the tertiary structural and thermal evolution of the central alps compressional and extensional structures in an orogenic belt the western alpine arc has been created during the cretaceous and the tertiary orogenies the interference patterns of the tertiary structures suggest their formation during continental collision of the european and the adriatic plates with an accompanying anticlockwise rotation of the adriatic indenter extensional structures are mainly related to ductile deformation by simple shear these structures developed at a deep tectonic level in granitic crustal rocks at depths in excess of 10 km in the early palaeogene period of the tertiary orogeny the main tertiary nappe emplacement resulted from a nw thrusting of the austroalpine penninic and helvetic nappes heating of the deep zone of the upper cretaceous and tertiary nappe stack by geothermal heat flow is responsible for the tertiary regional metamorphism reaching amphibolite facies conditions in the lepontine gneiss dome geothermal gradient 25 c km the tertiary thrusting occurred mainly during prograde metamorphic conditions with creation of a penetrative nw se oriented stretching lineation xi finite extension parallel to the direction of simple shear earliest cooling after the culmination of the tertiary metamorphism some 38 ma ago is recorded by the cooling curves of the monte rosa and mischabel nappes to the west and the suretta nappe to the east of the lepontine gneiss dome the onset of dextral transpression with a strong extension parallel to the mountain belt and the oldest s vergent backfolding took place some 35 to 30 ma ago during retrograde amphibolite facies conditions and before the intrusion of the oligocene dikes north of the periadriatic line the main updoming of the lepontine gneiss dome started some 32 30 ma ago with the intrusion of the bergell tonalites and granodiorites concomitant with s vergent backfolding and backthrusting and dextral strike slip movements along the tonale and canavese lines argand s insubric phase subsequently the center of main updoming migrated slowly to the west reaching the simplon region some 20 ma ago this was contemporaneous with the westward migration of the adriatic indenter between 20 ma and the present the western aar massif toce culmination was the center of strong uplift the youngest s vergent backfolds the glishorn anticline and the berisal syncline fold the 12 ma rb sr biotite isochron and are cut by the 11 ma old rhone simplon line the discrete rhone simplon line represents a late retrograde manifestation in the preexisting ductile simplon shear zone this fault zone is still active today the oligocene neogene dextral transpression and extension in the simplon area were concurrent with thrusting to the northwest of the helvetic nappes the prealpes 35 15 ma and with the jura thin skinned thrust 11 3 ma it was also contemporaneous with thrusting to the south of the bergamasc 35 5 ma and milan thrusts 16 5 ma the oligocene neogene dextral transpression in the central alps is of the same age as the thrusting to the west and southwest in the external french part and to the east in the internal italian part of the alpine arc of the western alps

magnetic susceptibility anisotropy strain and progressive deformation in permian sediments from the maritime alps france abstract the relationships among magnetic susceptibility anisotropy finite strain and progressive deformation have been studied in permian red shales and slates of the maritime alps southeastern france these rocks contain deformed reduction spots which serve as finite strain indicators the magnetic fabric of undeformed regions is modified during deformation to yield characteristic magnetic susceptibility anisotropy patterns and a magnetic equivalent of the deformation path derived from strain measurements the magnetic fabric changes progressively from oblate to prolate and back to oblate as deformation increases the quantitative relationships between natural strain and magnetic anisotropy in these rocks have been determined they differ between the less and more deformed areas perhaps due to a change in deformation mechanism accompanying an increase in metamorphism the relationships provide a rapid means of strain determination using magnetic measurements but their variation emphasizes the need for local structural control

the impact of horizontal grid spacing on the microphysical and kinematic structures of strong tropical cyclones simulated with the wrf arw model abstract using the advanced weather research and forecasting numerical model the impact of horizontal grid spacing on the microphysical and kinematic structure of a numerically simulated tropical cyclone tc and their relationship to storm intensity was investigated with a set of five numerical simulations using input data for the case of hurricane rita 2005 the horizontal grid spacing of the parent domain was systematically changed such that the horizontal grid spacing of the inner nest varied from 1 to 5 km by an increment of 1 km this while keeping geographical dimensions of the domains identical within this small range of horizontal grid spacing the morphology of the simulated storms and the evolution of the kinematic and microphysics field showed noteworthy differences as grid spacing increased the model produced a wider more tilted eyewall a larger radius of maximum winds and higher amplitude low wavenumber eyewall asymmetries the coarser resolution simulations also produced larger v

p and s receiver function analysis of seafloor borehole broadband seismic data 1 the crustal and lithospheric structure of the normal oceanic plates is investigated using converted wave techniques p and s receiver functions rfs and novel stacking analysis techniques without deconvolution applied to the data from two seafloor borehole broadband seismic stations located in the central philippine sea and in the northwest pacific ocean we observe sufficient energy from at least two discontinuities within the error bounds one from the crust mantle moho boundary and the other from the seismic lithosphere asthenosphere boundary lab synthetic seismograms for seafloor stations show that the water reverberations interfere with the vertical component of seismograms but to a lesser extent with the radial part of p receiver functions on the other hand s receiver functions are devoid of such effects since all the multiples and converted waves are separated in time by the primary s wave in time waveform modeling of rfs shows that the crustal thicknesses of the western philippine sea plate and northwest pacific plate are 7 8 km and that depths of lab are 76 1 8 km and 82 4 4 km respectively with an abrupt vs drop at lab of 7 8 as reported by kawakatsu et al 2009 the lab depth for the eastern philippine plate is found to be 55 km to confirm the robustness of this observation we further analyze vertical and radial components of the data without deconvolution for p wave backscattered reflection phases and p to s converted phases the result indicates that the reflected converted phases from moho and lab are observed at timings consistent with the receiver function results the effect of seismic anisotropy for observed rfs is also investigated

