the central and northern appalachian basin a frontier region for coalbed methane development abstract the appalachian basin is the world s second largest coalbed methane cbm producing basin it has nearly 4000 wells with 1996 annual production at 147 8 billion cubic feet bcf cumulative cbm production is close to 0 9 trillion cubic feet tcf the black warrior basin of alabama in the southern appalachian basin including a very minor amount from the cahaba coal field accounts for about 75 of this annual production and about 75 of the wells and the remainder comes from the central and northern appalachian basin the southwest virginia coal field accounts for about 95 of the production from the central and northern parts of the appalachian basin production data and trends imply that several of the appalachian basin states except for alabama and virginia are in their infancy with respect to cbm development total in place cbm resources in the central and northern appalachian basin have been variously estimated at 66 to 76 trillion cubic feet tcf of which an estimated 14 55 tcf 20 is technically recoverable according to a 1995 u s geological survey assessment for comparison in the black warrior basin of the 20 tcf in place cbm resources 2 30 tcf 12 is technically recoverable because close to 0 9 tcf of cbm has already been produced from the black warrior basin and the proved reserves are about 0 8 tcf for 1996 energy information administration eia 1997 u s crude oil natural gas and natural gas liquids reserves 1996 annual report u s department of energy doe eia 0216 96 145 pp these data imply that the central and northern appalachian basin could become increasingly important in the appalachian basin cbm picture as cbm resources are depleted in the southern appalachian basin black warrior basin and cahaba coal field cbm development in the appalachian states could decrease the eastern u s a s dependence on coal for electricity cbm is expected to provide over the next few decades a virtually untapped source of unconventional fossil fuel in the appalachian states where the cbm resources are large and the demand for cleaner fossil fuel energy is high

state of strain in a quartzite mylonite central australia abstract the finite strain due to mylonitization of a quartzite has been determined using measurements of deformed quartz grains and ribbons developed from quartz grains equant before the deformation the mylonites are developed in long narrow steeply dipping mylonite zones within the chewings range quartzite of central australia this quartzite is very pure 98 quartz the quartzite surrounding the mylonite zones appears unstrained the samples examined exhibit severe flattening strains k values of between 0 01 and 0 12 and r values of between 5 and 30 have been determined application of formulae to calculate volume change assuming the model of an ideal ductile deformation band structure indicate significant apparent volume losses with values between 0 69 and 0 95 such values seem unreasonably high as no geological evidence for large volume loss is seen the band structure model is considered inapplicable for these mylonite zones the observed structural features can best be explained by a deformation history involving severe bulk shortening normal to the zones

the limitations of three dimensional kinematic vorticity analysis abstract the kinematic vorticity number wk can be calculated for three dimensional as well as two dimensional geologic deformations for steady state deformations wk can be correlated to and analyzed in terms of finite strains the analysis shows that assumptions commonly made for two dimensional deformations are not applicable to three dimensional deformations a single wk describes an infinite number of three dimensional deformations further even knowledge of flow apophyses orientation instantaneous stretching axes orientation and or wk are not sufficient to describe deformation three dimensional deformations also require knowledge of the deformation type or boundary conditions of deformation e g transpression hence in addition to being difficult to estimate the value of knowing wk for three dimensional deformations is greatly reduced compared with plane strain the most useful methods of determining wk from naturally deformed rocks are presented

seal evaluation and confinement screening criteria for beneficial carbon dioxide storage with enhanced coal bed methane recovery in the pocahontas basin virginia abstract the geological storage of carbon dioxide in appalachian basin coal seams is one possible sink for sequestration of greenhouse gases with the added benefit of enhanced coal bed methane ecbm recovery the pocahontas basin part of the central appalachian basin of southwestern virginia is a major coal bed methane cbm province with production mostly from coal beds in the lower pennsylvanian pocahontas and new river formations as part of the southeast regional carbon sequestration partnership s phase ii research program a co 2 injection demonstration well was installed into lower pennsylvanian coal bed methane producing strata in southwest virginia samples of siliciclastic lithologies above coal beds in this oakwood field well and from several other cores in the nora field were taken to establish a baseline of the basic confinement properties of overlying strata to test seal competency at local and regional scales strata above cbm producing coal beds in the pocahontas and new river formations consist of dark gray shales silty gray shales heterolithic siltstones sandstones and shales lithic sandstones and quartzose sandstones standard measurements of porosity permeability and petrography were used to evaluate potential leakage hazards and any possible secondary storage potential for typical lithologies both lithic and quartz rich sandstones exhibit only minor porosity with generally low permeability 2 ecbm traps one of the most promising confining intervals above the major coal bed methane producing interval is the hensley shale member analyses of 1500 geophysical logs in southwest virginia indicate that this unit is moderately thick 50 ft 15 m laterally continuous 3000 km 2 and a homogenous shale which coarsens upward into siltstone and sandstone or is truncated by sandstone calculations from two mercury injection capillary porosimetry tests of the shale indicate that a displacement entry pressure of 207 psi 1427 kpa would generate an estimated seal capacity of 1365 ft 416 m of co 2 before buoyant leakage scanning electron microscopy indicates a microfabric of narrow pore throats between quartz grains floating in a clay matrix modeled median pore throat size between micro fabric matrix grains for the shale is estimated at 0 26 m these characteristics indicate that the shale where fractures and joints are limited would be an adequate regional confining interval for deeper co 2 storage with ecbm

three dimensional reference deformations and strain facies abstract in an attempt to categorize three dimensional deformations the concepts of kinematic axes three dimensional reference deformations and strain facies are utilized we have chosen 12 reference deformations each being an idealized end member of deformation involving a simultaneous combination of a three dimensional coaxial component constriction flattening or pure shear and an orthogonal simple shear component velocity and displacement fields infinitesimal deformation parameters and finite deformation parameters can be calculated for each reference deformation assuming steady state deformation there are three possibilities for the orientation of foliation and three possibilities for the orientation of lineation depending on the relative contributions of the coaxial and non coaxial components the six emerging combinations of foliation and lineation orientations each give rise to a characteristic strain facies each of the strain facies is correlated to the reference deformations and thus deformation parameters which caused its formation however since the coaxial deformation component accumulates more effectively than the non coaxial component a change from one strain facies to another i e a change in the orientation of lineation or foliation is possible during steady state deformation the strain facies emphasize the boundary conditions of deformation and together with the reference deformations provide a framework for three dimensional deformations

alleghanian tectono thermal evolution of the dextral transcurrent hylas zone virginia piedmont u s a abstract the hylas zone is the northernmost segment of the eastern piedmont fault system and lies in the grenville goochland terrane virginia like the other major segments the nutbush creek zone the hollister zone and the modoc irmo zone the hylas zone experienced late paleozoic dextral transcurrent shearing early deformation in the zone was ductile and produced type i and type ii s c mylonites under amphibolite grade metamorphic conditions later deformation was at the brittle ductile transition at which time feldspar underwent microfaulting and cataclasis while quartz formed ribbons the feldspar exhibits a strain dependent sequence of microstructures including kink bands antithetic extensional microfaults pull apart bends in the microfaults by development of transverse fractures and microboudinage correlation of mineral mechanical response with a thermal decay curve based on isotopic mineral ages yields a temporally constrained deformation history ductile dextral shearing occurred subsequent to the intrusion of the 330 ma petersburg granite and passed into the brittle ductile transition by approximately 260 ma dextral faulting terminated before 240 ma the appalachian dextral transcurrent faulting event therefore continued through permian in some areas

