on estimating crystal shape for crystal size distribution analysis abstract the accurate determination of three dimensional crystal habit long intermediate short axis is a requirement to enable correct stereological conversion of 2d crystal size measurements to true 3d crystal size distributions csds in this contribution we introduce a database and spreadsheet program which provides an objective estimate of true crystal habit from raw 2d measurements the database compares the sample s 2d measurements with 2d shape curves for random sections through 703 different habits the output gives the five best match curves and corresponding crystal habits based on a least squares fit between sample and database the minimum sample size required to give good shape estimates from 2d data is tested using random runs of sections through known shapes with different population densities at minimum 75 crystal sections are required to robustly determine crystal habit for csd measurements if crystals are tabular in shape with more acicular shapes requiring a minimum of 250 sections suggesting a sample size of 250 sections to be used for shape determination in natural examples where the true 3d shape is unknown the crystal habit of the best match shape can then be used to provide a more robust csd analysis which in turn can be used to investigate magmatic processes with more certainty

cross well continuity logging using guided seismic waves cross well seismic recording with sources and receivers in different wells can potentially image the internal structure of reservoirs with resolution on the order of a few feet transmission and reflection images can be made but both have inherent limitations the well separation is generally limited by the source strength to less than 2000 ft and coplanar wells are desired also adequate imaging requires a large number of source and receiver locations resulting in expensive acquisition costs removal of production tubing from both wells is often necessary adding even more to the cost given these limitations imaging methods are generally restricted to densely drilled mature fields where budgets for data acquisition are limited

transpressional tectonics during the emplacement of pasupugallu gabbro pluton western margin of eastern ghats mobile belt india evidence from ams fabrics abstract the pasupugallu gabbro anorthosite pluton intruded the transition zone between the mesoproterozoic eastern ghats granulites and the meso to paleoproterozoic amphibolites and migmatitic gneisses of east dharwar craton southern india the pluton is bound by shear zones at its entire eastern northern and southwestern margins the objective of this work is to study the internal fabric of the pluton to understand the tectonic setting during its emplacement essentially by means of anisotropy of magnetic susceptibility ams a total number of 107 samples have been subjected to ams and irm studies the magnetic fabric is principally ferromagnetic in origin as the magnetic susceptibility values are 10 3 si which is further supported by irm studies the magnetic fabrics correspond well with the field measurements and petrographic studies they show two lobes in both the northern and southern parts which display concentric inward dipping helicoidal foliation trajectories with interlayered steep and gently dipping domains the magnetic lineation pattern suggests that the magma might have ascended through the central lobes and extended towards outer margins particularly to the west the constrictional strains occur at the eastern margin while flattening strains mark the western margin ams studies together with our field structural observations suggest that the magma has been emplaced into a chamber dilational jog induced by crustal scale dextral transpressional tectonic regime probably during the onset of grenvilian event

tectonics of the southern portion of the ribeira belt apiai domain abstract the name ribeira belt was originally used in a reference to a broad belt of deformed crust which strikes subparallel to the southeastern brazilian coastline it was originally believed to be neoproterozoic brasiliano panafrican but present investigations indicate that this age seems to be mainly related to the extensive arc related plutonism and tectono metamorphism that affected its most representative formations whereas the time of deposition of the supracrustals would be significantly older in this study the main tectono stratigraphic features of the apiai domain of the ribeira belt are described the lithostratigraphy is reviewed as well the paleogeographic structural geochemical and radiometric data and their implications for the tectonic evolution models for the region the marine sediments of the apiai domain were laid down on the borders of the parana and luis alves cratons and on an intervening mesoproterozoic 1 8 1 1 ga ocean crust they were intensively deformed by ocean closure and collision of the cratonic fragments and they constitute the majority of the local supracrustals designated as the acungui supergroup symmetrical continental passive margin deposits are represented to the northwest by a more proximal facies itaiacoca group probably related to the parana paleocontinent and by the capiru formation to the southeast between them lies the central domain formed by the votuverava group characterized by the remains of gradually deepening carbonatic platform sediments of the lajeado subgroup which grade eastward into distal turbiditic sequences of the ribeira subgroup where ocean floor and immature island arc magmatic rocks are present during the neoproterozoic the apiai domain behaved as a single continental mass into which basic rocks were intruded between 1 1 and 0 85 ga between 0 7 and 0 6 ga the apiai domain evolved into a cordilleran type magmatic arc related to the evolution of a subduction zone possibly situated to the southeast of the luis alves cratonic fragment this subduction caused metamorphism and migmatization of the supra and infra crustal rocks of the region and produced the extensive calc alkaline granitoid plutonism between 0 6 and 0 45 ga the majority of the southeastern continental blocks amalgamated during closure of the adamastor ocean followed by development of a system of regional dextral transcurrent shear zones related to oblique collision and or escape tectonics pull apart basins opened up and were filled with molasse sequences the region was intruded by post tectonic granitoids and then underwent regional cooling