observations of the distribution of ice in hurricanes abstract observations of the type and distribution 0 c isotherm in three atlantic hurricanes are presented supercooled drops graupel columns and aggregated snowflakes were observed the supercooled drops were found only in convective updrafts stronger than 5 m s 1 but not all updrafts 5 m s 1 contained appreciable liquid graupel was found in all updrafts at temperatures 2 c and small columns were sometimes found in downdrafts nonconvective rainbands contained 15 30 l 1 of snow composed of columns and what appeared to be large aggregates other stratiform regions contained 1 15 l 1 of medium and large aggregates columns were occasionally found there also but only within about 15 km of convection hurricane convection is almost completely glaciated at the 5 c level it is suggested that the ice particles observed at 6 0 km inside the convection result primarily from downward mixing on both sides of the eyewall updraft of ice formed in the convective areas at higher colder levels the ice in t

quantitative correlation of texture and magnetic anisotropy of compacted calcite muscovite aggregates abstract deformation of carbonate rocks leads to crystallographic preferred orientations cpos of calcite which in turn generates an anisotropy of magnetic susceptibility ams the use of the diamagnetic anisotropy which arises from the preferential orientation of calcite for texture characterization is usually hindered by 1 the weakness of the anisotropy and 2 overlapping contributions from paramagnetic and ferromagnetic minerals to the ams in this study the diamagnetic paramagnetic and ferromagnetic sub fabrics of synthetic calcite muscovite samples have been separated using high field torque measurements the cpo of calcite and muscovite has been determined by neutron diffraction and the magnetic sub fabrics are compared to the ams that was re calculated from the cpo the isolated diamagnetic sub fabric shows a good correlation with the calcite texture for calcite concentrations above 70 the paramagnetic sub fabric is shown to be a reliable texture parameter for muscovite even at a concentration of 5 the results demonstrate the capability of the ams method as a texture parameter in impure carbonate rocks

a model study of gravity waves over hurricane humberto 2001 abstract atmospheric gravity waves are known to influence global circulations understanding these waves and their sources help to develop parameterizations that include their effects in climate and weather forecasting models deep convection is believed to be a major source for these waves and hurricanes may be particularly intense sources simulations of hurricane humberto 2001 are studied using the fifth generation pennsylvania state university national center for atmospheric research psu ncar mesoscale model mm5 humberto is simulated at both tropical storm and hurricane stages fourier transform and wavelet analysis are employed to investigate wave characteristics and their behavior in the lower stratosphere the fourier analysis gives a regional view of storm affects whereas wavelet analysis gives a local picture of isolated events analysis of the movement of convective sources and local winds gives further insight into the mechanisms that can cause gravity waves convectively generated grav

aircraft observations of ice crystal evolution in an altostratus cloud abstract observations from a lagrangian spiral descent within altostratus cloud associated with a cold front were used to study the evolution of ice particle spectra by following populations of ice crystals as they fell through the cloud the flight track was corrected for wind effects and was divided into distinct regions for spatial comparison of ice particle spectra analysis of size spectra for particles larger than 800 m revealed heterogeneity on horizontal scales of 5 km in average particle diameter and concentration in the temperature range 40 to 20 c the ice crystal evolution was dominated by diffusional growth although observations of the evolution of the bimodal size spectra suggested that aggregation was occurring between 20 and 10 c aggregation dominated evolution

methods for determining deformation history for chocolate tablet boudinage with fibrous crystals abstract chocolate tablet boudinage with fibrous crystal growths between the boudinaged plates from two localities were studied in one from leytron valais switzerland the deformation history was found to be a succession of plane strain increments with the shortening direction perpendicular to the boudinaged sheet and the extension direction showing a progressive change in orientation within the sheet the incremental and finite strains were evaluated the other specimen from parys mountain anglesey great britain was found to have a more complex history with diachronous break up of the competent layer and flattening strain increments it was found that under these circumstances the direct graphical methods of determining finite and incremental strains gave inconsistent results a numerical model was developed which allowed the simulation of chocolate tablet structure with a complex deformation history the model was applied to the anglesey specimen and three possible strain histories for this structure were tried

phyllosilicate fabric characterization by low temperature anisotropy of magnetic susceptibility lt ams 1 this paper examines the use and applicability of anisotropy of magnetic susceptibility at low temperature 77 k called lt ams paramagnetic susceptibility increases significantly with low temperature which permits high precision determination of the anisotropy of paramagnetic susceptibility of a rock from measurements at liquid nitrogen temperature we describe a new procedure that measures directional susceptibility in an oriented rock specimen while immersed in liquid nitrogen our procedure overcomes the problem of temperature heterogeneity within a rock sample while its susceptibility is being measured offering the opportunity to measure low temperature susceptibility in multiple orientations this non destructive method provides a way of characterizing the principal paramagnetic minerals present in a rock based on temperature induced changes of the anisotropy degree moreover the method offers a better resolved relationship between anisotropy degree and grain alignment which is used to quantify rock fabrics

