pore characterization of isolated organic matter from high matured gas shale reservoir abstract knowledge of pore structure of isolated organic matter om provides guidance for better understanding the origin distribution and characterization of pore system in gas shale reservoir and can be used to better comprehend the storage and transport mechanism of natural gas in shale reservoir pore structure characteristics of isolated organic matters and its corresponding bulk shales were investigated for five high matured marine shale samples from the lower silurian longmaxi formation in south china using x ray diffraction xrd total organic carbon content toc tests field emission scanning electron microscope fe sem observation and ultra low pressure nitrogen gas physisorption the results indicate that om hosted pores are abundant in bulk shale samples under fe sem observation the bet surface area and the bjh pore volume of isolated om are approximately three times greater than that of bulk shale samples pore size distribution psd of isolated om from five shale samples show a consistent variation pattern additionally with increasing toc content the psd curves of isolated om gradually grow down as result of the ductility of om bimodal psd in surface area and unimodal psd in pore volume exist in both isolated om and bulk shale samples indicating surface area is mainly associated with micropores and fine mesopores

controlling functions of hydrothermal activity to shale gas content taking lower cambrian in xiuwu basin as an example abstract lower cambrian is the main target intervals of marine shale gas exploration and exploitation in china shale gas bearing varies greatly among different intervals and how to determine favorable targets is an important problem to be solved in this article taking jiangye 1 well in xiuwu basin as an example according to core description logging data analysis section authentication mineral and elemental composition analysis bulk and effective porosity tests total organic carbon toc and gas content tests lower cambrian wangyinpu and guanyintang formations have been studied results show that toc content is the dominating factors for effective porosity and gas bearing content redox conditions and bioproductivity control the enrichment of sedimentary organic matter the water reducibility of sq1 varies greatly of sq2 and sq3 is generally strong reducibility of all the three sequences is stronger than those of sq4 and sq5 the bioproductivity of sq3 is the highest and little difference in the bioproductivity has been found between sq1 and sq2 both of which show higher values than sq4 and sq5 except for terrigenous siliceous minerals large amounts of hydrothermal origin siliceous minerals exist in lower cambrian wangyinpu and guanyintang formations specifically siliceous origin of sq1 varies greatly part of intervals are terrigeneous origin and part of intervals are hydrothermal origin most siliceous minerals of sq2 and sq3 are hydrothermal origin whose content takes up 10 30 compared with sq2 and sq3 content of hydrothermal origin siliceous minerals drops in sq4 and terrigeneous siliceous content increases siliceous minerals of sq5 originate from normal terrigeneous clastic deposition hydrothermal activities are helpful for the increase of reducibility of seawater and enhancing bioproductivity the sedimentary organic matter abundance is thus controlled and the enrichment of shale gas is further affected hydrothermal activities are generally developed in the early cambrian in south china the intervals deposited when frequent hydrothermal activities occurred are exactly favorable targets of shale gas in lower cambrian

a comparative discussion of the evidence for biogenic silica in wufeng longmaxi siliceous shale reservoir in the sichuan basin china abstract the siliceous wufeng longmaxi formation is the main shale gas play in china it contains a large amount of silica which has been reported to be of biogenic origin the previous evidences for a biogenic origin include the presence of siliceous skeletal debris resembling organisms such as sponge spicules various parameters such as the ratios of al al fe mn and si si fe al ca and a number of different correlations such as a positive relationship of silica content with total organic matter toc however these evidences especially various parameters and correlations become unpersuasive when comparing wufeng longmaxi formation siliceous shale with other shale in these parameters and correlations a series of petrographic thin section and scanning electron microscope sem observations elemental analysis toc analysis and mineral composition analysis were conducted to verify the unpersuasiveness of the existing evidences and then propose new evidences to demonstrate the abundance of biogenic silica in wufeng longmaxi siliceous shale it is shown that siliceous ellipsoids are a better mark of biogenic silica in wufeng longmaxi siliceous shale than sponge spicule radiolarian and foraminifera except for the barium ba concentration most elemental composition data cannot be used to distinguish biogenic silica from silica with an airborne volcanic ash origin furthermore the poor crystal morphology of the silica in wufeng longmaxi siliceous shale was a clear difference from the airborne volcanic ash derived silica in lucaogou formation and hydrothermal silica in nutitang and doushantuo formations hence the crystal morphology can be considered as a distinguishing feature for biogenic silica

spectrum of pore types and networks in mudrocks and a descriptive classification for matrix related mudrock pores matrix related pore networks in mudrocks are composed of nanometer to micrometer size pores in shale gas systems these pores along with natural fractures form the flow path permeability network that allows flow of gas from the mudrock to induced fractures during production a pore classification consisting of three major matrix related pore types is presented that can be used to quantify matrix related pores and relate them to pore networks two pore types are associated with the mineral matrix the third pore type is associated with organic matter om fracture pores are not controlled by individual matrix particles and are not part of this classification pores associated with mineral particles can be subdivided into interparticle interp pores that are found between particles and crystals and intraparticle intrap pores that are located within particles organic matter pores are intrap pores located within om interparticle mineral pores have a higher probability of being part of an effective pore network than intrap mineral pores because they are more likely to be interconnected although they are intrap om pores are also likely to be part of an interconnected network because of the interconnectivity of om particles in unlithifed near surface muds pores consist of interp and intrap pores and as the muds are buried they compact and lithify during the compaction process a large number of interp and intrap pores are destroyed especially in ductile grain rich muds compaction can decrease the pore volume up to 88 by several kilometers of burial at the onset of hydrocarbon thermal maturation om pores are created in kerogen at depth dissolution of chemically unstable particles can create additional moldic intrap pores

applications of chemostratigraphy in a characterization of shale gas sedimentary microfacies and predictions of sweet spots taking the cambrian black shales in western hubei as an example abstract exploratory research was conducted in this paper on the correlation of chemical elements with sedimentary microfacies and shale gas sweet spots through cluster analysis factor analysis and so on using a large amount of geochemical data of elements obtained from shale gas exploration of the cambrian niutitang formation in western hubei this paper screened the chemical element associations and parameter systems that can reflect sedimentary microfacies and sweet spot evaluations proposed a classification method for the chemostratigraphic facies of shales and finely depicted the sedimentary chemical microfacies of the shales in the cambrian niutitang formation a chemostratigraphic lithofacies paleogeography map of sq1 the first sequence strata in the cambrian niutitang formation in western hubei was compiled sweet spots were predicted and evaluated and favourable areas were predicted thereby providing important support for making a breakthrough in the exploration of the cambrian shale gas in the yichang area chemostratigraphy has a higher precision and a low characterization cost of reservoir sedimentary microfacies especially in areas lacking drilling data and seismic data and having a low exploration degree chemostratigraphy is an important means for identifying of shale sedimentary sequences and predicting shale sweet spot sections

grain growth kinetics in olivine aggregates abstract grain growth kinetics were studied in hot pressed fine grained olivine aggregates experimental conditions include pressures of 0 1 mpa 300 mpa and 1 gpa and temperatures of 1473 1573 and 1673 k with or without the presence of water at the initial stage of grain growth growth of larger grains occurs rapidly consuming smaller grains which results in significant pore entrapment almost homogeneous grain size distribution is established in this process after this stage grain size distribution remains almost homogeneous in most cases it was found that the presence of water enhances the grain growth kinetics when the amount of water is limited however when the amount of water is large the water containing pores significantly inhibit the grain boundary migration therefore the enhancement of grain growth due to the presence of water is due to the role of dissolved water in olivine rather than the mass transport through water abnormal grain growth was found in some samples in these cases normal grain growth was inhibited by the presence of a significant amount of water filled pores or grains with significantly larger size than the rest occurred in the starting materials in 0 1 mpa runs significant porosity developed and the grain growth rates were significantly lower than in those at high confining pressures these results show that both water and pores have important effects on grain growth kinetics in olivine when the effects of pores or secondary phases in inhibiting grain growth are unimportant the grain growth rate in olivine is very fast growth to 100 m size will occur in 102 to 103 hours at 1500 k thus fine grain size in olivine will be maintained only for a short geological time unless the grain boundaries are effectively pinned by secondary particles

estimation of marine shale methane adsorption capacity based on experimental investigations of lower silurian longmaxi formation in the upper yangtze platform south china abstract methane adsorption experiments were performed on eight lower silurian longmaxi moisture equilibrated shale samples from the upper yangtze platform south china at pressures up to 12 mpa at 20 c 40 c 60 c 80 c and 100 c to investigate the effects upon methane adsorption capacity and to estimate the variation of methane adsorption capacity as a function of depth and burial history the methane adsorption capacity of the longmaxi shale shows a significant positive correlation with total organic carbon toc content which is accompanied by an increase in bet brunauer emmett teller surface area and total pore volume a quadratic relationship was observed between clay content and methane adsorption capacity there is a threshold clay content 42 3 44 4 in this trend methane adsorption capacity declines with increasing clay content below the threshold and later increases with increasing clay content the langmuir pressure decreases exponentially with the reciprocal of temperature and the langmuir volume decreases linearly with temperature the isosteric heat of adsorption and standard entropy for the longmaxi shale ranges from 10 34 to 11 67 kj mol and from 57 04 to 61 32 j mol k respectively which are clustered around kerogen type i using these relationships a computational scheme was developed to calculate methane adsorption capacity as a function of toc content temperature and pressure based on the langmuir equation this algorithm was applied to estimate methane adsorption capacity of the longmaxi shale as a function of depth due to the dominating effect of pressure methane adsorption capacity increases initially with depth through a maximum and then decreases as a result of increasing temperature at a greater depth the maximum gas adsorption capacity is typically located at a depth range between 800 and 1350 m with toc content increasing the curves shift continuously towards higher adsorption capacity furthermore the maximum methane adsorption capacity moves higher and shifts to a deeper depth as toc content increases ultimately four principal dynamic evolutionary stages of methane adsorption capacity of the longmaxi shale over geologic time as a function of burial history were reconstructed