determination of fabric and strain ellipsoids from measured sectional ellipses implementation and applications abstract geologists examine fabrics to constrain models of formation or of deformation of rocks and it is often convenient to summarise the results by a fabric ellipsoid as fabric data are commonly collected on planar sections through the rock estimating a fabric ellipsoid from sectional ellipses often with arbitrary orientations is an important task an algebraic method to calculate such an ellipsoid presented in an earlier paper has been implemented with the program ellipsoid it is used here on examples that illustrate questions and issues that arise when collecting selecting and processing sectional fabric data and when assessing the results the quality of fit of the ellipsoid to the data is assessed in all cases examples include a case in which the average sizes of markers on individual sections can be used in the determination of the ellipsoid and other cases in which such sizes are not useful a case in which sectional ellipses are not obtained from closed markers and a case in which data scatter and insufficient coverage of section orientations lead to a hyperboloid instead of an ellipsoid

magma flow inferred from preferred orientations of plagioclase of the rio ceara mirim dyke swarm ne brazil and its ams significance

mineral lamination development in layered gabbros of the british palaeogene igneous province a combined anisotropy of magnetic susceptibility quantitative textural and mineral chemistry study mineral lamination development in layered gabbros of the british palaeogene igneous province a combined anistotropy of magnetic susceptibility textural and mineral chemistry study

magmatic fabric acquisition mechanisms in a syenite results of a combined anisotropy of magnetic susceptibility and image analysis study the structural significance of the anisotropy of magnetic susceptibility ams and acquisition mechanisms of silicate and ferrimagnetic mineral fabrics are investigated in the archean lebel syenite intrusion ontario canada bulk mineral subfabrics are determined by intercept counting of mineral phases in classified digital images of thin sections cut parallel to the principal planes of the magnetic fabric ellipsoids of the samples intensities shapes and principal direction orientations of the resulting intercept ellipsoids are generally similar to the corresponding ams ellipsoids differences are due mainly to bimodal distribution of mineral fabrics observed on foliation planes of some samples showing pre full crystallization textures and structural overprinting in samples deformed after crystallization subfabrics of clinopyroxene and magnetite in samples showing pre full crystallization microstructure are investigated by measuring inertia tensors of individual grain shapes the resulting inertia tensor ellipsoids indicate that magnetic fabrics in these rocks are strongly correlated to the shape preferred orientation of magnetite which is similar to the overall petrofabric of the samples crystal size distributions of clinopyroxene and magnetite indicate that they formed during in situ crystallization and that magnetite probably appeared late in the crystallization and flow history of the magma analysis of preferred orientations of these grains suggests that the petrofabrics of the samples were acquired during flow with strongly interacting grains analogous to a logjam in a river the final characteristics of the ams and silicate petrofabric are the end points of a continuous crystallization and flow history in the magma rather than transient late features

the sonju lake layered intrusion northeast minnesota internal structure and emplacement history inferred from magnetic fabrics abstract the sonju lake intrusion sli in northeastern minnesota is a layered mafic complex of keweenawan age 1096 1 0 8 ma related to the midcontinent rift the cumulate paragenesis of the intrusion is recognized as broadly similar to the skaergaard intrusion a classic example of closed system differentiation of a tholeiitic mafic magma the sli represents nearly closed system differentiation through bottom up fractional crystallization geochemical studies have identified the presence of a stratabound 50 100 m thick zone anomalously enriched in au pge similar to the pge reefs of the skaergaard intrusion this pge enriched zone is hosted within oxide gabbro cumulates about two third of the way up from the base of the intrusion we present a petrofabric study using the anisotropy of magnetic susceptibility ams to investigate the emplacement and flow patterns within the sonju lake intrusion petrographic and electron microprobe studies combined with ams and hysteresis measurements indicate the primary source of the magnetic signal is pseudo single domain psd magnetite or titanomagnetite low field ams was measured at 32 sites within the sonju lake intrusion which provided information about primary igneous fabrics the magnetic fabrics in the layered series of the sonju lake intrusion are consistent with sub horizontal to inclined emplacement of the intrusion and show evidence that the cumulate layers were deposited in a dynamic environment well aligned magnetic lineations consistently plunging shallowly toward the southwest indicate the source of the magma is a vertical sill like feeder presumably located beneath the finland granite the finland granite acted as a density trap for the sonju lake magmas forcing lateral flow of magma to the northeast the strongly oblate magnetic shape fabrics indicate the shallowly dipping planar fabrics were enhanced by compaction of the crystal mush

the relation between magnetite and silicate fabric in granitoids of the adamello batholith abstract the link between the macroscopic silicate fabric and the magnetite controlled ams anisotropy of magnetic susceptibility fabric in ferromagnetic rocks was investigated through a comprehensive comparison between different fabric measurement techniques sample lithologies include tonalites and granodiorites from the lago della vacca complex adamello batholith italy the datasets used to assess the link between subfabrics and the coherence between methods include 1 macroscopic silicate fabric measured directly in the field 2 macroscopic silicate fabric derived from image analysis ia of outcrop pictures and sample pictures 3 shape preferred orientations spo of mafic silicates 4 spo of magnetite and 5 calculated distribution of magnetite grains from computer assisted high resolution x ray tomography x ray ct images 6 fabrics derived from the ams macroscopic mineral fabrics measured in the field agree with the ia results and with the spo of mafic silicates obtained from the x ray ct imaging the x ray ct results show that the spo of the magnetite grains are consistent with the ams data whereas the spatial distribution of the magnetite grains is less compatible with the ams fabric this implies that the ams signal is mainly controlled by the shape of the magnetic carrier mineral rather than by the spatial arrangement of the magnetite grains an exception is the presence of magnetite clusters furthermore the spo of mafic silicates and the spo of the magnetite grains are consistent with the ams data another finding of this study is that the magnetic susceptibility correlates linearly with the amount of magnetite in the samples the coherent results obtained from a variety of methods reinforce the application of both ams measurements and ia as robust tools to analyse fabrics in granitic intrusions