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

magnetic susceptibility as a tool to study deformed calcite with variable impurity content 1 a set of calcite mylonites were systematically sampled along the basal shear zone of the morcles nappe located in the southwestern swiss alps to investigate the relationship among crystallographic preferred orientation cpo chemistry and anisotropy of magnetic susceptibility ams second phase minerals are 10 vol of the rock the substitution of trace impurities for ca in the calcite crystal lattice in particular fe mn mg and sr varies among the samples with total values ranging from 1450 190 ppm in the most pure sample to 2450 320 ppm for the most impure sample fe shows the largest variation among the sample group and varies by a factor of nearly four from the purest 230 30 ppm to the most impure sample 840 110 ppm all samples have negative bulk susceptibility and the concentration of ferromagnetic in a broad sense phases is very low a correlation is identified between trace element chemistry cpo of calcite and the magnetic susceptibility the bulk susceptibility and the ams vary systematically with fe and mn elemental concentration in the matrix calcite and this variation is apparent for the entire length of the shear zone a simple model that takes into account the cpo and trace element chemistry is used to explain the resulting bulk susceptibility and ams calcite mylonites and marbles from other locations fit the model indicative of a general relationship between cpo chemistry and ams in calcites where second phase minerals are sparse for lithologies that are dominated magnetically by calcite with a deficiency of secondary phases magnetic susceptibility can be used to rapidly screen rock samples for the variation of paramagnetic trace elements fe and mn and cpo which can then be used for detailed microfabric studies

magnetic fabric and deformation in the navia alto sil slate belt northwestern spain abstract ries and schackleton ries a c schackleton r m 1976 patterns of strain variation in arcuate fold belts philos trans r soc london a 283 281 288 discussed the distribution of finite strain in the ibero armorican arc and suggested that the arc was produced by tectonic bending of a straight or gently curved fold belt later investigations by others revealed different strain patterns in the fold thrust belt and so its evolution continues to be controversial this study focuses on the strain pattern in the navia alto sil slate belt the low field anisotropy of magnetic susceptibility ams was measured in ordovician black slates and cambrian to lower ordovician quartzites sampled around the arcuate belt the magnetic fabric is controlled primarily by the slaty cleavage in both lithologies the ams was also measured with a high field torsion magnetometer and the results indicate that paramagnetic minerals are responsible for the magnetic fabric in the slates and diamagnetic and paramagnetic minerals in the quartzites strain markers i e pressure shadows around pyrite grains and rutile distribution are found in the slates and the orientation of the principal axes of strain ellipsoids agrees with those of the ams ellipsoid a systematic variation in the orientation of the strain ellipsoid and anisotropy ellipsoid suggests that there is strain heterogeneity along the slate belt and that the arc did not form by tectonic bending

inverse magnetic fabric in carbonate bearing rocks abstract the observation of a magnetic susceptibility ellipsoid whose maximum axis corresponds to the minimum axis of petrofabric pole of bedding or schistosity is referred to as an inverse magnetic fabric the investigation of the magnetic properties of some ferroan carbonate monocrystals and paramagnetic limestones demonstrates that c axis preferred orientation of paramagnetic carbonates results in a maximum susceptibility parallel to the flattening direction inverse magnetic fabrics due to magnetite are also encountered in weakly deformed limestones a mineralogical model based on the property of single domain grains to have a zero susceptibility parallel to their long axis is proposed however more complex cases are also encountered

change of direction of overthrust shear in the helvetic nappes of western switzerland abstract the lowest of the helvetic nappes in western switzerland the morcles and the doldenhorn nappes are large scale recumbent folds in equivalent tectonic positions in the alpine chain a comparison of the orientations of stretching lineations in both nappes shows that the lineations in the two stratigraphically normal sequences trend n s whereas those in the two stratigraphically inverted sequences trend nw se a similar geometrical relationship has been found from an analysis of the calcite c axis directions of these limestones the two normal sequences show nw se directed c axes whereas the two inverted sequences show w e directed c axes these observations lead to the following conclusions 1 regionally consistent shear movements occurred over a strike distance of more than 60 km and these gave rise to similar deformation patterns in both nappes 2 a progressive rotation of these shear movements from a northerly direction in the earlier formed limbs to northwesterly in the later formed inverted limbs can be deduced the finite strain stretching lineations lag behind the crystallographic fabric axes formed in the later part of the deformation history

magnetic fabrics may proxy as neotectonic stress trajectories polis rift cyprus 1 the miocene polis rift opened along a nnw axis obviously in response to wsw relative extension and relative tension starting 5 myr ago however geologically young plate movements are believed to be closing the rift by sinistral transpression producing minor younger faults since 1 ma modern earthquake solutions give e w compression compatible with the younger faults magnetic fabrics using anisotropy of low field magnetic susceptibility ams and anisotropy of anhysteretic remanent magnetization are kinematically compatible with stress axes required by the fault and rift geometry and thus were acquired in 5 ma however by different statistical treatments and selecting samples from different subareas it is possible to reveal sedimentary depositional fabrics and perhaps also a composite ams fabric related to young transpression 1 ma

