internally consistent thermodynamic data set for dense hydrous magnesium silicates up to 35 gpa 1600 c implications for water circulation in the earth s deep mantle abstract fluid undersaturated high pressure experiments were carried out in the system mgo sio 2 h 2 o in a multi anvil apparatus from 15 5 to 21 5 gpa and from 1000 to 1200 c in order to constrain fluid absent solid solid reactions from the experimentally determined fluid absent phase equilibria thermodynamic parameters for high pressure hydrous phases were retrieved by a linear programming method together with dry mantle minerals from the existing data set and high pressure hydrous phases from our previous study an internally consistent set of thermochemical and thermophysical parameters for dense hydrous magnesium silicates dhmss was evaluated up to 35 gpa and 1600 c high pressure hydrous phases involved in the data set are phase a phase e clinohumite phase d superhydrous phase b hydrous wadsleyite and hydrous ringwoodite in addition by calculating water bearing reactions we evaluated water activities in the fluid phase coexisting with mantle minerals the water activity decreases with increasing pressure or temperature suggesting that the amount of silicate component dissolved in the fluid phase increases with pressure or temperature the calculated petrogenetic grid consisting of 89 univariant reactions can be used for the discussion of water circulations in the mantle in a subducting slab peridotite water in phase a as the post serpentine phase is transferred to other dhmss via solid solid reactions down to the bottom of the transition zone at around 660 km depth in the stagnant slab heated from the surrounding mantle a free fluid will be released by the dehydration of superhydrous phase b or phase d the released fluid will be trapped by wadsleyite or ringwoodite in the surrounding mantle in a cold subducting slab without stagnation at 660 km depth dhmss will survive into the lower mantle in an upwelling plume through the water bearing transition zone a free fluid will be produced when the plume passes 410 km depth finally water will be released to the earth s surface by magmatism the fluid generated in the deep mantle dissolves significant amounts of a silicate component therefore at 410 and 660 km depths some chemical differentiation will be processed

viscous flow features on the surface of mars observations from high resolution mars orbiter camera moc images 10 5 10 7 years of the material our shear stress estimates of 10 1 5 10 2 5 mpa yield strain rates on the order of 10 11 10 16 s 1 which are within the superplastic flow regime of ice mean annual surface temperatures age constraints and strain estimates show that it is possible for a meters thick ice dust mixture to undergo viscous deformation under past or present surface conditions for ice grain sizes 10 mm the meters thick layer in which the viscous flow features formed is morphologically similar to a degraded meters thick ice dust surface deposit dissected mantle terrain locations of the viscous flow features dissected mantle terrain and recent gullies are concentrated in the midlatitude regions and all three show identical distributions as a function of latitude with the maximum frequency of occurrence at 40 n and s the strong association between these small scale flow features and the dissected mantle terrain large scale viscous flow features and recent gullies imply that deposition deformation and removal of ice rich materials has played an important role in the modification of the surface in the midlatitudes of mars during the amazonian and possibly longer index terms 5470 planetology solid surface planets surface materials and properties 5416 planetology solid surface planets glaciation 1863 hydrology snow and ice 1827 1823 hydrology frozen ground 8168 tectonophysics stresses general keywords viscous flow viscous creep dissected mantle terrain ice rich deposits mars climate recent gullies

phase transformations in serpentine at high pressures and temperatures and implications for subducting lithosphere abstract serpentine may be regarded as a hydrous form of a 1 1 molecular mixture of olivine and pyroxene or a simplified hydrous pyrolite upper mantle composition the phase behaviour of two natural serpentines having the approximate compositions of mg0 99fe0 01 3si2o5 oh 4 and mg0 91fe0 09 3si2o5 oh 4 was investigated between 60 and 280 kbar inclusive at 700 1000 c in a diamond anvil pressure cell coupled with laser heating by incorporating earlier work the results suggest that at pressures greater than 30 kbar and temperatures in the range 600 1000 c serpentine displays the following sequence of phase transformations with increasing pressure serpentine 40 60 kb forsterite talc water 70 80 kbforsterite orthoenstatite water 100 kg forsterite clinoenstatite water 120 kb clinoenstatite phase a water 130 kb stishovite phase a brucite 180 kg stishovite phase b brucite 220 kb none of the high pressure phases expected in olivine and pyroxene such as the spinel modification of olivine the ilmenite and perovskite modifications of pyroxene was observed in serpentine up to about 280 kbar loading pressure on the basis of these results the effect of h2o on phase transformations of olivine and pyroxene at high pressures and high temperatures has been deduced it has been found that the modified spinel phase of mg2sio4 does not occur in the system having a 1 1 mixture of forsterite and enstatite and containing more than about 4 wt h2o the spinel phase of mg2sio4 does not appear at its equilibrium transition boundary modified spinel spinel in the same system containing more than about 3 wt h2o thus if more than about 4 wt h2o is present in the middle portion of a subducting lithosphere the so called 400 km seismic discontinuity observed in the normal mantle may not take place in the downgoing slabs where these transitions do occur at a low h2o content the associated change in density and accordingly the magnitude of discontinuities in the seismic wave velocities would be reduced by a factor of 2 3 if 2 wt h2o is present in the system

thermal hydrous and mechanical states of the mantle transition zone beneath southern africa abstract observations of p to s conversions from the seismic discontinuities near 410 and 660 km depth reveal the shoaling of the 410 km discontinuity and the deepening of the 660 km discontinuity beneath the archaean cratons in southern africa consequently the mantle transition zone is 20 km thicker than beneath post archaean regions and the global average the discontinuity structure combined with tomographically imaged seismic velocities suggests a relatively cold t 100 k and water enriched oh 20 35 saturation transition zone beneath the cratons the thicker than normal transition zone correlates with surface geology and does not follow the track of african plate motion as numerical simulations of small scale convection imply the observations suggest that cold thermal downwelling is not the primary cause of the anomalously thick transition zone beneath the cratons although it may exist in a confined area near the boundary between the kheis thrust belt and the namaqua natal belt if thermal downwelling exists its temperature anomaly at the 660 km discontinuity must be below the levels detectable by the method used in this study t 60 k the spatial correlation between surface geology high velocities beneath the cratons and the transition zone structure indicates that the cratonic keels extend to the base of the upper mantle substantially deeper than most estimates our results demonstrate the need to closely consider the effect of water content on seismic velocities beneath deep continental roots

iron water reaction under high pressure and its implication in the evolution of the earth we have established by experiments and thermodynamical calculations that a large amount of hydrogen can be dissolved in iron under high hydrogen pressure causing appreciable reduction of density and melting point more recent experiments have shown that the reaction of fe with hydrous silicates under high pressure and temperatures 5 gpa 1200 c 20 min yields iron hydride fehx olivine and pyroxene and that coagulation of iron particles is greatly facilitated in the partially molten state of the silicates on the basis of these experimental findings on fe h and fe h2o systems we propose that the fe h2o reaction should have played a crucial role in the evolution of the earth including in particular the core mantle separation and dissolution of hydrogen in the earth s core a tentative calculation on the mass flow in the evolution process was made by assuming a 10 90 mixture of low temperature lt and high temperature ht components for the primordial material and fe fe mg 0 11 for the whole mantle the composition of the core thus deduced together with compressibility data at high pressures is found to give reasonable values for the density deficit of the outer core if conversely we adopt the density reduction as input the composition of the outer core is estimated to be feh0 25c0 05o0 13s0 03 finally some implications of the present picture on other terrestrial planets are examined briefly

mars and earth comparison of cold climate features abstract on earth glacial and periglacial features are common in areas of cold climate on mars the temperature of the present day surface is appropriate for permafrost and the presence of water is suspected from data relating to the outgassing of the planet from remote sensing measurements over the polar caps and elsewhere on the martian surface and from recognition of fluvial morphological features such as channels these observations and the possibility that ice could be in equilibrium with the atmosphere in the high latitudes north and south of 40 latitude suggest that glacial and periglacial features should exist on the planet morphological studies based mainly on viking pictures indicate many features that can be attributed to the action of ice among these features are extensive talus aprons debris avalanches flows that resemble glaciers or rock glaciers ridges that look like moraines various types of patterned ground scalloped scarps and chaotically collapsed terrain that could be attributed to thermokarst processes and landforms that may reflect the interaction of volcanism and ice

melting of phase d in the lower mantle and implications for recycling and storage of h 2 o in the deep mantle we determined the melting phase relations and conditions of the dense hydrous magnesium silicate phase d nominally mgsi2o4 oh 2 on composition in mgo sio2 h2o msh mgo al2o3 sio2 h2o mash and feo mgo al2o3 sio2 h2o fmash and on a mixture of phase d olivine enstatite msh at 22 32 gpa and 1000 1800 c contrasting to previous studies we performed h2o undersaturated experiments bulk compositions were synthetic mixtures of brucite silica or brucite olivine enstatite on the silica rich side of the tie line perovskite h2o at 22 24 gpa the maximum thermal stability of phase d is between 1350 and 1400 c in msh and fmash but 1600 c at 24 gpa in the fe free al bearing bulk composition mash apparently addition of al2o3 increases the stability field of phase d by 200 c an effect that is counter balanced by addition of feo at 32 gpa the stability of phase d msh and fmash is between 1350 and 1400 c at 22 gpa phase d melts to a mg rich melt coexisting with mgsi ilmenite stishovite whereas at 24 32 gpa melt coexists with perovskite and stishovite even melts from bulk compositions in the silica rich part of the msh system molar bulk mg si 0 5 are magnesian rich mg si molar ratio of 2 5 and are distinct from aqueous fluids and hydrous melts at lower pressures the temperature stabilities determined in this study indicate that slabs that thermally relax when stagnating on top of the 660 km discontinuity or penetrating into the lower mantle will have their last dense hydrous magnesium silicate phase i e phase d melting and producing a magnesian and hydrous melt that will rise through the transition zone such a melt could be responsible for observed low velocity zones and may be neutrally buoyant at the 410 km discontinuity and will affect the structure and dynamics of the mantle

decomposition of phase d in the lower mantle and the fate of dense hydrous silicates in subducting slabs abstracthigh pressure high temperature quench type experiments were carried out on serpentine to pressures of 53 gpa andtemperatures between 800 1800oc x ray analyses show that recovered phase assemblages varied considerably for thedifferent high pressure and high temperature studies the dense hydrous magnesium silicate phases decompose sequentiallyas the pressure increases and appear to serve as reservoirs for h 2 o in the mantle eventually releasing it at the highestpressure superhydrous phase b is stable up to pressure equivalent to the boundary between the transition zone and lowermantle phase d decomposes at pressures of 44 gpa equivalent to about 1250 km depth this may de ne the lower depthlimit for the presence of dense hydrous magnesium silicates beyond this pressure only nominally anhydrous phases havebeen recovered in high pressure experiments this may indicate a lack of stoichiometric hydrogen bearing silicate phasesat higher pressure 1998 elsevier science b v all rights reserved keywords x ray diffraction analysis lower mantle serpentine high pressure