assessing spo techniques to constrain magma flow examples from sills of the karoo igneous province south africa abstract shape ellipsoids that define the petrofabrics of plagioclase in jurassic karoo dolerite sills in kwazulu natal south africa are rigorously constrained using the long axis lengths of plagioclase crystals and ellipse incompatibility this has been undertaken in order to determine the most effective technique to determine petrofabrics when using the spo 2003 programme launeau and robin 2005 the technique of segmenting an image for analysis is scrutinised and as a process is found redundant a grain size threshold is defined to assist with the varying grain sizes observed within and between sills where grains exceed the 0 2 mm size threshold images should be acquired at a high magnification i e 10 magnification petrofabrics are determined using the foliation and the lineation of the ellipsoid as defined by the maximum and minimum principal axes respectively of the resultant ellipsoid samples with strongly prolate fabrics are isolated allowing further constraint on the petrofabric to be made once the efficacy of the petrofabric determination process has been determined the resultant foliations and lineations then elucidate the most accurate petrofabric attainable the most accurate petrofabrics will be determined by using the correct magnification when the images are obtained and to run the analyses without segmenting the image the fabrics of the upper and lower contacts of the karoo dolerite sills are analysed in detail using these techniques and the fabrics are used as a proxy for magma flow

emplacement and deformation of mesozoic gabbros of the high atlas morocco paleomagnetism and magnetic fabrics a paleomagnetic and magnetic fabric study is performed in upper jurassic gabbros of the central high atlas morocco these gabbros were emplaced in the core of preexisting structures developed during the extensional stage and linked to basement faults these structures were reactivated as anticlines during the cenozoic compressional inversion gabbros from 19 out of the 33 sampled sites show a stable characteristic magnetization carried by magnetite which has been interpreted as a primary component this component shows an important dispersion due to postemplacement tectonic movements the absence of paleoposition markers in these igneous rocks precludes direct restorations a novel approach analyzing the orientation of the primary magnetization is used here to restore the magmatic bodies and to understand the deformational history recorded by these rocks paleomagnetic vectors are distributed along small circles with horizontal axes indicating horizontal axis rotations of the gabbro bodies these rotations are higher when the ratio between shales and gabbros in the core of the anticlines increases due to the uncertainties inherent to this work the igneous bodies recording strong rotations interpretations must be qualitative the magnetic fabric is carried by ferromagnetic s s minerals mimicking the magmatic fabric anisotropy of magnetic susceptibility ams axes using the rotation routine inferred from paleomagnetic results result in more tightly clustered magnetic lineations which also become horizontal and are considered in terms of magma flow trend during its emplacement nw se parallel to the general extensional direction in the western sector and ne sw parallel to the main faults in the easternmost structures

the relationships between the velocities attenuations and petrophysical properties of reservoir sedimentary rocks1 the authors have measured the velocities and attenuations of compressional and shear waves in 29 water saturated samples of sandstones and shales at a confining pressure of 60 mpa and at frequencies of about 0 85 mhz the measurements were made using a pulse echo method in which the samples diameter 5 cm length 1 5 cm to 2 5 cm were placed between perspex buffer rods inside a high pressure cell the velocity of each seismic wave was determined from the travel time difference of equivalent phase points corrected for diffraction effects of the signals reflected from the top and from the base of each samples attenuation was determined in a similar way by comparison of the diffraction corrected amplitudes of the signals the attenuation data are presented as quality factors q sub p and q sub s for compressional and shear waves respectively and shear waves respectively the results show that qs is strongly correlated with v sub s that q sub p is weakly correlated with v sub p and that q sub p is strongly correlated with q sub s center dot q sub p is strongly dependent on the volume percentage of the assemblage of intra pore minerals whether they are clays or carbonates it is concluded that themore attenuation mechanism is due to the local fluid flow arising from the differential dilation of the solid rock frame and the intra pore mineral assemblage which is a results of their very different elastic moduli less

