granite ascent and emplacement during contractional deformation in convergent orogens based on a case study in the central maine belt of west central maine u s a it is proposed that crustal scale shear zone systems provide an eaective focussing mechanism for transfer of granite melt through the crust in convergent orogens during contractional deformation flow of melt in crustal materials at depths below the brittle plastic transition is coupled with plastic deformation of these materials the flow is driven by pressure gradients generated by buoyancy forces and tectonic stresses within the oblique reverse central maine belt shear zone system stromatic migmatite and concordant to weakly discordant irregular granite sheets occur in zones of higher strain which suggests percolative flow of melt to form the migmatite leuco somes and viscous flow of melt channelized in sheet like bodies possibly along fractures cyclic fluctuations of melt pressure may cause instantaneous changes in the eaective permeability of the flow network if self propa gating melt filled tensile and or dilatant shear fractures are produced due to melt enhanced embrittlement in homogeneous migmatite and schlieric granite occur in zones of lower strain which suggests migration of partially molten material through these zones en masse by granular flow and channelized flow of melt carrying entrained residue founded on the central maine belt case study we develop a model of melt extraction and ascent using the driving forces stress conditions and crustal rheologies in convergent especially transpressive orogens ascent of melt becomes inhibited with decreasing depth as the solidus is approached for intermedi ate a h2o muscovite dehydration melting the water saturated solidus occurs between 400 and 200 mpa near the brittle plastic transition during high t low p metamorphism where the balance of forces favors sub horizontal fracture propagation emplacement of melt may be accommodated by ductile flow and or stoping of wall rock and inflation may be accommodated by lifting of the roof at shallower crustal levels and or sink ing of the pluton floor the resultant plutons have sub horizontal tabular geometries with floors that slope down to the ascent conduits although these plutons may have locally discordant relations with country rock structures when viewed at the crustal scale granite ascent and emplacement in convergent orogens are syn tec tonic processes 1998 elsevier science ltd all rights reserved

specific surface area and pore size distribution in clays and shales one of the biggest challenges in estimating the elastic transport and storage properties of shales has been a lack of understanding of their complete pore structure the shale matrix is predominantly composed of micropores pores less than 2 nm diameter and mesopores pores with 2 50 nm diameter these small pores in the shale matrix are mainly associated with clay minerals and organic matter and comprehending the controls of these clays and organic matter on the pore size distribution is critical to understand the shale pore network historically mercury intrusion techniques are used for pore size analysis of conventional reservoirs however for unconventional shale reservoirs very high pressures 414 mpa 60 000 psi would be required for mercury to access the full pore structure which has potential pitfalls current instrumental limitations do not allow reliable measurement of significant portions of the total pore volume in shales nitrogen gas adsorption techniques can be used to characterize materials dominated by micro and mesopores 2 50 nm a limitation of this technique is that it fails to measure large pores diameter 200 nm we use a nitrogen gas adsorption technique to study the micro and mesopores in shales and clays and compare the results from conventional mercury porosimetry techniques our results on pure clay minerals and natural shales show that i they have a multiscale pore structure at different dimensions ii fine mesopores with a characteristic 3 nm pore size obtained with n2 gas adsorption are associated with an illite smectite group of clays but not with kaolinite iii compaction results in a decrease of pore volume and a reduction of pore size in the inter aggregate macropores of the illitesmectite clays while the fine intra tachoid mesopores are shielded from compaction iv for natural shales mineralogy controls the pore size distributions for shales and the presence of micropores and fine mesopores in natural shales can be correlated with the dominance of the illite smectite type of clays in the rock our assessment of incompressible 3 nm sized pores associated with illite smectite clays provides an important building block for their mineral modulus

integrated nmr and fe sem methods for pore structure characterization of shahejie shale from the dongying depression bohai bay basin abstract of particular importance for shale reservoirs is the evaluation of pore structure characteristics that significantly influence a reservoir s storage capacity and flow mechanisms due to the presence of multiscale pore sizes in shale reservoirs a series of experiments including total organic carbon toc rock eval analysis x ray diffraction xrd field emission scanning electron microscopy fe sem and nuclear magnetic resonance nmr were conducted on shale samples from the lower submember of the third member es3l and upper submember of the fourth member of the eocene shahejie formation es4u in the dongying depression bohai bay basin the results indicate that calcite averaging 30 5 and clay averaging 29 1 are the dominant minerals based on analysis of geochemistry data the organic matter type of ly1 is i and ii four main types of reservoir spaces are observed in ly1 intercrystalline pores dissolved pores intergranular pores and microfractures shale samples in the study area have a wide range of pore size distributions and complex pore structures because of the wide range of transversal relaxation time t2 distributions and messy t2 curves of the nmr experiment per the nmr results the percentage of micropores mesopores and macropores ms1 ms2 and ms3 were calculated and the relationships between these proportions and pore structure parameters porosity permeability t2 cutoff value t2 geometric mean value and structural characteristics were investigated ms1 increased with a decrease of t2 cutoff values and geometric mean values suggesting that shale samples with higher ms2 and ms3 have better pore structures and strong percolation potential under similar porosity conditions samples with high permeability have a larger ms3 value laminated and layered shale samples have larger values of ms2 and ms3 than massive shale therefore ms1 ms2 and ms3 are useful to indicate the quality of pore structures the smaller the ms1 the better the pore structure finally taking three representative shale samples as an example the relationships between ms1 ms2 and ms3 and the effectiveness of the reservoir were discussed using the logging profile of ly1 the research concludes that ms1 ms2 and ms3 are effective nmr parameters for evaluating the effectiveness of the reservoir

analysis of the trace element content of coals from the carboniferous cumberland group near joggins nova scotia canada trace element concentrations including mg cr mn ni cu zn cd and pb are reported for six coal beds located in the cumberland group westphalian b or lower pennsylvanian at the joggins section nova scotia canada the coal beds were deposited on small flood plains the higher than usual heavy metal trace element concentrations in the coals may have been derived in the exposed cobequid massif located south of the joggins area

nuclear magnetic resonance characterization of shallow marine sediments from the nankai trough integrated ocean drilling program expedition 333 we measured nuclear magnetic resonance nmr relaxation times on samples from integrated ocean drilling program expedition 333 sites c0011 c0012 and c0018 we compared our results to permeability grain size and specific surface measurements pore size distributions from mercury injection capillary pressure and mineralogy from x ray fluorescence we found that permeability could be predicted from nmr measurements by including grain size and specific surface to quantify pore networks and that grain size is the most important factor in relating nmr response to permeability samples within zones of anomalously high porosity from sites c0011 and c0012 were found to have different nmr permeability relationships than samples from outside these zones suggesting that the porosity anomaly is related to a fundamental difference in pore structure we additionally estimated the size of paramagnetic sites that cause proton relaxation and found that in most of our samples paramagnetic material is present mainly as discrete clay sized grains this distribution of paramagnetic material may cause pronounced heterogeneity in nmr properties at the pore scale that is not accounted for in most nmr interpretation techniques our results provide important insight into the microstructure of marine sediments in the nankai trough

pore size controls on the base of the methane hydrate stability zone in the kumano basin offshore japan the base of the methane hydrate stability zone mhsz in the kumano basin offshore japan is marked by a bottom simulating reflection bsr on seismic data at integrated ocean drilling program site c0002 which penetrates this bsr the in situ temperature profile combined with bulk seawater methane equilibrium conditions suggest that the base of the mhsz is 428 m below seafloor bsf which is 28 m deeper than the observed bsr 400 m bsf we found that submicron pore sizes determined by mercury injection capillary pressure are sufficiently small to cause 64 of the observed uplift of the base of the mhsz by the gibbs thomson effect this is the most thorough characterization of pore sizes within the mhsz performed to date and illustrates the extent to which pore size can influence mhsz thickness our results demonstrate the importance of considering lithology and pore structure when assessing methane hydrate stability conditions in marine sediments

transpressive shear related to arc magmatism the paleoproterozoic storsjon edsbyn deformation zone central sweden 1 the polyphase 15 30 km wide and 200 km long storsjon edsbyn deformation zone sedz apparently separates two major paleoproterozoic provinces in central sweden four main phases of deformation have been recognized along the zone associated high strain rocks are characterized by their mineralogy microstructures kinematic patterns magnetic signatures and relative ages the mineral and stretching lineations are consistently steeply to moderately plunging analysis of mesoscopic shear zone populations of different generations suggests that most displacements are compatible with north south to northeast southwest bulk regional shortening the structural analysis suggests that the main ductile deformation along the sedz was due to dextral transpression with a steep coaxial component field evidence combined with published age data constrain the main deformation to the time interval circa 1 7 1 3 ga synkinematic titanite from a ductile protomylonite in the sedz yields an u pb age of 1674 6 ma the combined results imply transpressive deformation broadly synchronous with and spatially related to volcanism and plutonism in a continental margin magmatic arc setting

surface area porosity and water adsorption properties of fine volcanic ash particles our understanding on how ash particles in volcanic plumes react with coexisting gases and aerosols is still rudimentary despite the importance of these reactions in influencing the chemistry and dynamics of a plume in this study six samples of fine ash 500 a all the specimens had similar pore size distributions with a small peak centered around 50 a these findings suggest that fine ash particles have relatively undifferentiated surface textures irrespective of the chemical composition and eruption type adsorption isotherms for water vapour revealed that the capacity of the ash samples for water adsorption is systematically larger than predicted from the nitrogen adsorption a s values enhanced reactivity of the ash surface towards water may result from i hydration of bulk ash constituents ii hydration of surface compounds and or iii hydroxylation of the surface of the ash the later mechanism may lead to irreversible retention of water based on these experiments we predict that volcanic ash is covered by a complete monolayer of water under ambient atmospheric conditions in addition capillary condensation within ash pores should allow for deposition of condensed water on to ash particles before water reaches saturation in the plume the total mass of water vapour retained by 1 g of fine ash at 0 95 relative water vapour pressure is calculated to be 10 2 g some volcanic implications of this study are discussed

biotite and muscovite 40ar 39ar geochronological constraints on the post svecofennian tectonothermal evolution forsmark site central sweden in order to characterize the post svecofennian tectonothermal evolution of the fennoscandian shield 40ar 39ar biotite and some 40ar 39ar muscovite geochronological data are reported from a total of 30 surface outcrop and 1000 m long borehole samples at forsmark central sweden the thirteen surface samples were collected across three branches of a major wnw to nw trending system of deformation zones whereas the boreholes were drilled within a tectonic lens in between two of these zones the 40ar 39ar biotite ages indicate that the present erosion surface in central sweden cooled below 300 c at 1 73 1 66 ga and that the rocks could respond to stress by brittle deformation between 1 8 and 1 7 ga the variation in surface ages is suggested to be due to faulting along the large wnw to nw trending deformation zones following the establishment of a sub cambrian peneplain the minor variation of ages within a single crustal block may be due to disturbance along ene to nne trending fracture zones possible cooling paths derived from 40ar 39ar hornblende muscovite and biotite ages were calculated for the time interval from 1 80 to 1 66 ga when the area cooled from 500 c to 300 c between 1 70 and 1 64 ga uplift rates of c 22 m m y were calculated from borehole 40ar 39ar biotite data tectonothermal histories inferred from the combined cooling and uplift rates are related to simple slow cooling after the svecofennian orogeny to crustal movement in response to far field effects of c 1 7 ga orogenic activity further to the west or to a combination of these possibilities less

smectite diagenesis pore water freshening and fluid flow at the toe of the nankai wedge the presence of low chloride fluids in the lowermost sediments drilled at ocean drilling program site 808 at the nankai accretionary wedge has been considered as prime evidence for long distance lateral fluid flow from depth here we re evaluate the potential role of in situ reaction of smectite s to illite i in the genesis of this low chloride anomaly this reaction is known to be occurring at site 808 with both the s content and s to i ratio in the mixed layer clays decreasing substantially with depth we show that the bulk of the chloride anomaly can generate by in situ clay dehydration particularly if pre reaction smectite abundances ai approach 10 15 of the bulk sediment the ai values however are not well constrained at ai values 10 15 an additional source of low cl fluid centered close to the decollement could be required thus there remains the important possibility that the observed low cl anomaly is a compound effect of both lateral flow and in situ smectite dehydration

