melting and mingling of phonolitic pumice deposits with intruding dykes an example from the otago peninsula new zealand abstract a mound of bedded phonolitic pumice lapilli ash was deposited on the marine shelf modern otago peninsula new zealand during a shallow subaqueous eruption in the miocene basaltic dykes subsequently intruded the unconsolidated pumice deposit and formed an unusual peperite dyke sediment interaction began with weak steam driven mixing accompanied by fluidisation at the contact zone that produced a metres broad zone in which bulbous tongues up to 3 m of the dykes extended into and locally engulfed host sediment irregular sinuous contacts of dykes with the pumice are marked by black glass that formed by partial melting shearing and remoulding of the glassy pumice such melting and remoulding of host sediment is not a typical peperite feature temperature evolution volume of water vapour load pressure and time as well as initial contact temperature control the welding and remoulding of pumice and glass shards a slow cooling rate of the dykes at the dyke contacts is inferred from remoulding textures and is attributed to continuous feeding of the dyke seawater may have promoted softening and remoulding of the pumice because na and k if partially taken into the glass structure can decrease the melting point of glass dramatically and reduce the viscosity of the shards remoulding may have occurred by continuous conversion of seawater in the peperite to steam which is inferred to have enhanced transfer of na and k from seawater to pumice glass

rhyolitic globular peperites from the aznalcollar mining district iberian pyrite belt spain physical and chemical controls abstract globular peperites are exposed along the aznalcollar mining district iberian pyrite belt ipb spain these rocks originated by mingling of a low viscosity rhyolitic sill with unlithified wet sediments highly amygdaloidal up to 80 vol millimeters to centimeters across rhyolite globules extend from the upper contact of the sill for several centimeters into fine grained volcaniclastic host rocks the sill is very similar to other rhyolites in the ipb in terms of petrography and chemistry it is aphyric to very sparsely quartz phyric with small quartz phenocrysts vesicularity has been measured in the sill as vesicle area fraction determined by point counting over a rectangular grid and number density per unit area determined by counting every vesicle within the grid area amygdale distribution measured within the sill indicates a process by which vesicles migrated vertically from the lower portions of the sill to the roof zone we suggest that this migration process caused local density changes large enough to allow the rhyolitic magma to become buoyant enough to move through the overlying sediments producing globular peperites globular structures are preserved when rhyolite globules entered the wet sediment

magma sediment mingling in an ordovician rift basin the plouezec plourivo half graben armorican massif france the plouezec plourivo basin ppb armorican massif is an ordovician half graben filled with red bed deposits lying on a cadomian metamorphic basement peperites crop out along its northeast coastal sector in connection with diverse magmatic and hydrothermal products combining field structural observations and geochemical analyses of magmatic rocks leads us to propose a model of emplacement of peperites in an extensional setting the ppb peperites result from mingling between magma and initially wet sediment the main corresponding facies consist of rounded magmatic bodies corrugated lava sediment contacts and a remarkable thin sheet of fluidized sediment extending over about 100 m parallel and c 10 cm above the base of a porphyritic lava flow a few ppb peperites formed under a dominant brittle regime are autoclastic breccias at the base of a lava flow and polymict breccias including both fluidal and blocky volcanic clasts sediment fluidization formation of vapor films magma sediment density contrasts and non explosive fragmentation are the main mechanisms invoked to generate the ppb peperites the c 100 m extended sediment derived sheet lying near the base of a lava flow likely formed by diapiric rise of fluidized sediment through molten lava we show that silicic contamination accompanied these peperitic processes

coalbed methane completions a world view abstract cbm wells are cheap because they are usually shallow deeper wells tend to have lower coal permeability and productivity low permeability is the weak point achilles heel for cbm ventures and success will entail finding regions of enhanced permeability utilizing horizontal wells with the option of fracturing these wells and possibly in creating permeability by new paradigm methods such as shear stimulation and branch fracturing this paper discusses the role of permeability in choosing cbm completions as well as examples of those completions from around the world the guidelines offered are new and practical including perm bands and a decision tree and should benefit any cbm completion strategy

large scale rhyolite peperites jurassic southern chile development of a jurassic volcano tectonic rift basin in the southern andes created a setting in which thick rhyolitic volcaniclastic sequences accumulated in submarine environments and were penetrated by hypabyssal intrusions during or shortly after deposition in the ultima esperanza district of southern chile extensive masses of peperite were produced when rhyolite magma underwent quenching disruption and commingling with wet unconsolidated sediments during intrusion at shallow levels beneath the sea floor the peperite forms discordant intrusive masses with volumes of up to several cubic kilometers in which large widely spaced coherent rhyolite feeder pods are surrounded by and grade into closely packed and dispersed peperite closely packed peperite consists of tightly fitting clasts separated by sediment filled fractures in dispersed peperite the sediment forms a matrix surrounding large masses of fractured rhyolite and smaller more widely separated rhyolite clasts evidence of in situ quench fragmentation is well preserved on both outcrop and thin section scales thin sections show that clast margins and in some cases entire small clasts underwent cooling contraction granulation releasing shards of quenched rhyolite and fragments of phenocrysts into the adjacent sediment interaction between magma and wet sediment was non explosive and involved fluidization of the host sediments creating space for the intruding magma and causing pervasive injection of highly mobile sediment along thermal contraction cracks in quench fragmented rhyolite the ability of the magma to undergo complex intermixing with large volumes of sediment with widespread preservation of in situ fragmentation textures is interpreted to reflect a relatively low magma viscosity presumably caused by retention of volatiles in the magma at the ambient pressures involved beds of redeposited peperite within the rift basin fill indicate that some of the intrusive peperite masses reached the sea floor undergoing slumping and mass flow the peperites were thus an important local source of coarse grained debris during the evolution of the basin

stress relief coalbed methane drainage by surface vertical wells in china abstract this paper summarizes the status of engineering practice technology and research related to stress relief coalbed methane cbm drainage using surface wells in china during the past 10 years comments are provided on the theory and technical progress of this method in high gas mining areas such as the huainan huaibei and tiefa mining areas characterized by heavily sheared coals with relatively low permeability stress relief cbm surface well drainage has been successfully implemented and has broad acceptance as a cbm exploitation technology the fundamental theories underpinning stress relief cbm surface well drainage were established in china and include elements relating to 1 rock layer deformation theory vertical zoning and horizontal partitioning and the change in the stress condition in mining stopes 2 a theory regarding an abscission circle in the development of mining horizontal abscission fracture and vertical broken fracture in overlaying rocks and 3 the theory of stress relief inducing permeability increase in protected coal seams during mining and the gas migration accumulation theory of stress relief cbm surface well drainage three kinds of technical drainage modes are described protected seam surface well drainage in areas influenced by mining represented mainly in the huainan mining area gob surface well drainage most prominently in the tiefa mining areas and the multipurpose surface well drainage used in the huaibei mining areas serial well allocation in which wells are used for different purposes as extraction and mining proceeds and well bore configurations and designs suitable for this purpose are described the development and utilization of cbm is significant to energy saving emission reduction and to ensure safety in coal production

are segmented fracture zones weak analytical and numerical models constrain anomalous bathymetry at the clarion and murray fracture zones abstract between 150 w and 135 w the clarion fracture zone fz coalesces from six discrete fz traces to a single fz over a period of 30 million years coinciding with a change in plate motion that placed the associated transform fault tf in compression between 160 and 157 the murray fz is also comprised of several closely spaced

eocene propagating rifts in the southwest pacific and their conjugate features on the nazca plate we have mapped a 1200 km long nw se trending lineament in seasat and geosat radar altimeter data crossing a remote portion of the southwest pacific basin this lineament runs obliquely both to the fracture zones fzs and magnetic lineations between the austral and agassiz fzs by examining shipboard magnetics gravity and bathymetric profiles in this region and in the conjugate regions of the nazca plate we identify this feature as the site of a series of small ridge jumps highly asymmetrical spreading and small propagating rifts during the mid to late eocene chron c21 to chron c13 between the austral and agassiz fzs there is roughly 250 to 350 km of missing pacific plate crust which must have been transferred to the nazca plate by the propagating rifts and small ridge jumps on the nazca plate the conjugate area to the gravity lineament is now being subducted beneath the chile trench north of the challenger fz this area corresponds to a region of undecipherable magnetic anomalies south of the challenger fz there is evidence for a small 50 km ridge jump offshore of the chile trench this small ridge jump by itself is not sufficient to account for the missing crust on the pacific plate and we conclude that there must have been repeated small ridge jumps at the same site one consequence of these ridge jumps is that crust on the nazca plate entering the trench is not as old as would be predicted by simply mirror imaging the anomaly pattern on the pacific plate

flat subduction dynamics and deformation of the south american plate insights from analog modeling received 14 june 2007 revised 13 january 2008 accepted 12 march 2008 published 21 june 2008 1 we present lithospheric scale analog models investigating how the absolute plates motion and subduction of buoyant oceanic plateaus can affect both the kinematics and the geometry of subduction possibly resulting in the appearance of flat slab segments and how it changes the overriding plate tectonic regime experiments suggest that flat subductions only occur if a large amount of a buoyant slab segment is forced into subduction by kinematic boundary conditions part of the buoyant plateau being incorporated in the steep part of the slab to balance the negative buoyancy of the dense oceanic slab slab flattening is a long term process 10 ma which requires the subduction of hundreds of kilometers of buoyant plateau the overriding plate shortening rate increases if the oceanic plateau is large enough to decrease the slab pull effect slab flattening increases the interplate friction force and results in migration of the shortening zone within the interior of the overriding plate the increase of the overriding plate topography close to the trench results from 1 the buoyancy of the plate subducting at trench and 2 the overriding plate shortening experiments are compared to the south american active margin where two major horizontal slab segments had formed since the pliocene along the south american subduction zone flat slab segments below peru and central chile nw argentina appeared at 7 ma following the beginning of buoyant slab segments subduction in northern ecuador and northern chile the process of slab flattening resulting from the carnegie and iquique ridges subductions respectively seems to be active but not completed the formation of flat slab segments below south america from the pliocene may explain the deceleration of the nazca plate trenchward velocity citation espurt n f funiciello j martinod b guillaume v regard c faccenna and s brusset 2008 flat subduction dynamics and deformation of the south american plate insights

blocky versus fluidal peperite textures developed in volcanic conduits vents and crater lakes of phreatomagmatic volcanoes in mio pliocene volcanic fields of western hungary abstract volcanic fields in the pannonian basin western hungary comprise several mio pliocene volcaniclastic successions that are penetrated by numerous mafic intrusions peperite formed where intrusive and extrusive basaltic magma mingled with tuff lapilli tuff and non volcanic siliciclastic sediments within vent zones peperite is more common in the pannonian basin than generally realised and may be also important in other settings where sediment sequences accumulate during active volcanism hajagos hegy an erosional remnant of a maar volcano was subsequently occupied by a lava lake that interacted with unconsolidated sediments in the maar basin and formed both blocky and globular peperite similar peperite developed in kissomlyo a small tuff ring remnant where dykes invaded lake sediments that formed within a tuff ring lava foot peperite from both hajagos hegy and kissomlyo were formed when small lava flows travelled over wet sediments in craters of phreatomagmatic volcanoes at sag hegy a large phreatomagmatic volcanic complex peperite formed along the margin of a coherent intrusion all peperite in this study could be described as globular or blocky peperite globular and blocky types in the studied fields occur together regardless of the host sediment

endogenous growth of a miocene submarine dacite cryptodome rebun island hokkaido japan momo iwa rebun island hokkaido japan is a dacite cryptodome 200 300 m across and 190 m high the dome is inferred to have intruded wet poorly consolidated sediment in a shallow marine environment the internal structure of the dome is concentric with a massive core banded rim and narrow brecciated border all of which are composed of compositionally uniform feldspar phyric dacite boundaries between each of the zones are distinct but gradational the massive core consists of homogeneous coherent unfractured dacite and is characterized by radial columnar joints 60 200 cm across the banded rim encircles the massive core and is 40 m wide it is characterized by large scale flow banding parallel to the dome surface the flow banding comprises alternating partly crystalline and more glassy bands 80 150 cm thick the outermost brecciated border is up to 80 cm thick and consists of in situ breccia and blocky peperite the in situ breccia comprises polyhedral dacite clasts 5 20 cm across and a cogenetic granular matrix the blocky peperite consists of polyhedral dacite clasts 0 5 2 cm across separated by the host sediment mudstone the internal structures of the dome suggest endogenous growth involving a continuous magma supply during a single intrusive phase and simple expansion from the interior although much larger the internal structures of momo iwa closely resemble those of lobes in subaqueous felsic lobe hyaloclastite lavas

crustal age between the clipperton and clarion fracture zones magnetic anomalies of 52 80 ma age have been mapped in the equatorial pacific in a region where they were previously unrecognized these anomalies now at 7 n are best modeled with crustal rocks of negative inclination apparently because the crust was formed at a spreading ridge that was south of the magnetic equator in late cretaceous early tertiary time magnetic anomalies recorded along a 5900 km trackline that follows a flowline of crustal generation show one long period from 12 to 31 ma of apparent constant half spreading rate over the 0 to 80 ma represented