pure shear dominated transpression and vertical extrusion in a strike slip fault splay from the itapirapua shear zone ribeira belt brazil abstract the itapirapua shear zone is a major ne trending dextral transcurrent zone from the southern ribeira belt brazil which was active during the neoproterozoic brasiliano pan african orogeny related with west gondwana assembly macroscopic sigmoid shaped blocks in its northernmost splay termination present a ne trending subvertical tectonic foliation and subvertical stretching lineation suggesting a transpressional tectonics this paper investigates this splay termination using integration of data from geological mapping thermodynamic modeling microtectonics quartz c axis fabrics kinematic vorticity and finite strain analysis distinct rock assemblages are placed in tectonic contacts along the splay termination including statherian sillimanite biotite paragneiss and granitic orthogneiss apiai mirim complex statherian phyllites bairro dos prestes formation calymmian chlorite epidote actinolite metabasites fazenda velha suite ediacaran phyllites metalimestone and quartzite itaiacoca group and ediacaran granite tres corregos suite isochemical phase diagrams constrain synkinematic metamorphic conditions of 490 510 c and 11 12 5 kbar chlorite biotite phengite phyllite 520 560 c and 9 10 kbar biotite phengite phyllite and 680 690 c and 5 6 kbar sillimanite biotite paragneiss with isothermal decompression paths microstructural evidence suggests that increase in metamorphic temperatures were accompanied by changes in the dominant deformation mechanism in quartz aggregates from subgrain rotation to grain boundary migration recrystallization significant contribution of dissolution precipitation creep indicates water abundant deformational conditions strain ellipsoids are oblate shaped and present ne trending subvertical xy planes and subvertical x axes in agreement with field tectonic fabric quartz c axis fabrics in xz sections of the strain ellipsoid are dominated by symmetrical crossed girdles while the fabrics present dextral asymmetry in horizontal yz sections consistent with macroscopic structural deflection indicating a subvertical vorticity axis vorticity results indicate 48 59 of pure shear contribution the data indicate that strain in the itapirapua shear zone northern termination was accommodated by a pure shear dominated transpression with vertical extrusion at mid crustal conditions which contrasts with a transtensional deformation in the southeastern block

grain size dependence of the rock magnetic properties for a natural maghemite the natural maghemite from the robe river mining district australia is shown to be thermally very stable the maghemite hematite inversion occurs at 650 c for sized fractions 250 m to 5 m enabling determination of t c for maghemite at 610 c the maghemite is intimately intergrown with hematite and j s of the maghemite corrected for the hematite content is 64 am 2 kg j rs h cr and h c range between 7 46 10 18 am 2 kg 16 90 23 30 mt and 6 38 9 00 mt respectively indicating psd maghemite with grain sizes between 1 and 20 m the grain size dependence of the rock magnetic parameters of the maghemite is less prominent than those of magnetite of nominally the same size it is suggested that the lt behavior of arm can be diagnostic of the presence of maghemite upon cooling to 196 c it shows no change upon rewarming a gradual decrease in intensity occurs starting at 120 c

magnetic fabric vs magnetite and biotite shape fabrics of the magnetite bearing granite pluton of gameleiras northeast brazil abstract a well defined orientation pattern has been evidenced by the magnetic fabric lineation and foliation of the granite pluton of gameleiras northeast brazil this magnetic fabric is roughly parallel to the magmatic fabric defined by the elongate mafic enclaves and by the planar arrangement of tabular k feldspar phenocrysts low field anisotropy of magnetic susceptibility properties as well as magnetic mineralogy studies and optical microscopy observations indicate that multidomian iron rich magnetite is the main carrier of the magnetic susceptibility and its anisotropy to examine in more detail the relationships between the magnetic and magmatic fabrics measurements of two dimensional shape fabrics of grain populations of biotite and magnetite have been carried out on a total of 500 grains using an automatic shape fabric analysis procedure on carefully selected and oriented thin sections angular departure has been calculated between the maximum elongation of the mineral shape fabric of the given grain population and the maximum susceptibility axis of the corresponding macroscopic specimen we found that the fabric of biotite correlates strongly with the magnetic fabric 7 8 the fabric of magnetite although not as well defined mainly because of its weak shape anisotropy still correlates with the magnetic fabric 12 18 origin of low field magnetic fabric in the pluton of gameleiras is concluded to be controlled principally by the statistical alignment of the long axes of inequant magnetite grains magnetic interactions between the grains of magnetite where they form clusters may account for the observed scattering or abnormal magnitudes of the magnetic anisotropy concerning the orientation of the magnetic fabric as the long dimensions of the magnetites preferentially align with the boundaries of the other minerals particularly biotite and titanite the magnetic fabric as defined by the grains of magnetite is concluded to approximate closely the magmatic fabric defined by the shape fabric of biotite however as no correlation exists between shapes or clustering of magnetites and strain undergone by the deforming magma the strength of the magnetic fabric in ferromagnetic granites cannot be used in a simple way as a measure of strain intensity