the generation of ductile and brittle shear bands in a low angle mylonite zone in the saint barthelemy massif french pyrenees a ductile thrust zone developed in gneisses during retrogression from lower amphibolite facies conditions to the upper greenschist facies the last major structures formed in the zone are isolated shear bands divided into three types anastomosing inhomogenous ultramylonitic shear bands type i are subparallel to the mylonitic foliation in the gneiss sg most of these bands developed by ductile deformation processes only planar homogeneous ultramylonite bands type ii are usually oblique to sg they generated as pseudotachylyte bands by brittle fracturing and underwent strong subsequent ductile deformation type iii shear bands are planar and oblique to sg they consist of pseudotachylyte weakly affected by ductile deformation type i ii and iii bands seem to represent progressively younger structures on a local scale linked to falling p t conditions the systematic variation in orientation of the different shear bands with respect to sg is interpreted as being due to a different response of brittle and ductile structures to the orientation of the kinematic frame and the rock anisotropy

deformation path partitioning within a transpressive shear zone marble cove newfoundland detailed study of the structures in marble cove newfoundland indicates that they formed during a single transpressional event during which deformation was partitioned between dominantly strike slip and dominantly dip slip domains marble cove exhibits steeply dipping foliations steeply to shallowly plunging stretching lineations greenschist facies mineral assemblages and abundant quartz veins within the broad domain where stretching lineations plunge steeply sense of shear indicators and asymmetry of quartz c axis distributions in mylonitized quartz veins indicate dominantly reverse motion with a component of dextral shear adjacent greenschists exhibit orthorhombic symmetry and apparently accommodated pure shear the abrupt transition to a narrow high strain domain of shallowly plunging stretching lineations is accommodated by a rheologically distinct serpentinite body shear bands in this domain indicate dextral strike slip movement with a reverse component smaller conjugate shear bands are evident in thin section indicating a component of pure shear sense of shear indicators and asymmetry of c axis distributions in mylonitized quartz veins also record dextral strike slip and reverse shear with a component of pure shear crenulations and asymmetric folds in foliation overprint all other fabrics in marble cove and record a final phase of reverse shear with a dextral component with partitioning of this kind structures recording strike slip movement may be limited in areal extent and therefore less likely to be exposed than structures recording dip slip motion such partitioning within transpressional shear zones may therefore impede recognition of strike parallel motions within orogenic belts

the eigenvalues of steady flow in mohr space abstract the eigenvalues of the velocity gradients tensor and of the position gradients tensor describing instantaneous flow or incremental deformations are easily determined in mohr space as the points of intersection between a mohr circle and the horizontal mohr axis intersections occur only if the tensor has real eigenvalues eigenvectors associated with the eigenvalues are directions of no rotation a line of material particles under an eigenvector does not rotate during steady flow although the line is instantaneously stretching at a rate equal to its corresponding eigenvalue for non spinning steady sub simple shearing there will always be two eigenvectors the angle between the eigenvectors is dependent on the ratio of pure to simple shearing rates this angle decreases as the pure shearing component decreases relative to the simple shearing component superimposed increments of pure shear and simple shear produce an equivalent set of non rotated material lines but the deformation histories of these lines are rotational the influence of eigendirections on geological structures is constrained by the rheology of a rock during deformation in homogenous steady flow no influence may be obvious spatially periodic material softening along eigenvectors during bulk hardening may result in a complex fabric of intersecting shear zones the geometry of the fabric elements provides important information on the bulk deformation of the rock particularly on the bulk shear sense

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

middle proterozoic age for the montpelier anorthosite goochland terrane eastern piedmont virginia uranium lead dating of zircons from the montpelier anorthosite confirms previous interpretations based on equivocal evidence that the goochland terrane in the eastern piedmont of virginia contains grenvillian basement rocks of middle proterozoic age a very few prismatic elongate euhedral zircons which contain 12 29 ppm uranium are interpreted to be igneous in origin the vast majority of zircons are more equant subangular to anhedral contain 38 52 ppm uranium and are interpreted to be metamorphic in origin one fraction of elongate zircon and four fragments of a very large zircon occurring in a nelsonite segregation yield an upper intercept age of 1045 10 ma interpreted as the time of anorthosite crystallization irregularly shaped metamorphic zircons are dated at 1011 2 ma weighted average of the 207pb 206pb ages the u pb isotopic systematics of metamorphic titanite were reset during the alleghanian orogeny at 297 5 ma these data provide a minimum age for gneisses of the goochland terrane that are intruded by the anorthosite middle proterozoic basement rocks of the goochland terrane may be correlative with those in the shenandoah massif of the blue ridge tectonic province as suggested by similarities between the montpelier anorthosite and the roseland anorthosite although the areal extent of middle proterozoic basement and basement cover relations in the eastern piedmont remain unresolved results of this investigation indicate that the goochland terrane is an internal massif of laurentian crust rather than an exotic accreted terrane

coalbed methane resources of the appalachian basin eastern usa abstract in 2002 the u s geological survey usgs assessed the technically recoverable undiscovered coalbed gas resources in the appalachian basin and black warrior basin assessment provinces as about 15 5 trillion cubic feet although these resources are almost equally divided between the two areas most of the production occurs within relatively small areas within these provinces where local geological and geochemical attributes have resulted in the generation and retention of large amounts of methane within the coal beds and have enhanced the producibility of the gas from the coal in the appalachian basin coalbed methane cbm tests are commonly commercial where the cumulative coal thickness completed in wells is greater than three meters 10 ft the depth of burial of the coal beds is greater than 100 m 350 ft and the coal is in the thermogenic gas window in addition to the ubiquitous cleating within the coal beds commercial production may be enhanced by secondary fracture porosity related to supplemental fracture systems within the coal beds in order to release the methane from microporus coal matrix most wells are dewatered prior to commercial production of gas two total petroleum systems tps were defined by the usgs during the assessment the pottsville coal bed gas tps in alabama and the carboniferous coal bed gas tps in pennsylvania ohio west virginia eastern kentucky virginia tennessee and alabama these were divided into seven assessment units of which three had sufficient data to be assessed production rates are higher in most horizontal wells drilled into relatively thick coal beds than in vertical wells recovery per unit area is greater and potential adverse environmental impact is decreased

ages of regional metamorphism and ductile deformation in the central and southern appalachians abstract a summary of available geochronology of deformational fabrics formed at greenschist and higher grades in the central and southern appalachians is presented as a map showing the ages of regional metamorphism and ductile deformation the ca 480 435 ma taconic event affected most of the piedmont and blue ridge provinces the ca 380 340 ma acadian event was milder and was centered in the west central piedmont and eastern blue ridge the 330 230 ma alleghanian event exhibits an abrupt ductile deformation front in the eastern piedmont and extends an unknown distance eastward below the atlantic coastal plain