regional tectonic interpretation of image enhanced gravity and magnetic data covering the mid norwegian shelf and adjacent mainland abstract gravity and magnetic field data covering mid norway and the norwegian sea were processed in order to enhance tectonic features on various scales the local features were subjected to an unconventional processing technique involving a non linear adaptive wallis filter designed to enhance the smallest wave lengths when compared with recent structural information derived from seismic data the processed gravity and magnetic maps show the main structural trends major fault zones and basin boundaries thus proving their worth for regional tectonic mapping previously undetected nw se trending offshore crustal lineaments are revealed a landward prolongation of the bivrost lineament appears to continue subparallel towards proterozoic shear zones below the caledonian nappes in the rana area either along the western margin of the transscandinavian granite porphyry belt or the nw se trending mala skelleftea tectonic zone a large lineament is also observed as a landward prolongation of the surt lineament indicating a relationship with the storsjon edsbyn deformation zone a major deep crustal shear zone in the precambrian of sweden a slightly increased seismic activity which is possibly related to the present ridge push force is observed along parts of the previously unknown transfer zones combined gravity and magnetic modelling indicates a low crustal thickness in the northwesternmost part of the voring basin between the surt and the jan mayen lineaments the lack of correlation between the gravity and the magnetic patterns observed on the residual field maps suggests the presence of a shallow curie isotherm situated above or within the uppermost basement

elevated fluid pressure and extreme mechanical weakness of a plate boundary thrust nankai trough subduction zone pore fluid pressure is a key parameter governing both the shear strength of faults and the conditions for seismic and tsunamigenic slip on subduction zone megathrusts however quantitative constraints on this parameter based on in situ data in these or any faults have proven elusive using seismic interval velocities derived from a three dimensional seismic reflection survey we compute porosity fluid pressure and effective stress at the plate interface in the nankai trough subduction zone offshore southwestern japan to 20 km down the fault dip using well constrained locally calibrated empirical relationships between velocity porosity and effective stress we show that the fault and immediately subjacent footwall are nearly undrained implying that the subduction megathrust slips under a shear stress of

origins and ages of proterozoic granitoids in the bothnian basin central sweden isotopic and geochemical constraints abstract the paleoproterozoic bothnian basin in central sweden and south central finland is dominated by a 10 km thick sequence of metasediments mainly metaturbidites these have been intruded by granitoids which have traditionally been classified as early late and postorogenic relative to the c 1 9 1 8 ga s vecofennian orogeny the early orogenic granitoids are part of a calcalkaline suite ranging in composition from ultramafic to granitic while the late orogenic granitoids mainly are purely granitic and associated with abundant pegmatites the postorogenic group forms large massifs of mainly granitic composition and associated pegmatites are rare an early orogenic tonalite yields a u pb zircon age of 1877 6 ma which is within the age range for s vecofennian granitoids of this tectonic position elsewhere in sweden and finland a late orogenic granite belonging to the harno granites from the southern part of the bothnian basin gives a u pb monazite age of 1822 5 ma this provides a minimum age for the main phases of svecofennian deformation in the region and a correlation with the 1 84 1 83 ga old granite migmatite zone of southern finland is suggested a postorogenic granite belonging to the revsund granitoids gives a u pb zircon age of 1798 8 ma together with previously published age data this indicates that the revsund granitoids were emplaced successively during an age interval of at least between 1 80 and 1 77 ga ree patterns and trace element model calculations indicate that late orogenic granites could have been produced by partial melting of metasediments similar to those exposed at the surface a contribution from the early orogenic granitoids is possible but not discerned by these calculations the postorogenic granites on the other hand have too high concentrations of sr ba y and hree to be derived from such a metasedimentary source the initial e nd values for the early orogenic granitoids range between 2 and 1 corresponding values for both late and postorogenic granites range between 1 and 3 which is on average slightly higher than those for surrounding metasediments the initial sr isotope ratios for the harno granites are intermediate between those for the metasediments and the early orogenic granitoids while the initial sr isotope ratios for the revsund granites are distinctly lower the geochemical and isotopic data support a model in which the harno granites were derived mainly from bothnian basin metasediments with a contribution from early orogenic granitoids the composition of the revsund granitoids is however inconsistent with such a derivation for these rocks a deeper as yet unknown crustal source with a significant pre 1 9 ga crustal component is indicated

migmatization related to mafic underplating and intra or back arc spreading above a subduction boundary in a 2 0 1 8 ga accretionary orogen sweden abstract absolute ages of migmatization and protolith formation and constraints on the timing of ductile deformation in two major lithotectonic units in the south western part of a 2 0 1 8 ga orogenic belt in the fennoscandian shield south eastern sweden have been determined using u pb ion probe analysis of different generations of zircon in veined gneisses and leucocratic granite detrital and xenocrystic zircon in paragneiss and garnet bearing leucogranite respectively in the bergslagen lithotectonic unit show ages of 2 1 2 0 ga and 1 9 ga deposition of the sedimentary material occurred during or after a subduction related magmatic event at 1 91 1 87 ga two orthogneiss protoliths formed during this magmatic event around 1 88 ga while most zircon in the leucosome in a third migmatitic orthogneiss was inherited from a 1 85 ga igneous protolith a polyphase tectonothermal evolution with anatexis under low p metamorphic conditions around 1 86 ga m1 and 1 84 1 81 ga m2 is inferred for the migmatitic gneisses in the bergslagen unit garnet bearing leucogranite crystallised around 1 84 1 83 ga close in time to major folding of the m1 gneissic fabric a previously unrecognised 1 86 1 85 ga ductile deformational event under medium grade metamorphic conditions has been identified in the adjacent lithotectonic unit to the south smaland lithotectonic unit close in time to the m1 event in the bergslagen unit to the north by constraining the timing of anatexis and comparing with information bearing on crustal thickness excess mass at depth and the character and age of magmatic activity it is inferred that anatexis in the bergslagen lithotectonic unit is related to pulses of mafic underplating during the early stages of two separate subduction related magmatic episodes after the 1 91 1 87 ga magmatic event it is suggested that each pulse was related to intra or back arc spreading above a subduction boundary which had entered a retreating mode with separate long periods 20 50 ma of extension or transtension this study challenges the need to invoke crustal thickening related to plate collision at 1 9 1 8 ga as a mechanism to explain high grade metamorphism in the southern part of the 2 0 1 8 ga orogen instead a solely accretionary tectonic model involving an overriding plate along an active continental margin with significant extensional or transtensional crustal deformation is preferred

stretching lineations in transpressional shear zones an example from the sierra nevada batholith california abstract ductile shear zones and associated stretching lineations are generally considered to be the result of two dimensional simple shear deformations with stretching lineations interpreted to rotate into parallelism with the direction of tectonic transport with increasing deformation however stretching lineations perpendicular to the inferred tectonic transport direction are displayed by some shear zones field studies in the sierra nevada batholith have revealed a single shear zone the rosy finch gem lake shear zone that contains both steeply plunging stretching lineations in older metamorphosed sedimentary and granitic rocks and shallowly plunging stretching lineations in syntectonic granitoids dextral sense of shear indicators are found in all these units and deformation occurred simultaneously along the length of the shear zone theoretical strain modeling indicates that stretching lineations can be either horizontal or vertical within transpressional shear zones to investigate the kinematics of three dimensional deformation we examine the role of stretching lineations which form as a result of finite strain including the possibility of partitioning a component of the strike slip movement onto shear bands comparing the field data with the strain modeling we interpret the along strike variation in lineation behavior within the rosy finch gem lake shear zone to be a result of the differences in finite strain recorded by different units the older units showing steeply plunging lineation have recorded more finite strain across a narrower shear zone than the syntectonic granites which record shallowly plunging lineations we conclude that the orientation of the lineation within transpressional shear zones does not necessarily correlate with the transport direction but may reflect along strike variations in finite strain and or strain partitioning

fundamental processes controlling the first stage of alteration of a basalt glass by seawater an experimental study between 200 and 320 c the first stage of alteration of a basalt glass by seawater has been studied experimentally between 200 and 320 c under vapor pressure following both the chemical evolution of the reacting solutions during the experiments and the chemical and mineralogical transformations of the altered glass surface via microprobe scanning transmission electron microscope and resonant nuclear reactions the alteration is controlled by diffusion of dissolved species through an altered layer and not by surface chemical reaction selective removal of cations with respect to sio2 leads to the formation of a thick porous protonated surface layer enriched in sio2 aqueous diffusion of dissolved species from the reacting glass and from solution through the pores of this layer results in the formation of an amorphous silicate gel which is the precursor of normal crystalline clays saponites appearing in a later stage computer simulations of the alteration generated with the eq3 6 computer software package account for the chemical composition of the rim and the sequence of secondary minerals found in the experiments

magnetic fabrics and paleomagnetism of the storsjon edsbyn deformation zone central sweden abstract a regional deformation zone separating tectonomagmatic blocks in the central part of the fennoscandian shield has been studied using anisotropy of magnetic susceptibility and paleomagnetism in order to define the tectonic character and age of the zone and to put the deformation into a plate tectonic context the deformation zone the storsjon edsbyn deformation zone sedz separates the ratan granite of the trans scandinavian igneous belt tib and the southern svecofennian subprovince in the southwest from older svecofennian granitoids of the central svecofennian subprovince in the northeast the sedz is the most prominent deformation zone in a regional pattern of nw se trending shear zones on basis of ams data the width of the zone which cuts through 1 7 1 9 ga old rocks is estimated at 10 12 km in its central southern part and 20 25 km in its northern part the orientations of the susceptibility axes vary systematically across the zone in a way that suggests that the sedz is a pure shear dominated transpression zone caused by a compressive stress from the present ssw paleomagnetic data from a dolerite sill plat 10 plon 166 and from a dyke plat 25 plon 190 that cut the sedz indicate that no plastic deformation has occurred along the zone during the past 1 25 ga and probably not for the past 1 5 1 6 ga ams data do not point to any deformation of the 1 70 ga old ratan granite which further limits the time span of deformation the main phase of deformation most likely took place between 1 80 and 1 70 ga ago the geological evolution of this part of the fennoscandian shield at the time between 1 80 and 1 70 ga ago is very complex and in part still enigmatic this time period involves magmatism of the tib which is related to eastward subduction it also comprises the beginning of the gothian orogeny and the development of a regional system of transpressive deformation zones the compressive stress field from the present ssw indicated in this study is interpreted to be related to an initial stage of plate collision between the southwestern scandinavian subprovince and older parts of the fennoscandian shield this collision resulted in a system of regional nw se trending intra plate deformation zones one of which is the sedz

crustal structure of the indus tsangpo suture zone and its ophiolites in southern tibet abstract the 2000 km long indus tsangpo suture zone itsz in southern tibet contains remnants of neotethyan oceanic lithosphere ophiolitic melanges flysch units and continental rocks and has been interpreted as the boundary between the india and eurasia plates we have used field based structural analyses and geological mapping in five key ophiolite massifs luobusa zedang xigaze jiding and dongbo and petrofabric studies of core samples recovered through the luobusa scientific drilling project to document the structural architecture and the deformation history of the itsz the structural and kinematic analyses of the suture zone units indicate the occurrence of superposed deformation fabrics which developed first during the ophiolite emplacement and then during the subsequent india asia continental collision the suprasubduction zone ophiolites were emplaced southward onto the northern margin of the proto indian plate in the late cretaceous the continental collision between the ophiolite laden proto indian margin and the lhasa terrane of the eurasian plate in the early paleogene resulted in backthrusting and inversion of the structural order of the itsz the ophiolite massifs ophiolitic melanges and flysch units were thrust northward as nappe sheets over the eocene and younger forearc basin strata the itsz shows therefore a complex structural anatomy characterized by both south and north directed thrust faults and ductile and brittle deformation fabrics

