structural and anisotropy of magnetic susceptibility ams evidence for oblique impact on terrestrial basalt flows lonar crater india the anisotropy of magnetic susceptibility ams technique combined with the analyses of satellite images and the geological structure are examined on lonar crater a small 1 8 km diameter impact crater in india to evaluate the direction and obliquity of asteroid impact the advanced spaceborne thermal emission and reflection radiometer aster image 15 m resolution of the ca 52 ka lonar crater in the subhorizontal deccan basalt ca 65 ma shows that this simple bowl shaped impact crater has a near circular rim with a circularity of 0 95 most of the highly reflecting continuous ejecta blanket around the crater rim can be enveloped with an ellipse whose major e w axis is coincident with the diameter of the crater rim and minor n s axis is relatively displaced toward the west by 200 m the present ejecta distribution which appears to be close to its pristine shape extends to a distance of 700 m in all the directions from the crater rim except to the west where it extends to a distance of a little more than 1 km the circular shape of the crater rim the e w bilateral symmetry of the enveloping ellipse on the ejecta and the greater extension of the ejecta toward the west appear to be the result of an oblique impact from the east with an angle of incidence of 30 45 when compared with experiments the ams data suggest that the target basalts occurring at 2 km west southwest of the crater rim are highly shocked as indicated by the random orientation of their k 3 susceptibility axes in comparison to the unshocked basalts at 2 km east southeast of the crater the unshocked basalts show a bimodal distribution of susceptibility axes typical of lava flows moderate to strong westward shifts of the k 3 axes are seen for the majority of the shocked basalts on the crater rim and west southwest of the crater the shocked basalts also indicate an oblique impact from the east when compared with modeling and experiments a general lowering of degree of anisotropy of the lonar shocked basalts 1 01 compared to the surrounding unshocked basalts 1 03 is found to be a characteristic feature of impact crater target rocks variation in attitudes of the basalt flows on the lonar crater rim shows a bilaterally symmetrical distribution about an e w axial plane which includes quaquaversal dips of the flows all around the crater rim except to the west where overturned dips of the basalt flows are seen it appears that oblique impact and the symmetry in structural variations around the crater rim have a relationship for a small crater such as lonar

a new model for the emplacement of columbia river basalts as large inflated pahoehoe lava flow fields extensive flows of the columbia river basalt crb group in washington oregon and idaho are dominantly inflated compound pahoehoe sheet lavas early studies recognized that crb lavas are compound pahoehoe flows with textures suggesting low flow velocities but it was thought that the great thickness and extent of the major flows required very rapid emplacement as turbulent floods of lava over a period of days or weeks however small volume 1 km compound pahoehoe flows on kilauea hawai i demonstrate that such flows can thicken by at least an order of magnitude through gradual inflation and the same mechanism has been proposed for larger 10 20 km3 pahoehoe flows in iceland the vertical distribution of vesicles and other morphologic features within crb lava flows indicate that they grew similarly by inflation small pahoehoe lobes at the base and top of many crb pahoehoe lava flows indicate emplacement in a gradual piecemeal manner rather than as a single flood we propose that each thick crb sheet flow was active for months to years and that each group of flows produced by a single eruption a flow field was emplaced slowly over many years

the limiting pressure on a circular pile loaded laterally in cohesive soil in the analysis of the undrained loading of laterally loaded piles an important quantity is the ultimate lateral resistance at depth to purely horizontal movement if the soil is modelled as a perfectly plastic cohesive material then the calculation of this quantity reduces to a plane strain problem in plasticity theory in which the load is calculated on a long cylinder which moves laterally through an infinite medium an exact calculation of the load on such a cylinder is presented if this load is non dimensionalized with respect to the soil strength and the diameter of the pile it is found that the load factor varies between for a perfectly smooth pile and for a perfectly rough pile this result is discussed in the context of previous calculations for the lateral load capacity of piles and is compared with approximate calculations using cavity expansion theory and a wedge failure near the soil surface la resistance laterale limite en profondeur au seul mouvement horizontal represente un parametre im

characteristic magnetic behavior of subaerial and submarine lava units from the hawaiian scientific drilling project hsdp 2 1 this study presents rock magnetic properties and the magnetic mineralogy of subaerial and submarine lava flows of mauna loa and mauna kea volcanoes collected from the 3109 m deep hsdp 2 drill hole in hawaii three different groups of magnetic behavior are recognized in the subaerial lava flows related to the degree of high temperature oxidation during extrusion group 1 shows homogenous titanomagnetite with low xmt low curie temperatures tc 100 200 c and weak median demagnetizing fields 20 mt further subdivision into 1a and 1b subgroups is based on the low temperature behavior of magnetic susceptibility ms and hysteresis loops which indicate a contribution from ferrimagnetic cr al spinel below ca 160 c in the 1b type samples group 2 samples with exsolution lamellae of ilmenite in the titanomagnetites have higher tc 480 580 c and higher coercive forces 20 40 mt group 3 the highest oxidation stage is characterized by titanohematite bearing assemblages with enhanced median demagnetizing fields 35 85 mt and a significantly different low temperature ms behavior ms core logging shows a systematic variation occurs in the subaerial lava flows directly related to the degree of high temperature oxidation and their flow morphology aa lava flows have higher mean ms than other lava flow types besides these factors ms appears to be also affected by the magma composition of the various shield building stages mauna loa subaerial lava flows generally show lower mean susceptibilities 4 6 3 10 3 si than subaerial mauna kea lava flows 9 8 5 10 3 si as submarine lava flows show no group 3 assemblages no high temperature oxidation influenced these rocks some hyaloclastites and pillow breccias show low ms 1 10 3 si small amounts of nearly pure magnetite tc 580 c and high coercive forces up to 110 mt suggesting single domain and or superparamagnetic behavior the controlling mechanism of the magnetic properties in the submarine lava units is the cooling and quenching rate of lava flows which creates large grain size variations in titanomagnetites of varying compositions hydrothermal alteration as described from ocean floor or icelandic basalts is not an important process that influences the magnetic properties in the ocean island basalts from the hsdp 2 drill hole

upper bound and load displacement solutions for laterally loaded piles in clays based on energy minimisation introduction an important part of any foundation design procedure is the evaluation of the ultimate capacity and displacements under working loads the most widely used solution for ultimate loads of laterally loaded piles in clays is that of broms 1964 broms ignored the soil resistance down to a depth of one and a half diameters and used a constant resistance value of 9sud along the remainder of the pile where su is the undrained shear strength and d is the pile diameter while the value of 9sud closely corresponds to the bestknown lowerand upper bound solutions 9 14sud and 9 20sud respectively randolph houlsby 1984 martin randolph 2006 the omission of the upper soil resistance is somewhat arbitrary on the other hand associating a resistance value of 9sud with the upper soil would not be conservative as a wedge type mechanism will develop in that area murff hamilton 1993 reduction factors are therefore commonly applied to the ultimate soil resistance near the surface in p y curves e g matlock 1970 fleming et al 1992 murff hamilton 1993 dealt thoroughly with this problem by suggesting an upper bound failure mechanism comprising a conical wedge near the surface and a flowround plane strain mechanism below the wedge strictly speaking their upper bound solution is not rigorous since the transition from the wedge to the flow round mechanism is not continuous and the associated dissipation due to the abrupt change in the velocity field was not taken into account also energy dissipation due to relative shearing between the stratified flow round mechanisms was not considered in their solution in the present work a wedge type mechanism following the methodology of murff hamilton 1993 but eliminating the discontinuity at the outer boundary of the wedge is combined with the continuous flow round mechanism of klar osman 2008a to result in a fully compatible and continuous deformation field this deformation field allows rigorous calculations of upper bound values in addition since the mechanism is continuous with strain and strain rates defined everywhere the mobilisable strength design msd method bolton powrie 1988 osman bolton 2005 may be applied for estimation of displacements under working loads formulation figure 1 outlines the mechanism assumed for a long pile the pile rotates rigidly above a plastic hinge which develops at depth h a conical wedge type failure originating from depth z0 and extending to radial distance of rw develops near the surface below z0 a flow round mechanism prevails the parameters h rw and z0 are not known a priori and must be found by the upper bound minimisation process the suggested flow round mechanism corresponds to the solution of klar osman 2008a who utilised the airy stress function usually associated with elasticity to obtain a continuous kinematically admissible velocity field for the t bar problem the mechanism may be represented in a cylindrical coordination system r by the functions

