origin of the island arc moho transition zone via melt rock reaction and its implications for intracrustal differentiation of island arcs evidence from the jijal complex kohistan complex northern pakistan if the net fl ux to the island arc crust is primitive arc basalt the evolved composition of most arc magmas entails the formation of complementary thick ultramafi c keels at the root of the island arc crust dunite wehrlite and cr rich pyroxenite from the jijal complex constituting the moho transition zone of the kohistan paleo island arc northern pakistan are often mentioned as an example of high pressure cumulates formed by intracrustal fractionation of mantle derived melts which were later extracted to form the overlying mafi c crust here we show that calculated liquids for jijal pyroxenites wehrlites are strongly rare earth element ree depleted and display fl at or convex upward ree patterns these patterns are typical of boninites and are therefore unlike those of the overlying mafi c crust that have higher ree concentrations and are derived from light rare earth element lree enriched melts similar to island arc basalt this observation along with the lower 208 pb 204 pb and 206 pb 204 pb ratios of jijal pyroxenites wehrlites relative to gabbros rejects the hypothesis that gabbros and ultramafi c rocks derive from a common melt via crystal fractionation in the 208 pb 204 pb versus 206 pb 204 pb diagram ultramafi c rocks and gabbros lie on the same positive correlation suggesting that their sources share a common enriched mantle 2 em2 signature but with a major depleted component contribution for the ultramafi c rocks these data are consistent with a scenario whereby the jijal ultramafi c section represents a moho transition zone formed via melt rock reaction between subarc mantle and incoming melt isotopically akin to jijal gabbroic rocks the lack in the kohistan arc of cogenetic ultramafi c cumulates complementary to the evolved mafi c plutonic rocks implies either 1 that a substantial volume of such ultramafi c cumulates was delaminated or torn out by subcrustal mantle fl ow from the base of the arc crust in extraordinarily short time scales 0 10 0 35 cm yr or 2 that the net fl ux to the kohistan arc crust was more evolved than primitive arc basalt

petroleum potential and kinetic models for hydrocarbon generation from the upper cretaceous to paleogene latrobe group coals and shales in the gippsland basin australia abstract pyrolysis experiments open and closed systems and kinetic modelling of primary cracking of kerogen have been carried out to investigate hydrocarbon generation characteristics and source rock facies variability within the upper cretaceous to paleogene latrobe group in the gippsland basin on the basis of rock eval data the interbedded coals coaly shales and carbonaceous shales contain different types of kerogen type iii type ii iii type ii with variable potential for both gas and liquid hydrocarbon generation open system pyrolysis gas chromatography data indicate that the organically lean marginal marine shales of the santonian early campanian tricolporites apoxyexinus and nothofagidites senectus biozones produce gas and condensate however coal and coaly to carbonaceous shales sampled from the paleocene lygistepollenites balmei maastrichtian forcipites longus late campanian tricolporites lilliei and turonian phyllocladidites mawsonii palynological biozones are heterogeneous with the capacity to generate both low and high wax paraffinic naphthenic aromatic p n a oils and paraffinic oils with a high wax content the main phase of petroleum formation from these later biozones assuming a constant geological heating rate of 3 3 c ma is predicted to occur between 150 179 c indicating different orders of kinetic stability as a result of different types of organic matter and their state of preservation the thermally immature shales have variable bulk kinetic characteristics but the measured compositional kinetics and phase behaviour show that they have the potential to generate black oils at early stages of kerogen cracking and either light oils or wet gases at higher levels of thermal stress these findings suggest that upon thermal maturation the interbedded shales of the latrobe group may have contributed significant volumes of hydrocarbons to the oil and gas accumulations in the gippsland basin in addition this study not only supports the premise that over reliance on rock eval toc data alone can be misleading for assessment of petroleum generation but also represents a strategy for kerogen type and generative potential determination for fluvio deltaic coals and subordinate lithologies

the chlorine isotopic composition of martian meteorites 1 chlorine isotope composition of martian mantle and crustal reservoirs and their interactions the martian meteorites record a wide diversity of environments processes and ages much work has been done to decipher potential mantle sources for martian magmas and their interactions with crustal and surface environments chlorine isotopes provide a unique opportunity to assess interactions between martian mantle derived magmas and the crust we have measured the cl isotopic composition of 17 samples that span the range of known ages martian environments and mantle reservoirs the 37cl of the martian mantle as represented by the olivine phyric shergottites nwa 2737 chassignite and shergotty basaltic shergottite has a low value of approximately 3 8 this value is lower than that of all other planetary bodies measured thus far the martian crust as represented by regolith breccia nwa 7034 is variably enriched in the heavy isotope of cl this enrichment is reflective of preferential loss of 35cl to space most basaltic shergottites less shergotty nakhlites chassigny and allan hills 84001 lie on a continuum between the martian mantle and crust this intermediate range is explained by mechanical mixing through impact fluid interaction and assimilation fractional crystallization

shear wave properties and poisson s ratios of ultrahigh pressure metamorphic rocks from the dabie sulu orogenic belt china implications for crustal composition 1 shear wave velocities vs anisotropy and shear wave splitting have been measured at pressures up to 600 800 mpa for ultrahigh pressure uhp metamorphic rocks from the dabie sulu orogenic belt china with a focus on three types of eclogites type 1 eclogites are coarse grained unaltered samples showing high densities and high vs values 4 85 0 06 km s at 600 mpa type 2 eclogites are fine grained sheared samples with intermediate vs values 4 53 0 04 km s at 600 mpa and type 3 eclogites are overprinted by amphibolite facies metamorphism and display low vs values 4 33 0 09 km s at 600 mpa the compositional layering and retrograde metamorphism can result in significant anisotropy and shear wave splitting in eclogites suggesting their plausible contribution to seismic anisotropy in the lower crust upper mantle and particularly in subducted slabs integrating our p and s wave velocity results with reliable data from previous studies we estimated the pressure and temperature derivatives of vp vs and poisson s ratios for common rock types in the uhp metamorphic belt the geometric means were used as a mixture rule to invert the lithological and chemical compositions of the layered crust from seismic refraction velocities the inferred crustal composition suggests that the eclogite bearing uhp rocks are tectonic slices of crust that have been thrust along a series of shear zones during the continental collision between the north china and yangtze cratons over a normal uhp free middle lower crust with overall intermediate composition

structure of an island arc wide angle seismic studies in the eastern aleutian islands alaska new seismic wide angle data from the eastern aleutian islands show a mafic composition and a 30 km thick island arc crust traveltimes of p and s refracted arrivals and prominent crustal and mantle reflectors observed to offsets of over 300 km were used to derive velocity models for the eastern aleutian arc between the islands of atka and unimak using a three dimensional finite difference modeling and tomography code we interpret the highest crustal p wave velocities of 7 2 7 4 km s between about 12 and about 22 km depth to the south and north of the main volcanic line as remainders of preexisting oceanic crust into which arc magma is intruded apart from the pieces of oceanic crust the velocities suggest an overall mafic composition for the arc composed mainly of metabasalts diorite and diabase in the upper crust and garnet granulite or amphibolite to hornblendite in the lower crust reflected arrivals from the subducting pacific plate at depths of 45 55 km beneath the fore arc together with pn show a mantle wedge with p wave velocities as low as 7 4 km s increasing with depth to about 8 1 km s with an average of about 7 7 km s a mantle composition that grades from mainly pyroxenite probably ultramafic cumulates near the moho to dunite at greater depths best explains these observed velocities

high temperature and pressure seismic properties of a lower crustal prograde shear zone from the kohistan arc pakistan anastomosing shear zones exposed in the lower crust of the kohistan palaeoisland arc in pakistan have parageneses indicating increasing pressure during deformation therefore they represent a rare example of strain localization during crustal thickening we investigated the seismic properties of a sheared gabbro with constant bulk chemistry across one of these shear zones the compressional wave velocity was measured at confining pressures of up to 0 5 gpa and temperatures of up to 600 8c the density the average vp compressional p wave velocity and the acoustic impedance at room temperature increase from the undeformed protolith through the strain gradient to the intensely sheared mylonite the seismic anisotropy is largest for the strain gradient the vp dependence of the velocities on temperature is much higher in the mylonite than in the protolith the acoustic impedance contrast between protolith and mylonite is high enough to generate seismic reflections at low temperatures but not at high temperatures this suggests that the seismic reflectivity may also depend on the temperature consequently ductile shear zones can be detected in reflection profiles of crusts with low geothermal gradients and may be transparent in crusts with high geothermal gradients

multiple cold trap pyrolysis gas chromatography a new technique for modeling hydrocarbon generation abstract the newly developed multiple cold trap pyrolysis gas chromatography mctp gc technique allows us to calculate activation energies for the generation of individual hydrocarbons from source rocks this improves our ability to predict the timing of oil generation and the compositional changes of oil at the different stages of kerogen conversion the activation energies for n c 12 and n c 24 for a type ii kerogen toarcian shale are 57 5 0 8 kcal mol and 51 2 2 2 kcal mol with frequency factors of 8 71 10 16 min and 1 15 10 15 min respectively the relative rates of alkane generation are n c 24 n c 18 n c 12 n c 2 c 5 by comparing the rates of generation from kerogen and asphaltenes for monterey source rocks we conclude that normal alkanes can be generated directly without going through an asphaltene intermediate

a re evaluation of the stratigraphy and evolution of the kohistan arc sequence pakistan himalaya implications for magmatic and tectonic arc building processes new field mapping and structural data combined with published geochemical data from the kohistan arc in the nw himalaya enable a re evaluation of the arc stratigraphy key lithological units and their relationships are more clearly defined permitting the construction of a revised magmatic tectonic history for the arc the oldest units are transitional oceanic type basalts which form the basement to the subduction related sequence arc type gabbroic sheets and plutons intrude the oceanic basalts together these form the kamila amphibolite belt metasediments and basaltic lavas were deposited within an extensional basin onto the kamila amphibolite belt basement this sequence exposed across the arc forms a distinct stratigraphic unit which is formally defined here as the jaglot group sediment charged turbidity currents transported material into the basin whilst submarine eruptions contributed the basaltic component this period of extension culminated in the eruption of high mg boninites of the chalt volcanic group which overlie the rocks of the jaglot group the earliest granitoids of the kohistan batholith predate suturing and intrude the jaglot and chalt sequences at c 100 ma kohistan sutured to asia suturing being accompanied by thickening of the arc with the development of major intra arc shear zones and a penetrative regionally developed steep cleavage at c 85 ma intra arc rifting permitted the emplacement into the arc of the voluminous gabbronorites of the chilas complex which clearly intrudes the kamila amphibolite belt to the south and the jaglot group to the north the chilas complex has been regarded as part of the pre suturing juvenile arc sequence field evidence summarized here show this to be not so heat advection associated with emplacement of the complex caused amphibolite facies regional metamorphism melting of the lower arc and plutonism some of the resultant granitoid plutons were unroofed and eroded during a compressional phase at between 80 and 55 ma before emplacement of further plutons and extrusion of basaltic through to rhyolitic volcanic rocks at between 55 and 40 ma at least three phases of extension and rifting each separated by short lived phases of compression charac terized arc evolution much of the magmatism is controlled by extensional tectonics within the overriding plate of the kind commonly associated with a retreating subduction zone