the supply and accumulation of silica in the marine environment rivers and submarine hydrothermal emanations supply 6 1 1014g sio2 yr to the marine environment approximately two thirds of the silica supplied to the marine environment can be accounted for in continental margin and deep sea deposits siliceous deep sea sediments located beneath the antarctic polar front convergence account for over a fourth 1 6 1014g sio2 yr of the silica supplied to the oceans deep sea sediment accumulation rates beneath the polar front are highest in the south atlantic with values as large as 53cm kyr during the last 18 000 yr siliceous sediments in the bering sea sea of okhotsk and subarctic north pacific accumulate 0 6 1014g sio2 yr or 10 of the dissolved silica input to the oceans the accumulation of biogenic silica in estuarine deposits removes a maximum of 0 8 1014g sio2 yr although estuarine silica versus salinity plots indicate extensive removal of riverine silica from surface waters the removal rates must be considered as maximum values because of dissolution of siliceous material in estuarine sediments and bottom waters siliceous sediments from continental margin upwelling areas e g gulf of california walvis bay or peru chile coast have the highest biogenic silica accumulation rates in the marine environment 69 g sio2 cm2 kyr despite the rapid accumulation of biogenic silica upwelling areas account for less than 5 of the silica supplied to the marine environment because they are confined laterally to such small areas

evidence for 1 82 ga transpressive shearing in a 1 85 ga granitoid in central sweden implications for the regional evolution abstract two crustal scale shear zone systems the storsjon edsbyn deformation zone and the hassela shear zone join in the western part of central sweden and form an anastomosing pattern of ductile shear zones several of these up to 1 km wide zones truncate an intrusion previously defined as a component of the major ca 1 80 1 77 ga magmatic suite the revsund granitoids in north central sweden however within the southern part of the intrusion titanites that are components of the fabric in a pervasively deformed shear zone forsaan have a u pb tims age of 1816 2 ma zircon porphyroclasts in the same fabric yield a u pb sims age of 1849 14 ma overlapping with the u pb tims age of 1851 2 ma for titanites from an undeformed granitoid these results are interpreted to define the ages of ductile shearing and magma emplacement respectively this interpretation is supported by microstructures as well as the regional structural pattern characterised by shear zones enveloping virtually undeformed pods of the granitoid previously reported and locally existing magmatic flow structures indicate some syn emplacement deformation the kinematic results characterised by a high proportion of pure shear within the granitoid and oblique dextral shearing along its margin reflect strain partitioning under transpressive conditions the kinematic and geochronological results fit into the regional framework of late orogenic localised deformation along crustal scale shear zones recent absolute datings of shear fabrics defines ca 1 82 1 80 ga as a period of shear zone activity in central sweden temporally this period overlaps with the emplacement of s type granites and granitoids derived from deeper crustal levels a similar situation exists in southern finland structural geochronological and geophysical data suggest that the crustal scale shear zones in central sweden and southern finland may be related temporally and spatially the age and the post tectonic nature on a regional scale of the dated 1 85 ga granitoid have important regional implications as both the age of the intrusion and the ductile shearing are older than the established age range 1 80 1 77 ga of the revsund granitoids either an extended intrusive history for the suite is indicated or the granitoids in this part of the type areas should be excluded from the revsund suite their post tectonic nature implies that the pervasive svecokarelian deformation in the area occurred earlier than generally assumed 1 85 1 80 ga on the other hand approximately coeval calc alkaline granitoids to the south east of the investigated area are folded and foliated pervasively indicating a later svecokarelian evolution in that area i e that the granitoids are located in domains with separate orogenic evolutions

a chemical and thermodynamic model of aluminous dioctahedral 2 1 layer clay minerals in diagenetic processes regular solution representation of interlayer dehydration in smectite

alternating augite plagioclase wedges in basement dolerites of lockne impact structure sweden a new shock wave induced deformation feature this paper reports peculiar alternating augite plagioclase wedges in basement dolerites of lockne impact structure sweden the combined microscopic and spectroscopic studies of the micro nanoscale wedges reveal that these are deformation induced features first samples showing wedges 12 out of 18 studied are distributed in the impact structure within a radius of up to 10 km from the crater center second the margins between the augite and labradorite wedges are sharp and the 110 prismatic cleavage of augite develops into fractures and thereafter into wedges the fractures are filled with molten labradorite pushed from the neighboring bulk labradorite grain third compared to the bulk labradorite the dislocation density and the residual strain in the labradorite wedges are significantly higher a possible mechanism of genesis of the wedges is proposed the mechanism explains that passing of the shock waves in the basement dolerite induced i formation of microfractures in augite and labradorite ii development of the augite prismatic cleavages into the wedges which overprint the microfracture in the labradorite wedges and iii thereafter infilling of microfractures in the augite wedges by labradorite

brittle tectonic evolution and paleostress field reconstruction in the southwestern part of the fennoscandian shield forsmark sweden 1 six hundred fault slip data have provided robust paleostress fields within an approximately 35 km3 volume of paleoproterozoic 1 9 ga rocks in the southwestern fennoscandian shield forsmark sweden these rocks were affected by penetrative ductile strain from 1 87 to 1 86 ga folding ductile strain along discrete zones around 1 8 ga and semibrittle or brittle deformation around and after 1 8 ga compatible paleostress fields have been identified using site by site and merged data sets from outcrops and oriented drill cores transpressive deformation with a regional nnw sse 1 axis associated with clockwise stress deviation inside a tectonic lens resulted in dextral slip along regionally significant steep wnw ese and nw se deformation zones the semibrittle and most of the brittle structures including specifically the epidote bearing fractures were established during this oldest regime around 1 8 ga latest svecokarelian a younger paleostress field with a ne sw 1 axis which was also transpressive in character is inferred to have been active at 1 7 1 6 ga the best defined paleostress field is transpressive in character with a wnw ese 1 axis that resulted in sinistral reactivation along the wnw ese and nw se zones the main set of laumontite stepped faults developed at this stage at 1 1 0 9 ga sveconorwegian it is impossible to exclude fully the influence of reactivation during even younger phanerozoic tectonic events subordinate extensional paleostress fields were related either to the latest svecokarelian and sveconorwegian transpressive regimes due to 1 and 2 stress permutations or to regional extensional tectonic regimes during the meso or neoproterozoic or later during the permo carboniferous and or mesozoic

geology geochemistry age and geotectonic evolution of the dala granitoids central sweden abstract the dala granitoids and their associated volcanic products are part of a major palaeoproterozoic igneous complex the 1 85 1 67 ga transscandinavian igneous belt tib in the fennoscandian shield tib constitutes the south western border of the svecofennian domain which was formed by an orogenic episode at 1 93 1 83 ga earlier plate tectonic models proposed that tib is a postorogenic batholith complex which was formed in a compressional tectonic regime representing an andino type environment whereas an extensional tectonic regime has been proposed for the anorogenic 1 65 1 51 ga rapakivi granites in the svecofennian domain in this paper a key segment of tib the dala granitoids is discussed in order to focus attention on the post to anorogenic magmatic evolution in the svecofennian domain three types of granitoids jarna siljan and garberg can be distinguished within the dala granitoid complex the jarna granitoids are the most primitive and were emplaced at a significant depth in the crust at ca 1 79 ga the 1 70 1 68 ga siljan and garberg granites are more evolved and were emplaced at a shallow level in the crust closely associated in space time and origin with the volcanic dala porphyries field relationships as well as geochemical and geochronological data indicate magma genesis within a compressional tectonic regime for the 1 79 ga jarna granitoids however most of the dala granitoids appear to have formed in an extensional tectonic regime which was initiated during the last phase of tib magmatism this extensional igneous component is represented by the 1 70 1 68 ga high level siljan and garberg granites and their closely associated volcanic products the dala porphyries an improved model for the formation of the post to anorogenic magmatism in the svecofennian domain suggests that the dala granitoids represent a post to anorogenic igneous key complex which reflects the transition from a compressional to an extensional tectonic environment along a plate boundary

characterization of pore systems in seal rocks using nitrogen gas adsorption combined with mercury injection capillary pressure techniques abstract porous microstructure parameters of seal rock samples originating from different depths within brazilian geological formations were correlated to empirical models which predict the intrinsic permeability mercury injection capillary pressure micp and nitrogen gas adsorption n 2 ga were applied in combination as complementary techniques micp to obtain the porosity values and the size distribution of meso and macropores and n 2 ga associated with the brunauer emmett and teller bet theory to determine the specific surface area s o the barret joyner and hallenda bjh theory was applied to find the size distribution of the micro and mesopores the combination of the micp and n 2 ga curves showed that the samples analyzed present a polymodal pore size distribution psd and a total porosity ranging from 0 33 to 10 44 the s o values measured by n 2 ga were higher than those calculated by micp due to the majority of the samples having a mean pore size of 20 1000 a the intrinsic permeability could also be predicted applying the measured parameters s o psd curves and total porosity in the carman kozeny and series parallel models the ranges of permeability values obtained were 4 09 10 24 4 96 10 21 m 2 and 9 48 10 27 9 14 10 22 m 2 respectively these results were compared with values reported in the related literature and those obtained for four samples submitted to pressure pulse decay permeability pdp tests

extending nmr data for permeability estimation in fine grained sediments abstract we combine nuclear magnetic resonance nmr transverse relaxation time data and gamma ray data to estimate lithology dependent permeability in silt and clay rich sediments this approach extends the utility of the schlumberger doll research sdr permeability equation from reservoirs to aquicludes and seals and thus improves the value and robustness of nmr data data from keathley canyon northern gulf of mexico show that nmr data can be used to define permeability from 10 18 to 10 14 m 2 0 001 10 millidarcies as calibrated and tested by direct measurements on core samples we performed uniaxial constant rate of strain consolidation experiments on sediments from keathley canyon to determine core scale permeability permeabilities from these experiments were compared to permeabilities calculated from logging while drilling data a better fit between log derived permeability and laboratory measured permeability was obtained using the sdr equation with a variable coefficient a rather than a constant a as is typically used we show how a is a function of lithology and can be modeled from gamma ray data the relationship between a and gamma ray values suggests that variations in a are caused by platy clay minerals and the effect they have on the pore system our results provide improved means for permeability estimation for application in basin flow modeling hydrocarbon migration modeling and well completion design

unraveling 1 5 ga of brittle deformation history in the laxemar simpevarp area southeast sweden a contribution to the swedish site investigation study for the disposal of highly radioactive nuclear waste 1 5 ga of brittle deformation in sweden

early proterozoic continental tholeiites from western bergslagen central sweden iii geodynamic inferences abstract the 1 88 ga old within plate continental tholeiites belong to the mainly metavolcanic bimodal bergslagen supracrustal series bss in the svecofennian domain of the baltic shield the bss evolved in an intracontinental rift despite only moderate lithospheric extension the tholeiites are the near surface expression of a 10 20 km thick magmatic crustal underplate that probably underlies most of the sw svecofennian domain and caused the svecofennian crust to be three layered thick but yet isostatically stable underplating strengthened the lithosphere sufficiently to control the time of cratonization geodynamic models for the origin of the bss consistent with our interpretations are gravitational collapse of an overthickened continental accreted terrane margin or back arc processes related to a marginal volcanic arc 250 km further south a tentative reconstruction of relative plate motions during svecofennian time indicates predominantly longitudinal motion of the plates in question and complies with the relatively slow latitudinal drift of the shield at the time recent ion microprobe u pb ages of proterozoic zircons in svecofennian metasediments imply about 0 2 ga of pre svecofennian crustal evolution while the nd model ages of the most primitive metatholeiites may be indicative of initial mantle differentiation as early as 2 4 ga bp accompanying protocrust formation

granite magma formation transport and emplacement in the earth s crust the origin of granites was once a question solely for petrologists and geochemists but in recent years a consensus has emerged that recognizes the essential role of deformation in the segregation transport and emplacement of silica rich melts in the continental crust accepted petrological models are being questioned either because they require unrealistic rheological behaviours of rocks and magmas or because they do not satisfactorily explain the available structural or geophysical data provided flow is continuous mechanical considerations suggest that far from being geologically sluggish granite magmatism is a rapid dynamic process operating at timescales of or 100 000 years irrespective of tectonic setting