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

field impressed anisotropies of magnetic susceptibility and remanence in minerals the application of alternating af or direct df magnetic fields to samples containing dispersed particles of magnetite titanomagnetite or maghemite has been found to alter significantly the measured low field susceptibility anisotropy even though the particle orientation is unchanged the acquisition of isothermal remanent magnetization irm is also strongly dependent on the previous af treatment given to the samples a method of quantifying the changes brought about by application of the fields is described the samples studied were intrinsically isotropic or only weakly anisotropic and the computed impressed susceptibility or irm ellipsoids produced by the applied fields were ellipsoids of revolution with the unique axis aligned with the applied field axis the size and shape of the field impressed ellipsoids were strongly dependent upon particle size these effects might thus form the basis of a rapid nondestructive means of estimating particle size in rocks the results also have important implications for magnetic fabric analysis and the static af demagnetization of rocks in particular to ensure that the intrinsic magnetic fabric is measured without any field impressed component of anisotropy samples should not be subjected to static af demagnetization prior to the determination of either low field susceptibility anisotropy or irm anisotropy samples should also not carry a significant remanence such as an irm acquired in a field greater than about 5 mt prior to low field susceptibility anisotropy analysis

structural geology of impact craters abstract the formation of impact craters is a highly dynamic and complex process that subjects the impacted target rocks to numerous types of deformation mechanisms understanding and interpreting these styles of micro meso and macroscale deformation has proved itself challenging for the field of structural geology in this paper we give an overview of the structural inventory found in craters of all size ranges on earth and look into the structures of craters on other planetary bodies structural features are discussed here that are caused by i extremely high pressures and temperatures that occur during the initial passage of the shock wave through the target rock and projectile ii the resulting flow field in the target that excavates and ejects rock materials and iii the gravitationally induced modification of the crater cavity into the final crater form a special focus is put on the effects that low angle impacting bodies have on crater formation we hope that this review will help both planetary scientists and structural geologists understand the deformation processes and resulting structures generated by meteorite impact

pile stress estimation based on seismic deformation method with embedment effects on pile caps a pseudostatic analysis based on the beam on nonlinear winkler spring method considering the seismic earth pressure and side friction acting on embedded pile caps was developed to estimate pile bending moments and shear forces to verify the proposed method s effectiveness the authors conducted six dynamic centrifuge tests on a superstructure footing model supported by 2 2 piles in sand deposits comprising a dry sand layer over liquefied soil the seismic earth pressure vertical wall friction at the active and passive sides and friction at the sidewalls of the pile caps were separately measured by two dimensional load cells during shaking the seismic total earth thrust and side friction estimated by the proposed method showed good agreement with the experimental results for both the amplitude and phase difference to the superstructure and the pile cap inertia forces the estimated bending moment and shear force in the piles also showed reasonable agreement with the experimental results they were able to account for differences in the pile rigidity and soil relative density

characterization of the magnetic fabric of rocks abstract an inextensive system of magnetic susceptibility anisotropy factors is suggested which is sufficient in the majority of practical applications for characterizing the magnetic fabric of rocks the system involves three newly devised factors the corrected anisotropy degree the shape factor and the difference shape factor the first of these characterizes the quantity of anisotropy somewhat better than the commonly used anisotropy degree the shape factor characterizes the quality of anisotropy i e the shape of the susceptibility ellipsoid in a convenient way its definition is based on a certain analogy between the anisotropy ellipsoid and the strain ellipsoid the difference shape factor can replace the shape factor when only the differences between the principal susceptibilities are given while the mean susceptibility is unknown

paleomagnetism of impact spherules from lonar crater india and a test for impact generated fields article planetary surfaces have been ubiquitously melted by meteoroid impacts throughout solar system history the resulting impact melts form some of the youngest igneous samples from rocky bodies like the moon mars and asteroids upon cooling these melts may record any ambient planetary magnetic fields as well as postulated transient fields generated by impact plasmas impact generated fields have been proposed as a key alternative to the core dynamo hypothesis for the paleomagnetism of extraterrestrial bodies here we describe a paleomagnetic study of basaltic impact glasses from the lonar impact crater situated in the deccan traps in maharashtra india previous theoretical work predicts extremely strong magnetic fields possibly n1 000 times the earth s surface field may have been transiently generated during the lonar impact we find that the glasses contain a natural remanent magnetization nrm whose properties depend strikingly on sample mass small b0 5 g splash form samples demagnetize erratically and are inefficiently magnetized while larger irregularly shaped samples contain a stable component that is efficiently magnetized similar to lonar basalts however the rock magnetic recording properties of these samples are uncorrelated with mass therefore we conclude that the size dependence of the nrm reflects a difference in how the samples acquired thermoremanence the splash forms of the smaller samples indicate they cooled during flight and therefore that they were magnetized while in motion explaining their weak and unstable nrm this motional nrm is a new manifestation of thermoremanent magnetization not observed before in geologic samples no glasses contain evidence for any strong n 100 t impact generated fields

magnetic versus crystallographic fabrics in a basaltic lava flow combined anisotropy of magnetic susceptibility ams and crystallographic studies were performed within a quaternary lava flow for which we have a thorough knowledge of the flow direction microscope examinations microprobe analyses and studies of rock magnetic properties show that ams is carried by homogeneous multidomain ti rich titanomagnetite xc0 6 this mineral forming either subhedral isolate individuals or grouped in various elongated aggregates represents a late crystallized interstitial phase ams determined from samples collected in the lower the middle and the upper part of the flow is characterized by a well defined magnetic foliation whereas magnetic lineation is generally poorly grouped and therefore meaningless the foliation plane of the lower and upper part of the flow show an obliquity which is interpreted as an opposite imbrication indicating a westward flow in agreements with the known flow direction in the lower part of the lava flow the tight correlation between ams and plagioclase lattice preferred orientation suggests that a silicate framework control the titanomagnetite crystallization and thus the orientation of the ams ellipsoid d 2005 elsevier b v all rights reserved

magnetic susceptibility zonation of the melilititic riedheim dyke hegau volcanic field germany evidence for multiple magma pulses the olivine melilitic riedheim dyke complex is related to the tertiary alkaline magmatism within the hegau volcanic field magnetic susceptibility measurements and the mineral composition of oxides together with petrographic observations imply two phases of magma intrusion for the emplacement of this dyke the first intrusion forms the eastern and western margins of the dyke section with high magnetic susceptibility values of up to 75 10 3 si which are related to ferrimagnetic mg al cr bearing titanomagnetites with a magnetite component between 0 59 and 0 75 mol a generally lower magnetic susceptibility of up to 45 10 3 si and a significantly lower and homogeneous magnetite component of the titanomagnetites xmt 0 38 mol are recorded for the second intrusion into the central part of the dyke furthermore a dependence of magnetic susceptibility on the amplitude of the ac field was measured which is more pronounced in the second intrusion hd 25 than in the first one 6 hd 10 confirming the magneto mineralogical data secondary pervasive alteration is more pronounced in the first intrusion phase characterised by a very fine grained and glassy matrix that is more receptive to hydrothermal overprint than the well crystallised matrix of the second intrusion localised thermally induced alteration at the intimately fractured contact between the first and second intrusion phase has oxidised the titanomagnetite of the first intrusion phase but did not significantly effect the second intrusion differences between the dyke sections are also documented by the anisotropy of magnetic susceptibility ams which reflects a magmatic flow fabric with long axis of the ams ellipsoids magnetic lineation parallel to the flow direction and short axis normal to the n s trending dyke boundary the orientation of the magnetic fabric for the individual magma pulses is different with a more moderate plunge of the magnetic lineation within both the western 177 57 and eastern parts 181 50 of the first dyke intrusion compared to a nearly vertical orientation in the second central dyke intrusion 180 78 we suggest that the primary crystallisation history of the two intrusion phases caused the magnetic susceptibility zonation in the riedheim dyke complex

