organic matter cracking a source of fluid overpressure in subducting sediments the pressure of deep fluids in subduction zones is a major control on plate boundary strength and earthquake genesis the record by methane rich fluid inclusions of large 50 100 mpa and instantaneous pressure variations in the shimanto belt japan points to the presence of large fluid overpressure at depth 300 500 mpa 250 c to further analyze the connection between methane and fluid overpressure we determined with rock eval the potential for a worldwide selection of deep seafloor sediments to produce methane as a result of organic matter om cracking due to temperature increase during subduction the principal factor controlling the methanogenesis potential of sediments is om proportion while om nature is only a subordinate factor in turn om proportion is mainly controlled by the organic terrigenous input considering a typical sediment from ocean continent subduction zones containing 0 5 wt of type iii om cracking of om has two major consequences 1 methane is produced in sufficient concentration as to oversaturate the pore filling water the deep fluid in accretionary prisms is therefore a mechanical mixture of water rich and methane rich phases 2 ch4 production can generate large fluid overpressure of the order of several tens of mpa the conditions for these large overpressure are a low permeability of the upper plate 10 km where om thermal cracking occurs at these depths om thermal cracking appears as a source of overpressure larger than the last increments of smectite to illite reaction such large overpressures play potentially a role in facilitating slip along the plate interface conversely the scarcity of earthquakes in ocean ocean subduction zones such as marianna or barbados may be related to the low influx of detrital om and the limited methane overpressure generation at depth

long term impact of temperature on the hydraulic permeability of bentonite in a swedish repository for the disposal of heat emitting waste the long term thermal stability of the bentonite engineered barrier forms a key component of the safety case central to such consideration is the evolution of hydraulic permeability and a potential degradation of hydraulic properties in response to prolonged thermal exposure of the clay to address this issue a detailed programme of laboratory based experiments has been undertaken at both the british geological survey and studiecentrum voor kernenergie centre d etude de l energie nucleaire in order to examine the hydraulic behaviour of bentonite that had previously been exposed to elevated temperatures hydraulic properties were calculated from both steady state pressure gradients and from analysis of the pressure transients inspection of the data found no significant difference in hydraulic behaviour between the virgin material and clay samples taken from the canister retrieval test based on these observations the authors find no evidence for an adverse increase in hydraulic conductivity of bentonite as a result of prolonged thermal exposure to temperatures of 80 8c

kinetic constraints on illitization reactions and the effects of organic diagenesis in sandstone shale sequences abstract based on water rock interaction modelling and kinetic considerations the present study is aimed at testing the impact of organic matter maturation on two kinds of diagenetic reactions leading to the alteration of the petrophysical properties of sandstones 1 clay mineral conversion to illite with k feldspar being a local potential source of k and 2 dissolution precipitation processes produced in sandstones by the action of water soluble organic species derived from adjacent shales assuming firstly that the chemical reactions take place in closed systems the nature and timing of diagenetic reactions in marine sandstone shale formations were modelled for a 50 120 c temperature range in order to improve understanding of the factors that control the illitization reaction with k feldspar coexisting with aluminous clay illite is modelled here as a muscovite type mineral we tested the effects of an energy barrier on illite growth by allowing or preventing the muscovite illite precipitation reaction to occur while using several illitization reaction rates we also compared the stable mineral parageneses predicted for organic material free systems with those predicted in the case of organic diagenesis release of co 2 ch 4 acetic and oxalic acids similarities and discrepancies between numerical results and natural mineral assemblages suggest that the illitization reaction depends on the nature of the reacting clays kaolinite conversion to end member illite involves high energy conditions 2 kcal mol 1 which are not met when the pore water equilibrates with the mineral matrix from undersaturated conditions in a closed system to overcome this barrier the fluid should be oversaturated with respect to k feldspar an external source of k or a ph increase in an open system is necessary for this reaction no particular effect of organic diagenesis on this reaction was found in the present study on the other hand smectite to illite conversion involves a lower energy barrier and can operate in closed systems where k feldspars are the source of k the maturation of organic matter may speed up the smectite to illite conversion rate by increasing the gibbs free energy of illite growth interactions between sandstone and shale were examined by modelling the transfer of aqueous species of organic origin from shale to sandstone fluid expulsion from shale had little or no effect on diagenesis in adjacent sandstones during each flushing cycle mainly because organic protons and ligands were neutralized in the source rock however the diffusion of shale derived cations through sandstone as organometallic complexes mg ca fe al appears to be an efficient process during carbonate cementation in sandstones where oxidizing conditions enhance the decomposition of such complexes

chemical and isotopic characterization of water rock interactions in shales induced by the intrusion of a basaltic dike a natural analogue for radioactive waste disposal abstract disposal of nuclear waste in deep geological formations is expected to induce thermal fluxes for hundreds of years with maximum temperature reaching about 100 150 c in the nearfield argillaceous environment the long term behavior of clays subjected to such thermal gradients needs to be perfectly understood in safety assessment considerations in this respect a toarcian argillaceous unit thermally disturbed by the intrusion of a 1 1 m wide basaltic dike at the perthus pass herault france was studied in detail as a natural analogue the thermal imprint induced by the dike was evaluated by a mineralogical chemical and k ar study of the at the eastern contact with the dike the mineral and chemical compositions of both the shales and the basalt suggest water rock interactions subsequent to the intrusion with precipitation of palagonite and renewed but discrete deposition of carbonate a pencil cleavage developed in the shales during the dike emplacement probably favored water circulation along the contact strontium isotopic data suggest that the fluids of probable meteoric origin reacted with bathonian and bajocian limestones before entering the underlying toarcian shales by analogy with deep geological radioactive waste repositories the results report discrete mineralogical variations of the clays when subjected to temperatures of 100 150 c that are expected in deep storage conditions beyond 150 c significant mineralogical changes may alter the physical and chemical properties of the shales especially of the clay fraction also the development of structural discontinuities in the so called thermally disturbed zone might be of importance as these discontinuities might become zones for preferential fluid circulation finally the study emphasizes the use of rb sr and k ar isotopic systems as tracers of local circulating fluids related to low grade thermal imprints

the control of the smectite illite transition on passive roof duplex formation canadian rockies foothills alberta abstract the roof decollement to the passive roof duplex and triangle zone in the central foothills rocky mountain thrust belt is located within a sequence of siliciclastic sediments dominated by shale mudstone it is unclear why the decollement is found at a certain level in the stratigraphy when the whole package appears to have similar lithilogical and hence mechanical properties investigation of the mineralogy of the mudstones reveals that the clay fraction preserves a smectite to illite transition which formed during maximum burial conditions the top of the transition is associated with the top of the roof decollement in the region in the gulf of mexico the transition correlates with both a zone of overpressure favorable for detachment and a corresponding drop in density rise in porosity in the foothills the transition also records a drop in density and a concomitant drop in sonic velocity by analogy with the gulf of mexico the drop in density may record a paleo overpressured horizon that was favorable for detachment and formation of a roof decollement in the foothills

the thermal history of the bowen basin queensland australia vitrinite reflectance and clay mineralogy of late permian coal measures abstract the thermal history of the bowen basin queensland australia has been investigated using vitrinite reflectance data and clay mineralogy vitrinite reflectance data combined with a study of clay mineral reactions indicates that the maximum temperatures which induced organic maturation of the bowen basin coals and extensive clay mineralisation are not related to deep burial metamorphism during the latest middle triassic earliest late triassic as previously believed the results of the present study indicate that the development of a zone of high heat flow in the latest late triassic had a major control on the thermal history of the bowen basin high palaeogeothermal gradients estimated in the northern bowen basin are interpreted to result from convective heat transfer during a hydrothermal event variable heat distributions due to localised fracture enhanced permeable zones acting as hot reservoirs in the deeper part of the basin may have been responsible for some significant local thermal anomalies in the lower coal measures the estimated palaeogeothermal gradients in the southern bowen basin also indicate high heat flow in the lower sections of the stratigraphy sections in the southern bowen basin however are believed to reflect a rock dominated semi closed system with low water rock ratio where rocks are impervious to circulating fluids and thus heat transfer may have occurred by conduction the correlation between vitrinite reflectance and clay mineralogy shows a delay in illitisation reaction relative to organic maturity for many illite smectite i s mixed layer clays in the northern bowen basin this phenomenon can be explained as a result of insufficient time for the completion of mineral reactions and a variable potassium supply in relatively impermeable rocks the relationship between i s expandability and vitrinite reflectance for the bowen basin data compared to basins with known tectonic regimes suggests a thermal history in a rift setting for the bowen basin the effect of thin igneous intrusions on clay mineral reactions is very limited intensive illitisation due to heating of intrusions can only be observed in narrow zones immediately adjacent to intrusive bodies this further demonstrates that mineral reactions are too slow to record the effect of extremely short heating duration in contrast to organic maturity indicators these differences between mineral and organic parameters aid in the identification of local contact metamorphic effects