grain growth in partially molten olivine aggregates grain growth rates in partially molten olivine aggregates were determined experimentally at a pressure of 1 gpa the aim of the experiments with fine grained starting material solution gelation derived fo90 olivine with a grain size of 1 m with 2 and 4 wt added basaltic glass was to determine growth rates during steady state grain growth a series of experiments was conducted at a fixed temperature of 1 350 c for durations from 2 to 700 h and a second series at fixed duration 168 h at temperatures from 1 250 to 1 450 c the resulting activation energy e 390 kj mol and growth exponent n 4 3 are comparable to melt free results nichols and mackwell 1991 the observed grain size distributions are broader than those predicted for normal grain growth or ostwald ripening and most similar to the log normal distribution the observed melt distribution is influenced by the continuous rearrangement of neighboring grains during growth the relatively large growth exponent observed in this study and by nichols and mackwell 1991 where secondary phases are present suggests that grain growth in the upper mantle is slower than predicted by karato 1989

change in composition and pore structure of longmaxi black shale during oxidative dissolution abstract owing to the presence of chemically unstable compositions e g clay minerals carbonate pyrite and organic matter om which are closely related to shale structure failures or dissolution pores the methods to increase gas well long term productivity from tight shale matrix need to take into account the chemical interaction of shale with injected fluid in this study black shale samples obtained from lower silurian longmaxi formation in sichuan basin china were treated with 15 wt hydrogen peroxide h2o2 for the comprehensive understanding of the change in shale composition and the associated dissolution structures the measurements of mass loss total organic carbon content and mineralogical composition showed that carbonate reductive inorganic minerals containing ferrous iron e g pyrite and chlorite and om in samples exhibited strong dissolution however the other minerals behaved in a non reactive manner at the experimental time scale after the oxidative treatment for 240 h a large amount of oxidation induced fractures and dissolution pores were observed by field emission scanning electron microscopy the fractures mainly oriented parallel to lamination were attributed to the dissolution of om and structural alteration of clay minerals all the dissolution pores seemed to be strongly dependent on the loss of dolomite pyrite and om results from high pressure mercury intrusion and low pressure nitrogen adsorption analysis showed that these dissolution pores ranging from 10 to 500 nm in diameter exhibited a significant increase in pore volume due to the removal of interconnected pore filling om while the volume of pores 1 m in size exhibited a minor increase because the micrometer size dissolved particles appeared to be discrete or unconnected thus the oxidative dissolution could lead to the higher porosity and better connectivity of nanometer size pore networks in shale samples the induced fractures reduced the size of diffusion dominant zones in shale matrix and the dissolution pores increased the size of gas transport pathways into fractures these results indicate that the injection of h2o2 may play an important role in shale matrix stimulation by oxidative dissolution which is likely to improve matrix diffusivity

relationships between dynamically recrystallized grain size and deformation conditions in experimentally deformed olivine rocks new microstructural data on experimentally deformed wet and dry natural olivine rocks anita bay and aheim dunite together with the other reliable experimental data indicate that the experimental stress recrystallized grain size relationship in olivine rocks is largely independent of water content and temperature and is only slightly dependent on the flow properties of the material the experimental data cover a stress range of 30 300 mpa water contents from 30 ppm to 300 ppm and temperatures in the range 1100 1650 c local melt contents of up to 10 volume cannot be demonstrated to have a significant effect on the stress grain size relationship

heterogeneity of intergranular intraparticle and organic pores in longmaxi shale in sichuan basin south china evidence from sem digital images and fractal and multifractal geometries abstract previous studies have determined many types of pores in shale such as organic pores inorganic pores and microfractures in this study pores are classified as intergranular intraparticle and organic pores based on the location of their occurrence the heterogeneities of the three pore types and their effects on the occurrence of shale gas which is of utmost practical importance for shale gas exploration and development are discussed in this study the three types of pores are quantitatively characterized using fractal and multifractal methods the mean fractal dimension and mean width of the multifractal spectrum of these pores are found to be different i e 1 5985 and 1 665 for intraparticle pores 1 5869 and 1 475 for intergranular pores and 1 6 and 1 3725 for organic pores intraparticle pores have the highest heterogeneity intergranular pores have intermediate heterogeneity and organic pores have the lowest heterogeneity sem images show that organic pores have good connectivity homogeneous distribution and small range of aperture change but have the lowest heterogeneity even where pores are abundant thus they provide the largest shale gas occurrence space in contrast intergranular pores are less abundant have lower connectivity and have higher heterogeneity than organic pores thereby providing a relatively smaller shale gas occurrence space finally intraparticle pores are the least abundant and possess the poorest connectivity largest range of aperture change and highest heterogeneity of the three pore types thereby providing the smallest shale gas occurrence space we conclude that organic pores are crucial to the occurrence of shale gas and can provide a new index for the evaluation of shale gas exploration and development

organic matter hosted pore system marcellus formation devonian pennsylvania the marcellus formation of pennsylvania represents an outstanding example of an organic matter om hosted pore system most pores detectable by field emission scanning electron microscopy fe sem are associated with om instead of mineral matrix in the two wells studied here total organic carbon toc content is a stronger control on om hosted porosity than is thermal maturity the two study wells span a maturity from late wet gas vitrinite reflectance ro 1 0 to dry gas ro 2 1 samples with a toc less than 5 5 wt display a positive correlation between toc and porosity but samples with a toc greater than 5 5 wt display little or no increase in porosity with a further increasing toc in a subset of samples 14 across a range of toc 2 3 13 6 wt the pore volume detectable by fe sem is a small fraction of total porosity ranging from 2 to 32 of the helium porosity importantly the fe sem visible porosity in om decreases significantly with increasing toc diminishing from 30 of om volume to less than 1 of om volume across the range of toc the morphology and size of om hosted pores also vary systematically with toc the interpretation of this anticorrelation between om content and sem visible pores remains uncertain samples with the lowest om porosity higher toc may represent gas expulsion pore collapse that was more complete as a consequence of greater om connectivity and framework compaction whereas samples with higher om porosity lower toc correspond to rigid mineral frameworks that inhibited compactional expulsion of methane filled bubbles alternatively higher toc samples may contain om low initial hydrogen index relatively unreactive that is less prone to development of fe sem detectable pores in this interpretation om type controlled by sequence stratigraphic position is a factor in determining pore size distribution

rheological contrast at the continental moho effects of composition temperature deformation mechanism and tectonic regime abstract the rheological contrast at the moho is an important factor in continental tectonics this paper explores systematically the effects of composition temperature deformation mechanism and tectonic regime on the strength contrast considering four compositions for the lower crust felsic granulite mafic granulite wet diabase dry diabase and two for the lithospheric mantle dry and wet peridotite the strength contrast of the resulting eight compositional layerings is estimated as a function of moho temperature which is varied from 600 to 1500 k the moho temperature can be converted to surface heat flow if the thickness and composition of the crust are known besides a standard case crustal thickness 35 km the cases of a thick 50 km and thin 20 km crust are also considered with wet quartzite crustal rheology in the latter case results show a great variety of strength contrasts according to different conditions excluding the case of very low moho temperature tm 600 k when the behaviour of both lower crust and upper mantle is frictional brittle and therefore the strength contrast vanishes the strength contrast at a given strain rate is a strong function of composition temperature and tectonic conditions weak compositional stratification e g soft lower crust soft lithospheric mantle or hard lower crust hard lithospheric mantle results in lower contrasts than strong compositional stratification for any given compositional combination the absolute value of the strength contrast is higher in compressional as compared to extensional tectonic environments and tends to decrease with increasing temperature from a maximum of hundreds of mpa at low to intermediate moho temperatures 600 1200 k therefore rheological layering is favoured by strong intrinsic i e compositional strength contrasts between lower crust and upper mantle and relatively low moho temperatures

diffusion creep of dry melt free olivine 1 deformation experiments were conducted on fine grained 3 6 m fully synthetic fo90 olivine aggregates in a gas medium apparatus at 300 mpa confining pressure and temperatures of 1150 1360 c the strain rates of the solution gelation derived and therefore genuinely melt free dry samples are about two orders of magnitude lower than the strain rates for nominally melt free aggregates at the same pressure and temperature conditions and grain size benchmark deformation tests with anita bay dunite and mild steel reproduce published data the creep strength of melt added sol gel olivine is similar to the published creep strength of dry melt bearing olivine derived from natural rocks nonlinear least squares fits to the melt free deformation data give an activation energy of 484 kj mol a stress exponent of 1 4 and a grain size exponent of 3 over a range of stresses from 15 to 210 mpa these results suggest that small amounts of melt may be similarly effective in reducing the creep strength of upper mantle rocks as small amounts of water however a possible contribution of grain boundary composition to the observed differences in rheology in the absence of melt cannot be conclusively ruled out by the current experiments