intra vent peperites related to the phreatomagmatic 71 gulch volcano western snake river plain volcanic field idaho usa abstract the western snake river plain volcanic field in sw idaho contains up to 400 basaltic vents and centers that produced lava shields pahoehoe lava fields scoria cones and a great variety of phreatomagmatic volcanoes between late miocene and middle pleistocene time tephra deposits produced by phreatomagmatic eruptions are particularly well exposed in the walls of the snake river canyon where thick accumulations of pyroclastic rocks indicate widespread phreatomagmatic eruptive events throughout most of the volcanic history of the region previously many of the phreatomagmatic deposits were considered to be the products of subaqueous eruptions that took place on the floor of one or more large freshwater intra continental lakes recent field based observations confirm the presence of widespread phreatomagmatic pyroclastic rocks however some that had been interpreted as being subaqueous exhibit textural features that are more consistent with subaerial depositional environments intrusive and extrusive magmatic bodies with features associated with peperite formation have also been identified most of these peperites can be attributed to magma sediment mixing in intra crater conduit or vent settings and therefore they can only be used as widespread paleoenvironmental indicators with limitations to demonstrate magma and surface water e g lake non explosive interaction one of the studied sites 71 gulch volcano was previously used to indicate the presence of a shallow lake at this site there is clear field evidence that peperitic feeder dykes contacted muddy sandy siliciclastic sediments forming globular peperite the peperitic feeder dykes transition to pillowed ponded lava up section the ponded lavas are partially surrounded by a 5 m thick unit composed of gently dipping dune bedded volcanic glass shard rich unsorted tuff and lapilli tuff containing abundant impact sags caused by volcanic lithics we suggest that the 3d architecture of the erosional remnant of 71 gulch volcano does not require the presence of a lake at the time of its formation it is equally possible that that it represents a subaerial phreatomagmatic upper conduit crater filling succession this interpretation opens up many questions about the mio pliocene evolution of sw idaho the timing of the volcanism and its association with the evolution of the lacustrine systems in the region in addition re evaluations of the volcanic features in sw idaho have some general implications for the usage of phreatomagmatic pyroclastic rocks for paleoenvironmental reconstruction

a miocene basanite peperitic dyke at stanley northwestern tasmania australia abstract a miocene basanite dyke at stanley northwestern tasmania australia displays well preserved peperite texture the dyke is 2 m wide and has intruded basaltic breccia host sediment one contact of the dyke is fluidally shaped and amoeboid apophyses 10 25 cm long extend into the host sediment whereas the other contact is characterized by blocky peperite texture comprising tabular to wedge shaped clasts up to 30 cm across separated by host sediment the clasts have internal spherical fractures and some show splinter texture vesicles are common in the clasts and those intersected by clast margins have been filled with sediment the interior of the dyke comprises close packed blocky peperite consisting of tabular wedge shaped and polyhedral clasts tens of centimetres across separated by host sediment these clasts show well developed jigsaw fit texture the textures and structures in the basanite dyke are inferred to have formed in two stages an earlier hotter apophysis forming stage and a later cooler angular clast forming stage both of which occurred during the intrusion of magma into wet poorly consolidated sediment in a shallow marine environment during the apophysis forming stage the magma had relatively low viscosity and progressively displaced wet sediment the wet sediment around the dyke was partly fluidized by vaporization of pore water the angular clast forming stage reflects a change in the rheological behaviour of the magma from ductile to brittle most likely in response to decreasing temperature the chilled parts of the dyke were subject to stress arising from cooling contraction and also from continued pulsatory movement of hotter still ductile magma in the interior of the dyke resulting in brittle fragmentation brittle fragmentation was accompanied by movement of host sediment into the newly created open spaces forming blocky peperite spherical fractures splinter texture and sediment filled vesicles formed during the angular clast forming stage because the host sediment is texturally identical either side of the dyke increasing magma viscosity as temperature decreased combined with pulsatory intrusion were evidently important in the production of the blocky peperite

thermochemical structure and dynamics of the african superplume 1 we present a new three dimensional 3 d model of the thermochemical structure of the african superplume region obtained from simultaneous inversion of global seismic and convection related data convection related observations include the global free air gravity field tectonic plate motions dynamic surface topography and the excess ellipticity of the core mantle boundary a 3 d image of the chemically induced density perturbations provides direct evidence that intrinsically dense material is entrained within the superplume and concentrated into a rounded structure 1000 km above the core mantle boundary the thermally induced density perturbations are greater in magnitude than the chemically induced implying overall positive buoyancy throughout the superplume the observed morphology and density signatures are consistent with a thermochemical plume that has risen from a compositionally distinct pile at the base of the mantle and may be currently deforming under the influence of its intrinsic negative chemical buoyancy citation simmons n a a m forte and s p grand 2007 thermochemical structure and dynamics of the african superplume geophys res lett 34 l02301 doi 10 1029 2006gl028009

age spreading rates and spreading asymmetry of the world s ocean crust we present four companion digital models of the age age uncertainty spreading rates and spreading asymmetries of the world s ocean basins as geographic and mercator grids with 2 arc min resolution the grids include data from all the major ocean basins as well as detailed reconstructions of back arc basins the age spreading rate and asymmetry at each grid node are determined by linear interpolation between adjacent seafloor isochrons in the direction of spreading ages for ocean floor between the oldest identified magnetic anomalies and continental crust are interpolated by geological estimates of the ages of passive continental margin segments the age uncertainties for grid cells coinciding with marine magnetic anomaly identifications observed or rotated to their conjugate ridge flanks are based on the difference between gridded age and observed age the uncertainties are also a function of the distance of a given grid cell to the nearest age observation and the proximity to fracture zones or other age discontinuities asymmetries in crustal accretion appear to be frequently related to asthenospheric flow from mantle plumes to spreading ridges resulting in ridge jumps toward hot spots we also use the new age grid to compute global residual basement depth grids from the difference between observed oceanic basement depth and predicted depth using three alternative age depth relationships the new set of grids helps to investigate prominent negative depth anomalies which may be alternatively related to subducted slab material descending in the mantle or to asthenospheric flow a combination of our digital grids and the associated relative and absolute plate motion model with seismic tomography and mantle convection model outputs represents a valuable set of tools to investigate geodynamic problems

on the formation of deep seated subterranean peperite like magma sediment mixtures abstract in addition to large amounts of fragmented country rocks maar diatreme volcanoes commonly eject juvenile lapilli and cauliflower bombs containing many dispersed xenoliths and or xenocrysts derived from the country rocks surrounding the diatremes formation of these lapilli and bombs is attributed to thermohydraulic explosions in the root zones of the diatremes and their consequences the thermohydraulic explosions release shock waves which are capable of intensely fragmenting the surrounding country rocks vaporisation of water superheated during thermohydraulic explosions and its expansion to lower pressure causes ejection of major parts of the fragmented country rocks surviving sections of fragmented country rocks may collapse or slide into the partially evacuated root zone and thus form a mass flow deposit subsequent to each explosion when prior to a new explosion magma rises from the underlying feeder dyke into the root zone it intrudes this clastic debris inflates it and may mingle with the debris to form a peperite subsequent explosions can fragment and eject fragments of this peperite in the form of juvenile ash grains juvenile lapilli and bombs containing xenoliths or xenocrysts from the country rock debris lack of further explosions but continued rise and intrusion of magma will cause emplacement of such inflated peperite masses as plugs

hydraulic fracturing and wellbore completion of coalbed methane wells in the powder river basin wyoming implications for water and gas production excessive water production more than 7000 bbl month per well from many coalbed methane cbm wells in the powder river basin of wyoming is also associated with significant delays in the time it takes for gas production to begin analysis of about 550 water enhancement activities carried out during well completion demonstrates that such activities result in hydraulic fracturing of the coal water enhancement activities as the operators in the basin call this procedure consists of pumping 60 bbl of water min into the coal seam during approximately 15 min this is done to clean the wellbore and to enhance cbm production hydraulic fracturing is of concern because vertical hydraulic fracture growth could extend into adjacent formations and potentially result in excess cbm water production and inefficient depressurization of coals analysis of the pressure time records of the water enhancement tests enabled us to determine the magnitude of the least principal stress s3 in the coal seams of 372 wells these data reveal that because s3 switches between the minimum horizontal stress and the overburden at different locations both vertical and horizontal hydraulic fracture growth is inferred to occur in the basin depending on the exact location and coal layer relatively low water production is observed for wells with inferred horizontal fractures whereas all of the wells associated with excessive water production are characterized by inferred vertical hydraulic fractures the reason wells with exceptionally high water production show delays in gas production appears to be inefficient depressurization of the coal caused by water production from the formations outside the coal to minimize cbm water production we recommend that in areas of known vertical fracture propagation the injection rate during the water enhancement tests should be reduced to prevent the propagation of induced fractures into adjacent water bearing formations in areas where s3 is unknown a minifrac should be done to determine the magnitude of s3 to know whether fracture propagation will be vertical or horizontal so the water enhancement activities at the time of well completion are done to minimize water production and optimize gas production

dynamic mingling of magma and liquefied sediments abstract hydrodynamic mingling of magma and liquefied sediments is generally accepted to represent the key process in the formation of some peperites experimental studies on simulant liquids and calculations based on recent empirical findings in the field of polymer research were undertaken to investigate the effectiveness of this process these studies show that for a wide range of shear rates a laminar flow behaviour of the system magma liquefied sediment can be expected i e turbulent mingling is not a realistic scenario formation of peperitic fabrics with grain sizes on a cm scale can hydrodynamically be explained under realistic intrusion velocities in addition to the hydrodynamics cooling processes must also be considered during peperite formation calculations of the cooling history of the juvenile magmatic component under realistic cooling conditions demonstrate a significant limitation of the hydrodynamic mingling time the consequence for peperite formation under normal intrusion conditions is that domains of magmatic melt and domains of liquefied sediment smaller than 10 cm are not probable however as smaller domain sizes peperitic grain sizes exist in nature we conclude that either those peperites represent the products of explosive events or that hydrodynamic mingling was accompanied by additional fragmentation processes

origin and metamorphism of peperite and associated rocks in the devonian elwell formation northern sierra nevada california the late devonian elwell formation is part of a late paleozoic island arc assemblage exposed in the northern sierra nevada california in the 10 km interval from mount elwell plumas county to packer lake sierra county it consists largely of numerous andesitic sills interleaved with phosphatic radiolarian chert and turbidity current and debris flow deposits peperite formed by interaction of intrusive andesitic magma and still moist incompletely lithified chert not far beneath the sea floor occurs sparingly the whole assemblage was thoroughly recrystallized greenschist facies regional metamorphism during the late jurassic nevadan orogeny the phosphatic chert is composed of white fluorapatite rich lenses and nodules enclosed in a black matrix consisting of microgranular quartz and carbonaceous material probably graphite radiolaria family entactiniidae are so abundant that the chert is thought to have originated as radiolarian ooze the phosphatic lenses and nodules probably formed by direct inorganic precipitation of fluorapatite from pore water within decaying radiolarians at the sediment water interface the andesitic sills are generally aphyric and aphanitic original textures varied from hyalopilitic in sill interiors to pilotaxitic at sill margins the andesite was charged with plagioclase now albite microlites and quench morphologies occur where sills intruded the wettest chert relatively thick sills commonly display columnar structure whereas a few originally more viscous sills are flow laminated the top of a sill emplaced essentially at the sediment water interface is pillowed many sills bear xenoliths of phosphatic chert and scarce quartz megacrysts evidently derived from the underlying dacitic sierra buttes formation appear nearly everywhere concentrations of major element oxides and immobile trace elements indicate that the andesite originated as part of the tholeiitic rock association of island arcs rare earth abundance patterns are particularly diagnostic of this paleotectonic setting most peperite has poorly sorted coarse ash to coarse block andesitic fragments uniformly distributed through a voluminous black chert matrix where invaded chert retained the most pore water quenched andesitic magma formed irregularly shaped lapilli and small pillows that initially exhibited ductile behavior rapid cooling below the softening point of glass resulted in brittle fracture of the lapilli during dispersal through the chert by steam explosions steam explosions also incorporated into the peperite rigid clasts of locally dewatered chert and shattered already formed phosphatic nodules where the invaded chert was better lithified freezing sill margins simply granulated quietly in situ by thermal contraction cracking of microlitic glass fluid chert injected widely spaced contraction joints deep within the sills in all cases there was sufficient heated connate water to cause palagonitization and chloritization of andesitic fragments greenschist facies metamorphism produced two mineral assemblages in the interiors of andesitic sills the second perhaps reflecting locally higher pco 2 ph 2 o during metamorphism 1 albite quartz epidote actinolite chlorite ti rich mineral calcite stilpnomelane white mica and 2 albite quartz chlorite ti rich mineral calcite stilpnomelane white mica epidote rich specks occurring sporadically in the sills represent metasomatism on a scale of millimetres to centimetres such specks are mineralogically zoned in andesitic fragments in intensely recrystallized peperite additional examples of local meta somatic activity include syntectonic crystallization of calcite rhombohedra across original vesicle walls in a sill cleavage developed locally during regional metamorphism is parallel to axial planes of closely appressed folds that deformed andesitic fragments in peperite and flow laminae in sills

uncertainties in reconstructions of the pacific farallon vancouver and kula plates and constraints on the rigidity of the pacific and farallon and vancouver plates between 72 and 35 ma to study the rigidity of the pacific and farallon plates between 72 and 35 ma we analyzed the magnetic anomalies and fracture zones in the pacific ocean between longitudes 125 w 180 and latitudes 43 s 60 n a set of consistent rotations indicates that the pacific and farallon plates between the pioneer and agassiz fracture zones were rigid plates between 72 and 35 ma thus the location of a missing tertiary boundary within the pacific or antarctic plates is restricted to be south of latitude 43 s the farallon plate broke into two plates at the time of the change in the pacific farallon spreading direction north of the pioneer and mendocino fracture zones sometime between 59 and 49 ma the northern fragment termed the vancouver plate was subducted beneath most of north america we present rotations and uncertainties for the histories of motion of the pacific and kula plates from anomaly 32 to anomaly 25 of the pacific and vancouver plates from anomaly 21 to anomaly 13 and of the pacific and farallon plates from anomaly 32 to anomaly 13