sandstone diagenesis and reservoir quality prediction models myths and reality models and concepts of sandstone diagenesis developed over the past two decades are currently employed with variable success to predict reservoir quality in hydrocarbon exploration not all of these are equally supported by quantitative data observations and rigorous hypothesis testing simple plots of sandstone porosity versus extrinsic parameters such as current subsurface depth or temperature are commonly extrapolated but rarely yield accurate predictions for lithified sandstones calibrated numerical models that simulate compaction and quartz cementation when linked to basin models have proven successful in predicting sandstone porosity and permeability where sufficient analog information regarding sandstone texture composition and quartz surface area is available analysis of global regional and local data sets indicates the following regarding contemporary diagenetic models used to predict reservoir quality 1 the effectiveness of grain coatings on quartz grains e g chlorite microquartz as an inhibitor of quartz cementation is supported by abundant empirical data and recent experimental results 2 vertical effective stress although a fundamental factor in compaction cannot be used alone as an accurate predictor of porosity for lithified sandstones 3 secondary porosity related to dissolution of framework grains and or cements is most commonly volumetrically minor 2 exceptions are rare and not easily predicted with current models 4 the hypothesis and widely held belief that hydrocarbon pore fluids suppress porosity loss due to quartz cementation is not supported by detailed data and does not represent a viable predictive model 5 heat flow perturbations associated with allochthonous salt bodies can result in suppressed thermal exposure thereby slowing the rate of quartz cementation in some subsalt sands

progress of illitization along an imbricate frontal thrust at shallow depths in an accretionary prism abstract fossil imbricate thrusts branching from a decollement in an ancient accretionary prism the miura boso accretionary prism are exposed in the southern parts of the miura and boso peninsulas in central japan an analysis of the clay mineralogy of fault rocks along one of the imbricate thrust faults the shirako fault revealed local illitization of mixed layer illite smectite i s and the partial breakdown of kaolinite the shape of the i 001 s 001 reflection in the x ray diffraction pattern suggests that the illite fraction in i s crystallites within the fault gouge is 9 more than in the surrounding rocks these results imply that there has been a local temperature anomaly within the slip zone attributable to frictional heating induced by high velocity slip a thermal model coupled with a kinetic simulation of illitization in i s suggests that the reaction was probably facilitated by multiple high velocity slips at a peak temperature of 450 c suggesting repeated seismic rupture propagations to the prism toe as also inferred from the modern accretionary prism in the nankai trough

active mud volcanoes on the continental slope of the canadian beaufort sea the major geochemical characteristics of red sea brine are summarized for 11 brine filled deeps located along the central graben axis between 19 n and 27 n the major element composition of the different brine pools is mainly controlled by variable mixing situations of halite saturated solution evaporite dissolution with red sea deep water the brine chemistry is also influenced by hydrothermal water rock interaction whereas magmatic and sedimentary rock reactions can be distinguished by boron lithium and magnesium calcium chemistry moreover hydrocarbon chemistry concentrations and 13 c data of brine indicates variable injection of light hydrocarbons from organic source rocks and strong secondary bacterial or thermogenic degradation processes a simple statistical cluster analysis approach was selected to look for similarities in brine chemistry and to classify the various brine pools as the measured chemical brine compositions show remarkably strong concentration variations for some elements the cluster analysis indicates two main classes of brine type i brine chemistry oceanographer and kebrit deeps is controlled by evaporite dissolution and contributions from sediment alteration the type ii brine suakin port sudan erba albatross discovery atlantis ii nereus shaban and conrad deeps is influenced by variable contributions from volcanic magmatic rock alteration the chemical brine classification can be correlated with the sedimentary and tectonic setting of the related depressions type i brine filled deeps are located slightly off axis from the central red sea graben a typical collapse structure formation which has been defined for the kebrit deep by evaluating seismic and geomorphological data probably corresponds to our type i brine type ii brine located in depressions in the northern red sea i e conrad and shaban deeps could be correlated to volcanic intrusion extrusion related deep formation the chemical indications for hydrothermal influence on conrad and shaban deep brine can be related to brines from the multi deeps region in the central red sea where volcanic magmatic fluid rock interaction is most obvious the strongest hydrothermal influence is observed in atlantis ii brine central multi deeps region which is also the hottest red sea brine body in 2011 68 2 c

sulphide mineral reactions in clay rich rock induced by high hydrogen pressure application to disturbed or natural settings up to 250 c and 30 bar abstract as abiotic hydrogen redox reactivity is kinetically limited most of the possible redox reactions induced by hydrogen remain insignificant at low temperature even at a geologic time scale this is the case for sulphate and carbonate reduction but some h2 induced redox reactions may be significant at low temperature conditions in particular the pyrite reduction into pyrrhotite in this experimental study the geochemical impact of hydrogen in a clay rich rock containing 1 2 wt framboidal pyrite is evaluated under mid hydrothermal condition 90 to 250 c and with hydrogen partial pressure ranging from 3 to 30 bar this study demonstrates that the main geochemical perturbation induced by hydrogen in a claystone host rock formation is the destabilisation of pyrite which leads to the production of sulphide two different reaction mechanisms can be distinguished as a function of temperature and hydrogen pressure when temperature is lower than 150 c and the hydrogen partial pressure is below 6 bar pyrite solubility controls the sulphide concentration at low values by contrast at higher temperature or at higher hydrogen partial pressure the rate and extent of the reaction are driven by pyrrhotite precipitation a complete replacement of pyrite into pyrrhotite occurs within a short interval of time at t 90 c and p h2 10 bar the ph of the media is also a critical parameter controlling the extent of the reaction as alkaline conditions may promote pyrrhotite precipitation at lower temperature and hydrogen pressure these conclusions have a direct application in the safety assessment of nuclear waste repositories but may also be extended to other contexts such as the underground storage of hydrogen and given the wide range of temperatures used in the experiments can even be applied to hydrothermal hosted submarine systems where hydrogen is naturally produced by olivine serpentinization

the geochemistry of potassic lavas from vulsini central italy and implications for mantle enrichment processes beneath the roman region major and trace element and 143nd 144nd 0 51209 0 51216 and 87sr 86sr 0 70879 0 71105 isotope analyses are presented on a representative group of lavas from the vulsini district of the roman magmatic province three distinct series are identified the high k and low k series are similar to those described from other italian volcanoes while the third is represented by a group of relative ly undifferentiated leucite basanites which are thought to be near primary mantle melts major and trace element variations within the high k series are consistent with fractional crystallisation from a parental magma similar to the most magnesian leucitites crustal contamination resulted in an increase in 87sr 86sr with increasing fractionation but it was superimposed on magmas which had already inherited a range of incompatible element and isotope ratios from enrichment processes in the sub continental mantle these are reviewed using the available results from vulsini roccamonfina and ernici transition element abundances and ta yb ratios indicate that the pre enrichment mantle was similar to that of e type morb and that these elements were not mobilised by the enrichment process mixing calculations suggest that three components were involved in the enrichment process mantle comparable with the source of morb and two other components rich in trace elements one the low k component had high sr nd th ta and ba nb and no europium anomaly while the second had lower sr nd a negative europium anomaly and very high th ta it was also characterised by low nb ba and high rb ba ratios similar to those reported from phlogopite rich peridotite xenoliths the trace element enrichment processes are therefore thought to have occurred in the mantle wedge above a subduction zone with the trace element characteristics of the high k end member reflecting the subduction of sediments and the stabilisation of mantle phlogopite

a simplified dissolution precipitation model of the smectite to illite transformation and its application 1 by combining the compaction effect ec from a dissolution precipitation model dpm and the thermal effect et from a kinetic model km a simplified dpm is presented a pair of apparent activation energy e and frequency factor a to be used is proposed in the model which is chosen to cause the predicted smectite to fit x ray diffraction xrd data the proposed model is then applied to the illite smectite interstratifications of mudstone in well tazhong4 of the tarim basin in western china a km is also applied for the sake of comparison this case study shows that the most sensitive parameter governing smectite to illite s i transformation is the pair of e and a to calculate an accurate s i transformation history it is vital therefore to calibrate the e and a by using xrd data as a constraint in this specific case study the calibrated e ranges between 5 and 10 28 kcal mol 1 while a is between 9 0623 10 11 and 3 10 7 s 1 l mol 1 for the simplified dpm and e ranges between 3 and 5 while a is between 1 3888 10 11 and 3 5052 10 9 for the km the relation of e versus ln a appears nonlinear by using these e and a the present day values of the calculated smectite history agree well with the xrd determined data with mean absolute relative residuals of 4 45 for the simplified dpm and 5 67 for the km moreover the case study indicates that ec and et have the same importance for s i transformation as contributions of ec of 43 5 and of et of 56 5