magnetic fabrics of the morcles nappe complex abstract anisotropy of magnetic susceptibility ams measured with high fields at ambient and low temperatures 77 k has been used to separate ferromagnetic sensu lato paramagnetic and diamagnetic sub fabrics for deformed limestones located in a nappe structure from southwest switzerland the magnetic fabrics are dominantly controlled by paramagnetic and diamagnetic minerals and ferromagnetic minerals contribute significantly only at two of the eight study locations separation of the magnetic sub fabrics is possible in the root zone and overturned limb of the morcles nappe which contains a high ratio of diamagnetic matrix calcite to paramagnetic secondary phases each of the sub fabrics displays a relationship with structural cleavage and the crystallographic preferred orientation cpo of calcite in the root zone and overturned limb the maximum axis of the paramagnetic ams ellipsoid kmax lies close to the pole to cleavage with the intermediate kint and minimum kmin axes near the cleavage plane conversely the diamagnetic kmin lies close to the pole to cleavage with kmax and kint axes near the cleavage plane slight offsets in the poles to cleavage and in the principal ams directions are observed they are interpreted to be the consequence of a second phase deformation event affecting only the cpo but not the macroscopic structural elements the diamagnetic sub fabric reflects the cpo of calcite produced through recrystallization during nappe deformation iron rich calcite appears to control the paramagnetic sub fabric susceptibility ellipsoids approach oblate shapes for the diamagnetic sub fabric with the most extreme shapes reaching susceptibility differences k kmax kmin close to that of single crystal calcite whereas the paramagnetic sub fabric is represented mainly by prolate shape ellipsoids the low field ams ellipsoids show mixed oblate and prolate shapes without consistency within or between sites it is evident that when the magnetic sub fabrics of the root zone and overturned limb are separated their individual shapes and distribution of principal directions mirror the developed cpo

neogene lateral extension during convergence in the central alps evidence from interrelated faulting and backfolding around the simplonpass switzerland abstract the simplon fault zone occurs at the western end of the lepontine metamorphic dome in the central alps and represents a major low angle 25 dip normal fault associated with wsw ene directed lateral extension movement began in the early miocene and continued until at least 3 ma accumulating a total vertical throw of around 10 km corresponding to 24 km displacement parallel to the fault this displacement is partitioned between a broad zone of ductile mylonites in the footwall and a more discrete cataclastic detachment fault the simplon line in the central region simplon village to zwischbergen some 3 km of the total vertical displacement is accommodated by the discrete cataclastic zone due to the higher exposed structural level the importance of the cataclastic component increases towards the northwest in the northern steep belt around the simplonpass retrograde greenschist facies mylonite formation and younger cataclastic faulting associated with lateral extension occurred contemporaneously with sse vergent large scale backfolding representing nnw sse shortening and crustal thickening the combined effect was an overall shortening across the orogen accommodated by an extension parallel to the orogen allowing lateral escape of continental material normal faulting and the resultant lateral escape was not just superficial it extended to depths of at least 15 km and probably to depths exceeding 25 km the overall geometry and kinematics of the simplon fault zone and in particular the interplay between folding and faulting is very similar to that described from the metamorphic core complexes and detachment faults of the cordillera of the southwestern usa within the central alps extension was associated with rapid exhumation of the lepontine metamorphic dome as evidenced by very rapid cooling rates determined from mineral ages in the footwall similar to the cenozoic tectonics of the himalayas and tibet orogen parallel extension in the mountain belt may have been promoted by an overall reduction in the horizontal compressive stress in this direction more limited extension of the same age and orientation is known from a large area of the european foreland greater extension in the mountain belt compared with the foreland was accommodated by major strike slip transfer fault systems and was linked to coeval overthrusting of the lowlands towards the southwest in the external southwestern alps of haute provence france coeval folding and orogen parallel extension such as at the simplonpass were developed in a dextral transpressive regime due to oblique wnw ese convergence across the alps during the neogene

effect of progressive deformation on remanent magnetization of permian redbeds from the alpes maritimes france abstract the relationships among the anisotropy of magnetic susceptibility the finite strain and the characteristic remanent magnetization chrm have been investigated in deformed red sediments from the alpes maritimes in southeast france the magnetic properties of these rocks are due to hematite the finite strain is known from field studies of the shapes and orientations of green reduction spots and from optical microscopy and x ray texture goniometry studies of chlorite and illite the strain data permit a classification of the magnetic results according to four main stages of progressive deformation in the compaction stage magnetic anisotropy is flattened in the bedding due to compactional loading the chrm directions approximate to a fisherian distribution about a mean value close to the known permian direction for the region as deformation proceeds pencil structure first develops and the anisotropy is characterized by a prolate pattern with maximum axis parallel to the subhorizontal azimuth of the pencil structure and fold axes with increasing deformation the magnetic susceptibility ellipsoid becomes oblate and finally triaxial at these stages of high deformation the anisotropy patterns show that the hematite grain orientations are strongly influenced by the cleavage the remanence directions in deformed rocks do not correspond to a fisher distribution and eventually deviate strongly from permian directions these results show that paleomagnetic vectors are affected by the distortional strains which accomodate shape change in the rock simple tilt correction without compensation for the strain would yield incorrect paleopole positions an attempt has been made to compensate for the effects of deformation by regarding the remanent vector as a passive marker march 1932 equations for strain removal were applied to the remanence in two ways 1 a using strain data directly obtained in the field for each site and 2 b by converting the magnetic susceptibility anisotropy of each sample to a corresponding finite strain value correcting for the finite strain by both methods improves the within site grouping of paleomagnetic vectors in strongly deformed rocks strain removal assuming the march model results in overcorrection of the remanent magnetization data in low strain regions distortion may produce mechanical rotation of the hematite particles but recrystallization may alter the deformation mechanism in regions of high strain the limits of applicability of the passive marker treatment could not be tested adequately in the deformed red sediments of the alpes maritimes