hydrous phases and water transport in the subducting slab arc volcanoes are typically located 90 180 km above the surface of downgoing slabs as shown by wadati benioff deep seismic foci gill 1981 tatsumi 1989 the intimate relationship between the dip angles of the subducting slab and the locations of volcanic arcs indicates that subduction zone magmatism is triggered by material input from the subducting slab tatsumi and eggins 1995 the slab derived components are thought to be aqueous fluids or h2o rich partial melts of subducted oceanic crust therefore knowledge of the stability of hydrous phases and the chemical and physical properties of aqueous fluids in downgoing slabs is essential to understand the material transport in subduction zones in this section i will review the stability of hydrous phases in downgoing peridotite basalt and sediment systems and the chemical and the wetting properties of aqueous fluids recent experimental studies indicate that 3 4 gpa equivalent to 90 120 km depth is a key pressure where 1 the chemical compositions of silicate components dissolved in aqueous fluids equilibrated with mantle minerals approach the composition of mantle peridotite itself stalder et al 2001 mibe et al 2002 kawamoto et al 2004 2 the dihedral angle between olivine and aqueous fluids starts becoming smaller than 60 watson et al 1990 mibe et al 1998 1999 and 3 the immisciblity gap between peridotitic melts and aqueous fluids disappears and consequently hydrous minerals liberate supercritical aqueous fluids mibe et al 2004a 2006 the similarity between these pressures and the depths of downgoing slab underneath volcanic fronts where the maximum numbers of volcanoes are formed 124 38 km gill 1981 or 112 19 km tatsumi 1986 suggests that subduction zone magmatism can be triggered by the input of supercritical fluids from the downgoing peridotite and basalt many hydrous crystalline phases

the origin and earliest state of the earth s hydrosphere the origin and earliest history of the earth s hydrosphere the inventory of excess volatiles defined by rubey in 1951 can be constrained within wide but useful limits by a consideration of empirical and theoretical evidence from astrophysics and geology models for the evolution of the solar system from the protoplanetary nebula and for the growth of the earth to its present dimensions suggest quite strongly that the hydrosphere came into being during accretion its format with h2o mostly in the oceans co2 mostly in sediments and a residual atmosphere dominated by n2 co2 and h2o was established at a very early date and has persisted without large destabilizing climatic excursions until the present day alternative accounts of early history in which the earth either loses a massive primordial atmosphere or acquires its secondary atmosphere by gradual degassing seem improbable on the basis of a series of circumstantial but cumulatively persuasive arguments the difficulty of dissipating a massive atmosphere of solar composition in reasonable times the likelihood that accretion was a highly energetic process and that it triggered early segregation of the core and the tendency of the planet to accumulate volatiles preferentially in the later stages of accretion are examples of arguments favoring an early origin for the hydrosphere several geological isotope systems which can be sampled today require early separation of the atmosphere and probably the hydrosphere as a whole these systems record radiogenic enrichment patterns in the noble gases and stable isotope fractionations which suggest an early origin of the biosphere certain geological indicators of atmospheric composition and the broadly equable character of the rock record are also consistent with a hydrosphere established in the earliest stages of history and having an initial neutral or weakly reduced composition the climatic stability of such a hydrosphere poses crucial questions especially since the early sun was less luminous we find that it is not paradoxical to have an early earth with surface temperature close to that of the present day if the major hydrospheric constituent is liquid water a near global ocean and a cloudy atmosphere provide thermal feedbacks which suffice to maintain climatic stability against the perils of the deep freeze and the runaway greenhouse large quanltities of atmospheric greenhouse gases are not required for climatic stability although co2 may well have been present in amounts larger than today s large expanses of dry land are however difficult to accommodate in the picture which we present but the evidence favors differentiation of the continents later in geological history than the early times which we consider localized glacier ice is permitted and perhaps likely and may provide a milieu favorable for chemical evolution

water transportation from the subducting slab into the mantle transition zone using a recently developed petrogenetic grid for morb h2o we propose a new model for the transportation of water from the subducting slab into the mantle transition zone depending on the geothermal gradient two contrasting water transportation mechanisms operate at depth in a subduction zone if the geothermal gradient is low lawsonite carries h2o into mantle depths of 300 km with further subduction down to the mantle transition depth approximately 400 km lawsonite is no longer stable and thereafter h2o is once migrated upward to the mantle wedge then again carried down to the transition zone due to the induced convection at this depth hydrous phase olivine is stable and plays a role as a huge water reservoir in contrast if the geothermal gradient is high the subducted slab may melt at 700 900 c at depths shallower than 80 km to form felsic melt into which water is dissolved in this case h2o cannot be transported into the mantle below 80 km between these two endmember mechanisms two intermediate types are present in the high pressure intermediate type the hydrous phase a plays an important role to carry water into the mantle transition zone water liberated by the lawsonite consuming continuous reaction moves upward to form hydrous phase a in the hanging wall which transports water into deeper mantle this is due to a unique character of the reaction because phase a can become stable through the hydration reaction of olivine in the case of low pressure intermediate type the presence of a dry mantle wedge below 100 km acts as a barrier to prevent h2o from entering into deeper mantle 2006 published by elsevier b v on behalf of international association for gondwana research

the role of volatiles in the transition zone phase relations in the system mgo sio2 with low volatile contents of h2o f2 and cl2 were experimentally investigated at 100 234 kbar pressures and 850 2050 c temperatures using a split sphere anvil apparatus ussa 2000 superphase b mg10si3o14 oh f 4 was observed at 160 234 kbar fluorous phase b mg12si4o19f2 at 178 kbar and hydrous phase f mg4si7o16 oh 4 also at 178 kbar at lower pressures the volatiles were present in phase a mg7si2o8 oh f 6 phase c mg 7 x si 2 x o 9 x oh f 4 and phase e mg 2 x si 1 x o 4 x y oh f 2y with the exception of the fluorous phase b all these phases can coexist with stishovite at pressures above 130 kbar in a purely hydrous system the dehydration temperatures of the assemblage superphase b stishovite increase from 1200 c at 160 kbar to 1400 c at 234 kbar dehydration produces beta phase mg2sio4 possibly containing up to 7 wt of structural h2o about 3 wt of h2o in beta phase expands the stability of the assemblage beta phase stishovite at the expense of ilmenite by 30 kbar in more complex compositions the volatile solidus is below 1350 c thus at the temperatures which are much lower than the expected mantle temperatures at the relevant depths consequently most of the mantle is in a partially molten state the volatile bearing phases can only be present in the colder subducted slabs but not in the rest of the transition zone 400 670 km hydrous beta phase and stishovite are the most likely constituents of the slabs incongruent melting of the hydrous beta phase coexisting with stishovite producing garnet and melt could be the cause of deep focus earthquakes evidence for a mineralogically and chemically stratified upper mantle is reviewed and its structure is discussed in the context of the present results

the shock wave equation of state of brucite mg oh 2 new equation of state eos data for brucite mg oh 2 shocked between 12 and 60 gpa are reported when combined with earlier data of simakov et al 1974 it is found that brucite eos data between 12 and 97 gpa can be fit with a single linear u s u p relationship u s 4 76 0 11 1 35 0 05 u p the third order birch murnaghan equation parameters are k os 51 4 gpa and k os 5 0 0 4 the lack of a u s u p discontinuity indicates that no phase transformation with a significant volume change occurs to at least 97 gpa however thermodynamic and theoretical hugoniot calculations suggest brucite may dehydrate with only a small volume change a lower bound for this dehydration pressure under shock conditions is inferred to be 26 gpa we report the first partial release states measured for this material the data are in quantitative agreement with earlier shock recovery experiments lange and ahrens 1984 volatilization upon release begins at pressures as low as 12 gpa much less than predicted by the shock entropy method calculated phase boundaries using the present eos data are consistent with experimental data and indicate that brucite is unlikely to be stable under lower mantle conditions however brucite data in conjunction with data for silicates and oxides can be used to infer the effect of h 2o on lower mantle properties at high pressure bulk sound velocities calculated for mgo and mg oh 2 are very similar indicating that the presence of hydrous assemblages in the lower mantle may not produce anomalous bulk seismic velocities comparison of densities in brucite and other high pressure phases under mantle conditions indicates that the water content of the lower mantle is between 0 and 3 wt

cirque infills in the khibiny mountains kola peninsula russia palaeoglaciological interpretations and modern analogues in east antarctica we report here on cirque infills mapped in the khibiny mountains kola peninsula russia cirque infills are morainic deposits located near the headwalls of valleys and cirques their location and shape often with concave margins towards the valley side indicate that they were deposited by ice flowing up valley into the mountains rather than by local glaciers we suggest that they formed during the last deglaciation when khibiny was a nunatak and fennoscandian ice sheet lobes extended into valleys and cirques of the massif the formation of cirque infills is probably more related to ice sheet dynamic factors occurring when the ice margin retreated from the cirques than to climate driven interruption in the ice marginal retreat glacial conditions similar to those prevalent when the khibiny cirque infills were formed occur today in antarctica where the ice sheets engulf nunatak ranges in heimefrontfjella antarctica the formation of supraglacial moraines at the head of cirques are linked to blue ice conditions indicating locally low accumulation rates a dry continental climate and sublimation dominated ablation we suggest that these antarctic moraines are modern analogues of cirque infills on the kola peninsula and possibly that the cirque infills may be used as palaeoenvironmental indicators copyright 2007 john wiley sons ltd

lower mantle water reservoir implied by the extreme stability of a hydrous aluminosilicate plumes are thought to transport water rich material from the deep mantle to earth s surface high pressure experiments identify a hydrous mineral phase that is stable under lower mantle conditions and could provide a source for this water

thermochemistry and phase equilibria of hydrous phases in the system mgo sio2 h2o implications for volatile transport to the mantle calorimetric phase equilibrium and in situ equation of state data for antigorite talc and dense hydrous magnesium silicate dhms phases have been obtained to construct a self consistent thermodynamic data set that ensures internal consistency well behaved extrapolation and physically reasonable values of h s v k k and for talc antigorite and hydrous phase a used in conjunction with temperature profiles of subducting oceanic lithosphere the calculated phase equilibria show that there is no barrier to subducting substantial amounts of water to depth of 400 600 km in colder slabs since the slab can remain in the stability field of hydrous phases throughout its descent once water is brought to these depths it can probably diffuse into hotter mantle regions via hydrous mg2sio4 or by other mechanisms indicating that the transition zone is unlikely to be dry

phase transitions of serpentine in the lower mantle abstract phase transformations in natural serpentine and chlorite have been studied at 25 50 gpa and 900 1280 c by in situ x ray diffraction measurements using the multianvil apparatus with sintered diamond anvils antigorite was found to transform to a phase assemblage including phase h at pressures above about 35 40 gpa corresponding to those in the upper part of the lower mantle the zero pressure bulk modulus k 0 of phase h was determined to be 160 gpa assuming its pressure derivative k 4 the thermal stability of phase h is significantly enhanced by a solid solution with a alooh component suggesting that aluminous phase h in cold slabs would deliver a certain amount of water into the deepest part of the lower mantle