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

behavior of pile foundations in laterally spreading ground during centrifuge tests eight dynamic model tests were performed on a 9 m radius centrifuge to study the behavior of single piles and pile groups in liquefiable and laterally spreading ground pile diameters ranged from 0 36 to 1 45 m for single piles and from 0 73 to 1 17 m for pile groups the soil profile consisted of a gently sloping nonliquefied crust over liquefiable loose sand over dense sand each model was tested with a series of realistic earthquake motions with peak base accelerations ranging from 0 13 g to 1 00 g representative data that characterize the important aspects of soil pile interaction in liquefiable ground are presented dynamic soil pile and soil pile cap forces are backcalculated directions of lateral loading from the different soil layers are shown to depend on the mode of pile deflection relative to the soil which depends on the deformed shape of the soil profile the pile foundation stiffness and the magnitude of loads imposed by the nonliquefied crust procedures for estimating the total horizontal loads on embedded piles and pile caps i e passive loads plus friction along the base and sides are evaluated due to liquefaction of the sand layer beneath the crust the relative displacement between the pile cap and free field crust required to mobilize the peak horizontal loads is much larger than expected based on static pile cap load tests in nonliquefied soils

lateral spreading forces on bridge piers and pile caps in laterally spreading soil effect of angle of incidence in this paper the kinematic forces which may be applied to bridge piers or pile caps from laterally spreading surficial cohesive soil layers nonliquefied crusts through which they pass are considered such forces often represent the largest load component acting on a structure and or foundation during liquefaction induced lateral spreading both circular and square structural inclusions are considered and particular attention is paid to the orientation of the inclusion to the direction of spreading here defined as the angle of incidence experimental modeling was conducted using a modified direct shearbox to simulate the spreading of kaolin past structural inclusions at various load displacement data and particle image velocimetry analysis revealed that the ultimate load for both square and circular cases may be determined using a wedge based upper bound plasticity analysis for circular sections this ultimate load is independent of due to radial symmetry the ultimate load on square sect

petrographic and geophysical assessment of coal quality as related to briquetting the miocene lignite of the lower rhine basin germany in the lower rhine basin germany tertiary lignites are mined primarily for electrical power generation and briquetting purposes until 2000 when the mine was closed coals from the bergheim open pit mine were used for briquetting after 2000 briquettes were produced from the hambach open pit mine but did not show the same quality and hardness as those from the bergheim pit in this context the macropetrographic and microlithotype composition of the hambach lignites was studied in detail samples were taken from the three profiles s1 s2 and s3 and a well r1 all of the samples were macropetrographically described analyzed in their microlithotype composition and coals from profile s3 were analyzed for their briquetting compression strength three horizons of high gelite content were detected in the main seam two of them with negligible thickness and one with a thickness of up to 1 m briquettes produced from these horizons are characterized by significantly reduced hardness by careful interpretation of subtle changes in geophysical log data it was possible to map the occurrence of these gelite horizons as a consequence of these studies an excavation plan was set up by the rwe rheinbraun to avoiding mining of critical strata for briquetting purposes

effect of relative lake level changes in mire lake system on the petrographic and floristic compositions of a coal seam in the most basin miocene czech republic abstract exposures in the bilina opencast mine provide a direct evidence that the 3 5 m thick upper bench of the main seam in the most basin passes over a distance of about a kilometre into a hundred metres thick equivalent of clastic deltaic sediments with gilbert type mouth bars and thus clearly corroborates the co existence of lacustrine delta mire system deposition of the delta and the upper bench of the main seam were affected by five short term lacustrine incursions possibly related to tectonic subsidence before final lacustrine transgression took place between the temporary lacustrine incursions delta mouth bars prograded into an extensive mire being separated only by a shallow compaction lake along mouth bars foreland however most clastics introduced from delta were caught by dense vegetation in a narrow proximal zone of mire and did not affect more distal parts of relatively dry woodland mire with water table fluctuating around the surface it is therefore characterised by low ash yield and increased resinite fusinite and inertodetrinite contents palynological data indicate that the peat forming vegetation of the upper bench of the main seam was dominated by taxodiaceae glyptostrobus athrotaxis and calamus palm accompanied by paludal species of the family pinaceae and rich undergrowth of ferns and vaccinium type ericaceae progradation of delta mouth bars to the proximity of the study section is documented by increasing proportion of allochthonous elements produced by plants colonizing the flood plain and delta plain areas nyssa taxodium parrotia ulmus pyramidalis and comptonia pinus oviformis associations in contrast during periods of temporary lacustrine transgressions the mire was replaced by open water environment which favoured deposition of clay rich coals or partings 30 of ash yield of the flooding horizons in spite of fact that delta body retreated to the basin margin and the clastics were introduced from a larger distance rare palynomorphs indicate only sparse vegetation cover of aquatic plants during this time clay content seems to be the best indicator of the water level fluctuations facies indices e g tpi and gi show only poor correlation to hydrological and floristic changes detected in the mire lake system

fabric of the rio ceara mirim mafic dike swarm northeastern brazil determined by anisotropy of magnetic susceptibility and image analysis 1 anisotropy of magnetic susceptibility ams and petrofabric studies of the early cretaceous rio ceara mirim dike swarm reveal that shape preferred orientation of opaque grains controls the magnetic fabric the 350 km long swarm is characterized by relatively thick dikes of the order of 20 m up to 150 m in width the strong magnetic susceptibility of these rocks around 5 10 2 si is attributed to magnetite with low ti content the magnetite usually forms euhedral to subhedral equant to skeletal grains the resulting ams has a large proportion of abnormal fabric types as observed in 58 of the 50 dikes studied the remaining 42 of the dikes show a normal fabric regionally characterized by steep magnetic foliations and subhorizontal lineations in the central eastern part of the swarm however the lineation plunges downdip suggesting a magmatic feeder zone the shape alignment of the plagioclase supports the inferred regional flow pattern indicating a primary origin for the normal ams inverse to highly imbricate magnetic fabrics have lineations perpendicular to or at a high angle to the dike wall a shape lineation of opaque grains lies generally close to the magnetic lineation while the foliation is provided by the oblate shaped plagioclase fabric petrofabric studies indicate that the abnormal magnetic fabric is unrelated to flow competition of interstitial magnetite grains crystallizing either along as well as perpendicular to the magma stretching direction seems to account for the weak magnetic anisotropy and the irregular distribution of the ams types on the swarm

hydrothermal alteration at the lonar lake impact structure india implications for impact cratering on mars the 50 000 year old 1 8 km diameter lonar crater is one of only two known terrestrial craters to be emplaced in basaltic target rock the 65 million year old deccan traps the composition of the lonar basalts is similar to martian basaltic meteorites which establishes lonar as an excellent analogue for similarly sized craters on the surface of mars samples from cores drilled into the lonar crater floor show that there are basaltic impact breccias that have been altered by post impact hydrothermal processes to produce an assemblage of secondary alteration minerals microprobe data and x ray diffraction analyses show that the alteration mineral assemblage consists primarily of saponite with minor celadonite and carbonate thermodynamic modeling and terrestrial volcanic analogues were used to demonstrate that these clay minerals formed at temperatures between 130 c and 200 c by comparing the lonar alteration assemblage with alteration at other terrestrial craters we conclude that the lonar crater represents a lower size limit for impact induced hydrothermal activity based on these results we suggest that similarly sized craters on mars have the potential to form hydrothermal systems as long as liquid water was present on or near the martian surface furthermore the fe rich alteration minerals produced by post impact hydrothermal processes could contribute to the minor iron enrichment associated with the formation of the martian soil

soil deformation measurement using particle image velocimetry piv and photogrammetry a deformation measurement system based on particle image velocimetry piv and close range photogrammetry has been developed for use in geotechnical testing in this paper the theory underlying this system is described and the performance is validated digital photography is used to capture images of planar soil deformation using piv the movement of a fine mesh of soil patches is measured to a high precision since piv operates on the image texture intrusive target markers need not be installed in the observed soil the resulting displacement vectors are converted from image space to object space using a photogrammetric transformation a series of validation experiments are reported these demonstrate that the precision accuracy and resolution of the system are an order of magnitude higher than previous image based deformation methods and are comparable to local instrumentation used in element testing this performance is achieved concurrent with an order of magnitude increase in the number of meas

shock experiments up to 30 gpa and their consequences on microstructures and magnetic properties in pyrrhotite 1 shock experiments with pressures ranging from 3 to 30 gpa have been conducted on a mixed assemblage of hexagonal and monoclinic pyrrhotite all samples were studied with respect to their particular shock induced microstructures and magnetic properties at high and low temperatures up to 8 gpa microstructures in shocked pyrrhotite are characterized by mechanical deformation producing a damage of the crystal structure at pressures of 20 gpa and upward amorphization and mechanical twinning are the dominant structural features induced by shock within the lower pressure range coercivity saturation isothermal remanent magnetization and coercivity of remanence increase with shock pressures in agreement with more single domain sd like behavior simultaneously the peak of hexagonal pyrrhotite decreases and the 34 k transition of monoclinic pyrrhotite broadens and is depressed magnetic hardening is triggered by grain size reduction but also by the formation of sd within discrete multidomain grains planar deformation features subdivide such multidomain grains into lath shaped domains with average sizes lying in the sd range the planar deformation features disappear at 20 gpa and irregular nanometer sized amorphous domains occur instead pressure release from 30 gpa finally triggers partial melting of pyrrhotite the sharp interfaces between molten and crystalline pyrrhotite document a rapid change of thermal conditions within molten pyrrhotite quenched iron crystals occur the presence of native iron strongly influences the magnetic properties depending on the particular amount in the studied sample and likely affects the magnetic properties of impact lithologies on earth and extraterrestrial material