formation of the rocky mountains western united states a continuum computer model one hypothesis for the information of the rocky mountain structures in late cretaceous through eocene time is that plate of oceanic lithosphere was underthrust horizontally along the base of the north american lithosphere the horizontal components of the motion of this plate are known from paleomagnetism and the edge of the region of flat slab can estimated from reconstructed patterns of volcanism new techniques of finite element modeling allow prediction of the thermal and mechanical effects of horizontal subduction on the north american plate a model that has a realistic temperature dependent rheology and a simple plane layered initial condition is used to compute the consequences of horizontal underthrusting in the time interval 75 million to 30 million years before present successful prediction of this model include i the location amount and direction of horizontal shortening that has been inferred from laramide structures ii massive transport of lower crust from southwest to northeast iii the location and timing of the subsequent extension in metamorphic core complexes and the rio grande rift and iv the total area eventually involved in basin and range style extension in a broad sense this model has predicted the belt of laramide structures the transport of crust from the coastal region to the continental interior the subsequent extension in metamorphic core complexes and the rio grande rift and the geographic region of late tertiary basin and range extension its principal defects are that i many events are predicted about 5 million to 10 million years too late and ii the wave of crustal thickening does not travel far enough to the east reasonable modifications to the oceanic plate kinematics and rheologies that were assumed may correct these defects the correspondence of model predictions to actual geology is already sufficiently close to show that the hypothesis that horizontal subduction caused the laramide orogeny is probably correct the rocky mountain thrust and reverse faults formed in an environment of east west to northeast southwest compressive stress that was caused by the viscous coupling between the oceanic plate and the base of the north american crust nonuniform crustal thickening by simple shear transport also caused relative uplifts therefore this model is consistent with both of the range forming mechanisms that have been inferred 1 a new proposal that arises from this simulation is that horizontal subduction also caused the subsequent extensional basin and range taphrogeny by stripping away the mantle lithosphere so that the crust was exposed to hot asthenosphere after the oceanic slab dropped away

peperitic textures of ordovician dacitic synsedimentary intrusions in argentina s puna highland clues to emplacement conditions abstract synsedimentary crystal rich dacitic sills laccoliths and cryptodomes emplaced in early ordovician submarine thin bedded silt sandstone sequences show a variety of magma water interaction features megapeperites occurring along the igneous contact contain angular dacitic megaclasts that are dispersed in dominantly structureless host sediment they result mainly from quench fragmentation of magma and dynamic stressing of cooling magma bodies on contact with wet sediments combined in some instances with fluidization of the sediments or minor explosive expansion of water incorporated by magma breaching the sediment water interface or stopping of water saturated roof sediments by shallowing intrusions globular peperites having bulbous to globular dacitic clasts immersed in the host sediment with evidence of fluidization along the contact zone are also recognized at the top and base of sills in this case a vapor film might have formed at the magma sediment interface insulating the magma from direct contact with the sediment and suppressing quench fragmentation and steam explosions the diversity of peperite textures observed in the same intrusive and sedimentary rocks appears to be mainly the result of different levels of emplacement of the synsedimentary dacitic intrusions scarcity of peperites related to mafic sills is attributed to their having been emplaced late during the evolution of the basin

olivine basalt and trachyandesite peperites formed at the subsurface surface interface of a semi arid lake an example from the early miocene bigadic basin western turkey abstract miocene successions in western turkey are dominated by lacustrine fluvial and evaporitic sedimentary deposits these deposits include considerable amounts of volcaniclastic detritus derived from numerous ne trending volcanic centres in western turkey as well as in the bigadic region early miocene syn depositional ne trending olivine basalt and trachyandesite bodies that formed as intrusions and lava flows occur within the bigadic borate basin olivine basalts occur as partly emergent intrusions and trachyandesite dykes fed extensive lava flows emplaced in a semi arid lacustrine environment peperites associated with the olivine basalt and trachyandesites appear to display contrasting textural features although all the localities include a large variety of clast morphologies from blocky to fluidal fluidal clasts mainly globular ameboidal and pillow like varieties are widespread in the peperite domains associated with olivine basalts apparently due to large volume sediment fluidisation in contrast fluidal clasts related to trachyandesites are restricted to narrow zones near the margins of the intrusions and have commonly elongate and polyhedral shapes with digitate margins rather than globular and equant varieties blocky and fluidal clasts in the olivine basalt peperite display progressive disintegration suggesting decreasing temperature and increasing viscosity during fragmentation abundance of blocky clasts with respect to fluidal clasts in the trachyandesite peperite indicates that the fluidal emplacement and low volume sediment fluidisation in the early stages were immediately followed by quench fragmentation due to the high viscosity of the magma size texture and abundance of the blocky and fluidal clasts in the olivine basalt and trachyandesite peperites were mainly controlled by sediment fluidisation pulsatory magma injection and magma properties such as composition viscosity vesicularity and size abundance and orientation of phenocrysts variously combining these contrasting features to varying degrees may form diverse juvenile clast shapes in peperitic domains

the late cretaceous to recent tectonic history of the pacific ocean basin abstract a vast ocean basin has spanned the region between the americas asia and australasia for well over 100 myr represented today by the pacific ocean its evolution includes a number of plate fragmentation and plate capture events such as the formation of the vancouver nazca and cocos plates from the break up of the farallon plate and the incorporation of the bellingshausen kula and aluk phoenix plates which have been studied individually but never been synthesised into one coherent model of ocean basin evolution previous regional tectonic models of the pacific typically restrict their scope to either the north or south pacific and global kinematic models fail to incorporate some of the complexities in the pacific plate evolution e g the independent motion of the bellingshausen and aluk plates thereby limiting their usefulness for understanding tectonic events and processes occurring in the pacific ocean perimeter we derive relative plate motions with 95 uncertainties for the pacific farallon vancouver kula pacific bellingshausen pacific and early pacific west antarctic spreading systems based on recent data including marine gravity anomalies well constrained fracture zone traces and a large compilation of magnetic anomaly identifications we find our well constrained relative plate motions result in a good match to the fracture zone traces and magnetic anomaly identifications in both the north and south pacific in conjunction with recently published and well constrained relative plate motions for other pacific spreading systems e g aluk west antarctic pacific cocos recent pacific west antarctic spreading we explore variations in the age of the oceanic crust seafloor spreading rates and crustal accretion and find considerable refinements have been made in the central and southern pacific asymmetries in crustal accretion within the overall pacific basin where both flanks of the spreading system are preserved have typically deviated less than 5 from symmetry and large variations in crustal accretion along the southern east pacific rise i e pacific nazca farallon spreading appear to be unique to this spreading corridor through a relative plate motion circuit we explore the implied convergence history along the north and south america s where we find that the inclusion of small tectonic plate fragments such as the aluk plate are critical for reconciling the history of convergence with onshore geological evidence

faster seafloor spreading and lithosphere production during the mid cenozoic concurrent changes in seawater chemistry sea level and climate since the mid cretaceous are thought to result from an ongoing decrease in the global rate of lithosphere production at ridges the present day area distribution of seafloor ages however is most easily explained if lithosphere production rates were nearly constant during the past 180 m y we examined spatial gradients of present day seafloor ages and inferred ages for the subducted farallon plate to construct a history of spreading rates in each major ocean basin since ca 140 ma revealing dramatic cenozoic events globally seafloor spreading rates increased by similar to 20 during the early cenozoic due to an increase in plate speeds in the pacific basin since then subduction of the fast spreading pacific farallon ridge system has led to a 12 decrease in average global spreading rate and an 18 or more decrease in the total rate of lithosphere production by the most conservative estimates these rapid changes during the cenozoic defy models of steady state seafloor formation and demonstrate the time dependent and evolving nature of plate tectonics on earth

magma composition and viscosity as controls on peperite texture an example from passamaquoddy bay southeastern canada silurian mafic lava flows and rhyolite sills in the passamaquoddy bay area southeastern canada interacted with wet sediment to produce peperitic breccia the pahoehoe type mafic flows flowed over and bulldozed into wet unconsolidated silt and sand to produce both blocky and fluidal peperite at their lower contacts soft sediment deformation structures in the siltstone adjacent to the flows irregularly shaped vesicles in the siltstone and siltstone filled vesicles in the mafic lava all indicate the sediment was wet at the time of flow emplacement sills of rhyolite emplaced into the same sedimentary sequence also interacted with the wet sediment and produced peperite at both the upper and lower contacts evidence for the rhyolitic magma interacting with wet sediment includes sediment filled vesicles in rhyolite quartz filled vesicles in siltstone and angular non vesicular shards of rhyolite in clastic dykes peperite formed by this process is exclusively blocky the rhyolitic magma in the passamaquoddy bay sequence and other examples of high viscosity magma producing only blocky peperite suggest that in contrast to low viscosity magmas which produce a combination of blocky and fluidal peperite only blocky peperite will form associated with highly viscous rhyolite magma the sediment that interacted with both the mafic and rhyolitic lavas is of similar texture indicating that in this case sediment texture did not control peperite type the change from fluidal to blocky peperite texture may also be controlled in part by the magma temperature and or confining pressure and the generation and maintenance of a steam film at the magma wet sediment interface

stability analysis of a horizontal coalbed methane well in the rocky mountain front ranges of southeast british columbia canada abstract this study describes a wellbore stability analysis undertaken for a horizontal coalbed methane well in the mist mountain formation se british columbia canada three triaxial compression tests with ultrasonic velocities were conducted on 38 mm diameter core plugs taken from a large fresh block of seam 7 due to the small size of the tested samples the laboratory derived strength values were reduced to reflect the in situ stress conditions considered relevant for a 156 mm diameter horizontal well the vertical stress gradient was calculated by integrating a bulk density log from an offset well horizontal maximum and minimum stresses were estimated from regional stress data whereas formation pressure was estimated on the basis of a local hydrological study the 2d elastoplastic stabview numerical modeling code was used to forecast horizontal wellbore stability the sensitivity of the predicted yielded zone size was examined for varying linear and non linear rock strength criteria horizontal in situ stresses bottom hole pressures formation pressure drilling depth and wall coating efficiency stability analysis was performed at bottom hole pressures ranging from overbalanced to underbalanced in order to simulate the conditions expected during drilling and production the effects of weak bedding planes and varying well trajectories were also investigated when drilling at 650 m depth under underbalanced to slightly overbalanced conditions a high probability of getting the drill pipe stuck was predicted stabview showed that if the 38 mm diameter core plug strengths were used directly for forecasting purposes the predicted yielded zone would be almost 20 overgauge when drilling at balanced conditions when peak cohesion of coal was reduced by 50 to reflect the conditions expected along weak intervals of a horizontal wellbore the predicted enlarged borehole was almost 85 overgauge under the same drilling conditions the most unstable trajectory has n s azimuth which is perpendicular to the maximum horizontal stress in the study area stabview indicates that a production liner should be inserted immediately following the drilling of the horizontal well in this structurally complex geologic setting since pressure drawdown and reservoir pressure depletion would undoubtedly lead to enlarged yielded zones and collapse of the wellbore over time

a model for the plate tectonic evolution of the east central pacific based on seasat investigations abstract a complete seasat dataset is used to investigate the small scale bathymetry of a 15 by 15 area of the east central pacific northeast of pitcairn island which was involved in the miocene ridge jump and reorientation two fracture zones fz1 and fz2 are mapped along 450 km at an azimuth of n95 e while the signature of the austral fracture zone disappears east of 135 w several seamounts are discovered or confirmed along the oeno henderson ducie lineament and the degree of isostatic compensation of a number of islands at the eastern end of the tuamotu group is studied islands of the northern branch have practically no signatures in the geoid while the southern ones must have formed on lithosphere at least 10 ma old on the basis of these constraints we present a model of the evolution of spreading since 40 ma b p in which the deactivation of the austral fracture zone and the transfer of its offset to fz1 in the late oligocene is interpreted as due to rift propagation triggered by a northern tuamotu hotspot we propose that the oeno ducie chain is the surface expression of a southern tuamotu hotspot deviated 15 in azimuth by the presence of a young and fresh fracture zone thus our model predicts that hotspots and ridge systems can have a moderate influence on each other s kinematics and surface expressions which does not however extend to permanent trapping

an analytical model of coal wellbore stability based on block limit equilibrium considering irregular distribution of cleats abstract an analytical model of coal wellbore stability is established based on the block limit equilibrium method taking the irregular distribution of cleats into account because coal seam is cut into discontinuous blocks with different shapes and sizes block slip can be treated as the symbol of coal wellbore instability according to the geometric characteristic of blocks blocks surrounding the wellbore can be divided into 3 categorizes type i type ii and type iii to evaluate the block slip the stress distribution near the wellbore is determined based on the continuous medium mechanics and the fracture mechanics using mohr coulomb criterion and limit equilibrium method the critical conditions of block slip are derived by defining the failure coefficient including type i type ii and type iii the proposed model is verified by comparison of the obtained results from the proposed analytical method with the discrete element method as well as the actual drilling it can be proved that the proposed model can predict accurately block slip additionally the effect of drilling fluid pressures on the wellbore stability is specially investigated the results show that with the increasing of drilling fluid pressure the degree of wellbore collapse may be more severe meanwhile the analysis method of reasonable drilling fluid pressure for coal drilling is proposed based on the interval theory combining the slip area of blocks finally the parametric study is focused on investigating the effects of the internal friction angle of face cleats the cohesion of face cleats and the tensile strength of butt cleats on the failure coefficients of blocks