the hyco shear zone in north carolina and southern virginia implications for the piedmont zone carolina zone boundary in the southern appalachians the recently recognized hyco shear zone is a first order structure in the southern appalachians that separates sharply contrasting rocks of the carolina and milton terranes in north central north carolina and southern virginia traditionally this boundary has been viewed as a comformable contact between infrastructural milton rocks and suprastructural carolina rocks in contrast our work indicates that shallowly dipping sillimanite gneisses of the milton terrane comprise the footwall of the ductile shear zone whereas moderately to steeply dipping greenschist to amphibolite facies carolina terrane gneisses and metavolcanics form the hangingwall the hyco shear zone has a sharply arcuate surface trace it trends east northeast in the area of hyco lake north carolina and abruptly changes trend to north northeast near the north carolina virginia state line the zone is moderately to steeply south southeast dipping along the hyco lake segment and structures there indicate dominantly dextral strike slip along the virginia segment the zone is moderately to shallowly east dipping with structures indicating thrusting of the carolina terrane over the milton terrane timing constraints on synkinematic plutons indicate that the shear zone is an early alleghanian feature the geometry kinematics and timing of the shear zone are compatible with the interpretation that the hyco lake and virginia segments of the zone represent lateral and frontal ramps respectively in an overall alleghanian thrust regime recognition of the shear zone in conjunction with geological geophysical and isotopic contrasts across the zone negates established views that the milton rocks are a comformable higher grade portion of the carolina terrane these contrasting features instead are remarkably similar to those found along the central piedmont suture the tectonic boundary between the piedmont and carolina zones from south carolina to central north carolina we propose that the hyco shear zone is the northern equivalent of this structure thus our new data on the hyco shear zone have significant regional implications concerning the nature timing and kinematics of this zone boundary

kinematic vorticity and strain rate patterns associated with ductile extrusion in the chelmos shear zone external hellenides greece abstract kinematic vorticity strain rate finite strain and structural data have been used to describe the heterogeneous nature of ductile deformation in an extruding crustal scale shear zone the chelmos shear zone csz of the external hellenides the csz has a curved shape which is marked by a frontal flat and a steep zone the spatial variation in the kinematic vorticity number is strongly correlated with the geometry and the structural depth of the shear zone the pure shear component of deformation decreases from back to front and from top to bottom the ductile thinning normal to the shear zone s boundaries is higher in the steep zone and decreases westwards quartz grain size and strain rate in the csz is distributed into two approximately homogeneous domains the higher strain rate is recorded in the steep zone and the base of the frontal flat zone with lower rates in the upper parts of the frontal flat zone based on mesoscopic structural data and the spatial distribution of the shear strain rate the existence of a west dipping back flow zone in the boarder zone between these two domains is inferred the overall pattern of deformation in the csz implies that tectonic extrusion from the steep zone occurred at the final stages of ductile deformation and was associated with the formation of the backflow zone in the front of the shear zone ductile deformation of rocks probably started close to simple shear on a planar low angle shear zone progressively became penetrative and more general shear occurred as the csz steepened up this progressive increase in pure shearing may have occurred in a heterogeneous manner and was higher close to both the eastern margin of the steep zone and the top of the frontal flat zone solid state extrusion in the csz was also associated with a heterogeneous and progressive increase in strain rate

geology and coal bed methane resource potential of the gondwana barapukuria coal basin dinajpur bangladesh abstract with an area of 5 16 km2 the barapukuria coal deposit is one of the five largest gondwana coal basins in bangladesh and is located in the north west of the country close to the towns of dinajpur and saidpur the existence of the basin was initially indicated by a negative gravity anomaly in oil and gas exploration exploration for the deposit was commenced by the geological survey of bangladesh gsb with seven surface boreholes that confirmed the existence of a significant coal deposit the deposit occurs as an asymmetrical synclinal structure with an axis striking approximately n s the deposit is limited to the east by a large normal fault which has displaced archaean metamorphics against the gondwana sediments the coal bearing sediments are comprised of gondwana permian age sandstones siltstones subordinate carbonaceous shales and six correlated coal seams the gondwana sediments are unconformably overlain by tertiary and quaternary deposits against which the coal seams are successively subcropped to the west within the structural limits of the basin approximately 377 mt coal in situ has been quantified in the six coal seams that range in depth from 118 to 518 m below surface due to the synclinal nature of the deposit the upper coal seams designated i to v occur over diminishing areal extent with decreasing depth the principal seam of interest is the lowermost seam vi with a variable thickness across the deposit from 22 m in the northern part of the deposit to more than 42 m in the southern and eastern areas development of the barapukuria mine the country s first coal mine commenced in 1996 with the construction of two vertical shafts coal production from seam vi began in 2005 and continues at the present time seam vi coal is high volatile b bituminous rank about 34 mt of coal has been estimated as recoverable resources utilising descensional multi slice longwall mining the mine design and development have been severely constrained by adverse seam gradients and the presence of the overlying water bearing tertiary dupi tila sediments the potential of coal bed methane extraction has been investigated as an alternative to underground mining the study considers the barapukuria deposit in terms of its geological structure geothermal gradient and the rank porosity and permeability of the coal seams as determined by several phases of exploration of the area the methane content of the bituminous coal at barapukuria varies within the range 6 51 12 68 m3 t representing a potential resource of more than 5 gm3 of gas

kinematic significance of l tectonites in the footwall of a major terrane bounding thrust fault klamath mountains california usa abstract detailed geologic mapping cross section reconstructions strain analyses and kinematic analyses enable the reconstruction of a one kilometer wide domain of l tectonites in the east west striking subhorizontal to gently south dipping pigeon point high strain zone pphsz associated with a major thrust fault separating oceanic and arc affinity terranes in the klamath mountains california l tectonites are associated with 1 a convex upward warp of the upper high strain zone boundary 2 a transition from mafic metavolcaniclastic rocks to micaceous quartzites 3 folds subparallel with mineral lineations 4 emplacement of synkinematic ultramafic mafic intrusive bodies and 5 a local temperature increase from greenschist to amphibolite facies conditions pure shear dominated deformation accommodated zone normal shortening and transport parallel elongation coupled with subordinate top to the west directed thrust style simple shear l tectonite formation was controlled by the shape of the high strain zone boundary driving lateral flow into the apex of the lens shaped zone in response to a favorable kinematic geometry and bulk strain in the constrictional field localized magmatic heating best explains the shape of the high strain zone boundary but l tectonites are not partitioned into a single rheological domain during terrane amalgamation strain path partitioning occurred with localized top to the west directed simple shear partitioned into a structurally overlying thrust zone and pure shear dominated subvertical shortening and transport parallel elongation partitioned into the pphsz

