in particular we examined the conditions necessary for slab stagnation assuming a very small absolute value of the clapeyron slope which were proposed based on recent high pressure high temperature high p t experiments our calculations show that slabs tend to stagnate above the 660 km boundary with an increasing absolute value of the clapeyron slope viscosity jump at the boundary and trench retreat velocity and a decreasing initial dip angle stagnant slabs could be obtained numerically for a realistic range of parameters obtained from high p t experiments and other geophysical observations combining buoyancy high lower mantle viscosity and trench retreat we found that a low dip angle of a descending slab at the bottom of the upper mantle plays an important role in slab stagnation two main regimes underlie slab stagnation buoyancy dominated and viscosity dominated regimes in the viscosity dominated regime it is possible for slabs to stagnate above the 660 km boundary even when the value of the clapeyron slope is 0 mpa k

counter regional normal faults in shale dominated deltas origin mechanism and evolution abstract the niger and brunei deltas are two of the major prolific petroleum deltas of the world as a result large datasets of 2d and 3d seismic are available however some of the structures remain poorly understood because they are poorly imaged and a shale diapir interpretation has often prevailed these two deltas are in places driven by particular landward structures described as counter regional normal faults crnf these faults initiated on the apex of early folds as the shelf break propagated seaward during a first stage of deformation crnf started as diffuse faults rather than localised single faults later as the sediment load increased in the area affected by the crnf a major landward dipping fault developed controlling the delta front emplacement finally the fault was choked by the sedimentary system and another fault landward or seaward developed the description of the pre existing fold structures controlling the development of crnf allows a reassessment of the structural evolution of shale gravity driven tectonics it is agreed that in many cases the existence of mud diapirs and ridges may be discarded

kinetics of the olivine spinel transformation in subducting lithosphere experimental constraints and implications for deep slab processes abstract the persistence of metastable olivine to depths greater than 400 km in subducting slabs has implications for the generation of deep focus earthquakes the magnitude of buoyancy forces driving plate motion and the state of stress in the slab the depth to which metastable olivine can survive in a subduction zone and the depth interval over which transformation to or mg fe 2sio4 occurs have been evaluated from experimental kinetic data for the mg2geo4 and ni2sio4 transformations and the mg2sio4 transformation the data were extrapolated using a kinetic model for grain boundary nucleation and interface controlled growth under non isothermal and non isobaric conditions the results predict that metastable mg1 8fe0 2sio4 olivine survives to depths greater than 500 km in the cold interior of rapidly subducting slabs of old lithosphere the onset of transformation to mg fe 2sio4 spinel depends only on growth kinetics and coincides with the 550 50 c isotherm including the effects of latent heat production causes the transformation to occur by a runaway process over a very narrow depth interval at the onset of transformation high nucleation rates and low growth rates are consistent with the formation of very fine grained reaction products which are required for the transformational faulting mechanism of deep focus earthquakes when olivine crosses the equilibrium boundaries at higher temperatures e g higher than 700 c at 400 km depth transformation to or occurs much closer to equilibrium at a depth controlled by nucleation kinetics in this case the effect of latent heat production on the transformation kinetics is small and microstructural evolution is unlikely to result in transformational faulting below the depth of olivine breakdown cold slabs are likely to have a complex rheological structure owing to temperature dependent microstructural evolution during the phase transformation

single crystal x ray structure study of synthetic pyrope almandine garnets at 100 and 293 k the crystal structures of synthetic pyrope mg3ai2si3012 almandine feai2si3012 and the solid solution garnet compositions py8o alm2o py6o alm4o and py2o alm8o have been refined in space group ia1d from high precision x ray diffraction data with sin 0 0 4 a i measured at 100 and 293 k there is no indication of lower symmetry for pyrope almandine or solid solution members experimentally determined atomic coordinates and displacement parameters for the solid solution compositions are in good agreement with those linearly interpolated from the end members thus there are no apparent structural features that could account for substantial nonideal enthalpies of mixing in the system pyrope almandine the tetrahedral rotation angle is inversely correlated with the x o distance fe2t substitution on the eight coordinated x site of pyrope or increasing temperature decreases the rigid tetrahedral rotation in garnet the large and anisotropic displacement parameters for the x site cations in garnet are mainly a result of anisotropic thermal vibrations along the longer x o bonds which produce nonrigid polyhedral behavior for the dodecahedral site the tetrahedra and octahedra behave as rigid bodies these strong vibrations of the former give rise to the relatively large heat capacities and third law entropies in garnet previous proposals concerning subsite dodecahedral ordering in pyrope must be revised

single crystal elasticity of diopside to 14 gpa by brillouin scattering the single crystal elastic moduli cij of diopside have been measured up to 14 gpa using brillouin spectroscopy from which the aggregate compressional and shear velocities adiabatic bulk modulus shear modulus and their pressure derivatives were obtained a least squares fit of the velocity pressure data to third order finite strain equation yields k