a diagenesis model for geomechanical simulations formulation and implications for pore pressure and development of geological structures forward basin modelling is routinely used in many geological applications with the critical limitation that chemical diagenetic reactions are often neglected or poorly represented here a new temperature dependent kinetic diagenesis model is formulated and implemented within a hydromechanical framework the model simulates the macroscopic effects of diagenesis on 1 porosity loss 2 sediment strength 3 sediment stiffness and compressibility 4 change in elastic properties 5 increase in tensile strength due to cementation and 6 overpressure generation a brief overview of the main diagenetic reactions relevant to basin modelling is presented and the model calibration procedure is demonstrated using published data for the kimmeridge clay formation the calibrated model is used to show the implications of diagenesis on prediction of overpressure development and structural deformation the incorporation of diagenesis in a uniaxial burial model results in an increase in overpressure of up to 9 mpa due to both stress independent porosity loss and overpressure generated by disequilibrium compaction caused by a reduction in permeability finally a compressional model is used to show that the incorporation of diagenesis within geomechanical models allows the transition from ductile to brittle behaviour to be captured due to the increase in strength that results in an over consolidated stress state this is illustrated by comparison of the present day structures predicted by a geomechanical only model where a ductile fold forms and a geomechanical model accounting for diagenesis in which a brittle thrust structure is predicted

re evaluation of frictional heat recorded in the dark gouge of the shallow part of a megasplay fault at the nankai trough abstract because a megasplay fault branching from the deep subduction boundary megathrust in the nankai trough is thought to be the source of large tsunamis associated with past tonankai earthquakes investigation of the heat signal due to frictional slip recorded in the fault is important for estimating the earthquake slip parameters we performed x ray diffraction and infrared spectroscopic analyses of a megasplay fault rock sample and re examined previously reported trace element and isotope compositions but observed no specific change related to high temperature 250 c in addition although a qualitative increase of the illite content in illite smectite mixed layer minerals within the slip zone sample was previously reported our kinetic evaluation of illitization taking into consideration the coseismic temperature change due to frictional heating and heat conduction revealed that the illitization reaction hardly progresses at temperatures under 250 c alternatively we suggest that the illite content in mixed layer minerals might increase progressively via a comminution dissolution recrystallization process during multiple past slips accurate assessment of the slip behavior of the megasplay fault could be efficiently obtained by drilling to penetrate the fault zone at a deeper depth of approximately 1 5 km where records of high temperatures would be detectable

tephra fountaining rheomorphism and spatter flow during emplacement of the pitigliano tuffs latera caldera italy abstract toward the end of the main ash flow phase ca 156 ka of the latera caldera central italy explosive eruptions near the nw caldera rim produced coarse grained tephra exposed in 35 m high faces of the toscapomice casa collina quarry the pyroclastic sequence fills a narrow sw ne paleovalley and records the near continuous eruption of a compositionally zoned magma batch white phonolitic pumice clasts abruptly grade upward to and partly intrude black spatter like pumice fragments also of phonolite composition this sequence in turn is overlain by densely welded tuff that grades upward to tephriphonolitic scoriae and ash the upper welded part of this sequence referred to as the vulcanite complessa di pitigliano has long been among the more enigmatic deposits in the latera area this sequence displays evidence for both fall and flow emplacement and is here interpreted as an ash fountain fed deposit that locally welded as spatter yet became sufficiently fluidized in distal parts to behave as a spatter rich pyroclastic flow this mechanism requires that the eruption underwent abrupt transition from a vigorously convecting column to a weakly convecting ash fountain and that this period of explosive activity culminated with unusually high accumulation rates the rapidly emplaced tephra retained sufficient heat to weld by compaction and undergo rheomorphism close to the vent yet contained high enough proportions of fluidized dust to have flowed outward along the northern caldera rim and eventually to have welded by vapor phase sintering

hydrothermal alteration of the ediacaran doushantuo formation in the yangtze gorges area south china abstract the geochemical and fossil record preserved in the ediacaran age 635 551 ma doushantuo formation of south china has been extensively examined to explore the impact of changing climate and the oxidation state of the oceans on the development and distribution of early multicellular life in the yangtze gorges area this formation shows many of the geochemical trends and features thought to typify global ocean chemistry in the ediacaran period but there are indications that post sedimentary processes modified these signals this study of clay minerals and organic matter builds a more detailed picture of the type and degree of post sedimentary alteration at different stratigraphic levels of the formation and focuses on how this alteration influenced stable carbon and oxygen isotope records in the cratonward jiulongwan and huajipo sections of the doushantuo formation its lower part members 1 and 2 consists largely of dolomitic shale rich in authigenic saponite that crystallized in an alkaline sedimentary basin saponite has been altered to chlorite via corrensite across tens of meters of strata in lower member 2 with increased alteration downward toward the cap dolostone the greater chloritization is accompanied by lower 18 o and higher d values of trioctahedral clays this pattern of alteration of trioctahedral clays is likely due to hydrothermal fluid activity in the underlying relatively permeable nantuo formation and cap dolostone a concomitant increase of solid bitumen reflectance toward the base of the formation supports this idea in the uppermost part of the formation in the yangtze gorges area member 4 a typical open water marine dolomitic shale rich in illite and organic matter increases in the methylphenanthrenes ratio index and solid bitumen reflectance correlate with decrease of the bulk rock k al ratio upward providing evidence for hot fluid migration above the nearly impermeable shale clay from the upper part of the formation is enriched in 18 o but not in d relative to clay from the lower parts indicating progressive 18 o enrichment of hydrothermal fluids that percolated upward and laterally through permeable 18 o rich carbonates a maximum hydrothermal alteration temperature of 200 c is estimated from a calibration curve for illitization during burial diagenesis but given that the hydrothermal activity probably occurred in short pulses the temperature could have been much higher k ar ages are consistent across different size fractions of fine illite from member 4 shale 430 ma and from a k bentonite bed near the base of member 2 in the jiuqunao section 325 ma 25 km from jiulongwan and huajipo these age values show that the diagenetic illite of the doushantuo formation is a product of either deep burial diagenesis overprinted by spatially limited hydrothermal activity or of two localized hydrothermal events patterns of carbonate 13 c and 18 o depletion in the basal doushantuo formation are similar to chloritization trends and 18 o variation in diagenetic clay minerals given independent evidence for 13 c depletion of hydrothermal fluids these trends indicate carbonate fluid isotope exchange commensurate with the degree of post sedimentary alteration supporting a model of lithologically controlled differential diagenesis induced by hydrothermal fluids as the main control on c and o isotope variability in this stratigraphic interval this model could potentially explain other notable 13 c excursions higher up in member 3

origin of illite in the lower paleozoic of the illinois basin evidence for brine migrations in the lower paleozoic of the illinois basin three illite polytypes are found 2m 1 of detrital origin and 1m d and 1m of diagenetic origin illite polytype quantification of detrital 2m 1 illite and diagenetic 1m d and 1m illite combined with k ar age dating allows extrapolation to apparent detrital and diagenetic illite ages kinetic modeling of smectite illitization combined with the calculated age of illitization can evaluate different origins of illite the diagenetic illite in the lower paleozoic of the illinois basin is interpreted not to have formed solely by burial diagenesis but mainly during multiple brine events the upper ordovician maquoketa group contains diagenetic illite dominantly 1m d with minor 1m with an extrapolated age of 360 m y 356 377 m y and formed from smectite at temperatures of 50 100 c this age falls within the span of dates for illite smectite i s in k bentonites from the upper mississippi valley and is interpreted to be a combined result of illitization by burial diagenesis and either a hydrothermal brine from the southern and deeper part of the basin or a k rich brine from the michigan basin upper mississippi valley area or forest city basin in ordovician and cambrian shale partings and sandstone older than the maquoketa group the diagenetic illite 1m d in shale and 1m in sandstone has an age of 300 m y and formed at temperatures 140 c this late paleozoic age falls within the range of illites from sandstone in the upper mississippi valley and k bentonites of the appalachian basin it coincides with the alleghany orogeny and is interpreted as having formed by gravity driven flow from the uplifted alleghanian ouachita orogenic belt that drove hot 140 c fluids through the illinois basin

shallow seismicity of arc continent collision near lae papua new guinea abstract in northeastern new guinea the narrow ramu markham valley rmv separates island arc rocks to the north from those of continental origin to the south and appears to be the western onland extension of the new britain trench to explore the tectonic processes at the leading edge of the island arc during collision we operated a portable seismic network for six weeks near the city of lae at the eastern end of the rmv we observed a narrow near vertical belt of seismicity between 10 and 30 km depth that we call the lae seismic zone lsz starting at the rmv in the southwest and trending northeasterly cutting across surface geologic structure the truncation of the lsz along a steep plane by the ramu markham fault zone rmfz and earthquake first motions suggest that the earthquakes occur in the hanging wall of a steep n dipping fault that crops out at the rmfz we also consider that the lsz is within the lower plate of a gently dipping thrust below 20 km depth the microearthquake zone is truncated by a gently ne dipping plane coinciding in depth and dip with nodal planes of recent large mb 5 6 and 6 0 thrust earthquakes we suggest that the huon peninsula is being emplaced onto the australian plate along a gently 25 dipping thrust fault that is 20 km deep beneath lae the rmfz may be a steeply dipping thrust fault that connects with this gently n dipping thrust but accommodates little convergence at present the lsz trends nearly perpendicular to an anticlinal range which appears to be sheared in a left lateral sense p wave first motions for earthquakes in the lsz with steep 70 to 90 dip nodal planes that strike parallel to the lsz suggest a component of south side up displacement also hence the crustal block south of the lsz may be rising relative to the huon peninsula and the rapid quaternary uplift rates estimated for the lae coastal region may be higher than the uplift rate of the huon peninsula as a whole we suggest that the lsz reveals a tear of small offset in the huon terrane but may be similar to a structure that produced a magnitude 7 earthquake near madang in 1970