appalachian carboniferous dextral strike slip faults an example from brookneal virginia the northern appalachian dextral fault system of late paleozoic age is also present in the central and southern appalachians an example of a dextral strike slip fault is the 4 km wide brookneal shear zone in the southwest virginia piedmont the shear zone is in part superimposed on the melrose granite where an s c mylonite was produced by dynamic recrystallization of all constituent minerals the arvonia metasedimentary and charlotte belt metavolcanic rocks contain spaced dextral shear bands at a consistent 24 3 to the shear zone boundary a minimum displacement estimate of 17 km was obtained from rotated foliation measurements in the melrose granite the age of movement on the brookneal shear zone has been constrained by isotopic dating to between 324 and 300 ma other faults in the southern appalachians including the nutbush creek and modoc zones show similar ages and relative offsets possible plate tectonic models that could account for the late paleozoic dextral fault system throughout the appalachians include 1 tectonic escape resulting from the collision of a plate with north america to the north of the canadian appalachians 2 postcollision interplate readjustments involving counterclockwise rotation of africa relative to north america and 3 oblique convergence of eastern north america with an oceanic plate moving west

kinematics of rock flow and the interpretation of geological structures with particular reference to shear zones abstract current interpretations of structures are generally based on homogeneous and steady deformation models despite the fact that both the heterogeneity of rocks materially rheologically and geometrically and the time dependence of imposed geological conditions give rise to significant heterogeneous and non steady flow in concert with field observations we emphasize that the expectation of heterogeneity and non steadiness is the key to understanding natural deformation and that in order to carry out successful structural analysis and tectonic interpretation it is necessary to recognize the first order distinction between imposed boundary conditions typically used to define the tectonic regime e g transcurrent transpression and the response recorded by rocks within the zone structures and fabrics using s c fabric as an example it is demonstrated how flow with a non zero spinning component resulting from the rheological contrasts and or geologically realistic time dependent boundary displacement can drastically change the ideal geometric and kinematic relations between the fabric and the host zone in agreement with both theoretical analysis and field observation it is shown that natural flow regimes range from pure shear to pure rotation including super simple shear in consideration of the heterogeneity and non steadiness of natural deformation kinematic analysis is justifiable only within a homogeneous domain and steady period flow kinematics and mechanisms are interrelated in that firstly mechanisms provide internal constraints on kinematics ensuring that only certain flows are possible and secondly flow kinematics will favour development of certain mechanisms

lateral extrusion in transpression zones the importance of boundary conditions the homogeneous transpression strain model formulated by sanderson and marchini journal of structural geology 6 449 458 1984 has proved to be a useful tool in the analysis of complex three dimensional deformation patterns however some of the boundary conditions introduced in the mathematical model may be unrealistic and unnecessarily restrictive in this paper a strain matrix for unconfined transpression and transtension is derived in which material is allowed to move not only vertically but also horizontally in and out of the deforming zone parallel to its length lateral extrusion three end member plane strain components are defined wrench simple shear pure shear in xy lateral stretch and pure shear in yz vertical stretch these biaxial strains can be viewed as the apices of a strain triangle for unconfined transpression or transtension the edges of the triangle correspond to triaxial pure shear non coaxial biaxial lateral extrusion and the triaxial confined transpressional or transtensional strain of sanderson and marchini during unconfined transpression the orientation and in particular the geometry k value of the finite strain ellipsoid depends upon not only the amount of shortening across the zone and the amount of strike slip parallel to the zone but also upon the ratio of vertical to lateral stretch this can present serious difficulties when attempting to use finite strains to infer the direction and magnitude of zone boundary displacements examples of transpression zones in which there is evidence of a component of lateral extrusion are described from sw cyprus and central scotland these examples illustrate that antithetic strike slip shearing is a kinematic requirement of laterally unconfined transpression implying that synchronous shear sense indicators may give opposite senses of movement in shear zones specific geometric and mechanical boundary conditions together with internal fault zone rheologies may favour the lateral extrusion of material kinematic partitioning can occur to form fault bounded domains in which end member biaxial and or non coaxial strains are developed analysis of such domains can give a clearer understanding of regional scale triaxial deformations these findings illustrate the importance of establishing displacement boundary conditions when qualitatively or quantitatively analysing crustal deformation zones

southward extrusion tectonics during the carboniferous africa north america collision abstract from the devonian to the permian north america and africa shared the same orogenic history involving plate convergence followed by continent continent collision that closed the proto atlantic ocean conventionally it is held that this resulted in thrust and nappe tectonics with a westward vergence in the appalachians and an eastward vergence in the mauritanides in contrast to the movement picture suggested by the thrusting model medium to late carboniferous displacements along major fault zones are mainly dextral strike slip in the southeastern appalachians and sinistral in the western mauritanides an alternative kinematic model is presented here it is suggested that the southern appalachian piedmont and western senegal mauritania provinces moved southward relative to north american and african cratons this escape tectonics during continental collision would result from 1 1 a plate convergence vector oriented at a medium oblique angle to preexisting zones of weakness within the north american margin and 2 2 indentation of the appalachians by the reguibat uplift of west africa

s c mylonites two types of foliations are commonly developed in mylonites and mylonitic rocks a s surfaces related to the accumulation of finite strain and b c surfaces related to displacement discontinuities or zones of relatively high shear strain there are two types of s c mylonites type i s c mylonites described by berthe et al typically occur in deformed granitoids they involve narrow zones of intense shear strain which cut across mylonitic foliation type ii s c mylonites described here have widespread occurrence in quartz mica rocks involved in zones of intense non coaxial laminar flow the c surfaces are defined by trails of mica fish formed as the result of microscopic displacement discontinuities or zones of very high shear strain the s surfaces are defined by oblique foliations in the adjacent quartz aggregates formed as the result of dynamic recrystallization which periodically resets the finite strain clock these oblique foliations are characterized by grain elongations alignments of segments of the grain boundary enveloping surfaces and by trails of grains with similar c axis orientations examples of this aspect of foliation development in mylonitic rocks are so widespread that we suggest the creation of a broad class of s c tectonites and a deviation from the general tradition of purely geometric analysis of foliation and time relationships kinematic indicators such as those discussed here allow the recognition of kilometre scale zones of intense non coaxial laminar flow in crustal rocks and unambiguous determination of the sense of shear

a preliminary assessment of in place coalbed methane resources in the virginia portion of the central appalachian basin abstract in the central appalachian basin virginia leads in coalbed methane drilling and production even though it only contains a small fraction of the total coal resources and basin area in 1992 coalbed methane surpassed conventional and shale gas as virginia s largest source of natural gas by the end of 1996 there were 814 wells producing coalbed methane in virginia average daily production per well in 1996 was 114 mcf 3 2 mm 3 cumulative production of coalbed methane from 1988 through 1996 is 121 542 188 mcf 3 445 073 mm 3 factors influencing this trend include the presence of abundant coal in place including coal remaining in ground after mining sufficient overburden high gas content coal beds high gas permeability existing pipeline infrastructure and legislative clarification of uncertain coalbed gas ownership development of coalbed methane in virginia began in late 1988 production is from coal beds in the southwestern virginia coalfield a structurally distinct area along the southeastern margin of the central appalachian basin ten coal beds within the lower pennsylvanian pocahontas and lee formations and the lower pennsylvanian portion of the norton formation have been targeted for production of coalbed methane estimated coal in place for these coal beds is about 14 9 billion short tons estimated gas contents of the coal beds range from 256 ft 3 7 9 m 3 t to 698 ft 3 ton 21 5 m 3 t these data yield an estimated in place coalbed methane resource of 6 7 tcf 0 18 tm 3 for virginia the u s geological survey reported the in place coalbed methane resource for the entire central appalachian basin to be 5 tcf 0 13 tm 3 with 3 07 tcf 0 08 tm 3 technically recoverable an estimated in place coalbed methane of 6 7 tcf 0 18 tm 3 is more compatible with 3 07 tcf of technically recoverable coalbed methane for the central appalachian basin