compaction driven evolution of porosity and permeability in natural mudstones an experimental study this paper describes a series of experiments designed to investigate the influence of lithology on the compactional loss of porosity and permeability in mudstones two intact samples of london clay with clay fractions of 40 and 67 were compacted to 33 mpa effective stress clay fraction permeability porosity pore size distribution and specific surface area were measured and their evolution was monitored throughout the compaction process electron microscopy was combined with mercury porosimetry to trace the collapse of the pore structure with increasing effective stress in both cases porosity loss occurred primarily by the collapse of large pores this process is more obvious in the coarser grained sample because throughout the compaction process it has a much broader range of pore radii and a much greater mean pore radius consistent with the pore size distributions the permeability of the coarser sample ranges from 10 10 m s 1 to 10 12 m s 1 while that of the finer grained sample ranges from 4 10 12 m s 1 to 5 10 14 m s 1 during progressive compaction from 2 to 33 mpa the compressibility of the finer grained sample is greater than that of the coarser grained sample 0 15 as opposed to 0 07 however in both cases the compressibility is much lower than that inferred for lithologically similar samples compacted over geological timescales the demonstration that both porosity and lithology clay fraction influence the permeability of mudstones should allow the development of more realistic porosity permeability relationships which take into account lithological variations exhibited by mudstones

alteration of volcanic matter in deep sea sediments evidence from the chemical composition of interstitial waters from deep sea drilling cores six deep sea drilling project dsdp sites 252 285 315 317 336 386 were examined for the chemical composition of the dissolved salts in interstitial waters the oxygen isotopic composition of the interstitial waters and the major ion composition of the bulk solid sediments an examination of the concentration depth profiles of dissolved calcium magnesium potassium and h218o in conjunction with oxygen isotope mass balance calculations confirms the hypothesis that in dsdp pelagic drill sites concentration gradients in ca mg k and h218o are largely due to alteration reactions occurring in the basalts of layer 2 and to alteration reactions involving volcanic matter dispersed in the sediment column oxygen isotope mass balance calculations require substantial alteration of layer 2 up to 25 of the upper 1000 m but only minor exchange of ca mg and k occurs with the overlying ocean this implies that alteration reactions in layer 2 are almost isochemical

pore structure and fractal characteristics of ordovician majiagou carbonate reservoirs in ordos basin china fractal analysis was performed on carbonate core plug samples from the ordovician majiagou carbonate reservoirs in the ordos basin using mercury intrusion capillary pressure micp nuclear magnetic resonance nmr and the x ray computed tomography ct measurements to improve our understanding of the pore structure characteristics the relationships between pore structure parameters and the fractal dimensions were investigated the pore systems are dominated by secondary intercrystalline pores and enlarged dissolution pores as well as microfractures the fractal curves from micp analysis break into two segments at the swanson s parameter the small pore throat systems can be described by the fractal theory whereas pores connected by relatively large throats greater than the pore throat radius at the pittman s hyperbola s apex are not cylindrical in shape cannot be described by a capillary tube model and tend to have apparent fractal dimensions larger than 3 0 the fact that the entirety of the capillary curve cannot be fit by a single fractal dimension implies that there are multiple pore systems present with different fractal dimensions the ct analysis shows that the pores are dispersed in the three dimensional spaces mainly with elliptical shapes the nmr measurements are sensitive to pore body size and micp probes pore throat dimensions the latter being complementary to the pore body size distribution none of the ct micp and nmr techniques provide right or wrong answers to the pore throat systems but they probe different aspects of the pore systems this study assumes the pore shapes to be spherical in general and then the fractal dimension is calculated from the nmr transverse relaxation time t2 spectrum the fractal dimensions of all the samples are calculated and the accuracy of the fractal model is verified by the high regression coefficients almost all the pore systems can be described by fractal theory and the fractal dimensions are strongly correlated with the t2 values separating the immovable fluid and the free fluid microfractures may bias t2 toward larger values making it hard to derive fractal dimensions from nmr measurements the coexistence of small pores pore radius 50 m results in a heterogeneous pore distribution and a high fractal dimension reservoir quality increases with the complexity degree of the microscopic pore structure conversely samples that are dominated by small pore systems tend to have a lower fractal dimension and a less complex pore structure

porcelaneous cement and microporosity in california miocene turbidites origin and effect on reservoir properties abstract southern california miocene sands are cemented with porcelaneous cement a mixture of opal a opal ct microquartz and montmorillonite clay this cement was observed filling interparticle pore space in sandstones from the beta and wilmington fields in the los angeles basin the silica minerals result from recrystallization of siliceous organisms such as diatom frustules and sponge spicules which are incorporated into the turbidite sands the montmorillonite sources include detrital clay and alteration of unstable grains about 70 of the bulk volume of the cement is micropore space this microporosity constitutes from one fifth to four fifths of the total porosity in these sandstones rocks with large amounts of microporosity have low permeabilities since fluid flow through the micropore system is restricted recrystallization of the porcelaneous cement with further burial would result in a chert cemented sandstone it is suggested that biogenic silica may be one source of chert cements observed in ancient turbidites

svecofennian detrital zircon ages implications for the precambrian evolution of the baltic shield metasediments intruded by 1 90 1 87 ga old plutonic rocks form the oldest major proterozoic crustal component in the svecofennian domain of the baltic fennoscandian shield their ndtdm model ages and conventional multigrain zircon u pb ages between 2 4 and 2 1 ga have previously been interpreted either as mixing ages between 1 9 ga old juvenile materials and a minor archaean component or as actual rock and protolith ages to resolve the ensuing controversy 120 individual detrital zircons from svecofennian metasediments in sweden and finland were analysed using the shrimp ion microprobe the oldest materials in this array are a 3 44 ga old zircon from the tampere schist belt in finland and a 3 32 ga old crystal from southeastern sweden about 30 of the analysed crystals are 2 97 2 60 ga old while 65 have ages between 2 12 and 1 88 ga thus there is no evidence of 2 6 2 1 ga old protoliths but the age range of the proterozoic zircons indicates that a major area of 2 1 1 9 ga old crust was in erosional position 1 9 ga ago this implies that the formation of palaeoproterozoic crust in the baltic shield or its one time close neighbourhood must have commenced 100 200 ma earlier than hitherto assumed in conjunction with previously obtained isotopic data the youngest detritus ages of the present study constrain the age of svecofennian sedimentation it can also be concluded that the archaean zircons found in quartzites from southern sweden may have been derived from source areas to the southwest of the central svecofennian marine depositional basin the so called bothnian basin separating southern sweden from the archaean craton in the northeastern part of the shield

continental margin magmatism and migmatisation in the west central fennoscandian shield the ljusdal batholith ljb is a major component of the central svecofennian domain in sweden it is separated from the bothnian basin to the north by the 1 82 1 80 cia crustal scale hassela shear zone hsz the ljb has emplacement ages of 1 86 1 84 cia is mainly alkali calcic metaluminous has epsilon nd values between 0 3 and 1 2 and was formed in a magmatic arc setting during the svecokarelian orogeny the ljb was affected by at least three fold episodes large scale folded screens of migmatised metasedimentary rocks occur in the eastern part of the batholith and to the north of the hsz there is a 50 km wide diatexite belt the transition belt trb consisting of 1 88 1 85 ga granitoids is located at the northwestern extension of this belt a calc alkaline and peraluminous composition combined with negative epsilon nd values 1 7 to 0 8 indicates a large proportion of metasediments in the source for these granitoids u pb sims data on zircon rims from migmatites and leucogranites to the north and east of ljb yield ages of 1 87 1 86 ga i e coeval with the granitoids of the ljb and the trb there is thus a close relationship between the ljb the trb and the migmatites in both space and time syn migmatitic shearing along the hsz indicates that a proto hsz was initiated already at c 1 86 ga and the location of the proto hsz is inferred to be controlled by two older nuclei present in the lower parts of the crust as crustal scale shear zone systems are known to act as ascent pathways for sheet like flow in active orogenies the trb may represents accumulations of melts that were attracted and extracted by the proto hsz and intruded in a block that was not pervasively affected by subsequent shear along the hsz an active continental margin setting for the ljb implies subduction at c 1 86 ga and provides a heat source for both the migmatites and the trb a later migmatisation at 1 82 ga has been recorded to the south of the hsz within the ljb the 1 82 ga stromatic migmatites are folded by f 2 folds and the fabric is truncated by 1 80 cia pegmatites

timing of magmatism and migmatization in the 2 0 1 8 ga accretionary svecokarelian orogen south central sweden the palaeoproterozoic 2 0 1 8 ga svecokarelian orogen in central sweden consists of a low pressure predominantly medium grade metamorphic domain central part of bergslagen lithotectonic unit enclosed to the north and south by low pressure migmatite belts two periods of metamorphism 1 87 1 85 and 1 83 1 79 ga are known in the migmatite belts in this study new u th pb ion microprobe data on zircon and monazite from twelve samples of locally migmatized gneisses and felsic intrusive bodies determine both protolith and metamorphic ages in four sample areas north of stockholm inside or immediately adjacent to the medium grade metamorphic domain two orthogneiss samples from the rimbo area yield unusually old protolith ages of 1909 4 and 1908 4 ma while three orthogneisses from the skutskar and forsmark areas yield more typical protolith ages between 1901 3 and 1888 3 ma migmatized paragneiss samples from this and two earlier studies contain a significant detrital component sourced from this 1 9 ga magmatic suite they are interpreted to be deposited contemporaneously with or shortly after this magmatism migmatization of the paragneiss at rimbo was followed by intrusion of leucogranite at 1846 3 ma even in the other sample areas to the north hedesunda tierp skutskar and forsmark metamorphism including migmatization is constrained to the 1 87 1 85 ga interval and penetrative ductile deformation is limited by earlier studies in the forsmark area to 1 87 1 86 ga however apart from a metamorphic monazite age of 1863 1 ma precise ages were not possible to obtain due to the presence of only partially reset recrystallized domains in zircon or highly discordant u rich metamict and altered metamorphic rims migmatization was contemporaneous with magmatic activity at 1 87 1 84 ga in the bergslagen lithotectonic unit involving a mantle derived component and there is a spatial connection between migmatization and this magmatic phase in the hedesunda tierp sample area the close spatial and temporal interplay between ductile deformation magmatism and migmatization the p t metamorphic conditions and the continuation of similar magmatic activity around and after 1 8 ga support solely accretionary rather than combined accretionary and collisional orogenic processes as an explanation for the metamorphism the generally lower metamorphic grade and restricted influence of the younger metamorphic episode at least at the ground surface level distinguishes the central part of the bergslagen lithotectonic unit from the migmatite belts further north and south

granite magma generation ascent and emplacement within a transpressional orogen crustal thickening during transpressive orogenesis may produce anatectic granites which may then localize deformation leading to transcurrent movement granites may be transported from sites of generation through the mid crust in dyke like channelways within relatively narrow strike slip shear zones which link to major fault zones in the upper crust extensional jogs within fault systems provide developing sites for the assembly of plutons from magma arriving from below the model is based upon observations from the cadomian belt of nw france which exposes sections through middle and upper levels of the late precambrian crust within different elements of the orogen the mechanism provides a favourable alternative to diapirism and explains the common collocation of granites and shear zone fault systems within orogenic belts

origin of continental crust of 1 9 1 7 ga age nd isotopes in the svecofennian orogenic terrains of sweden initial nd isotopic ratios are reported for 57 samples representing all crustal components in the central and southern parts of the 1 9 1 7 ga old svecofennian orogenic terrains of sweden and the 1 8 1 7 ga old transscandinavian granite porphyry belt transscandinavian igneous belt u pb zircon ages are determined where the magmatic ages were not sufficiently constrained the nd isotopic results show that there are no archaean crustal blocks within the studied 1 9 1 7 ga old crustal segment this is consistent with results from finland the main input of recycled archaean crust to the svecofennian was in the form of sediments which are concentrated in the central svecofennian subprovince of north central sweden this is consistent with the vicinity of this subprovince to the archaean craton of the baltic shield these turbidite sediments contain up to 40 archaean material but s type granitoids associated with them have a smaller archaean component around 20 most of the quantitatively predominant i type granitoids and volcanics as well as all the basaltic rocks studied have nd from 1 to 3 and consist of 90 material newly derived from the mantle 1 9 1 7 ga ago we argue that the archaean material was introduced in the form of sediments but we cannot distinguish between pelagic sediments delivered on subducting oceanic crust and turbidite accumulations like the ones seen in north central sweden in either case an overall 15 archaean contribution for the swedish svecofennian was reasonably well homogenized with mantle derived magmatic products for this to occur an active near surface tectonic environment such as a complex of subduction zones must have been necessary