empirical and numerical approaches for geomechanical characterization of coal seam reservoirs abstract the effects of fractures or joints on geomechanical properties of coal when transitioning from small samples to larger field scales have long been recognized two geomechanical characterization methodologies for of a coal seam for reservoir engineering are presented which attempt to account for these scale effect the first is a well established empirical rock mass classification method the geological strength index gsi the second is a newly developed numerical technique termed the synthetic rock mass srm gsi was developed to empirically account for the influence of rock joint density and joint surface conditions on the behaviour of the rock mass the established gsi to strength and deformation theories are reviewed and an approach to account for joint stiffness based on the minimum confining stress is presented the srm approach to jointed rock mass geomechanical characterization is a numerical modeling technique which combines the bonded particle model for rock and discrete fracture network simulation the intact or matrix of the srm is calibrated to laboratory data the dfn inserted creating a numerical representation of the rock mass which can then be tested at any scale in each case the approaches attempt to geomechanically characterize strength modulus etc the large scale behaviour of the coal seam where the properties can then be used for continuum type simulation reservoir simulation borehole stability etc

assessing the mechanical stability of horizontal boreholes in coal horizontal wells are used in some geological settings in the petroleum industry to produce methane from coal seams horizontal directional drilling is used in the mining industry to enhance the effectiveness of coal degasification procedures and to aid in the delineation of coal reserves coals tend to be mechanically weak hence they are prone to borehole instability related problems during drilling completion and production operations this paper includes a review of the mechanical properties of selected coals and provides two empirical cross plots that can be used for estimating coal strength from index tests and geophysical logs linear elastic borehole stability models are demonstrated to be appealing because they are easily implemented require a minimum of input data and are well suited to rapid parameter sensitivity analyses using experience obtained drilling vertical wells in a given setting a methodology is described for calibrating linear elastic models to provide realistic borehole stabil

interactions between andesitic magma and poorly consolidated sediments examples in the neogene shirahama group south izu japan abstract the upper miocene lower pliocene shirahama group of south izu japan is a sequence of volcanielastic shallow sea sediments and subaqueous lava flows it is gently warped with indistinct preferred orientation and is cross cut by many andesitic intrusive bodies which range in size from less than a meter to several hundred meters the intrusive bodies exhibit various shapes and weak preferred orientation and often have hyaloclastic and peperitic textures along their peripheries hydrothermally altered and chaotically disturbed zones of host rocks also occur along the contacts the areas where the intrusive bodies are abundant are almost coincident with the areas where the more inclined beds and synsedimentary faults are developed the intrusive bodies dragged the surrounding beds with or without synsedimentary faults some intrusions occurred along the faults conjugate sets of the faults indicate that they were produced under unstable stress conditions these relationships between the beds and the intrusive bodies are assumed to have originated mostly by interaction between hot magma and poorly consolidated wet sediments at a shallow depth beneath the sea floor when the intrusions took place the stress conditions in the beds were irregular and unstable judging from the shapes and orientation of the intrusive bodies and also from the deformation characteristics of the enclosing beds some of the intrusive bodies are probably feeder dikes which supplied lave to the shirahama group

a numerical study on optimization of multilateral horizontal wellbore patterns for coalbed methane production in southern shanxi province china abstract china s southern shanxi province contains thick gassy coals of anthracite rank these high methane content higher than 500 ft 3 ton coals necessitate pre mining methane drainage to enhance the health and safety of underground coal workers both traditional vertical wells and multilateral horizontal wells which were shown to perform better have been drilled in the area in order to effectively reduce the gas content of coals however optimization of well drilling patterns is crucial to improve the gas drainage by boosting well performance and resulting in significant additional recovered gas in a cost effective manner in this study exploration borehole data from an undeveloped coalbed methane field in china s qinshui basin was obtained where permeability is expected to range from 0 1 to 10 md reservoir modeling conducted in this study concludes that in the presence of low permeability coals less than 1 0 md well patterns can be optimized to maintain high methane production rates in this work relationships to determine combinations of horizontal lateral spacing and permeability that yield similar production curves were developed in order to maximize production pinnate wells with laterals spaced at 600 ft intervals in reservoirs with 2 0 md permeability performed similar to those with 200 ft lateral intervals in 0 5 md reservoirs additional similar relationships were drawn for reservoirs ranging from 0 1 to 8 0 md furthermore because of the qinshui basin s potential high stress regime pitchfork and pinnate horizontal well patterns were analyzed based on their potential for catastrophic wellbore failure at well junctions and producing well branches analyses concluded that pitchfork wells had a significantly lower risk for significant wellbore loss due to borehole collapse while providing the opportunity for higher gas recovery in reservoirs exhibiting directional permeability

mantle convection and the recent evolution of the colorado plateau and the rio grande rift valley the colorado plateau contains late cretaceous marine strata that are at a mean elevation of 2 km the timing and amount of uplift since the cretaceous has generated considerable debate with the exception of a few studies topography supported by vertical stresses generated by viscous fl ow in the mantle has not been explicitly considered to contribute to the elevation of this region herein we compute the viscous fl ow beneath north america that is driven by density anomalies inferred from joint seismic geodynamic modeling we fithat the colorado plateau overlies a strong mantle upwelling that is coupled to the sinking farallon slab currently beneath the eastern united states consequently the colorado plateau is currently a focused dynamic topography high within the western u s cordillera moreover this strong upwelling impacts the base of the lithosphere at an oblique angle east of the plateau directly below the rio grande rift we attribute this fl ow as being responsible for some of the recent magmatic activity along the jemez lineament as well as contributing to the recent rifting process in the rio grande rift valley

peperite a review of magma sediment mingling the study of peperite is important for understanding magma water interaction and explosive hydrovolcanic hazards this paper reviews the processes and products of peperite genesis peperite is common in arc related and other volcano sedimentary sequences where it can be voluminous and dispersed widely from the parent intrusions it also occurs in phreatomagmatic vent filling deposits and along contacts between sediment and intrusions lavas and hot volcaniclastic deposits in many environments peperite can often be described on the basis of juvenile clast morphology as blocky or fluidal but other shapes occur and mixtures of different clast shapes are also found magma is dominantly fragmented by quenching hydromagmatic explosions magma sediment density contrasts and mechanical stress as a consequence of inflation or movement of magma or lava magma fragmentation by fluid fluid shearing and surface tension effects is probably also important in fluidal peperite fluidisation of host sediment hydromagmatic explosions forceful intrusion of magma and sediment liquefaction and shear liquification are probably the most important mechanisms by which juvenile clasts and host sediment are mingled and dispersed factors which could influence fragmentation and mingling processes include magma host sediment and peperite rheologies magma injection velocity volatile content of magma total volumes of magma and sediment involved total volume of pore water heated presence or absence of shock waves confining pressure and the nature of local and regional stress fields sediment rheology may be affected by dewatering compaction cementation vesiculation fracturing fragmentation fluidisation liquefaction shear liquification and melting during magma intrusion and peperite formation the presence of peperite intraclasts within peperite and single juvenile clasts with both sub planar and fluidal margins imply that peperite formation can be a multi stage process that varies both spatially and temporally mingling of juvenile clast populations formed under different thermal and mechanical conditions complicates the interpretation of magma fragmentation and mingling mechanisms

granulation of weak rock as a precursor to peperite formation coal peperite coombs hills antarctica abstract peperite formed by mingling of magma with coal and with fragmented coal plus other country rock is exposed at coombs hills antarctica in rocks of the mawson formation where ferrar supergroup basalt encountered the beacon supergroup continental sedimentary succession an internally laminated 0 5 m thick coal bed passes gradationally through a coal fragment dominated peperite into a glass rich basalt dominated coal fragment matrix peperite and then into coherent basalt initial interaction of magma with water saturated coal and host sediments locally brecciated the coal subsequent mingling of basalt with a slurry of coal fragments and water driven by viscosity and density contrasts between the basalt and the slurry and by flow inhomogeneities in intruding magma led to increasingly complex mingling of the two fluids via bifurcation of fingering viscous flows this mingling was complicated by the participation of phases with time and space dependent thermal properties and viscosity coal fragments coal water slurry and basaltic magma and the generation of multiple gas phases through devolatilisation of heated coal the initial elastic response of the coal fragments to stress resulted in a fluidal mingling of coal and basalt facilitated by softening of coal during heating associated with intrusion and b localised formation of blocky coal clasts during high stress events associated with passage of a liquid and or a gas phase s through the coal the presence of fluidal and blocky shaped coal fragments in the coal peperite with both curved and planar surfaces bounding single coal clasts suggests that clast morphology in the magma sediment dispersion was controlled at very small scales by the time temperature and stress dependent qualities of the coal fluidal and blocky clast shapes in the coal peperite coupled with vesicles in the coal clasts suggest that transient properties of either the host or intrusion during non explosive magma sediment interaction may exert a strong control on clast morphology and mingling characteristics

coal permeability improving mechanism of multilevel slotting by water jet and application in coal mine gas extraction multilevel slotting by water jet is one of the effective methods used to improve the coal seam permeability as the example of the 1603 working face of guhanshan coalmine first using acoustic emission technology we analyzed the mechanical properties and crack propagation characteristics of the multilevel slotting coal under the condition of uniaxial loading then using the particle flow software pfc2d we numerically simulated the fracture stress and porosity evolutions of the multilevel slotting coal and analyzed the coal permeability improving mechanism of the slot crack network meanwhile the borehole gas extraction slotted by water jet underground was field tested the study found that the coal s body strength could be weakened significantly when the number of slots was increased and the multilevel distribution of the slots induced a great amount of crack growth and extension which formed the slot crack network reduced the stress concentration and increased the coal porosity field tests demonstrated that the gas extraction effect underground was significantly improved the ability of gas extraction of multilevel slotting borehole was enhanced by 5 10 times compared with the conventional borehole and the coal permeability coefficient was increased by about six times

coalbed methane from hazard to resource abstract coalbed gas which mainly consists of methane has remained a major hazard affecting safety and productivity in underground coal mines for more than 100 years coalbed gas emissions have resulted in outbursts and explosions where ignited by open lights smoking or improper use of black blasting powder and machinery operations investigations of coal gas outbursts and explosions during the past century were aimed at predicting and preventing this mine hazard during this time gas emissions were diluted with ventilation by airways e g tunnels vertical and horizontal drillholes shafts and by drainage boreholes the 1970 s energy crisis led to studies of the feasibility of producing the gas for commercial use subsequent research on the origin accumulation distribution availability and recoverability has been pursued vigorously during the past two decades since the 1970 s research investigations on the causes and effects of coal mine outbursts and gas emissions have led to major advances towards the recovery and development of coalbed methane for commercial use thus coalbed methane as a mining hazard was harnessed as a conventional gas resource

pumiceous peperite in a submarine volcanic succession at mount chalmers queensland australia pumiceous peperite comprising irregularly shaped apophyses of feldspar phyric rhyolitic tube pumice and siltstone occurs within well bedded volcaniclastic sandstone and siltstone facies of the early permian berserker beds at mount chalmers australia the tube pumice structure is preserved where sericite or silica have replaced the glass of vesicle walls and vesicles have been infilled by silica in some instances the peperite occurs gradationally above or below intervals of coherent feldspar phyric rhyolite that are also predominantly pumiceous the siltstone in the pumiceous peperite is texturally homogeneous locally vesicular and contains shards and crystals derived from disintegration of the pumiceous rhyolite pumiceous rhyolite and peperite occur at various positions in the stratigraphy and may represent interconnected intrusive digits or lobes intrusion of the lobes was accommodated by expansion of the pore water and possible fluidisation of the host sediment resulting in local destruction of bedding the lobes developed chilled margins at contacts with wet sediment and inflated in response to vesiculation and the supply of new magma cooling of the lobes was possibly accompanied by development of microfractures in the glassy vesicle walls rupture of the chilled margin and propagation of fractures into the interior could have temporarily and locally depressurised the lobes resulting in failure disintegration and mixing with the adjacent wet and or steam rich sediment hot pumiceous rhyolite in lobe interiors may have interacted directly with the wet sediment and been dismembered by quench fragmentation and or steam explosions bubbles of magmatic gas and or steam were trapped in the sediment that mixed with the pumiceous rhyolite the development of pumiceous texture in the sills was favoured by emplacement beneath a thin cover of wet sediment in a relatively shallow submarine shelf setting in which the confining pressure was sufficiently low to permit vesiculation this setting was also important in limiting the extent of degassing of the pumiceous rhyolite during cooling

production characteristics and the key factors in high rank coalbed methane fields a case study on the fanzhuang block southern qinshui basin china abstract the temporal and spatial production characteristics of coalbed methane cbm wells in the fanzhuang block of the southern qinshui basin the first commercial cbm producing basin in china were studied to determine the dominant factors the study indicates that gas production differs significantly in different wells adjacent to or located in different tectonic areas in combination with the production characteristics in the temporal and spatial variations the impact of seven factors burial depth thickness of coal gas content porosity permeability effect of fracturing structural setting and hydrogeological conditions on the gas production was analyzed based on bivariate correlation analysis and gray system theory which are suitable for solving the complex interrelationships between multiple factors and variables the results indicate that hydraulic fracturing is an effective guarantee of high production cbm wells in the first several months during a high rank cbm field development however the effect of hydraulic fracturing on enhancing the gas production of cbm wells decreases with time because the initial reservoir permeability lower than the hydraulic fracture permeability limits the adsorption diffusion and flow of cbm this limitation inevitably leads to a slow gas production rate when the adsorbed cbm from the initial reservoir becomes the main gas source instead of the fracturing affected zone gas content and permeability are two key factors that dominate cbm well productivity because they perform elementary roles in controlling the volume of gas sources and conductivity respectively the structural setting and hydrogeological condition are also two important factors that dominate cbm well productivity because they can influence the spatial distribution of permeability and gas content as well as other factors such as aquifers