structural evolution of organic matter and implications for graphitization in over mature marine shales south china abstract to characterize the degree of organic matter graphitization in the over mature lower paleozoic marine shales from south china a suite of kerogen samples covering different maturity ro ranging from 1 2 to 4 2 were analyzed by laser raman microprobe lrm transmission electron microscope tem and fourier transform infrared spectroscopy ftir techniques chemical structures and related major changes caused by thermal evolution history were systematically discussed the results indicate that with the thermal maturity increasing the aliphatic side chains fall off gradually and the aromatic rings increase continuously the ordered structure of shales continues to enhance leading to the increasing of graphitization degree the parameters of lrm i e position of g and d bands peak position difference rbs full width at half maximum fwhm and intensity ratio id ig highlight the turning point at maturity level around rmcro 3 5 which represents the chemical structure jump of the kerogen this chemical structure jump can be characterized by the continuous decreasing of amorphous carbon before the rmcro exceeded 3 5 and the sharp increasing degree of aromatic conjugation after that point tem analysis indicates that the carbon layers of shale samples with rmcro exceeds 3 5 show better ordering and continuity than that of low maturity shale samples the ftir analysis suggests that there are relatively high aromatics c c chains and very few aromatic c h chains in the high maturity samples this critical chemical structure jump at rmcro 3 5 could be interpreted as the structure of organic matter begins to transform from amorphous carbon to crystalline graphite in shales due to the increasing degree of graphitization graphitized shale is characterized by stable chemical structure condensed and orderly carbon layer constructure and ultra low resistivity

effects of partial melting on seismic velocity and attenuation a new insight from experiments the effects of partial melting on seismic velocity and attenuation have long been studied by focusing on the direct effects of melt such as the poroelastic effect the direct effects are generally very small for a very small melt fraction because geochemical studies have shown that the melt fraction during partial melting is very small 0 1 it is difficult to explain upper mantle low velocity regions by the direct effects of melt recent experimental studies by using a rock analog have captured a significant enhancement of polycrystal anelasticity just before partial melting in the absence of melt this newly recognized effect enables us to interpret seismological and geochemical observations consistently the new anelasticity model significantly changes the interpretation of upper mantle seismic structures this review summarizes the recent progress in the understanding of polycrystal anelasticity starting from a basic knowledge of linear anelasticity

relationships among composition porosity and permeability of longmaxi shale reservoir in the weiyuan block sichuan basin china abstract shale composition might influence the petrophysical properties of shale reservoirs the relationships among composition porosity and permeability of longmaxi shale in weiyuan area sichuan basin china were systematically investigated by the integration of geochemical mineralogical and petrophysical data the cumulative pore volume of the organic rich longmaxi shale is mainly contributed of pores with diameter of 2 nm 100 nm the total organic carbon toc content is the main control on porosity as the percentage of organic porosity is 60 for the organic rich shales the clay content is positively correlated with porosity partly due to the clay associated interparticle pores and pores developed in organo clay complex carbonate and quartz content dilute the toc and clay content which accounts for their negative relationships with porosity in terms of shale composition the clay content exerts the strongest influence on permeability at low clay contents 30 the clay content exhibits a negative impact on permeability because abundant clay minerals block pore throats reduce the resistance to mechanical compaction and result in low permeability the influence of the pore network on permeability is evident from a positive correlation between the pore volume percentage of meso pores volmes and permeability which is due to a fine and coarse meso pores including a large fraction of organic pores which have better connectedness than other interparticle mostly 50 nm and intraparticle mainly isolated pores and b large quantities of fine and coarse meso pores increasing the capacity to access other pores which form the dominated pathways for gas flows according to the above illustrated relationships appropriate porosity and permeability indicating fine storage capacity and favorable flow capacity occur in the longmaxi shale in weiyuan block which implies good reservoir quality and excellent exploration prospects in this region

large occurrence patterns of new zealand deep earthquakes characterization by use of a switching poisson model the paper studies the statistical properties of deep earthquakes around north island new zealand we first evaluate the catalogue coverage and completeness of deep events according to cusum cumulative sum statistics and earlier literature the epicentral depth and magnitude distributions of deep earthquakes are then discussed it is worth noting that strong grouping effects are observed in the epicentral distribution of these deep earthquakes also although the spatial distribution of deep earthquakes does not change their occurrence frequencies vary from time to time active in one period relatively quiescent in another the depth distribution of deep earthquakes also hardly changes except for events with focal depth less than 100 km on the basis of spatial concentration we partition deep earthquakes into several groups the taupo bay of plenty group the taranaki group and the cook strait group second order moment analysis via the two point correlation function reveals only very small scale clustering of deep earthquakes presumably limited to some hot spots only we also suggest that some models usually used for shallow earthquakes fit deep earthquakes unsatisfactorily instead we propose a switching poisson model for the occurrence patterns of deep earthquakes the goodness of fit test suggests that the time varying activity is well characterized by a switching poisson model furthermore detailed analysis carried out on each deep group by use of switching poisson models reveals similar time varying behavior in occurrence frequencies in each group

experimental investigations on the geometry and connectivity of pore space in organic rich wufeng and longmaxi shales abstract the nano scale pore systems of organic rich shale reservoirs were investigated from upper ordovician wufeng and lower silurian longmaxi formations in southeast sichuan basin these two formations are the most important target plays of shale gas development in china the purpose of this article is to assess the geometry and connectivity of multi scale pore systems and to reveal the nature and complexity of pore structure for these over mature gas shales to achieve these objective total organic carbon mineralogy image analyses by focused ion beam sem low pressure nitrogen adsorption mercury injection capillary pressure micp and spontaneous fluid deionized di water and n decane imbibition were performed most of the visible pores from sem work in wufeng and longmaxi shales are within nm and m size regimes and belong to organic matter om pores the shapes of om pore in longmaxi samples are elliptical bubble like irregular or rounded wufeng pores are mainly irregular linear and faveolated even though two shales have small depth difference as well as similar thermal maturity kerogen type and toc content nano scale pores in longmaxi are mainly associated with narrow platelike or slitlike pores with pore size of 3 50 nm while inkbottle pores are dominant in wufeng samples and over 88 of the pore volume is contributed by pores with diameter

the effect of melt distribution on the rheology of plagioclase rocks abstract synthetic plagioclase aggregates were fabricated by hot isostatic pressing glass powder with an60ab40 composition at a confining pressure of 300 mpa and a temperature of 1223 k the residual glass content 15 vol was reduced to 1 3 vol by annealing the specimens at temperatures between 1423 and 1523 k at 0 1 mpa high resolution electron microscopy showed that the residual glass was confined to grain triple junctions when these samples were annealed at 0 1 mpa and above the solidus 1620 k they also contained silica rich amorphous phases at grain boundaries other samples were hot pressed at 1423 k they often have grain boundaries containing thin amorphous films 5 50 nm wide the chemical composition of the films differs from pure labradorite with up to 80 wt sio2 the volume fraction of si rich glass increases up to 2 vol for samples that contain 1 wt water uniaxial creep experiments were performed at temperatures of 1373 1638 k and stresses between 2 and 50 mpa the plagioclase aggregates deformed by grain size sensitive creep with a stress exponent n 1 the activation energy for grain boundary diffusion controlled creep of the partially molten aggregates was 400 20 kj mol 1 it remained unchanged with varying glass content and glass topology the strength of samples containing glass along grain boundaries is 4 10 times less than without amorphous grain boundary films the transition between diffusion and dislocation creep is shifted towards higher stresses for samples that contain glass films at grain boundaries

characteristics and evolution of pyrobitumen hosted pores of the overmature lower cambrian shuijingtuo shale in the south of huangling anticline yichang area china evidence from fe sem petrography abstract organic pores one of the significant pore types in shale reservoir can be formed in both primary organic matter kerogen and secondary organic matter such as solid bitumen and pyrobitumen compared to the primary organic pores that are mainly observed in immature kerogen secondary organic pores in migrated organic matter solid bitumen and pyrobitumen are more abundant and well connected to the matrix in this study the petrographic characteristics between the organic matter and matrix as observed in field emission scanning electron microscopy fe sem images were used to characterize the pore system in the overmature lower cambrian shuijingtuo niutitang equivalent shale in the south of huangling anticline yichang area china pyrobitumen hosted pores were observed to be the predominant pore type in the organic rich shuijingtuo shales the porous pyrobitumen occurs primarily in the original interparticle pores filled with microcrystalline quartz which is the primary petrographic evidence to identify the migrated organic matter pore filling organic matter and precipitation of authigenic quartz rather than mechanical compaction resulted in further loss of a large number of interparticle pores the porous organic matter that filled in the intraparticle space within the early formed framboidal pyrite and the pre existing dissolution pores within the quartz and pyrite grains is pyrobitumen this pyrobitumen had migrated as a mobile phase into the aforementioned pores spaces in the initial phase of hydrocarbon emplacement during the petroleum expulsion and migration process with increasing thermal maturity this migrated organic matter thermally transformed into pyrobitumen and nanoscale pores were developed with thermal cracking into gas the results show that the pore volume and surface area are positively correlated with the total organic carbon toc content indicating that organic matter primarily controls shale porosity for the shuijingtuo shales

scaling of stagnant lid convection with arrhenius rheology and the effects of mantle melting summary on the basis of numerical modelling and scaling analysis a few modifications are proposed for the scaling of stagnant lid convection in order to make it more applicable to the thermal evolution of terrestrial planets the effect of using arrhenius rheology as opposed to more popular linear exponential rheology is first investigated and the stability analysis of top thermal boundary layer is shown to be able to capture systematic differences caused by the different kinds of temperature dependent viscosity the local stability analysis is then extended to handle the effects of mantle melting such as dehydration stiffening and compositional buoyancy a new heat flow scaling law incorporating these effects suggests that mantle melting may reduce the conventional prediction of surface heat flux by up to a factor of 5 10 and its potential impact on our understanding of planetary evolution is briefly discussed