guidelines for assessing the petroleum potential of coaly source rocks using rock eval pyrolysis abstract coaly source rocks are sufficiently different from marine and lacustrine source rocks in their organic matter characteristics to warrant separate guidelines for their assessment using rock eval pyrolysis the rank threshold for oil generation is indicated by the increase in bi s1 toc at rank sr 9 10 tmax 420 430 c ro 0 55 0 6 and the threshold for oil expulsion is indicated by the peak in qi s1 s2 toc at rank sr 11 12 5 tmax 430 440 c ro 0 65 0 85 the pronounced rank related increase in hi s2 toc prior to oil expulsion renders the use of immature samples inappropriate for source rock characterisation a more realistic indication of the petroleum generative potential and oil expulsion efficiency of coaly source rocks can be gained from samples near the onset of expulsion alternatively effective hi values i e his near the onset of expulsion can be estimated by translating the measured his of immature samples along the maturation pathway defined by the new zealand or other defined coal band coaly source rocks comprise a continuum of coaly lithologies including coals shaly coals and coaly mudstones determination of the total genetic potential of coaly source rock sequences is best made using lithology based samples near the onset of expulsion

eclogite facies shear zones deep crustal reflectors strongly foliated eclogite facies rocks in 30 150 m thick shear zones of caledonian age occur within a grenvillian garnet granulite facies gabbro anorthosite terrain in the bergen arcs of norway the predominant eclogite facies mineral assemblages in the shear zones are omphacite garnet zoisite kyanite in gabbroic anorthosite and omphacite garnet in gabbro eclogite facies rocks in shear zones are generally fine grained alternating omphacite garnet and kyanite clinozoisite rich layers define gneissic layering a strong shape preferred orientation of omphacite kyanite and white mica phengitic muscovite and or paragonite define the foliation the anorthositic eclogites show omphacite b axis maxima approximately normal to the foliation and c axis girdles within the foliation plane p wave velocities v determined at confining pressures to 600 mpa for samples from eciogite facies shear zones range from 8 3 to 8 5 km s l and anisotropy ranges from 1 to 7 the few samples with more pronounced anisotropy tend to be approximately transversely isotropic with minimum velocities for propagation directions normal to foliation and maximum velocities for propagation directions parallel to foliation the fast propagation direction lies within the c axis girdles parallel to foliation and the slow propagation direction is parallel to the b axis concentration normal to foliation in samples for which omphacite crystallographic preferred orientation was determined v for the granulite facies protoliths average about 7 5 km s high calculated reflection coefficients for these shear zones 0 04 0 14 indicate that they are excellent candidates for deep crustal reflectors in portions of crust that experienced high pressure conditions but escaped thermal reactivation

elasticity of single crystal orthoferrosilite the elastic moduli of a synthetic single crystal of pure fesio3 orthoferrosilite have been measured at 1 bar and 20 c by brillouin spectroscopy the moduli are in megabars c11 1 98 c22 1 36 c33 1 75 c44 0 59 c55 0 58 c66 0 49 c12 0 84 c13 0 72 c23 0 55 a comparison of the pyroxene crystal structure with elasticity data shows that distortion of the tetrahedral chains parallel to c is related to c33 straight or extended chains increase c33 and highly kinked chains weaken the structure however the ferrosilite data show that beyond a certain degree of distortion the tetrahedral chains are essentially passive previous models of pyroxene elasticity have indicated that c11 should be most sensitive to composition this is supported by the current study and is reflected in the elasticity data via a positive linear correlation of c11 with the size of the m1 octahedron as measured by the average m1 0 distance the average longitudinal modulus c 11 c11 c22 c33 3 varies linearly with composition in the system orthoenstatite orthoferrosilite whereas the average shear moduli c 44 and c 12 are constant for fe contents of at least 20 by comparison data for the solid solution forsterite fayalite are consistent with a linear variation of modulus versus composition between the end members for all three average moduli we suggest that this difference between orthopyroxene and olivine is due to a strong preference of fe2 for the m2 octahedral site in pyroxene the isotropic shear modulus is 30 lower for ferrosilite than enstatite despite a similar contrast in end member values of the olivine data are consistent with a linear variation of between fo100 and fa100 at high temperatures fe and mg in orthopyroxene will be randomly distributed and a linear variation of with molar content of fe is expected a comparison of laboratory elasticity data with observed mantle properties shows that vp vs and of the upper mantle are satisfied by pure olivine however the data strongly suggest that without the coexistence of a garnet phase no more than 10 orthopyroxene may be present in a model mantle assemblage ca clinopyroxene increases the upper limit on mantle garnet content but does not greatly affect constraints on the quantity of orthopyroxene in the upper mantle

geochemical truths in large data sets i geochemical screening data abstract organic geochemistry especially when undertaken on a well by well or outcrop by outcrop basis arguably lacks statistically significant numbers of analyses to establish reliable trends can a reliable vitrinite reflectance vs depth trend be established from say 12 analysed samples when the number of analysed samples are in the hundreds or even thousands much clearer general trends are established and anomalous measurements more readily recognised interpretation of anomalies is itself highly instructive but forms another paper in this paper a global data set of some 5000 source rock samples is assembled from the open literature and released data e g open file reports and the results discussed to produce practical oil industry interpretations from basic screening data a complex conclusion can be extracted from simple data sets and are supported by mass balance and kinetic theory it is concluded that interpretation always falls back on a comparison of new data with pre existing knowledge in the form of tables and plots total organic carbon toc values are generally log normally distributed so that using mean standard deviation values will under estimate the upside potential when fed into risked probabilistic hydrocarbon charge prediction models kerogen type is initially best determined using plots of rock eval s 2 vs toc rather than the hydrogen index hi s 2 toc vs oxygen index oi s 3 toc or pseudo van krevelen plot the intercept of the s 2 vs toc plot predicts the average dead carbon inertinite content of the source rock set with the slope corresponding to the hydrogen index of the labile component hi l maturity trends of the hydrogen index vs t max or r o show reversals at high maturities as supported by the kinetics of the thermal breakdown of the three standard kerogen types at elevated maturities type iii kerogens have higher hydrogen indices than types i and ii kerogens a feature that must be taken into account when correcting mature kerogens to their original hi values hi o the reduction in hydrogen index is a measure of generation with the corresponding increase in production index pi s 1 s 1 s 2 being effectively a measure of hydrocarbon retention a cross plot of hi vs pi can be interpreted in terms of expulsion efficiencies expelled generated minus retained hydrocarbon measured data support a pore saturation and or generation pressure driven process for expulsion and indicate a limiting pore saturation equivalent to a production index of 0 6 for rich 2 toc source rocks

structure and growth of the izu bonin mariana arc crust 1 seismic constraint on crust and mantle structure of the mariana arc back arc system 1 a high resolution seismic velocity model is presented for the crust and upper mantle of the mariana arc back arc system mabs based on active source seismic profiling the major characteristics are 1 slow mantle velocity of 8 km s 1 in the uppermost mantle especially and deep reflectors under the mariana arc ma and the west mariana ridge wmr 2 a deep reflector in the upper mantle beneath the relative thick crust of the mariana trough mt axis 3 distribution of lower velocity lower crusts 6 7 6 9 km s 1 beneath the volcanic front and adjacent to the mt and 4 high velocity lower crust 7 2 7 4 km s 1 beneath the boundary regions between the ma and mt and between the wmr and the parece vela basin pvb adding to structural characteristics of crust and upper mantle beneath the mabs of the characteristics described above characteristic 1 suggests that the origins of the slow mantle velocity and the deep reflectors be explained by transfer of the lower crustal residues to the upper mantle across the moho considering that the wmr is extinct arc currently on the other hand characteristic 2 suggests that the origin of deep reflectors beneath the mt axis might be lower velocity materials due to the diffractive signals with strong amplitudes characteristic 3 suggests that the lower velocity lower crust advanced crustal growth and characteristic 4 suggests that the high velocity lower crust beneath arc back arc transition zone is composed of mafic ultramafic materials created by extensive partial melting of mantle peridotites or last stage of the arc magmatism rather than serpentinized peridotite

seismic properties of rocks from an exposure of extended continental crust new laboratory measurements from the ivrea zone abstract compressional wave velocities for new samples from the ivrea verbano zone ivz and strona ceneri zone scz have been measured to 600 mpa in order to better understand the petrologic controls on velocity and to provide an expanded base for seismological models of the crust as represented by these terrains these data coupled with previous measurements show that preferred orientation of mica controls both the velocity hysteresis with pressure and seismic anisotropy of scz and ivz schists and gneisses ivz paragneisses form the basis of a linear velocity density relationship for metagraywackes of various metamorphic grade this relationship falls close to that expected for mafic rocks and overlaps velocity density data for ivz mafic gneisses one dimensional near vertical reflection models based on these data and recent structural reconstructions of the terrain show that lower crustal reflectivity can be related to high reflection coefficients associated with interlayered sequences of upper amphibolite granulite facies paragneiss mafic gneiss and ultramafic rocks transparent upper crustal levels in the model result from the overall similarity of velocities for schists gneisses and granites from the structurally and lithologically complex scz a mean lower crustal velocity of 7 1 km s is calculated for the part of the ivz composed of interlayered mafic gneiss and paragneiss and for another area dominated by a mafic layered igneous complex the velocity density analysis coupled with this observation emphasize the ambiguity inherent in interpretation of crustal composition from p wave velocity data in the absence of other constraints