the structural glaciology of kongsvegen svalbard and its role in landform genesis mapping of the structural glaciology of kongsvegen svalbard reveals evidence for four main deformational structures these are stratification longitudinal foliation thrusts and crevasse traces these structures are considered in terms of their contribution to debris entrainment transport and subsequent landform development stratification is associated with small amounts of supraglacial debris that has been folded with flow parallel axes longitudinal foliation in places incorporates basal glacial sediments along folds with flow parallel axes and thrusts transport basal debris to the glacier surface crevasse traces are not significant in terms of debris entrainment the entrainment of basal debris along longitudinal foliation is not a universally recognised process at kongsvegen this process is attributed to the development of a transposition foliation in combination with incorporation of debris rich basal ice or soft basal sediment in the fold complex mapping of the landforms in the proglacial area shows that debris incorporated along longitudinal foliation is released as foliation parallel ridges and that transverse ridges mark debris bearing thrusts the role of longitudinal foliation in landform development has never been documented in this manner although the preservation potential of such ridges may be limited recognition of foliation parallel ridges in the pleistocene landform record has important implications for the interpretation of the dynamics of former ire masses

coals of the brazil formation pennsylvanian in indiana observations of correlation inconsistencies and their implications the coals of the upper part of the mansfield brazil and the lower part of the staunton formations atokan and desmoinesian pennsylvanian in indiana illinois basin are characteristically thin and discontinuous as a result problems with correlation and identification of the seams have persisted for both researchers and industry these discrepancies affect coal exploration mine planning and subsequently coal fired utilities this study presents exploration and operational examples demonstrating some of the correlation problems associated with the coals of the brazil formation and the upper block and lower block in particular and the surrounding upper part of the mansfield formation and lower part of the staunton formations based on exploration boreholes mine scale observations and coal quality and petrographic data this study suggests that 1 the coal mapped as the upper block coal member of clay county may in fact be the same seam as the lower block coal member of daviess county and 2 the lower block coal of clay county is not present south of the switz city area of central greene county in

phase relations of peridotites under h2o saturated conditions and ability of subducting plates for transportation of h2o phase relations of peridotites under h2o saturated conditions up to 28 gpa and 2600 c have been clarified based on the high pressure experimental results in the mgo feo sio2 h2o mgo sio2 al2o3 h2o cao mgo al2o3 sio2 h2o and natural systems based on the phase assemblages deduced and the chemical compositions of the phases the maximum h2o contents for two bulk rock compositions lherzolite and harzburgite have been calculated using mass balance then the potential ability of subducting plates for transportation of h2o is discussed by simple models combining the phase relations and the thermal structures of subduction zones as a function of the age of subducting plate a 15 130 ma the subduction velocity u0 2 25 18 cm year and angle 30 and 60 and the mantle potential temperature tp 1300 and 1350 c the results confirm the importance of choke point a cusp around 6 2 gpa and 550 c at which the stability field of major hydrous phases is minimized in terms of temperature although the choke point is exceeded by the mg sursassite bearing assemblage that has the maximum h2o content of 0 4 0 7 wt around 5 7 gpa and 550 700 c if the geotherm of the coldest part across the subducting plate passes below the choke point maximum 4 6 wt h2o can subduct whereas h2o less than 0 4 0 7 wt can subduct above the choke point the critical conditions are clarified as follows if 30 and tp 1300 c a 15 ma with u0 9 cm year or a 30 ma with u0 2 25 cm year is the critical condition if 60 and tp 1300 c or 30 and tp 1350 c the critical conditions slightly shift to an older age or a greater velocity e g a 30 ma with u0 3 5 cm year the slab thermal parameter au0sin is useful to predict roughly the critical condition however within the younger plate the spatial extent of a cold region with major hydrous phases is thinner hence less h2o is subducted even with the same slab thermal parameter this indicates that the age of the plate and the subduction velocity act differently on the h2o transportation ability of subducting plates

effect of h2o on phase transformations of mantle silicates at high pressures and temperatures the effect of h2o on the high pressure phase transformations in a 1 1 mixture of forsterite and enstatite has been investigated on the basis of experimental data available in the mgo sio2 h2o system at pressures up to 280 kbar it has been found that the modified spinel phase of mg2sio4 does not occur at high pressure in this system where more than about 4 wt h2o is present in addition the spinel phase of mg2sio4 does not appear at its equilibrium transition boundary modified spinel spinel if more than about 3 wt h2o is present in the system thus if more than about 4 wt h2o is present in the chemical composition of downgoing slabs the so called 400 km seismic discontinuity in the normal mantle may not occur in the subduction zone at all

the high pressure stability of mg sursassite in a model hydrous peridotite a possible mechanism for the deep subduction of significant volumes of h2o the stability of the high pressure phase mg sursassite previously mgmgal pumpellyite in ultramafic compositions has been determined in experiments in the system mgo al2o3 sio2 h2o mash the breakdown of mg sursassite forsterite enstatite to pyrope vapour with increasing temperature was bracketed at 6 0 and 7 0 gpa below 6 0 gpa mg sursassite forsterite vapour reacts to chlorite enstatite this reaction provides a mechanism for transfer of water from chlorite to mg sursassite bearing assemblages at pressures of 7 0 gpa and above the assemblage mg sursassite phase a enstatite was found phase relations involving mg sursassite and phase a are considered for bulk compositions with a low water content the vapour absent reaction mg sursassite forsterite pyrope phase a enstatite determines the upper pressure stability of mg sursassite and provides a mechanism for the complete transfer of water from mg sursassite to phase a bearing assemblages mg sursassite plays an important role in peridotite compositions in the subducting slab because at temperatures below 700 c it can transfer water from hydrous phases such as antigorite and chlorite to high pressure stable phases such as phase a

kilometer thick ice accumulation and glaciation in the northern mid latitudes of mars evidence for crater filling events in the late amazonian at the phlegra montes article i nfo article history accepted 25 august 2009 available online 25 september 2009 amazonian non polar ice deposits on mars record periods and events when the climate differed substantially from that of today particularly evident are examples of ice rich deposits in the martian mid latitudes lobate debris aprons lineated valley fill and concentric crater fill uncertain however is the amount of ice remaining in these deposits today and the thickness of ice that might have existed when they formed here we use hrsc ctx and hirise imagery and mola topographic data to document an occurrence of concentric crater fill within which the past minimum volume of ice can be constrained an 8 km impact crater is superposed on the rim of a 32 km impact crater near the contact between the phlegra montes and the vastitas borealis formation in the northern mid latitudes of mars we find evidence for flow from the larger crater into the perched smaller crater that indicates an earlier period of significant ice accumulation and glaciation within this double crater lobate ridges observed outside of the perched younger crater suggest that ice filled and overtopped the crater rim providing minimum estimates of ice thickness and volume within the system glacial ice must have been at least 1000 m thick to overtop the rims of both craters and induce gravitational flow onto the surrounding plains with a minimum volume of ice of 750 km 3 this is the first volumetric measurement of this kind on mars for concentric crater fill craters and the thickness is comparable to that measured in a lineated valley fill glacial system along the dichotomy boundary at a similar latitude we also document late stage episodes of more localized glacial flow that include ridges on valley walls that we interpret as late stage glacial high stands and concentric crater fill ccf that characterizes most of the present day crater floor similar deposits in a crater 60 km to the northeast suggest that such episodes were at least regional in nature this sequence provides evidence for significant spin axis orbital parameter driven shifts in the late amazonian climate of mars and suggests that regional ice sheets may have existed in the mid latitudes of mars within the last several hundred million years

stability of dense hydrous magnesium silicate phases and water storage capacity in the transition zone and lower mantle abstract we evaluated the water storage capacity in the mantle based on the phase relations of silicate systems containing water we conducted high pressure and temperature synthesis experiments on some silicate systems such as the superhydrous phase b phase c and phase g phase d and f compositions in the mgo sio2 h2o system and the cmas pyrolite 2 wt h2o system up to the uppermost part of the lower mantle superhydrous phase b is stable at temperatures below 1200 c at 18 gpa and below 1300 c at 20 gpa the following reaction sequences were observed with increasing temperature from 1200 to 1600 c in the pressure range from 18 to 20 gpa superhydrous phase b phase b liquid wadsleyite periclase liquid anhydrous phase b periclase liquid phase g is stable at temperatures below 1000 c at 18 gpa below 1100 c at 20 22 gpa and below 1200 c at 25 gpa wadsleyite stishovite liquid are stable above 1000 c at 18 gpa ringwoodite or phase e stishovite liquid above 1100 c at 22 gpa ilmenite stishovite liquid above 1100 c at 23 5 gpa and perovskite stishovite liquid above 1200 c at 25 gpa superhydrous phase b is stable at 1200 c at 18 5 and 25 gpa in cmas pyrolite 2 wt h2o composition whereas it decomposes at around 1400 c at 25 gpa in the composition there may be a layered structure in the mantle in its water storage potential solubility of water per unit mass i e the upper and lower mantles have relatively small water storage potentials whereas the transition zone has a larger potential the water content in the transition zone might be large because the primordial water trapped in the lower mantle and the recycled water transported by the slab subduction might have been released upwards and stored in the transition zone during geological time

tropical to mid latitude snow and ice accumulation flow and glaciation on mars images from the mars express hrsc high resolution stereo camera of debris aprons at the base of massifs in eastern hellas reveal numerous concentrically ridged lobate and pitted features and related evidence of extremely ice rich glacier like viscous flow and sublimation together with new evidence for recent ice rich rock glaciers at the base of the olympus mons scarp superposed on larger late amazonian debris covered piedmont glaciers we interpret these deposits as evidence for geologically recent and recurring glacial activity in tropical and mid latitude regions of mars during periods of increased spin axis obliquity when polar ice was mobilized and redeposited in microenvironments at lower latitudes the data indicate that abundant residual ice probably remains in these deposits and that these records of geologically recent climate changes are accessible to future automated and human surface exploration

water in the terrestrial planets and the moon abstract models of impact induced dehydration and the magma ocean have recently appeared in literature if it is assumed that all of the terrestrial planets except mercury accreted through similar physical processes and from materials having similar compositions then according to these models water in venus earth and mars should have undergone similar processes of evolution during accretion a consequence of this could be that earth s hydrosphere is derived from water released from melts when the paleogeotherm dropped below the temperature of mantle solidus stripping the free h 2 o above the water line reaction forsterite enstatite water forsterite enstatite phase a from depths near 350 km the absence of a hydrosphere and or icesphere on venus and mars is likely due to their high internal temperature profiles which have probably never dropped below the respective solidi of these planets thus most of the free h 2 o above the water line of venus and mars is still trapped inside mantle melts the partial melting zone mars cools probably much faster than venus thus some of the h 2 o evolved from the magma ocean above the partial melting zone still remains on the martian surface whereas all was lost from venus the fact that plate tectonics is not apparent on the surfaces of venus and mars is probably also due to the presence of a partial melting zone inside these planets and the co 2 dominant atmospheres of today s venus and mars may be evidence that a large scale hydrosphere never existed or not for long on these planets all h 2 o was probably lost from the moon if complete melting and solidification occured early in lunar history the impact induced magma ocean probably contained at least 0 35 wt h 2 o but is more likely to be in the vicinity of 0 5 wt for both earth and venus