the experimental deformation of dunite deformation experiments have been carried out on two dunites anita bay of 100 m grain size and aheim of 900 m grain size at strain rates from 10 3 to 10 6 s 1 and temperatures from 1000 c to 1300 c in a gas medium deformation apparatus at 300 mpa confining pressure most of the tests were under wet conditions defined by the presence of small amounts of water from hydrous minerals initially present constant strain rate and relaxation experiments covering ranges of flow stress down to about 70 mpa and 7 mpa respectively show that there is a change in flow law in going below about 100 mpa differential stress and that the coarser grained rock is stronger than the finer grained one power law parameters above the transition are n 4 48 0 31 and q 498 38 kj mol 1 for aheim dunite and n 3 35 0 17 and q 444 24 kj mol 1 for anita bay dunite while below the transition relaxation tests on anita bay dunite give n 2 44 0 18 and q 386 27 kj mol 1 it is concluded that there is a weakening effect of water that this effect is mainly in the grain boundaries and that grain boundary sliding is probably a significant deformation mechanism at the lower stresses under wet conditions

reconciling mantle attenuation temperature relationships from seismology petrology and laboratory measurements seismic attenuation measurements provide a powerful tool for sampling mantle properties laboratory experiments provide calibrations at seismic frequencies and mantle temperatures for dry melt free rocks but require 102 103 extrapolations in grain size to mantle conditions also the effects of water and melt are not well understood at the same time body wave attenuation measured from dense broadband arrays provides reliable estimates of shear wave attenuation qs 1 affording an opportunity for calibration we reanalyze seismic data sets that sample arc and back arc mantle in central america the marianas and the lau basin confirming very high attenuation qs 25 80 at 1 hz and depths of 50 100 km at each of these sites independent petrological studies constrain the temperature and water content where basaltic magmas last equilibrated with the mantle 1300 1450 c the qs measurements correlate inversely with the petrologically inferred temperatures as expected however dry attenuation models predict qs too high by a factor of 1 5 5 modifying models to include effects of h2o and rheology dependent grain size shows that the effects of water enhanced dissipation and water enhanced grain growth nearly cancel so h2o effects are modest therefore high h2o in the arc source region cannot explain the low qs nor in the back arc where lavas show modest water content most likely the high attenuation reflects the presence of melt and some models of melt effects come close to reproducing observations overall body wave qs can be reconciled with petrologic and laboratory inferences of mantle conditions if melt has a strong influence beneath arcs and back arcs

bulk flow strength of forsterite enstatite composites as a function of forsterite content creep experiments have been conducted to investigate the effect of varying forsterite content vfo on the bulk flow strength of dry forsterite enstatite fo en aggregates in order to evaluate the applicability of existing theoretical models to two phase rocks as well as to understand the rheology of polyphase systems in general the experiments were performed at temperatures of 1423 1593 k stresses of 18 100 mpa oxygen fugacities of 10 14 10 2 5 mpa and 0 1 mpa total pressure the fine grained fo 10 17 mm en 14 31 mm composites of various fo volume fractions vfo 0 0 2 0 4 0 5 0 6 0 8 and 1 were synthesized by isostatically hot pressing in a gas medium apparatus at 1523 and 350 mpa our experiments show that flow strength contrasts between fo and en are in the range of 3 8 at the given experimental conditions with fo as the stronger phase the measured stress exponent n and activation energy q values of the fo en composites fall between those of the endmembers the n values show a nearly linear increase from 1 3 to 2 0 while the q values display a non linear increase from 472 to 584 kj mol with en volume fraction from 0 to 1 0 there is no clear dependence of creep rates on oxygen fugacity for the fo en composites the mechanical data and tem microstructural observations suggest no change in deformation mechanism of each phase when in the composites compared to when in a single phase aggregate the en deformed mainly by dislocation creep while the fo deformed by dislocation accommodated diffusion creep for our grain sizes and experimental conditions comparisons between the measured composite strengths and various theoretical models indicate that none of the existing theoretical models can give a precise predication over the entire vfo range from 0 to 1 however the theoretical models based on weak phase supported structures wps yield a good prediction for the flow strengths of the composites with vfo 0 6 no model gives a good prediction for the bulk strength of two phase composites in the transitional regime vfo 0 4 0 6 applications of the wps and sps based models in the transitional regime result in under and over estimations for the composite flow strength respectively thus the effect of rock microstructure should be taken into consideration in modeling the bulk flow strengths of the crust and upper mantle using laboratory determined flow laws of single phase aggregates d 2001 elsevier science b v all rights reserved

organic matter hosted pore system in the wufeng longmaxi o3w s11 shale jiaoshiba area eastern sichuan basin china abstract the first commercial shale gas with the capability to produce 203 000 cubic meters per day were discovered in the wufeng longmaxi o 3 w s 1 l shale namely the upper ordovician wufeng shale o 3 w and the lower silurian longmaxi shale s 1 l of well jy1 jiaoshiba area eastern sichuan basin china in this study fe sem co 2 and n 2 sorption and micp were used to characterize the pore morphology type size and specific surface area of the wufeng longmaxi shale we focused our research on well jy1 to establish a standard well cross section to allow comparison with well studied gas shales such as barnett marcellus kimmeridge clay and others fe sem visible mineral pore sizes range from 4 nm to 3416 nm with an average of 118 nm within the wufeng longmaxi shale om hosted pore sizes vary from 5 nm to 1021 nm with an average of 68 nm within the wufeng longmaxi shale micropore volumes vary from 0 0048 cm 3 g to 0 0078 cm 3 g with an average of 0 0059 cm 3 g mesopore volumes range from 0 0108 cm 3 g to 0 0166 cm 3 g with an average of 0 0139 cm 3 g macropore volumes range from 0 00005 cm 3 g to 0 00274 cm 3 g with an average of 0 00108 cm 3 g and surface areas range from 22 05 m 2 g to 36 37 m 2 g with an average of 27 68 m 2 g the average pore diameters of wufeng longmaxi shales range from 5 31 nm to 7 40 nm toc has a significant effect on bulk shale porosity porosity measured by fe sem ranges from 0 46 to 1 54 but covers only a small fraction of the shale total porosity as the fe sem detection limit is in a m range the majority of shale pore space pores 2 and n 2 adsorption and have an obvious relationship with the toc therefore the wufeng longmaxi shale has a predominantly organic matter pore system

sims u pb zircon ages and ni mo pge geochemistry of the lower cambrian niutitang formation in south china constraints on ni mo pge mineralization and stratigraphic correlations abstract in comparison with previous studies on the ni mo pge ore deposits within the deep water lower cambrian black shales of the niutitang formation around hunan and guizhou provinces this study focused on the shallow water ni mo pge enriched layer of the niutitang formation around hubei province by means of an integrated geochronological pge ree and trace element geochemical study the results suggest the ni mo pge enriched layer has a dominant seawater origin whereas the ni mo pge ore deposits have mixed seawater hydrothermal and terrigenous origins trace metals precipitated from ambient seawater under anoxic suboxic settings at exceedingly slow sedimentation rates with episodic injections of fresh oxidized seawater organic matter played an important role in sourcing transporting and precipitating trace metals however decay of organic material by means of sulfate reducing reactions and or fluid reworking overprinted primary relationships with trace metal contents however the positive linear relationships are clearly shown between organic carbon and trace metal contents new sims u pb ages constrained the depositional age of the ni mo pge enriched layer to be 532 527 ma which argues against previous assumption that the anoxic event recorded in the ni mo pge took place at the ediacaran cambrian boundary furthermore new radiometric ages suggest the shuijingtuo niutitang formation could be correlated with shiyantou formation dahai and upper zhongyicun members whereas yanjiahe formation correlated with daibu and lower zhongyicun members in yunnan province respectively

anelasticity and viscosity of partially molten rock analogue toward seismic detection of small quantities of melt 1 anelasticity and diffusion creep viscosity of partially molten rock analogue were measured experimentally at various melt fractions 0 0025 0 04 the presence of even a small quantity of melt phase causes a significant increase in attenuation and dispersion and decrease in viscosity melt effect similar changes are additionally caused by the presence of a secondary solid component chemical effect the similitude that was observed in the anelasticity of melt free systems when scaled by the maxwell frequency for temperature and grain size effects was observed too in that of melt bearing systems when scaled by the maxwell frequency for melt and chemical effects the combined melt and chemical effects on anelasticity offer a potential means of identifying small quantities of melt with seismic velocity perturbations

the sinian cambrian formation shale gas exploration and practice in southern margin of huangling paleo uplift abstract the sinian doushantuo and the cambrian niutitang formations in southern china have a good shale gas resource potential although 20 wells have already been drilled in these formations the shale gas production has been much lower than expected due to the high thermal maturity of the rocks and the severely disturbed geological structure of the corresponding area an industrial gas flow was discovered only in the weiyuan region to achieve the shale gas breakthrough of paleo shale strata it is necessary to find a shale reservoir with low thermal maturity and weak geological deformation on the basis of the study on the weiyuan huangling and other paleo uplifts a shale gas accumulation mechanism named shale gas accumulating around the edges of paleo uplifts was proposed it has been suggested that the shale gas is usually contained within the slope belt of a paleo uplift margin characterized by a shallow burial depth stable structure activity and a low level of thermal maturity taking into account this accumulation mechanism a large number of wells have been drilled on the southern edge of the huangling paleo uplift western hubei province organic enriched shales with high shale gas content and low thermal maturity have been found within the sinian doushantuo and the cambrian niutitang formations to tackle the problems deriving from the low exploration level complex geological structure low temperature and low pressure in the region we proposed and applied innovative fracturing process new complex fracturing techniques and new recovering technology systems high and stable shale outputs were obtained from the niutitang formation well yangye 1hf hf horizontal well fracturing and from the doushantuo formation well yangye 2hf 7 83 10 4 and 5 53 10 4 m 3 day respectively these outputs were achieved following horizontal well section fracturing which resulted in a significant breakthrough for the production capacity of the low pressure shale gas reservoir in the complex tectonic region outside of the sichuan basin