hydrogeology and mechanics of subduction zone forearcs fluid flow and pore pressure at subduction zones fluid flow pore pressure and tectonic processes are tightly interconnected excess pore pressure is driven by tectonic loading and fluids released by mineral dehydration and it has profound effects on fault and earthquake mechanics through its control on effective stress the egress of these overpressured fluids which is in part governed by the presence of permeable fault zones is a primary mechanism of volatile and solute transport to the oceans recent field measurements new constraints gained from laboratory studies and numerical modeling efforts have led to a greatly improved understanding of these coupled processes here we summarize the current state of knowledge of fluid flow and pore pressure in subduction forearcs and focus on recent advances that have quantified permeability architecture fluxes the nature and timing of transience and pressure distribution thus providing new insights into the connections between fluid metamorphic mechanical and fault slip proc

ductile shear zones related to crustal shortening and domain boundary evolution in the central fennoscandian shield the paleoproterozoic part of the fennoscandian shield is composed of crustal components formed in different tectonic settings and generally separated by well defined shear

volcanic ash particles as carriers of remanent magnetization in deep sea sediments from the kerguelen plateau abstract carbonate sediments from the kerguelen plateau odp leg 120 of eocene to pliocene age were investigated with rock magnetic petrographic and geochemical methods to determine the carriers of remanent magnetization magnetic methods showed that the major magnetic minerals were titanomagnetites slightly larger than single domain particles submicrometre to micrometre size grains of titanomagnetite were identified as inclusions in volcanic glass particles or as crystals in lithic clasts volcanic fallout ash particles formed the major fraction of the magnetic extract from each sediment sample three groups of volcanic ashes were identified trachytic ashes basaltic ashes with sideromelane and tachylite shards and palagonitic ashes these three groups could be equally well defined based on their magnetic hysteresis properties and alternating field demagnetization curves the highest coercivities of all samples were found for the tachylite due to the submicrometre size titanomagnetite inclusions in the matrix trachytic ashes had intermediate magnetic properties between the single domain type tachylites and the palagonitic altered basaltic ashes with low coercivities samples which contained mixtures of these different volcanic ashes could be distinguished from the three types of ashes based on their magnetic characteristics there was neither evidence of biogenic magnetofossils in the transmission electron micrographs nor did we find magnetic particles derived from continental antarctica the presence of dispersed volcanic fallout ashes between visible ash layers suggests continuous explosive volcanic activity on the kerguelen plateau in the south indian ocean since the early eocene the continuous fallout of volcanic ash from explosive volcanism on the kerguelen archipelago is the source of the magnetic particles and thus responsible for the magnetostratigraphy of the nannofossil oozes drilled during leg 120

a seismotectonic picture of the inner southern western alps based on the analysis of anomalously deep earthquakes abstract the anomalously deep seismicity beneath the western po plain is here analyzed to shed light on the complex and still poorly understood tectonic configuration of the internal side of the western alps area the original dataset including 590 earthquakes deeper than 20 km recorded during the last 25 years has been accurately relocated with hypodd using both catalog and cross correlation differential times we found that the distribution of seismic events faithfully mirrors the presence of two distinct tectonic domains axial belt domains 1 and 2 originally belonging to the paleogene alpine wedge and now anomalously juxtaposed beneath the sedimentary infill of the western po plain shallow low magnitude earthquakes 8 km and accommodated in correspondence of the fault could be linked to its neogene activity coeval with the northward translation of the retreating adriatic slab

tectonics versus eustatic control on supersequences of the zagros mountains of iran abstract at least 12 km of strata ranging in age from the latest precambrian to the recent are exposed in the zagros mountains of iran this sedimentary cover is characterized by distinct stratal packages separated by major unconformities forming twelve supersequences they are informally named as 1 late precambrian cambrian hakhamanesh supersequence 2 ordovician kourosh supersequence 3 silurian camboojiyeh supersequence 4 devonian darioush supersequence 5 mississippian pennsylvanian khashayar supersequence 6 permian triassic ashk supersequence 7 jurassic farhad supersequence 8 early cretaceous mehrdad supersequence 9 late cretaceous ardavan supersequence 10 paleocene oligocene sassan supersequence 11 oligocene miocene ardeshir supersequence and 12 miocene pleistocene shapour supersequence these supersequences and their correlatives in neighboring areas have been used to infer tectonic events the dominant interpretation has been that local or regional epeirogenic movements were responsible for the formation of these supersequences unconformities are considered as indications that epeirogenic movements associated with tectonic events affected the area the present investigation provides an alternative to the established view of the phanerozoic supersequences of the zagros mountains a good correlation exists between the lithofacies of supersequences in the zagros mountains and the second order eustatic sea level changes deposition of deep water marine shales occurred during periods of eustatic sea level rise platform wide unconformities coincided with eustatic sea level lows in fact supersequences of the zagros mountains are nearly identical to those described from the north american craton and the russian platform suggesting that these stratal packages are global these observations suggest that supersequences of the zagros mountains formed by second order eustatic sea level changes and not by local or regional epeirogenic movements although tectonic events did not produce supersequences of the zagros mountains they influenced regional lithofacies patterns through the formation of intrashelf depressions such as the hormoz salt basin during the precambrian and the dezful embayment and the lorestan basin during the mesozoic tectonic events also affected sedimentation during the tertiary collision of arabia and the central iran microplate through uplift erosion and the formation of the zagros foreland basin the results of this investigation necessitate a re evaluation of the role and the significance of pre tertiary tectonic events commonly used to interpret the geological evolution of the zagros mountains

an investigation into pore structure and petrophysical property in tight sandstones a case of the yanchang formation in the southern ordos basin china abstract the complex and heterogeneous pore structures caused by complex diagenesis and sediment properties such as rock compositions and grain size play a critical role in macroscopic evaluating tight sandstone reservoir performance in order to gain insight into the genetic mechanism of the pore structure and evaluate reservoir quality in tight sandstone reservoirs this study investigated the impacts of diagenesis and sediment properties on pore structures and the relationship between microscopic pore structure parameters and macroscopic petrophysical performance based on the analysis of pore structure features including the morphology pore throat types sizes combinations distribution of combinations and pore connectivity sedimentary and diagenetic features and petrophysical properties samples from tight sandstones of the yanchang formation in southern ordos basin in china were evaluated by integrating scanning electron microscopy sem thin sections mercury injection porosimetry mip nuclear magnetic resonance nmr and gas n2 he porosity and permeability measurements three pore throat combinations were identified which represent the full range distribution of pores mp micropores dominanted pore throat combination iap intragranular pores dominanted pore throat combination and iep intergranular pores dominanted pore throat combinations the type and intensity of diagenesis and sediment properties grain size and ductile component content were found to result in differences in pore throat size and the distribution of pore throat combinations sandstones with coarser grain size and lower concentrations of ductile components have experienced weak compaction thick chlorite rim and minor kaolinite carbonate cementation were found to retain large iep pore space and wide strip shaped throat formed the intergranular pore throat inter t and intergranular pore intragranular pore throat inter intra t the intra intst t intragranular pore group of interstitial cement pores throat sandstones were characterized by intense dissolution and kaolinite cementation which resulted in small iep pore space and large mp iap pore space the intst t group of interstitial cement pores throat sandstones were characterized by intense compaction and kaolinite carbonate cementation compaction and cements destroyed iep pore space and formed mp pore space effectively connected pore space volume of iep and throat radius were positively correlated to porosity and permeability four pore structures are distinguished according to the proportion of effectively connected pore space and the radii of strip shaped throats the macroscopic behaviors and the geological genesis of the four pore structures are investigated

microporosity development in shallow marine sediments from the nankai trough abstract i characterized microporosity by performing low pressure nitrogen adsorption measurements on 13 shallow marine mudstone samples from the nankai trough offshore japan the samples were from two reference sites on the incoming philippine sea plate and one site above the accretionary prism i determined pore size distributions using the barrett joyner hallenda bjh model and merged these with existing mercury injection capillary pressure micp measurements to construct a full distribution covering micro to macropores i found that overall pore sizes decrease with consolidation and that microporosity content pores ca 2 sr si show inconsistent relationships with microporosity development and cannot confirm or deny the role of ash alteration in this process the strongest correlation observed at the three sites was between microporosity volume and clay mineral fraction this suggests that microporosity content is determined mainly by detrital clay abundance and development of clay as an ash alteration product with some contribution from amorphous silica cement precipitated in the zones of anomalous high porosity

fractal analysis of tight shaly sandstones using nuclear magnetic resonance measurements assessing quantitatively the microscopic pore structures of porous rocks including irregularities of pore shapes and pore size distributions is becoming one of the most challenging efforts nuclear magnetic resonance nmr measurements were used to provide insights into the pore geometry pore size and shape and pore connectivity of the chang 7 tight shaly sandstones in situ permeability 0 1 md in ordos basin the incremental transverse relaxation time t2 distributions for the 100 brine saturated samples display unimodal and bimodal behaviors presenting a geometrical arrangement composed of small to large pore size domains the nmr parameters such as bulk volume irreducible bvi capillary and clay bound water free fluid index ffi movable water the value of t2 separating the bvi from ffi the amplitude weighted mean on a logarithmic scale t2gm and the value of t2 that shows the highest frequency on the t2 spectrum t2peak for each sample were determined then the fractal theory was adopted to quantitatively express the complexity and heterogeneity of the sandstones the results show that only minor primary intergranular porosity remains and variable amounts of micropores and secondary intragranular porosity with poor connectivity occur in the chang 7 tight shaly sandstones assuming spherical pores a new model to calculate the fractal dimension of pore structure from the nmr t2 distributions is proposed the fractal dimensions of all the samples are calculated and the accuracy of the proposed model is verified by the regression coefficients the microscopic pore structures are heterogeneous in these tight sandstones according to the high value of fractal dimensions micropores are the primary causes of heterogeneity in tight sandstones and samples with unimodal t2 distribution behaviors and high content of short components have the highest fractal dimension and heterogeneity the calculated fractal dimension is strongly correlated with t2peak and t2gm therefore the fractal model proposed in this study can be used to calculate the fractal dimensions and evaluate the heterogeneities of the porous rocks satisfactorily the fractal model proposed in this study helps to quantitatively assess the pore structures of tight sandstones using nmr measurements

investigation of pore structure and petrophysical property in tight sandstones abstract laboratory measurements include porosity permeability high pressure mercury intrusion hpmi nuclear magnetic resonance nmr measurements and microscopic analysis of thin sections and scanning electron microscope sem were used to gain insight into the nature of the pore throat structure including pore geometry pore size distribution and pore connectivity of bashijiqike tight gas sandstones in keshen 5 keshen 6 keshen 8 keshen 9 and keshen 13 wellblock of kuqa depression the relationships between microscopic pore structure parameters and macroscopic petrophysical behaviors were investigated by regression analysis the results show that various types of pores with wide ranges of pore radius are observed the pore throats are very small commonly rapex controls permeability in tight gas sandstones the nmr pore size distribution is broader than the hpmi pore throat distribution in the nmr analysis only the pore systems connected by the relatively large pore throats should be accounted as movable and some portion of large pores which are not connected by effective large pore throats are not effectively movable the effective movable porosity is calculated by excluding those pores restricted by the tiny pore throats the content of effective movable porosity from nmr measurements shows good correlation relationship with the porosity connected by large pore throats in hpmi analysis three typical types of pore structures are recognized through thin section sem analysis combined with the capillary curve and nmr t2 spectrum and the microscopic and macroscopic characteristics of the three pore structures are investigated the pore structure were comprehensively evaluated and characterized by linking nmr t2 spectrum with hpmi analysis