is this magnetic fabric normal a review and case studies in volcanic formations abstract when studying weakly anisotropic rocks non standard relationships between magnetic and expected petrofabric axes are sometimes observed in particular the so called inverse or intermediate fabrics a review of possible explanations for these effects is presented and leads to the conclusion that a majority of abnormal magnetic fabrics often encountered in magnetite rich volcanic rocks are due to abnormal preferred orientations or distributions of magnetite grains through case studies in dikes from skye island yemen and the iberian peninsula and magma and ash flows from the ethiopian traps and southern corsica the various possible origins of such fabrics are examined it is possible to retrieve reliable magma flow directions from these sites provided proper data selection is performed leading to non unique interpretations

effects of axial load and slope arrangement on pile group response in laterally spreading soils abstractthis paper presents the results of a series of dynamic centrifuge tests that were conducted for 2 2 pile groups in a three layer laterally spreading soil profile consisting of a nonliquefiable cohesive crust overlying loose liquefiable sand overlying dense sand two main variables are considered both of which received little attention in previous work on piles in laterally spreading soils namely 1 the axial load carried by the foundation and 2 whether the slope boundary conditions are infinite or finite the data show that the presence of axial load reduces the lateral stiffness of the foundation resulting from p effects and reduces their capacity to resist lateral kinematic loads from spreading soil this degradation in lateral response bending may be accompanied by substantial settlement of the foundation as a competing failure mode that must also be considered in design furthermore the mechanical response of the liquefied soil appears to vary greatly with the slope boundary condi

petrology and organic geochemistry of the lower miocene lacustrine sediments most basin eger graben czech republic abstract thirty samples of the lacustrine sediments from three localities of the most basin including coal samples were studied by petrological and organic geochemical methods the consistent results indicate the relatively stable surface development of the sediments in the environment of the holesice lom and osek members biological material with contribution of microbial activity participated in the storing which led to the formation of clayey coal in the results of the chemical composition dominated sesqui diand triterpene compounds completely different sediments of libkovice member contained low proportions of small organic particles dispersed in the sediment in the extracts of these samples prevailed hopanes perylene and sulphur after the action of microorganisms the base of the organic fraction also formed remains of terrestrial plants and liptinite macerals especially alginite liptodetrinite and bituminite that are typical for lacustrine sediments

origin and implications of two verwey transitions in the basement rocks of the vredefort meteorite crater south africa abstract two populations of magnetite exist in the shocked basement rocks of the vredefort meteorite impact crater one associated with original crustal genesis and metamorphism around 3 0 ga and the other related to the impact itself at 2 02 ga pre impact magnetite is mostly micron to millimeter in size lying within the multidomain to pseudo single domain range the second population of magnetite is less than 10 m in size and formed within the interstices of planar deformation features or within the reaction rims of biotite both of which were created during impact our study shows that each of these populations possesses specific verwey transition temperatures one around 124 k associated with pre impact magnetite and the other around 102 k associated with impact related magnetite the high temperature verwey transition is attributed to stoichiometric magnetite while the low temperature verwey transition to non stoichiometric magnetite pre impact rocks containing both verwey transitions are ubiquitous throughout the crater pseudotachylites formed during impact have a single verwey transition spanning temperatures from 94 to 111 k heating the basement rocks above 550 600 c for 3 min or above 500 c for 1 h irreversibly modifies the 124 k verwey transition by shifting it to lower temperatures based on these findings it is possible that no wholesale heating of the crater occurred above 550 600 c for 3 min or above 500 c for 1 h during or since the time of impact although some places of more localized heating are identified an unresolved problem remains to reconcile these data with temperatures thought to exist in the crust during and after impact

the internal structure of lava flows insights from ams measurements ii hawaiian pahoehoe toothpaste lava and a ā abstract we studied the anisotropy of magnetic susceptibility ams of 22 basaltic flow units including s type pahoehoe p type pahoehoe toothpaste lava and a emplaced over different slopes in two hawaiian islands systematic differences occur in several aspects of ams mean susceptibility degree of anisotropy magnetic fabric and orientation of the principal susceptibilities among the morphological types that can be related to different modes of lava emplacement ams also detects systematic changes in the rate of shear with position in a unit allowing us to infer local flow direction and some other aspects of the velocity field of each unit a flows are subject to stronger deformation than pahoehoe and also their internal parts behave more like a unit according to ams the central part of pahoehoe commonly reveals a different deformation history than the upper and lower extremes probably resulting from endogenous growth

distribution anisotropy the cause of ams in igneous rocks understanding of ams in pristine basic igneous rocks in terms of flow orientation of ellipsoidal magnetite grains is thwarted by the fact that these grains 1 typically are irregularly equant or skeletal rather than distinctly ellipsoidal and 2 usually crystallize interstitially and late after magma flow has ceased however the distribution of such grains will be relatively anisotropic if they grew in residual liquid volumes within a preferredly oriented by flow silicate template this constraint may impose a slight preferred shape orientation to the irregular magnetite grains during their growth but in addition we suggest it is the anisotropic magnetic interaction between the grains which is the basic cause of ams experiments involving the casting of magnetite epoxy mixtures in various foliated or lineated glass templates have yielded samples with the expected ams symmetry i e k3 perpendicular to glass plates or k1 parallel to glass rods slicing of near isotropic synthetic blank and natural rock cores and interleaving with glass slides showed a progressive increase in anisotropy of the blank from 0 4 to 2 and the natural rock from 0 9 to 2 9 in both the k3 axis migrates to be perpendicular to the glass slides

paleomagnetism and tectonics from the late pliocene to late pleistocene in the xalapa monogenetic volcanic field veracruz mexico

climatic instability before the miocene climatic optimum reflected in a central european lacustrine record from the most basin in the czech republic abstract the work investigates the extensive freshwater lacustrine deposits of the most formation which formed in the period between 17 7 ma and ca 15 9 ma in order to describe climate changes just before the miocene climatic optimum mco the most basin an incipient rift within the european cenozoic rift system exhibited a sedimentary environment that was sufficiently stable to preserve orbital signatures of environmental changes changes in the mineral composition of the sediments were characterised in terms of variations in their elemental composition particularly their al si and k ti element ratios and fe sr and zr elemental abundances which were efficiently obtained using x ray fluorescence spectroscopy with a density of 3 4 samples per metre of core approximately 15 20 samples per precession cycle the sediments are distinguished by the presence of distinct and correlated horizons 1 10 cm thick containing sr ba rich crandallite a mineral from the aluminium phosphate sulphate aps group chemo magneto and cyclostratigraphy were used to correlate eight cores with lengths up to 240 m and to date the sediment discrepancies at scales of up to two precession cycles each ca 20 kyr typically 4 m per cycle were observed the primary age model was based on magnetic polarity analysis 5 reversals and later refined at the metre scale using cyclostratigraphy we interpret the onset of the basin wide lacustrine phase in the most basin as being a consequence of the enhanced input of fluvial clastic sediment to the former peat swamps during the high eccentricity period at 17 7 17 55 ma i e immediately after the initial decay of the east antarctic ice sheet according to levy et al 2016 the most important environmental change recorded by the lacustrine interval in the most basin occurred at 16 44 ma during an eccentricity maximum and is nearly coeval with further shrinkage of the east antarctic ice sheet the second stage of monotonous lacustrine deposition which exhibited enhanced precession controlled compositional variability in 16 1 16 0 ma witnessed the onset of the mco sediments younger than 15 9 ma are missing due to erosional removal after subsequent basin inversion the sediments of the most formation represent an archive of environmental change in central europe during the early stages of the mco and have a temporal resolution ca 5 kyr