flow behavior of fine grained synthetic dunite in the presence of 0 5 wt h2o the deformation behavior of synthetic dunite mg forsterite plus 2 5 vol enstatite with a grain size of 1 m has been investigated in combined constant displacement rate and temperature stepping experiments at temperatures of 850 to 1000 c strain rates of 10 7 to 10 5 s 1 and a confining pressure of 600 mpa nominally dry material behaved purely elastically in contrast samples with 0 5 wt added water flowed at stresses between 9 and 81 mpa reaching strains up to 12 fitting a dorn type power law to the wet data yielded stress exponents n of 1 7 0 4 and apparent activation energies in the range 302 22 kj mol 1 the wet deformed samples showed polygonal grains no crystallographic preferred orientation no subgrains low dislocation densities and evidence for grain boundary cavitation grain growth was minor it is concluded that the wet samples probably deformed by a grain size sensitive grain boundary sliding dominated mechanism though the nature of the accommodation process remains unclear and the possibility of transitional behavior between dislocation creep and diffusion creep cannot be eliminated application of the results to upper mantle shear zones supports previous speculation that the presence of such zones can lead to a significant weakening of the top 10 to 20 km of the upper mantle during extension of the continental lithosphere

variations in grain size and viscosity based on vacancy diffusion in minerals seismic tomography and geodynamically inferred mantle rheology the effect of grain size on mantle viscosity is comparable to that of temperature and pressure the current 3 d distribution of grain size in the mantle is however unknown to explore the possible variability of grain size we use the following geodynamic inferences of effective viscosity vacancy diffusion rates in upper mantle minerals and perovskite in the lower mantle lateral variations in temperature derived from seismic images and different geotherms an important outcome of this modeling is a new mapping of lateral viscosity variations throughout the mantle the corresponding 3 d variations in grain size are characterized by 2 orders of magnitude changes we find a correlation between grain size variability in the mantle and absolute viscosity changes with depth our findings suggest that the traditional assumption of arrhenius temperature dependence for vacancy diffusion in the lower mantle is not sufficient to constrain the deformation mechanisms that determine its effective bulk viscosity

pore structure characterization for the longmaxi and niutitang shales in the upper yangtze platform south china evidence from focused ion beam he ion microscopy nano computerized tomography and gas adsorption analysis abstract pore structure is of great importance in the occurrence of shale gas in this study pores in shale samples from the lower silurian longmaxi and lower cambrian niutitang shales in chongqing in the upper yangtze platform south china were examined using focused ion beam he ion microscopy fib him nano computerized tomography nano ct and gas adsorption analysis the results show that most pores in measured samples of the niutitang shale are mineral matrix pores and have poor connectivity including both intraparticle and interparticle pores organic matter pores in measured samples of the niutitang shale are rare and have small diameters in measured samples of the longmaxi shale om pores mostly macropores and large mesopores are the most abundant the nano ct results revealed that the abundance of om pores led to good pore connectivity in the longmaxi shale samples whereas the prevalence of mineral matrix pores resulted in poor connectivity in the niutitang shale samples n2 and co2 adsorption analyses showed that the mean value of micropore mesopore volumes in the niutitang and longmaxi shales samples are 0 0332 ml g and 0 0261 ml g respectively the mean values of micropores mesopores surface area in the niutitang and longmaxi shales samples are 33 84 m2 g and 32 46 m2 g respectively thus there is little difference between measured samples of the longmaxi and niutitang shales in terms of volume and surface area of micropores mesopores the equal vitrinite reflectance equal ro values of measured samples of the longmaxi shale are lower than those of the niutitang shale samples over maturity equal ro 3 resulted in a reduction of the number of pores in organic matter small pore size and poor connectivity in measured samples of the niutitang shale relatively low maturity 2

ejecta megaregolith accumulation on planetesimals and large asteroids megaregolith accumulation can have important thermal consequences for bodies that lose heat by conduction as vacuous porosity of the kind observed in the lunar megaregolith lowers thermal conductivity by a factor of 10 i have modeled global average ejecta accumulation as a function of the largest impact size with no explicit modeling of time in conjunction with an assumed cratering size distribution exponent b the largest crater constrains the sizes of all other craters that significantly contribute to a megaregolith the largest impactor mass ratio is a major fraction of the catastrophic disruption mass ratio and in general the largest crater s diameter is close to the target s diameter total accumulation is roughly 1 5 of and proportional to the target s radius global accumulations estimated by this approach are higher than in the classic housen et al 1979 study by a factor of roughly 10 this revision is caused mainly by higher typical largest crater size for b 2 the single largest crater typically contributes close to 50 of the total of new nonrecycled ejecta megaregolith can be destroyed by sintering a process whose pressure sensitivity makes it effective at lower temperature on larger bodies planetesimals 100 km in diameter may be surprisingly well suited about as well suited as bodies two to three times larger in diameter for attaining temperatures conducive to widespread melting a water rich composition may be a significant disadvantage in terms of planetesimal heating as the shallow interior may be densified by aqueous metamorphism and will have a low sintering temperature

dislocation creep of fine grained olivine 1 deformation experiments conducted in a gas medium apparatus at temperatures from 1200 to 1350 c with a fine grained solution gelation derived fe bearing olivine show a stress dependence of the strain rate at stresses above 150 mpa which is much stronger than previously reported for polycrystalline samples the data can be fit by a power law with n with n 7 8 or equally well by a peierls creep law with exponential stress dependence due to the observed strong stress dependence the samples deform at significantly higher strain rates at a given stress than single crystals or coarse grained polycrystals with n 3 5 tem observations indicate the presence of dislocations with at least two different burgers vectors with free dislocations predominantly of screw character subgrain walls are present but are only weakly developed and have small misorientation angles both the rheology and dislocation structures are consistent with creep rate limited by dislocation glide or cross slip for aggregates with grain sizes smaller than or approaching the recrystallized grain size deformation mechanism maps extrapolated to lithospheric temperatures using the melt free diffusion creep rheology of faul and jackson 2007 the dislocation creep rheology of hirth and kohlstedt 2003 and the results described here indicate that deformation conditions of ultramylonitic shear zones fall near the triple point of peierls dislocation and diffusion creep

effective shear and bulk viscosity of partially molten rock based on elastic moduli theory of a fluid filled poroelastic medium summary the effective bulk and shear viscosity of the matrix of a partially molten rock are important properties for the process of melt migration and matrix compaction a set of porosity dependent effective bulk and shear viscosity models is presented based on a self consistent poroelastic formulation for partially molten rock where the melt occurs in spherical ellipsoidal film like or tubular inclusions for these melt geometries a graphical user interface operated matlab program is provided which allows the calculation of effective bulk and shear viscosities as a function of porosity as well as effective elastic moduli and seismic velocities for all melt geometries an inverse porosity dependence of the effective bulk viscosity is found depending on the assumed melt geometry this formulation predicts both the effective bulk and shear viscosity to drop to zero at and above finite melt fractions of 20 50 per cent fitting equations are derived allowing direct implementation into two phase flow melt matrix formulations

geological controls and estimation algorithms of lacustrine shale gas adsorption capacity a case study of the triassic strata in the southeastern ordos basin china abstract high pressure methane adsorption experiments on a series of triassic lacustrine shale moisture equilibrated samples from the southeastern ordos basin china were conducted at pressure up to 20 mpa two of which were measured at 30 c 40 c 50 c 60 c and 70 c and seven were performed under reservoir temperature from 48 c to 62 c to investigate the effect of organic matter content maturity mineralogical compositions and reservoir conditions temperature and pressure on the methane sorption capacity the total organic carbon contents tocs range from 0 91 wt to 6 11 wt the thermal maturities as inferred from rock eval analysis range from low mature to high mature the minerals of the shale samples are dominated by clays 36 57 wt and quartz 19 44 wt for the entire shale samples the dominant clay minerals are mixed layer illite smectite with some illite and no smectite exists corresponding to a stage of late diagenesis the studied samples have n2 bet surface areas ranging between 1 47 and 9 21 m2 g and pore volumes of 0 013 0 034 cm3 g the methane sorption capacities of moisture equilibrated shale samples show a positive correlation with toc contents and bet surface areas no relationship was observed between the clay contents and methane sorption capacities indicating that clay minerals do not significantly contribute to methane sorption capacity in these organic shales the langmuir pressure pl increases exponentially with temperature and the langmuir volume vl decreases linearly with temperature a computational scheme has been developed to calculate the methane sorption capacity of shales as a function of toc content temperature and pressure based on langmuir sorption isotherm function using this algorithm methane sorption capacity of organic shales as function of depth can be obtained due to the predominating effect of pressure the methane sorption capacity increases with depth initially through a maximum and then decreases due to the influence of increasing temperature at a greater depth the maximum gas sorption capacity typically occurs at a depth range between 400 and 900 m with toc content increasing the maximum methane sorption capacities of organic shales and the corresponding depths increase

mantle heterogeneity and off axis volcanism on young pacific lithosphere plate tectonics and mantle plumes explain most volcanism on earth but there are numerous actively forming linear volcanic chains in the middle of tectonic plates that are not explained by these theories using the multidisciplinary geophysical dataset of the melt and glimpse experiments we show that associated with 3 volcanic chains west of the east pacific rise there are low seismic velocities and densities in the asthenosphere that extend to the east pacific rise spreading center analogous to the hawaiian swell the low density anomalies produce swells beneath the volcanoes on young seafloor the associated gravity anomalies are part of a set of gravity lineaments that have been previously interpreted as being due to thermo elastic cracking of the lithosphere or small scale convection the correlation between the surface volcanism and subsurface density and velocity anomalies and their extension to the spreading center suggest that pre existing buoyant or fertile asthenospheric mantle heterogeneities are stretched in the direction of plate motion by shear between the plate and the underlying mantle these heterogeneities seed small scale convection producing upwelling and pressure release melting forming volcanic chains that extend nearly to the ridge axis