magma flow inferred from ams fabrics in a layered mafic sill insizwa south africa the insizwa sill is a 25 km diameter 1000 m thick layered mafic intrusion part of the karoo igneous province in south africa the peridotitic and gabbronoritic rocks are undeformed and mineral fabrics demonstrably result from magma flow a horizontal centimeter scale model layering is visible in numerous outcrops plagioclase crystals are both tabular and elongated their preferred orientation parallel to the layering forms a foliation and a nw se lineation respectively interpreted as the magma flow plane and flow direction throughout the 78 stations of this study 699 specimens magnetic susceptibilities km range from 750 to 10 000 10 6 si the magnetic anisotropy pj ranges from 1 03 to 1 08 magnetic ellipsoids are both prolate and oblate average tjc0 anisotropy of magnetic susceptibility ams fabrics are dominated by multidomain to pseudo single domain magnetite high field magnetic experiments indicate that the paramagnetic contribution from the mafic silicates is less than 50 for low susceptibility rock types the anisotropy results from magnetite grain shape solely as shown by no significant increase in pj with increasing km the magnetic lineation 305j 0 5j is consistent throughout the sill at various scales and coincides with the mineral lineation in average in contrast the magnetic foliation 125j ne 10j is generally perpendicular to the mineral foliation and to the layering several explanations for this odd configuration are discussed the variations of magnetic parameters across the layering and field observations point to a multiple injection the magnetic lineation is consistent with the presence of a single feeder dike situated to the se of the sill d 2002 elsevier science b v all rights reserved

magnetic anisotropy produced by magma flow theoretical model and experimental data from ferrar dolerite sills antarctica summary volcanic rocks forming sills dykes or lava flows may display a magnetic anisotropy derived from the viscous flow during their emplacement we model a sill as a steadystate flow of a bingham fluid driven by a pressure gradient in a horizontal conduit the magma velocity as a function of depth is calculated from the motion and constitutive equations vorticity and strain rate are determined for a reference system moving with the fluid the angular velocity and the orientation of an ellipsoidal magnetic grain immersed in the fluid are calculated as functions of time or strain magnetic susceptibility is then calculated for a large number of grains with a uniform distribution of initial orientations it is shown that the magnetic lineation oscillates in the vertical plane through the magma flow direction and that the magnetic foliation plane changes periodically from horizontal to vertical the results are compared with the magnetic fabric of ferrar dolerite sills victoria land east antarctica derived from low field susceptibility measurements

transmission and detection of guided seismic waves in attenuating media we can use guided seismic waves to map properties of reservoirs between wells with the low velocity layers acting as waveguides when guided waves are detected they are an indication of the continuity of the bed examined guided waveforms are characterized by time frequency representations to study important physical properties of the beds acting as waveguides we used full waveform seismic modeling in viscoelastic media to examine the required velocity contrasts and distances over which guided wave signals can be used in one set of models sandstones are the central waveguide lithology in another set shales we applied these models referred to here collectively as shaly sandstone waveguides to a range of geological circumstances where either the sands or the shales represent the low velocity layers within a reservoir to study the distances over which guided waves can be detected we compared the amplitudes of the signals computed for the models using a realistic source strength to the signal levels determined from published borehole noise studies in shaly sandstone waveguides we find it is feasible to use particle velocity measurements to record guided waves above seismic noise levels in the frequency range of 60 to 800 hz at well separations exceeding a distance of 800 m however pressure detectors such as hydrophones may only be useful up to distances of 400 m between wells in addition to the issues of shaly sandstone waveguides and practical distances between wells we present an application of guided waves using crosswell seismic data from the gypsy test site in oklahoma a site originally established by british petroleum in this field example within a sandstone reservoir we demonstrate the sensitivity of leaky mode amplitudes to source receiver location another telltale characteristic of continuity in the type of reservoir studied at the gypsy test site where there is a low shear velocity contrast between the host medium and the waveguide is the head wave followed by the leaky mode

two and three dimensional shape fabric analysis by the intercept method in grey levels the count intercept is a robust method for the numerical analysis of fabrics launeau and robin 1996 it counts the number of intersections between a set of parallel scan lines and a mineral phase which must be identified on a digital image however the method is only sensitive to boundaries and therefore supposes the user has some knowledge about their significance the aim of this paper is to show that a proper grey level detection of boundaries along scan lines is sufficient to calculate the two dimensional anisotropy of grain or crystal distributions without any particular image processing populations of grains and crystals usually display elliptical anisotropies in rocks when confirmed by the intercept analysis a combination of a minimum of 3 mean length intercept roses taken on 3 more or less perpendicular sections allows the calculation of 3 dimensional ellipsoids and the determination of their standard deviation with direction and intensity in 3 dimensions as well the feasibility of this quick method is attested by numerous examples on theoretical objects deformed by active and passive deformation on bse images of synthetic magma flow on drawing or direct analysis of thin section pictures of sandstones and on digital images of granites directly taken and measured in the field

west gondwana amalgamation based on detrital zircon ages from neoproterozoic ribeira and dom feliciano belts of south america and comparison with coeval sequences from sw africa