the concept of steady state foliation abstract a steady state foliation is thought of as a foliation with constant orientation and intensity in a rock undergoing steady state flow the problem discussed is whether such straininsensitive foliations exist in rocks and how they might be distinguished from the more familiar strain sensitive foliations steady state foliations would be useful indicators of stress or of strain rate yet misleading if used as indicators of finite strain one requirement for maintenance of steady state foliations is operation of processes that locally weaken grain shape preferred orientation or reduce grain aspect ratios or destroy lithological layering during flow these are the inverses of the processes normally discussed in connection with foliation development many such processes are known though the details of how and when they operate efficiently enough to stabilize a foliation are unknown there is however a tendency for some of them to operate more efficiently at high strains high temperatures and in flow regimes with high vorticity natural and experimental high temperature shear zones are accordingly one environment in which steadystate foliations may be encountered an experiment is described in which a thin specimen of para dichlorobenzene was given a large shearing deformation at 90 of its absolute melting point a steady state foliation was not produced but the technique is a promising one for further microstructural studies where in situ observation of material undergoing large deformations is desirable

strain compatibility and shear zones is there a problem in analyzing deformation in rocks it is important to ensure that the solutions obtained satisfy strain compatibility this creates a challenge to understanding patterns of strain associated with shear zones in which measured strain may appear incompatible with the strain in the shear zone walls flattening strains are common in natural shear zones with locally straight and parallel boundaries to satisfy compatibility conditions such strains require volume loss across the shear zone or deviations from plane strain with or without discontinuities between the shear zone and the wall rock in the case of shear zones for which there is no evidence of volume loss or discontinuities along the shear zone walls problems of strain compatibility may be resolved if individual shear zones are linked together in an appropriate fashion shear zones commonly occur in anastomosing arrays and simple configurations of such arrays and the strains associated with them are examined it is shown that local transpression with strain compatibility can be accounted for in this way quite complex local strain patterns can develop in simple arrays

secondary cleavages in ductile shear zones abstract secondary cleavages developed at late stages in ductile shear zones show several features that are inconsistent with progressive simple shear in the zone these are the orientation of a single secondary cleavage oblique to the shear zone boundaries conjugate sets with opposite senses of shear and multiple sets with the same sense of shear these features can be explained if the bulk flow is partitioned into slip along discrete failure planes parallel to the primary foliation s coaxial stretching along the foliation and spin

coal reservoir characteristics and coalbed methane resource assessment in huainan and huaibei coalfields southern north china abstract the huaibei and huainan coalfields in southern north china contain abundant coalbed methane cbm resources 1 1 10 12 m 3 net accumulated thicknesses of all minable coal seams are 18 32 m in huainan and 8 18 m in huaibei coalfields coal rank in the huainan coalfield high volatile a and b bituminous r o 0 65 0 85 is generally controlled by geothermal metamorphism in comparison coal rank in the huaibei coalfield varies from high volatile a bituminous to semi anthracites 0 8 to 2 8 r o and is controlled by the influence of the cretaceous yanshanian magmatic metamorphism in both coalfields coal reservoirs have low permeability values of 0 0013 0 224 md and porosity of 0 9 10 9 pores in coals are dominated by those with diameter 2 in both coalfields the abundance of microfractures in coals is related to the coal structures commonly more abundant in sheared coals 200 per 9 cm 2 than in the normally structured coals 2 the in place gas content is generally 8 16 m 3 t in huaibei and 10 30 m 3 t in huainan coalfields these data yield an estimated in place cbm resource of 375 247 10 9 m 3 for the huaibei and 722 677 10 9 m 3 for the huainan coalfields based on the cbm resource investigation and reservoir evaluation the most prospective target areas for cbm production are evaluated which include the nanping taoyuan mines of the southern suxian deep coal district and zhuxianzhuang and luling mines in eastern suxian area of the huaibei coalfield and the area around the panji 2 mine in panji xieqiao coal mining districts in the huainan coalfield

volume loss and tectonic flattening strain in granitic mylonites from the blue ridge province central appalachians abstract granitic mylonites from the blue ridge province in the central appalachians demonstrate the contribution of various deformation mechanisms to the strain geometry that developed during greenschist facies deformation in thrust related shear zones strain accumulated through cataclasis in feldspar crystal plastic processes in quartz and a significant contribution of pressure solution in both feldspar and quartz strain analysis was performed using r f f techniques on quartz grain shapes and by measuring stretched and boudinaged feldspars petrographic and geochemical evidence indicates that deformation ranged from isovolumetric to upwards of 60 bulk rock volume loss quartz and feldspar strain values plot within the field of apparent flattening feldspars in both xz and yz sections are boudinaged and separated by transverse veins and record a true tectonic flattening strain strain data indicate that the bulk deformation path in shear zones throughout the blue ridge province significantly deviated from plane strain

quantitative kinematic flow analysis from the main central thrust zone nw himalaya india implications for a decelerating strain path and the extrusion of orogenic wedges quantitative kinematic indicators from the main central thrust zone mctz in the nw himalaya have been used to characterize the type of flow during deformation different generations of tension gashes have been rotated by variable angles with respect to the mylonitic foliation forming associated fringe folds these record the late stage brittle ductile flow and reveal that a strong pure shear component of deformation occurred throughout the mctz to characterize earlier deformation increments fabrics from highly deformed quartz ribbons were analyzed well developed shape and lattice preferred orientation patterns show a systematic change of the glide systems and suggest inverted palaeotemperatures within the mctz investigations of the c axes patterns reveal a strong asymmetry at the top of the mctz whereas the samples from the base of the mctz show almost perfectly symmetrical type i crossed girdles deformation within the mctz probably started close to simple shear flow at higher temperatures which progressively became a more general shear during cooling and ended in a pure shear dominated flow during the final stages of brittle ductile deformation i e a decelerating strain path using the higher himalaya crystalline as an example a kinematic model for the extrusion of crustal wedges above major thrust zones is suggested

an inverse approach to constraining strain and vorticity using rigid clast shape preferred orientation data abstract we describe a three part approach for modeling shape preferred orientation spo data of spheroidal clasts the first part consists of criteria to determine whether a given spo and clast shape are compatible the second part is an algorithm for randomly generating spheroid populations that match a prescribed spo and clast shape in the third part numerical optimization software is used to infer deformation from spheroid populations by finding the deformation that returns a set of post deformation spheroids to a minimally anisotropic initial configuration two numerical experiments explore the strengths and weaknesses of this approach while giving information about the sensitivity of the model to noise in data in monoclinic transpression of oblate rigid spheroids the model is found to constrain the shortening component but not the simple shear component this modeling approach is applied to previously published spo data from the western idaho shear zone a monoclinic transpressional zone that deformed a feldspar megacrystic gneiss results suggest at most 5 km of shortening as well as pre deformation spo fabric the shortening estimate is corroborated by a second model that assumes no pre deformation fabric