an intraslab seismic sequence activated by the 2011 tohoku oki earthquake evidence for fluid related embrittlement 1 using quantitative analysis of waveforms we investigate a seismic cluster that occurred at a depth of 67 km in the philippine sea slab 8 months after the 11 march 2011 megathrust tohoku oki earthquake mw 9 0 the sequence started with an m 4 1 normal fault event on 14 november in the deepest part of the cluster and subsequent earthquakes migrated upward by 6 km along a narrow conduit like zone the earthquakes have stress drops of 0 5 40 mpa and groups of earthquakes with coherent waveforms are observed we explain these observations in terms of fluid related embrittlement and the migration of overpressured fluids the low permeability plate interface of the pacific plate may have been broken by the coseismic or postseismic slips of the tohoku oki earthquake with the fluids subsequently being liberated from the underlying crust of the pacific slab and migrating into the philippine sea slab due to the pore pressure gradient the tensional stresses generated by the coseismic slip promoted the efficient upward migration of fluids and also acted to enhance the deviatoric stress around the source area the heightened pore pressures and the resulting reduced effective normal stress lowered the strength of the faults sufficiently to bring the system into the brittle regime under the enhanced deviatoric stress the lag of 8 months may represent the time needed for the unsealing of the plate interface the upward migration of fluids and the increase in pore pressure to become sufficient to overcome the lithostatic pressure

development of symmetrical and asymmetrical fabrics in sheet like igneous bodies the role of magma flow and wall rock displacements in theoretical and natural cases abstract two orientations of fabrics are recognised in vertical dykes a symmetric orientation associated with magma injected into non deforming wall rocks and an asymmetric orientation usually associated with external non coaxial shearing or magma injected into an active fault the notion of two fabric arrangements stems from two planes of symmetry the dyke symmetry plane dsp and the fabric symmetry plane fsp this paper uses conceptual models to simulate all possible orientations of magma flow indicators that might be produced within a vertical dyke emplaced under coeval internal and external stresses the effect of magmatic buoyancy related stresses are portrayed in terms of magma flow velocities mfv and the external non coaxial tectonic related stresses in terms of wall displacement velocities divided by two wmv 2 the tectonic setting is that of a sinistral transcurrent fault using these assumptions five cases are proposed mfv wdv 2 mfv wdv 2 mfv wdv 2 mfv

authigenic quartz microfabrics in cretaceous turbidites evidence for silica transformation processes in sandstones abstract lower cretaceous sandstone turbidites in the scapa field north sea contain a complex variety of authigenic quartz microfabrics early diagenetic microfabrics predate burial calcite cements and compaction they comprise abundant grain rimming microquartz intergranular aggregates of microquartz with authigenic illite smectite and localized isopachous cryptocrystalline quartz and chalcedonite fringes these precipitates contain evidence of precursor opal ct in the form of dissolved recrystallized or pseudomorphed lepispheres and rim cements late diagenetic quartz microfabrics are postcompactional and either replace or overgrow burial calcite cements they display a paragenetic trend from microporous fibrous silica quartzine or chalcedonite to equant syntaxial and mosaic meso uartz cements none of these contain evidence for opal ct precursors and they are likely to have precipitated directly from silica rich pore fluids cathodoluminescence examination of calcite cemented sandstone intervals reveals that siliceous sponge spicules were a major depositional component and were the most likely silica source for opal ct and subsequent quartz cementation dissolution of biogenic silica and formation of opal ct began shortly after deposition with replacement of opal ct by quartz during burial of the scapa member to 1 2 km the early diagenetic silica transformations are identical to those recorded from cenozoic porcelanites and cherts thermodynamic models developed for the diagenesis of biogenic cherts can therefore be applied to the scapa sandstones and qualitatively explain the development of contrasting quartz microfabrics on a bed to bed or smaller scale in contrast direct precipitation of chalce onic quartz during late diagenesis required a resurgence of high supersaturations this is difficult to account for without some import of silica to the sandstones and or cooling of pore fluids precipitation most probably occurred from allochthonous deep basinal brines associated with early stages of hydrocarbon migration

porosity of devonian and mississippian new albany shale across a maturation gradient insights from organic petrology gas adsorption and mercury intrusion the evolution of porosity in shales with increasing maturity was examined in a suite of five new albany shale samples spanning a maturity range from immature vitrinite reflectance ro 0 35 to postmature ro 1 41 devonian to lower mississippian new albany shale samples from the illinois basin used in this study contain marine type ii kerogen having total organic carbon contents from 1 2 to 13 0 wt organic petrology co2 and n2 low pressure adsorption and mercury intrusion capillary pressure techniques were used to quantify pore volumes pore sizes and pore size distributions increasing maturity of the new albany shale is paralleled by many changes in the characteristics of porosity the total porosity of 9 1 vol in immature new albany shale decreases to 1 5 vol in the late mature sample whereas total pore volumes decrease from 0 0365 to 0 0059 cm3 g in the same sequence reversing the trend at even higher maturity the postmature new albany shale exhibits higher porosity and larger total pore volumes compared to the late mature sample with increasing maturity changes in total porosity and total pore volumes are accompanied by changes in pore size distributions and relative proportions of micropores mesopores and macropores porosity related variances are directly related to differences in the amount and character of the organic matter and mineralogical composition but maturity exerts the dominant control upon these characteristics we conclude that organic matter transformation due to hydrocarbon generation and migration is a pivotal cause of the observed porosity differences

stratigraphic evidence for the hirnantian latest ordovician glaciation in the zagros mountains iran abstract high latitude hirnantian diamictites dargaz formation and lower silurian kerogenous black shales sarchahan formation are locally exposed in the zagros mountains the glaciogenic dargaz deposits consist of three progradational retrogradational cycles each potentially controlled by the regional advance and retreat of the hirnantian ice sheet glacial incisions of sandstone packages change laterally from simple planar to high relief

late pleistocene flank collapse of zempoala volcano central mexico and the role of fault reactivation abstract zempoala is an extinct pleistocene 0 7 0 8 ma stratovolcano that together with la corona volcano 0 9 ma forms the southern end of the sierra de las cruces volcanic range central mexico the volcano consists of andesitic and dacitic lava flows and domes as well as pyroclastic and epiclastic sequences and has had a complex history with several flank collapses one of these collapses occurred during the late pleistocene on the s se flank of the volcano and produced the zempoala debris avalanche deposit this collapse could have been triggered by the reactivation of two normal fault systems e w and ne sw although magmatic activity cannot be absolutely excluded the debris avalanche traveled 60 km to the south covers an area of 600 km 2 and has a total volume of 6 km 3 with a calculated heim coefficient h l of 0 03 based on the textural characteristics of the deposit we recognized three zones proximal axial and lateral distal zone the proximal zone consists of debris avalanche blocks that develop a hummocky topography the axial zone corresponds with the main debris avalanche deposit made of large clasts set in a sandy matrix which transformed to a debris flow in the lateral distal portion the deposit is heterolithologic in composition with dacitic and andesitic fragments from the old edifice that decrease in volume as bulking of exotic clasts from the substratum increase several cities cuernavaca jojutla de juarez alpuyeca with associated industrial agricultural and tourism activities have been built on the deposit which pose in evidence the possible impact in case of a new event with such characteristics since the area is still tectonically active

pore structure evaluation of tight reservoirs in the mixed siliciclastic carbonate sediments using fractal analysis of nmr experiments and logs abstract the study on mixed depositional reservoirs is widely attended in recent years however the mixed depositional reservoirs are generally characterized by complex pore structure which is caused by strong heterogeneity complex mineral compositions and varying pore sizes presenting a major challenge to describe the difference in pore structure between different samples to address this challenge the pore structure of mixed depositional reservoirs was evaluated by the fractal dimensions and the influences of various mineral compositions on pore structure were analyzed the fractal dimensions derived from nmr measurements or nmr logging data can be divided into two segments at t 2cutoff values representing different fractal values and characteristics of pore structure for the e 3 2 formation in yingxi field the fractal dimension of movable fluid pores ranges from 2 628 to 2 917 average 2 765 whereas the bound fluid pore systems are not following the fractal theory meanwhile the fractal dimensions show a negative relationship with movable fluid porosity and permeability the effects of various mineral compositions on fractal laws of the pore networks are different fractal dimension increases with the increases of clay mineral contents and the decrease of dolomite content while the effect of calcite content on fractal laws of the pore system is uncertain and quartz from different genetic type represents different effect on fractal dimensions this study is contributed for petroleum exploitation in mixed depositional reservoirs and shows that the fractal dimension can comprehensively indicate the complexity of the pore structure in mixed depositional reservoirs

40ar 39ar age constraints on the timing of tertiary crustal extension and its temporal relation to ore forming and magmatic processes in the eastern rhodope massif bulgaria we quantify the timing of the tertiary crustal extension in the eastern rhodope massif of south bulgaria using 40 r 39 r geochronology to constrain the temporal evolution of exhumation of the metamorphic domes 40 r 39 r analyses of mineral phases with different closure temperatures extracted from metamorphic rocks collected in the footwall and the hanging wall of the extensional system reveal the low temperature cooling history towards shallow crustal levels the results reveal that subsequent to regional amphibolite facies metamorphism i the hanging wall gradually cooled between 500 and 300 c during the paleocene to late eocene 64 34 ma starting at a low rate of 25 c ma and increasing to 50 67 c ma during 38 34 ma ii cooling below 400 300 c of the footwall beneath the extensional detachments occurred in the middle late eocene 39 35 5 ma at an average rate of 35 c ma 40 r 39 r data from the metamorphic basement has been combined with 40 r 39 r data from the volcanic and hydrothermal rocks in the vicinity to the extensional domes to determine the temporal relationships between extensional tectonics ore forming and magmatic processes in the region extension of the high grade basement the ore formation and volcanism overlaps within a 5 ma lasting time interval especially during the cooling and exhumation of the footwall the eastern rhodope massif records an early stage of eocene extension within the aegean extensional province where distinct crustal scale processes occurred simultaneously implying the presence of cause and effect processes and thus represents a key example of coeval continental extension magmatism and hydrothermal activity in the late stage evolution of the orogens

oligo miocene carbonate platform evolution in the northern margin of the asmari intra shelf basin sw iran abstract this study is based on seven outcrops along a regional transect in the central subdivision of the zagros foreland basin this ne sw trending transect extends for 140 km and covers the northern margin of the asmari intra shelf basin in dip direction from proximal to distal results of facies analysis led to the recognition of eight facies associations planktonic wkt nummulitic eu f r alg lr pkt coralgal f r bdt lr lpbf p g epy r pbf p g dol m and trgs along the depositional dip direction they are dominated by large and flat rotalids e g nummulites lepidocyclina and spiroclypeus coral and coralline red algae e g build up features porcellaneous benthic foraminifera e g archaias peneroplis and borelis and fossiliferous lime mud spatial and temporal distribution of these facies associations conform five platform types with different depositional profiles a a nummulites bearing mixed terrigenous carbonate distally steepened ramp lower rupelian b a nummulitidae lepidocyclina bearing carbonate distally steepened ramp upper rupelian lower chattian c a coral bearing flat topped open shelf middle upper chattian d an aquitanian homoclinal ramp and e a very shallow water burdigalian carbonate shelf amongst these platform types the late rupelian early chattian carbonate ramp additionally consists of three successive phases and the middle late chattian flatted top open shelf was developed in two phases the changes in platform type resulted from changes in the carbonate producing biotas sediment redistribution processes and significant impact of relative sea level changes