2d and 3d nanopore characterization of gas shale in longmaxi formation based on fib sem abstract studying complex pore structures is the key to understanding the mechanism of shale gas accumulation fib sem focused ion beam scanning electron microscope is the mainstream and effective instrument for imaging nanopores in gas shales based on this technology 2d and 3d characteristics of shale samples from lower silurian longmaxi formation in southern sichuan basin were investigated 2d experimental results show that the pores in shale are nanometer sized and the structure of those nanopores can be classified into three types organic pores inorganic pores and micro fractures among the three types organic pores are dominantly developed in the om organic matter with three patterns such as continuous distributed om om between clay minerals and om between pyrite particles and the size of organic pores range from 5 nm to 200 nm inveresly inorganic pores and micro fractures are less developed in the longmaxi shales 3d digital rocks were reconstructed and segmented by 600 continuous images by fib cutting and sem imaging simultaneously the pore size distribution and porosity can be calculated by this 3d digital core showing that its average value is 32 nm and porosity is 3 62 the 3d digital porosity is higher than its helium porosity which can be regarded as one important parameter for evaluation of shale gas reserves the 2d and 3d characterized results suggest that the nanometer sized pores in organic matter take up the fundamental storage space for the longmaxi shale these characteristics have contributed to the preservation of shale gas in this complex tectonic area

seismic properties of anita bay dunite an exploratory study of the influence of water as a pilot study of the role of water in the attenuation of seismic waves in the earth s upper mantle we have performed a series of seismic frequency torsional forced oscillation experiments on a natural anita bay dunite containing accessory hydrous phases at high temperatures to 13008c and confining pressure pc o f 200 mpa within a gas medium high pressure apparatus both oven dried and pre fired specimens wrapped in ni fe foil within the poorly vented assembly were recovered essentially dry after 50 100 h of annealing at 13008c followed by slow staged cooling the results for those specimens indicate broadly similar absorptionband viscoelastic behaviour but with systematic differences in the frequency dependence of strain energy dissipation q 1 attributed to differences in the small volume fraction of silicate melt and its spatial distribution in contrast it has been demonstrated that a new assembly involving a welded pt capsule retains aqueous fluid during prolonged exposure to high temperaturescallowing the first high temperature torsional forced oscillation measurements under high aqueous fluid pore pressure pf at temperatures 410008c a marked reduction in shear modulus without concomitant increase in q 1 is attributed to the widespread wetting of grain boundaries resulting from grain scale hydrofracturing and the maintenance of conditions

geological controls on the accumulation of shale gas a case study of the early cambrian shale in the upper yangtze area abstract the results of sedimentological mineralogical geochemical and petrophysical studies on the early cambrian shale in the upper yangtze area are summarized to provide insights on the paleoenvironmental conditions diagenetic evolution and preservation conditions that give rise to shale gas accumulation the lower cambrian organic rich qiongzhusi shale is mainly developed in the outer shelf facies of an intracratonic sag average total organic carbon toc 1 3 2 5 and in the southeast margin average toc 3 5 5 5 of the upper yangtze area the thermal maturity values reqv of the qiongzhusi shale range from 2 19 to 4 23 while first increasing and then decreasing from the center of the sichuan basin outward the average porosities of the qiongzhusi shale from the outer shelf facies association fa5 in the intracratonic rift range from 1 5 to 3 41 and those from the outer shelf facies association fa4 in the southeast sichuan and guizhou areas range from 1 32 to 2 56 the organic matter om content and the development degree of om pores are the main factors that control the porosity and pore structure of the qiongzhusi shale for the outer shelf deposits in the intracratonic rift a quartz detrital origin content ranging between 25 and 35 is most favorable for providing an effective support framework for om pore development due to the mixture of brittle and clay minerals for the outer shelf deposits in the southeastern margin of the upper yangtze area the high om content and poor compaction resistance cause a poor development of om pores with a smaller average pore diameter than that in the outer shelf shale of the intracratonic rift in addition the carbonization of om in the overmature qiongzhusi shale change the microstructure and decrease the om pore volume due to poor preservation conditions the gas content is generally low in the organic rich shale in the eastern and southeastern parts of the upper yangtze region the qiongzhusi shale in the interior of the sichuan basin with good preservation conditions high pressure coefficients and high gas contents is a favorable area for shale gas accumulation and potential exploitation

shear wave attenuation and dispersion in melt bearing olivine polycrystals 2 microstructural interpretation and seismological implications 1 the torsional forced oscillation tests of melt bearing olivine aggregates reported by jackson et al 2004 consistently show a peak in attenuation that is absent from melt free aggregates tested under similar conditions and grain sizes characterization by sem shows that the melt resides in triple junction tubules and larger pockets as previously described tem imaging and eds analysis reveals that olivine olivine grain boundaries are characterized by a region 1 nm wide which is structurally and chemically distinct from olivine grain interiors from the possible mechanisms that can produce an anelastic attenuation peak melt squirt can be eliminated for our samples and experimental conditions we attribute the observed attenuation peak to elastically accommodated grain boundary sliding requiring that the grain boundaries are weak relative to olivine grain interiors but have a significantly higher viscosity than bulk melt while the nanometer scale grain boundary structure in the melt bearing aggregates is essentially the same as for melt free aggregates studied previously elastically accommodated sliding in the latter is apparently inhibited by tight three grain edge intersections the exponentially increasing high temperature background attenuation in both types of aggregate is attributed to diffusionally accommodated grain boundary sliding extrapolation to mantle grain sizes shows that the broad peak may be responsible for nearly frequency independent attenuation in partially molten regions of the upper mantle

infrasonic monitoring at stromboli volcano during the 2003 effusive eruption insights on the explosive and degassing process of an open conduit system 1 stromboli is an open conduit volcano characterized by persistent conduit degassing and explosive dynamics during the 2003 effusive eruption we monitored this activity with a five element array deployed at 450 m from the active craters the array allows us to track in real time changes of explosive activity in terms of source position and excess pressure release infrasonic monitoring located the new active vents in the same preeruptive position revealing that the collapse of the crater terrace has not changed the geometry of the shallow feeding system elevation of the infrasonic source is stable at 750 m above sea level coincident with the elevation of the crater terrace this suggests a shallow position of the magma column or if the source is embedded in the conduit diffraction at the crater rim at the end of the eruption back azimuth analysis indicates that explosive activity was progressively reestablished at all of the craters following a ne toward sw direction along the collapsed trench the array detected significant small amplitude 1 pa infrasonic activity occurring at a rate of approximately one pulse every 2 s and generally located in only one vent at a time this persistent activity is not related to strombolian explosion but we infer it is reflecting the overpressurized degassing of the magma column amplitude distribution of 7 million infrasonic signals shows that this degassing is 1 order of magnitude more energetic than the explosions besides infrasonic amplitude distribution presents a decay with a double slope indicating that explosions and degassing are driven by conduit dynamics acting at two different rates

source and seal coupling mechanism for shale gas enrichment in upper ordovician wufeng formation lower silurian longmaxi formation in sichuan basin and its periphery abstract in recent years theoretical geologic research has made important progress in shale gas exploration and development and new discoveries such as the jiaoshiba weiyuan and changning shale gas fields provide geological cases to define key controls on shale gas accumulation in wufeng formation longmaxi formation marine shale strata a mechanism coupling source and seal development for shale gas enrichment is proposed in this study based on detailed research results of isochronous stratigraphic distribution of source rock and seals and source seal dynamic evolution great thickness wide distribution and high total organic carbon content toc of sources are key controls on the shale gas content and storage capacity in organic matter hosted pores micro cracks and bedding fissures is intensively developed the wufeng formation and the lower part of the first member of the longmaxi formation wf2 lm4 graptolitic zone are favorable sources that feature a slow deposition rate well graptolitic zone favorable organic organism type and high toc the organic matter type is benefit to the development of organic matter pores because the planktonic algae tends to generate and expulse large amounts of hydrocarbon and form many organic matter pores both high biogenic quartz and high toc ensure development of abundant organic matter hosted pores and result in a three dimensional network of interconnected organic matter pores that allows shale gas storage and flow the seal can be divided into direct and indirect seals the direct seal refers to the middle and upper parts of the first member of the longmaxi formation lm5 and higher graptolitic zone that are characterized by low toc and low porosity the indirect seal refers to the regionally distributed lower middle triassic gypsum layer s and mudstone that maintain regional geopressure systems the shale gas fields of jiaoshiba fushun yongchuan and changning have high geopressure coefficient factors 1 5 2 0 and 1 5 respectively in the absence of the lower middle triassic gypsum layer s and mudstone regional seals the high pressure system was destroyed and resulted in low normal geopressure shale gas reservoirs for instance the pengshui and zhaotong wells the static match and dynamic match of source and seal constrain the location of shale gas reservoirs and the degree of shale gas enrichment the model of a mechanism coupling source and seal for shale gas enrichment provides new ideas and methods for the assessment of shale gas this model promotes the evaluation of shale gas from the static parameters approach to the source and seal dynamic approach in the sichuan basin and its peripheral areas the promising areas for shale gas accumulation are those with favorable sources in the wf2 lm4 graptolitic zone and the presence of the lower middle triassic gypsum layer s and mudstone regional seal