kinetic study of marine and lacustrine shale grains using rock eval pyrolysis implications to hydrocarbon generation retention and expulsion abstract the kinetic parameters of marine and lacustrine shale grains 4 mm were retrieved by using rock eval pyrolysis in comparison with finely ground powder

the effect of oil expulsion or retention on further thermal degradation of kerogen at the high maturity stage a pyrolysis study of type ii kerogen from pingliang shale china high maturity oil and gas are usually generated after primary oil expulsion from source rocks especially from oil prone type i ii kerogen however the detailed impacts of oil expulsion or retention in source rock on further thermal degradation of kerogen at the high maturity stage remain unknown in the present study we collected an ordovician pingliang shale sample containing type ii kerogen the kerogens which had previously generated and expelled oil and those which had not were prepared and pyrolyzed in a closed system to observe oil expulsion or oil retention effects on later oil and gas generation from kerogen the results show that oil expulsion and retention strongly impacts on further oil and gas generation in terms of both the amount and composition in the high maturity stage gas production will be reduced by 50 when the expulsion coefficient reaches 58 and gas from oil expelled kerogen less oil retained is much drier than that from fresh kerogen the oil expulsion also causes n alkanes and gas compounds to have heavier carbon isotopic compositions at high maturity stages the enrichment of 13c in n alkanes and gas hydrocarbons are 1 and 4 6 respectively compared to fresh kerogen oil expulsion may act as open system opposite to the oil retention that influences the data pattern in crossplots of 13c2 13c3 versus c2 c3 13c2 13c3 versus 13c1 and 13c1 13c2 versus ln c1 c2 which are widely used for identification of gas from kerogen cracking or oil cracking these results suggest that the reserve estimation and gas source correlation in deep burial basins should consider the proportion of oil retention to oil expulsion the source rocks have experienced

thermal cracking of kerogen in open and closed systems determination of kinetic parameters and stoichiometric coefficients for oil and gas generation abstract the purpose of the study is to compare artificial maturation of kerogens representative of the main types of organic matter kerogen types i ii ii s and iii in open and anhydrous closed pyrolysis systems the generated compounds are fractionated according to their thermal stability into six chemical classes c 1 c 2 c 5 c 6 c 14 c 15 saturates c 15 aromatics and nsos which include resins and asphaltenes in both systems primary cracking of kerogen can be described by two main reactions oil generation together with early gas generation followed by late gas production mass balances obtained in the two pyrolysis systems are reasonably similar although some secondary cracking of the nsos and underestimation of methane potential due to incomplete pyrolysis may occur in the open system kinetic parameters of thermal cracking are derived from experiments in the open system using an optimization procedure which determines a unique frequency factor and a weight distribution of chemical classes for a discrete series of activation energies the resultant frequency factors are checked with those obtained for specific molecular tracers such as n c 12 and n c 24 alkanes generated from kerogens in open and closed systems under isothermal conditions the results show that using a unique frequency factor as determined by optimization is correct for type i ii and ii s kerogens this factor is more questionable however when the distribution of activation energies is very broad such as for type iii coals based on this study a strategy for determination of kinetic parameters on any new source rock sample is proposed

superposition of replacements in the mafic granulites of the jijal complex of the kohistan arc northern pakistan dehydration and rehydration within deep arc crust abstract a deep level crustal section of the cretaceous kohistan arc is exposed in the northern part of the jijal complex the occurrence of mafic to ultramafic granulite facies rocks exhibits the nature and metamorphic evolution of the lower crust mafic granulites are divided into two rock types two pyroxene granulite orthopyroxene clinopyroxene plagioclase quartz 1 and garnet clinopyroxene granulite garnet clinopyroxene plagioclase quartz 2 two pyroxene granulite occurs in the northeastern part of the jijal complex as a relict host rock of garnet clinopyroxene granulite where the orthopyroxene rich host is transected by elongated patches and bands of garnet clinopyroxene granulite garnet clinopyroxene granulite together with two pyroxene granulite has been partly replaced by amphibolite hornblende garnet plagioclase quartz 3 the garnet bearing assemblage 2 is expressed by a compression dehydration reaction hornblende orthopyroxene plagioclase garnet clinopyroxene quartz h 2 o subsequent amphibolitization to form the assemblage 3 is expressed by two hydration reactions garnet clinopyroxene plagioclase h 2 o hornblende quartz and plagioclase hornblende h 2 o zoisite chlorite quartz the mafic granulites include pod and lens shaped bodies of ultramafic granulites which consist of garnet hornblendite garnet hornblende clinopyroxene 4 associated with garnet clinopyroxenite garnetite and hornblendite field relation and comparisons in modal chemical compositions between the mafic and ultramafic granulites indicate that the ultramafic granulites were originally intrusive rocks which dissected the protoliths of the mafic granulites and then have been metamorphosed simultaneously with the formation of garnet clinopyroxene granulite the results combined with isotopic ages reported elsewhere give the following tectonic constraints 1 crustal thickening through the development of the kohistan arc and the subsequent kohistan asia collision caused the high pressure granulite facies metamorphism in the jijal complex 2 local amphibolitization of the mafic granulites occurred after the collision

thermal cracking history by laboratory kinetic simulation of paleozoic oil in eastern tarim basin nw china implications for the occurrence of residual oil reservoirs abstract the thermal stability of paleozoic oil in eastern tarim basin nw china was investigated through laboratory kinetic simulation experiments laboratory cracking of a selected marine oil sample from ordovician strata in well lg 1 of tarim basin was performed by confined dry pyrolysis system at t 300 650 c p 50 mpa results indicated the oil required higher temperature for cracking at laboratory heating rates oil cracking started at 390 400 c and the laboratory cracking was completed at around 650 c at geological heating rates the onset temperature is about 148 162 c for cracking start and was completed at 245 276 c the oil cracking history was recovered using the acquired kinetic parameters and the geothermal history of td 2 and the threshold temperature for oil cracking under geological conditions was calculated the oil cracking started at 165 c r o 1 45 and stopped in early devonian 390 ma and the oil cracking rates in the strata of o 1 reached 60 70 at the end of silurian the calculated oil generation and oil cracking windows overlapped to some extent and were completed rapidly the possible geological controls for the occurrence of residual oil reservoirs in eastern tarim basin have been discussed including the high stability of the paleozoic oil in tarim basin the fast heating rate and longer duration time for oil cracking the slight biodegradation in later uplift the good preservation of the paleo reservoirs and the moderate structural adjustment which were critical for the exploration of residual oil and gases in this area

contrasting metamorphic p t time paths of the kohistan granulites and tectonics of the western himalayas in the swat indus kohistan area lower crustal rocks of the kohistan arc including amphibolites granulites and ultramafic rocks are widely exposed detailed petrological structural studies reveal that the chilas jijal metamorphic complex comprises essentially intermediate to high pressure granulites with a granulite amphibolite transition controlled by extensive retrograde metamorphism and ductile deformation contrasting patterns of compositional zoning in garnet and orthopyroxene suggest complicated p t paths in the granulites geothermobarometry based on garnet bearing granulites identify two distinct p t time paths a high pressure anticlockwise path of the jijal complex and a low pressure retrograde path of the chilas complex these p t time paths represent the evolution of middle to lower crustal rocks of the kohistan arc the anticlockwise p t time path combined with published isotopic ages reveals that i the high pressure granulitefacies metamorphism is related to the kohistan asia collision and ii the crust of the kohistan arc had been thickened at least 55 km before the india asia collision

seismological evidence for variable growth of crust along the izu intraoceanic arc 1 the processes that create continental crust in an intraoceanic arc setting are a matter of debate to address this issue we conducted an active source wide angle seismic study to examine along arc structural variations of the izu intraoceanic arc the data used were acquired over a 550 km long profile along the volcanic front from sagami bay to tori shima the obtained structural model showed the existence of felsic to intermediate composition middle crust with a p wave velocity vp of 6 0 6 5 km s 1 in its upper part and 6 5 6 8 km s 1 in its lower part the thickness of the middle crust varied markedly from 3 to 13 km the underlying lower crust also consisted of two layers vp of 6 8 7 2 km s 1 in the upper part and vp of 7 2 7 6 km s 1 in the lower part the upper of these layers was interpreted to consist of plutonic gabbro and the lower layer was interpreted to be mafic to ultramafic cumulates average crustal velocities calculated from our model showed remarkable lateral variation which correlated well with arc volcanism low average crustal seismic velocities 6 7 km s 1 due to thick middle crust were obtained beneath basaltic volcanoes e g o shima miyake jima hachijo jima aoga shima while higher average velocities 7 1 km s 1 were obtained beneath rhyolitic volcanoes e g nii jima kurose south hachijo caldera myoji knoll and south sumisu caldera we concluded from these observations that continental crust grows predominantly beneath the basaltic volcanoes of the izu arc and that rhyolitic volcanism may be indicative of a more juvenile stage of crustal evolution or remelting of preexisting continental crust or both

evolution of the petrological and seismic moho implications for the continental crust mantle boundary the chemical and petrological composition of mafic rocks from the lower continental crust are discussed by comparing mafic granulites and meta gabbroic rocks from the ivrea zone and the northern hessian depression nhd xenolith suite both regions contain contrasting types of meta mafic lithologies i former basaltic rocks with trace element patterns ranging from morb iike to subduction related or intra plate tholeutes and u ca and al enriched plagiodase dominated gabbroic rocks showing positive eu anomalies generated by complex deep crustal magmatic processes such as fractionation accumulation of plagiodase and pyroxene and crustal contamination the absence of typical garnet omphadte parageneses in these rocks indicates that the eclogite stability field was not reached during palaeozoic orogenic processes a compilation of experimentally determined p wave velocities and densities for mafic granulites gabbroic rocks eclogites and peridotites is used to evaluate key physical properties of lower crustal mafic rocks during crystal thickening caused by continent continent collision in a step by step scenario it is demonstrated that the position of the seismic moho defined as a first order velocity discontinuity and the petrological moho defined as the boundary between non peridotitic crustal rocks and olivine dominated rocks is not identical for the case that mafic rocks are transformed into edogites at the base of orogenically thickened crust p wave velocities of eclogites largely overlap with those of peridotites although their densities are significantly higher than common upper mantle rocks as a consequence refraction seismic field studies may not detect edogites as crustal rocks this means that the seismic moho detected by refraction seismic field studies appears at the upper boundary between edogites and overlying crustal units since edogites generally have higher densities than peridotites they might be recycled into the deeper lithosphere thereby transferring excess eu into the upper mantle this process could be a due for understanding the negative euanomaly in the upper continental crust which is apparently not balanced quantitatively by the abundance of common mafic crustal rocks