magnetic fabric constraints on the initial geometry of the sudbury igneous complex a folded sheet or a basin shaped igneous body abstract interpreted either as a folded igneous sheet or a basin shaped intrusion the origin of the palaeoproterozoic sudbury igneous complex sic ontario canada has been debated by geologists for over a century most recent proposals view the sic to have been emplaced as a horizontal impact melt and subsequently folded after solidification this requires the sic to have folded from an originally horizontal sheet to the present basinal geometry with dips of 30 in the north range and 70 in the east range the fold scenario would require the sharply curved juncture between the north and east ranges north lobe to be deformed in the solid state due to folding in order to test the fold model the rock fabric was investigated in the east and north ranges and the north lobe of sic at 256 sites with the aid of anisotropy of magnetic susceptibility ams a sampling transect through an undeformed portion of the sic in the western north range reveals that the gabbro norite exhibits sic contact parallel magnetic foliation and down dip magnetic lineation both of which respectively correlate to an igneous foliation and lineation the granophyre in contrast features spatially consistent magnetic lineation that is oriented orthogonal to the sic contact this magnetic lineation can be correlated to a mineral fabric characterised by aligned acicular crystals of plagioclase and is interpreted to be a wall orthogonal crystallisation texture the east and north ranges in the eastern sic reveal similar patterns of ams fabrics the magnetic lineation of the granophyre is orthogonal to the basal contact of the sic in the east and north ranges and in the fold like north lobe between the two ranges an axial planar magnetic foliation is developed in the granophyre as the north lobe is approached but the magnetic lineation is nevertheless contact orthogonal and well defined this ams fabric is interpreted to be a combination of an original igneous contact orthogonal lineation and a foliation resulting from tectonic overprint the preservation of the contact orthogonal magnetic lineation implies low levels of tectonic overprint conservative shortening strains estimated from ams numerical modelling suggest

guided seismic waves in layered poroviscoelastic media for continuity logging applications model studies1 the gas industry is continuing to concentrate its research and development efforts on new and advanced technology to improve reservoir descriptions through the producing life and development history of heterogeneous gas reservoirs a very important aspect of this need is the ability to reduce the uncertainty of estimating probable reserves and to lower the operating costs to recover incremental reserves in producing and depleted gasfields established methods for reducing uncertainty in heterogeneous reservoir compartments such as vsp and cross well techniques may enhance resolution but they are currently not economically justifiable in on shore gasfields continuity logging using guided waves is an alternative approach to analysing inter well seismic data to confirm the continuity of heterogeneous gas reservoir compartments in particular the continuity of sand and shale stratigraphy in gas reservoirs the solution of a coupled system of differential equations based on biot and homogenization theories is adapted to calculate guided seismic waves trapped in low velocity layers the general solution is for a 3d source in a horizontally layered poroviscoelastic medium having isotropic and laterally homogeneous material properties a unified representation of the medium that includes fluid solid interactions and viscoelastic losses is incorporated into the solution the guided wave part of the vector wave field and fluid pressure of the complete wave motion in layered dissipative media is verified and used to simulate dispersion and attenuation of guided seismic waves for continuity logging applications the results of this work suggest that the multimode wave solution is appropriate to simulate guided seismic wave signatures to indicate continuity of layered earth structures in poroviscoelastic reservoirs in particular the normal mode information can be used for planning continuity logging surveys and for interpreting the corresponding seismic data further fluid pressure waveforms show that maximum amplitude normal modes can be detected at layer interfaces in fluid filled porous media and the corresponding airy phase wave groups may carry information on the formation permeability

handaxes and the pick chopper industry of pleistocene china the presence of handaxes bifaces large cutting tools in paleolithic industries in china and elsewhere in east asia and their relationship with western acheulian bifaces have been discussed and debated for a long time most researchers concur that handaxes occur in some paleolithic industries in certain regions of central and south china however chinese handaxes exhibit some unique characteristics compared with their western acheulian counterparts either in terms of their quantity in lithic assemblages or based upon their specific technological and morphological features analyses indicate that most chinese handaxes are variants of picks a type of large digging tool found in pick chopper industries over a vast region complementary to choppers which are a kind of large cutting tool produced and used in the region for a long period of time raw material impact adaptation to certain habitat close ties with the pebble tool tradition and the relative isolation of local populations may all have contributed to the uniqueness and diversity of this type of lithic artifact in the region such stone tools may have played very important roles in human survival and adaptation in the intermontane basins and woodlands in tropical and subtropical environments in central and south china throughout the pleistocene

crystal size distribution csd in rocks and the kinetics and dynamics of crystallization ii makaopuhi lava lake crystal size distribution csd theory has been applied to drill core samples from makaopuhi lava lake kilauea volcano hawaii plagioclase and fe ti oxide size distribution spectra were measured and population densities n were calculated and analyzed using a steady state crystal population balance equation n n0 exp l g slopes on ln n versus crystal size l plots determine the parameter g a product of average crystal growth rate g and average crystal growth time the intercept is j g where j is nucleation rate known temperature depth distributions for the lava lake provide an estimate of effective growth time allowing nucleation and growth rates to be determined that are independent of any kinetic model plagioclase growth rates decrease with increasing crystallinity 9 9 5 4 10 11 cm s as do plagioclase nucleation rates 33 9 1 6 10 3 cm3 s ilmenite growth and nucleation rates also decrease with increasing crystallinity 4 9 3 4 10 10 cm s and 15 2 2 10 3 cm3 s respectively magnetite growth and nucleation rates are also estimated from the one sample collected below the magnetite liquidus g 2 9 10 10 cm s j 7 6 10 2 cm3 s moments of the population density function were used to examine the change in crystallization rates with time preliminary results suggest that total crystal volume increases approximately linearly with time after 50 crystallization a more complete set of samples is needed for material with 50 crystals to define the entire crystallization history comparisons of calculated crystallization rates with experimental data suggests that crystallization in the lava lake occurred at very small values of undercooling this interpretation is consistent with proposed thermal models of magmatic cooling where heat loss is balanced by latent heat production to maintain equilibrium cooling