complex rotation of maximum horizontal stress in the wufeng longmaxi shale on the eastern margin of the sichuan basin china implications for predicting natural fractures abstract the in situ stress state of the eastern margin of the sichuan basin where there is a complicated fault zone is poorly understood this study offers vital insights into the in situ stress state based on information from 17 wellbores in the wufeng longmaxi shale near the eastern boundary fault i e the qiyueshan fault of the sichuan basin china drilling induced tensile fractures and borehole breakouts revealed a decrease in the angle between the shmax maximum horizontal stress orientation and fault strike when the wellbores are close to the damage zone of the qiyueshan fault this stress rotation may be caused by the lateral contrast in the poisson s ratio between the country rock and damage zone of the qiyueshan fault a high angle between the shmax orientation and fault strike also appeared in the individual fault blocks of the qiyueshan fault as a result of local stress concentration the higher magnitudes of horizontal stresses indicate stronger lateral compression in the qiyueshan fault zone owing to the lateral compression of a sandwich consisting of a high e young s modulus roof and low e shale intervals natural fractures mainly appeared in the low e shale intervals when the wellbore was close to the fault damage zone the low fracture intensity in the low e shale intervals of the wellbores located at the boundaries of the stress concentration blocks may be associated with an extensional stepover process

influence of mineral fraction on the rheological properties of forsterite enstatite during grain size sensitive creep 2 deformation experiments 1 in order to understand the effects of secondary minerals on the flow properties of rocks we have conducted uniaxial compression experiments on polycrystalline forsterite fo enstatite en samples at constant temperature and strain rate the flow stress of the samples decreases with increasing enstatite volume fraction fen for samples with 0 fen 0 5 and increases with increasing fen for samples with 0 5 fen 1 the values of the preexponential term stress and grain size exponents and activation energy in the constitutive equation for a wide range of fen were determined samples with a low fen 0 03 deformed at strain rates of 2 10 5 to 2 10 4 s exhibit creep characteristics that correspond to dislocation accommodated grain boundary sliding creep i e stress exponent n 3 whereas diffusion accommodated grain boundary sliding creep is typical of high fen samples i e stress exponent n 1 the change of flow strength as a function of fen during grain size sensitive creep is primarily due to changes in grain size of both phases and secondarily due to changes in the volume fraction of phases with different flow strengths viscosities of all samples can be reproduced in a viscosity model that takes into account 1 the grain sizes estimated by the grain growth laws established in our part 1 paper and 2 flow laws determined for the individual phases in this case forsterite and enstatite furthermore we demonstrate that our model can be extended to make predictions of viscosity in other mineral assemblages

evidence for low viscosity garnet rich layers in the upper mantle abstract the rheological properties of upper mantle rocks play an important role in controlling the dynamics of the lithosphere and mantle convection experimental studies and microstructures in naturally deformed mantle rocks usually imply that olivine controls the upper mantle rheology here we show for the first time evidence from the geometry of folded compositional layers in mantle rocks from western norway that garnet rich rocks can have lower solid state viscosities than olivine rich rocks modeling of melt free and dry rheology of garnet and olivine confirms that the reversed viscosity contrast between garnet rich and olivine rich layers for this folding event can be achieved over a relatively wide range of temperatures at low stress conditions when the fine grained garnet deforms by diffusion creep while the coarse grained olivine deforms by dislocation creep and or diffusion creep in general modeling of the fold viscosity contrast shows that in the stable subcontinental lithospheric mantle or convecting mantle such a reversed viscosity contrast can be formed due to diffusion creep processes in fine grained garnets in a dry mantle environment or at conditions where the garnet pyroxene layer is partially molten i e close to solidus liquidus conditions in the upper mantle alternatively in cold plate tectonic settings e g in subduction zones some water weakening is a feasible mechanism to create the reversed viscosity contrast between garnet and olivine

anelasticity from seismic to tidal timescales theory and observations abstract we examine strain energy dissipation of earth s normal modes and body tides in order to compare these observations with predictions from an experimental model of intrinsic dissipation for this comparison we employ a recently developed self consistent treatment of modes and tides that includes the separation of dynamical processes self gravity and inertia from intrinsic attenuation we select a set of normal modes and tides with similar depth sampling centered on the lower mantle without contributions from the core this dataset ranges from 7 min to 18 6 yr or about 6 decades in frequency the results show that the attenuation of the higher frequency modes defines a broad plateau in dissipation inferred experimentally to occur at the transition from elastic to anelastic behavior whereas the attenuation of lower frequency tides falls on a frequency dependent absorption band this reconciles published seemingly contradictory models of dissipation for modes versus tides the absorption band for modes terminates at periods where tidal models infer its onset microphysically the experimental data can be explained by elastically accommodated grain boundary sliding producing a broad plateau at short periods transitioning to diffusionally assisted grain boundary sliding at longer periods corresponding to an absorption band extrapolation of the fit to the experimental data with parameters adopted for the lower mantle can reconcile the seismological and geodetic observations

deformation of peridotite at high pressure in a new molten salt cell comparison of traditional and homologous temperature treatments abstract we have conducted a series of constant strain rate experiments on a synthetic peridotite composed of isostatically hot pressed olivine and orthopyroxene over a pressure range of 700 2200 mpa and a temperature range of 1250 1700 k by using a sample assembly in which specimens are surrounded by molten salt the data are of much higher quality than previously obtained in solid pressure medium apparatus we find that both the temperature and pressure dependence of creep in our experiments can be combined quantitatively as the homologous temperature dependence of creep this quantitative relationship between creep and melting greatly simplifies the thermodynamic treatment of creep and provides a simple model for the extrapolation of laboratory creep data for peridotite to conditions throughout the earth s upper mantle

key reservoir parameter for effective exploration and development of high over matured marine shales a case study from the cambrian niutitang formation and the silurian longmaxi formation south china abstract success has been achieved in the exploration and development of marine shales of the lower silurian longmaxi formation in southern china but there has been almost no commercial shale gas produced from the lower cambrian niutitang formation in much of the same area breakthroughs have been made with shale gas in the niutitang formation in yichang city south china by the china geological survey cgs how to evaluate and exploit the niutitang shale more quickly accurately and efficiently remains a major question this paper proposed that the key reservoir parameter for effective exploration and development of marine shales is based on the thermal maturity shale samples from chongqing city of both the longmaxi formation and the niutitang formation were selected for the analysis of total organic carbon toc content mineral composition and equivalent vitrinite reflectance eq ro as well as for the characterization of organic matter pores om pores using focused ion beam scanning electron microscopy fib sem selected shale samples from yichang city of the niutitang formation were also studied for comparison results show that shale samples from chongqing present a large number of om pores in the longmaxi formation but almost no om pores in the niutitang formation while shale samples from yichang present a large number of om pores in the niutitang formation commercial gas has been produced from shale reservoirs with abundant om pores such as the longmaxi shale in chongqing and the niutitang shale in yichang by contrast there is no gas production from shale reservoirs with no om pores as is the case for the niutitang shale in chongqing thus om pores is an indicator for the evaluation of marine shale gas potential because these shales have similar toc content mineral composition and kerogen type but different thermal maturity om porosity is mainly controlled by the thermal maturity and the key geological parameter for shale reservoir potential is thus a suitable thermal maturity marine shale reservoirs favorable for gas production generally have an eq ro ranging from 2 0 to 3 0 which is mainly controlled by ancient burial depth of reservoirs this means exploration and development of highly over matured marine shales should be focused on less buried areas such as the edge of paleo uplift

melting induced crustal production helps plate tectonics on earth like planets abstract within our solar system earth is the only planet to be in a mobile lid regime it is generally accepted that the other terrestrial planets are currently in a stagnant lid regime with the possible exception of venus that may be in an episodic lid regime in this study we use numerical simulations to address the question of whether melting induced crustal production changes the critical yield stress needed to obtain mobile lid behaviour plate tectonics our results show that melting induced crustal production strongly influences plate tectonics on earth like planets by strongly enhancing the mobility of the lid replacing a stagnant lid with an episodic lid or greatly extending the time in which a smoothly evolving mobile lid is present in a planet finally we show that our results are consistent with analytically predicted critical yield stress obtained with boundary layer theory whether melting induced crustal production is considered or not

constraints on the anisotropic contributions to velocity discontinuities at 60 km depth beneath the pacific strong sharp negative seismic discontinuities velocity decreases with depth are observed beneath the pacific seafloor at 60 km depth it has been suggested that these are caused by an increase in radial anisotropy with depth which occurs in global surface wave models here we test this hypothesis in two ways we evaluate whether an increase in surface wave radial anisotropy with depth is robust with synthetic resolution tests we do this by fitting an example surface wave data set near the east pacific rise we also estimate the apparent isotropic seismic velocity discontinuities that could be caused by changes in radial anisotropy in s to p and p to s receiver functions and ss precursors using synthetic seismograms we test one model where radial anisotropy is caused by olivine alignment and one model where it is caused by compositional layering the result of our surface wave inversion suggests strong shallow azimuthal anisotropy beneath 0 10 ma seafloor which would also have a radial anisotropy signature an increase in radial anisotropy with depth at 60 km depth is not well resolved in surface wave models and could be artificially observed shallow isotropy underlain by strong radial anisotropy could explain moderate apparent velocity drops 6 in ss precursor imaging but not receiver functions the effect is diminished if strong anisotropy also exists at 0 60 km depth as suggested by surface waves overall an increase in radial anisotropy with depth may not exist at 60 km beneath the oceans and does not explain the scattered wave observations