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

a new inference of mantle viscosity based upon joint inversion of convection and glacial isostatic adjustment data we present new profiles of mantle viscosity derived on the basis of non linear occam style joint inversions of an extensive set of data associated with mantle convection and glacial isostatic adjustment gia the convection related observables include satellite derived free air gravity harmonics the geodetically inferred excess ellipticity of the cmb and tectonic plate motions the gia constraints involve two classes of observables previously shown to be relatively insensitive to errors in the late pleistocene ice history the so called fennoscandian relaxation spectrum frs and a set of site specific decay times determined from the postglacial sea level history in hudson bay and sweden the inverted viscosity profiles show a significant three orders of magnitude increase from the upper mantle mean value of f4 10 20 pa s to a high viscosity 10 23 pa s peak at

implications of slab mineralogy for subduction dynamics phase relations among mantle minerals are perturbed by the thermal environment of subducting slabs both under equilibrium and disequilibrium metastable conditions such perturbations yield anomalies not only in seismic velocities but also in density the buoyancy forces arising from these density anomalies may exert several important effects they contribute to the stress field within the slab in a fashion consistent with observed patterns of seismicity they may affect subduction rates both by inducing time dependent velocity changes under equilibrium conditions and by imposing velocity limits through a thermal feedback loop under disequilibrium conditions they may affect slab morphology possibly inhibiting penetration of slabs into the lower mantle and allowing temporary stagnation of deflected or detached slabs latent heat release from phase transitions under disequilibrium conditions in slabs can yield isobaric superheating which may generate adiabatic shear instabilities capable of triggering deep seismicity 2001 elsevier science b v all rights reserved

adiabatic temperature profile in the mantle abstract the temperature at the 410 km discontinuity is re evaluated by comparing the depth of the discontinuity with the olivine wadsleyite transition pressure obtained using in situ x ray diffraction experiments by katsura et al 2004a and equation of state eos of mgo by tange et al 2009 tange scale and matsui et al 2000 the newly estimated temperature is 1830 48 k 70 k higher than that by our previous estimation the eoses of the major mantle minerals olivine wadsleyite ringwoodite and perovskite are also recalculated using the tange scale the adiabatic temperature gradient is calculated using the thermal expansion coefficient obtained from these eoses the adiabatic temperature gradient gradually decreases with increasing depth without a phase transition and abruptly increases in association with phase transitions the adiabatic temperature gradients are found to be 04 0 5 and 0 3 k km in the upper and lower parts of the mantle respectively the temperatures at a depth of 200 km the bottom of the mantle transition zone the top of the lower mantle and a depth of 2700 km are found to be 1720 40 2010 40 1980 40 and 2730 50 k the mantle potential temperature is found to be 1610 35 k

the influence of olivine metastability on the dynamics of subduction abstract both seismological observations and mineral physics experiments suggest that old and cold subducting slabs might contain a wedge of metastable olivine mo dynamically consistent models of subducting slabs in which the kinetics of the olivine to spinel wadsleyite or ringwoodite transition is treated in a simplified way are carried out to evaluate the buoyancy effect of mo on the subduction velocity assuming slab thicknesses according to the cooling half space model we find that mo forms in slabs with ages greater than approximately 70 myr and that a significant slowing down of subduction velocity occurs for ages greater than 100 myr because a decrease in the subduction velocity for old lithospheric ages is not observed our models suggest that the amount of mo in slabs is less than approximately 5000 km2 in cross section and that for old lithosphere the cooling half space model is not applicable