effect of h2o released by dehydration of serpentine and chlorite on compressional wave velocities of peridotites at 1 gpa and up to 1000 c abstract compressional wave velocities v p of serpentine bearing wehrlite 0 2 wt h 2 o serpentinized dunite 4 1 wt h 2 o chlorite bearing websterite 1 3 wt h 2 o and chlorite bearing dunite 0 6 wt h 2 o were measured at 1 gpa and up to 1000 c during heating to and cooling from 1000 c during heating the serpentine bearing rocks showed a sudden decrease in v p at 600 700 c when serpentine dehydration took place similarly the chlorite bearing rocks exhibited a sharp change in v p at 800 900 c due to chlorite dehydration during cooling experiments on both serpentine and chlorite bearing rocks v p showed a linear increase down to room temperature suggesting that no rehydration reaction took place with decreasing temperature the decrease in v p due to dehydration reactions was relatively small 1 5 in rocks with low h 2 o content 0 2 1 3 wt whereas the dehydration reaction of serpentinized dunite with higher 4 1 wt h 2 o led to a marked decrease in v p 5 1 which is comparable to the degree of v p reduction reported from the low velocity anomaly regions in subducting slabs the effect of h 2 o fluid on the v p of peridotite is evaluated by assessing the ratio of v p values v p v p 0 under both wet and dry conditions the v p v p 0 ratio was 0 97 0 99 in rocks with 0 2 1 3 wt h 2 o but was markedly lower in rocks with 4 1 wt h 2 o 0 87 the run products showed variable geometries of fluid filled pores which clearly depended on the h 2 o content of the rock studied the run products with 0 2 1 3 wt h 2 o had relatively small and isolated fluid filled pores whereas run products with 4 1 wt h 2 o contained relatively large fluid filled pores that were interconnected our results suggest that connected fluid filled pores cause a significant decrease in v p but that isolated fluid pores have little effect on v p

petrofabric p wave anisotropy and seismic reflectivity of high grade tectonites abstract ji s salisbury m h and hanmer s 1993 petrofabric p wave anisotropy and seismic reflectivity of high grade tectonites tectonophysics 222 195 226 in order to understand seismic anisotropy and its influence on the reflectivity of lower crustal fault zones we have undertaken experimental measurements of p wave velocities up to 600 mpa for 20 granulite and upper amphibolite facies mylonites from the snowbird tectonic zone canada the rocks whose composition ranges from ultramafic to felsic have experienced extremely large ductile strain it is found that the amphibolitic mylonites exhibit significant vp anisotropy 6 13 at 600 mpa whereas the pyroxene bearing granulite facies mylonites and the quartz or feldspathic tonalitic granitic and diatexitic mylonites are quasi isotropic in order to constrain interpretation of the measured vp properties microstructural analyses have been systematically performed in the samples studied it is shown that the interaction between feldspar and quartz or pyroxene and the absence of amphibole cause anisotropy in the granulite facies mylonites to be low the amphibolitic mylonites are strongly anisotropic because of a large volume fraction of hornblende with strong lpo 001 lineation and 100 foliation the anisotropy pattern in the amphibolitic mylonites is consistently orthorhombic vp x vp y vp z where x is parallel to stretching lineation y is normal to the lineation in the foliation plane and z is normal to the foliation plane but the anisotropy pattern in the mica rich mylonites is transversely isotropic vp x vp y vp z if sufficiently large volumes of the crust display such patterns this difference may be an important indicator for kinematic analysis in the middle to lower crust using modern seismic techniques the study demonstrates that while seismic reflectivity is strongly lithology controlled fabric induced anisotropy can both enhance and decrease seismic reflectivity hence the discontinuity of seismic reflections along ductile shear zones in the lower crust is not necessarily indicative of the discontinuity of the shear zones but may indicate changes in composition or metamorphic grade

chemical structure changes of lacustrine type ii kerogen under semi open pyrolysis as investigated by solid state 13c nmr and ft ir spectroscopy abstract at present there is a lack of research on the structural changes of lacustrine type ii kerogen which is regionally distributed but has significant potential for hydrocarbon resources in our previous work a series of non hydrous temperature based semi open pyrolysis experiments have been performed on the chang 7 oil shale to simulate the thermal maturation from 0 53 ro to 1 68 ro of lacustrine type ii kerogen in that work the parallel reaction pathway for kerogen decomposition was supported the aim of this work is to reveal the structural changes of the post pyrolysis kerogen integrated analysis including elemental analysis programmed pyrolysis rock eval fourier transform infrared ft ir spectroscopy and solid state 13c nuclear magnetic resonance 13c nmr spectroscopy were conducted on the native unheated and post pyrolysis rocks and kerogens based on the compositional features of the hydrocarbon products structural changes of the post pyrolysis kerogen were investigated and insights on the initial chemical structure of the kerogen were also obtained before the peak hydrocarbon generating stage ro 1 09 the reactions in the previous two stages produce a highly aromatic kerogen the increased aromaticity of the highly matured kerogen is most likely to be caused by aromatization or dehydrogenation of hydroaromatics and coking of aromatic bitumen not by fusing or condensation of aromatic rings

continental crust crustal underplating and low q upper mantle beneath an oceanic island arc a detailed structural model of the crust subducting slab and underlying upper mantle across the northern izu ogasawara bonin island arc system is derived from a marine seismic reflection and ocean bottom seismographic refraction survey and subsequent forward modeling combined with tomographic inversion the model indicates that the crust is thickest beneath the presently active rift zone and a granitic crust may have formed in the mid crust a highly attenuative mantle that is one with low quality q seems to be confined mainly beneath the presently active rift zone in contrast high p wave velocity persists in the lower crust between the forearc and eastern margin of the back arc basin suggesting a large scale magma input responsible for the arc formation

thermal history of sedimentary basins maturation indices and kinetics of oil and gas generation temperature is the most sensitive parameter in hydrocarbon generation thus reconstruction of temperature history is essential when evaluating petroleum prospects no measurable parameter can be directly converted to paleotemperature maturation indices such as vitrinite reflectance tmax from rock eval pyrolysis spore coloration thermal alteration index tai or concentration of biological markers offer an indirect approach all these indices are a function of the thermal history through rather complex kinetics frequently influenced by the type of organic matter their significance and validity are reviewed besides the problems of identification e g vitrinite and interlaboratory calibration it is important to simultaneously interpret kerogen type and maturation and to avoid difficult conversions from one index to another geodynamic models where structural and thermal histories are connected are another approach to temper ture reconstruction which could be calibrated against the present distribution of temperature and the present value of maturation indices kinetics of kerogen decomposition controls the amount and composition of hydrocarbons generated an empirical time temperature index tti originally introduced by lopatin does not allow such a quantitative evaluation due to several limitations no provision for different types of kerogen and different rates of reactions poor calibration on vitrinite reflectance it is of limited interest unless one has no access to a desk top computer kinetic models based on a specific calibration made on actual source rock samples can simulate the evolution of all types of organic matter and can provide a quantitative evaluation of oil and gas generated examples from the jurassic source rocks of the paris basin monterey formation of california green river shales of utah paleozoic source eds of the algerian sahara and miocene rocks of the mahakam delta indonesia illustrate various aspects of the discussion geological geochemical models are the most efficient way to integrate geological seismic and geochemical data and they should greatly help to reduce the risk in exploration

elasticity of a grossular pyrope almandine garnet the single crystal elastic properties of a natural grossular rich garnet solid solution have been measured at ambient conditions using brillouin spectroscopy this garnet sample is unusual for a grossular in that it contains appreciable pyrope and almandine components with a composition of gr48 4py27 6alm23 4sp0 6 it is thus suitable for investigating the variation of elastic properties with composition in ca rich garnet solid solutions that are stable only at high pressure the values obtained for the bulk modulus k 170 4 6 and for the shear modulus 101 6 3 of the garnet examined in this study vary by less than 1 from those obtained from a weighted sum of the end member moduli this suggests that any composition in the grossular pyrope almandine system which comprise the majority of upper mantle garnets is accurately estimated with this simple approach more complex elasticity composition variations observed for the grossular andradite garnets may be specific to garnet solid solutions where the cation substitutions occur at six coordinated crystallographic sites

discontinuous change in temperature derivative of vp in lower crustal rocks 1 compressional wave velocities vp of gabbronorite pyroxene granulite wehrlite and websterite were measured up to 1000 c at 1 gpa during heating and cooling the wehrlite and websterite which contain secondary hydrous minerals show irreversible change in temperature derivative of vp vp t during heating these rocks show sudden decrease in vp when dehydration reactions took place during cooling the rocks show a linear increase in vp in contrast the gabbronorite and pyroxene granulite which are nearly dry crystalline assemblage show reversible and discontinuous change in vp t at around 400 c it changes from 2 4 and 2 1 10 4 km s 1 c 1 to 4 7 and 4 5 10 4 km s 1 c 1 this reversible and discontinuous change in vp t is difficult to explain by the previously proposed mechanisms such as thermal cracking dehydration reaction and or partial melting the data suggest that this reversible and discontinuous change would be associated with phase transition in plagioclase

expulsion of oil from petroleum source rocks inferences from pyrolysis of samples of unconventional grain size oil expulsion efficiencies from different lithologies have been investigated and compared employing pyrolyses of samples of unconventional grain size from 300 mg hc g corg show that liquid range hydrocarbons are expelled from coal when the generated oil exceeds the coal sorption capacity this suggests that expulsion of oil from liptinite poor or in general h poor humic coals is primarily limited by the release of generated liquid hydrocarbons from kerogen because such coals generally do not generate sufficient amounts of liquid hydrocarbons to overcome the coal sorption capacity