processes of magma wet sediment interaction in a large scale jurassic andesitic peperite complex northern sierra nevada california the middle jurassic tuttle lake formation in the northern sierra nevada california comprises a thick volcaniclastic sequence deposited in a submarine island arc setting and penetrated by numerous related hypabyssal intrusions a composite andesite diorite intrusive complex 4 5 km long and 1 5 km thick was emplaced while the host tuttle lake sediments were still wet and unconsolidated large parts of the intrusive complex consist of peperite formed where andesitic magma intruded and intermixed with tuff lapilli tuff and tuff breccia the southern half of the complex consists of augite phyric andesite containing peperite in numerous small isolated pockets and in more extensive laterally continuous zones the peperites comprise three main types recognized previously in other peperite studies fluidal peperite consists of small 30 cm closely spaced at least partly interconnected globular to amoeboid andesite bodies enclosed by tuff this peperite type developed during intrusion of magma into fine grained wet sediment along unstable interfaces and fluidization of the sediment facilitated development of complex intrusive geometries blocky peperite and mixed blocky and fluidal peperite formed where magma intruded coarser sediment and underwent variable degrees of brittle fragmentation by quenching and dynamic stressing of rigid margins possibly aided by small steam explosions the northern half of the intrusive complex consists predominantly of a different type of peperite in which decimetre scale plagioclase phyric andesite clasts with ellipsoidal elongate or angular polyhedral shapes are closely packed to widely dispersed within disrupted host sediment textural features suggest the andesite clasts were derived from conduits through which magma was flowing and preserved remnants of the conduits are represented by elongate sinuous bodies up to 30 m or more in length disruption and dispersal of the andesite clasts are inferred to have occurred at least partly by steam explosions that ripped apart a network of interconnected feeder conduits penetrating the host sediments closely packed peperite is present adjacent to mappable intrusions of coherent andesite and along the margin of a large mass of coarse grained diorite these coherent intrusions are considered to be major feeders for this part of the complex examples of magma wet sediment interaction similar in scale to the extensive peperites described here occur elsewhere in ancient island arc strata in the northern sierra nevada based on these and other published examples large scale peperites probably are more common than generally realized and are likely to be important in settings where thick sediment sequences accumulate during active volcanism careful mapping in well exposed terrains may be required to recognize large scale peperite complexes of this type

wrench related dome formation and subsequent orogenic syntax bending in a hot orogen variscan ibero armorican arc the ouessant island france

effect of drilling fluids on coal permeability impact on horizontal wellbore stability the objective of this study was to evaluate a series of mud systems and additives typically used in coalbed methane drilling in terms of formation of an instantaneous filter cake ability of the coal reservoir to rid itself of the filter cake during production and overall impact on coal permeability to achieve this a series of laboratory tests were conducted initially using artificially cleated gypstone rock to simulate coal this was followed by the use of large diameter coal cores which unfortunately did not allow for the tests to be done under in situ confining stress conditions the three mud systems tested against coal xantham gum hec and na cmc did not have a negative impact on coal permeability in contrast to previous laboratory data that showed large decreases two fluid loss control additives which have been used successfully in drilling clastic and carbonate rocks were also tested using a non ionic polymer mud system during simulated drilling these additives flc 2000 and q stop were very effective in building a thin filter cake on the coal surface almost instantaneously to the point that no solids were detected in the downstream fluid accumulator during simulated production a small pressure drop was sufficient to remove the filter cake coal permeability to water returned to its original pre test value which suggested that there was no permanent permeability damage caused by the two additives when coal derived fines were added to the drilling mud in another experiment using the same coal the near wellbore coal permeability was reduced by 87 5 indicating severe damage to the cleat system and in agreement with previously reported laboratory data following the very good performance of flc 2000 and q stop in the laboratory tests these two additives were then used in field applications their presence in the drilling fluid resulted in the successful drilling of 953 m and 1400 m of total horizontal length in the deep mannville coals in alberta at true vertical depth of 1400 m and 1150 m respectively no borehole instability problems were encountered during drilling of the two horizontal wellbores the monitored mud losses were low in both cases with the horizontal well 2 experiencing lower mud loss possibly as a result of the absence of large fractures encountered along the horizontal path horizontal well 1 remained stable which allowed sufficient time to insert a production liner

the stability of methane capture boreholes around a long wall coal panel this paper describes the application of computational modelling to the prediction of the stability of methane drainage boreholes during the extraction life of an active long wall coal panel within a united kingdom coal mine the modelling was undertaken to investigate the affects that changes in the roof geology and roadway support system may have on the deformation and closure of the gas drainage boreholes drilled from the tailgate across the goaf of an active long wall panel the paper also outlines the development of an analytical model to estimate the bending deformation axial strain and the rupture of borehole casing due to rock shear this model was used in conjunction with the geomechanical strata models to predict the distance behind the face line at which excessive borehole deformation and closure would occur this method was used to evaluate the optimum roadway support system and spacing between boreholes to maintain effective borehole drainage subject to the range of geological conditions encountered during the panel retreat a good correlation was obtained between the model predictions and the geomechanical and gas drainage data measured at a uk colliery

geology of coalbed methane reservoirs in the southeast qinshui basin of china abstract the no 15 coal seam of the pennsylvanian taiyuan formation and the no 3 coal seam of the permian shanxi formation in the southeast qinshui basin are relatively thick 3 m laterally continuous and are of anthracite rank ro 2 2 4 5 the depth of these coal seams is generally between 200 and 700 m a tectonic thermal event during the jurassic to cretaceous yanshanian orogeny controlled coalification and thermogenic hydrocarbon generation because the generation of late stage bacterial gas coalbed methane in the southeast qinshui basin occupies two zones which are the mixed thermogenic and late stage bacterial gas zone near the basin margins and the dominantly thermogenic gas zone in the structurally deep part of the basin basin hydrodynamics causes low gas content in the shallow subsurface 20 m3 t because cleats are rare and are mostly filled with calcite the permeability of the coalbed methane reservoir is controlled by shear fractures the recharge and flow of groundwater not only control gas content but also control reservoir pressure abnormally high pressure reservoir in the deep stagnant zone is a favorable area for coalbed methane exploration and development the current coalbed methane wells are generally completed in the deep stagnant zone

morphology and growth style of a miocene submarine dacite lava dome at atsumi northeast japan abstract a miocene submarine lava dome at tate iwa atsumi yamagata japan displays well preserved primary morphological features the dome currently rises above a wave cut coastal platform and is 55 m high and 90 180 m across it comprises a massive core and a lava lobe hyaloclastite rim both of which are composed of compositionally uniform feldspar phyric dacite sio2 64 wt the boundary between these two zones is distinct but gradational the massive core consists of homogeneous coherent dacite and is characterized by flow banding along the margin and by columnar joints radiating from the centre to the margin the lava lobe hyaloclastite rim encircles the massive core and consists of a complex of 80 90 dacitic lava lobes and 10 20 hyaloclastite the lava lobes are 1 6 m thick 3 12 m wide and more than 5 m long each lobe consists of a radially columnar jointed core and a glassy rim 10 30 cm thick the hyaloclastite comprises polyhedral dacite clasts 5 100 cm across in a matrix of dacite fragments up to 5 mm across the lava lobes and hyaloclastite have gradational contacts in places paleobathymetric studies based on foraminifera in sediment beneath the dome and the k ar age of the dome suggest that it was extruded in a middle bathyal environment 1500 2000 m below sea level at 12 9 0 6 ma the internal structures of the dome suggest that it formed by a combination of exogenous growth involving extrusions of small dacite lobes and endogenous growth involving a continuous magma supply and simple expansion from the interior the presence of small lava lobes along the rim suggests that the magma had relatively low viscosity at the time of extrusion in spite of its high silica content magma temperatures calculated by two pyroxene and fe ti oxide geothermometers were 999 1042 and 957 1005 c respectively the inferred low viscosity may be attributed to the high temperature of the magma and or a high confining pressure resulting from the deep sea environment

a new method of drilling long boreholes in low permeability coal by improving its permeability abstract when drilling holes for gas pre extraction from soft coal seams having low permeability phenomena such as hole collapse and drill pipe sticking can occur these problems are due to the coal s low intensity and high gas pressure both of which severely limit the efficiency of gas extraction based on an analysis of borehole collapse in soft seams and on a study of the pore formation mechanism in stiff layers this paper proposes a new drilling technique that uses a high pressure pulsed water jet this technique can be used to drill holes in stiff layers of the roof floor until the soft layers of the coal seam are reached this method can improve the gas extraction rate according to damage models for rock a theoretical analysis and numerical simulation was performed for a high pressure pulsed water jet this analysis examined the instantaneous dynamic loads the damage features when using a flexible impact regime the changes in fracture field patterns and the high pressure pulsed water jet s oscillatory effect upon the gas flow of coal mass the impact and vibration effects of a high pressure pulsed water jet could effectively contribute to crushing of the coal to improvement of the coal s cracking and connectivity rate and to improvement in the permeability of the coal additionally the high pressure pulsed water jet s dynamic pressure and flow rate must be calculated for breaking rock during drilling and slotting the developed system was applied in the sanhui mine of sichuan province china the hole drilled by the new method is 2 7 times deeper than that of the hole drilled in the coal seam in the yutianbao mine the average length was 148 m when drilling between the roof and the seam and this value was more than 2 4 times deeper than that previously drilled in the coal seam the gas flow was about 1 06 m 3 min per meter which is more than 5 times that of a traditional hole

the tectonic fabric of the ocean basins 1 we present a global community data set of fracture zones fzs discordant zones propagating ridges v shaped structures and extinct ridges digitized from vertical gravity gradient vgg maps we use a new semi automatic fz tracking program to test the precision of our hand digitized traces and find a mean absolute deviation of less than 3 4 km from the raw vgg minima that most clearly delineate each feature and less than 5 4 km from the fz location predicted by fitting model profiles to the vgg data that represent the morphology of the individual fzs these offsets are small considering gravity data only provide an approximation for the underlying basement morphology we further investigate the origin of non fz seafloor fabric by combining published abyssal hill heights computed from gravity anomalies with global half spreading rates a residual abyssal hill height grid with spreading rate effects removed combined with our interpreted tectonic fabric reveals several types of seafloor fabric distinct from typical abyssal hills where discordant zones do not overprint abyssal hill signals residual abyssal hill height anomalies correspond to seafloor that accreted near mantle thermal anomalies or zones of melt depletion our analysis reveals several areas where residual abyssal hill height anomalies reflect pseudo faults and extinct ridges associated with ridge propagation and or microplate formation in the southern pacific ocean

late paleozoic peperites in west junggar china and how they constrain regional tectonic and palaeoenvironmental setting abstract late paleozoic peperites have been identified for the first time at the bottom of tailegula formation in west junggar china this finding is significant for the reconstruction of late paleozoic evolution in the junggar region the peperites form successions up to 500 m thick interbedded with basaltic lava and sedimentary rocks four types of peperites are described and interpreted as resulting from basaltic lava bulldozed into wet unconsolidated sediments at their basal contacts zircon la icp ms u pb dating of a tuff lens enclosed by lava showed that the peperites formed in the late devonian ca 364 ma the peperite bearing units probably formed at a water depth of less than 3 km and are generally undeformed occurring in continuous stratigraphic sections distributed regionally over a distance of 100 km on either side of the darbut and baijiantan ophiolitic belts in contrast to the highly deformed slices of ophiolite they demonstrate that the darbut and baijiantan ophiolitic belts should not be interpreted as significant plate boundaries and represent the underlying ocean crust uplifted along tectonic lineaments within a continuous shallow remnant ocean basin the peperites formed during the spreading phase of the remnant ocean basin and represent the final stages of creation of oceanic crust

textural variations and fragmentation processes in peperite formed between felsic lava flow and wet substrate an example from the cretaceous buan volcanics southwest korea abstract multiple exposures of peperite within the cretaceous buan volcanics southwest korea have been examined in order to determine variations in their textural characteristics and to investigate their mode of formation along undulating boundaries between rhyolite lava flow and deformed host sediment expressed as a series of load and flame structures exposures commonly contain two distinct types of peperite type 1 peperites are composed mostly of rounded juvenile clasts at their base and polyhedral juvenile clasts at their upper levels interpreted to have formed via a two stage process firstly abrasion of juvenile clasts occurred after their fragmentation due to shear stress imparted by the overlying and still moving lava flow forming rounded juvenile clasts subsequent in situ quenching fragmentation of the lava flow produced clasts with platy to polyhedral shapes immediately after emplacement of the lava flow type 2 peperites laterally extend into the interior of featureless rhyolite as layers that decrease in thickness with increasing distance away from the flame zone these layers exhibit horizontal textural variations ranging from poorly sorted mixtures of ash to block sized angular juvenile clasts in the proximal zone to closely packed polyhedral and tabular juvenile clasts with jigsaw crack textures in the middle and distal zones type 2 peperite are inferred to have formed due to internal steam explosions that resulted from an expansion of heated pore water leading to an increase in pore fluid pressure that had been vertically injected into the interior of the rhyolite from the flame zone the proximal zone composed mainly of poorly sorted mixtures of juvenile clasts represents the explosion sites juvenile clasts in the middle and distal zones are interpreted to have formed due to three separate processes the development of fractures in the rhyolite during the internal steam explosions injection of the host sediment through the fractures and in situ quenching fragmentation deformation of the host sediment exerted an important control on peperite forming processes with the internal steam explosions suggested to have formed the closely packed juvenile clasts with a jigsaw crack texture rather than the clasts that are widely dispersed