the tellnes ilmenite deposit rogaland south norway magnetic and petrofabric evidence for emplacement of a ti enriched noritic crystal mush in a fracture zone abstract the tellnes ilmenite deposit a world class titanium deposit occurs in the ana sira anorthosite rogaland anorthosite province south norway it is mainly made up of an ilmenite rich norite that has been previously interpreted as injected in a crystal mush state in a weakness zone of the enclosing anorthosite this emplacement mechanism has produced a faint orientation in the ore due to the flow of the mush the internal flow structure of the orebody is studied here using the low field anisotropy of magnetic susceptibility ams method partial anhysteretic remanent magnetization paarm indicates that coarse magnetite is the main mineral responsible for the magnetic fabric parallelism of the magnetic fabric with the shape preferred orientation of the ore forming minerals is checked using image analysis ia from oriented sections intercept method interpretation of the ams data verified by paarm and ia provides information on the magmatic foliation and lineation emplacement flow of the ilmenite norite crystal mush occurred in the direction of the orebody parallel to its walls and with an average se 18 plunge the feeder zone was likely situated below a network of veins on the se end of the orebody the sickle shaped outcrop of the deposit suggests a transcurrent dextral opening of a wnw ese striking weakness zone across the anorthosite pluton

using ams combined with mineral shape preferred orientation analysis to understand the emplacement fabrics of the apiai gabbro norite ribeira belt se brazil the apiai gabbro norite is a massive fine grained neoproterozoic intrusion emplaced in a core of synformal structure that deforms low grade marine metasedimentary rocks of the ribeira belt of south eastern brazil the lack of visible magmatic layering or any internal fabric has been a major limitation in deciding whether the emplacement occurred before or after the regional folding to assist in the tectonic interpretations we combine low field anisotropy of magnetic susceptibility ams and silicate shape preferred orientation spo to reveal the internal structure of the mafic intrusion magnetic data indicate a mean susceptibility of about 10 2 si and a mean anisotropy degree p of about 1 08 essentially yielded by titanomagnetite the magnetic and silicate foliations for p 1 10 are parallel to each other while the lineations tend to scatter on the foliation plane in agreement with the dominant oblate symmetry of the ams and spo ellipsoids for lower p values the magnetic and silicate fabrics vary from coaxial to oblique and for p 1 05 their shapes and orientations can be quite distinct the crystal size distribution csd of plagioclase for p 1 05 is log linear in agreement with a bulk simple crystallisation history these results combined show that for a strong spo corresponding to a magnetic anisotropy above 1 10 ams is a reliable indicator of the magmatic fabric they indicate that the apiai gabbro norite consists of sill like body that was inclined gently to the north by the regional folding

magma dynamics beneath kameni volcano thera greece as revealed by crystal size and shape measurements size distributions of plagioclase crystals in series of recent porphyritic dacite lavas from kameni volcano greece can be modelled by mixing two populations of crystals each with overlapping linear crystal size distributions csd termed microlites and megacrysts the magmas bearing the microlites and megacrysts started to crystallise 6 13 and 24 96 years respectively before each eruption the dates of initiation of crystallisation of the megacrysts indicate that they are left overs of earlier injections of new magma into a shallow chamber some magma remains after each eruption and continues to crystallise new magma with few or no crystals is then introduced and the microlites crystallise from the mixed magma eruption followed 6 13 years after mixing such a model would suggest that some porphyritic magmas are products of a shallow magma chamber that is never completely emptied just topped up from time to time

comparing magnetic and magmatic fabrics to constrain the magma flow record in la gloria pluton central chile abstract this contribution illustrates a case study of a pluton la gloria pluton lgp where magnetic and magmatic fabrics are locally decoupled we compare the magmatic fabric with the available magnetic fabric data to explore their abilities and elucidate the magma flow record of lgp results indicate that magnetic controlled by multi domain magnetite and magmatic fabrics are generally consistent throughout lgp foliations define an axisymmetric pattern that gradually changes from vertical near lateral margins to less steep in the pluton interior whereas lineations are subhorizontal following the elongation direction of the pluton however samples at the pluton center show marked differences between both fabrics magnetic fabrics indicate subhorizontal magnetic lineations and foliations and magmatic fabrics indicate subvertical lineations and foliations both magnetic and magmatic fabrics are interpreted to record strain caused by magma flow during thermal convection and lateral magma propagation at the transition between low and high crystallinity stages we suggest that fabrics acquisition and consistency were determined by shear conditions pure simple shear rates ratio and the orientation of the magma flow direction with respect to a rigid boundary critical crystalline region of the pluton magmatic fabric differs at the center of the pluton because pure shear is dominant and ascendant flows are orthogonal to the horizontal rigid boundary lgp represents a whole scale partly molten magma reservoir where both thermal convection and lateral propagation of the magma are recorded simultaneously this study highlights the importance of characterizing both fabrics to properly interpret magma flow recorded in plutons