slab stiffness control of trench motion insights from numerical models 1 subduction zones are not static features but trenches retreat roll back or advance here we investigate the dominant dynamic controls on trench migration by means of two and three dimensional numerical modeling of subduction this investigation has been carried out by systematically varying the geometrical and rheological model parameters our viscoplastic models illustrate that advancing style subduction is promoted by a thick plate a large viscosity ratio between plate and mantle and a small density contrast between plate and mantle or an intermediate width w 1300 km advancing slabs dissipate 45 to 50 of the energy in the system thin plates with relatively low viscosity or relatively high density or wide slabs w 2300 km on the other hand promote subduction in the retreating style i e slab roll back the energy dissipated by a retreating slab is 35 to 40 of the total dissipated energy most of the energy dissipation occurs in the mantle to accommodate the slab motion whereas the lithosphere dissipates the remaining part to bend and unbend with a simple scaling law we illustrate that this complex combination of model parameters influencing trench migration can be reduced to a single one plate stiffness stiffer slabs cause the trench to advance whereas more flexible slabs lead to trench retreat the reason for this is that all slabs will bend into the subduction zone because of their low plastic strength near the surface but stiff slabs have more difficulty unbending at depth when arriving at the 660 km discontinuity those bent slabs tend to cause the trench to advance in a similar way variation of the viscoplasticity parameters in the plate may change the style of subduction a low value of friction coefficient weakens the plate and results in a retreating style while higher values strengthen the plate and promote the advancing subduction style given the fact that also on earth the oldest and therefore probably stiffest plates have the fastest advancing trenches we hypothesize that the ability of slabs to unbend after subduction forms the dominant control on trench migration

stagnation of subducting slabs in the transition zone due to slow diffusion in majoritic garnet subducting slabs of oceanic lithosphere often stagnate before reaching the lower mantle laboratory experiments under high pressures and temperatures show that pyroxene a common mineral in such slabs is transformed to its dense high pressure counterpart majorite garnet at a very slow rate temporarily keeping the slabs buoyant compared to the surrounding mantle

the interaction of a subducting lithospheric slab with a chemical or phase boundary we have used a finite element model of time dependent convection to determine the conditions for penetration of the subducted plate into the lower mantle a temperature dependent and non newtonian rheology is applied to achieve platelike behavior of the upper and sinking thermal boundary layer of convection the 650 km discontinuity is taken as either a chemical or phase boundary or as a combination of both it is represented by a marker chain which effects additional buoyancy when distorted out of its equilibrium position when the compositional density contrast is greater than about 5 the descending slab is deflected sidewards at the boundary and two layer convection prevails a resulting depression of the boundary in the range of 50 200 km should be detectable with seismic methods below 5 density difference the slab plunges several hundred kilometers into the lower mantle and below 2 it will probably not stop before reaching the core mantle boundary and extensive mixing would be expected with a pure phase change a negative clapeyron slope of about 6 mpa k 60 bar k is required to establish a type of leaky double layer convection a more moderate slope can aid a small compositional density difference to prevent slab penetration into the lower mantle with the present uncertainties about the physical nature of the 650 km discontinuity a variety of convective styles appears possible on dynamical grounds

the influence of trench migration on slab penetration into the lower mantle abstract a two dimensional numerical convection model in cartesian geometry is used to study the influence of trench migration on the ability of subducted slabs to penetrate an endothermic phase boundary at 660 km depth the transient subduction history of an oceanic plate is modelled by imposing plate and trench motion at the surface the viscosity depends on temperature and depth a variety of styles of slab behaviour is found depending predominantly on the trench velocity when trench retreat is faster than 2 4 cm a the descending slab flattens above the phase boundary at slower rates it penetrates straight into the lower mantle although flattening in the transition zone may occur later leading to a complex slab morphology the slab can buckle independent of whether it penetrates or not especially when there is a localised increase in viscosity at the phase boundary flattened slabs are only temporarily arrested in the transition zone and sink ultimately into the lower mantle the results offer a framework for understanding the variety in slab geometry revealed by seismic tomography

the influence of half graben syn depositional tilting on thickness variation and seam splitting in the brunner coal measures new zealand abstract the brunner coal measures buller coalfield new zealand comprise a fluviatile sequence of eocene age that is generally 30 100 m thick the sequence rests on basement and is dominated by coarse to granular very coarse sandstone the measures contain one mineable coal seam the buller seam member that is laterally extensive and up to 20 m thick it is characterized by simple splitting with a thin upper split a thick lower split and a split separation of up to 30 50 m locally the buller seam member exhibits splitting to form numerous thin seams areas of shale out comprise thin linear belts between areas of thick coal with a low ash yield the coincidence of faults and maximum thickness of seam isopachs indicates that the thickness and splitting characteristics of the buller seam member were largely controlled by syn depositional faulting and tilting of small half graben blocks thickness variation in basal sequences is primarily due to syn depositional faulting syn depositional tilting of fault blocks also influenced the migration of river channels and hence the stacking and distribution of sandstone and locally thick mudstone units overlying coal