numerical simulation of radial cloud bands within the upper level outflow of an observed mesoscale convective system abstract turbulence affecting aircraft is frequently reported within bands of cirrus anvil cloud extending radially outward from upstream deep convection in mesoscale convective systems mcss a high resolution convection permitting model is used to simulate bands of this type observed on 17 june 2005 the timing location and orientation of these simulated bands are similar to those in satellite imagery for this case the 10 20 km horizontal spacing between the bands is also similar to typical spacing found in a recent satellite based climatology of mcs induced radial outflow bands the simulated bands result from shallow convection in the near neutral to weakly unstable mcs outer anvil the weak stratification of the anvil the ratio of band horizontal wavelength to the depth of the near neutral anvil layer 5 1 to 10 1 and band orientation approximately parallel to the vertical shear within the same layer are similar to corresponding aspects of horizontal convective rolls in the atmospheric boundar

thermal alteration of the magnetic mineralogy in ferruginous rocks the northampton ironstone contains the paramagnetic minerals siderite and berthierine and a trace of the ferrimagnetic mineral magnetite the magnetic fabric of this sedimentary rock as defined by the anisotropy of magnetic susceptibility is controlled by bedding compaction but is inverse i e the maximum susceptibility axes are normal to the bedding plane this inverse fabric is attributed to the dominating presence of siderite the rocks were incrementally heated to 600 c and the magnetic fabric was measured at room temperature and at near liquid nitrogen temperature after each heating step cooling the samples in liquid nitrogen enhances the paramagnetic contribution to the magnetic fabric after heating the samples above 250 c the room temperature magnetic fabric became normal with the minimum susceptibility axes perpendicular to the bedding plane the low temperature magnetic fabric remains inverse until the samples are heated to about 500 c after heating to higher temperatures a normal fabric was observed at both room temperature and low temperature rock magnetic evidence shows that magnetite is created during the heating the start of mineralogical changes in the rock was detected by electron spin resonance spectroscopy powder x ray diffraction and acquisition of isothermal remanence berthierine starts to break down at approximately 250 c and is totally oxidized by 500 c the creation of magnetite in the heating experiments corresponds with this mineralogical change the change in the room temperature magnetic fabric is associated with the decomposition of berthierine part of which alters to magnetite the new magnetite phase has a normal magnetic fabric which overprints the inverse magnetic fabric of siderite

anisotropy of diamagnetic susceptibility in thassos marble a comparison between measured and modeled data abstract a study of shear zones within the calcite marble complex of the island of thassos greece shows that the low field anisotropy of magnetic susceptibility ams technique can be successfully applied to diamagnetic rocks for characterizing rock fabrics the strain path involves both an early pure shear stage and a simple shear overprint that is documented by a transition from triaxial neutral to uniaxial prolate shapes of ams ellipsoids the maximum susceptibility is oriented perpendicular to the rock foliation reflecting the preferred orientation of calcite c axes in the protolith as well as in the mylonites for three samples that represent different types of calcite fabrics the ams was recalculated from neutron and electron backscatter diffraction textural data a comparison of the measured and modeled data shows a good coincidence for the orientation of the principal ams axes and for the recalculated anisotropy data both measured and modeled data sets reflect the change from neutral to distinct prolate ellipsoids during progressive deformation

finite strain patterns and their significance in permian rocks of the alpes maritimes france abstract more finite strain data has been obtained from autochthonous permian mudstones of the alpes maritimes s e france these new data were computed from field measurements of green spots on all available sections deformed mudcracks and from the quantitative correlation between magnetic susceptibility anisotropy and finite strain in these rocks previously published finite strain data and the new results are presented on a series of structural maps and cross sections for the dome de barrot the tinee and vionene region and the roya region as in previous studies difficulties arise in explaining the apparently variable extension parallel with the 100 subhorizontal bedding cleavage intersection either this is real or there were large volume changes during the tectonic deformation study of quartz fibres developed in deformed mudcracks in the tinee valley suggest that early in the tectonic history incremental stretching directions were parallel with the bedding cleavage intersection while later they were down dip in the 100 trending cleavage since these permian rocks have remained stuck to the argentera basement they also record displacements and deformations in the basement the early 100 subhorizontal stretching is consistent with nw se dextral strike slip basement faulting while later down dip stretching in the cleavage is consistent with contraction faults in the basement this information and new palaeomagnetic data on the same samples are combined with recent geophysical evidence and regional tectonic studies to provide a new precision to the tectonic history of this part of the western alpine external zone