variations in magnetic properties of target basalts with the direction of asteroid impact example from lonar crater india abstract the lonar crater in maharashtra state india has been completely excavated on the deccan traps basalt approximately 65 ma at approximately 570 47 ka by an oblique impact of a possible chondritic asteroid that struck the preimpact target from the east at an angle of approximately 30 45o to the horizon where the total duration of the shock event was approximately 1 s it is shown by our early work that the distribution of ejecta and deformation of target rocks around the crater rim are symmetrical to the east west plane of impact misra et al 2010 the present study shows that some of the rock magnetic properties of these shocked target basalts e g low field anisotropy of magnetic susceptibility ams natural remanent magnetization nrm bulk susceptibility and high coercivity and high temperature hc ht magnetization component are also almost symmetrically oriented with reference to the plane of impact studies on the relative displacements of k3 minimum ams axes of shocked basalts from around the crater rim and from the adjacent target rocks to the approximately 2 3 km west of the crater center suggest that the impact stress could have branched out into the major southwestward and northwestward components in the downrange direction immediately after the impact the biaxial distribution of ams axes in stereographic plots for the unshocked basalts transforms mostly into triaxial distribution for the shocked basalts although transitional type distribution also exists the degree of anisotropy p of ams ellipsoids of the shocked basalts decreases by approximately 2 when compared with those of the unshocked target approximately 1 03 the nrm am 1 values of the shocked basalts on the rim of the lonar crater do not show much change in the uprange or downrange direction on and close to the east west plane of impact and the values are only approximately 1 5 times higher on average over the unshocked basalts around the crater however the values become approximately 1 4 16 4 times higher for the shocked basalts on the crater rim which occur obliquely to the plane of impact the target basalts at approximately 2 3 km west of the crater center in the downrange also show a significant increase up to approximately 26 times higher in nrm the majority of the shocked basalt samples approximately 73 from around the crater rim in general show a lowering of rem except those from approximately 2 3 km west of the crater center in the downrange where nearly half of the sample population shows a higher rem of approximately 3 63 in average the shocked target basalts around the lonar crater also acquired an hc ht magnetization component due to impact these hc ht components are mostly oriented in the uprange direction and are symmetrically disposed about the east west plane of impact making an obtuse angle with the direction of impact the low coercivity and low temperature lc lt components of both the unshocked and shocked basalts are statistically identical to the present day field pdf direction this could be chemical and or viscous remanent magnetization acquired by the target basalts during the last 570 47 ka subsequent to the formation of the lonar crater the shocked lonar target basalts appear to have remagnetized under high impact shock pressure and at low temperature of approximately 200 300 c where ti rich titanomagnetite was the main magnetic remanence carrier

40ar 39ar age of the lonar crater and consequence for the geochronology of planetary impacts asteroid impacts play an important role in the evolution of planetary surfaces in the inner solar system the large majority of impacts occur on bodies e g asteroids the moon mars covered by primitive igneous rocks however most of the impacts recorded on earth occur on different rock types and are poor proxies for planetary impacts the lonar crater is a 1 88 km diameter quaternary age crater fig 1 located on the ca 66 ma deccan basaltic traps in maharashtra india and is one of the very few craters on earth emplaced directly on basaltic lava flows we carried out 12 40 ar 39 ar step heating experiments on 4 melt rock samples in order to 1 obtain a precise age for the lonar crater 2 study the response of isotopic chronometers during impacts on mafic target rocks and 3 better understand the dating of extraterrestrial impact craters we obtained 10 plateau and 9 inverse isochron ages on various aliquots combination of selected data into a global inverse isochron yielded an age of 570 47 ka mswd 1 1 p 0 24 in comparison previous nonisotopic investigations on rocks thought to be affected by secondary processes yielded a range of much younger ages ca 12 62 ka the measured 40 ar 36 ar trapped values offer a direct comparison with the atmospheric benchmark value and allow us to test the inherited 40 ar degassing capacity of basaltic impact melt rocks the 40 ar 36 ar ratio of 296 5 1 7 is indistinguishable from the atmospheric composition and suggests that inherited 40 ar is absent from the melt rock this result substantiates diffusion models that predict a near complete degassing of low viscosity melt e g basalts during impact and demonstrates for the first time that inherited 40 ar is less problematic for 40 ar 39 ar dating of impact events in basaltic igneous rocks compared to si rich rocks these results provide direct evidence that basaltic melt rocks are excellent candidates for recording the timing of planetary impact events and as far as dating is concerned should be the preferred targets of sample recovery by future missions

geology of lonar crater india lonar crater india is one of the youngest and best preserved impact structures on earth the 1 88 km diameter simple crater formed entirely within the deccan traps making it a useful analogue for small craters on the basaltic surfaces of the other terrestrial planets and the moon in this study we present a meter scale resolution digital elevation model geological map of lonar crater and the surrounding area and radiocarbon ages for histosols beneath the distal ejecta impact related deformation of the target rock consists of upturned basalt fl ows in the upper crater walls and recumbent folding around rim concentric subhorizontal noncylindrical fold axes at the crater rim the rim fold hinge is preserved around 10 15 of the crater although tearing in the rim fold is inferred from fi eld and paleomagnetic observations no tear faults are identifi ed indicating that large displacements in the crater walls are not characteristic of small craters in basalt one signifi cant normal fault structure is observed in the crater wall that offsets slightly older layer parallel slip faults there is little fl uvial erosion of the continuous ejecta blanket portions of the ejecta blanket are overlain by aerodynamically and rotationally sculpted glassy impact spherules in particular in the eastern and western rim as well as in the depression north of the crater known as little lonar the emplacement of the continuous ejecta blanket can be likened to a radial groundhugging debris fl ow based on the preserved thickness distribution of the ejecta the effi cient exchange of clasts between the ejecta fl ow and the underlying histosol and the lack of sorting and stratifi cation in the bulk of the ejecta the ejecta profi le is thickened at the distal edge and similar to fl ejecta structures observed on mars

shock pressure estimates in target basalts of a pristine crater a case study in the lonar crater india the study of shock pressure indicators can provide important clues for understanding the cratering process though the estimation of shock pressures in weakly shocked rocks is commonly difficult in this study we selected a very young and well preserved impact structure the lonar crater in india the crater devoid of any tectonic overprint can be assumed as pristine we used a combination of rock magnetic and microfracture studies to estimate shock pressure in the crater rim on the basis of present results the magnetic fabrics are interpreted to be of magmatic origin related to the deccan basalt emplacement the high coercivity component of the natural remnant magnetization in the crater rim basalt is similar to that in the unshocked basalt the lack of any shock related magnetic overprint on the crater rim basalt is therefore evident in the lonar crater in contrast radial and concentric microfractures observed in basalts at the crater rim and farther away show symmetric distribution with respect to the crater the concentric microfractures consistently overprint the radial microfractures we infer that the radial and concentric microfractures were developed during propagation of the early compressional and the late decompressional shock wave components respectively the results of our rock magnetic and microfracture studies when interpreted in light of published experimental and numerical simulation studies on the lonar basalt reveal that the shock pressure in the lonar crater rim was less than 0 5 gpa but greater than 0 2 gpa this shock pressure was high enough to produce fractures but too low to affect the magnetic fabrics these results give new information on the relationship between shock pressure and resulting microfractures

a logging correlation scheme for the main coal seam of the north bohemian brown coal basin and the implications for the palaeogeographical development of the basin

field dependence of ac susceptibility in titanomagnetites abstract ac susceptibility measurements as a function of field amplitude hac and of frequency show a strong field dependence for a set of synthetic titanomagnetites fe3 xtixo4 and for certain basalts from the soh 1 hawaiian drill hole and from iceland in phase susceptibility is constant below fields of about 10 100 a m and then increases by as much as a factor of two as hac is increased to 2000 a m both the initial field independent susceptibilities and the field dependence of susceptibility are systematically related to composition initial susceptibility is 3 si for a single crystal sphere of tm0 x 0 and decreases with increasing titanium content field dependence is nearly zero for tm0 and increases systematically to a maximum near tm60 x 0 6 this field dependence can in some cases be mistaken for frequency dependence and lead to incorrect interpretations of magnetic grain size and composition when titanomagnetite is present