seismic velocities from the kohistan volcanic arc northern pakistan the rocks bounded by the main mantle thrust and the northern suture in northern pakistan constitute an exhumed section through a cretaceous volcanic arc samples have been collected from all the principal lithological groups of the arc and p and s wave seismic velocities have been measured in the laboratory with the prime objective of comparing the velocities with those determined by seismic refraction experiments on modern volcanic arcs velocities were measured at up to 0 7 gpa and consideration has been given to the effect of confining pressure pore pressure and temperature and to the deformation and metamorphism involved in the himalayan collision the reconstructed velocity section through the arc shows a distinct upper crust comprising granitic dioritic intrusions metasediments and volcanics with a p wave velocity of 6 2 6 4 km s 1 depending on the parameters used beneath the lower crust of amphibolitcs and pyroxene granulite has a velocity mainly about 6 4 6 7 kms 1 though the garnet granulitcs extend to 7 8 km s 1 the more mature arc with a higher proportion of granitic rocks would show a slightly lower upper crustal velocity than the younger arc velocity inversions might be expected with a thermal gradient of as little as 10 15 c km 1 depending on the pore pressure in general the proposed velocity structure is comparable with that of volcanic arcs and with many other sections of the continental crust

p and s wave velocities of the lowermost crustal rocks from the kohistan arc implications for seismic moho discontinuity attributed to abundant garnet abstract p vp and s wave vs velocities of garnet free two pyroxene granulite and garnet bearing garnet granulite and garnet pyroxenite lowermost crustal rocks collected from the kohistan arc northern pakistan were measured at 0 1 1 0 gpa and 25 400 c garnet granulite had higher vp 0 31 km s and vs 0 27 km s than two pyroxene granulite although vp and vs increased with increasing volume percent of garnet plagioclase free garnet pyroxenite showed significantly higher vp and vs than plagioclase rich garnet granulite mainly due to the low vp and vs of plagioclase in contrast we observed two quasi linear relationships between vp vs and sio2 content for the garnet bearing and garnet free rocks the garnet bearing rocks had relatively higher vp and vs and stronger sio2 dependences than the garnet free rocks the stronger sio2 dependences of vp and vs in the garnet bearing rocks suggest that the garnet formation in mafic to ultramafic rocks e g pyroxenite and hornblendite having relatively lower sio2 leads to more pronounced increases in vp and vs than that of relatively felsic rocks e g felsic to mafic granulite indeed the vp and vs of the garnet pyroxenite were significantly higher than those of garnet granulite but comparable to those of dunite the significantly high vp and vs of the garnet pyroxenite yielded high reflection coefficients between the garnet granulite and garnet pyroxenite of up to 0 13 for p waves and 0 14 for s waves comparable to values expected for moho reflection thus the lithological boundary between plagioclase rich garnet granulite and plagioclase free garnet pyroxenite in the lowermost crust of the kohistan arc corresponds to the seismic moho discontinuity

extrapolation of the kinetics of oil and gas formation from laboratory experiments to sedimentary basins it is generally accepted that the formation of oil and gas from sedimentary organic matter or kerogen is adequately described by kinetic models based on first order kinetics with rate constants obeying an arrhenius equation these models which are extensively used in oil exploration to assess the petroleum potential of sedimentary basins are based on geological observations1 2 3 4 5 6 but are formally quite similar to models designed to simulate oil shale pyrolysis7 8 9 or coal processing10 11 12 the idea of blending these two approaches is not new see for example ref 2 but until now the most sophisticated attempts reproduced only the gross features of kerogen cracking on a geological timescale5 or were uncontrolled by geochemical measurements13 14 here we show that the kinetic parameters determined from the laboratory pyrolysis of an immature kerogen sample apply to the conditions of sedimentary basins altough the time and temperature scale are completely different

the chemical kinetics of the semi open hydrous pyrolysis system time series analysis of lithostatic pressure and fluid pressure abstract as a problem that has plagued geochemists the perspective of time has long been recognized as an important factor in organic matter evolution and hydrocarbon generation this article discusses two time series analysis methods based on econometrics damping trend and autoregressive integrated moving average arima to mine the potential value of data and abstract useful information from pyrolysis experiments the case studies use marine source rocks depth of 3119 3230 m in the lh29 2 well from the enping formation in the baiyun sag the deep water area depth of 300 m of the northern south china sea which has a geological background of high temperature high pressure and rapid burial in the late stage a tubular plug flow microreactor is used to artificially mature the source rock in the laboratory and the conditions of hydrous pyrolysis are listed as follows temperatures of 250 c 300 c 350 c 400 c 450 c and 500 c lithostatic pressure of 33 89 mpa fluid pressure of 16 38 mpa and time duration of 72 h the results revealed that as the degree of maturation increased ro from 0 27 to 2 04 the cumulative yield of hydrocarbon gas increased rapidly max 311 64 ml g toc the yield of the expelled oil increased first and then decreased peak 350 69 mg g toc at 350 c and the yield of residual oil extracted from residue decreased gradually although the kinetic parameters of kerogen can be calculated by conventional pyrolysis experiments the long term cumulative effect of episodic hydrocarbon expulsion in real conditions is often neglected the major contributions of our statistical approach for geological applications are described as follows 1 the recognition of qualitative changes within hydrocarbon generation and expulsion 2 the characterization of episodic hydrocarbon expulsion that describes the evolution of the lithostatic pressure and fluid pressure 3 the disclosure of new influencing factors abstracted from time series models to describe the frequency distribution of hydrocarbon expulsion and 4 an evaluation of the dependency of new variables

petrological model of the northern izu bonin mariana arc crust constraints from high pressure measurements of elastic wave velocities of the tanzawa plutonic rocks central japan abstract ultrasonic compressional wave velocities vp and shear wave velocities vs were measured with varying pressure up to 1 0 gpa in a temperature range from 25 to 400 c for a suite of tonalitic gabbroic rocks of the miocene tanzawa plutonic complex central japan which has been interpreted as uplifted and exposed deep crust of the northern izu bonin mariana ibm arc the vp values of the tonalitic gabbroic rocks increase rapidly at low pressures from 0 1 to 0 4 gpa and then become nearly constant at higher pressures above 0 4 gpa the vp values at 1 0 gpa and 25 c are 6 3 6 6 km s for tonalites 56 4 71 1 wt sio2 6 8 km s for a quartz gabbro 53 8 wt sio2 and 7 1 7 3 km s for a hornblende gabbro 43 2 47 7 wt sio2 combining the present data with the p wave velocity profile of the northern ibm arc we infer that 6 km thick tonalitic crust exists at mid crustal depth 6 1 6 3 km s vp overlying 2 km thick hornblende gabbroic crust 6 8 km s vp our model shows large differences in acoustic impedance between the tonalite and hornblende gabbro layers being consistent with the strong reflector observed at 12 km depth in the ibm arc the measured vp of tanzawa hornblende bearing gabbroic rocks 7 1 7 3 km s is significantly lower than that vp modeled for the lowermost crustal layer of the northern ibm arc 7 3 7 7 km s at 15 22 km depth we propose that the ibm arc consists of a thick tonalitic middle crust and a mafic lower crust

fabric related velocity anisotropy and shear wave splitting in rocks from the santa rosa mylonite zone california the directional dependence of p and s wave velocities have been measured at pressures up to 600 mpa and temperatures up to 700 c in rocks from the santa rosa mylonite zone southern california during tectonism these were progressively deformed from granodiorite protolith to mylonite and ultimately phyllonite the mineralogical and chemical composition of protolith and mylonite is nearly identical thus these rocks provide excellent material for documenting the effect of microstructural and textural changes on rock anisotropy velocity anisotropy increases significantly with the degree of deformation whereas average velocities and densities do not change at low pressure 50 mpa the velocity anisotropy ranges from 1 7 in granodiorite up to 19 in phyllonite and is due to both oriented microfractures and crystallographic preferred orientation at high pressure 600 mpa the residual anisotropy up to 12 is mainly due to preferred mineral orientation in particular of biotite significant shear wave splitting is measured parallel to the foliation plane and shows a good correlation with the biotite texture these observations confirm that oriented microcracks and preferred orientation of minerals should be taken into account in the interpretation of seismic reflection and refraction data in terranes with deformed rocks

p wave velocity and anisotropy of lawsonite and epidote blueschists constraints on water transportation along subducting oceanic crust p wave velocity vp and the anisotropy of lawsonite and epidote blueschists were measured up to 1 0 gpa and 400 c using the ultrasonic pulse transmission technique the slowest vp in the direction normal to foliation is similar between lawsonite and epidote blueschists 7 0 7 2 km s at 1 0 gpa and room temperature while the fastest vp in the direction parallel to lineation markedly differs between lawsonite blueschists 7 4 7 6 km s at 1 0 gpa and room temperature and epidote blueschist 7 9 km s at 1 0 gpa and room temperature crystallographic orientation measurements for main constituent min erals revealed that both epidote 0 1 0 axes fastest vp direction in epidote single crystal and amphibole 0 0 1 axes fastest vp direction in amphibole single crystal are preferentially oriented parallel to lin eation to enhance vp anisotropy of the epidote blueschist in contrast lawsonite 0 0 1 axes fastest vp direction in lawsonite single crystal are oriented subnormal to foliation whereas amphibole 0 0 1 axes are oriented subparallel to lineation so that relatively weak vp anisotropy was observed in the lawsonite blueschist our experimental results in conjunction with recent seismological observations suggest that the vp of the subducting oceanic crust at 50 km has been observed in several subducting slabs however the high vp values at 50 km depth are difficult to be explained by blueschists this indicates that the blueschist would be at least partially transformed to hydrous mineral bearing eclogite at 50 km depth in subducting oceanic crusts