role of shear in development of the helvetic fold thrust belt of switzerland the geometric features of the helvetic nappes of the alps show intense internal deformation set up predominantly by simple shear during nappe transport the nappes are bounded by thrusts that parallel incompetent layers and ramp upward stratigraphically across competent units in the direction of tectonic transport stratal layering is oblique to nappe boundaries thrust surfaces formed after ductile shear zones developed in underlying pre triassic gneissic basement the broad zone of shearing narrowed down as deformation increased to form zones of intense shear and ultimately to form thrust faults contraction along competent layers obliquely inclined to shear surfaces produced buckle folds the geometry of these folds was modified by further shearing as their normal limbs became aligned in the extension field of the strain ellipse for simple shear producing normal faults

neogene kinematics of the central and western alps evidence from fission track dating zircon and apatite fission track analysis has established the continuation of a zone of rapid change in mineral ages extending from the simplon fault zone in the simplon alps through the rhone valley and along the southeastern side of the mont blanc and belledonne massifs apatite fission track ages to the northwest of this zone generally range from 1 4 to 6 ma whereas those to the southeast range from 6 to 13 ma corresponding values for zircon are 11 13 and 16 26 ma respectively the zone corresponds to the position of the frontal pennine thrust in the mont blanc belledonne region this structure a prominent feature on recent deep seismic profiles may have been reactivated in the neogene with an important normal fault component this is suggested by apatite and zircon fission track ages in the footwall that are younger than those in the hanging wall and by the observed elimination of the lower pennine or simplon nappes along this fault zone in the rhone valley mont blanc belledonne region resulting in the juxtaposition of north penninic and helvetic ultra helvetic nappes at the current erosion level the distribution of fission track ages reflects this movement and the related neogene exhumation of the mont blanc and belledonne external massifs which has continued until less than 1 4 m y ago i e it is almost certainly still active and has tilted the overlying nappe sequence

magnetic anisotropy reveals neogene tectonic overprint in highly strained carbonate mylonites from the morcles nappe switzerland magnetic anisotropy reveals neogene tectonic overprint in higly strained carbonate mylonites from the morcles nappe switzerland

microfabrics in carbonate mylonites along a large scale shear zone helvetic alps abstract carbonate mylonites with varying proportions of second phase minerals were collected at positions of increasing metamorphic grade along the basal thrust of the morcles nappe helvetic nappes switzerland variations of temperature stress and strain rate changes in chemistry of solid and fluid phases and differing degrees of strain localization and annealing were tracked by measuring the shapes mean sizes and size distributions of both matrix and second phase grains as well as crystal preferred orientation cpo of the matrix field structures suggest that strain rate was constant along the fault the mean and distribution of the calcite grain sizes were affected most profoundly by temperature increased temperature presumably accompanied by decreased stress correlated with larger mean sizes and wider size distributions at a given location the matrix grains in mylonites with more second phase particles are on average smaller have narrower size distributions and have more elongate shapes for example mylonites with 50 vol of second phases have matrix grain sizes half that of pure mylonites changes in calcite chemistry and the presence of synkinematic fluids seemed to influence microfabric only weakly temporal variations in conditions such as exhumation induced cooling apparently provoke changes in temperature stress and strain rate along the nappe these changes result in further strain localization during retrograde conditions and cause the grain size to be reduced by an additional 50 the matrix cpo strengthens with increasing temperature or strain but weakens and rotates with increasing second phase content these fabric changes suggest differing rates of grain growth grain size reduction and development of cpo owing to variations in the deformation conditions and perhaps mechanisms to interpret natural mylonite structures or to extrapolate mechanical data to natural situations requires careful characterization of the microfabric and in particular second phase minerals

magnetic anisotropy rock fabrics and finite strain in deformed sediments of sw sardinia italy abstract although some empirical relationships have been established between the anisotropy of magnetic susceptibility ams and the state of finite strain in studies from specific geologic areas the mechanisms governing correlations are not well understood a comparative study has been made in order to elucidate the ams strain relationship by investigating mineral preferred orientations and the responsible microstructural deformation processes detailed analyses are presented from low grade metamorphic slates of a palaeozoic sequence exposed in the variscan of sw sardinia rock magnetic experiments suggest that paramagnetic minerals dominate the ams in these rocks excellent agreement was found between magnetic fabrics and lattice preferred orientations 001 of mica and chlorite determined from x ray texture goniometry measurements depending on the oblate or prolate ellipsoidal shape of anisotropy the minimum principal axes of ams and x ray textures can coincide with the poles to slaty cleavage or the maximum principal axes can coincide with the bedding cleavage intersection respectively the measured ams and x ray textures only partially reflect the finite strain determined from deformed micro pebbles and reduction spots axial orientations of magnetic fabrics mica and chlorite preferred orientations and finite strain ellipsoids are generally in good agreement depending on development of oblate or prolate fabric ellipsoidal shapes linear correlations can be established for magnitudes of minimum and intermediate axes of the ams and finite strain ellipsoids but shape comparisons are complex microstructural studies by scanning electron microscopy sem indicate that the preferred orientation of the phyllosilicates is caused by different grain scale deformation mechanisms such as kinking micro folding and preferential growth thus magnetic fabrics and mineral preferred orientations evidently result from different deformation mechanisms than the finite strain they reflect the heterogeneous deformation due to micro mechanical reorientation processes of mineral grains while finite strain reflects the homogeneous deformation accommodated cumulatively by the strain markers