structural effects of meteorite impact on basalt evidence from lonar crater india received 31 january 2005 revised 17 august 2005 accepted 26 august 2005 published 8 december 2005 1 lonar crater is a simple bowl shaped near circular impact crater in the 65 myr old deccan volcanic province in india as lonar crater is a rare terrestrial crater formed entirely in basalt it provides an excellent opportunity to study the impact deformation in target basalt which is common on the surfaces of other terrestrial planets and their satellites the present study aims at documenting the impact deformational structures in the massive basalt well exposed on the upper crater wall where the basalt shows upward turning of the flow sequence resulting in a circular deformation pattern three fracture systems radial concentric and conical fractures are exposed on the inner crater wall on the fracture planes plumose structures are common uplift and tilting of the basalt sequence and formation of the fractures inside the crater are clearly related to the impact event and are different from the preimpact structures such as cooling related columnar joints and fractures of possible tectonic origin which are observed outside the crater slumping is common throughout the inner wall and listric faulting displaces the flows in the northeastern inner wall the impact structures of lonar crater are broadly similar to those at other simple terrestrial craters in granites and clastic sedimentary rocks and even small scale experimental craters formed in gabbro targets as lonar crater is similar to the strength controlled laboratory craters impact parameters could be modeled for this crater provided maximum depth of fracture formation would be known citation kumar p s 2005 structural effects of meteorite impact on basalt evidence from lonar crater india j geophys res 110 b12402 doi 10 1029 2005jb003662

understanding oblique impacts from experiments observations and modeling natural impacts in which the projectile strikes the target vertically are virtually nonexistent nevertheless our inherent drive to simplify nature often causes us to suppose most impacts are nearly vertical recent theoretical observational and experimental work is improving this situation but even with the current wealth of studies on impact cratering the effect of impact angle on the final crater is not well understood although craters rims may appear circular down to low impact angles the distribution of ejecta around the crater is more sensitive to the angle of impact and currently serves as the best guide to obliquity of impacts experimental studies established that crater dimensions depend only on the vertical component of the impact velocity the shock wave generated by the impact weakens with decreasing impact angle as a result melting and vaporization depend on impact angle however these processes do not seem to depend on the vertical component of the velocity alone finally obliquity influences the fate of the projectile in particular the amount and velocity of ricochet are a strong function of impact angle

ams nrm interferences in the deccan basalts toward an improved understanding of magnetic fabrics in flood basalts the evaluation of flow direction in volcanic rocks is among the most important applications of magnetic fabrics studies a statistically significant sample set of titanomagnetite bearing lava flows from the malwa plateau the northern part of the deccan traps in india has been investigated for a possible interference of induced and natural remanent magnetization nrm the nrm alters the scalar anisotropy of magnetic susceptibility ams parameter and the orientations of the ams principal magnetic axes which are crucial for the evaluation of the flow direction for cleaning of the nrm component the lava samples have been demagnetized by use of an alternating field af tumbling demagnetizer peak fields of 100 mt as previous studies have shown that static af demagnetization can bias the results samples with normal magnetic fabrics demonstrate a redistribution of their principal axes after the demagnetization the evaluated flow directions show a more differentiated flow pattern of the malwa area which seems to fit better into the regional geological setting in samples with inverse magnetic fabrics carrying a higher portion of single domain particles ams principal axes remain unchanged after the demagnetization indicating that these samples with high coercivity of magnetic carriers are not suitable for geological interpretations according to these results we propose that the ams measurements after tumbling demagnetization give a better reflection of the intrinsic anisotropy of magnetic carriers at least for samples with normal magnetic fabrics and therefore a more precise and better reflection of the actual mineral fabric

the microstructural response of quartz and feldspar under shock loading at variable temperatures shock recovery experiments were carried out on westerly granite and hospital hill quartzite targets in the peak pressure range 8 to 25 gpa preshock temperatures of 25 450 and 750 c and pulse durations of 2 to 7 s using internally heated momentum traps and explosive plane wave generators optical and transmission electron microscopy analyses of quartz and feldspar shocked at 25 c revealed the previously documented progression with increasing pressure 1 fracturing 2 planar fractures and shock mosaicism 3 shock mosaicism and planar deformation features pdfs and 4 isotropization this same sequence is observed for experiments at elevated preshock temperature but with specific microstructures occurring at lower pressures than those in previous experiments at room temperature at 750 c strong shock mosaicism partially thermally recovered is characteristic of feldspar shocked to 8 gpa whereas 15 gpa is required for its development in quartz and for the generation of pdfs in both minerals the results suggest that threshold pressures for formation of the various microstructures and phases are expected to vary systematically as a function of the preshock temperature of the target material we suggest that pdfs are generated in the shock transition by progressive heterogeneous phase transformation of the crystal structure to form dense glass or high pressure polymorphs the onset pressures for pdfs in specific crystallographic orientations is not influenced strongly by temperature but the character of the pdfs does change as preshock temperature is increased at the same peak shock stress the change from multiple sets of thin pdfs at low temperature to thicker single sets of pdfs at moderate temperature and finally to complete isotropization at high temperatures reflects a change in the phase transformation mechanism as a function of temperature in contrast development of shock mosaicism in quartz and feldspar occurs throughout the duration of shock loading and is better developed at elevated temperatures where the kinetics are enhanced by the additional thermal energy in the target

magnetic anomaly near the center of the vredefort structure implications for impact related magnetic signatures a strong magnetic anomaly near the center of the ancient and deeply eroded vredefort structure is attributed to remanent magnetization caused by a large meteorite impact at 2 0 ga the rocks underlying the anomaly are archean gneisses thought to represent mid crustal depths that were uplifted to the surface during the postulated impact event measurements of the remanent magnetization of the basement rocks yielded consistent vectors of declination 25 inclination 56 k 18 16 that correspond to the paleomagnetic pole position at time of impact petrologic studies indicate that during impact large volumes of rock were heated enough to cause thermal remagnetization in the ambient field thermal effects of all large impacts on cratons may induce a remanent magnetization of sufficient intensity to cause anomalies in the geomagnetic field that are detectable even by satellites

modified jeffery model influence of particle concentration on mineral fabric in moderately concentrated suspensions 1 a modified jeffery model involving particle interactions allows the simulation of preferred orientation of crystals and the anisotropy of magnetic susceptibility in magmatic flow with up to 40 of rigid particle fraction numerical simulations are compared to analogue and natural fabrics a study of the role of particle concentration shows that the increasing percentage of crystal fraction in dilute suspensions leads to progressive attenuation of the fabric intensity and cyclicity at high strains in simple shear flow the lineation converges to a constant value close to the shear plane with increasing particle concentration the fabric diverges from the shear direction reflecting the effect of increased crystal tiling the model can be applied to quantify mineral preferred orientations of crystal mushes in magmatic fabric studies

new palaeomagnetic data from the mahabaleshwar plateau deccan flood basalt province india implications for the volcanostratigraphic architecture of continental flood basalt provinces abstract new magnetostratigraphic data from seven western ghats sections in the deccan volcanic province are presented these are combined with an established geochemically defined stratigraphy and volcanological logs to provide a correlated chronological eruptive framework we identify two magnetic polarities in five of the sections and these are assigned to chrons 29r and 29n importantly the reversal boundary represents an identifiable isochronous surface within the volcanic pile this surface occurs at different elevations as does the altitude of the geochemically defined formation boundary i e ambenali mahabaleshwar fms which defines a second isochronous surface inspection reveals significant differences in the number and thickness of lava units preserved between these two surfaces this indicates that there was significant local topography c 80 m across deccan volcanic province lava fields during their development an interpretation consistent with topographies observed across modern and historical examples e g hawaii iceland these data also indicate that the geochemical stratigraphies of continental flood basalt provinces can mask local and sub regional detail in lava stacking patterns when applied at smaller spatial scales 2 10 4 m finally transitional r n directions preserved in some eruptive units place constraints upon the rates of eruption and indicate c 2 ka periods of volcanic repose

experimental generation of shock induced pseudotachylites along lithological interfaces to understand the mechanism of formation of shock induced pseudotachylites and particularly the role that rock heterogeneities and interfaces play in their formation shock recovery experiments were carried out on samples consisting of two distinct lithologies dunite and quartzite it was possible to generate melt veins of 1 6 m width along lithological interfaces at moderate shock pressures 6 to 34 gpa the magnitudes of displacement along the interface strain rate and the kinetic heat production indicate that friction is an important heat source that largely contributes to the energy budget of the melt veins the experimentally produced veins resemble natural s type pseudotachylites the geometry of the veins depends on the orientation of the interface with respect to the shock front and includes strong variations in thickness formation of melt pockets and injection veins sudden changes in vein orientation and sharp vein margins two types of melt were observed vesicle free and vesicular melts dense vesicle free melt rock is likely to represent high pressure melts vesicular melts were also generated during shock compression but they remained in a molten state during pressure release and continued shearing intermingling of comminuted olivine and melt suggests that ultracataclasis of olivine induced by a dynamic tensile failure is a precursor stage to frictional melting shock wave interferences at the lithological interface provide the necessary stress conditions to start dynamic failure of olivine the composition of the frictional melts ranges from olivine normative to enstatite normative and is thus largely determined by olivine melting the validity of the sequence of friction melting susceptibilities of rock forming minerals inferred from tectonically produced pseudotachylites is confirmed and can now be applied to ultra high strain rates during shock compression