constraints on deformation path from finite strain gradients we present a methodology for analyzing finite strain gradients in high strain zones in order to place constraints on the zone s possible deformation path to accomplish this the high strain zone is divided into several sub zones within each of which finite strain is described by a single ellipsoid based on knowledge of the spatial and temporal evolution of deformation strain observed in less deformed sub zones is then mathematically removed from more deformed sub zones to calculate incremental finite strains the mean kinematic vorticity number of each of these increments must be constant if deformation was steady state we use the methodology to analyze two natural examples of high strain zones at different scales both natural examples have non steady state likely deformation paths which may be a common characteristic of high strain zones although results of the methodology are not unique identification of likely paths considerably narrows the range of possible deformation paths consequently useful kinematic information can be extracted from finite strain data even in instances where the detailed spatial and temporal evolution of a high strain zone cannot be determined conclusively

character of the alleghanian orogeny in the southern appalachians part ii geochronological constraints on the tectonothermal evolution of the eastern piedmont in south carolina a nearly concordant u pb zircon age of 550 4 ma is interpreted to closely date crystallization of the epizonal little mountain metatonalite in the southeastern part of the charlotte belt in south carolina this confirms field studies which indicate that the charlotte belt contains a plutonic metaigneous complex that developed as a sub volcanic arc infrastructure contemporaneous with vulcanism manifested in the carolina slate belt both paleontological and geochronological controls indicate that the south carolina slate belt is mostly younger than 570 ma cambrian whereas the slate belt in north carolina and virginia is mostly of late proterozoic age a regionally significant mid paleozoic ca 340 360 ma thermal event is suggested by discordant 40ar 39ar whole rock age spectra of slate phyllite in the northwestern carolina slate belt and from hornblende in the southeastern charlotte belt it is uncertain if this event was associated with deformation in the eastern piedmont however mid paleozoic deformation has been previously documented elsewhere in the western piedmont a slightly disconcordant u pb zircon age of 317 4 ma is interpreted to closely date initial crystallization of the deformed edge field granite and confirms a record of late paleozoic penetrative deformation in the kiokee belt of south carolina u pb isotope data for the lake murray orthogneiss and clouds creek granite are discordant and suggest that the magmas of these plutons were derived by partial melting of a sialic precam brian source and then emplaced in the eastern piedmont at ca 315 ma prior to or during the early stages of the alleghanian orogeny the thermal maximum of alleghanian regional metamorphism amphibolite facies in the kiokee belt greenschist facies in the southeastern part of the carolina slate belt occurred during ca 295 315 ma during the late carboniferous and early permian the eastern piedmont experienced differential uplift erosion and relatively rapid postmeta morphic cooling isothermal surfaces were folded into an antiform synform antiform configuration corresponding to the kiokee carolina slate and charlotte belts respectively the geochronological data provide the following calibration for the late paleozoic deformational chronology recorded in the kiokee and carolina slate belts d2 lake murray deformation ca 295 315 ma d3 clarks hill deformation ca 285 295 ma and d4 irmo deformation ca 268 290 ma

the deformation matrix for simultaneous simple shearing pure shearing and volume change and its application to transpression transtension tectonics simultaneous simple shearing and pure shearing with or without additional volume change can be combined into a single upper triangular deformation matrix the off diagonal term is named the effective shear strain and is a simple function of the pure shearing and simple shearing components a three dimensional deformation matrix for the simultaneous combination of coaxial deformation with or without additional volume change and up to three simple shearing systems with mutually orthogonal shear planes is also presented by using this matrix one can easily extract the various properties of incremental as well as finite strain and the progressive as well as finite rotation of passive markers during deformation the case of transpression transtension is revised using the unified deformation matrix the orientation of the major axis of the strain ellipsoid 1 is always horizontal if the deformation is transtensional switches from horizontal to vertical during transpressional wrenching 1 wk 0 81 for constant vorticity deformations and is always vertical for highly transpressional deformations wk 0 81 for transpression material lines initially rotate towards the horizontal shearing direction but generally turn to rotate towards the vertical axis after a certain strain for transtension all material lines rotate towards a direction in the horizontal plane which is oblique to the shearing direction

character of the alleghanian orogeny in the southern appalachians part i alleghanian deformation in the eastern piedmont of south carolina the eastern piedmont province in south carolina contains a sequence of cambrian volcanic and sedimentary rocks that was penetratively deformed d1 and regionally metamorphosed m1 to the greenschist facies during the early and or middle paleozoic the eastern piedmont was subsequently affected by late paleozoic alleghanian polyphase deformation d2 d4 and regional metamorphism the earliest alleghanian event d2 is associated with amphibolite facies regional metamorphism and felsic plutonism in a mid crustal infrastructure at ca 295 315 ma the gradational interface between infrastructure and overlying suprastructure contained a steep m2 metamorphic gradient between amphibolite facies below and greenschist facies above numerous sheets of felsic orthogneiss and a deformation front marking the upper limit of intense d2 penetrative deformation d3 is represented by northwestward vergent folding of s1 and s2 foliations and m2 isothermal surfaces the kiokee belt in south carolina is interpreted as a d2 infrastructure exposed within the core of a d3 antiform this interpretation suggests that an alleghanian infrastructure may be present in the subsurface beneath much of the piedmont and coastal plain the polygenetic modoc zone forms the northwest boundary of the kiokee belt it is interpreted to represent an interface between d2 infrastructure and suprastructure which was rotated into a steep northwest dipping attitude during development of the kiokee belt antiform between ca 267 and 290 ma portions of the kiokee belt modoz zone and carolina slate belt were overprinted by ductile deformation d4 along steeply dipping northeast trending dextral shear zones

the alleghanian southern appalachian piedmont a transpressional model alleghanian dextral transpression produced multiple strike slip shear zones forming a contractional mega duplex in the central and southern appalachian piedmont structural upwelling along the zones is identifiable as crustal arching on seismic reflection profiles that roughly corresponds to the piedmont gravity high the structural upwelling coincides both temporally and spatially with areas of peak alleghanian plutonism and metamorphism the compositionally bimodal plutons generally occur in or around the fault zones and are isotopically primitive geobarometry of cognate xenocryst inclusions of coexisting plagioclase and pyroxene from a granitoid indicates 8 11 kbar or 31 to 42 5 km depth to proposed source region this depth roughly corresponds to the pre erosional location of multiple reflections beneath the arches on seismic profiles that are interpreted as the moho the granitoids are proposed to have formed by partial melting of the lowermost crust through heat from mafic intrusions and decompression resulting from crustal arching beneath the strike slip faults the granitoids ascended along the strike slip faults and were emplaced in or near them the crustal arching and melting processes appear to be important mechanisms in the development of strike slip orogens