stability of phase a in antigorite serpentine composition determined by in situ x ray pressure observations abstract here we precisely determined the low pressure stability limit of phase a in the mg end member antigorite bulk composition defined as the reaction forsterite water phase a enstatite water line or water storage line in a multi anvil apparatus pressures were determined by in situ synchrotron x ray diffraction measurements using nacl as an internal pressure standard results demonstrate that the water line is located at 800 c and 8 5 gpa and at 550 c and 5 1 gpa with a clapeyron slope of 13 6 mpa c we also examined the conditions for the formation of phase a by the decomposition of antigorite on the basis of the phase relations in the systems mgo sio 2 h 2 o msh and mgo al 2 o 3 sio 2 h 2 o mash a descending slab peridotite retains water in phase a beyond the stability of antigorite only when temperature in the slab is lower than 550 or 660 c at 5 1 gpa corresponding to 160 km depth in the system msh or mash respectively the double seismic planes observed within the slabs may be caused by the dehydration reaction of antigorite or chlorite their merging depths which could represent the high pressure stability limit of antigorite or chlorite are 160 km or deeper beneath northeast japan aleutian kamchatka and kuril water included in hydrous slab peridotite is transported into the transition zone and deeper mantle in these areas but recycled to the surface in other subduction zones

a sedimentological and isotopic study of the origin of supraglacial debris bands kongsfjorden svalbard hubbard b glasser n f hambrey m j etienne j l 2004 a sedimentological and isotopic study of the origin of supraglacial debris bands kongsfjorden svalbard journal of glaciology 50 169 157 170 rae2008

constraints on martian lobate debris apron evolution and rheology from numerical modeling of ice flow radar observations in the deuteronilus mensae region by mars reconnaissance orbiter have constrained the thickness and dust concentration found within mid latitude ice deposits providing an opportunity to more accurately estimate the rheology of ice responsible for the formation of lobate debris aprons based on their apparent age of 100 myr we developed a numerical model simulating ice flow under martian conditions using results from ice deformation experiments theory of ice grain growth based on terrestrial ice cores and observational constraints from radar profiles and laser altimetry by varying the ice grain size the ice temperature the subsurface slope and the initial ice volume we determine the combination of parameters that best reproduce the observed lda lengths and thicknesses over a period of time comparable to the apparent ages of lda surfaces 90 300 myr we find that an ice temperature of 205 k an ice grain size of 5 mm and a flat subsurface slope give reasonable ages for many ldas in the northern mid latitudes of mars assuming that the ice grain size is limited by the grain boundary pinning effect of incorporated dust these results limit the dust volume concentration to less than 4 however assuming all ldas were emplaced by a single event we find that there is no single combination of grain size temperature and subsurface slope which can give realistic ages for all ldas suggesting that some or all of these variables are spatially heterogeneous based on our model we conclude that the majority of northern mid latitude ldas are composed of clean 64 vol coarse p1 mm grained ice but regional differences in either the amount of dust mixed in with the ice or in the presence of a basal slope below the lda ice must be invoked alternatively the ice temperature and or timing of ice deposition may vary significantly between different mid latitude regions either eventuality can be tested with future observations

the earth as a planet paradigms and paradoxes the independent growth of the various branches of the earth sciences in the past two decades has led to a divergence of geophysical geochemical geological and planetological models for the composition and evolution of a terrestrial planet evidence for differentiation and volcanism on small planets and a magma ocean on the moon contrasts with hypotheses for a mostly primitive still undifferentiated and homogeneous terrestrial mantle in comparison with the moon the earth has an extraordinarily thin crust the geoid which should reflect convection in the mantle is apparently unrelated to the current distribution of continents and oceanic ridges if the earth is deformable the whole mantle should wander relative to the axis of rotation but the implications of this are seldom discussed the proposal of a mantle rich in olivine violates expectations based on evidence from extraterrestrial sources these and other paradoxes force a reexamination of some long held assumptions

water storage in the mantle the origins of the oceans and earth s volatile atmosphere are major unsolved problems in earth sciences the recent study by finger et al of the crystal chemistry of a water bearing mineral phase cryptically named phase b and grown under conditions equivalent to a depth in the earth of 360 km dramatically demonstrates that several times the earth s visible water budget could be stored in the mantle

block coals from indiana inferences on changing depositional environment significant differences in coal petrography palynology and coal quality were found between the lower block and upper block coal members brazil formation pennsylvanian in daviess county indiana the lower block coal member ranges in thickness from 51 to 74 cm and the upper block coal member ranges from 20 to 65 cm average sulfur content and ash yield of the lower block coal 0 98 7 65 are lower than in the upper block coal megascopically the coals show distinct differences the lower block is a banded coal with numerous thin fusain horizons and a thin clay parting in the lower third of the seam the upper block coal has a dulling upward trend with a bright clarain found at the base that grades into a clarain and then into a durain in the upper portion of the seam vitrinite content of the lower block coal ranges from 63 to 78 with the highest vitrinite content found in the middle portion of the seam in the upper block coal vitrinite content ranges from 40 to 83 with the highest values found in the lower part of the seam ash yield is higher in the upper part of the upper block coal reaching up to 40 the lower block coal is dominated by lycopod trees and tree ferns the upper block coal shows marked differences in spore assemblages between lower and upper parts of the seam the lower half is dominated by large lycopod trees and tree ferns similar to the lower block coal the upper half is dominated by small lycopods mainly densosporites and radiizonates these differences between the lower block and upper block coal members are significant correlation tools applicable to mining exploration and chronostratigraphy

stability fields of mg pumpellyite composition at high pressures and temperatures mg pumpellyite was observed to break down to the assemblage pyrope kyanite coesite h2o in the pressure range 60 80 kbar to the assemblage pyrope kyanite stishovite h2o in the range 100 140 kbar and to the asemblage pyrope corundum stishovite h2o in the range 160 220 kbar at 800 1000 c in a diamond anvil cell coupled with laser heating mg pumpellyite may exist in the coldest part of a subducting lithosphere down to a depth of about 300 km

feo and h2o and the homogeneous accretion of the earth abstract we present new shock devolatilization recovery data for brucite mg oh 2 shocked to 13 and 23 gpa these data combined with previous data for serpentine mg3si2o5 oh 4 are used to constrain the minimum size terrestrial planet for which planetesimal infall will result in an impact generated water atmosphere assuming a chondritic abundance of minerals including 3 6 by mass water in hydrous phyllosilicates we carried out model calculations simulating the interaction of metallic iron with impact released free water on the surface of the accreting earth we assume that the reaction of water with iron in the presence of enstatite is the prime source of the terrestrial feo component of silicates and oxides lower and upper bounds on the terrestrial feo budget are based on mantle feo content and possible incorporation of feo in the outer core we demonstrate that the iron water reaction would result in the absence of atmospheric hydrospheric water if homogeneous accretion is assumed in order to obtain1025g of atmospheric water by the end of accretion slightly heterogeneous accretion with initially 36 by mass iron planetesimals as compared to a homogeneous value of 34 is required such models yield final feo budgets which either require a higher feo content of the mantle 17 wt or oxygen as a light element in the outer core of the earth

effects of h2o on the phase behaviour of the forsterite enstatite system at high pressures and temperatures and implications for the earth abstract in addition to many of the naturally occurring hydrous minerals known in the system mgo sio2 h2o various dense hydrous magnesium silicates 10 a phase phases a b c and d have been synthesized by high pressure and high temperature experiments in the past two decades in conjunction with these high pressure hydrous phases the effects of h2o on the observed phase transformations in the forsterite mg2sio4 enstatite mgsio3 system at high pressures and high temperatures are investigated on the basis of both experimental data and theory for forsterite the modified spinel phase may exist up to 7 1 wt h2o along with enstatite phase a up to 9 9 wt h2o along with stishovite phase a and up to only 3 2 wt h2o along with stishovite phase b the spinel phase of mg2sio4 is no longer stable when more than 3 2 wt h2o is present although both stishovite and the ilmenite type mgsio3 do not occur in dry mg2sio4 at high pressures a small amount of h2o would yield assemblages containing stishovite and the ilmenite phase in mg2sio4 at high pressures the post spinel phase assemblage perovskite periclase may be stable along with phase d up to 11 wt h2o in the case of enstatite except for the assemblage modified spinel stishovite which exists along with phase a up to 7 1 wt h2o and for the perovskite type mgsio3 along with periclase and phase d which exists up to 15 wt h 2 o all the high pressure phase transformations observed in dry mgsio3 may not occur at high pressures if 2 3 wt h2o is present based on experimental observations the various high pressure hydrous phases are stable from as low as 40 kbar to more than 280 kbar at various temperatures thus there is no lack of storage phases for h2o in the deeper interior of the earth s mantle according to the impact induced dehydration model advanced recently by shock wave experiments it is estimated that the earth s interior contains probably at least more than five times its present water contents in the near surface geochemical reservoirs hydrosphere crust so long as both forsterite olivine and h2o coexist in the upper mantle even in trace amounts there must exist a water line which is defined by the reaction 5mg 2 sio 4 3h 2 o 3mgsio 3 mg 7 si 2 o 14 h 6 forsterite water enstatite phase a in the upper mantle the equilibrium boundary of the water line has been in fact determined in two different phase assemblages by experiments but was not noticed if the earth s surface was covered by large scale melts during and shortly after its accretion h2o would be stored in phases a b below the water line and would liberate as water above the water line during freezing today s oceans were most likely derived from water released in the mantle when the palaeogeotherm dropped below the solidus of mantle materials stripping the free water above the water line from depths near 350 km thus the oceans were formed rapidly and early in the earth s history and slow degassing is still going on today the low velocity zone observed in today s mantle is interpreted as a region containing free water between the water line and the stability field of amphiboles in the suboceanic mantle and between the water line and the stability field of phlogopite in the subcontinental mantle in other words the low velocity zone is the free water zone and the water line is the base of the low velocity zone in the earth s mantle

sulfur variability and petrology of the lower block coal member pennsylvanian in southwest indiana abstract the lower block coal member pennsylvanian atokan westphalian c is an economic low to medium sulfur low ash coal resource in the illinois basin sulfur content is generally low averaging 1 0 in the study area but varies over short distances higher sulfur areas occur as isolated pods and epigenetic pyrite increases significantly in the upper third of the selected columns in higher sulfur areas sulfur variations cannot be predicted by typical geologic characteristics such as roof lithology seam thickness or seam elevation petrographic analysis shows that pyrite is generally associated with brighter microlithotypes except in higher sulfur areas where infilling pyrite forms are associated with inertite higher sulfur areas reflect the water chemistry of the paleomire during and shortly after peat accumulation locally abundant pyrofusinite provided additional pore space for pyrite precipitation