geochemical characteristics of marine and terrestrial shale gas in china abstract although the annual production of shale gas in china was 13 10 8 m 3 in 2014 a systematic study on geochemical and isotopic characteristics of these unconventional gases has not been well addressed in the present study almost all shale gas samples available in china including marine shale gas from the wufeng longmaxi formation in the sichuan basin o 3 w s 1 l and terrestrial shale gas from chang 7 member t 3 y 7 in the ordos basin were collected and analyzed for their geochemical and isotopic compositions the shale gas from the wufeng longmaxi shale is dry gas with an average methane content of 98 38 and records a highest content of ch 4 in the world 99 59 which is consistent with the very high thermal maturity levels of the gas shales that have equivalent vitrinite reflectance eqvro values between 2 4 and 3 6 the 13 c 1 values are correspondingly heavy and record a heaviest 13 c 1 values 26 7 for the shale gases found in the world as well the average values of 13 c 1 13 c 2 and 13 c 3 for the wufeng longmaxi shale gas are 31 3 35 6 and 47 2 respectively displaying a complete carbon isotopic reversal i e 13 c 1 13 c 2 13 c 3 2 h ch4 and 2 h c2h6 has an average value of 148 and 173 respectively also yielding a hydrogen isotopic reversal i e 2 h ch4 2 h c2h6 the chang 7 shale has an average toc content of 13 81 with vitrinite reflectance vro values between 0 7 and 1 2 the chang 7 shale gas is wet gas with an average methane content of 84 90 and is rich in heavy gaseous hydrocarbons c 2 c 5 the respective values of 13 c 1 13 c 2 and 13 c 3 are 48 7 36 4 and 31 3 displaying a positive carbon isotopic distribution pattern i e 13 c 1 13 c 2 13 c 3 the average 2 h ch4 2 h c2h6 and 2 h c3h8 values are 256 244 and 188 respectively and are characterized by a positive distribution pattern i e 2 h ch4 2 h c2h6 2 h c3h8 the differences in gas wetness and carbon and hydrogen isotopic distribution patterns between the shale gases from the wufeng longmaxi and chang 7 shale are attributed to variations in thermal maturity levels co 2 is present in low content in both the wufeng longmaxi and chang 7 shale gases mostly less than 1 13 c values for the co 2 in the wufeng longmaxi formation are between 8 9 and 9 2 indicating an inorganic origin from the cracking of carbonate mineral in the shales under high temperatures in contrast 13 c values of the co 2 in the chang 7 shale gas range from 8 2 to 22 7 indicating an organic origin from the thermal degradation of organic matter helium in both the wufeng longmaxi and chang 7 shale gases is dominantly of curst origin in terms of their r ra ratios that vary from 0 01 to 0 08 positive carbon isotopic distribution pattern is typical of primitive thermogenic gas however it can be converted into complete or partial carbon isotopic reversal patterns due to secondary alteration the causes that yield carbon isotopic reversal include 1 mixing of gases with the same source but different thermal maturity levels 2 secondary cracking of oil or wet gas 3 formation water involved reactions 4 gas diffusion and 5 carbon isotope exchange between alkane gases at high temperature among them carbon isotopic exchange between alkane gases at high temperature is a key factor nine plots have been drawn based on the shale gases from china usa and canada among them the plot of 13 c 2 versus wetness demonstrates a lying s shape with two inflection points on the gas wetness axis the wetness value of 1 4 represents a critical point from pyrolytic gas primary cracking gas to cracking gas secondary cracking gas and whereas the wetness value of 6 marks the end of oil generation on the diagram of wetness versus 13 c shale gases with wetness values greater than 1 6 are characterized by positive carbon isotopic distribution pattern whereas a complete or partial carbon isotopic reversals are observed for shale gases with wetness values less than 1 6

foundering of lower island arc crust as an explanation for the origin of the continental moho a long standing theory for the genesis of continental crust is that it is formed in subduction zones however the observed seismic properties of lower crust and upper mantle in oceanic island arcs differ significantly from those in the continental crust accordingly significant modifications of lower arc crust must occur if continental crust is indeed formed from island arcs here we investigate how the seismic characteristics of arc crust are transformed into those of the continental crust by calculating the density and seismic structure of two exposed sections of island arc kohistan and talkeetna the kohistan crustal section is negatively buoyant with respect to the underlying depleted upper mantle at depths exceeding 40 kilometres and is characterized by a steady increase in seismic velocity similar to that observed in active arcs in contrast the lower talkeetna crust is density sorted preserving only relicts about ten to a hundred metres thick of rock with density exceeding that of the underlying mantle specifically the foundering of the lower talkeetna crust resulted in the replacement of dense mafic and ultramafic cumulates by residual upper mantle producing a sharp seismic discontinuity at depths of around 38 to 42 kilometres characteristic of the continental mohorovicic discontinuity the moho dynamic calculations indicate that foundering is an episodic process that occurs in most arcs with a periodicity of half a million to five million years moreover because foundering will continue after arc magmatism ceases this process ultimately results in the formation of the continental moho

simple kinetic models of petroleum formation part i oil and gas generation from kerogen modern basin analysis uses kinetic models to predict the extent of petroleum generation within potential source rocks the global kinetic model presented here assigns kinetic parameters based on gross depositional environment and stratigraphic age this is useful in areas of low geochemical knowledge including exploration frontiers five kerogen kinetic organofacies each characterized by a specific organic matter input and early diagenetic overprint can broadly be related to sedimentary facies age associations even using seismic sequence stratigraphy alone a aquatic marine siliceous or carbonate evaporite any age b aquatic marine siliciclastic any age c aquatic non marine lacustrine phanerozoic d e terrigenous non marine ever wet coastal mesozoic and younger and f terrigenous non marine coastal late palaeozoic and younger routine pyrolysis data allow partitioning of organic carbon in the immature source rock into four initial components oil oil generative gas generative and inert separate kinetic parameters for the oil and gas generative fractions allow computation of the evolving concentration and composition of the products it was assumed that the activation energy distributions for each fraction were normally distributed non linear regression of large combined laboratory and field data sets varying by up to 12 orders of magnitude in heating rate established optimum values for the required ten 5 2 kinetic parameter sets a emean e differences in kinetic parameters can be reconciled with known chemical properties although our knowledge base is still inadequate to construct kinetic models from first principles mean activation energies governing oil generation increase systematically in the order a f causing a corresponding increase in generation temperature at a reference heating rate 2 c ma 1 the oil generation window 10 90 oil generative kerogen degraded increases from ca 95 135 c to 145 175 c organofacies c has the tightest energy distribution and narrowest oil generation window the gas generation window ranges from ca 105 155 c to 175 220 c thermal stress results from a combination of temperature and time an order of magnitude increase decrease in heating rate elevates depresses reaction temperatures by ca 15 c heating rates in subsiding sedimentary basins can vary by two orders of magnitude dramatic differences in generation temperature can result if the heating rate and organofacies effects compound thus global oil and gas generation temperature thresholds constitute blunt instruments with which to screen the petroleum potential of sedimentary basins because unexpelled oil provides a potential feedstock for oil to gas cracking in the source rock quantitative models of petroleum generation become really useful only when coupled with models of oil gas cracking and expulsion for example the frequently observed association between gas provinces and coals cannot be explained solely by their generation behaviour

pressure dependence and anisotropy of p wave velocities in ultrahigh pressure metamorphic rocks from the dabie sulu orogenic belt china implications for seismic properties of subducted slabs and origin of mantle reflections the compressional wave velocities vp pressure derivatives vpv and anisotropy a of three types of eclogites and country rocks from the dabie sulu ultrahigh pressure uhp metamorphic belt china have been measured under confining pressures up to 800 mpa type 1 eclogites which are coarse grained and subjected to almost no retrograde metamorphism experienced recovery accommodated dislocation creep at peak metamorphic conditions in the diamond stability field type 2 eclogites are fine grained reworked type 1 materials that experienced recrystallizationaccommodated dislocation creep under quartz coesite boundary conditions during the early stage of exhumation type 3 eclogites are retrogressed samples that were overprinted by significant amphibolite facies metamorphism during a late stage of exhumation within the crust type 1 eclogites are richer in al2o3 and mgo but poorer in sio2 and na2o than type 2 and type 3 eclogites anisotropy of type 1 and type 2 eclogites is generally low b4 because volumetrically important garnet is elastically quasi isotropic while type 3 eclogites can exhibit high anisotropy n10 due to the presence of strongly anisotropic retrograde minerals such as amphibole plagioclase and mica the transition of the pressure dependence of velocity from the poroelastic to elastic regimes occurs at a critical pressure pc which depends mainly on the density and distribution of microcracks and in turn on the exhumation history of rocks the vp pressure relationship can be expressed by vp a lnp 2 blnp c pvpc and vp v0 dp pzpc where p is the confining

lacustrine type i kerogen characterization at different thermal maturity levels application to the late cretaceous yacoraite formation in the salta basin argentina abstract a maturation series from the late cretaceous to danian yacoraite formation in the salta basin argentina was selected to investigate the evolution of organic matter properties from source rock samples mainly containing lacustrine type i kerogen organic petrography determined the thermal maturity and the spatial distribution of organic matter particles rock eval analyses and kerogen isolation procedures were then applied to assess the hydrocarbon generation potential of the investigated intervals biomarker ratios as well as the molecular composition of organic compounds present in four immature to early mature rock samples and their corresponding aliphatic and aromatic fractions were investigated to complete the lacustrine organic matter characterization based on petrographic results immature to early mature yacoraite samples have a large content of yellow brownish liptinites alginites whereas mature samples are characterized by abundant solid bitumen three kerogen samples from the yacoraite formation at different thermal maturity levels were also selected for analysis of bulk kinetic parameters e g activation energy distribution frequency factor using programmed open system pyrolysis in this way bulk kinetic parameters were calculated as a function of the thermal maturity for these three lacustrine kerogen samples bulk kinetic results show both an increasing activation energy and loss of petroleum generation potential as thermal degradation proceeds the investigated yacoraite kerogen samples show single activation energy distributions which are typical for a type i kerogen of lacustrine origin finally it was demonstrated that the organic matter om characteristics from the yacoraite formation argentina could be compared to the typical type i kerogen from the green river formation usa showing similar om characteristics petroleum potential and activation energy distributions the novelty of the geological and geochemical information brought in this article about yacaroite system in argentina provides premises for further investigation

examination of downward hydrocarbon charge within the bakken three forks petroleum system williston basin north america abstract the bakken and three forks formations of the williston basin have been targeted by over 10 000 unconventional style wells horizontal drilling coupled with hydraulic fracturing exploration and developmental drilling initially focused on the middle bakken but later expanded into the underlying upper three forks located directly below the bakken and eventually the middle and lower three forks which are positioned 10s to 100 feet below the bakken hydrocarbons oil and associated gas within both formations are believed to be sourced from the upper and lower bakken shale members which are both highly organic rich 10 toc thermally mature petroleum source beds however minimal literature exists examining the relationship between hydrocarbons generated by the lower bakken shale and expelled downward into the various reservoirs of the three forks core plug oil and water saturation data from 65 partial to complete three forks cores were utilized to map out fluid saturation trends within the upper middle and lower three forks over 500 core chip analyses from 52 cores were used to spatially delineate the present day average hydrogen index thermal maturity of the lower bakken shale while a lower shale isopach map was created from wireline logs of 240 wells lastly the geochemical and standard core plug data from four complete bakken three forks cores were used to calculate and compare the volumetric amount of oil generated and expelled from the lower bakken shale with the original oil in place ooip of the entire three forks section the results show a strong spatial relationship between increased thickness thermally maturity of the lower bakken shale and increased core plug oil saturations across the upper to middle three forks members and a similar but less pronounced relationship with the lower three forks the calculated lower bakken shale expelled oil volumes ranged from 13 to 51 million barrels of oil mmbo per section 640 acres which overall equaled to exceeded the ooip of the entire three forks section 9 25 mmbo section these spatial and volumetric relationships indicate that local hydrocarbon generation and expulsion from the lower bakken shale is the primary control for hydrocarbon charge within the underlying three forks formation where in some locations hydrocarbons have been pushed downwards 200 ft understanding downward hydrocarbon charge has implications in exploring for and developing hydrocarbon resources within the bakken three forks as well as numerous other unconventional petroleum systems