revel a model for recent plate velocities from space geodesy 1 we present a new global model for recent plate velocities revel describing the relative velocities of 19 plates and continental blocks the model is derived from publicly available space geodetic primarily gps data for the period 1993 2000 we include an independent and rigorous estimate for gps velocity uncertainties to assess plate rigidity and propagate these uncertainties to the velocity estimates the velocity fields for north america eurasia and antarctica clearly show the effects of glacial isostatic adjustment and australia appears to depart from rigid plate behavior in a manner consistent with the mapped intraplate stress field two thirds of tested plate pairs agree with the nuvel 1a geologic 3 myr average velocities within uncertainties three plate pairs caribbean north america caribbean south america and north america pacific exhibit significant differences between the geodetic and geologic model that may reflect systematic errors in nuvel 1a due to the use of seafloor magnetic rate data that do not reflect the full plate rate because of tectonic complexities most other differences probably reflect real velocity changes over the last few million years several plate pairs arabia eurasia arabia nubia eurasia india move more slowly than the 3 myr nuvel 1a average perhaps reflecting long term deceleration associated with continental collision several other plate pairs including nazca pacific nazca south america and nubia south america are experiencing slowing that began 25 ma the beginning of the current phase of andean crustal shortening

paleozoic fluidization folding and peperite formation northern sierra nevada california recognition of peperite is important in establishing broad contemporaneity of magmatism and sedimentation at an occurrence of peperite discovered recently among late paleozoic island arc deposits in the northern sierra nevada it is possible to reconstruct the peperite forming process largely from field observations alone the generally concordant upper margin of a basalt intrusion adjoins thinly laminated basaltic tuff in the taylor formation that was water saturated and unlithified at the time of intrusion the water saturated ash initially was heated by the intrusion at approximately constant essentially hydrostatic pressure concurrently the top of the intrusion was quenched and divided by shrinkage fractures pressure momentarily approached zero as the shrinkage fractures opened abruptly causing vaporization of the pore water and substantial expansion and fluidizing flow of the resulting steam the unlithified ash was swept into the shrinkage fractures and where the downward propagating fractu

fluidization of host sediments and its impacts on peperites forming processes the cretaceous buan volcanics korea abstract in the cretaceous buan volcanics sw korea blocky and fluidal peperites are developed in a bed of poorly sorted massive pumiceous lapilli tuff hot sediments as a result of the vertical to subvertical intrusion of the trachyandesitic dikes into the bed blocky peperites are composed of polyhedral or platy juvenile clasts with a jigsaw crack texture fluidal peperites are characterized by fluidal or globular juvenile clasts with irregular or ragged margins the blocky peperites are ubiquitous in the host sediments whereas the fluidal peperites only occur in fine grained zone well sorted fine to very fine ash that are aligned parallel to the dike margin the development of the fine grained zone within the poorly sorted host sediments is interpreted to form by grain size segregation caused by upward moving pore water fluidization that has resulted from heat transfer from intruding magma toward the waterlogged host sediments during intrusion with the release of pore water and the selective entrainment of fine grained ash the fine grained zone formed within the host sediments subsequent interactions between the fine grained zone and the intruding magma resulted in ductile deformation of the magma which generated fluidal peperites outside the fine grained zone because of the relative deficiency of both pore water and fine grained ash intruding magma fragmented in a brittle manner resulting in the formation of blocky peperites the results of this study suggest that redistribution of constituent particles ash and interstitial fluids during fluidization resulted in heterogeneous physical conditions of the host sediments which influenced peperite forming processes

characteristics and origin of peperite involving coarse grained host sediment peperite involving basalt and polymictic volcanic conglomerate occurs in the pliocene ba volcanic group at yaqara in northern viti levu fiji because the host sediment is coarse grained and dominated by basalt clasts the peperite could be easily overlooked and mistaken for another coarse volcaniclastic facies however the presence of groups of basalt clasts that show jigsaw fit texture fluidally shaped basalt clasts with complete glassy margins gradational contacts with adjacent sedimentary facies and the absence of stratification indicate that molten basalt mingled with unconsolidated gravel using these criteria we show that other superficially similar coarse polymictic facies with fluidal basalt clasts are not peperite both blocky and fluidal basalt clasts occur together in the peperite the amoeboid basalt clasts in the fluidal peperite result from dismembering of ductile low viscosity relatively hot magma at this stage propagating magma lobes were probably insulated from direct contact with the wet sediment by a vapour film the angular polyhedral basalt clasts in the blocky peperite indicate brittle disintegration of somewhat cooler higher viscosity magma the presence of jigsaw fit texture and polyhedral clasts with glassy margins suggest that quench fragmentation of the basalt was important in the formation of the blocky peperite although there is no positive evidence for steam explosivity the presence of steam could be recorded by small quartz filled cavities that occur within the host sediment the co existence of fluidal and blocky basalt clasts is interpreted to reflect successive ductile then brittle fragmentation of intruding magma the change from fluidal to blocky peperite might have resulted from progressive cooling of the magma during intrusion and also from the breakdown of fluidisation when the limited supply of fine sediment in the host gravel was exhausted

sea level fluctuations driven by changes in global ocean basin volume following supercontinent break up abstract long term variations in eustatic sea level in an ice free world which existed through most of the mesozoic and early cenozoic eras are partly driven by changes in the volume of ocean basins previous studies have determined ocean basin volume changes from plate tectonic reconstructions since the mesozoic however these studies have not considered a number of important elements that contribute to ocean basin volume such as regional differences in sedimentation or uncertainties within the plate tectonic model itself such as spreading asymmetries and the incomplete representation of back arc basins in the mesozoic additionally studies on long term changes in sea level related to the extension and rifting of passive margins have not been performed on a global scale and likely significantly underestimated the influence of this process in order to improve reconstructions of sea level on geologic time scales and assess the uncertainty in deriving the volume of ocean basins based on a global plate kinematic model we investigate the influence of back arc basins spreading asymmetry large igneous provinces lips sediment thickness and passive margins on ocean basin volume since 200 ma we find that less constrained plate tectonic elements such as the presence of back arc basins or spreading asymmetry may contribute up to 120 m or 150 m to sea level respectively changes in the sea level related to sedimentation and lips are respectively 75 165 m and 45 m changes in sea level associated with passive margin formation are almost negligible at present day though were much larger in the cretaceous and the assumed sedimentation style strongly influences the rate and magnitude of sea level change we incorporate predictions for these components during times where ocean basins are predominantly synthetic reconstructions and find that sea level driven by fluctuating ocean basin volume has changed by 200 m since the jurassic which is comparable to previous estimates our revised estimates will need to be combined with other processes driving long term sea level change including mantle convection driven dynamic topography and glacio eustasy for constructing a complete eustatic sea level curve understanding and quantifying the uncertainties in the volume of ocean basins has implications for modelling subduction flux the oceanic carbon cycle and heatflow and is important for exploring earth s evolutionary cycles especially during times in the geologic past where much of the ocean basin history has been lost

volcano sedimentary characteristics in the abu treifiya basin cairo suez district egypt example of dynamics and fluidization over sedimentary and volcaniclastic beds by emplacement of syn volcanic basaltic rocks abstract this paper describes the neogene lava sediment mingling from the abu treifiya basin cairo suez district egypt the lava sediment interactions as peperites have been identified for the first time at the study area and can be used as paleoenvironmental indicators the identification of peperite reflects contemporaneous time relationship between volcanism and sedimentation and this finding is of primary importance to address the evolutional reconstruction of the abu treifiya basin characterization of the facies architecture and textural framework of peperites was carried out through detailed description and interpretation of their outcrops the peperites and sedimentary rocks are up to 350 m thick and form a distinct stratigraphic framework of diverse lithology that is widespread over several kilometers at the study area lateral and vertical facies of the peperites vary from sediment intercalated with the extrusive intrusive basaltic rocks forming peperitic breccias to lava sediment contacts at a large to small scales respectively peperites encompass five main facies types ascribed to i carbonate sediments hosted fluidal and blocky peperites ii lava flow hosted blocky peperites iii volcaniclastics hosted fluidal and blocky peperites iv sandstone siltstone rocks hosted blocky peperites and iv debris flows hosted blocky peperites soft sediment deformation structures vesiculated sediments sediments filled vesicles and fractures in lava flows indicate that lava flows mingled with unconsolidated wet sediments all the peperites in this study could be described as blocky or fluidal but mixtures of different clast shapes occur regardless of the host sediment the presence of fluidal and blocky juvenile clasts elucidates different eruptive styles reflecting a ductile and brittle fragmentation the gradual variation from fluidal to blocky peperite texture producing the vertical grading is affected by influencing factors e g the viscosity magma temperature confining pressure sediment fluidization and vapor film at the magma sediment interactions peperites in the study area record deposition within a shallow marine and fluvio lacustrine environment accumulated in a rift related basin developed during pre to syn rift phase respectively the facies transitions peperites in this area resulted from the explosive and sediment depositional processes which were mingled separately by volcanism under contrast geological conditions the development of such contrast in the depositional sequences reflects variation in the accommodation to sediment supply in the same accumulation space inside the depocenters during the rifting of the abu treifiya basin hydrothermal mineralizations comprising quartz and carbonate are restricted to peperites and lava flows

new petrological and geochemical data on mid paleozoic island arc volcanics of northern sierra nevada california evidence for a continent based island arc the mid paleozoic volcanics of northern sierra nevada consist of the sierra buttes rhyolites the taylor basalts and andesites and the keddie ridge basalt latite rhyolite suite the sierra buttes calc alkaline rhyolites display strong light rare earth element enrichment and negative end values the taylor basalts and andesites in the northern hough and genesee blocks exhibit calc alkaline affinities ree rare earth element patterns highly enriched in lree whereas in the southern hough block they are tholeiitic flat rare earth element patterns the abundance of silicic lavas the low end values of both the sierra buttes and taylor volcanics and the 18o values of the sierra buttes rhyolite and bowman lake trondjhemite provide evidence that the northern sierra nevada island arc was continent based the keddie ridge differentiated volcanics characterized by high zr y nb k and light rare earth elements are geochemically similar to a shoshonite suite their eruption at the end of the mid paleozoic v

stratigraphy and structure of coalbed methane reservoirs in the united states an overview stratigraphy and geologic structure determine the shape continuity and permeability of coal and are therefore critical considerations for designing exploration and production strategies for coalbed methane coal in the united states is dominantly of pennsylvanian cretaceous and tertiary age and to date more than 90 of the coalbed methane produced is from pennsylvanian and cretaceous strata of the black warrior and san juan basins investigations of these basins establish that sequence stratigraphy is a promising approach for regional characterization of coalbed methane reservoirs local stratigraphic variation within these strata is the product of sedimentologic and tectonic processes and is a consideration for selecting completion zones coalbed methane production in the united states is mainly from foreland and intermontane basins containing diverse compressional and extensional structures balanced structural models can be used to construct and validate cross sections as well as to quantify layer parallel strain and predict the distribution of fractures folds and faults influence gas and water production in diverse ways however interwell heterogeneity related to fractures and shear structures makes the performance of individual wells difficult to predict

jurassic submarine arc apron deposits and associated magma wet sediment interaction northern sierra nevada california abstract jurassic metavolcanic rocks of the northern sierra terrane in northern california are part of an extensive triassic jurassic arc constructed along the western margin of north america in the english mountain area nevada and sierra counties a well exposed volcaniclastic sequence 3 6 km thick records jurassic island arc activity in a submarine environment in the lower part of the sequence thinly bedded andesitic volcanic sandstone turbidites and mudstones of the lower to middle jurassic sailor canyon formation were deposited below storm wave base in a long lived marine basin this unit is overlain conformably by the middle jurassic tuttle lake formation which records rapid accumulation of coarse grained calc alkaline volcanic debris in the proximal parts of a submarine apron around a major volcano that developed within the earlier sailor canyon basin the formation consists primarily of massively bedded matrix supported polymict basaltic to andesitic volcanic breccias deposited from submarine debris flows intercalated pillow hyaloclastite breccias formed during local extrusion of lavas on the seafloor numerous intrusions cut the sequence and are petrographically and chemically identical to clasts in the debris flow deposits peperite occurs along intrusion margins and as abundant isolated pockets indicating intrusion of magma into wet unconsolidated sediments elongate intrusive pods to 13 6 m in length are associated with smaller intrusive pillows and are inferred to represent a network of feeder tubes that extended from larger coherent intrusions and supplied magma to complex zones of magma wet sediment interaction at shallow levels beneath the seafloor syndepositional intrusive activity of this type including formation of abundant peperite probably is a characteristic feature of submarine volcaniclastic sequences developed in proximal island arc settings