unusually strong vertical motions in a caribbean hurricane abstract unusually strong updrafts and downdrafts in the eyewall of hurricane emily 1987 during its rapidly deepening phase are documented by both in situ aircraft measurements and a vertically pointing doppler radar updrafts and downdrafts as strong as 24 and 19 m s 1 respectively were found mean updrafts and downdrafts were approximately twice as strong as those found in other hurricanes updrafts had approximately the same width as downdrafts the most vigorous updrafts were located in the front quadrants of the storm and most of the strongest downdrafts were found in the rear quadrants the downdrafts could not be explained in terms of evaporative or melting cooling or precipitation drag evidence is presented that moist symmetric instability initiated by precipitation loading may have been responsible for the strong downdrafts

the correlation of magnetic anisotropy with strain in the chelmsford formation of the sudbury basin ontario abstract a quantitative correlation has been established between finite strain and the anisotropy of magnetic susceptibility ams in sandstones of the precambrian chelmsford formation of the sudbury basin ontario investigations of the progressive acquisition of isothermal remanent magnetization and its destruction with reverse field and thermal demagnetization as well as microscopic examination of polished thin sections show that both pyrrhotite and magnetite are present in the sandstone measurements of the ams have been carried out at 16 sites distributed throughout the chelmsford formation outcrop considerable variation in the shapes of the magnetic susceptibility ellipsoids axes k max k int k min exists within each site with the k max and k int axes contained in the cleavage planes where developed the magnitudes of the magnetic susceptibility axes have been quantitatively correlated with strain measurements carried out by clendenen et al this issue two different strain to magnetics correlations have been carried out between the site mean strain determined using deformed concretions and the mean values of the ams at each site and between individual specimen strain values determined at the microscopic scale and the individual specimen ams in both cases separate correlations were made between strain long intermediate and short axes and their corresponding magnetic k max k int and k min axes at 10 sites the site mean strain values were derived from strain analysis of the concretions and at an additional 6 sites the site mean strain values were derived from the ams to strain correlation 527 individual cores were converted to equivalent strain values using the ams structural correlation of individual specimens this study extends the use of ams methods to include strain determination in sandstones and provides an order of magnitude increase in the available number of such data for further structural analysis

inverse magnetic fabric in deformed limestones of the morcles nappe switzerland anisotropy of magnetic susceptibility ams was measured at 15 sites in deformed helvetic limestones of the morcles nappe in western switzerland inverse magnetic fabrics characterized by axes of maximum susceptibility subperpendicular to bedding or cleavage were observed at four sites in the root zone of the nappe acquisition and thermal demagnetization of isothermal remanent magnetization show that the ferromagnetic mineralogy is dominated by pyrrhotite with various proportions of magnetite hematite and goethite the matrix minerals were studied in thin section with a staining technique to distinguish different carbonates by x ray texture goniometry and by microprobe analysis observations of ams at room and liquid nitrogen temperatures and of the temperature dependence of bulk susceptibility lead to the conclusion that the inverse fabrics result from a paramagnetic component due to fe2 ions in the calcite matrix

homogeneous ice nucleation in subtropical and tropical convection and its influence on cirrus anvil microphysics abstract this study uses a unique set of microphysical measurements obtained in a vigorous convective updraft core at temperatures between 33 and 36 c together with a microphysical model to investigate the role of homogeneous ice nucleation in deep tropical convection and how it influences the microphysical properties of the associated cirrus anvils the core and anvil formed along a sea breeze front during the cirrus regional study of tropical anvils and cirrus layers florida area cirrus experiment crystal face the updraft core contained two distinct regions as traversed horizontally the upwind portion of the core contained droplets of diameter 10 20 m in concentrations of around 100 cm 3 with updraft speeds of 5 10 m s 1 the downwind portion of the core was glaciated with high concentrations of small ice particles and stronger updrafts of 10 20 m s 1 throughout the core rimed particles up to 0 6 cm diameter were observed the anvil contained high concentrations of both small particles and

dual aircraft investigation of the inner core of hurricane norbert part ii mesoscale distribution of ice particles abstract horizontal fields of cloud microphysical parameters vertical air motion and horizontal wind at the 6 km level in hurricane norbert 1984 were obtained by mapping and interpolating data collected on board a wp 3d aircraft along numerous flight tracks executed within the central region of the storm although the storm was characterized by a strong vortex of winds reaching peak values 50 m s 1 all around the storm the precipitation was concentrated on the southwest side of the storm a sloping eyewall was located within 20 to 30 km of the eye stratiform precipitation dominated the region outside the eyewall a 25 km wide band of maximum stratiform precipitation was centered 60 70 km southwest of the storm center the ice particles at flight level tended to be relatively large both in the eyewall and in the outer band of stratiform precipitation particles were smaller and more numerous 100 300 l 1 in the zone between the eyewall and outer stratiform band these particles occurred on the out