shear strain localization from the upper mantle to the middle crust of the kohistan arc pakistan shear structures from mantle to middle crust levels of the kohistan palaeo island arc in pakistan are described pre himalayan ductile shear zones show a wide variety in size and shape and developed from gabbro subsolidus to amphibolite facies conditions their lithological context and geological history give insights into mechanisms that initiate shear strain localization factors that control stabilization of deformation in shear zones and flow properties at the mantle crust transition shear strain localization began within compositional gradients gabbros were more prone to localization into anastomosing patterns than diorites and granites which show more homogeneous strain shear strain localization during cooling led to less numerous but longer and thicker shear zones viscous heating within shear zones resulted in melt production and segregation in deformation structures and seems to have taken part in the plutonic history of the arc using kohistan as an example we suggest that the plutonic lower crust of arcs is strongly affected by subhorizontal synmagmatic shear zones probably consistent with the bulk flow direction of the subduction zone these features can obviously be preserved in collision orogens and may be mistaken for structures documenting the continental collision

laboratory measurement of p wave velocity in crustal and upper mantle xenoliths from ichino megata ne japan ultrabasic hydrous lower crust beneath the ne honshu arc abstract ultrasonic laboratory measurements of p wave velocity vp were carried out up to 1 0 gpa in a temperature range of 25 400 c for crustal and mantle xenoliths of ichino megata northeast japan the rocks used in the present study cover a nearly entire range of lithological variation of the ichino megata xenoliths and are considered as representative rock samples of the lower crust and upper mantle of the back arc side of the northeast ne honshu arc the vp values measured at 25 c and 1 0 gpa are 6 7 7 2 km s for the hornblende gabbros 38 6 46 9 wt sio2 7 2 km s for the hornblende pyroxene gabbro 43 8 wt sio2 6 9 7 3 km s for the amphibolites 36 1 44 3 wt sio2 8 0 8 1 km s for the spinel lherzolites 46 2 47 2 wt sio2 and 6 30 km s for the biotite granite 72 1 wt sio2 combining the present data with the vp profile of the ne honshu arc iwasaki t kato w moriya t hasemi a umino n okada t miyashita k mizogami t takeda t sekine s matsushima t tashiro k miyamachi h 2001 extensional structure in northern honshu arc as inferred from seismic refraction wide angle reflection profiling geophys res lett 28 12 2329 2332 we infer that the 15 km thick lower crust of the ne honshu arc is composed of amphibolite and or hornblende pyroxene gabbro with ultrabasic composition the present study suggests that the vp range of the lower crustal layer 6 6 7 0 km s in the ne honshu arc which is significantly lower than that obtained from various seismic measurements e g the northern izu bonin mariana arc 7 1 7 3 km s is due to the thick hydrous lower crustal layer where hornblende plagioclase and magnetite are dominant

a determination of the three dimensional seismic properties of anorthosite comparison between values calculated from the petrofabric and direct laboratory measurements bernard eront and david mainprice zaboratoire de tectonophysique i h iversit montpe lier ii montpe lier france nikolas i christensen department of earth and atmospheric sciences purdue unh ersity west lafayette btdiana we have undertaken a coinparative study of the seisnfic properties of an anorthosite the seisnfic properties have been calculated froin the lattice preferred orientation lpo of plagioclase 90 by volume and olivine 10 by voluine and the elastic constants of these minerals laboratory measurements of vp 24 directions and vs 6 directions have been made on the same sample at room temperature and pressures up to 1 0 gpa the twe techniques agree with 0 1 km s for all orientations studied when the voigt averaging method is used hill and reuss averaging methods give calculated velocities significantly lower than the experimental ones a study of the difference between the velocity values given by the two methods reveals a systematically larger departure in orientations normal to the foliation the orientation dependent difference between the two tedmiques can be explained if there are small errors in the elastic constants for single crystal plagioclase used in the initial calculations the axial lpo symmetry of the plagioclase with all the crystallographic b axes parallel to the specimen symmetry axis allowed us to calculate c22 norinal to 010 directly from the laboratory measurement of vp some constraints can be put on c22 c44 c66 c12 and c23 on average our data require 10 modification of the single crystal constants reported by ryzhova 1964

gas geochemistry from conventional to unconventional domains abstract gas geochemistry is developing into a powerful tool to understand geological processes and affirm source origins of geo fluids major and trace gases including abundances and isotopes have shown considerable application in natural gas systems for example progress in unconventional gases such as shale gas tight gas and extreme conditions in the deep oceans represent more emerging areas and application of these novel gas related techniques examples where gas geochemistry continues to place key constraints on the origin and migration characteristics of natural gas the p t characteristics of fluids in both subaerial and deep geothermal reservoirs and the dynamics of the accumulation cycles to name but a few this volume will reflect this diversity in scope and application of gas geochemistry focusing on deeper and broader applications in unconventional domains of novel gas geochemical techniques and applications

seismic anisotropy of metapelites from the ivrea verbano zone and serie dei laghi northern italy abstract laboratory measurements of compressional and shear wave velocities up to 600 mpa confining pressure were carried out on amphibolite to granulite facies metapelites from the serie dei laghi and ivrea verbano zone northern italy the metapelite samples show moderate to high compressional wave anisotropy and significant shear wave splitting for propagation directions parallel to foliation serie dei laghi samples are generally transversely isotropic for compressional wave propagation a pattern that based on calculated velocities is the consequence of strong preferred orientation of micas ivrea verbano samples generally have an orthorhombic anisotropy pattern for compressional waves that is caused by the preferred orientation of both mica and sillimanite shear wave anisotropy and shear wave splitting patterns differ significantly for the two fabric types intense static recrystallization can obliterate seismic anisotropy but partial static recrystallization does not appreciably reduce anisotropy we conclude that seismic anisotropy may occur in mid to lower continental crust where it is predominantly composed of metapelitic rocks and if there is a consistent regional fabric this seismic anisotropy may be diminished if there is no consistent regional fabric or if postmetamorphic intrusions have caused static recrystallization

experimental investigation of oil generation retention and expulsion within type ii kerogen dominated marine shales insights from gold tube nonhydrous pyrolysis of barnett and woodford shales using miniature core plugs abstract although oil retention has recently emerged as a key topic of unconventional shale resource assessment oil retention and expulsion controls in organic rich shales during thermal maturation remain poorly constrained this study presents an experimental comparison of oil generation retention and expulsion in two immature type ii kerogen dominated marine shales the mississippian barnett shale and the upper devonian lower mississippian woodford shale mainly with respect to the combined effects of the organic macerals and rock fabric involved in both cases miniature core plugs drilled from the given samples were isothermally pyrolyzed at 130 to 425 c for 72 h under a confining pressure of 68 mpa during gold tube nonhydrous pyrolysis corresponding to the thermally immature early stage of the oil window the main stage of the oil window the late stage of the oil window the main stage of oil cracking to wet gas and the late stage of oil cracking yields of generated oil retained oil and expelled oil for the two studied samples were systematically quantified on the basis of mass balance calculation of measured oil and gas yields as well as rock eval analyses on pyrolyzed subsamples through the six stages of petroleum formation investigated the principal difference in oil generation was observed in the two studied samples with approximately 38 to 68 greater yields of generated oil equivalent to 130 mg oil g toco for the woodford shale when it evolved into the main and late stages of the oil window these elevated yields of generated oil for the woodford shale were compensated for by additional oil generation resulting from conversion of abundant type i kerogen like algae such as tasmanites and leiosphaeridia which lag in onset and have a shorter period of petroleum generation upon maturation as a response to the difference in oil generation oil retention was found to be significantly enhanced for the woodford shale at equivalent stages with 0 2 to 1 7 times more free oil equivalent to 24 105 mg oil g toco and 0 7 to 3 9 times more sorbed oil equivalent to 58 76 mg oil g toco being retained than that of the barnett shale although this effect was not pronounced for oil expulsion in contrast to the barnett shale relatively low expelled oil yields and expulsion efficiencies both indicate highly limited oil expulsion in the woodford shale implying that the woodford shale whose mineral composition and lithofacies are similar to those of the barnett shale may have a relatively low permeability rock fabric to prevent oil from being expelled furthermore not only significantly higher oil saturation index osi values but also a wider range of maturity at which the oil crossover effect osi 100 mg g toc occurs is expected for the woodford shale when extrapolation to a geological setting occurs these data suggest that the presence of abundant type i kerogen like algae and relatively low permeability rock fabric in the woodford shale are critical to significant oil retention during oil generation and expulsion which jointly raise the possibility of potential commercial shale oil within type ii kerogen dominated marine shales

structure and composition of the aleutian island arc and implications for continental crustal growth we present results of a seismic reflection and refraction investigation of the aleutian island arc designed to test the hypothesis that volcanic arcs constitute the building blocks of continental crust the aleutian arc has the requisite thickness 30 km to build continental crust but it differs strongly from continental crust in its composition and reflectivity structure seismic velocities and the compositions of erupted lavas suggest that the aleutian crust has a mafic bulk composition in contrast to the andesitic bulk composition of continents the silicic upper crust and reflective lower crust that are characteristic of continental crust are conspicuously lacking in the aleutian intraoceanic arc therefore if island arcs form a significant source of continental crust the bulk properties of arc crust must be substantially modified during or after accretion to a continental margin the pervasive deformation intracrustal melting and delamination of mafic to ultramafic residuum necessary to transform arc crust into mature continental crust probably occur during arc continent collision or through subsequent establishment of a continental arc the volume of crust created along the arc exceeds that estimated by previous workers by about a factor of two