early permian volcano sedimentary successions beishan nw china peperites demonstrate an evolving rift basin abstract the lower permian volcano sedimentary zhesi group has been investigated in the hongliuhe and liuyuan areas in beishan china which is significant for the reconstruction of late paleozoic evolution in the southern part of the central asian orogenic belt a variety of volcanic facies were distinguished in the upper zhesi group pillow basalt with interstitial limestone thin interbedded limestone and basalt closely packed pillows pillow fragmented hyaloclastite breccia and peperite laser 40 ar 39 ar whole rock dating of the basalt yielding an age of 277 11 ma as well as early permian brachiopod fossils in the limestone interbedded with the basalt indicate that basalt was erupted in the early permian the identification of the peperite and other facies originating from magma sediment mingling reveals that the basaltic lava flows were derived from autochthonous basaltic magmatism and formed as part of the lower permian succession the peperite also indicates that these subaqueous basaltic lava flows are not dismembered ophiolitic components but formed in an autochthonous extensional setting in the early permian the clastic rocks in the lower zhesi group underlying the basaltic flows and peperites in the hongliuhe and liuyuan areas show a general fining upwards sequence indicating that they were deposited in a progressively deepening basin overlying the devonian hongliuhe suture zone subaqueous volcanism in a rift basin or basins accompanied by coeval deposition of carbonate sediment and mud built up the peperite bearing volcanogenic sedimentary successions from among the various tectonic hypotheses for the beishan region this study demonstrates that by early permian the region was developing post collisional rift basins

comparison between two palaeozoic island arc terranes in northern california eastern klamath and northern sierra nevada geodynamic constraints abstract the palaeozoic geodynamic environment of northern california is considered to be one of offshore island arcs bounded by marginal seas the petrological and geochemical features of the eastern klamath and northern sierra nevada island arc sequences are important indicators of the geodynamic evolution of the cordillera the eastern klamath pre early devonian island arc sequence consists of pillowed basalts andesites and boninites overlain by low k rhyolites both suites erupted in a submarine environment these volcanics characterized by almost flat ree patterns and high nd represent a primitive intraoceanic island arc the mid palaeozoic volcanic succession of northern sierra nevada is formed of calc alkaline rhyolites conformably overlain by either calc alkaline in the north or low k tholeiite in the south basalts and andesites the volcanic episode ended in the early carboniferous with a differentiated shoshonitic suite all the massive or pillowed flows are interbedded with volcaniclastic sediments suggesting that they were erupted partly in a shallow water environment the geochemical features of the volcanics moderate to high lree enrichment and low nd values are evidence for the involvement of a crustal component in the magma genesis the mid palaeozoic volcanic sequence therefore represents a continent based island arc this microcontinent could be the sonomia microplate excluding the eastern klamath plate thus these two northern californian palaeozoic sequences cannot be considered as lateral counterparts but could represent the remnants of oceanic and continental island arcs as observed in the present day east pacific areas along the eurasiatic margin

variation in peperite textures associated with differing host sediment properties peperites formed by mixing of magma and wet sediment are well exposed along punta china baja california mexico where two sills intrude a section of lava flows limestones and volcaniclastic rocks irregular lobes and dikes extend from the sills several meters into host sediments including highly comminuted flow top breccias lithic lapilli tuff breccias and shelly micrites whereas intrusive contacts with lava flows are sharp and planar where one sill intruded both coarse grained volcaniclastic rock and fine grained limestone textural differences between the hosts produced strikingly different styles of peperite blocky masses of the basaltic intrusions up to 1 m in size were dispersed for distances up to 3 m into host lithic lapilli tuff breccias the blocks consequently underwent in situ fragmentation as they were rapidly quenched the high degree of dispersion resulted from steam explosions as the magma enveloped pockets of water in the coarse grained permeable host elutriation of fine grained material from vertical pipes in tuff breccia above the lower sill provides evidence for meter scale fluidization of the host the contact zone between the basaltic magma and the shelly micrite host resembles a mixture of two viscous immiscible fluids fluidal peperite intrusion occurred behind a stable vapor film which entrained lime mud particles and carried them off grain by grain as magma advanced into the host thin section scale elutriation pipes formed microglobular peperite represents a frozen example of a fuel coolant interaction fci between basaltic magma and fluidized micrite host the intimate intermixing of magma and host at the submillimeter level is attributed to fluid instabilities developed along the magma vapor host interface such intimate intermixing of magma and water bearing fragmental debris is commonly a precursory step toward explosive hydrovolcanism

non explosive magma water interaction in a continental setting miocene examples from the eastern cordillera central andes nw argentina the middle upper miocene las burras almagro el toro bat igneous complex within the eastern cordillera of the central andes 24 s nw argentina has revealed evidence of non explosive interaction of andesitic magma with water or wet clastic sediments in a continental setting including peperite generation we describe and interpret lithofacies and emplacement mechanisms in three case studies the las cuevas member 11 8 ma comprises facies related to i andesite extruded in a subaqueous setting and generating lobe hyaloclastite lava and ii marginal parts of subaerial andesite lava dome s in contact with surface water comprising fluidal lava lobes hyaloclastite and juvenile clasts with glassy rims the lampazar member 7 8 ma is represented by a syn volcanic andesite intrusion and related peperite that formed within unconsolidated water saturated coarse grained volcaniclastic conglomerate and breccia the andesite intrusion is finger shaped and grades into intrusive pillows pillows are up to 2 m wide tightly packed near the intrusion fingers and gradually become dispersed in the host sediment 50 m from the parent intrusion the almagro a member 7 2 ma shows evidence of mingling between water saturated coarse grained volcaniclastic alluvial breccia and intruding andesite magma the resulting intrusive pillows are characterized by ellipsoidal and tubular shape and concentric structure the high level penetration of magma in this coarse sediment was unconfined and irregular magma was detached in apophyses and lobes with sharp contacts and fluidal shapes and without quench fragmentation and formation of a hyaloclastite envelope the presence of peperite and magma water contact facies in the bat volcanic sequence indicates the possible availability of water in the system between 11 7 ma and suggests a depositional setting in this part of the foreland basin of the central andes characterized by an overall topographically low coastal floodplain that included extensive wetlands

multi branched horizontal wells for coalbed methane production field performance and well structure analysis abstract horizontal wells such as multi lateral and multi branched horizontal wells mbhws have been effectively used in the development of coalbed methane cbm fields especially for coal beds with very low permeability and low compressive strength in which the performance of conventional fracture stimulated vertical wells is ineffective in this study the performance of mbhws in the liulin block of the ordos basin in central north china is analyzed and compared to that of hydraulically fractured vertical wells the field pilot data show that the gas production rate of most fractured vertical wells decreased rapidly after a short period of time far below expectation while the performance of mbhws is satisfactory and relatively stable during 3 years of production a numerical simulation model was established based on the coal reservoir characteristics the productivities of different well types are predicted and compared to the field data the poor performance of the fractured vertical wells is thought to be caused by the early closure of the fractures and proppant embedded in the coal matrix or by a poor proppant delivery inside the fractures the high and stable productivity of the mbhws is attributed to their large drainage volume and to the stability of the wellbores simulation results show that the parameters of a mbhw such as the branch angle length and spacing can be optimized to maximize its productivity though the drilling cost of a mbhw is relatively high in comparison to vertical wells its high and stable productivity can compensate for the drilling cost therefore mbhws are thought to be more appropriate than vertical wells for the successful exploitation of the cbm resource potential in the liulin block and surrounding area

integration of vertical and in seam horizontal well production analyses with stochastic geostatistical algorithms to estimate pre mining methane drainage efficiency from coal seams blue creek seam alabama coal seam degasification and its efficiency are directly related to the safety of coal mining degasification activities in the black warrior basin started in the early 1980s by using vertical boreholes although the blue creek seam which is part of the mary lee coal group has been the main seam of interest for coal mining vertical wellbores have also been completed in the pratt mary lee and black creek coal groups of the upper pottsville formation to degasify multiple seams currently the blue creek seam is further degasified 2 3 years in advance of mining using in seam horizontal boreholes to ensure safe mining the studied location in this work is located between tuscaloosa and jefferson counties in alabama and was degasified using 81 vertical boreholes some of which are still active when the current long mine expanded its operation into this area in 2009 horizontal boreholes were also drilled in advance of mining for further degasification of only the blue creek seam to ensure a safe and a productive operation this paper presents an integrated study and a methodology to combine history matching results from vertical boreholes with production modeling of horizontal boreholes using geostatistical simulation to evaluate spatial effectiveness of in seam boreholes in reducing gas in place gip results in this study showed that in seam wells boreholes had an estimated effective drainage area of 2050 acres with cumulative production of 604 mmscf methane during 2 years of operation with horizontal borehole production gip in the blue creek seam decreased from an average of 1 52 mmscf to 1 23 mmscf per acre it was also shown that effective gas flow capacity which was independently modeled using vertical borehole data affected horizontal borehole production gip and effective gas flow capacity of coal seam gas were also used to predict remaining gas potential for the blue creek seam

internal structure and emplacement of an upper pliocene dacite cryptodome milos island greece the upper pliocene kalogeros cryptodome is exposed on the northeastern part of milos greece the dacite cryptodome is 800 1300 m across and at least 120 m high it is inferred to have intruded wet unconsolidated pumiceous sediments in a shallow marine environment the kalogeros cryptodome includes five facies the coherent dacite facies 80 vol consists of massive non vesicular dacite and is characterised by radial columnar joints 20 250 cm across the banded dacite facies 15 vol encircles the coherent core and is up to 40 m thick it comprises alternating bands 0 5 4 m thick of pale grey and black dacite the fractured dacite facies less than 1 vol forms an irregular zone 1 3 m thick at the outer margin of the cryptodome the outermost massive dacite breccia facies less than 2 vol consists of blocky to polyhedral dacite clasts 1 40 cm in diameter and is characterised by domains of jigsawfit and clast rotated breccia the stratified dacite breccia 2vol is clast to matrix supported monomictic poorly sorted and composed of dacite clasts up to several metres in diameter the facies association collectively records endogenous growth of a cryptodome that involved a continuous magma supply during a single intrusive phase and simple expansion inflation during emplacement the margins of the kalogeros cryptodome were quench fragmented forming an outer domain of intrusive hyaloclastite and intensely fractured dacite the near solid outer carapace insulated the hotter less viscous interior laminar shear accompanied inflation generating large scale flow banding around the outer part of the core once stagnant concentric isotherms were established within the cryptodome and controlled the orientation of columnar joints cryptodomes are characterised by a well developed internal concentric distribution of distinctive textural domains modest autoclastic breccia and the absence of redeposited autoclastic facies

ridge spotting a new test for pacific absolute plate motion models relative plate motions provide high resolution descriptions of motions of plates relative to other plates yet geodynamically motions of plates relative to the mantle are required since such motions can be attributed to forces e g slab pull and ridge push acting upon the plates various reference frames have been proposed such as the hot spot reference frame to link plate motions to a mantle framework unfortunately both accuracy and precision of absolute plate motion models lag behind those of relative plate motion models consequently it is paramount to use relative plate motions in improving our understanding of absolute plate motions a new technique called ridge spotting combines absolute and relative plate motions and examines the viability of proposed absolute plate motion models we test the method on six published pacific absolute plate motions models including fixed and moving hot spot models as well as a geodynamically derived model ridge spotting reconstructs the pacific farallon and pacific antarctica ridge systems over the last 80 myr all six absolute plate motion models predict large amounts of northward migration and monotonic clockwise rotation for the pacific farallon ridge a geodynamic implication of our ridge migration predictions is that the suggestion that the pacific farallon ridge may have been pinned by a large mantle upwelling is not supported unexpected or erratic ridge behaviors may be tied to limitations in the models themselves or for indo atlantic models discrepancies in the plate circuits used to project models into the pacific realm ridge spotting is promising and will be extended to include more plates and other ocean basins

revision of paleogene plate motions in the pacific and implications for the hawaiian emperor bend reply understanding the relative motion between the pacific plate and its neighboring plates in the paleogene has important consequences for deciphering the relationship between absolute and relative plate motions in the pacific ocean basin the history of circum pacific subduction and the cause of the hawaiian emperor bend heb we quantitatively model the farallon vancouver pacific antarctic seafloor spreading history from 67 to 33 ma based on a comprehensive synthesis of magnetic anomaly and fracture identifications we find a well constrained increase from 75 5 mm yr to 101 5 mm yr in pacific farallon full spreading rates between 57 6 ma and 55 9 ma followed by a stepwise increase to 182 2 mm yr from 49 7 to 40 1 ma the increases in pacific farallon spreading rates are not accompanied by any statistically significant change in spreading direction the 57 6 55 9 ma surge of pacific farallon spreading reflects an eastward acceleration in farallon plate motion as it precedes west pacific subduction initiation and is not associated with any significant change in pacific antarctic spreading we interpret the increase in pacific farallon spreading rates after ca 50 ma as a consequence of further acceleration in farallon plate motion we find no indication of a major change in pacific plate absolute motion at this time our model suggests that changes in relative motion direction between the pacific and farallon and pacific and antarctic plates were insignificant around the formation time of the heb ca 47 5 ma and the bend is largely a consequence of hawaiian hotspot motion which ceased rapid motion after 47 ma

current status and geological conditions for the applicability of cbm drilling technologies in china a review abstract coalbed methane cbm drilling technology is critical in achieving efficient cbm development the geological conditions for cbm development in china are complex including special terrain high rank coal areas deep coal seams multiple superposed coal seams and coal measure gas symbiosis areas steeply inclined coal seam areas and tectonic coal seam areas therefore it is critical to apply the optimum drilling technology in each different area this paper first reviews the current cbm drilling technologies and gas production behaviors in china it is found that although vertical wells and cluster well groups are common well types for cbm development in china u v and l shaped horizontal wells and multilateral horizontal wells have been favored for cbm development in recent years the paper then discusses the applicability of different well types to geological conditions and proposes a modification method for well design in various geologic conditions this method uses the coal structure ro in situ stress and ratio of critical desorption pressure to the reservoir pressure as the main inputs