the evolution of latera caldera central italy in the light of subsurface data subsurface geothermal exploration has considerably added to our knowledge of the latera volcanic complex a syenitic body is located about 2 km below the present day surface k ar data point a 0 9 ma age the primary magma was a silica saturated trachyte undersaturated hauyne bearing products are found near the carbonatic wall rocks and have been interpreted as reaction products subsurface data from deep drilling and geophysical surveys suggest that the latera caldera resulted from three main successive collapse phases i formation of an old caldera now buried related to the eruption of ignimbrites from the syenitic magma chamber ii sinking of the eastern sector as a consequence of the formation of the nearby bolsena caldera 0 3 ma iii multistage formation of the present latera caldera 0 16 ma

the silidor deposit rouyn noranda district abitibi belt geology structural evolution and paleostress modeling of an au quartz vein type deposit in an archean trondhjemite late orogenic gold bearing quartz vein deposits within the rouyn noranda mining district occur mainly within archean tonalitic plutons of the blake river group southern abitibi belt the silidor deposit is a representative example of a pluton hosted lode gold deposit the silidor mine contained 2 95 million tons mt mined and estimated reserves grading 5 1 g t au 15 t au the mineralized zone is 900 m in length and has a vertical extent of 900 m an average thickness of 3 5 m and trends northwest southeast with a dip of 50 to 70 ne its alteration envelope consists of a red hematite altered trondhjemite measured 18 o values for quartz veins 7 7 10 9 and 34 s values for pyrite 6 1 to 9 4 imply oxidizing conditions during gold deposition the mineralized zone comprises vein quartz white gray and smoky varieties beige mineralized trondhjemite and green carbonate sericite fuchsite breccia which resulted from shearing and metasomatism of an early northwest southeast dioritic dike a quantitative microtectonic study 400 measurements was carried out on the powell tonalitic sill in the silidor mine area to reconstruct the deformation before during and after the mineralizing events the reduced stress tensors display large variations in 1 orientation trending successively northwest southeast northeast southwest and finally north south the silidor deposit is the result of several vein filling events which occurred during evolution from strike slip faulting to reverse faulting regimes with 1 remaining northeast southwest but with exchange of orientation of 2 and 3 such variations may reflect an oblique collision and processes of stress permutation paleostress mapping of archean terranes can be used as a targeting tool for mesothermal lode gold deposits reduced stress tensors were used for the computation of paleostress maps using a distinct element model the silidor au quartz mineralization appears on these paleostress maps in an area characterized by low mean stress throughout the deformation history of the area near the horne creek fault this study emphasizes the role of second order faulting in the location of low and high pressure zones in the archean crust and the possible role of a tectonic indentor in the location of au mineralization

modeling mineral reactions in compacting sedimentary basins smectite illite reaction of sediment minerals in sedimentary basins is modelled as a one step dehydration reaction the water released from the mineral reaction can affect compaction process so as to retard porosity reduction and thus may cause overpressuring especially in the reaction region the coupled nonlinear model equations have been solved numerically and the asymptotic analysis has been used to get the analytical solutions of the nonlinear model equations in some regions of most practical interests the comparison of the obtained asymptotical solutions with the numerical results and real data shows very good agreement

diagenesis of the purington shale in the illinois basin and implications for the diagenetic state of sedimentary rocks of shallow paleozoic basins abstract the clay minerals micas and feldspars of the pennsylvanian age purington shale have been more diagenetically active than generally recognized they have undergone diagenetic changes comparable to those of cenozoic and mesozoic sedimentary rocks buried three to four times as deeply and heated to approximately twice the temperature the purington shale on the western shelf of the illinois basin has experienced maximum burial of 1 0 km and was never heated to more than 60 c except for a very brief time at about 80 c the illite smectite i s of the purington shale has 90 illite the chemical compositions of the feldspar assemblage in the 0 09 0 063 mm fraction differ from most modern detrital suites of feldspars but are similar to diagenetic sequences described by others from much greater burial depths and are extensively but not completely albitized the simplest interpretation of the apparently advanced stage of diagenesis is that the diagenetic processes have been operating at less press

evolution of the latera geothermal system ii metamorphic hydrothermal mineral assemblages and fluid chemistry abstract the latera field vulsini volcanic complex latium italy is one of the geothermal areas of the peri tyrrhenian belt along which a regional high thermal anomaly has been detected so far nine deep wells have been drilled within the latera caldera and four of them have been productive the geothermal reservoir is located within the fractured carbonatic rocks of the tuscan nappe the overlying volcanic units sealed by hydrothermal minerals mainly calcite and anhydrite act as an impervious cover the fluid produced by the wells comes from a deep aquifer about 1000 1500 m depth which at present is not connected with the shallow aquifer in the volcanoclastic units fluid temperatures range between 200 and 230 c in hole temperatures as high as 343 c at 2775 m depth have been measured in dry wells the study of the newly formed mineral assemblages from both volcanic and sedimentary units as sampled from the geothermal wells can be used to reconstruct the thermal evolution of the geothermal field the intrusion of a syenitic melt up to a depth of about 2000 m dated 0 86 ma represents the major thermal event for the units in the area and is assumed to represent the first step in the geothermal evolution of the latera system the above mentioned newly formed mineral assemblages can be divided into three groups a contact metasomatic calcite anhydrite diopsidic pyroxene grossularitic garnet phlogopite wollastonite or monticellite b high temperature hydrothermal calcite anhydrite k feldspar vesuvianite melanitic garnet tourmaline amphibole epidote sulphides c low temperature hydrothermal calcite anhydrite k feldspar clay minerals sulphides group a minerals are now relics part of b and all of c group are still in equilibrium with the existing conditions in different parts of the geothermal system thermodynamic calculations on the observed mineral assemblages permitted estimates of the p t conditions and gas fugacities

a thermodynamic model for the prediction of pore water composition of clayey rock at 25 and 80 c comparison with results from hydrothermal alteration experiments abstract this study proposes a thermodynamic model that is able to predict the pore water chemical composition of clayey rocks at temperatures up to 80 c the model is based on equilibrium with a quartz kaolinite calcite dolomite mg chlorite mineralogical buffer and accounts for the sorption properties of both the montmorillonite and illite phases hydrothermal alteration experiments were also performed at 80 c on centimeter sized samples from the callovo oxfordian clay rich formation paris basin france to assess the validity of the proposed model at this temperature the experiments were performed in both open and closed systems and the initial co2 g partial pressure pco2 g used in each system was fixed to log pco2 g 0 4 after 15 months of alteration the aqueous and gas phases were extracted at 80 c and analyzed the evolution of the clay mineralogy was also characterized using x ray diffraction profile modeling of experimental patterns and transmission electron microscopy tem the composition of the callovo oxfordian pore water predicted by our model at 25 c is in good agreement with that reported in the literature and measured in the geological formation at 80 c experiments in open systems were used to assess the kinetics of alteration process and the time needed to reach equilibrium for several dissolution precipitation mineral reactions for the closed system it is shown that the proposed model well predicts the chemical composition of the fluid extracted at 80 c considering the existing variability in the solubility constants for both mg chlorite and kaolinite minerals despite the need for additional alteration experiments to better constrain the temperature dependence of the predicted pco2 g values the proposed model provides reliable predictions of pore fluid composition at 80 c a temperature expected in the framework of radioactive waste storage

influence of kinetics on the smectite to illite transition in the barbados accretionary prism low chloride pore fluids observed along faults in clay rich accretionary complexes are commonly attributed to the release of interlayer water during the smectite to illite transformation however to date there has been no thorough analysis of the location and quantity of fluids that may be generated by this mechanism to address this problem a temperature and time dependent rate expression describing the dehydration reaction was coupled to a kinematic model of the northern barbados accretionary complex temperatures in the complex were estimated by modeling heat flow through the prism sediments as they thicken arcward the sediments temperature time histories were computed using a model for the velocities of sediment motion through the complex in this model the prism sediments follow uniformly diverging paths from the toe while the underthrust sediments undergo uniaxial strain the model predictions are validated against clay mineralogy data from barbados island mudstones our results show that the location of the peak dehydration rate is 20 km farther arcward in the underthrust sediments than in the prism complex the fresh water produced by the reaction results in pore waters that are 10 30 fresher at a distance of 50 70 km from the prism toe this constraint indicates a probable fluid migration path of more than 50 km from the reaction zone to the sites where freshened pore fluids have been observed the peak rate of fluid production when expressed as the volume of fluid per volume of sediment per second is 2 l0 15

from detrital heritage to diagenetic transformations the message of clay minerals contained within shales of the palaeoproterozoic francevillian basin gabon unmetamorphosed and undeformed marine siliciclastics rocks of the fb fc and fd of the francevillian series gabon were deposited in an epicontinental basin clay minerals found in black shale siltstone and sandstone are dominantly illite and chlorite except in two levels of the fb formation which contain smectite rich randomly ordered mixed layers their survival in a 2 1 ga old sedimentary series is not related to the abundance of organic matter total organic carbon or toc nor redox conditions at the time of deposition as indicated by the fe speciation fehr fet and fepy fehr ratios rather it results from an incomplete illitization reaction that reflects potassium deficiency the k2o al2o3 ratio of shale siltstone and sandstone vary along the series and appear to conserve the signature of the original chemical composition of the rocks k feldspars which are present in the fc and fd formations are missing in the fb formation consequently the smectite layers do not appear to be inherited from a detrital input in the basin but must be considered as representative of an intermediate stage of the illitization reaction reached during diagenesis