stability of hydrous phases in the transition zone and the upper most part of the lower mantle phase relation for mg2sio4 20 4 wt h2o composition was studied in the pressure range from 11 gpa to 22 5 gpa the sequence of the phase transitions in the temperature range from 800 c to 1000 c with increasing pressure was as follows forsterite water phase a clinoenstatite water phase e water superhydrous phase b phase f water brucite phase f water coexistence of brucite and phase f was observed at pressures above 20 gpa these phases are stable at least up to 22 5 gpa and around 1000 c and are the candidates for the hydrous phase in a cold slab descending into the base of the transition zone and the uppermost part of the lower mantle

mid mantle anisotropy in subduction zones and deep water transport the earth s transition zone has until recently been assumed to be seismically isotropic increasingly however evidence suggests that ordering of material over seismic wavelengths occurs there but it is unclear what causes this we use the method of source side shear wave splitting to examine the anisotropy surrounding earthquakes deeper than 200 km in slabs around the globe we find significant amounts of splitting 2 4 s confirming that the transition zone is anisotropic here however there is no decrease in the amount of splitting with depth as would be the case for a metastable tongue of olivine which thins with depth suggesting this is not the cause the amount of splitting does not appear to be consistent with processes in the ambient mantle such as lattice preferred orientation development in wadsleyite ringwoodite or mgsio3 perovskite we invert for the orientation of several mechanisms subject to uncertainties in mineralogy and deformation and the best fit is given by updip flattening in a style of anisotropy common to hydrous phases and layered inclusions we suggest that highly anisotropic hydrous phases or hydrated layering is a likely cause of anisotropy within the slab implying significant water transport from the surface down to at least 660 km depth

the evolution of surface flow stripes and stratigraphic folds within kamb ice stream why don t they match flow stripes seen in satellite imagery of ice streams and ice shelves are caused by surface undulations with kilometer scale spacing and meter scale relief and generally indicate current or recent fast ice flow on a similar scale folding of internal ice stratigraphy depicted in cross flow ice penetrating radar profiles is also a common occurrence in ice streams suggesting a possible relationship between the two sets of features we have traced surface flow stripes in radarsat and modis imagery on kamb ice stream west antarctica from the onset of streaming flow into the near stagnant trunk we compare the morphology and evolution of the surface flow stripes to the folds seen in the internal stratigraphy in cross ice stream radar profiles we find essentially no correspondence in the observed locations or spacings between the radar internal layer folds at depths greater than 100 m and the flow stripes on the surface the gap in the radar data and the surface mappings in the top 100 m of firn prevents a precise depiction of how the flow stripes and fold patterns at depth diverge we explore hypotheses about how flow stripes and internal stratigraphic folds can originate and evolve differently as ice flows downstream we suggest that flow stripes are subject to surface processes that can modify their morphology independently of the internal stratigraphy leading to changes in the pattern of flow stripes relative to the internal layers below

possible climate related signals in high resolution topography of lobate debris aprons in tempe terra mars lobate debris aprons are common features in the midlatitudes of mars that are assumed to be the result of the flow of ice rich material we produce high resolution digital elevation models of two of these features in the tempe terra region of mars using hirise stereo images we identify two main topographic features of different wavelength using a power spectrum analysis approach short wavelength features between approximately 10 and 20 m in length correspond to a polygonal surface texture present throughout our study area long wavelength features between approximately 700 and 1800 m in length correspond to broad ridges that are up to 20 m in amplitude we interpret both topographic signals to be the likely result of climate change affecting the debris contribution and or the flow regime of the lobate debris aprons the apparent surface age of about 300 ma could be evidence of an astronomical forcing mechanism recorded in these lobate debris aprons at this time in mars history citation grindrod p m and s a fawcett 2011 possible climate related signals in high resolution topography of lobate debris aprons in tempe terra mars geophys res lett 38 l19201 doi 10 1029 2011gl049295

vertical variations of mercury in pennsylvanian coal beds from indiana abstract twenty three in situ coal sections were sampled in indiana mines to investigate mercury hg concentrations with a special reference to in seam vertical variations in hg distribution in addition to raw coal corresponding float fractions were also analyzed to evaluate the effectiveness of hg reduction during conventional pre combustion washing hg content in indiana coals in the locations studied averages 0 11 mg kg which after recalculation into equal energy units corresponds to 9 2 lb hg 1012 btu 39 5 kg hg 1010 mj hg content is reduced after washing to 0 07 mg kg on average corresponding to an equal energy hg loading of 5 2 lb hg 1012 btu 22 3 kg hg 1010 mj a large portion of hg appears to be associated with pyrite as in the springfield coal member of the petersburg formation pennsylvanian in the samples from the danville coal member of the dugger formation pennsylvanian hg is associated to a larger extent with organic matter large differences in hg content may exist between different portions of a coal bed in a single location indicating that very careful complete sampling is necessary to get representative hg concentration data

late amazonian glaciation at the dichotomy boundary on mars evidence for glacial thickness maxima and multiple glacial phases lineated valley fill lvf in fretted valleys at the dichotomy boundary has been interpreted as glacial in origin unknown are 1 the original thickness of the glacier ice 2 the amount of ice surface lowering through sublimation and retreat to its presently observed level and 3 whether there were multiple periods of glaciation we address these questions through analysis of an lvf glacial system the elevation difference between the upper limit of a previous highstand and the current surface of the lvf at the study site is 920 m we interpret this difference to be the minimum amount of ice surface lowering of the glacier system consistent with a general lowering of the ice surface are multiple moraines and or trimlines and changes in lvf flow patterns as the ice retreated and decreased in thickness the superposition of several lobes onto the current surface of the lvf indicates that a phase of alpine glaciation followed the lowering of the valley glacial system these data suggest that the late amazonian glaciation that produced lvf in this region involved significantly larger amounts of ice than previously thought and that subsequent alpine glaciation followed

comment on a new hydrous silicate a water reservoir in the upper part of the lower mantle by eiji ohtani hiroki mizobata yasuhiro kudoh toshiro nagase haruo arashi hisayoshi yurimoto and isoji miyagi on the basis of the available powder x ray diffraction data chemical composition raman spectrum and synthesis p t conditions it is concluded that the so called new phase claimed by ohtani et al 1997 is in reality the phase d reported earlier by liu 1987 irifune et al 1996 and kuroda and irifune 1997 phase f first reported by kanzaki 1991 is also probably in reality the phase d the powder x ray diffraction pattern of the so called phase f studied by kudoh et al 1995 bears no resemblance to that reported by kanzaki 1991 suggesting a totally different material was employed in the study of kudoh et al 1995

reply to comment on a new hydrous silicate a water reservoir in the upper part of the lower mantle by eiji ohtani hiroki mizobata yasuhiro kudoh toshiro nagase haruo arashi hisayoshi yurimoto and isoji miyagi phase g reported by ohtani et al 1997 and kudoh et al 1997a is identical with the new phase d reported by kuroda and irifune 1998 and yang et al 1997 however there is ambiguity on existence of phase d defined by liu 1987 there are following possibilities on existence of liu s phase d 1 the product was a mixture of phase g and the other contaminant phases 2 it realy exists stably in different pressure and temperature conditions from those studied by our works or 3 the phase is a metastable phase formed due to a short run duration and or no sealing of water in the diamond anvil cell therefore it is not appropriate to use the name phase d for the dense hydrous magnesium silicate phase g reported by us ohtani et al 1997

geomorphological characterisation and interpretation of a mid latitude glacier like form hellas planitia mars we describe and interpret the surface terrain types associated with a widely reported 4 km long midlatitude martian viscous flow feature vff the feature is located in the southern hemisphere on the poleward facing rim of a 60 km diameter crater in eastern hellas planitia high resolution imaging science experiment hirise images analysed in both 2d and 3d reveal that the upper margin of the feature is bounded by steep 30 headwalls typically some tens of metres high that are formed from unconsolidated material and characterised by a series of slope parallel linear incisions below these incised headwalls the feature flows at a general angle of 10 from a broad upper basin to a confined lower tongue that is bounded by a nested sequence of elongate raised ridges these characteristics are typical of several vffs in the region and are strikingly similar to moraine bounded valley glaciers on earth and we sub classify this feature as a glacier like form glf 1 the glf comprises five distinctive surface terrain types that contrast sharply with surface characteristics outside its bounding moraines four of these terrains scaly terrain polygonized terrain linear terrain and mound and tail terrain are located within the glf s innermost bounding moraine while the fifth rectilinear ridge terrain is located between its frontal moraines these terrains are mapped characterised and associated with possible mechanisms of formation to draw inferences about the glf s glaciology and glacial history this analysis suggests that the glf reached its maximal extent in the geologically recent past and that it may have been partially wetbased at that time subsequent to this phase the glf experienced an extended period of general recession that has been punctuated by several episodes of still stand or advance currently the glf s basin appears to be composed of a lower zone that is dominated by an exposed former glacier bed and an upper zone that may still contain a now degraded and dust mantled viscous mass similar to many partially glacierized basins on earth

rheology of the lithosphere selected topics we review recent results concerning the rheology of the lithosphere with special attention to the following topics 1 the flexure of the oceanic lithosphere 2 deformation of the continental lithosphere resulting from vertical surface loads and forces applied at plate margins 3 the rheological stratification of the continents 4 strain localization and shear zone development and 5 strain induced crystallographic preferred orientations and anisotropies in body wave velocities we conclude with a section citing the 1983 1986 rock mechanics literature by category

raman spectra of phase e at various pressures and temperatures with geophysical implications abstract variations in raman spectra of phase e were investigated up to 340 kbar at room temperature and in the range 83 870 k at atmospheric pressure phase e appears to remain intact up to at least 870 k however the oh raman band of phase e was not observable at temperatures above 473 k during heating and it was not detected in the recovered sample the temperature variation in raman frequencies of phase e also showed abnormal behavior above 473 k thus it is suggested that phase e dehydrated and converted to an imperfect forsterite above 473 k only the two most intense raman bands of phase e were reliably measured in the high pressure experiments with the exception of the oh raman band the raman frequencies of phase e increase with increasing pressure but decreased with increasing temperature the frequency of the oh raman band increases with increasing temperature which parallels that observed in both phase a and the hydrous phase the temperature dependency was observed to be linear below 500 k and the pressure dependency to be non linear within the experimental uncertainties and the range investigated it appears that phase e may be regarded as the hydrous form of forsterite and it is further suggested that phase e and the hydrous phase may be competitive hydrous phases in the upper mantle and transition zone

intra crater glacial processes in central utopia planitia mars abstract we describe and interpret a series of previously unidentified glacial like lobes 34 43 n 107 125 e that were discovered as part of a survey of large d 5 km impact craters in utopia planitia one of the great northern plains of mars the lobes have characteristics that are consistent with a glacial origin evidence includes curvilinearity of form lineations and ridges and surface textures that are thought to form by the sublimation of near surface volatiles the lobes display morphologies that range from wedge shaped to near circular to elongate the flow directions are towards the northern walls in the case of craters with large single lobes and in all directions in the case of the largest d 30 km craters concentric crater fill is also interspersed within craters of our study region with such craters having much higher filling rates than those with flow lobes we suggest that the impact crater population in south west utopia planitia demonstrates a spectrum of glacial modifications from low levels of filling in the case of craters with elongate lobes at one extreme to concentric crater fill in highly filled craters at the other