occurrences of large magnitude earthquakes in the kachchh region gujarat western india tectonic implications abstract moderate to large damaging earthquakes in the peninsular part of the indian plate do not support the long standing belief of the seismic stability of this region the historical record shows that about 15 damaging earthquakes with magnitudes from 5 5 to 8 0 occurred in the indian peninsula most of these events were associated with the old rift systems our analysis of the 2001 bhuj earthquake and its 12 year aftershock sequence indicates a seismic zone bound by two linear trends nnw and nne that intersect an e w trending graben the bouguer gravity values near the epicentre of the bhuj earthquake are relatively low 2 mgal the gravity anomaly maps the distribution of earthquake epicentres and the crustal strain rate patterns indicate that the 2001 bhuj earthquake occurred along a fault within strain hardened mid crustal rocks the collision resistance between the indian plate and the eurasian plate along the himalayas and anticlockwise rotation of the indian plate provide the far field stresses that concentrate within a fault bounded block close to the western margin of the indian plate and is periodically released during earthquakes such as the 2001 m w 7 7 bhuj earthquake we propose that the moderate to large magnitude earthquakes in the deeper crust in this area occur along faults associated with old rift systems that are reactivated in a strain hardened environment

early svecofennian stratigraphy of southern and central norrland sweden and the possible existence of an archaean basement west of the svecokarelides abstract the stratigraphy of supracrustal sequences of seven different areas in southern and central norrland sweden are compared all the sequences belong to the svecofennian part of the early proterozoic svecokarelian fold belt it is concluded that quartzites and meta arkoses are usually found at high stratigraphic levels they are sparse or absent in the north but are more abundant in southern norrland this may suggest that a granitic archaean or early proterozoic basement was exposed to erosion somewhere southwest of the regions under consideration future research should aim at clarifying the age and extent of this basement and the provenance of the various metasedimentary rocks

seafloor nuclear magnetic resonance assay of methane hydrate in sediment and rock 1 proton nuclear magnetic resonance nmr of liquid water can be used to indirectly detect and assay methane hydrate in opaque earth materials it is also potentially useful for quantifying pore size control of hydrate formation and for estimating in situ hydraulic permeability of hydrate affected earth formations the method is quantitative nondestructive and volumetrically averaging over a spatially selected region in the first controlled validation of this measurement we have used nmr to measure changes in the liquid water content of sediment and rock resulting from methane hydrate formation hydrates were artificially formed at the seafloor by introducing methane into tubes containing sediments or rock saturated with seawater after several weeks the samples were visited by a remotely operated vehicle on which nmr equipment was mounted reduction of the nmr signal indicated hydrate had formed in the sample within a well defined measurement volume hydrate content determined by nmr quantitatively predicted the volume of methane gas evolved during subsequent dissociation

northeastern extension of the new madrid north fault new madrid seismic zone central united states abstract analysis of electric and geologic logs of 517 shallow wells 91 m 300 ft deep in southeastern missouri has revealed a subsurface structural high herein called the charleston uplift trending n46 e from near new madrid missouri to cairo illinois that juxtaposes paleocene flour island formation against eocene claiborne group the charleston uplift is 30 km 19 miles long 7 2 km 4 5 miles wide and has a relief of 36 m 120 ft at the unconformity surface between the paleogene and quaternary sections two seismic reflection soundings one conducted north of the uplift and the second conducted within the uplift indicate 60 m 198 ft of apparent structural relief on the underlying top of the paleozoic 47 m 155 ft on the top of the late cretaceous and 19 m 63 ft on a tertiary reflector the charleston uplift is interpreted to be the northeastern extension of the new madrid north fault of the new madrid seismic zone and locally the western margin fault zone of the reelfoot rift although no surface faulting has been mapped along the charleston uplift the uplift appears to have influenced the holocene course of the mississippi river and displaced the paleocene quaternary unconformity thus indicating quaternary displacement of the charleston uplift across southeastern missouri which may continue beneath the ohio river valley into adjacent illinois and kentucky thus the charleston uplift strongly suggests quaternary structural continuity between the reelfoot rift and rough creek graben of kentucky although currently seismically quiet the 12 february 2012 m 3 9 earthquake and probably the 31 october 1895 m 6 6 charleston earthquake occurred on this structure thereby illustrating the seismic potential of this structure and extending the new madrid north fault system at least 30 km 19 miles

characterization of gas shale pore systems by porosimetry pycnometry surface area and field emission scanning electron microscopy transmission electron microscopy image analyses examples from the barnett woodford haynesville marcellus and doig units the nanometer scaled pore systems of gas shale reservoirs were investigated from the barnett marcellus woodford and haynesville gas shales in the united states and the doig formation of northeastern british columbia canada the purpose of this article is to provide awareness of the nature and variability in pore structures within gas shales and not to provide a representative evaluation on the previously mentioned north american reservoirs to understand the pore system of these rocks the total porosity pore size distribution surface area organic geochemistry mineralogy and image analyses by electron microscopy were performed total porosity from helium pycnometry ranges between 2 5 and 6 6 total organic carbon content ranges between 0 7 and 6 8 wt and vitrinite reflectance measured between 1 45 and 2 37 the gas shales in the united states are clay and quartz rich with the doig formation samples being quartz and carbonate rich and clay poor higher porosity samples have higher values because of a greater abundance of mesopores compared with lower porosity samples with decreasing total porosity micropore volumes relatively increase whereas the sum of mesopores and macropore volumes decrease focused ion beam milling field emission scanning electron microscopy and transmission electron microscopy provide high resolution 5 nm images of pore distribution and geometries image analysis provides a visual appreciation of pore systems in gas shale reservoirs but is not a statistically valid method to evaluate gas shale reservoirs macropores and mesopores are observed as either intergranular porosity or are confined to kerogen rich aggregates and show no preferred orientation or align parallel with the laminae of the shale networks of mesopores are observed to connect with the larger macropores within the kerogen rich aggregates

origin of a zone of anomalously high porosity in the subduction inputs to nankai trough abstract one poorly understood feature of the subduction inputs to the nankai trough subduction zone sw japan is a stratigraphic interval with an anomalously high porosity zone hpz which is up to 240 m thick and located within the clay and volcanic ash rich shikoku basin facies to investigate the origin of their peculiar physical properties we integrated logging while drilling lwd data shipboard density measurements and visual descriptions of core samples recovered from four drill sites of the ocean drilling program and integrated ocean drilling program we combined those observations with scanning electron microscopy sem and laboratory consolidation tests on both hpz samples and artificial mixtures of ash glass shards smectite and vesicular pumice smectite lwd data indicate that the hpz mudstones have a large proportion of dispersed volcanic ash 20 30 the consolidation tests show that the rate of porosity loss with increasing effective stress consolidation behavior is consistent among hpz specimens and matches artificial mixtures containing up to 60 volcanic material however absolute values of porosity remain higher for hpz samples compared to artificial mixtures so processes in addition to the mechanical effects of volcanic clasts must be contributing we suggest that hydration and partial dissolution turns clusters of volcanic glass into aggregates with distinct microfabric sem images confirm the presence of strengthened grain to grain contacts which probably inhibit the collapse of the intra aggregate pore space the aggregates behave like grains so that cohesive strength of the bulk sediment and rate of porosity loss remain nearly unchanged during burial the two step diagenetic process of dissolution and precipitation depends critically on a threshold abundance of fine grained dispersed volcanic ash pumice older units in the shikoku basin with only traces of dispersed ash show no such effects hpzs should be expected in other subduction zones with similar compositional and diagenetic prerequisites

the estimation of diffuse strains in the toe of the western nankai accretionary prism a kinematic solution arcward changes in the vertical spacing of seismically defined stratigraphic reflectors and sediment porosities determined from drill cores and seismic interval velocities suggest a compact kinematic solution for estimating diffuse deformation within accretionary prism toes the method involves the solution of the lagrangian form of the conservation of mass equation for the two dimensional finite deformation gradient field within discrete deforming domains we apply this technique to the unfaulted protothrust zone ptz along a western transect across the nankai accretionary prism in the vicinity of deep sea drilling project sites 582 and 583 the results yield horizontal shortening estimates of about 1 7 km or about 20 this shortening appears to be accommodated through different strain responses depending on the consolidation state of the sediments at the time of accretion shallow sediments respond to horizontal shortening dominantly by expelling pore fluids producing volume strains up to 30 while deeper sediments accommodate horizontal shortening dominantly through vertical extension reaching 70 in the footwall of the frontal thrust horizontal shear strains within the ptz are not well resolved by this solution due to uncertainties in the porosity distribution but they generally appear to be quite small

unraveling 1 5 ga of brittle deformation history in the laxemar simpevarp area southeast sweden a contribution to the swedish site investigation study for the disposal of highly radioactive nuclear waste 1 the swedish nuclear fuel and waste management company skb is undertaking site investigation at two locations in sweden forsmark and laxemar simpevarp with the aim of identifying a suitable area for the construction of a deep repository for the disposal of highly radioactive nuclear waste fault slip data from outcrops and oriented drill cores were used to compute paleostress states and to unravel the sites brittle deformation history results from the laxemar simpevarp area show that its suggested brittle history results from multiple reactivation of fracture and fault sets caused by the many orogenic episodes that affected the region during at least 1 5 ga of geological evolution in the brittle deformational regime two compressional approximately nw nnw se sse and nne ssw oriented shortening events generated sets of conjugate steep strike slip fractures these sets formed during the late stages of the svecokarelian and possibly also of the gothian orogeny soon after the region entered the brittle deformation domain the mesoproterozoic sveconorwegian orogeny generated fractures and faults that are assigned to a third set of conjugate strike slip faults which constrain an approximately e w 1 the caledonian shortening oriented approximately nw se to e w reactivated the latter but also formed a new similarly oriented set of subvertical strike slip fractures permian transtension was oriented nw sw and caused a prominent set of moderately dipping nw se trending normal faults in the precambrian basement of the study area two other approximately nw sw and nw se oriented shortening events are recorded in ordovician limestones and can be tentatively linked to the far field effects of the laramide and alpine orogenies

uranium content and distribution in whole coal samples sydney coalfield upper carboniferous nova scotia canada abstract uranium poor bituminous coal channel samples mean and standard deviation 0 51 0 99 ppm from the sydney coalfield in nova scotia show top and bottom enrichment trends as are known from german british and american coals of upper carboniferous age breger and schopf 1955 francis 1961 gluskoter et al 1977 the trends appear to be related to sedimentary processes rather than to secondary geochemical enrichment effects on the coal

the quantification and application of handheld energy dispersive x ray fluorescence ed xrf in mudrock chemostratigraphy and geochemistry abstract traditionally analytical techniques such as wavelength dispersive x ray fluorescence wd xrf inductively coupled plasma icp and mass spectrometry icp ms instrumental neutron activation analysis inaa or stationary bench top energy dispersive x ray fluorescence ed xrf have been used to generate quantitative geochemical results however a more efficient means of data collection using portable ed xrf instrumentation now allows the investigator to acquire rapid non destructive quantitative measurements on drill core and clean flat rock surfaces in addition to pressed powder pellets typically used in wd xrf analysis similar to traditional xrf methods quantification using the handheld ed xrf requires a matrix specific calibration unfortunately very few internationally accepted mudrock or shale reference materials exist and their elemental ranges provide inadequate coverage for the geochemical diversity of mudrocks in order to return reliable calibrated results a unique set of reference materials has been developed that incorporates a wide range of mudrock elemental compositions the current method provides elemental calibrations for major elements heavier than sodium and the following trace elements ba v cr ni cu zn rb sr y zr nb mo th and u a comparison of handheld energy dispersive and wavelength dispersive x ray fluorescence ed xrf and wd xrf results from pressed powder pellets of mississippian age barnett shale of north central texas usa is presented in order to evaluate the reliability of the reference calibration and the quantification of unknown samples using two different instrument platforms it will be demonstrated that calibrated results from the handheld ed xrf effectively define chemostratigraphic changes in real time as a consequence quantified results can be used immediately to assess changes in bulk mineralogy paleo redox conditions and to link down core geochemical changes to stratigraphic sedimentological and paleoenvironmental observations