palaeomagnetism of the vredefort meteorite crater and implications for craters on mars magnetic surveys of the martian surface have revealed significantly lower magnetic field intensities over the gigantic impact craters hellas and argyre than over surrounding regions the reduced fields are commonly attributed to pressure demagnetization caused by shock waves generated during meteorite impact in the absence of a significant ambient magnetic field lower than average magnetic field intensities are also observed above the vredefort meteorite crater in south africa yet here we show that the rocks in this crater possess much higher magnetic intensities than equivalent lithologies found elsewhere on earth we find that palaeomagnetic directions of these strongly magnetized rocks are randomly oriented with vector directions changing over centimetre length scales moreover the magnetite grains contributing to the magnetic remanence crystallized during impact which directly relates the randomization and intensification to the impact event the strong and randomly oriented magnetization vectors effectively cancel out when summed over the whole crater seen from high altitudes as for martian craters the magnetic field appears much lower than that of neighbouring terranes implying that magnetic anomalies of meteorite craters cannot be used as evidence for the absence of the planet s internally generated magnetic field at the time of impact

tektite like bodies at lonar crater india implications for the origin of tektites homogeneous dense glass bodies both irregular and splash form with high silica contents 67 sio2 occur in the vicinity of lonar crater india their lack of microlites and mineral remnants and their uniform chemical composition virtually preclude a volcanic origin they are similar to tektites reported in the literature while such a close association of tektite like bodies with impact craters is already known aouelloul crater mauritania zhamanshin crater u s s r the tektite like bodies at lonar crater are unique in that they occur in an essentially basaltic terrain our geochemical data are consistent with these high silica glass bodies being impact melt products of two thirds basalt and one third local intertrappean sediment chert the tektite like bodies of the impact craters lonar zhamanshin and aouelloul are generally similar strong terrestrial geochemical signatures reflect the target rock ree patterns and abundance ratios and demonstrate their terrestrial origin resulting from meteorite impact as has been suggested by earlier workers

single domain particles in rocks and magnetic fabric analysis magnetic susceptibility anisotropy is commonly used as a guide for determining stress and flow axes in rocks and for assessing the suitability of anisotropic rocks for palaeomagnetic purposes we have recently demonstrated however in laboratory produced samples that as theoretically expected susceptibility anisotropy is dependent on particle size multidomain particles of magnetite or similar strongly magnetic particles with shape anisotropy exhibit a maximum susceptibility parallel to their easy remanent magnetization axes whereas uniaxial single domain particles exhibit a maximum susceptibility perpendicular to their easy magnetization axes hence susceptibility anisotropy does not yield an unambiguous determination of particle alignment in rocks independent of domain state by demonstrating uniaxial single domain anisotropy characteristics for the first time in a rock specimen we show here that susceptibility measurements by themselves may not correctly identify the degree or type of alignment of ferro or ferrimagnetic particles in rocks in particular apparently foliated rocks can actually be lineated and vice versa moreover rocks with low anisotropy of susceptibility can have a much higher anisotropy of remanence remanence anisotropy methods are shown to give unambiguous determinations of the degree and type of alignment

modification of the magnetic mineralogy in basalts due to fluid rock interactions in a high temperature geothermal system krafla iceland summary active high temperature 150 c geothermal areas like the krafla caldera ne iceland often show distinct magnetic lows in aeromagnetic anomaly maps suggesting a destruction of magnetic minerals by hydrothermal activity the main alteration processes in such an environment are low temperature oxidation 350 c maghemitization and fluid rock interactions we investigated the rock magnetic properties natural remanent magnetization nrm magnetic susceptibility and their temperature and field variation and the mineralogy using x ray diffraction microscopic methods and electron microprobe analyses of two drill cores kh1 and kh3 from the rim of the krafla caldera the drill cores have distinctly lower nrm values average 3 a m 1 compared to younger surface basalts average 20 a m 1 along with a large variation in magnetic susceptibility 1 3 10 7 4 9 10 5 m3 kg 1 the secondary mineral assemblage sulphides sphene rutile and chlorite indicates an alteration within the chlorite smectite zone for both cores without depth zoning optical miscroscopy in combination with the bitter technique and backscatter electron microscopy along with the thermomagnetic analyses allow distinguishing two different magnetomineralogical groups of titanomaghemite 1 titanomaghemite with intermediate titanium concentration and probably high vacancy concentration and 2 titanomaghemite with low titanium concentration and low vacancy concentration the mineral assemblages textures and magnetic properties deduced from the mentioned magnetic measurements indicate two stage transformation mechanism 1 dissolution of titanium at low ph under oxidizing conditions the ulvospinel component of titanomagnetite and ilmenite forms rutile or sphene and fe2 migrates out of the spinel lattice forming titanomaghemite 2 formation of pyrite and dissolution of remaining titanomaghemite under reducing and acidic conditions the latter mechanism produces ghost textures all titanomaghemite is transformed and only their former grain shapes are preserved with only paramagnetic minerals left and ferrimagnetic minerals nearly dissolved this mechanism could explain the significant magnetization loss which is seen in many local magnetic anomaly lows within the oceanic crust and volcanic islands like iceland or hawaii the production of nanoporous textures in titanomaghemites is suggested as a mechanism for the enhancement of the magnetic susceptibility values related to the hydrothermal alteration of krafla

paleomagnetic and ams studies of the el castillo ignimbrite central east mexico source and rock magnetic nature abstract lithological petromagnetic paleomagnetic and magnetic fabric studies are employed to determine the flow direction and the location of the source of the 2 44 to 2 21 ma el castillo ignimbrite in the central east mexico based on the increasing matrix to pumice ratio and decreasing pumice size the ignimbrite field is divided into the northwestern central and south southeastern sectors lithological comparisons among the three sectors reveal that the ignimbrite had flowed from nw to se and the source is in the nw part of the study area thermomagnetic results concur with the increasing matrix proportions from the proximal to the distal sector the coercivity and magnetization ratios of the hysteresis parameters are lower in the se sector than in the nw and central sectors the dominant flow direction inferred through magnetic fabrics at most sites is nw to se which coincides with the direction inferred from lithological comparisons however at some sites magnetic fabrics demonstrate flow towards ene or other various directions the paleomagnetic analysis and field observations reveal that these anomalous directions are a consequence of anticlockwise block rotation and tilting due to normal and lateral faulting in the region

liquefaction induced softening of load transfer between pile groups and laterally spreading crusts laterally spreading nonliquefied crusts can exert large loads on pile foundations causing major damage to structures while monotonic load tests of pile caps indicate that full passive resistance may be mobilized by displacements on the order of 1 7 of the pile cap height dynamic centrifuge model tests show that much larger relative displacements may be required to mobilize the full passive load from a laterally spreading crust onto a pile group the centrifuge models contained six pile groups embedded in a gently sloping soil profile with a nonliquefied crust over liquefiable loose sand over dense sand the nonliquefied crust layer spread downslope on top of the liquefied sand layer and failed in the passive mode against the pile foundations the dynamic trace of lateral load versus relative displacement between the free field crust and pile cap is nonlinear and hysteretic and depends on the cyclic mobility of the underlying liquefiable sand ground motion characteristics and cyclic degradation and cracking of the nonliquefied crust analytical models are derived to explain a mechanism by which liquefaction of the underlying sand layer causes the soil to pile cap interaction stresses to be distributed through a larger zone of influence in the crust thereby contributing to the softer load transfer behavior the analytical models distinguish between structural loading and lateral spreading conditions load transfer relations obtained from the two analytical models reasonably envelope the responses observed in the centrifuge tests