kinetic studies of asphaltene pyrolyses and their geochemical applications abstract pyrolysis kinetics are determined for a series of asphaltene samples associated with different types of kerogens the activation energy distributions obtained for asphaltenes related to type i kerogens cover a wide range with significant hydrocarbon generation with activation energies above 350 kj mol the ranges of activation energy distributions are relatively narrow for asphaltenes associated with type ii and iii kerogens with little hydrocarbons generated with activation energies above 350 kj mol if the type of associated kerogen can be reasonably constrained the pyrolysis kinetics of the asphaltenes is potentially a very useful tool for assessing the maturity levels of reservoired oils the results of pyrolysis kinetics indicate that there is still significant potential for asphaltenes to regenerate hydrocarbons

interpreting rock eval pyrolysis data using graphs of pyrolizable hydrocarbons vs total organic carbon kerogen the major organic component of sedimentary rocks is commonly analyzed by rock eval pyrolysis plotting the data on a graph of s 2 vs total organic carbon toc and determining the regression equation is the best method for determining the true average hydrogen index and measuring the adsorption of hydrocarbon by the rock matrix such a plot also indicates the type of kerogen present and avoids the problem of increasing hydrogen index with total organic carbon content with the s 2 vs toc diagram the organic component of different suites of samples may be compared and their petroleum generation potentials established as an example the diagrams are used to evaluate the sedimentary environments and petroleum potential of the paleogene evaporitic sediments of the mulhouse basin alsace france

high pressure high temperature seismic velocity structure of the midcrustal and lower crustal rocks of the ivrea verbano zone and serie dei laghi nw italy the ivrea verbano zone and the adjacent serie dei laghi in the inner arc of the western alps nw italy display an upended cross section through much of the thickness of the continental crust as it existed in that region in triassic jurassic time we collected a suite of oriented rock samples that represent most of the volume of the rocks of the region p and s wave velocity measurements were made in three orthogonal directions related to the mesoscopic fabric of the rocks at room temperature and up to 550 mpa confining pressure combined high temperature and high pressure measurements were made up to 700 c on a subset of the samples the lithologic units were divided into 23 different principal rock types and we present velocity data averaged in terms of these groups vertical and horizontal velocity and anisotropy sections are computed from the measured velocity data based on a restored geologic section these show that vp and vs both increase and anisotropy decreases systematically with depth of burial reflecting variations in rock type and metamorphic grade with depth vp and vs anisotropy arises mainly because of crystallographic preferred orientation or mineralogical banding with the slowest direction tending to be normal to the foliation or banding the vp velocity sections were used to compute synthetic seismic reflection profiles for the region when it lay at the bottom of the continental crust these correspond well with contemporary deep reflection profiles for regions of comparable tectonic evolution

3d seismic study of a ductile shear zone from laboratory and petrofabric data saint barthelemy massif northern pyrenees france in order to constrain interpretations of seismic reflection records more effectively the seismic properties of a middle crustal section exposed in the saint barthelemy massif have been determined the massif transected by a 200 m thick shear zone has been systematically sampled for density measurements and modal analysis has been performed in order to define the spatial variations of physical properties seismic velocities vp v5 shear wave birefringence have been measured on five representative samples to 600 mpa and 600 c simultaneously in the three structural directions x y and z for two samples the expep mental data have been compared with calculated values based on petrofabric analyses the lattice preferred orientation lpo is determined using universal stage electron channelling microscopy and neutron diffraction goniometry using the experimental and calculated velocity data we establish a lateral homogeneous anisotropie model

seismic structure of the continental crust based on rock velocity measurements from the kapuskasing uplift the michipicoten greenstone belt mgb wawa gneiss terrane wgt and kapuskasing structural zone ksz in ontario canada are regarded as a 25 km thick partial cross section through the crust of the superior province we measured compressional wave velocities vp at confining pressures up to 600 mpa for representative rock samples from these terranes vp for mgb is variable 6 1 7 km s and depends on composition and anisotropy compressional wave velocities for low anisotropy quartzofeldspathic gneisses and intrusive rocks from the wgt and the ksz show little variation over a wide range of silica content but mafic gneisses and anorthositic rocks show a wide velocity range over a narrower silica range a trend corroborated by data for other high grade rocks a model of the continental crust based on the laboratory data shows three megalayers with differing seismic characteristics the shallowest levels mgb are seismically heterogeneous with high average velocities 6 6 km s at 100 mpa because of the dominance of metabasalts the balance of the upper crust wgt is seismically homogeneous as it is dominated by a variety of isotropic quartzofeldspathic rocks with average velocities of 6 35 km s at 100 mpa and 6 6 km s at 600 mpa the uppermost lower crust ksz is layered seismically heterogeneous and transversely isotropic the average velocity at 600 mpa is 6 84 km s the boundary between wgt and ksz is marked by a velocity increase of between 0 2 and 0 3 km s an increase similar to that commonly associated with midcrustal discontinuities i e conrad in shield areas here this boundary corresponds to the amphibolite granulite facies transition and to a change from a tonalitic middle crust to a lithologically heterogeneous uppermost lower crust refraction results show an anomalous high velocity zone in the upper crust under the ksz that on the basis of laboratory velocity data can be correlated with ksz lithologies these data indicate that ksz rocks can be traced to the west to depths as great as 20 km levels deeper than 20 km not exposed at the surface in the ksz are characterized by velocities greater than 7 0 km s and may be dominated by mafic and anorthositic lithologies or by more garnet rich rocks the velocity model of the superior province crust based on geological reconstruction and laboratory velocity data is in general agreement with the velocity structure to depths of about 25 km determined for the crust below the mgb from refraction experiments the velocity structure of this model is also generally similar to the velocity structure of shield areas

state of the art of research in kinetic modelling of oil formation and expulsion abstract the last ten years have seen a rapid development in the understanding of petroleum generation and expulsion by a combined use of natural series and experimental simulation this knowledge is now used to develop mathematical models which reproduce the kinetics of petroleum generation and migration in the purpose of basin evaluation by a combination of observation of homogeneous geochemical series experimental simulation and mathematical modelling it has been now established that parameters governing the quantity and composition of petroleum are temperature type of organic matter time or heating rate catalysis by clay minerals which would produce important amounts of isoalkanes is not necessary to produce petroleum the role of minerals although still controversial is rather to retain the heavy fraction of petroleum pressure seems to have a limited influence within the range for effective source rocks kerogen is a tremendously complex macromolecule which is now insufficiently characterized to develop fundamental predictive models of thermal cracking i e involving intermediates such as radicals and olefins such models presently apply only to the cracking of simple molecules hexane hexadecane at limited degrees of cracking for this reason kinetic models are still empirically calibrated on pyrolysis experiments and or on natural maturation trends the most popular models involve a series or a continuous distribution of parallel reactions to describe primary cracking i e direct formation of mobile compounds from kerogen these are generally calibrated against open system pyrolysis with various temperature programs consideration of natural maturation trends i e decrease in petroleum potential may be used also for calibration but discrepancies of organic matter properties availability of deep samples and uncertainties on thermal history limit the effectiveness of such methods whatever the method main activation energies are found in the range 45 60 kcal mol secondary cracking which refers generally to cracking of mobile compounds cannot be modelled from open system pyrolysis nor from natural series unknown residence times but only from closed system pyrolysis although models of primary and secondary cracking still need experimental improvements and more realistic kinetic schemes their ability to predict quantities and composition of petroleum depends primarily on migration which is poorly known indeed migration controls the residence time of petroleum in hot zones of sedimentary basins and thus determines the extent of oil conversion into gas as reproduced by recent numerical models preliminary studies documenting the interactions between thermal cracking and expulsion are shown from haltenbanken area and paris basin in the last few years a kind of agreement has been reached that primary migration was most likely occuring in a separate phase from water and that a sufficient concentration of petroleum must be generated for expulsion to start indeed high expulsion efficiencies over 50 are systematically found for rich and mature source rocks a further understanding of primary migration requires observations of natural series petrophysical studies of source rocks porosities under 10 permeabilities in the nanodardy range thermodynamic investigation of unconventional multiphase organic systems kerogen liquid s gas and experimental simulation under stress this on going research should enable models to track correctly migration paths and thermal history of petroleum fluids as necessary to model their composition

kinetics of oil group type generation and expulsion an integrated application to dongying depression bohai bay basin china pyrolysis of two kerogens isolated from the e2 3s 3 3 and e2 3s 1 4 source rocks in the niuzhuang sag dongying depression bohai bay basin china was performed in a confined system the products were extracted with solvent and separated using micro column chromatography into group type fractions saturates aromatics resins and asphaltenes with the kerogen residue in each case undergoing swelling with a variety of solvents the kinetics for generation and retention of crude oil and its group type fractions from the kerogens were studied and the kinetic parameters applied to modeling generation and retention of crude oil and its fractions from the e2 3s 3 3 and e2 3s 1 4 source rocks on the basis of burial and thermal history of the niuzhuang sag the results show that the normal oil was generated at about 4 26 ma and 24 85 ma ago but expelled at about 3 96 ma and 17 46 ma ago respectively from e2 3s 3 3 and e2 3s 1 4 source rocks the current proportions of the expelled saturates aromatics and nsos are about 60 15 and 25 respectively

laboratory seismic measurements an aid in the interpretation of seismic field data this contribution reports data and evidence from laboratory measurements of compressional and shear wave velocities and mineralogical microstructural and chemical analyses in crustal rocks that may provide an aid to understanding and interpreting geophysical data it is shown that the correlation of laboratory seismic data with stratigraphic field data can provide the necessary data base for constructing a seismic model of the earth s crust in a particular geological area

absolute reflection coefficients from deep seismic reflections abstract many deep seismic reflection profiles show bright sub horizontal layered reflections in the lower continental crust accurate estimates are obtained for normal incidence reflection coefficients for the brightest of these reflections by using a marine seismic acquisition system that has been calibrated using deep water sea bottom multiples minimum bounds are placed upon these reflection coefficients by assuming minimum losses due to scattering anelastic attenuation and geometric spreading reflection coefficients of around 0 1 are obtained from the layered lower crust and around 0 15 from the moho it is argued that constructive interference between successive reflections from a layered sequence of reflectors is often unimportant consequently these coefficients can be used to place useful limits on the absolute acoustic impedance contrasts present at depth