u pb geochronologic nd isotopic and geochemical evidence for the correlation of the chopawamsic and milton terranes piedmont zone southern appalachian orogen abstract we report u pb crystallization ages from four metavolcanic rocks and two granitic gneiss samples as well as whole rock chemical analyses and sm nd isotopic ratios from 25 metaigneous and metasedimentary rocks from the chopawamsic and milton terranes southern appalachian orogen a metarhyolite sample from the chopawamsic formation and a metabasalt sample from the ta river formation in the chopawamsic terrane have indistinguishable u pb crystallization ages of documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmaryrd usepackage textcomp usepackage portland xspace usepackage amsmath amsxtra usepackage ot2 ot1 fontenc newcommand cyr renewcommand rmdefault wncyr renewcommand sfdefault wncyss renewcommand encodingdefault ot2 normalfont selectfont declaretextfontcommand textcyr cyr pagestyle empty declaremathsizes 10 9 7 6 begin document landscape 471 4 pm 1 3

strain in ductile shear zones in the caledonides of northern sweden a three dimensional puzzle small scale ductile shear zones are well developed in amphibolites of caledonian nappes of the swedish lapland strain in the shear zones is recorded by the shapes of originally sub equant aggregates of plagioclase feldspar classical strain analysis on two dimensional xz profiles across the shear zones leads to results that indicate large volume losses associated with the shear strain large volume losses are however incompatible with geochemical analysis which shows little chemical variation across the shear zones by including data from xy and yz sections information on the three dimensional state of strain can be obtained these data indicate that deformation is not confined to a two dimensional plane particle extension within the shear zone parallel to the shear plane and perpendicular to the shear direction has also occurred the state of strain and strain path in the shear zone can be modeled in a general way by combining stretches in x y and z with simple shearing and volume loss end member models correspond to plane strain with volume loss kx ky 1 kz 1 transpression kx 1 ky 1 kz and pure shear kx 1 kz ky 1 these models produce identical strain ratios and orientations on the xz section but differ in stretch in y and in area of the strain ellipse on the xz section extension in y or x allows for reconciliation of the geometrical and geochemical data for part of an individual shear zone but poses a problem of strain compatibility at the edges and terminations of the shear zones the shear zones show a complex anastomosing pattern in three dimensions and their connectivity provides a way in which strain compatibility is maintained

vorticity analysis in a metachert from the sanbagawa belt sw japan abstract common tectonic features of deformed metachert include both sets of extended and shortened veins and quartz c axis preferred orientation patterns in such rocks information is also commonly available on the orientation and magnitude of the finite strain these features can be used to derive two independent estimates of the degree of non coaxiality during deformation in an example from the sanbagawa belt sw japan the two methods give consistent results and show that deformation was intermediate between simple and pure shear such types of progressive deformation distributed over a broad region could cause substantial subvertical thinning and be a significant factor in the exhumation of high p t rocks in the region

northern ancestry for the goochland terrane as a displaced fragment of laurentia comment and reply reply we welcome the opportunity to discuss further our ideas regarding translational tectonics along the iapetan margin of laurentia we look forward to seeing published papers on the alleghanian history of the goochland terrane based on recent abstracts of our colleagues from william and mary but

the eastern piedmont fault system and its relationship to alleghanian tectonics in the southern appalachians alleghanian continental collision across the southern appalachians resulted in northwestward over thrusting in the blue ridge and valley and ridge and emplacement of a large crystalline nappe in the piedmont however fault patterns in the eastern piedmont fault system are consistent with the geometry expected in a strike slip fault network formation of the eastern piedmont fault system mainly postdates the last regional metamorphism in the piedmont and is interpreted to be an alleghanian structure penecontemporaneous with thrusting in the western part of the appalachian orogen this discrepancy in tectonic style across the orogen is attributed to lateral movement of parts of the raleigh and kiokee belts and of the precambrian paleozoic basement of northern florida out of the principal collision zone during latter stages of the alleghanian collision a modern analogy for such lateral movement is the present strike slip regime in turkey which represents post collisional lateral escape of the anatolia

general shear deformation in the pinaleno mountains metamorphic core complex arizona abstract granitic mylonites from the pinaleno mountains metamorphic core complex in southeastern arizona record general shear deformation the mean kinematic vorticity number w m was estimated using 1 the strain ratio r s and the angle between the long axis of the strain ellipsoid with respect to the high strain zone boundary and 2 the porphyroclast hyperbolic distribution method w m for protomylonites and mylonites ranged from 0 6 to 0 9 ultramylonites record lower w m values 0 1 0 3 suggesting that the incremental vorticity changed during deformation three dimensional strain analysis indicates that deformation in protomylonites and mylonites approximates plane strain and has a monoclinic symmetry the vorticity path followed by rocks tectonically exhumed in the footwall of major extensional fault systems may evolve from a significant pure shear component early in the deformation towards simple shear as overburden load decreases during uplift

strain and kinematic analysis in general shear zones we present a unifying theory for the development and distribution of strain markers and kinematic indicators in zones of general shear and thus provide a framework in which data previously considered contradictory may be understood rigid and deformable porphyroclast systems including and complex grains are potential indicators of both strain and flow the shapes and distribution of such porphyroclast systems may be used to distinguish among different tectonic regimes general shear is divided into two fields sub simple shear in which the rotational component of the strain is less than that for simple shear and super simple shear in which the rotational component is greater than for simple shear sub simple shear may involve narrowing or broadening of shear zones super simple shear regimes are possible in local regions such as the vicinities of deformable porphyroclasts but must be enclosed by regimes of sub simple shear the polar mohr constructions for finite deformation and flow are useful to analyze general shear in theory the hyperbolic net is employed for practical plotting of real data and derivation of the kinematic vorticity number wn this number represents the relative contributions of pure and simple shear in steady flow in nature deformation is thought to build up and decay by processes that may invalidate the assumption of constant flow regime we therefore introduce the concept of accelerating deformation and analyze the implications of non steady flow for the shearing histories of deformed objects

early geochemical evolution of an oceanic island arc and backarc fiji and the south fiji basin the initial 25 to 35 ma of oceanic arc volcanism in fiji the early arc stage was dominated by eruption of lree depleted low k tholeiitic basalts and andesites the oldest volcanics include the highest hfse group morb like in composition plus high mg basalts and basic andesites with flat ree patterns as low as 4x chondritic concentrations these erupted either within the volcanic arc during its first 5 ma or in an adjacent backarc during its first ma of formation subsequent volcanics of the early arc stage apparently erupted onto early backarc basin crust most are intermediate between earlier extremes in hfse contents but at least one volcano produced strongly lree depleted island arc tholeiites in contrast medium k tholeiitic and calc alkaline andesites erupted during the mature arc stage parental basalts were enriched in lree but depleted in hree relative to earlier basalts due to a change in source composition counterflowing morb source asthenosphere within the mantle wedge dominated vol