water film in liquefied sand and its effect on lateral spread a one dimensional 1d saturated sand layer of 2 m in thickness in which a silt seam is sandwiched is liquefied by an instant shock it is found that a water film is easily formed beneath the silt seam with a thickness as thin as a few millimeters just after liquefaction in loose sand and that the film lasts longer than the postliquefaction settlement the effect of the water film on pore pressure distribution and sand settlement is intensively studied one gram shake table tests are then carried out for 2d models with or without seams of silt within a saturated sand layer in the former case water films formed beneath silt seams just after liquefaction enable the soil mass above them to glide because of an unbalanced force along the water films not only during but also after shaking in the latter case the soil deforms continuously mostly during shaking and stops afterward thus a significnat effect of water films formed beneath thin low permeability sublayers in a liquefied loose sand on the failure mode and timing in lateral spread is clearly demonstrated by these simple model tests

physical interpretation of hysteresis loops micromagnetic modeling of fine particle magnetite 1 hysteresis measurements have become an important part of characterizing magnetic behavior of rocks in paleomagnetic studies theoretical interpretation is often difficult owing to the complexity of mineral magnetism and published data sets demonstrate remanence and coercivity behavior that is currently unexplained in the last decade numerical micromagnetic modeling has been used to simulate magnetic particles such simulations reveal the existence of nonuniform remanent states between single and multidomain known as the flower and vortex configurations these suggest plausible explanations for many hysteresis measurements yet fall short of explaining high saturation remanence high coercivity data such as those commonly observed in fine grained submarine basalts in this paper we review the theoretical and experimental progress to date in understanding hysteresis of geological materials we extend numerical simulations to a greater variety of shapes and sizes including random assemblages of particles and shapes more complex than simple rods and cubes our simulations provide plausible explanations for a wide range of hysteresis behavior

magnetic fabric and its significance in the 1400 ma mealy diabase dykes of labrador canada an anistropy of magnetic susceptibility ams study of the relatively fresh mealy diabase dyke swarm indicates a correlation between the ams and the deformational effects in the rocks several ams components were revealed during experimental work on 211 samples that had been heated to 640 c during a paleomagnetic study and 22 fresh samples progressively treated in alternating fields seventeen sites with slight or no deformation have a magnetic fabric composed of two major components the stable component attributed to a primary shape anisotropy has minimum and maximum principal susceptibility directions preferentially oriented vertically and along dyke strike n 60 e respectively this configuration is consistent with an origin due to a post emplacement stress field whereby horizontal extension acted on a vertical sheet of partially crystallized magma the orientation of this component with respect to the present horizontal suggests that the dykes have not been tilted since their emplacement the unstable component removed by fields up to 250 mt is attributed to induced domain anisotropy produced by mild tectonic stress during the grenville orogeny the approximate orientation of its principal components as found by the method of substitutional ellipsoids suggests an east west directed maximum stress four other sites with noticeable deformation have magnetic fabric that could not be reliably analyzed but which may be largely composed of domain and stress induced anisotropies developed during the grenville orogeny

magma flow in the east greenland dyke swarm inferred from study of anisotropy of magnetic susceptibility magmatic growth of a volcanic margin summary volcanic passive margins vpms are characterized by large volumes of melt emplaced within the lithosphere during break up processes several data and a recently proposed conceptual model of volcanic margin development suggest that vpms are fed from localized crustal zones of magma storage underlying large polygenetic volcanoes localized above diapir like instabilities of the asthenosphere we investigated the magma flow pattern within the coastparallel dyke swarm of the east greenland vpm which is the only outcropping vpm over a distance of 125 km the 44 sampled dykes are representative of the successive families of intrusions igneous petrofabrics are constrained by the measurements of the anisotropy of magnetic susceptibility the magnetic fabrics are of medium to low anisotropy p 0 flow related fabrics are recorded in 75 per cent of the sampled dykes we infer the flow directions from the imbrication geometry of the magnetic foliation planes at the dyke margins and check the results by measuring the preferred orientation of plagioclase in thin sections cut in the magnetic principal planes due to probable fabric superposition the magnetic lineation represents the zone axis for the distribution of magnetic foliation plane we obtained 23 reliable flow directions that are predominantly horizontal and directed away from identified crustal reservoirs this flow pattern supports the proposed model of vpm growth and emphasizes the localized nature of the magma sources in the mantle the entire flood basalt sequence appears to have been fed by a restricted number of crustal reservoirs and associated dyke swarms

characterization of magnetite particles in shocked quartz by means of electron and magnetic force microscopy vredefort south africa submicroscopic opaque particles from highly shocked granite gneisses close to the core of the vrede fort impact structure have been investigated by means of micro analytical techniques with high spatial resolution such as electron diaraction orientation contrast imagery and magnetic force microscopy the opaque particles have been identified as nano to micro sized magnetite that occur in several distinct modes in one sample magnetite occurs along relict planar deformation features pdfs in quartz generally accepted as typical shock lamellae the magnetite particles along shock lamellae in quartz grains virtually all show uniform crystallographic orientations in most instances the groups of magnetite within diaerent quartz grains are systematically misori entated such that they share a subparallelh101i direction the magnetite groups of all measured quartz grains thus appear to have a crystallographic preferred orientation in space in a second sample orientations of magnetite particles have been measured in microfractures non di agnostic of shock of quartz albite and in the alteration halos e g biotite grains breaking down to chlorite the crystallographic orientations of magnetite particles are diverse with only a minor portion having a preferred orientation scanning electron microscopy shows that magnetite along the relict pdfs is invariably asso ciated with other microcrystalline phases such as quartz k feldspar and biotite petrographic observations sug gest that these microcrystalline phases crystallized from locally formed micro melts that intruded zones of weakness such as microfractures and pdfs shortly after the shock event the extremely narrow widths of the pdfs suggest that heat may have dissipated rapidly re sulting in melts crystallizing relatively close to where they were generated magnetic force microscopy confirms the presence of magnetic particles along pdfs the smallest particles 5 lm with high aspect ratios 15 1 usually exhibit intense uniform magnetic signals characteristic of single domain magnetite consistent oasets between attractive and repulsive magnetic signals of individual single domain particles suggest consistent directions of magnetization for a large proportion of particles

impact fracturing and structural modification of sedimentary rocks at meteor crater arizona 1 meteor crater provides a rare opportunity to study impact deformation of sedimentary target rocks and isolate those features from preexisting tectonic deformation and impact generated reactivation of preexisting tectonic features this study reports over 2500 new measurements of orientations of bedding faults and fractures in crater walls and in surrounding bedrock target rocks are characterized by horizontal bedding planes that are cut by at least three prominent sets of preimpact tectonic fracture systems the crater rim is also cut by three distinct groups of fractures radial concentric and conical fractures when the crater rim is restored to preimpact condition the radial and concentric fractures resemble preimpact fracture populations indicating that crater wall deformation and rim uplift were partly accommodated by activation of preexisting fractures in contrast the conical fractures are dissimilar to the preimpact fractures and apparently formed as a direct result of impact deformation some of the preimpact fractures were transformed into tear faults during the impact event and motion along those faults appears to have controlled the geometry of the impact deformational features the crater rim is thus square in plan view rather than circular faults occurring in the crater diagonals are prominent ones allowing greater vertical displacement the deformation pattern of meteor crater is different from that at lonar crater which was excavated in basalt with fewer preimpact fractures the differences between deformation at meteor crater and lonar crater may reflect the same disparities seen in simple craters produced in different target lithologies on mars and other planetary surfaces

magma flow directions inferred from preferred orientations of phenocryst in a composite feeder dike miyake jima japan abstract the feeder dike formed by the eruption of the 1983 miyake jima japan is composite based on field observations such as cooling joints and zonal arrangement of it three dimensional orientation measurements on phenocrysts contained in the dike combined with the field observations indicate that the dike was emplaced by three magma pulses the first and second pulses were intruded horizontally the final pulse however was intruded vertically such directional variations are consistent with the eruptive sequence of the active centers observed during the eruption therefore these techniques may be useful to determine the location of old vents and other volcanic structures

international geomagnetic reference field the eleventh generation the eleventh generation of the international geomagnetic reference field igrf was adopted in december 2009 by the international association of geomagnetism and aeronomy working group v mod it updates the previous igrf generation with a definitive main field model for epoch 2005 0 a main field model for epoch 2010 0 and a linear predictive secular variation model for 2010 0 2015 0 in this note the equations defining the igrf model are provided along with the spherical harmonic coefficients for the eleventh generation maps of the magnetic declination inclination and total intensity for epoch 2010 0 and their predicted rates of change for 2010 0 2015 0 are presented the recent evolution of the south atlantic anomaly and magnetic pole positions are also examined