the structure of a super aluminous version of the dense hydrous magnesium silicate phase d the dense hydrous magnesium silicate phase d which has the ideal formula mgsi2h2o6 may be an important link in a chain of hydrous phases that carry h2o in the ultramafic portions of subducting lithosphere into the earth s lower mantle we have synthesized a new al rich form of phase d containing up to 50 wt al2o3 using a multi anvil device at 1300 c and 25 gpa the phase with the formula mg0 2fe0 15al1 8h1 8sio6 was initially produced in a bulk composition designed to synthesize al and fe rich magnesium silicate perovskite with a composition similar to that produced in experiments on mid ocean ridge basalt bulk compositions at lower mantle conditions further experiments using a starting mixture based on the composition of this al rich phase resulted in the synthesis of 60 70 m long single crystals at similar conditions the recovered crystals were slightly richer in h2o mg0 2fe0 12al1 5si0 92h3 1o6 and their unit cell parameters were similar to those of mgsi2h2o6 phase d a refinement of the crystal structure was carried out in the p 31 m space group and revealed a more disordered cation distribution than magnesium silicate phase d all cation oxygen distances are similar suggesting a high degree of si al disorder although the stability field of this new variant of phase d is yet to be determined this phase may be an important host for h2o within portions of subducted oceanic crust in the lower mantle

a millennium of variable ice flow recorded by the ross ice shelf antarctica an enhanced composite advanced very high resolution radiometer avhrr image is used to map flow stripes and rifts across the ross ice shelf antarctica the patterns of these flow related features reveal a history of discharge variations from the ice streams feeding the eastern part of the shelf the most profound variations are visible in the track of rifts downstream of crary ice rise flow stripe bends to the west of this ice rise and adjacent to steershead ice rise and changes in the northern margin of ice stream b the track of rifts downstream of crary ice rise indicates that the ice rise has existed for at least 700 years the character of this track changes about 350 km downstream indicating a rearrangement of flow patterns about 550 years ago the large bulge in the flow stripes to the west of crary ice rise is shown in detail with bent flow stripes extending for several hundred kilometers along flow this feature formed from the south possibly due to a change in the discharge of ice stream a the avhrr image documents a complex history associated with the shutdown of ice stream c with changes in the margins of ice stream c and the northern margin of ice stream b and the grounding of steershead ice rise with an associated bending and truncation of flow stripes landsat imagery shows a region that appears to be actively extending just downstream of the ice rise as the shelf continues to respond to recent changes in ice stream discharge we present a four stage flow history which accounts for the features preserved in the ice shelf

comparison of near coincident crustal refraction and extended vibroseis reflection data peace river region canada a 10 km long uncorrelated vibroseis data set was processed to test the feasibility of using industry reflection data for deep crustal imaging in the peace river region and elsewhere in the western canada sedimentary basin these results were compared with a crustal refraction interpretation of a line 10 km to the north the vibroseis data were extended from a conventional 3 s to 14 s two way travel time using the self truncating sweep method the reflection section contains a prominent eastward dipping event at 9 4 s 29 km depth which corresponds to the zero offset two way travel time of an intracrustal boundary in the refraction model this may represent the riel discontinuity imaged at similar depths in southern alberta a series of near vertical incidence reflections over 1 1 5 s terminating at 13 s corresponds well with the refraction moho at 12 8 s 41 km depth this suggests that locally the crust mantle boundary is a complex possibly layered transition zone of 3 5 km thickness

stability of hydrous magnesium silicates in the mantle transition zone phase relations in the mg oh 2 sio2 system have been studied up to 18 gpa a new hydrous phase phase e mg2 3si1 3h2 4o6 was encountered at 13 17 gpa and 1000 c phase f mg1 2si1 8h2 4o6 another new hydrous phase was observed at 15 5 gpa and 800 c the stability field of phase a was also briefly studied these new hydrous phases might be stabilized in the mantle transition zone especially in subducting slabs at those depths

application of palynology and petrography in the correlation of the pennsylvanian brazil and staunton formation coals in the eastern part of the illinois basin abstract the coals of the brazil and the lower part of the staunton formations atokan and early desmoinesian pennsylvanian in indiana illinois basin are typically thin and discontinuous as a result both researchers and the industry have experienced problems with coal bed identification and correlation the discrepancies in coal nomenclature and frequent miscorrelations affect coal exploration mine planning and communication between mines and customers our previous study based on exploration boreholes mine scale observations and coal quality and petrographic data from daviess greene and clay counties indiana suggested that the coal mapped as the upper block coal member of clay county might be the same seam as the lower block coal member of daviess county this study is an extension of the previous research conducted farther south to pike warrick and spencer counties indiana in the southern part of indiana correlation of these late atokan and early desmoinesian coal beds is even more difficult because of the absence of well defined marker horizons and limited mining and subsurface well data although palynological and coal petrography data generally correspond these data alone cannot resolve the correlation of the coal beds in this southern region with the coals of clay or greene counties and they must be supplemented with the analysis of associated limestones the ability to accurately identify the perth limestone member which occurs close to the buffaloville coal member of the brazil formation and the holland limestone member which occurs higher up in the staunton formation will help to distinguish between brazil and staunton formation coals

geochemistry of coals from the elk valley coalfield british columbia canada abstract the elk valley coalfield of british columbia is one of the major coal producing areas in canada the coals are of cretaceous and jurassic cretaceous age and range in rank from high volatile to low volatile bituminous romax 0 8 1 6 coal seams from outcrops and active mines in this coalfield were analysed for rank and maceral composition using reflected light microscopy for geochemistry using aas inaa and icpes and also by proximate and ultimate analyses the elk valley coal seams contain low average concentrations of hazardous elements such as as mo pb and se however there are seams that contain relatively high concentrations of some of these elements such as 8 mg kg and 108 mg kg of arsenic when the geochemistry of coal seams is compared within the different parts of the coalfield the elemental composition amongst the seams from various sections located in the central area of the coalfield is similar coal seams in the northern area of the coalfield have different geochemistry than coal seams in other areas of the coalfield seams in the northern area have much higher as br cr cu fe k and na content but contain less ca

petrogenetic grid in the system mgo sio2 h2o up to 30 gpa 1600 c applications to hydrous peridotite subducting into the earth s deep interior 1 a semiquantitative petrogenetic grid in the system mgo sio2 h2o up to 30 gpa and 1600 c was constructed using schreinemakers analysis on previous experimental data the grid includes stability relations of hydrous wadsleyite hydrous ringwoodite and dense hydrous magnesium silicates dhmss phase a phase d phase e and superhydrous phase b a sequence of chemical reactions among these hydrous phases was clarified in the mantle transition zone 410 660 km depth hydrous wadsleyite and hydrous ringwoodite are stable even at a standard mantle temperature of 1600 c whereas in the other depths nominal hydrous phases including dhmss are stable below 1400 c newly found phase transitions in hydrous wadsleyite and hydrous ringwoodite are multiphase and multireaction because their compositions are on neither mgo sio2 nor mg2sio4 h2o tie lines different from single transition in the dry mg2sio4 system the grid indicates that water in the subducting slab peridotite would be transported to the bottom of the upper mantle by several dhmss and hydrous polymorphs of olivine via solid solid reactions after antigorite decomposition finally dhmss would dehydrate to liberate free water at the upper mantle lower mantle boundary layer or deeper level we also examined a relation between the predicted depth distributions of dehydration reactions in slab peridotite along several possible pressure temperature paths and the mode of seismic frequency in each subduction zone the result suggests a possible origin of intermediate to deep seismicity by the dehydration of hydrous phases in the subducting slab

predicted elastic properties of the hydrous d phase at mantle pressures implications for the anisotropy of subducted slabs near 670 km discontinuity and in the lower mantle the dense hydrous magnesium silicate called the d phase is the most likely candidate to recycle hydrogen into the lower mantle in subduction zones as seismology represents the preferred method to detect this mineral in subduction zones the single crystal elastic tensor has been calculated using first principle methods a triple cell p3 m1 was used to account for an ordered ideal composition of the d phase to lower mantle pressures the elastic tensor of the mineral at ambient conditions is predicted to be c11 387 7 c33 287 7 c44 100 4 c12 108 0 c13 51 1 c14 14 6 in gpa with bulk modulus at zero pressure ko 163 gpa and a statistical error of about 4 0 gpa for all constants the pressure derivatives of the elastic constants have been determined to pressure of 80 gpa our tensor correctly predicts the published experimental measurements of linear compressibility along the a and c axes the logarithmic pressure derivative of the c a axial ratio and bulk modulus at zero pressure it contradicts the experimentally measured elastic tensor reported by liu l g okamoto k yang y j chen c c lin c c 2004 elasticity of single crystal phase d a dense hydrous magnesium silicate by brillouin spectroscopy solid state commun 132 517 520 which fails to reproduce the experimental compressibility data using the elastic constants and density predicted to 85 gpa the seismic anisotropy of p and s waves has been calculated as a function of pressure the single crystal has high p wave velocities and shear wave splitting in the basal plane below 20 gpa at high pressures the maximum p wave velocities have threefold symmetry normal to a axes in the basal plane whereas the maximum shear wave splitting is parallel to a axes with twofold symmetry the d phase has high vp and vs anisotropy at ambient pressure 17 6 for vp and 19 9 for vs the vp anisotropy decreases with increasing pressure to about 30 gpa while it remains constant at 8 from 30 to 85 gpa the vs anisotropy decreases to 17 at 20 gpa and then increases to 22 at 85 gpa the isotropic velocity ratios of s to p rs p bulk sound to s r s and density to s r s are calculated as a function of pressure the rs p shows very little variation with pressure with low value of 0 6 whereas both r s and r s increase with pressure to peak values of 2 8 and 2 0 respectively at about 60 gpa the presence of the d phase in subducted horizontal stagnant plates in the circum pacific could contribute to a number of seismic observations such as the observed velocity heterogeneity at depths between 500 and 1000 km and the fast s waves travelling horizontally with horizontal polarization in this depth range further the lower density of the d phase compared with

northern mid latitude glaciation in the late amazonian period of mars criteria for the recognition of debris covered glacier and valley glacier landsystem deposits lobate debris aprons lda and lineated valley fill lvf have been known to characterize the mid latitude regions of mars since documented by viking their flow like character suggested that deposition of ice in talus pile pore space caused lubrication and flow during an earlier climatic regime a number of factors have remained uncertain however including the detailed structure and texture of lda lvf the relationships between them their direction of flow the origin and abundance of the lubricating agent and their exact mode of origin e g ice assisted rock creep ice rich landslides rock glaciers debris covered glaciers we use new high resolution stereo camera hrsc image and topography data in conjunction with a range of other post viking data sets and new insights provided by cold based terrestrial glacial analogs to assess the characteristics of lda lvf in the northern mid latitudes of mars we find evidence that the characteristics and flow patterns of the lda and lvf are most consistent with late amazonian debris covered glacial valley landsystems the broad distribution and integrated characteristics of the lda lvf systems suggest that earlier in the amazonian climatic conditions were such that significant snow and ice accumulated on mid latitude plateaus and in valleys producing integrated glacial landsystems the remnants of which are preserved today beneath residual sublimation till derived from adjacent valley walls atmospheric general circulation models suggest that these climatic conditions occurred when mars was at a spin axis obliquity of 35 and the atmosphere was relatively dusty glacial flow modeling under these conditions produces patterns similar to those documented in the lda lvf and sharad radar data suggests that significant amounts of ice remain sequestered below the sublimation lag today