40 ar 39 ar ages and stratigraphy of the latera caldera italy the latera caldera is a well exposed volcano where more than 8 km3 of mafic silica undersaturated potassic lavas scoria and felsic ignimbrites were emplaced between 380 and 150 ka isotopic ages obtained by 40ar 39ar analysis of single sanidine crystals indicate at least four periods of explosive eruptions from the caldera the initial period of caldera eruptions began at 232 ka with emplacement of trachytic pumice fallout and ignimbrite they were closely followed by eruption of evolved phonolitic magma after roughly 25 ky several phonolitic ignimbrites were deposited and they were followed by phreatomagmatic eruptions that produced trachytic ignimbrites and several smaller ash flow units at 191 ka compositionally zoned magma then erupted from the northern caldera rim to produce widespread phonolitic tuffs tephriphonolitic spatter and scoria bearing ignimbrites after 40 ky of mafic surge deposit and scoria cone development around the caldera rim a compositionally zoned pumice sequence was emplaced around a vent immediately northwest of the latera caldera this activity marks the end of large scale explosive eruptions from the latera volcano at 156 ka

40ar 39ar laser dating of single grains ages of quaternary tephra from the east eifel volcanic field frg four late pleistocene tephra deposits from the east eifel volcanic field have been dated by 40ar 39ar single grain laser fusion of k feldspar and phlogopite crystals this is a high speed and high precision technique which because it is grain specific can directly detect the presence of older contaminating material our results indicate that the huttenberg tephra from wehr volcano erupted 213 4 ka bp and that the rieden volcanic complex erupted at least over the period 410 to 470 ka bp essential rieden phonolite lapilli contain abundant sanidine with apparent ages older than the eruption age

nature of mixed layer clays and mechanisms of their formation and alteration abstract mixed layer clay minerals are intermediate products of reactions involving pure end member clays they come from natural environments ranging from surface to low grade metamorphic and hydrothermal conditions most often mixed layering is essentially two component but more complicated interstratifications have also been documented variable tendency to form regular 1 1 interstratifications has been observed and explanations of this phenomenon have been proposed mixed layer clays are either di or trioctahedral di trioctahedral interstratifications are rare most mixed layer clays contain smectite or vermiculte as a swelling component exceptions are all trioctahedral serpentine chlorite in low temperature environments and mica chlorite and talc chlorite at high temperatures solid state transformation and dissolution crystallization are the two mechanisms responsible for the formation of different mixed layer clays in general the weathering reactions that produce mixed layering are revers

why does not lithology correlate with gamma ray spikes in the shaley source rocks of the upper jurassic alge member southwestern barents sea abstract prominent high value gamma ray spikes in the maximum flooding surfaces of the middle oxfordian kimmeridgian succession alge member display stratigraphic and regional variations in the southwestern barents sea these variations suggest heterogeneities in the composition of the alge member thus challenging the common perception that this interval is a homogenous succession of organic rich black shale this study explores the overall variation in clay mineral composition source rock quality minerals and macerals core logs and seismic facies of the alge member gamma log fluctuations were found to be independent of these variations uranium precipitates on sea bottom sediments when conditions change from oxic to anoxic fluctuations in sea level may result in such changes and hence guide gamma ray responses sea level fluctuations also lead to a changing distance to the shoreline which again influences sediment types grain sizes and source rock quality thus indirectly sea level appears to be the common denominator which sometimes matches source rock richness with spikes on gamma logs presence and absence of gamma ray spikes are hence an additional tool to reveal the redox conditions in the sw barents sea which has implications for the understanding of the paleogeography or paleobathymetry during deposition

review of major shale dominated detachment and thrust characteristics in the diagenetic zone part ii rock mechanics and microscopic scale abstract characterising large shale thrust zone behaviour down to the diagenetic metamorphic boundary is both simple and complex the task in critical taper analogue and numerical models has been successfully approximated using simple material parameters yet the weakness of shales thrusts on a case by case basis show great variability in key factors across a wide range of scales understanding of these variables and their relationships to different tectonic settings is patchy due to the different objectives of workers studying the various systems e g seismic hazards hydrocarbon exploration structural geology research and the types of available geological and geophysical data early research recognized that megathrusts feature creeping and locked patches which may be described using the rate and state formalism in addition to temperature differential stress and strain rate key controlling factors on thrust weakness are mineralogy amount of weak phase present structure localization mechanisms grain size and shapes porosity permeability and pore fluid pressure the smectite illite transition has been a focus of seismic hazard research due to its coincidence with the top of the seismogenic zone while there may be a relationship other factors such as pore fluid pressure variations or structure localization are also important the critical taper model is a simple means of determining whether basic rock mechanics data e g frictional strength pore fluid pressure is appropriate for natural wedges for example aseismic basal detachments of gravity driven systems smaller critical taper wedges appear to retain higher pore fluid pressures along the basal detachment than seismogenic basal detachments higher critical taper wedges in many continental and deltaic fold and thrust belts high organic carbon content is a very important factor in shale weakness due to 1 the overall more ductile and well cleaved nature of the shale when organic content is high 2 the presence of high overpressures due to maturation of organic material and 3 metamorphism of carbon to low friction graphite this multifaceted influence of organic carbon content is just one example of the diversity of potential influences on shale thrust zone weakness which enable shales to be weak despite considerable lateral deposition related and vertical burial related changes in composition some key variations between different types of fold and thrust belt gravity driven accretionary prism andean himalayan type lie in systematic variations in clay mineralogy magnitudes and origins of overpressures seismic versus aseismic detachments and different structural localization mechanisms further research is required to explore the viability of such distinctions and their impact on structural styles

problems with argon k ar ages in gulf coast shales abstract k ar ages of gulf coast shales do not correspond to diagenetic events but are a combination of inherited detrital ages and authigenic overprints the key to understanding k ar ages of shales is the fate of the 40 ar when the host minerals dissolve or react during the illitisation reaction is 40 ar incorporated within the illite or is it lost to the porewaters ages are modelled as due to a single illitisation reaction assuming a uniform precursor sediment and open system import of k both whole rock and clay mineral fraction data can be reproduced by modelling the 40 ar incorporated into illite is a surprisingly high proportion 75 100 of that produced within detrital phases smectite k feldspar mica perhaps implying that the illitisation reaction is a solid state transformation or that 40 ar is imported into the shales along with incoming k the model does not provide a good fit to the data below 4000 m when the illitisation reaction is apparently complete but shales lose 40 ar by solid state diffusion or recrystallisation

40ar 39ar dating of the bandelier tuff and san diego canyon ignimbrites jemez mountains new mexico temporal constraints on magmatic evolution abstract the jemez mountains volcanic field jmvf located in north central new mexico has been a site of basaltic to rhyolitic volcanism since the mid miocene with major caldera forming eruptions occurring in the pleistocene eruption of the upper bandelier tuff ubt is associated with collapse of the valles caldera whereas eruption of the lower bandelier tuff lbt resulted in formation of the toledo caldera these events were previously dated by k ar at 1 12 0 03 ma and 1 45 0 06 ma respectively pre bandelier explosive eruptions produced the san diego canyon sdc ignimbrites sdc ignimbrite b has been dated at 2 84 0 07 ma whereas sdc ignimbrite a which underlies b has been dated at 3 64 1 64 ma both of these dates are based on single k ar analyses 40ar 39ar dating of single sanidine crystals from these units indicates revision of the previously reported dates isochron analysis of 26 crystals from the ubt gives a common trapped 40ar 36ar component of 304 5 indicating the presence of excess 40ar in this unit and defines an age of 1 14 0 02 ma isochron analysis of 26 crystals from the lbt indicates an atmospheric trapped component and an age of 1 51 0 03 ma an age of 1 78 0 04 ma based on the weighted mean of 5 individual analyses is indicated for sdc ignimbrite b whereas 3 analyses from sdc ignimbrite a give a weighted mean age of 1 78 0 07 ma evidence for xenocrystic contamination in the sdc ignimbrites comes from analyses of a correlative air fall pumice unit in the puye formation alluvial fan giving ages of 1 75 0 08 and 3 50 0 09 ma the presence of xenocrysts in bulk separates used for the original k ar analyses could account for the significantly older ages reported geochemical data indicate that sdc ignimbrites are early eruptions from the magma chamber which evolved to produce the lbt as compositions of sdc ignimbrite b are virtually identical to least evolved lbt samples differentiation during the 270 ka interval between eruption of sdc ignimbrite b and the lbt produced an array of high silica rhyolite compositions which were erupted to form the lbt mixed pumices associated with eruption of the lbt indicated an influx of more mafic magma into the system which produced shifts in some incompatible trace element ratios lavas and tephras of the cerro toledo rhyolite record the geochemical evolution of the bandelier magma system during the 370 ka interval between eruption of the lbt and the ubt the combined geochronologic and geochemical data place the establishment and evolution of the bandelier silicic magma system within a precise temporal framework beginning with eruption of the sdc ignimbrites at 1 78 ma and define a periodicity of 270 370 ka to ash flow eruptions in the jmvf these intervals are comparable to those in other multicyclic caldera complexes and are a measure of the timescales over which substantial fractionation of large silicic magma bodies occur