slow si al interdiffusion in garnet and stagnation of subducting slabs abstract si 4 m 2 2al 3 m mg fe ca interdiffusion rates in majoritic garnet have been determined at pressure of 17 gpa and temperatures of 1550 1700 c using a kawai type high pressure apparatus the diffusion profiles were measured across the interface between pyropic garnet and majoritic garnet samples by an analytical transmission electron microscope and the rate of the si 4 m 2 2al 3 interdiffusion was determined to be a d si al m 2 s 1 2 10 10 exp 364 kj mol 1 rt we found that the diffusion rate is low compared to the si diffusion rate in other silicate minerals relevant to the deep mantle slow kinetics of the pyroxene garnet transformation due to the low diffusion rate indicates that large low density metastable regions may exist in the slab greatly contributing to the slab stagnation around the transition region stagnant slabs possibly stay in this region over 10 8 yr because of the sluggish pyroxene garnet transformation but may eventually fall into the lower mantle after the completion of the transformation

transgressive channel filling in the breathitt formation upper carboniferous eastern kentucky coal field usa abstract carbonaceous shales of brackish or marine origin in the breathitt formation may exhibit sharp bases with local channel form scours minor channels at the bases of these shales exhibit three general types of fill 1 shale 2 bioturbated heterolithic strata and 3 coal overlain by shale or bioturbated heterolithic strata most of the scours at the bases of the channels were formed during a depositional hiatus that preceded transgression some may also have been formed by transgressive reworking of underlying estuarine and deltaic siliciclastics the channel fills are bioturbated and may contain crudely cyclical rhythmites subordinate and dominant siltstone laminae couplets wave ripples and bimodal current ripple trends the fills are interpreted to represent estuarine sedimentation during marine transgression channels are capped by sideritic bioturbated sandstones that separate the fills from the overlying dark shales deposited under brackish to marine water conditions some of these sandstones may represent local transgressive surfaces the occurrence of these types of channels in different parts of the coal bearing breathitt formation supports the hypothesis of multiple transgressions during the late carboniferous in the central appalachian basin

the influence of olivine metastability on deep subduction of oceanic lithosphere abstract the dynamics of subduction of oceanic lithosphere is mainly controlled by thermal buoyancy forces and mineralogy in self consistent models the influence of metastable olivine mo on the dynamics and evolution of subducting oceanic lithosphere is investigated we consider both phase boundaries olivine ol to spinel sp 410 km and sp to perovskite pv magnesiowustite mw 660 km treating the kinetics of the phase transition in a simplified way while models do not allow the formation of mo penetrate straight into the lower mantle slabs with a sufficient amount of mo flatten out at the 660 km boundary before penetrating at a later stage furthermore our models show that the effect of mo to slow down subduction velocities within the transition zone is rather moderate

overriding plate controls on subduction evolution geologic and geophysical observations indicate that the thickness density and strength of the lithosphere vary on the earth however the role of the overriding plate lithosphere properties on the evolution and morphology of subduction is not well understood this paper presents time dependent numerical models of subduction that vary the overriding plate thickness strength and density and allow for a plate interface that evolves with time via an anisotropic brittle failure rheology we examine the effect of these parameters on subduction evolution in particular the emergence of a asymmetric versus symmetric subduction b trench retreat versus advance c subduction zone geometry d slab stagnation versus penetration into the lower mantle and e flat slab subduction almost all of the models presented result in sustained asymmetric subduction from initiation trench advance occurs in models with a thick and or strong overriding plate slab dip measured at a depth below the plate boundary interface has a negative correlation with an increase in overriding plate thickness overriding plate thickness exerts a first order control over slab penetration into the lower mantle with penetration most commonly occurring in models with a thick overriding plate periods of flat slab subduction occur with thick strong overriding plates producing strong plate boundary interface coupling the results provide insight into how the overriding plate plays a role in establishing advancing and retreating subduction as well as providing an explanation for the variation of slab geometry across subduction zones on earth where similar patterns of evolution are observed