peperite formed by lava flows over sediments an example from the central parana continental flood basalts brazil pahoehoe flows interbedded with sediments have been identified in the superior portion of parana continental flood basalts pcfb west portion of parana state southern brazil in the study area peperites are generated by the interaction between lava flows and wet lacustrine sediments silt and clay evidence that the sediments were unconsolidated or poorly consolidated and wet when the lava flowed over them includes vesiculated sediment sediment in vesicles and fractures in lava flow and in juvenile clasts in the peperite and soft sediment deformation hydrodynamic mingling of lava and wet sediments coarse mingling is predominant and volcanic rocks and textures related to explosive phase of molten fuel coolant interaction mfci are not observed in study area locally centimeter sized areas display direct contact between ash sized juvenile clasts and sediments formed by the collapse of a vapor film the textures of fluidal peperites in the central pcfb indicate that the relevant factors that led to a coarse mingling between lava sediment are 1 lava properties low viscosity 2 fine grained unconsolidated or poorly consolidated wet sediment and 3 a single episode of interaction between lava flows and sediment

extrapolating oceanic age distributions lessons from the pacific region abstractextrapolation of the age distribution of oceanic lithosphere has played a significant role in assessments of variations in global mean spreading rate global mean ocean basin depth and implications for global mean sea level subduction has already removed 50 of oceanic lithosphere younger than 55 7 ma making some level of extrapolation a necessary part of global plate reconstructions an area equal in size to the pacific basin oceanic lithosphere must be extrapolated for ages older than 29 1 ma three modes of extrapolation are identified mode 1 extrapolation uses the preserved history as recorded on one plate to infer the history of the previously adjacent plate this mode of extrapolation is exemplified by the inferred history of the farallon vancouver nazca and cocos plates relative to the pacific plate on which this record is preserved mode 2 involves extrapolation beyond the preserved age extent of a given ridge system no observable data exist that directly constrain the motions bey

creation of the cocos and nazca plates by fission of the farallon plate abstract throughout the early tertiary the area of the farallon oceanic plate was episodically diminished by detachment of large and small northern regions which became independently moving plates and microplates the nature and history of farallon plate fragmentation has been inferred mainly from structural patterns on the western pacific plate flank of the east pacific rise because the fragmented eastern flank has been subducted the final episode of plate fragmentation occurred at the beginning of the miocene when the cocos plate was split off leaving the much reduced farallon plate to be renamed the nazca plate and initiating cocos nazca spreading some oligocene farallon plate with rifted margins that are a direct record of this plate splitting event has survived in the eastern tropical pacific most extensively off northern peru and ecuador small remnants of the conjugate northern rifted margin are exposed off costa rica and perhaps south of panama marine geophysical profiles bathymetric magnetic and seismic reflection and multibeam sonar swaths across these rifted oceanic margins combined with surveys of 30 20 ma crust on the western rise flank indicate that i localized lithospheric rupture to create a new plate boundary was preceded by plate stretching and fracturing in a belt several hundred km wide fissural volcanism along some of these fractures built volcanic ridges e g alvarado and sarmiento ridges that are 1 2 km high and parallel to absolute farallon plate motion they closely resemble fissural ridges described from the young western flank of the present pacific nazca rise ii for 1 2 m y prior to final rupture of the farallon plate perhaps coinciding with the period of lithospheric stretching the entire plate changed direction to a more easterly nazca like course after the split the northern cocos part reverted to a northeasterly absolute motion iii the plate splitting fracture that became the site of initial cocos nazca spreading was a linear feature that at least through the 680 km of ruptured oligocene lithosphere known to have avoided subduction did not follow any pre existing feature on the farallon plate e g a fracture zone trail of a transform fault iv the margins of surviving parts of the plate splitting fracture have narrow shoulders raised by uplift of unloaded footwalls and partially buried by fissural volcanism v cocos nazca spreading began at 23 ma reports of older cocos nazca crust in the eastern panama basin were based on misidentified magnetic anomalies there is increased evidence that the driving force for the 23 ma fission of the farallon plate was the divergence of slab pull stresses at the middle america and south america subduction zones the timing and location of the split may have been influenced by i the increasingly divergent northeast slab pull at the middle america subduction zone which lengthened and reoriented because of motion between the north america and caribbean plates ii the slightly earlier detachment of a northern part of the plate that had been entering the california subduction zone contributing a less divergent plate driving stress and iii weakening of older parts of the plate by the galapagos hotspot which had come to underlie the equatorial region midway between the risecrest and the two subduction zones by the late oligocene

a 65 ma palaeomagnetic pole for the pacific plate from the skewness of magnetic anomalies 27r 31 s u m m a r y we use the skewness of seafloor spreading magnetic anomalies 27r 31 to determine a revised late maastrichtian early palaeocene palaeomagnetic pole for the pacific plate we used numerical experiments to estimate the potential information in magnetic profiles that had not been previously analysed for skewness information the results indicated that profiles obtained between the murray and galapagos fracture zones would be the most useful because in this region very different values of remanent magnetic effective inclination are predicted for small changes in the assumed palaeomagnetic pole position furthermore these data would constrain the pole in the direction most poorly constrained by prior data using 50 skewness estimates from 17 profiles we compute a well constrained pole that agrees with a pole computed from other types of data with similar ages these other data include a seamount palaeomagnetic pole effective inclinations from two submarine ridges palaeolatitudes determined from azimuthally unoriented cores of submarine basalt and from a piston core in deep sea sediments two palaeo equators from equatorial sediment facies and amplitude data from magnetic lineations combining all the data we determine a best fit 65 ma palaeomagnetic pole for the pacific plate that is focated at 71 6 n 7 9 8 the 95 per cent confidence ellipse for the new pole a 2 9 major semiaxis oriented 75 clockwise of north and a 1 8 minor semiaxis is 50 per

carson pass kirkwood paleocanyon system paleogeography of the ancestral cascades arc and implications for landscape evolution of the sierra nevada california tertiary strata of the central sierra nevada are dominated by widespread voluminous volcanic breccias that are largely undivided and undated the origin of which is poorly understood these dominantly andesitic strata are interpreted to be eruptive products of the ancestral cascades arc deposited and preserved within paleocanyons that crossed the present day sierra nevada before basin and range faulting began there these strata are thus important not only for understanding the paleogeography of the ancestral cascades arc but also for reconstructing the evolution of the sierra nevada landscape our regional scale mapping shows that paleocanyon fills of the central sierra nevada are dominated by intrusions and vent proximal facies along the present day sierran crest with more distal facies extending westward down the paleocanyons vent proximal facies consist of lava domes that collapsed to generate block and ash flow tuffs which in turn were remobilized down canyon to produce coarse grained volcanic mudflow and dilute flow fluvial deposits lava flows are rare instead magmas invaded wet volcaniclastic sediment to form in situ peperite piles that were partly remobilized to form debris flows or block and ash flows with peperite domains detailed mapping and dating of previously undifferentiated tertiary strata in the carson pass kirkwood area of the central sierra nevada has allowed us to identify 6 unconformity bounded sequences preserved within a paleocanyon as deep as 650 m cut into mesozoic granitic basement the carson pass kirkwood paleocanyon trends ne sw with a paleo transport direction roughly parallel to the modern mokelumne river drainage toward the sw sequence 1 consists of oligocene silicic ignimbrites sourced from nevada sequences 2 through 6 consist of dominantly andesitic rocks of the miocene ancestral cascades arc with 40 ar 39 ar ages ranging from 14 69 0 06 ma to 6 05 0 12 ma these new dates provide constraints on the ages of unconformities vertical relief on the unconformities within the paleocanyon ranges from 12 to 303 meters with paleoslope gradients range from 3 to 48 no evidence exists for widening or deepening of the paleocanyon into mesozoic basement during tertiary time so we infer that unconformity 1 the paleocanyon floor and walls was inherited from cretaceous time the deepest unconformities within the paleocanyon fill reincised into granitic basement in the early miocene unconformity 2 between 14 and 10 ma unconformity 5 and between 10 and 6 ma unconformity 6 the paleocanyon was also beheaded cut off from sources to the east by ca 10 ma we suggest that the early miocene reincision records tectonism related to the onset of arc magmatism in the sierra nevada the middle miocene reincision may record the onset of basin and range faulting in the central sierra the late miocene reincision may correspond to uplift attendant with the northward sweep of the triple junction through the latitude of the central sierra paleocanyons of the central sierra differ from those of the northern and southern sierra by showing steeper local paleorelief and the bouldery stream deposits attest to higher axial gradients than envisioned for other parts of the range this may indicate that the uplift history of the range is not uniform from segment to segment

the uncertainties of finite rotations in plate tectonics incomplete knowledge of the pattern of magnetic lineations and fossil transform faults represented by sea floor spreading data on two plates generated by the same spreading center leads to uncertainties in a reconstruction of the past relative configuration of the plates a reconstruction may be represented by the finite rotation that describes one configuration relative to another in this paper a method of reconstruction is provided that reflects the uncertainties in the data the method minimizes a weighted least squares measure of fit as a function of the rotation parameters for a given rotation the measure of fit represents the sum of squares of the weighted distances of fixed and rotated data points representing corresponding former plate margin segments from a common plate margin the common margin is estimated from the locations of both fixed and rotated data points the estimated margin consists of a set of great circle arcs it is shown how the method of reconstruction may be utilized to obtain an uncertainty region for the pole and angle of rotation that characterize the finite rotation these techniques are then used to study the uncertainties of reconstructions in the south pacific for the times of anomalies 13 and 18 the best fit reconstructions and the uncertainty region for the anomaly 18 pole are in good agreement with previous work however the uncertainties in the anomaly 13 pole were substantially underestimated by previous investigators

recent tectonic plate decelerations driven by mantle convection 1 we explore recent changes in tectonic plate velocities using a model of mantle flow that is based on a new high resolution global tomography model derived from simultaneous inversions of global seismic geodynamic and mineral physical data sets this plate coupled mantle convection model incorporates a viscosity structure that reconciles both glacial isostatic adjustment and global convection related data sets the convection model successfully reproduces present day plate velocities and global surface gravity and topography constraints we predict time dependent changes in mantle buoyancy that give rise to present day decelerations of several major plates in particular the fast moving pacific and nazca plates we verify the plausibility of these predicted plate decelerations using space geodetic and oceanic magnetic anomaly constraints on tectonic plate motions these plate kinematic constraints are employed to determine a new global map of present day plate decelerations that agree well with the mantle flow predictions

the use of numerical simulation in predicting coalbed methane producibility from the gates coals alberta inner foothills canada comparison with mannville coal cbm production in the alberta syncline abstract two medium to low volatile bituminous rank coals in the lower cretaceous gates formation mannville equivalent inner foothills of alberta were cored as part of a coalbed methane exploration program the target seams seam 4 and seam 10 were intersected at 652 m and 605 m respectively the coals were bright banded relatively competent and reasonably cleated with cleat spacing between 5 20 mm the fmi formation micro imaging log identified two primary fracture directions corresponding to both face and butt cleats which were developed almost equally in some coal intervals the amount of shearing was limited in spite of the presence of numerous thrust faults and fold structures in the corehole vicinity total gas content was high with an average of 17 7 cm 3 g arb 568 1 scf t an adsorption isotherm of the thick seam 4 showed gas saturation levels of 90 at in situ reservoir conditions methane content was 92 96 and carbon dioxide levels were less than 2 isotopic studies on the methane confirmed the thermogenic origin of the gas as anticipated based on the coal rank the coal seams were fracture stimulated using 50 50 nitrogen and fresh water along with 9 to 12 tons of 12 20 mesh sand used as a proppant it is believed that the coals were not stimulated properly because of the small proppant volume and the complex and often unpredictable fracture pattern in coals particularly in the inner foothills region that has high stress anisotropy an injectivity test showed coal absolute permeability to be less than 1 md the skin to be 2 indicating a slightly damaged coal and water saturation in the cleats to be 90 a four month production test was conducted gas rates declined from 930 to 310 m 3 d 33 to 11 mcfd and water rates were low constructive interference in depressurizing the coal reservoirs and accelerating gas production over short periods of time was demonstrated coal quality data from a nearby underground mine shows that drilling horizontal wellbores in the gates coals would be challenging because of unfavourable geomechanical properties such as low cohesion and unconfined compressive strength values and structural complexity

a method to predict geomechanical properties and model well stability in horizontal boreholes abstract a methodology is proposed to quickly assess the stability risk for horizontal wells drilled in coal seams the first task involves the estimation of strength and deformation parameters of the coal by indirect methods such as the use of core description to assign a geological strength index gsi the second task involves the use of a finite element analysis called flac to investigate factors such as the depth of fluid penetration while drilling the horizontal well and the stability of the wellbore during simulated production these two factors are important because coal fines generated by the drill bit action are carried by the drilling fluid into the cleat system of the coal thereby plugging the permeability pathways and causing formation damage on the other hand a wellbore that may become unstable during pressure drawdown would require a perforated or slotted production liner in this study the conditions of drilling and production necessary for a stable horizontal well drilled into a mannville coal seam at 750 800 m in the central alberta plains were studied modeling showed that the depth of fluid penetration would be at least 2 2 m if there is no filter cake formation while drilling underbalanced drilling fluid penetration would be minimal if a filter cake is formed under overbalanced conditions furthermore flac analysis showed that drilling a smaller diameter hole 5 cm would be preferable because this size results in a stable wellbore during production compared to the standard 15 cm diameter hole