mineralogical chemical and k ar isotopic changes in kreyenhagen shale whole rocks and 2 μm clay fractions during natural burial and hydrous pyrolysis experimental maturation abstract progressive maturation of the eocene kreyenhagen shale from the san joaquin basin of california was studied by combining mineralogical and chemical analyses with k ar dating of whole rocks and hydrous pyrolysis was intended to alleviate the problem of mineral and chemical variations in initially deposited rocks of naturally matured sequences however experiments on aliquots from thermally immature kreyenhagen shale outcrop sample did not mimic the results from naturally buried samples experiments conducted for 72 h at temperatures from 270 to 365 c did not induce significant changes at temperatures above 310 c in the mineralogical composition and k ar ages of the rock and large amounts of smectite layers in the illite smectite mixed layers of the pyrolyzed outcrop

claystone porosity and mechanical behavior vs geologic burial stress abstract a dataset was assembled from studies on 35 preserved claystone cores from different locations around the world and burial depths from

recent deep sourced methane mud discharge at the most active mud volcano in the western mediterranean abstract active mud volcanism in the west alboran basin wab is closely associated with tectonically mobilized overpressurized shales and shale diapirism this appears to control mud expulsion at carmen mud volcano a cone shaped structure 65 m high and 1 km in basal diameter the presence of gas rich mud breccia living chemosynthetic fauna the absence of hemipelagic draping and the abrupt transition that occurs between high dissolved sulfate in the uppermost interval and low sulfate together with high methane concentrations in the lowermost sediment interval all point to a recent expulsion of mud breccia at the summit of carmen mv for the lowermost interval the depletion of major elements i e ca2 and mg2 and the enrichment of trace species i e li and b in the pore water all indicate a deep fluid source the 18opw 5 7 vsmow and dpw 10 vsmow of pore water in the lowermost interval correspond with smectite dehydration as the main pore water freshening mechanism water formation temperatures calculated with empirical geo thermometers k na k mg 18opw dpw and dissolved b reveal that fluids were generated at temperatures of 140 20 c taking a regional geothermal gradient for the wab of 25 27 c km this points to a fluid source from 5 1 km sediment depth this is not only consistent with the depth of overpressurized shales and megabreccia of lower to middle miocene age but it also fits nicely with the upper middle miocene seawater value for the porewater 87sr 86sr derived from dissolving carbonates the stable carbon and hydrogen isotopic composition of methane 13cmethane 59 4 vpdb and dmethane 184 vsmow for the deepest samples of summit core gp05pc is consistent with the mentioned deep origin mud breccia expulsion of overpressurized deep sedimentary units would be accompanied by rigorous degassing leading to rapid instantaneous replacement of pore fluid by bottom water in the upper sediments the absence of oxidized sediment draping the seawater like pore water composition in the uppermost part of the mud breccia interval and the abrupt methane to sulfate transition all provide evidence for a very recent mud expulsion the distinctively kink shaped pore water cl profile in core gp05pc has been used in a numerical transport reaction model to derive the timing for this event this eruptive event appears to have taken place very recently namely 12 5 yrs prior to the 2012 coring thus in the year 2000 ce

effects of smectite on the oil expulsion efficiency of the kreyenhagen shale san joaquin basin california based on hydrous pyrolysis experiments the amount of oil that maturing source rocks expel is expressed as their expulsion efficiency which is usually stated in milligrams of expelled oil per gram of original total organic carbon oil expulsion efficiency can be determined by heating thermally immature source rocks in the presence of liquid water i e hydrous pyrolysis at temperatures between 350 c and 365 c for 72 hr this pyrolysis method generates oil that is compositionally similar to natural crude oil and expels it by processes operative in the subsurface consequently hydrous pyrolysis provides a means to determine oil expulsion efficiencies and the rock properties that influence them smectite in source rocks has previously been considered to promote oil generation and expulsion and is the focus of this hydrous pyrolysis study involving a representative sample of smectite rich source rock from the eocene kreyenhagen shale in the san joaquin basin of california smectite is the major clay mineral 31 wt in this thermally immature sample which contains 9 4 wt total organic carbon toc comprised of type ii kerogen compared to other immature source rocks that lack smectite as their major clay mineral the expulsion efficiency of the kreyenhagen shale was significantly lower the expulsion efficiency of the kreyenhagen whole rock was reduced 88 compared to that of its isolated kerogen this significant reduction is attributed to bitumen impregnating the smectite interlayers in addition to the rock matrix within the interlayers much of the bitumen is converted to pyrobitumen through crosslinking instead of oil through thermal cracking as a result smectite does not promote oil generation but inhibits it bitumen impregnation of the rock matrix and smectite interlayers results in the rock pore system changing from water wet to bitumen wet this change prevents potassium ion transfer and dissolution and precipitation reactions needed for the conversion of smectite to illite as a result illitization only reaches 35 to 40 at 310 c for 72 hr and remains unchanged to 365 c for 72 hr bitumen generation before or during early illitization in these experiments emphasizes the importance of knowing when and to what degree illitization occurs in natural maturation of a smectite rich source rock to determine its expulsion efficiency complete illitization prior to bitumen generation is common for paleozoic source rocks e g woodford shale and retort phosphatic shale member of the phosphoria formation and expulsion efficiencies can be determined on immature samples by hydrous pyrolysis conversely smectite is more common in cenozoic source rocks like the kreyenhagen shale and expulsion efficiencies determined by hydrous pyrolysis need to be made on samples that reflect the level of illitization at or near bitumen generation in the subsurface

characterization of illite clays associated with the sinongduo low sulfidation epithermal deposit central tibet using field swir spectrometry abstract field measurements using shortwave infrared swir reflectance from drill hole samples provided an effective method to map variations in illite crystallinity and the illite assemblage minerals associated with hydrothermal alteration zonation of the sinongduo low sulfidation epithermal ag pb zn deposit tibetan plateau china the swir mineral spectral information was combined with electron probe micro analysis epma measurements and microscope observations to provide geological insights into a the likely metallogenic fluid nature of the mixture of magmatic fluids and a cooler water source b the illite physico chemical properties of the associated hydrothermal fluids c the illite montmorillonite and sericite evolutionary interactions among these fluids country rocks and alteration minerals and d the alteration minerals relationships and illite crystallinity to the economic mineralization the results suggest that illite characterizations can be used as an indicator for epithermal deposit prospecting

hydrothermal clay mineral formation in the uraniferous paleoproterozoic fa formation francevillian basin gabon abstract the spatial distribution of neoformed clay minerals was investigated in the paleoproterozoic fa formation of the francevillian basin south east gabon which hosts high grade u ore deposits associated with the only known occurrence of natural nuclear reactors illite appears as the main clay phase in the lower fluvial unit in the mineralized upper fluvio deltaic tidal unit the clay assemblage is more diversified and commonly characterized by illite chamosite berthierine and chamosite berthierine mixed layers usually in association with alteration products of u bearing minerals the clay mineral assemblage thus potentially constitutes a mineralogical marker for the regional distribution of u ore deposits polytype species of the clay phases indicate mineral transformations in an environment characterized by a high fluid rock ratio according to crystalline structure mineral chemistry thermodynamic modeling and geochronology clay phases seem to be mainly hygrometer rather than exclusively a thermometer and their formation as well as associated dissolution precipitation of u bearing minerals took place between ca 2040 and 2010 ma ago at temperatures of about 240 30 c using previous burial estimates this suggests the operation of hydrothermal processes controlled by an external heat source likely associated with volcanism during deposition of the fd and fe formations hydrothermal activity involving oxidized fluids would have driven u remobilization and ultimately formation of high grade u ore deposits the thermal history proposed here allows for a better understanding of the conditions during burial of the sedimentary succession and the origin of its rich u endowment