former extent of glacier like forms on mars abstract mars mid latitude glacier like forms glfs have undergone substantial mass loss and recession since a hypothesised last martian glacial maximum lmgm stand to date there is a lack of knowledge of the nature and timing of the lmgm the subsequent mass loss and whether this mass loss has been spatially variable here we present the results of a population scale inventory of recessional glfs derived from analysis of 1293 glfs 3 identified within context camera ctx imagery to assess the distribution and controls on glf recession a total of 436 glfs were identified showing strong evidence of recession 197 in the northern hemisphere and 239 in the southern hemisphere relative to their parent populations recessional glfs are over represented in the low latitude belts between 25 and 40 and in areas of high relief suggesting that these zones exert some control over glf sensitivity and response to forcing this analysis is complemented by the reconstruction of the maximum extent and morphology of a specific glf for which high resolution imaging science experiment hirise derived digital elevation data are available using nye s nye j f 1951 proc roy soc lond ser a mat phys sci 207 554 572 perfect plastic approximation of ice flow applied to multiple flow lines under an optimum yield strength of 22 kpa we calculate that the reconstructed glf has lost an area of 6 86 km 2 with a corresponding volume loss of 0 31 km 3 since the lmgm assuming the loss reconstructed at this glf occurred at all mid latitude glfs yields a total planetary ice loss from mars glfs of 135 km 3 similar to the current ice volume in the european alps on earth

constraints on the speciation of hydrogen in earth s transition zone abstract the thermodynamic stability of hydrous b type phases relative to hydrous and phases is examined the stability of phase b mg12si4o19 oh 2 and superhydrous b mg10si3o14 oh 4 relative to hydrous phase with an end member formula of mg7si4o14 oh 2 appears to be controlled by reactions that depend on whether coexisting mgsio3 resides in the garnet structure or is present as a pyroxene in majorite garnet bearing systems the volume of b bearing assemblages is smaller than those containing hydrous phase the corresponding volume change between b assemblages relative to hydrous phase bearing assemblages is ambiguous the increase in volume between superhydrous b bearing assemblages and hydrous phase bearing assemblages produces a free energy difference that is significantly greater than that expected from thermal contributions to the free energy phase b bearing assemblages also have a smaller volume than hydrous phase assemblages but the difference in volume is a factor of two smaller than that associated with superhydrous b this may account for the greater stability range of superhydrous b compared to phase b in contrast pyroxene bearing assemblages clearly favor the formation of hydrated phase in accord with these expectations heavily hydrated and phases those with greater than 1 wt h2o have been synthesized in the past primarily from melt rich or pyroxene bearing assemblages to confirm these trends we conducted synthesis experiments on samples at pressures between 15 and 25 gpa utilizing the laser heated diamond cell with chrysotile san carlos olivine bamble enstatite and a garnet lherzolite as starting compositions with several weight percent water added to the anhydrous materials at transition zone pressures each of these materials yields a b phase as the main crystalline hydrous phase the combination of our calculations and experiments thus indicates that the b phases are probably the main repository for hydrogen in the mantle between 400 and at least 520 km depth particularly as their thermal stability is expected to be enhanced through the incorporation of levels of fluorine similar to those present in xenolithic phlogopites and amphiboles

an inventory and population scale analysis of martian glacier like forms abstract martian glacier like forms glfs indicate that water ice has undergone deformation on the planet within its recent geological past but the driving mechanisms behind the origin evolution and dynamics of these landforms remain poorly understood here we present the results of a comprehensive inventory of glfs derived from a database of 8058 context camera ctx images to describe the physical controls on glf concentration and morphometry the inventory identifies 1309 glfs 727 glfs in the northern hemisphere and 582 in the southern hemisphere clustered in the mid latitudes centred on a mean latitude of 39 3 in the north and 40 7 in the south and in areas of rough topography morphometric data show inter hemispheric similarity in glf length mean 4 66 km and width mean 1 27 km suggesting a common evolutionary history and a poleward orientation of glfs in both hemispheres indicating a sensitivity to climate and insolation on a local scale elevation is shown to be the most important control on glf location with most glfs occurring above an altitude threshold of 3000 m aod and in areas of moderate but not high relief we propose therefore that martian glfs may not exhibit accumulation or ablation areas as is the norm for terrestrial glacial systems but reflect ice motion in response to local relief within a widely distributed reservoir of ice deposited within prescribed latitudinal and elevational ranges

amazonian northern mid latitude glaciation on mars a proposed climate scenario recent geological observations in the northern mid latitudes of mars show evidence for past glacial activity during the late amazonian similar to the integrated glacial landsystems in the dry valleys of antarctica the large accumulation of ice many hundreds of meters required to create the observed glacial deposits points to significant atmospheric precipitation snow and ice accumulation and glacial flow in order to understand the climate scenario required for these conditions we used the lmd laboratoire de meteorologie dynamique mars gcm general circulation model which is able to reproduce the present day water cycle and to predict past deposition of ice consistent with geological observations in many cases prior to this analysis however significant mid latitude glaciation had not been simulated by the model run under a range of parameters in this analysis we studied the response of the gcm to a wider range of orbital configurations and water ice reservoirs and show that during periods of moderate obliquity 25 35 and high dust opacity sdust 1 5 2 5 broad scale glaciation in the northern mid latitudes occurs if water ice deposited on the flanks of the tharsis volcanoes at higher obliquity is available for sublimation we find that high dust contents of the atmosphere increase its water vapor holding capacity thereby moving the saturation region to the northern mid latitudes precipitation events are then controlled by topographic forcing of stationary planetary waves and transient weather systems producing surface ice distribution and amounts that are consistent with the geological record ice accumulation rates of 10 mm yr

formation of glaciers on mars by atmospheric precipitation at high obliquity surface conditions on mars are currently cold and dry with water ice unstable on the surface except near the poles however geologically recent glacierlike landforms have been identified in the tropics and the midlatitudes of mars the ice has been proposed to originate from either a subsurface reservoir or the atmosphere we present high resolution climate simulations performed with a model designed to simulate the present day mars water cycle but assuming a 45 obliquity as experienced by mars a few million years ago the model predicts ice accumulation in regions where glacier landforms are observed on the western flanks of the great volcanoes and in the eastern hellas region this agreement points to an atmospheric origin for the ice and reveals how precipitation could have formed glaciers on mars

stability of hydrous silicate at high pressures and water transport to the deep lower mantle hydrous magnesium rich silicates play an important role in transporting water into the deep mantle when oceanic plates subduct as slabs but were thought to dissociate at pressures of 44 gpa in situ x ray measurements in conjunction with a multi anvil apparatus show that hydrous phases of magnesium rich silicate are stable under lower mantle conditions up to 50 gpa and may transport water to deeper layers of the mantle the presence of water strongly influences the structure composition and dynamics of the earth s deep mantle1 2 3 4 hydrous magnesium rich silicates play an important role in transporting water into the deep mantle when oceanic plates subduct as slabs the highest pressure form of such hydrous silicates phase d was reported to dissociate into an assemblage of nominally anhydrous phases plus water at pressures of about 44 gpa equivalent to 1 250 km depth5 in this way free water would be released in the middle region of the lower mantle which suggests that no water can reach the deeper regions of the lower mantle here we use in situ x ray measurements in conjunction with a multi anvil apparatus using sintered diamond anvils to show that hydrous phases are stable under lower mantle conditions up to 50 gpa we found that phase d transforms to an assemblage with another hydrous silicate mgsih2o4 named phase h at pressures above about 48 gpa our results suggest that phase h is the dominant hydrous silicate in descending slabs and may be found at depths far deeper than 1 250 km we conclude that a significant amount of water is retained in the descending slabs and may be delivered to the deepest part of the lower mantle

a teleseismic and petrological study of the crust and upper mantle beneath the geothermal anomaly urach sw germany abstract teleseismic p wave travel time residuals recorded by a mobile shortperiod network are interpreted using the composition of crustal and upper mantle xenoliths a three dimensional inversion of the p residuals revealed a small scale anomalous domain with a velocity reduction of 3 in the crust and a broad low velocity anomaly of 4 beneath the moho down to a depth of 50 km xenoliths of the miocene urach volcanic field uvf 1300 km2 355 eruptive centres mostly diatremes comprise phlogopite bearing clinopyroxene rich mantle xenoliths evidence for large ion lithophile element lil metasomatism in an originally depleted harzburgitic mantle reflecting chemical modification of the upper mantle beneath the uvf the metasomatism caused partial melting in the spinel peridotite stability field indicated by glasses in xenoliths and a diapiric uprise of the partially molten metasomatized mantle the observed reduction of the p wave velocity of 4 in the lithospheric mantle can be explained by a local enrichment of phlogopite accompanied by increased temperatures the crustal low velocity body coincides very well with the postulated volume of an ancient intracrustal magma chamber or system of chambers required by the composition of xenoliths the magnetization of the diatremes and the spatial distribution of the volcanic eruption centres

cold based mountain glaciers on mars western arsia mons surface environmental conditions on mars are currently extremely cold and hyperarid most equivalent to polar deserts on earth coupling newly acquired mars data with fieldbased observations regarding the flow surface morphology and depositional history of polar glaciers in antarctica we show that the multiple facies of an extensive fan shaped deposit on the western flanks of arsia mons volcano are consistent with deposition from cold based mountain glaciers an outer ridged facies that consists of multiple laterally extensive arcuate and parallel ridges resting without disturbance on both well preserved lava flows and an impact crater is interpreted as drop moraines formed at the margin of an ablating and predominantly receding cold based glacier a knobby facies that consists of equidimensional knobs each to several kilometers in diameter is inward of the ridges this facies is interpreted as a sublimation till derived from in situ downwasting of ashrich glacier ice a third facies comprising distinctive convex outward lobes with concentric parallel ridges and aspect ratios elongated downslope likely represents rock glacier deposits some of which may still be underlain by a core of glacier ice taken together these surficial deposits show that the western flank of arsia mons was occupied by an extensive mountain glacial system accumulating on and emerging from the upper slopes of the volcano and spreading downslope to form a piedmont like fan