constrictional strain in a non coaxial shear zone implications for fold and rock fabric development central mojave metamorphic core complex california finite strain and fold analyses of footwall mylonites in the central mojave metamorphic core complex cmmcc reveal two distinct deformation paths that generated non coaxial constrictional strain the first path recorded in the waterman hills accomplishes constrictional strain through the formation of l tectonites at the grain scale the second path recorded in the mitchel range involves a combination of plane strain at the grain scale and y axis shortening through syn mylonitic folding the ductile shear zone in the waterman hills is approximately 500 m thick and is developed entirely within a miocene syn kinematic granodiorite strain magnitude decreases structurally downward the mylonites contain abundant ne directed non coaxial microstructures yet are l tectonites rf o analysis of quartz ribbon grain shapes indicate prolate strains k 6 and bulk chemical data suggest that mylonitization was isochemical or involved volume loss therefore ductile shearing in the waterman hills involved true constrictional strain at the grain scale immediately to the southeast in the mitchel range the lateral continuation of the shear zone is more than 1000 m thick and primarily involves lithologically heterogeneous pre tertiary basement the mylonitic fabric comprises a well developed foliation and ne trending stretching lineation rf o strain analysis was applied to grain shapes of cataclasized and strongly altered garnet porphyroclasts in a peraluminous granite in contrast to the waterman hills finite strains in these l s tectonites approximate plane strain k 1 1 however the mylonitic fabric is strongly folded about axes uniformly oriented subparallel to the stretching lineation the coaxial folds range from open to isoclinal we interpret the folds to have nucleated with axes parallel to the stretching lineation during mylonitization and to have accomplished y axis shortening in the shear zone macroscopic folds of the brittle detachment spatially correspond to open folds in the ductile shear zone suggesting that y axis shortening continued after the fault zone had reached the brittle regime corrugations and folds oriented subparallel to the transport direction are characteristic features of fault zones in cordilleran metamorphic core complexes therefore constrictional strain may be common in core complexes strain compatibility with upper plate rocks in core complexes may be maintained by y axis shortening along conjugate strike slip faults a nearly uniaxial stress field 3 2 1 is consistent with most of the structures formed in basin and range extension and could generate the observed constrictional strain

analysis of deformation paths in shear zones the geometry of ductile shear zones can be used to solve problems of regional tectonics if the deformation path of material in the zones is sufficiently understood flow in many shear zones may have deviated from simple shear and consequently data on the final deformation state such as finite strain and volume change are insufficient for reconstruction of the deformation path even if flow parameters were constant during progressive deformation additional information on the flow vorticity number is also needed and can be obtained from fabric elements such as sets of folded boudinaged veins rotated porphyroblasts and blocked rigid objects mohr circle constructions are presented as a tool to calculate deformation parameters from fabric data to represent the deformation path graphically and to reconstruct flow parameters from the shape of this path if the vorticity number or the volume change rate changed during progressive deformation the deformation path can be partly reconstructed using sets of fabric elements which register mean and final values of these parameters

high strain zones a unified model abstract where a shear zone is bounded by undeformed wall rocks and there is no volume change the deformation path within the zone on the bulk scale approximates a simple shear where the zone boundaries are stretched and the shear direction between the two boundaries is parallel to one of the principal stretching directions of the boundaries the deformation path within the zone is not a simple shear but still has monoclinic symmetry both simple shear and general monoclinic deformation paths should be regarded as special cases in nature because generally not only are the zone boundaries stretched but also the shear is oblique to the principal stretching directions of the boundaries in this general case the deformation path is triclinic we establish a model which includes this general case also taking into consideration volume change five independent parameters are required to characterize the rate of deformation of the flow four are sufficient to characterize the flow kinematics the model is generally triclinic and orthorhombic and monoclinic deformations are subgroups by varying the values of the characterizing parameters the various types of high strain zones can be represented the kinematics of flow within such zones and the accumulated finite deformation geometry are investigated many field observations such as for example lineations in transcurrent shear zones that vary between vertical and horizontal cleavage transected folds and the absence of sheath folds in some shear zones where folds have been significantly rotated can sometimes be better interpreted in the context of our general model

the use of mohr circles to describe non coaxial progressive deformation abstract mohr circles are useful in strain analysis but are also potentially powerful tools to translate geological fabric data into tensors describing the deformation and to reconstruct flow parameters this paper shows how mohr circles can be used to visualize the effects of variable flow parameters such as stretching rate volume change rate and vorticity number on parameters of cumulative deformation as described by the position gradient tensor a mean vorticity number is introduced as a deformation parameter besides finite cumulative strain and volume change

landscape response to climate change insights from experimental modeling and implications for tectonic versus climatic uplift of topography we present the results of an experimental investigation of the concurrent action of tectonic uplift and climate variation on relief evolution we designed an experimental apparatus that allows the study of erosion of laboratory scale topographies that evolve under given uplift and rainfall rates for constant uplift and rainfall rates the experimental topography evolves toward a statistical steady state defined by a mean elevation constant with time starting from such a steady state and keeping the input uplift rate constant a subsequent change in the rainfall rate yields a change in the mean elevation of the landscape to a new equilibrium elevation an increase in precipitation yields a lower mean steady state elevation whereas for a decrease in precipitation the surface is uplifted we define this phenomenon as a climatically induced surface uplift as opposed to a tectonically induced surface uplift the climatically and tectonically induced surface uplifts correspond to different dynamics of denudation so that it is theoretically possible to differentiate between the climatic or tectonic causes of surface uplift from records of output sediment fluxes

a fundamental problem with the kinematic interpretation of geological structures abstract non steady flows are ubiquitous in nature not only do imposed boundary conditions vary with time and rock rheology change during the course of deformation but also deformation is generally heterogeneous and all of these conditions lead to non steady flow histories in modern kinematic analysis flow apophyses the instantaneous stretching axes and the vorticity vector collectively referred to as the eigen directions of deformation are used in place of bruno sander s kinematic axes for deformation with a steady flow history this practice is well justified and has led to great advances in structural geology but for non steady flow histories the geometrical relationships among eigen directions flow pattern vary with time this makes it inappropriate to correlate an association of structures and fabrics with certain time invariant flow patterns and hence raises the question how should we interpret geological structures and fabrics kinematically without the assumption of homogeneous and steady deformation we suggest that the answer lies primarily in forward modeling of deformation based on a knowledge of rock properties

impact of geological modeling processes on spatial coalbed methane resource estimation spatial coalbed methane cbm resource estimation is based on spatial distributions of coal coal adsorbed gas content and coal density however the spatial distribution of gas content can be generated via two different geological modeling processes 1 the gas content distribution is generated by geological modeling based on the interpreted gas content at boreholes 2 distributions of gas content related logs or coal properties are generated firstly then the gas content distribution is calculated based on the spatial distributions of logs or coal properties by the relationship between the gas content and logs or coal properties this paper presents a study to compare the impact of these two processes on cbm resource estimation for coal seam no 3 cs 3 in southeast qinshui basin china well logs from 22 wells laboratory data from five wells and well tops from 131 wells for cs 3 are used in log interpretation and geological modeling the simple kriging sk is used to build the structural model and the coal distribution weighted and unweighted omni directional variograms for structural residual and coal thickness are calculated using an in house program logs of gamma ray gr and density den or rhob are distributed in 3d by using sequential gaussian simulation sgs with sk algorithm artificial neural network ann is used to build the relationship of the measured raw gas content rgc gas content in raw coal basis with the logs of gr den and measured depth md then the rgc is distributed in 3d by the two geological modeling processes cbm resources are calculated in 3d based on the cells volume coal density and rgc results show that rgc increases with an increase in burial depth total cbm resources for the study area calculated by these two processes are similar for cs 3 but the distribution probability of high gas content is highly different which is important for locating wells