characteristics and implication of clay minerals in the northern and southern parts of the chelung pu fault taiwan abstract in this study we report the characteristics of clay minerals present in the chelung pu fault in taiwan in the 1999 chi chi earthquake different slip motions were recorded along the chelung pu fault in the northern and southern parts of the fault the characteristics of clay minerals present in the fault zones can be attributed to the differences in motion we analyzed the shallow drill core samples obtained from the northern and southern sites penetrating the fault the clay minerals identified in most of the samples from both the sites are smectite illite and chlorite there are illite smectite mixed layers with a high illite content and no chlorite smectite mixed layer in some samples no smectite is detected we also examined the iron content and symmetry of iron and magnesium in the silicate and hydroxide layers in chlorite at the northern site the total iron content in chlorite of gouge is larger than that of the host rocks on the other hand at the southern site the total iron content varies widely it is hypothesized that the smectite consumption and differences in the characteristics of chlorite may be controlled by the differences in the lithology fluid chemistry fluid temperature or fault activities heating or breakage between the northern and southern sites

the geochemistry and petrogenesis of the lavas of the vulsinian district roman province central italy the vulsinian lavas are dominated by a suite of undersaturated leucite bearing basic to intermediate compositions the remaining lavas are mainly oversaturated and have shoshonitic affinities one hundred and thirty five samples have been analysed for major elements and most for 20 trace elements twenty seven lavas have been analysed for ree they are all perpotassic for the undersaturated lavas k2o na2o 2 8 and have very high lil element concentrations e g rb 400 800 ppm th 25 150 ppm ree reecho c 200 lree hree cho c 20 even in the most basic rocks

roles of sorting and chemical weathering in the geochemistry and magnetic susceptibility of xiashu loess east china abstract uncertainties in paleoenvironmental interpretations for traditional chemical analysis of bulk samples result from different grain size sub populations of sediments containing variable distributions of elements and minerals therefore it is important to understand the elemental and mineral distribution in different grain sizes in determining the quantitative relationship between chemical weathering and climatic change we sieved a series of xiashu loess samples into three sub populations of different grain sizes 45 m respectively and then analyzed each population for rubidium rb strontium sr rare earth elements and magnetic susceptibility in comparison with elemental concentrations of bulk samples clay mineralogy and illitic crystallinity our results show that distinct elemental distributions and magnetic susceptibilities for different grain size sub populations are controlled by sorting and or chemical weathering although we also suggest that the xiashu loess may have the same provenance as the central chinese loess maximum concentrations of rb and fine grained magnetic minerals in the less than 2 m sub population coupled with our finding of maximum sr in the larger than 45 m fraction indicate that sr was lost during chemical weathering grain size sub population analysis is therefore an effective method for extracting paleoenvironmental information because individual sub populations show minimal variations in initial rb sr ratios compared to bulk analysis of all sizes together furthermore a negative correlation between rb sr ratios and sr concentrations for the r 2 0 97 may indicate that clay is a sensitive indicator of intensity of chemical weathering and is an ideal sub population for determining rb sr ratios but not for magnetic susceptibility

fluid circulation in the depths of accretionary prisms an example of the shimanto belt kyushu japan accretionary prisms constitute ideal targets to study fluid circulation and fluid rock interactions at depths beyond the reach of active margin deep drilling the highest grade rocks from the shimanto belt on kyushu were buried under 3 5 kbars at 300 c toriumi and teruya 1988 they contain abundant quartz veins formed throughout burial and exhumation and variably affected by brittle and ductile deformation cathodoluminescence cl reveals the existence of two distinct types of quartz characterized by a blue and brown color respectively cl blue quartz fills macro veins width 10 m while cl brown quartz is present in micro veins width 1 10 m and ductilely recrystallized domains on the basis of microstructures the fluids associated with the cl blue and cl brown quartz are interpreted as external and local respectively quartz growth rims of alternating cl colors as well as mutually cross cutting veins show that the two fluids cyclically wetted the host rock from fluid inclusions analysis the fluid associated with cl blue quartz has a salinity similar to seawater while the fluid associated with cl brown quartz is less saline in addition cl blue quartz is richer in aluminum than the cl brown one in contrast to the salinity aluminum signature the 18o isotopic signature of both quartz types is similar and buffered by host rock the difference between the preservation of the salinity signature of the fluid and the loss of its 18o signature is explained by quicker exchange kinetics and larger host rock buffering capacity for isotopic reequilibration the local fluid associated with cl brown quartz reflects the dilution of pore water by the pure water produced by prograde dehydration reactions of clay minerals the external fluid associated with cl blue quartz is interpreted as seawater or pore water from shallow depth 1 2 km below seafloor sediments we propose that downward percolation of shallow water to depths 10km is a transient process associated with mega earthquakes

compaction processes and rock properties in uplifted clay dominated units the egersund basin norwegian north sea abstract a thick succession of fine grained sediments in any sedimentary basin can serve as source if organic rich and top seals both sealing and petroleum generation capacity of any fine grained succession is dependent on compaction history mechanical and chemical compactions of the sediments in the egersund basin a thick succession of fine grained sediments of upper jurassic lower cretaceous age overly middle jurassic reservoir sands the egersund basin however has experienced a complex depositional and tectonic history particularly late exhumation neogene which complicates the overall burial thermal and pressure history in this study petrophysical and acoustic properties bulk density and p wave velocity of 10 exploration wells from two neighboring blocks in the egersund basin were utilized to investigate compaction processes in the area in addition x ray diffraction xrd and scanning electron microscopy sem analyses from selected wells and available total organic carbon toc data were used as guide to interpret the compaction processes and resulting rock properties the results show that the transition from mechanical to chemical compaction is not sharp the onset of chemical compaction imposes a measurable deviation in the burial depth trends of the petrophysical properties expected from purely mechanical compaction the continuation of the depth related trends however indicates that chemical compaction may occur in concurrent with continuing mechanical compaction the observed compaction varies between the different clay dominated stratigraphic units indicating that the major control on both mechanical and chemical compaction is the primary sediment composition

a unified approach to mechanical compaction pressure solution mineral reactions and the temperature distribution in hydrocarbon basins abstract in modelling sediment compaction and mineral reactions the rheological behaviour of sediments is typically considered as poroelastic or purely viscous in fact compaction due to pressure solution and mechanical processes in porous media is far more complicated a generalised model of viscoelastic compaction and the smectite to illite mineral reaction in hydrocarbon basins is presented a one step dehydration model of the mineral reaction is assumed the obtained non linear governing equations are solved numerically and different combinations of physical parameters are used to simulate realistic situations in typical sedimentary basins comparison of numerical simulations with real data has shown very good agreement with respect to both the porosity profile and the mineral reaction

effects of smectite dehydration and illitisation on overpressures in sedimentary basins a coupled chemical and thermo hydro mechanical modelling approach abstract diagenetic smectite dehydration and smectite to illite transition in clay rich sediments can contribute to the generation of overpressure in sedimentary basins because of the release of water associated with these mineralogical reactions however the challenge of deciphering the contribution of smectite dehydration and illitisation to fluid pressure amongst other mechanisms generating overpressure requires the different mechanisms at play to be jointly considered here we developed a coupled chemical and thermo hydro mechanical code named surp to calculate the overpressure generation in a sedimentary pile because of sediment compaction during its burial temperature increase water flow and because of the release of water by clay dehydration and illitisation for this purpose a revised thermodynamic model describing smectite dehydration by a solid solution approach was considered together with the different thermo hydro mechanical processes occurring in sedimentary basins the surp code was applied to the case study of an overpressured passive margin in the niger delta composed of thick shale layers in a sedimentary pile in this geological scenario smectite dehydration was simulated and could explain 10 30 20 50 bar of the present day overpressure in the main reservoirs in addition to compaction disequilibrium

exceptional preservation of expandable clay minerals in the ca 2 1 ga black shales of the francevillian basin gabon and its implication for atmospheric oxygen accumulation abstract clay minerals are exceptionally well preserved in marine black shale of the ca 2 1 ga francevillian group in southeastern gabon the fb formation of the francevillian group is characterized by smectite rich clay minerals including randomly ordered r0 type and ordered r1 type mixed layer illite smectite i s the preservation of r0 type clay minerals suggests unexpectedly slow mineral transformation and a moderate degree of diagenesis which is unique considering the paleoproterozoic age of the sedimentary rocks r0 and r1 type smectite rich particles occur in stratigraphic intervals with high organic carbon content and are associated with carbonaceous filamentous structures suggesting formation of clay organic matter complexes our data suggests that clay minerals may have enhanced organic matter preservation providing the oldest example where a link between clay minerals and organic matter sequestration can be established our findings are consistent with the hypothesis that clay minerals enhanced organic carbon burial and aided in atmospheric oxygen accumulation through time