effect of a hadean terrestrial magma ocean on crust and mantle evolution this paper presents a model for the thermal and chemical evolution of a global magma ocean created by impact heating during the earth s accretion detailed calculations are given for a melt depth of 120 km for end member picritic and peridotitic compositions application of fluid mechanics and heat transfer principles shows as a first approximation that the chemical evolution can be portrayed by idealized fractional crystallization occurring only on the the bottom of the magma ocean the fractional crystallization sequence for the picritic model is 90 km of mafics overlain by 15 km of ol sp gabbronorite and topped by 15 km of iron rich leucodiorite whereas the peridotite sequence consists of 99 km of dunite harzburgite and websterite overlain by 5 km of ol sp gabbronorite and capped by 16 km of ferroleucogabbronorite although subsolidus convection would rehomoginize all but the felsic layers of the picritic model the layers of the peridotite would remain intact owing to their stable density profile the mineralogy of the felsic layers is largly independent of the basic model assumptions however the composition of the mafic layers is model dependent the most likely results for the mafic mafic layers lherzolite or primitive mantle peridotite are similar to mantle xenoliths suggesting that a terrestrial magma ocean may have existed however comparison of the chemistry of the calculated upper felsic layer with that of the canadian shield shows that crystallization of a global magma ocean would not directly produce the archean continental crust multiple melting and differentiation of the fe leucodiorite to fe leucogabbronorite layer and of the underlying primitive mantle would be required to form an archean granitoid crust

phase transformations in serpentine and transportation of water into the lower mantle phase transformations in serpentine the major hydrous mineral in the upper part of the subducting slabs have been studied at pressures to 26 gpa and at temperatures between 500 and 1400 c while serpentine completely dehydrates at temperatures higher than 600 800 c and at pressures to 12 gpa phase assemblages including some dense hydrous magnesium silicates dhms such as phases a e superhydrous b and d were formed at higher pressures phase d was found to possess a stability field of particularly wide pressure and temperature regime suggesting that this phase may play an important role in transportation of water into the lower mantle via subduction of cold slabs

the distribution of hydroxyl in garnets from the subcontinental mantle of southern africa 166 garnets of dominantly mantle origin were analyzed for oh content by infrared ir spectroscopy ir spectra in the 3400 3700 cm 1 region display consistent absorption patterns attributable to oh structurally bound within the garnet crystal occasionally contaminated by low intensity oh absorptions from microscopic inclusions the principal structural oh absorption occurs near 3570 cm 1 with the appearance of additional absorptions near 3512 cm 1 and 3650 cm 1 dependent on garnet composition or paragenesis samples derive from a wide variety of rock types occurring as xenoliths in kimberlites of southern africa oh abundances using the best currently available calibration range from less than 1 up to 135 ppm h 2o and increase in the general order as follows on craton eclogites group 1 basaltic kimberlite alnoite alkali basalt the oh contents of common lithospheric granets from coarse peridotites including several phlogopite bearing samples are typically less than 20 ppm h 2o for tectonic settings of kimberlites both on and off the archaean kaapvaal craton ti rich garnets from deformed peridotites are richer in oh supporting previous suggestions of association of these xenoliths with putative megacryst magmas subcalcic cr rich xenocrysts diamond inclusion garnets and garnets from diamondiferous eclogites have very low oh contents similar to eclogites and depleted peridotites without macroscopic diamonds the oh content of southern african peridotite and eclogite garnets are significantly lower on average than those previously examined from the colorado plateau diatremes while details of emplacement related h mobility in garnets remain to be established our results suggest that garnets record useful information on the role of water or other hydrous volatile species in petrological processes at their source regions in the mantle although garnets do not appear to constitute a large reservoir of mantle hydrogen the large stability range of oh bearing garnet in the crust and mantle implies wide applicability as a qualitative hydrobarometer

composition of the core ii effect of high pressure on solubility of feo in molten iron abstract an experimental and theoretical investigation of the effect of pressure on the solubility of feo in molten iron has been carried out analyses of shock wave compression data on iron oxides combined with measurements of the fe o bond length in metallic oxides suggest that the partial molar volume of feo v dissolved in molten iron is substantially smaller than that of molten wustite hence the effect of high pressure should be to increase the solubility of feo in molten iron at a given temperature this inference is confirmed by an experimental investigation of the effect of pressure on the position of the fe feo eutectic thermodynamic calculations based on these experiments yield an estimate for v which is in reasonable agreement with the theoretical estimates the experimental value of v is used to calculate the effect of high pressure upon the fe feo phase diagram solubility of feo in molten iron increases sharply with pressure the liquid immiscibility region contracts and disappears around 20 gpa and it is predicted that the fe feo phase diagram should resemble a simple eutectic system above about 20 gpa analogous calculations predict that the solubility of feo in molten iron in equilibrium with magnesiowustite mg 0 8 fe 0 2 o at 2500 c increase from 14 mol p 0 to above 25 mol at 20 gpa if the core formed by segregation of metallic iron originally dispersed throughout the earth it seems inevitable that it would dissolved large amounts of feo thereby accounting for the observation that the density of the outer core is substantially smaller than that of pure iron under corresponding p t conditions

an alternative interpretation of late amazonian ice flow protonilus mensae mars abstract the morphological properties of glacial deposits located within a cirque like alcove in eastern protonilus mensae mars mars grid reference 54 55 lon 40 80 lat have been interpreted as indicative of an early phase of glaciation involving ice flowing out from the main glacierized valley and into a higher elevation box canyon or alcove this interpretation implies that the elevation of the glacial deposits currently located within the alcove mark a minimum former ice elevation in this catchment providing a regional datum for former ice thicknesses with implications for martian climate reconstruction here we raise the possibility of an alternative interpretation detailed geomorphological mapping and evaluation of the deposits remaining within the alcove suggest that they may have been formed by the more conventional mechanism of ice flowing out from the alcove and not into it both small scale and catchment scale morphologies allied to the site s location and orientation within an otherwise conventionally glacierized catchment are consistent with outbound flow this alternative hypothesis has important implications for ice thicknesses both in the local area and by extension regionally

shock wave equation of state of serpentine to 150 gpa implications for the occurrence of water in the earth s lower mantle the shock equation of state of serpentine has been determined to 150 gpa four distinct regions occur along the hugoniot a low pressure phase a mixed phase region a high pressure phase and a very high pressure phase the low pressure phase lpp exists under shock pressures to about 40 gpa this material exhibits shock properties that are partially consistent with those of low pressure serpentine but steep release paths and a low value of k 2 77 suggest transformation to another possibly amorphous assemblage thermodynamic calculations indicate that under equilibrium conditions serpentine would decompose to oxides plus water at conditions below 10 gpa along the hugoniot a mixed phase region begins at 40 gpa with complete transition to a high pressure phase occurring by about 55 gpa the high pressure phase hpp occurs at shock pressures between 55 gpa and 125 gpa model hugoniots based on perovskite plus periclase plus water and brucite plus periclase plus stishovite reproduce the serpentine hpp hugoniot within experimental error so definitive identification of the hpp as a distinct hydrous mineral phase or as a free water containing mixture is not possible above 125 gpa a transition to a very compressible phase possibly a hydrous partial melt occurs the serpentine hpp hugoniot is about 15 20 less dense than the earth s lower mantle models of the lower mantle based on shock equations of state for olivine pyroxene and serpentine indicate that for an atomic mg mg fe ratio of 0 80 the presence of 2 wt h 2o is consistent with seismically determined lower mantle density estimates greater amounts of h 2o can be accommodated if accompanied by an increase in fe content calculated hugoniot sound speeds of the serpentine hpp although poorly constrained are broadly consistent with lower mantle sound speeds thus the high pressure density and sound speed of an h 2o rich magnesium silicate determined from shock equation of state experiments indicate that the observed seismic properties of the lower mantle allow the existence of several weight percent of water in the lower mantle

stabilities and equations of state of dense hydrous magnesium silicates abstract the thermodynamic stability of high pressure phases in the ternary system mgo sio2 h2o is reviewed with special emphasis on hydrated phases including the alphabet phases on the basis of recent experimental data a stability diagram for these phases along a geotherm appropriate for a subducting slab is constructed this suggests that at realistic water contents the breakdown of antigorite will produce olivine plus phase a in the upper mantle but that the ability of wadsleyite to accommodate wt levels of water means that phases e and d are unlikely to occur in the upper portion of the transition zone for the lower part of the transition zone in which ringwoodite becomes stable the coexisting hydrous phase would be superhydrous phase b provided ringwoodite is not able to accommodate significant amounts of water at the top of the lower mantle phase d is stable but only at temperatures below 1300 c as the maximum solubility of h2o in magnesium silicate perovskite is also quite low slabs may dehydrate somewhat as they enter the lower mantle the available thermodynamic data for these phases is also reviewed from the most recent measurements of equations of state it is concluded that the elasticity of the phases in the mgo sio2 h2o ternary system is primarily dependent upon the density and not upon the water content it is therefore concluded that the presence of even significant amounts of hydrated phases in subducting slabs could not be unequivocally identified from seismological observations

the relationship between the physical properties of the assumed pyrolite composition and depth distributions of seismic velocities in the upper mantle abstract assuming that the upper mantle consists of pyrolite composition we determined values of derivatives of bulk modului and shear modului with respect to pressure and temperature and values of the gruneisen anderson parameter for composite minerals of pyrolite composition by comparing depth distributions of p and s wave velocities calculated from the values of physical properties obtained from high pressure and high temperature experiments with those of iasp91 for this purpose we determined the above described values which have not been determined well in high pressure and high temperature experiments within a certain range for each parameter using genetic algorithm ga as a result the values of physical properties for wadsleyite were determined so that seismic velocities can decrease the values of derivative of bulk modulus for perovskite and magnesiowustite were determined so that seismic velocities can increase on the other hand the values of derivative of shear modulus for perovskite and magnesiowustite were determined to be the same values as standard values or the values were determined so that seismic velocities can decrease the values of physical properties for pyroxene garnet and majorite except the values of derivative of bulk modulus with respect to pressure for orthopyroxene and garnet were determined so that seismic velocities can increase depth distributions of seismic velocities calculated from the determined values of physical properties indicate that the velocity jump corresponding to the 410 km seismic discontinuity occurs at a depth shallower than that for iasp91 the amount of velocity jump at the 660 km seismic discontinuity obtained in this study reaches 3 5 for p wave which is smaller than that 5 8 for iasp91 we also investigated the effect of mantle geotherm on depth distributions of seismic velocities the results show that the seismic velocities increase 0 5 when the mantle geotherm becomes low by 100 k for all the depths concerned however the amount of p wave velocity jump at the 660 km seismic discontinuity obtained in this study is too small to explain that for iasp91 for any mantle geotherms if we assume that the upper mantle consists of pyrolite composition these suggest that the amount of p wave velocity jump at the 660 km seismic discontinuity for iasp91 is overestimated

martian flow features moraine like ridges and gullies terrestrial analogs and interrelationships ridges that resemble terrestrial moraines are commonly visible at the foot of many mid latitude crater walls in mars global surveyor mars orbiter camera images these moraine like ridges are often associated with hillside gullies mantling material and glacier like flows and are usually in contact with crater fill suggesting possible interrelationships we consider terrestrial glacier systems that may be analogs of martian moraine like ridges and glacier like flows and suggest that the formation of some gullies and crater fill is intimately tied to ice deposition ice flow and rock glacier processes upper limits on age suggest the possibility that many of these features formed during the last or last few high obliquity cycles