insights in the pore structure fluid mobility and oiliness in oil shales of paleogene funing formation in subei basin china abstract pore structure is an important factor influencing reservoir properties of oil shales routine core analysis thin section scanning electron microscope sem mercury injection capillary pressure micp tests nuclear magnetic resonance nmr and computed tomography ct were used to provide insights into the pore throat distribution in oil shales of member 2 of paleogene funing formation e1f2 in subei basin china with the special aim to unravel the effect of pore structure on fluid mobility and oiliness the relationships between nmr parameters petrophysical property and capillary parameters are investigated the results show that rock composition in the oil shales consist of quartz feldspar carbonate particles clay minerals and organic matters pore systems consist of large scale interparticle pores intragranular dissolution pores and small scale micropores within clay minerals and the organic matter pores four types of pore structure type type type and type are divided according to the patterns of capillary curves capillary parameters nmr t2 transverse relaxation time spectrum and bvi bulk volume of immovable fluid values from type to type pore structure the maximum mercury saturation shgmax and mercury extrusion efficiency are decreasing and the shgmax are less than 50 averagely indicating the oil shales are characterized by very poor pore connectivity the t2 spectrum changes from bi modal behavior to uni modal and the right peaks become lower or even disappearing from type to type pore structure fluid mobility is not primarily controlled by pore size but dependent on the content of short t2 components pore structure controlled fluid mobility and determined the microscopic oiliness and macroscopic oil bearing property or hydrocarbon productivity the comprehensive study above gains insights into the microscopic pore structure and their controls on fluid mobility and oiliness in shale oil reservoirs and this may have implications for resource potential evaluation and effective exploitation of oil shales

spectrum of pore types and networks in the deep cambrian to lower ordovician dolostones in tarim basin china abstract the complex tectonic activities and multi stage diagenetic modifications lead to the formation of a heterogeneous pore network spectrum ranging from macropores centimeter size to nanometer size pores three types of matrix dolomites dolomicrite microbial dolomite and crystalline dolomites and two types of dolomite cements saddle dolomite or crystalline dolomites are recognized in the cambrian to lower ordovician dolostones the pore systems include open vugs enlarged dissolution pores fabric dissolution pores intercrystal dissolution pores micro fractures as well as intracrystal pores forming dual or multiple pore networks the nmr t2 spectra are mainly characterized by bi modal distributions and mostly right skewed the very low t2 components 1000 ms represent the vuggy pores with pore sizes spanning from hundreds of m to thousands of microns the transition zones 100 ms

the depositional evolution of the svecofennian supracrustal sequence in finland and sweden abstract on the basis of six new zircon ages from metavolcanic rocks together with other isotopic geophysical and geological data the chronological and tectono stratigraphic evolution of the early proterozoic svecofennian supracrustal rocks in finland and sweden are discussed these data suggest that a nw se displacement from the bothnian bay to lake ladoga and a sinking of the southwestern block was initiated 1950 2000 ma ago accumulation of pelitic sediments and greywackes on the subsiding archaean basement continued until about 1860 ma in south central and northern sweden shallow submarine and subaerial volcanics were extruded 1880 1890 ma ago the thick sedimentary piles and volcanic rocks were subsequently intruded by plutonic rocks forming large batholiths 1860 1890 ma ago

a method for estimating microporosity of fine grained sediments and sedimentary rocks via scanning electron microscope image analysis this study presents a method of two dimensional scanning electron microscope image analysis that directly quantifies microporosity abundance in clay rich fine grained sediments the method is novel in that it is specifically designed to circumvent the challenge to porosity quantification posed by mineral surface charging and topographical artifacts created during ar ion cross section polishing it utilizes the finding that differences in circularity values can be used to distinguish micropores from blemishes in a thresholded image this method is powerful because it is fast and provides a direct microporosity estimation technique to augment or replace experimental data the pore size range to which the method is applicable is clear and can be selected depending on the application of the analysis when used appropriately the method can be implemented on microporous sediments and sedimentary rock in general the method is developed using marine muds of pliocene and miocene ages from the nankai margin burial depths from approximately 200 to 1100 m the close match between imaging derived microporosity and bulk n2 microporosity measurements shows that porosity in these young and relatively shallowly buried sediments is dominated by pores of sizes that can be imaged by scanning electron microscopy in kumano forearc basin sediments of the nankai trough results of this method show a significant increase in microporosity with burial depth probably due to microporosity preservation during compaction and possibly early volcanic ash diagenesis

deep burial microporosity in upper jurassic haynesville oolitic grainstones east texas abstract secondary micromoldic porosity generated during deep burial diagenesis occurs pervasively in upper jurassic haynesville oolitic grainstones in east texas and constitutes the major pore type in these gas reservoirs petrographic and geochemical relationships establish that development of this microporosity postdates emplacement of bitumen and most pressure solution fabrics in the reservoir grainstones microporosity development is strictly controlled by depositional texture and is restricted to either active shoal complex grainstones or thicker grainstones shed downramp by storm processes haynesville diagenetic and porosity relationships are consistent along the entire length of the east flank of the east texas basin a distance greater than 100 km identical relationships have also been observed along the west flank of this basin haynesville micromoldic porosity development is confined principally to ooids but also occurs in normally stable calcitic skeletal grains like oysters resultant micropores are a few microns across or less complete dissolution of ooids to form oomoldic macroporosity is not observed in haynesville limestones nearly all primary porosity in the haynesville is now occluded by carbonate cement confirmation of a late deep burial origin for haynesville secondary microporosity is based on physical relationships observed in numerous cores regional petrography and geochemical data collectively these observations demonstrate that haynesville sediments were never locally or regionally exposed to freshwater but have undergone progressive burial diagenesis punctuated by a major late dissolution event which created the microporosity key observations which support haynesville deep burial microporosity development include 1 petrographic relationships which demonstrate microporosity developed after emplacement of bitumen 2 lack of subaerial exposure features in core both atop shoal complexes and at the contact between the haynesville and bossier sequences 3 absence of freshwater porosity fabrics 4 lack of precompactional freshwater cements 6 pervasive pressure solution in the microporous grainstones including extensive grain interpenetration 6 preservation of abundant microporosity directly adjacent to pressure solution seams in porous grainstones 7 development of identical microporosities in mineralogically stable calcitic grains which rarely leach in freshwater 8 microporosity development which postdates formation and cementation of fractures in the reservoir facies and 9 calcite cements occluding primary porosity whose geochemical attributes are inconsistent with precipitation from freshwater but are consistent with a burial origin this regional core based case study reveals that the contact between the haynesville and overlying bossier shale is a marine drowning unconformity physical petrographic and geochemical evidence for regional subaerial exposure at the end of haynesville deposition due to a eustatic fall in sea level is not present questioning the validity of interpreting local or global sea level history from seismic and well log data in the absence of critical core control

importance of volcanic glass alteration to sediment stabilization offshore japan a minor amount ca 1 wt of amorphous silica cement sourced from volcanic glass inhibits consolidation of hemipelagic sediment approaching the nankai trough subduction zone throughout the shikoku basin the distribution and nature of the cement were examined via secondary and backscattered electron imaging the amorphous silica occurs as altered material in contact with volcanic glass coating grains including grain contacts and filling pores based on chemical and petrographic evidence the cement is probably sourced from volcanic glass this is in contrast to a previous suggestion that this silica cement is sourced dominantly from biogenic silica amorphous silica sourced from disseminated volcanic glass shards has the ability to form a thin coating on clay dominated sediment throughout the shikoku basin measured amorphous silica content in hemipelagic sediments suggests that the cementing process is active throughout the shikoku basin at sites separated by 500 km the cementation process may occur in other locations where sediment containing hydrated disseminated volcanic glass is buried sufficiently for heat to facilitate alteration i e central america cascadia and the gulf of alaska

an improved technique for computing permeability from nmr measurements in mudstones 1 we develop a technique for extending nuclear magnetic resonance nmr permeability estimation to clay rich sediments our technique builds on the schlumberger doll research sdr equation by using porosity grain size specific surface and magnetic susceptibility data to yield more accurate permeability estimation in mudstones with large pore surface areas and complex mineralogies based on measurements of natural sediments as well as resedimented laboratory mixtures of silica bentonite and kaolinite powders we find that our method predicts permeability values that match measured values over four orders of magnitude and among lithologies that vary widely in grain size mineralogy and surface area our results show that the relationship between nmr data and permeability is a function of mineralogy and grain geometry and that permeability predictions in clay rich sediments can be improved with insights regarding the nature of the pore system made by the kozeny theory this technique extends the utility of nmr measurements beyond typical reservoir quality rocks to a wide range of lithologies

surface area control of organic carbon accumulation in continental shelf sediments the relationship between organic carbon oc and grain size found in most continental shelf sediments is here reinterpreted in terms of the surface area of the sediments cores from many north american shelf environments show downcore decreases in oc to similar refractory background concentrations if expressed relative to the surface area of the sediments this consistent concentration is 0 86 mg oc m 2 which is equivalent in concentration to a monolayer of organic matter coating all mineral surfaces a more global collection of sediment water interface samples show that this relationship is even more extensive with exceptions occurring in areas of very high riverine sediment input organic pollution or low oxygen water columns density separations indicate that organic matter is largely adsorbed to mineral grains the microtopography of surfaces was examined with n2 sorption and most surface area was found to be inside pores of 10 nm width these data lead to a hypothesis that organic matter is protected by its location inside pores too small to allow functioning of the hydrolytic enzymes necessary for organic matter decay such protection would likely work in concert with other protection mechanisms such as humification this consistent surface area correlation with oc concentration may explain control of spatial and temporal variations in oc burial rates by sedimentation rates the pore protection hypothesis provides a causal mechanism for this observed control

occurrence of zeolites in sedimentary rocks an overview zeolites have been known since the mid 1750s but prior to the early 1950s most reported occurrences of zeolites were in fracture fillings and amygdules in igneous rocks particularly basaltic lava flows indeed most of the large attractive zeolite specimens in museum collections were obtained from lavas in recent years zeolites have been recognized as important rock forming constituents in low grade metamorphic rocks and in a variety of sedimentary rocks most zeolites in sedimentary rocks are finely crystalline that is they occur as microscopic or submicroscopic crystals and they are therefore of little appeal to mineral collectors however deposits of this type are voluminous and have great geologic significance and economic potential zeolites are among the most common authigenic silicate minerals that occur in sedimentary rocks and they form in sedimentary rocks of diverse lithology age and depositional environment about twenty species of zeolites have been reported from sedimentary rocks but only eight zeolites commonly make up the major part of zeolitic rocks these are analcime chabazite clinoptilolite erionite heulandite laumontite mordenite and phillipsite this chapter will consider chiefly the zeolites in sedimentary rocks with emphasis on volcaniclastic deposits which contain the largest concentrations of zeolites the occurrence of zeolites in lava flows is mentioned only briefly journal articles on the occurrence and origin of natural zeolites have multiplied at a rapid rate since the mineralogy and geology of natural zeolites was first published in 1977 as volume 4 of the mineralogical society of america s reviews in mineralogy the present review will highlight areas of more recent research on the occurrence and origin of zeolites and some of the coexisting minerals a wide variety of zeolites has been identified in sedimentary deposits with the most common being clinoptilolite analcime heulandite laumontite and phillipsite less abundant zeolites include chabazite erionite mordenite natrolite

some geochemical aspects of sedimentary rocks in proximity of coals sydney coalfield upper carboniferous cape breton island nova scotia canada abstract channel samples of roof and seat rocks lutites siltstone of 10 successional coals in addition to red mudstone and calcareous siltstones have been collected from the sydney coalfield nova scotia the channel samples are confined to within 150 cm above the top of coals and to within 20 cm below the bottom of coals whole rock and trace elemental analyses are reported wt of oxides of si al total fe ca mg na k t1 mn and ppm s for cu ni pb zn cr co ga v as u and th respectively th u ratios organic carbon and carbonate carbon of selected roof rock samples are also reported the comparatively small stratugraphic mean variations of na 2 k 2 o and na 2 o al 2 o 3 are open to interpretation but may indicate either a common sedimentary source or a similar diagenetic history during basin development assumed is that the oxide ratios originated from detrital feldspars and clays the probability model for uranium is pearson s type vii curve the relationship between uranium thorium and assumed organic calcite in selected calcareous siltstones is examined stratigraphic variation of the geochemistry is assumed to be cycle controlled excepting probably as v and cu which under the stated conditions are amenable to mathematical modeling of sedimentary cycles