magmatic lineations inferred from anisotropy of magnetic susceptibility fabrics in units 8 9 and 10 of the rum eastern layered series nw scotland the eastern layered series of the rum layered suite nw scotland comprises a sequence of sixteen 30 150 m thick cyclic units the upper troctolite olivine gabbro parts of each of these units exhibit small scale modal layering and a pervasive layerparallel mineral lamination that is often associated with soft sediment deformation structures a sporadic macroscopic magmatic lineation measurable on mineral lamination surfaces is also observed in places anisotropy of magnetic susceptibility ams fabrics were studied in three of these cyclic units 8 9 and 10 in the northern part of the eastern layered series magnetic fabrics measured in the troctolites and gabbros yield one dominant trend in which magnetic foliations parallel magmatic layering and magnetic lineations trend nw se and plunge gently magnetic fabrics measured for two detailed traverses through unit 10 on the northern side of hallival also yield one dominant trend similar to that measured elsewhere in the eastern layered series however toward the centre of unit 10 in each traverse magnetic lineations sometimes plunge approximately downdip sw on the magnetic foliation planes the implications of these results are discussed with reference to previous textural and fabric observations on rum a model is suggested in which weak linear arrangements of cumulus olivine and plagioclase crystals are developed due to slumping and soft sediment deformation of unconsolidated crystal mushes during central sagging of the rum layered suite 2007 elsevier b v all rights reserved

composite magmatic magnetic fabrics evidences late ams in syn tectonic dikes in the monteiro sume plutonic volcanic complex ne brazil abstract interpretations of flow fabrics in dikes using anisotropy of magnetic susceptibility ams are based on the orientation of the magnetic fabric recorded next to the dike walls however uncertainties remain when ams is sensitive to parameters such as grain size and composition of the magnetic carriers and deformation of the magma we study subvolcanic andesite to dacite dikes associated with granite plutons that intrude the basement rocks the dikes have magnetic susceptibilities mostly between 10 3 and 10 2 si carried by fe ti oxides ams shows fabrics that would be consistent with a lateral movement of the magma however the anisotropy of anhysteretic remanence aar and silicate shape preferred orientation spo indicate that the melt moved upward based on the steeply plunging lineations detected by aar and spo furthermore the obliquity of the aar foliations in the dike margins indicates a component of transtension resolved in the dike walls as there is no evidence for internal deformation of titanomagnetite ams would record its late growth in the tectonic extension direction the magnetic subfabric concealed by late ams therefore documents an earlier tectonic episode and evidence the limits of using just ams directions to constrain the emplacement of syntectonic magmas

using magma flow indicators to infer flow dynamics in sills abstract fabrics from anisotropy of magnetic susceptibility ams analyses and shape preferred orientation spo of plagioclase are compared with field structures such as bridge structures intrusive steps and magma lobes formed during magma intrusion in jurassic sills this is to constrain magma flow directions in the sills of the karoo igneous province along the kwazulu natal north coast and to show how accurately certain structures predict a magma flow sense thus improving the understanding of the karoo sub volcanic dynamics the ams fabrics are derived from magnetite grains and are well constrained however the spo results are commonly steeply inclined poorly constrained and differ to the ams fabrics both techniques resulted in asymmetrical fabrics successful relationships were established between the ams fabric and the long axes of the magma flow indicators implying adequate magma flow prediction however where numerous sill segments merge either in the form of magma lobes or bridge structures the coalescence process creates a new fabric between the segments preserving late stage magma migration between the merged segments overprinting the initial magma flow direction

magnetic susceptibility and partial anhysteretic remanence anisotropies in the magnetite bearing granite pluton of tourao ne brazil abstract rock magnetism and magnetic fabric studies were performed in the tourao granite western part of serido belt ne brazil this pluton 350 km2 is composed of k rich calc alkalic monzogranites and was emplaced between a set of ne and e trending dextral strike slip shear zones electronic and optical microscopy thermomagnetic curves hysteresis data and coercivity spectra revealed that magnetite fine and coarse grained is the unique ferromagnetic mineral in these rocks anisotropy of low field magnetic susceptibility ams was measured in 83 sites and for many sites from central and southern parts of the intrusive body a large scatter was noticed anisotropy of partial anhysteretic remanence paar was determined for 29 sites in the 0 50 mt paar0 50 and 19 sites in the 50 90 mt paar50 90 windows to isolate the fabric contribution of the remanence bearing grains magnetite in most sites ams is dominantly carried by magnetite whereas in some sites the paramagnetic contribution exceeds 60 of the bulk susceptibility the paar0 50 is assumed to be related to coarse grained early crystallized magnetites while the paar50 90 is interpreted as due to fine needle shaped magnetites hosted in biotites the combined analysis of these magnetic techniques permits interpretation in terms of fabric formation in the tourao granite and the inference that at least two successive kinematic events were recorded in this intrusive body devoid of any solid state deformation overprint the ams and paar0 50 fabrics for most of the sites correlate with the early nne trending magmatic fabric whereas paar50 90 reveals a different fabric probably related to late partitioning of magmatic straining along the e trending shear zones in the southern part of the body a completely different paar0 50 fabric is correlated with the late intrusion of charnockite stocks