deep hydrothermal activity driving the lusi mud eruption abstract the lusi mud eruption in east java continues unabated after more than a decade of activity as a pulsating geyser system bursting mud clasts water and gas the origin of the fluids and their properties at depth are not well constrained thus hampering our understanding and modelling of the system previous geochemical and geophysical studies show that lusi is a sediment hosted hydrothermal system with two sources of mud at depths between 0 3 2 km and another between 3 5 4 75 km here we present results of mineral thermometry using raman spectroscopy and chlorite composition on clasts erupted at lusi the results show that some of these specimens originate from the two main fluid sources and at depths consistent with the geochemical and geophysical interpretation two main clast lithotypes erupt at lusi the first lithotype is a light grey shale returned to the surface from the upper kalibeng formation the primary mud source and equilibrated at temperatures below 200 c the second lithotype is a black shale whose source is the ngimbang formation at 3800 m depth two distinct temperature clusters are recorded in these black shales one at 179 17 c consistent with the temperature estimate at 3800 m depth with the pre eruption geothermal gradient while younger minerals in the same specimen recorded substantial anomalous heating at 250 c these high temperatures indicate interaction with a heat source associated with the eruption through mixing with hydrothermal fluids this temperature jump suggests rapid heating at 4000 m depth consistent with a scenario of a magmatic intrusion and hydrothermal fluids circulation this rapid and significant temperature increase would initiate devolatilisation reactions of hydrous minerals within the deep sedimentary package and generate substantial highly overpressured fluids at depths significantly below the main source of erupted mud we infer that reactive and thermal pressurisation led to a deep and metastable system susceptible to e g seismic activity ultimately opening fluid pathways towards the surface along the watukosek fault system the two temperatures clusters recorded in the clasts show that conductive heat flow was the dominant heat transport prior to the eruption while the system is now driven by large scale convection and advective heat transport the lusi eruption occurred in a highly populated area forcing the evacuation of several tens of thousands of people this system appears unstoppable and poses a real and present hazard for the settlements still surrounding the eruption site continuous research is necessary to understand this spectacular phenomenon both for its important scientific relevance and the societal impact of this natural disaster

diagenesis and reservoir quality prediction the modern concept of diagenesis was introduced by walther one hundred years ago to encompass the postdepositional processes that affect sediments from deposition to low grade metamorphism since walther 1893 diagenetic studies have been concerned with an extraordinary variety of chemical and physical interactions each of which has the potential to significantly affect the final composition and texture of a sedimentary rock the issues to which those studies have been applied are equally varied and include 1 improved techniques to predict the producibility of hydrocarbon reservoirs 2 improved techniques to predict subsurface fluid pressures 3 better constraints on the timing of fluid flow events 4 reconstruction of global climate change and 5 evaluation of groundwater contamination commercial applications of diagenetic studies have traditionally focused on the producibility of hydrocarbon reservoirs as such a review of this topic serves as an effective illustration of how basic research has been commercialized and a useful focus for the following dicussion however it is worth noting that decreased industrial research funding coupled with increased government funding for environmental research have recently resulted in a gradual evolution of diagenetic publications away from the producibility of hydrocarbon reservoirs toward the producibility of uncontaminated groundwater and other environmental issues despite the shift in emphasis many of the basic research issues remain unchanged whether one is focused on deep hydrocarbon reservoirs or shallow aquifers

evidence of incremental growth in the vulsinian calderas central italy abstract a comparative work on the vulsini calderas has been carried out fundamentally from volcanological field study drilling and gravity anomalies data on the basis of a detailed stratigraphy four volcanic complexes have been recognized in the vulsini volcanic district from the oldest to the youngest paleo bolsena bolsena montefiascone and latera the latter two complexes having a contemporaneous evolution in their activity each complex gave rise to several little calderas caused by piecemeal collapses due to moderate size explosive eruptions or coherent subsidence of a superficial piston like block nevertheless the extensional volcano tectonic regime affecting this area could have accounted for as much of the total subsidence as the caldera forming eruptions bolsena and latera calderas respectively 16 km and 8 km in average diameter represent the main depressions of the vulsini district and their topographic features are still well preserved several collapses forming the main poligenetic calderas of bolsena and latera are masked at present by the bolsena lake the younger volcanic covering the lacustrine deposits and erosion in a minor amount only the little montefiascone and vepe calderas which represent the youngest collapses of the vulsini area have not been masked bolsena caldera could be considered a depression caused mostly by a subsidence hinged to the southwest by down sagging and by collapses which occurred after the most important explosive eruptions of the paleo bolsena bolsena and montefiascone volcanic complexes meanwhile latera caldera is mostly due to a piecemeal collapse linked to several moderate size ignimbrite units which were emplaced throughout the explosive activity of the latera complex therefore the vulsinian calderas did not form by catastrophic eruptions because several and frequent moderate size eruptions downsagging and tectonic hinged subsidence concur indicating an incremental growth

geology alteration system and uranium metallogenic potential of pasha ladoga basin russia the mesoproterozoic pasha ladoga basin is located at the margin of the karelian craton and svecofennian belt in northwest russia it is the only basin in russia that is currently recognized to host unconformity type uranium mineralization e g karku deposit mineralization is associated with the priozersk formation which comprises a basal sequence of immature arkosic sandstones and conglomerates interpreted as high energy braided stream channel and channel bar facies within an alluvial fan depositional environment diagenetic and hydrothermal alteration of the priozersk sandstones is similar to that observed in unconformity related uranium deposits of the athabasca basin canada and includes three main stages 1 an early diagenetic assemblage comprising illite smectite k rectorite calcite minor chlorite and kaolinite precipitated at 100 150 c 2 a peak diagenetic hydrothermal assemblage composed of kaolinite dickite fe and fe mg chlorite calcite and sulfides formed at 150 250 c 3 late diagenetic hydrothermal event involving fracture controlled kaolinite and late hematite similar to the athabasca basin type uranium mineralization the karku deposit exhibits anomalous concentrations of lree nb pb and positive correlations between u and cu zn ag and pb that is a geochemical signature of unconformity type uranium mineralization based on oxygen and hydrogen stable isotope study it was found that fluids in equilibrium with early and peak diagenetic clays were consistent with oxidized basinal brines and reduced basement fluids in contrast to the athabasca basin mineralizing fluids at the karku area were more reduced and potassic a new geological model for the karku deposit is proposed based on petrographic observations and sandstones geochemistry the proposed model envisages the permeable rocks of paleoregolith and the coarse grained basal part of the priozersk formation as the main pathway for migration of uraniferous fluids responsible for the formation of karku uranium deposit from the perspective of the geological setting the karku deposit differs from deposits of the athabasca basin in that it occurs in a rapidly deposited rift related basin with associated mafic magmatism the host sandstone sequence is relatively thin e g priozersk formation and exhibits abrupt lateral facies variations and the widespread presence of early diagenetic interstitial swelling clays based on these sedimentological characteristics it is considered that the karku deposit setting precludes optimum conditions to create high tonnage high grade unconformity type u deposits as found in the athabasca basin

cause and timing of the thermal over maturation of hydrocarbon source rocks of the ecca group main karoo basin south africa abstract the source rocks of the main karoo basin south africa are believed to have undergone thermal over maturation close to the jurassic aged karoo large igneous province klip dolerite intrusions yet the cause and timing of this source rock exhaustion event likely to have extensively destroyed their shale gas potential remain controversial based on drill core samples from the central main karoo basin we investigated the clay mineralogy of the 2 1 1 and 2 1 phyllosilicate groups and have carried out 40ar 39ar radiometric dating of illite the x ray diffractograms xrd and mineral chemistry reveal that chlorite and illite phases of samples close to the dolerite intrusions are characterized by higher crystallinity with a chemical composition indicative of formation in a metamorphic environment in contrast chlorite and illite distal to any dolerite intrusion show lower crystal growth rates with chemical compositions suggesting formation in a diagenetic environment 40ar 39ar radiometric dating indicates that illite in samples distal to the dolerite intrusions formed between 292 and 245 ma with some ages clustering around 281 ma the oldest ages are consistent with a detrital fraction probably recycled from the erosion of the ash bed at the top of the underlying dwyka group however ages around 281 ma can be linked with estimated depositional age of the ecca group at 280 ma while the youngest ages may reflect late diagenesis to regional metamorphism illite fractions from samples close to dolerite shows formation age between 204 and 170 ma consistent with the time of the klip dolerite sills and dykes intrusions at 180 ma this illustrates that the ages of these illites were partially or totally re set due to recrystallization in a late thermal anomaly induced by the intrusion of dolerites the correlation between the timing of the youngest mineral transformation processes and the klip represents strong evidence suggesting that source rocks of the ecca group experienced a thermal overprinting event 180 ma ago this late thermal anomaly is consistent with previous data illustrating thermal over maturation and metamorphic devolatilization of ecca group shales situated close to the dolerite intrusions

clay mineral diagenesis and source rock assessment in the bornu basin nigeria implications for thermal maturity and source rock potential abstract an understanding of the mineral and organic matter modifications during burial are critical in assessments of potential source rocks in petroleum exploration studies here we examined the relationships between clay mineral diagenesis and organic thermal indicators vitrinite reflectance and rock eval tmax to constrain the thermal maturity and hydrocarbon potential of source rocks in the mbeji 1 well in the northeastern part of the cretaceous tertiary bornu basin x ray diffraction mineralogical data show that the