grain size sensitive seismic wave attenuation in polycrystalline olivine 1 in order to investigate the processes responsible for the attenuation of seismic shear waves in the earth s upper mantle four olivine polycrystals ranging in mean grain size d from 3 to 23 m have been fabricated characterized and mechanically tested in torsion at high temperatures and seismic frequencies both the shear modulus which governs the shear wave speed vs and the dissipation of shear strain energy q 1 have been measured as functions of oscillation period to temperature t and for the first time grain size at sufficiently high t all four specimens display similar absorption band viscoelastic behavior adequately represented for 1000 t 1200 or 1300 c and 1 to 100 s by the expression q 1 a tod 1 exp e rt with a 7 5 102 s m 0 26 and e 424 kj mol 1 this mildly grain size sensitive viscoelastic behavior of melt free polycrystalline olivine is attributed to a combination of elastically and diffusionally accommodated grain boundary sliding the latter becoming progressively more important with increasing t and or to extrapolation to the larger mm cm grain sizes expected in the earth s upper mantle yields levels of dissipation comparable with those observed seismologically implying that the same grain size sensitive processes might be responsible for much of the observed seismic wave attenuation the temperature sensitivity of vs is increased substantially by the viscoelastic relaxation allowing the lateral variability of wave speeds to be associated with relatively small temperature perturbations

the role of water in the deformation of dunite specimens of two natural dunites anita bay of 100 m grain size and aheirn of 900 m grain size have been deformed in experiments at temperatures between 1200 and 1400 c and constant strain rates between 10 4 and 10 6 s 1 in a gas medium deformation apparatus at 300 mpa confining pressure prior to these experiments the specimens were given a heat treatment in a controlled oxygen fugacity furnace at 1200 c for 60 hours to dehydrate the trace layer silicate minerals present and drive off adsorbed water the predried specimens are much stronger than specimens tested under wet conditions in an earlier study the predried specimens also do not show the apparent grain size dependence seen under wet conditions infrared absorption measurements on the present specimens and those of the earlier study indicate that for a given rock flow stress can be correlated with the intensity of a residual water related broad absorption the addition of water to a predried specimen results in both a mechanical reweakening and an intensifying of the broadband infrared component the weakening of the dunites under wet conditions is probably strongly influenced by the presence of small amounts of a water related species in the grain boundaries but intragranular weakening may also be contributing it is suggested that the concentration of the water related species in the grain boundaries is governed by its concentration in the small melt fraction present the amounts of water that have been found to be of importance for the strength of these dunites are of the order of 0 01 wt amounts much less than most estimates of the water content of the earth s undepleted upper mantle such water may have an important role in determining upper mantle flow behavior stress strain curves for all experiments are available with entire manuscript on microfiche order from american geophysical union 2000 florida avenue n w washington dc 20009 document b84 008 2 50 payment must accompany order

morphology genesis and distribution of nanometer scale pores in siliceous mudstones of the mississippian barnett shale research on mudrock attributes has increased dramatically since shale gas systems have become commercial hydrocarbon production targets one of the most significant research questions now being asked focuses on the nature of the pore system in these mudrocks our work on siliceous mudstones from the mississippian barnett shale of the fort worth basin texas shows that the pores in these rocks are dominantly nanometer in scale nanopores we used scanning electron microscopy to characterize barnett pores from a number of cores and have imaged pores as small as 5 nm key to our success in imaging these nanopores is the use of ar ion beam milling this methodology provides flat surfaces that lack topography related to differential hardness and are fundamental for high magnification imaging nanopores are observed in three main modes of occurrence most pores are found in grains of organic matter as intraparticle pores many of these grains contain hundreds of pores intraparticle organic nanopores most commonly have irregular bubblelike elliptical cross sections and range between 5 and 750 nm with the median nanopore size for all grains being approximately 100 nm internal porosities of up to 20 2 have been measured for whole grains of organic matter based on point count data from scanning electron microscopy analysis these nanopores in the organic matter are the predominant pore type in the barnett mudstones and they are related to thermal maturation nanopores are also found in bedding parallel wispy organic rich laminae as intraparticle pores in organic grains and as interparticle pores between organic matter but this mode is not common although less abundant nanopores are also locally present in fine grained matrix areas unassociated with organic matter and as nano to microintercrystalline pores in pyrite framboids intraparticle organic nanopores and pyrite framboid intercrystalline pores contribute to gas storage in barnett mudstones we postulate that permeability pathways within the barnett mudstones are along bedding parallel layers of organic matter or a mesh network of organic matter flakes because this material contains the most pores

evolution of a polymineralic mantle shear zone and the role of second phases in the localization of deformation 1 the influence of second phases e g pyroxenes on olivine grain size was studied by quantitative microfabric analyses of samples of the hilti massif mantle shear zone semail ophiolite oman the microstructures range from porphyroclastic tectonites to ultramylonites from outside to the center of the shear zone starting at conditions of ridge related flow they formed under continuous cooling leading to progressive strain localization the dependence of the average olivine grain size on the second phase content can be split into a second phase controlled and a dynamic recrystallization controlled field in the former the olivine grain size is related to the ratio between the second phase grain size and volume fraction zener parameter in the latter dynamic recrystallization manifested by a balance between grain growth and grain size reduction processes yields a stable olivine grain size in both fields the average olivine and second phase grain size decreases with decreasing temperature combining the microstructural information with deformation mechanism maps suggests that the porphyroclastic tectonites 1100 c and mylonites 800 c formed under the predominance of dislocation creep since olivine rich layers are intercalated with layer parallel polymineralic bands in the mylonites nearly equiviscous conditions can be assumed in the ultramylonites diffusion creep represents the major deformation mechanism in the polymineralic layers it is this switch in deformation mechanism from dislocation creep to diffusion creep that forces strain to localize in the fine grained polymineralic domains at low temperatures 700 c underlining the role of the second phases on strain localization in cooling mantle rocks

crystallographic preferred orientation produced by diffusional creep of harzburgite effects of chemical interactions among phases during plastic flow 1 experimental deformation experiments have been conducted on fine grained two phase aggregates of olivine and orthopyroxene to investigate the role of grain and phase boundary sliding on rheology and fabric development a suite of large strain 1 general shear experiments conducted at t 1200 c and p 1 6 gpa on aggregates ranging from 65 to 0 vol orthopyroxene to characterize the evolution of fabric were complemented by small strain axial compression experiments at t 1200 c and p 0 3 gpa to better constrain the rheology microstructural and rheological data suggest that deformation of these two phase aggregates in the diffusion creep regime occurs via interface reaction controlled diffusion creep that is accompanied by extensive migration of olivine orthopyroxene phase boundaries the resulting rheologies suggest that olivine orthopyroxene composites are weaker than the olivine end member at the conditions tested physically this behavior arises because long range i e grain scale diffusion of si4 is unnecessary in these pseudobinary two phase aggregates we further demonstrate that interface controlled diffusion creep leads to strong crystallographic preferred orientations cpo of the component minerals which develops in the near absence of dislocation activity the cpo formed in these anhydrous low stress experiments has the olivine a axis aligned perpendicular to the flow direction type b fabric argued by some to be the unique result of deformation under conditions of high differential stress and high water fugacity phase boundary dynamics thus are argued as a significant factor in the accumulation of strain in polyphase aggregates

silicon diffusion in forsterite aggregates implications for diffusion accommodated creep silicon diffusion rates were determined in fine grained 4 5 m hot pressed forsterite aggregates at 900 to 1200 c and 0 1 mpa using a 30si tracer and standard sims analysis there is no measurable difference in diffusion rates between samples buffered by excess mgo or sio2 nor samples run in dry n2 or h2 co2 the results yield the arrhenius parameters d0 bulk 5 4 10 9 m sec and q 203 36 kj mol at 1200 c the grain boundary diffusion rate of 30si is similar to 26mg si 10 times greater 10 less than fe and 105 less than o in addition the 30si grain boundary diffusion rate is 109 greater than the si volume diffusion rate and indicates that diffusional transport of si in forsterite aggregates is dominated by grain boundaries

rheology of fine grained forsterite aggregate at deep upper mantle conditions high pressure and high temperature deformation experiments on fine grained synthetic dunite forsterite aggregate were conducted to determine the dominant deformation mechanism in the deep upper mantle the sintered starting material has 90 forsterite 10 enstatite and an average grain size of 1 m deformation experiments were performed using a deformation dia apparatus at pressures of 3 03 5 36 gpa temperatures of 1473 1573 k and uniaxial strain rates of 0 91 10 5 to 18 6 10 5 s 1 at dry circumstances 50 h 106si the steady state flow stress was determined at each deformation condition derived stress strain rate data is analyzed together with that reported from similar but low pressure deformation experiments using flow law equations for diffusion creep stress exponent of n 1 grain size exponent of p 2 and for dislocation accommodated grain boundary sliding gbs disl n 3 p 1 the activation volume for diffusion creep v dif and for gbs disl v gbs of dunite is determined to be 8 2 0 9 and 7 5 1 0 cm3 mol respectively calculations based on these results suggest that both diffusion creep and dislocation creep play an important role for material flow at typical deformation conditions in the earth s asthenospheric upper mantle whereas the contribution of gbs disl is very limited and dislocation creep is the dominant deformation mechanism during the deformation of olivine in sheared peridotite xenolith though these conclusions are not definitive these are the first results on potential deformation mechanisms of forsterite aggregate based on extrapolation in the pressure temperature stress and grain size space