calcite fabrics in a natural shear environment the helvetic nappes of western switzerland the aim of this contribution is to describe and interpret the crystallographic orientations and microstructures of calcite in the upper jurassic limestones of the helvetic nappes between the mont blanc and aar massifs over a distance along strike of about 180 km the c axis preferred orientation pattern which could be inferred is regionally very constant the c axis point maxima are everywhere subperpendicular to the regional strike of the chain there is an obliquity between the orientation of the macroscopically dominant cleavage and the microscopically visible long axes of individual grains the c axis maxima in most specimens are parallel to the axis of shortening of the microscopic grain shape fabric this fabric geometry indicates either continuous shear deformation or alternatively a two stage deformation history the obliquity of the grain shape fabric may be due to the fact that the flattening plane of the individual grains reflects only the last increment of a continuous shear process or it may represent a later finite deformation which has led to the formation of a regionally developed second cleavage there is a systematic relationship between the direction of these late shear movements and the main overthrust direction as given by the finite strain pattern this suggests that the microfabric of the rocks was acquired during a progressive rotation with time of the main overthrust direction the observed pattern of preferred orientation has been correlated by several authors with intracrystalline deformation mechanisms a combination of slip on r and twinning on e however the e twinning observed in the specimens investigated is younger than the development of the crystallographic fabric a new method for stress determination from e twinning is proposed

mathematical simulations of anisotropy of magnetic susceptibility on composite fabrics 1 the anisotropy of magnetic susceptibility ams is an integral measure of the preferred orientation of all minerals present in a rock when the ams is carried by paramagnetic minerals alone the principal directions of the susceptibility ellipsoid should reflect the crystallographic orientation of the minerals the relationship between the ams and deformation depends on several factors which control the development of lattice preferred orientation lpo in a rock a mathematical model is presented that simulates the magnetic susceptibility ellipsoid for samples composed of more than one mineral phase measurements of the ams are compared with fabric based anisotropy models for black slates from the navia alto sil slate belt in northern spain the ams is carried by paramagnetic minerals as has been confirmed by high field torque magnetometry low temperature ams and magnetization curves the lpo of mica and chlorite has been determined by x ray texture goniometry pole figures and orientation ellipsoids show the changes in the degree of alignment of the phyllosilicates the models have been tested in samples displaying three types of pole figures a high intensity point maximum a medium intensity elliptical maximum and a girdle shaped distribution at one site displaying kink bands the lpo shows variations between these types at the outcrop scale the case studies illustrate the success in modeling different lpo types

distinctive diamagnetic fabrics in dolostones evolved at fault cores the dead sea transform abstract we resolve the anisotropy of magnetic susceptibility ams axes along fault planes cores and damage zones in rocks that crop out next to the dead sea transform dst plate boundary we measured 261 samples of mainly diamagnetic dolostones that were collected from 15 stations to test the possible effect of the iron content on the ams we analyzed the fe concentrations of the samples in different rock phases dolostones with mean magnetic susceptibility value lower than 4 10 6 si and iron content less than 1000 ppm are suitable for diamagnetic ams based strain analysis the dolostones along fault planes display ams fabrics that significantly deviate from the primary sedimentary fabric the characteristics of these fabrics include well grouped sub horizontal minimum principal ams axes k 3 and sub vertical magnetic foliations commonly defined by maximum and intermediate principal ams axes k 1 and k 2 axes respectively these fabrics are distinctive along fault planes located tens of kilometers apart with strikes ranging between nnw sse and nne ssw and different senses of motion the obtained magnetic foliations k 1 k 2 are sub parallel within 20 to the fault planes based on rock magnetic and geochemical analyses we interpret the ams fabrics as the product of both shape and crystallographic anisotropy of the dolostones preferred shape alignment evolves due to mechanical rotation of subordinate particles and rock fragments at the fault core preferred crystallographic orientation results from elevated frictional heating 300 c during faulting which enhances c axes alignment in the cement supported dolomite breccia due to crystal plastic processes the penetrative deformation within fault zones resulted from the local fault related strain field and does not reflect the regional strain field the analyzed ams fabrics together with fault plane kinematics provide valuable information on faulting characteristics in the uppermost crust

from qualitative to quantitative magnetic anisotropy analysis the prospect of finite strain calibration abstract a method of separating low field susceptibility anisotropies due to ferrimagnetics and the matrix proposed hitherto in cases where the principal axis of these two components are merged is generalized in cases where the axes are distinct the method consists of analysing in specimens close in the same sample anisotropies the differences of which are due to the variation of respective percentages of the two components although the strain rate remains constant one thus uses the cause which itself renders global anisotropy unusable a first application is presented where a control using the anisotropy of isothermal remanent magnetization allows the validity of the method to be tested a discussion of the choice of the best ellipsoid relative either to the matrix or to the ferrimagnetics to give the best indication of relative finite strain rate is opened

differences between magnetic and mineral fabrics in low grade cleaved siliciclastic pelites a case study from the anglo brabant deformation belt belgium abstract theoretically within a given pelitic rock in which the main paramagnetic carriers are white mica and chlorite and in which judging from the ams parameters ams is controlled by the paramagnetic carriers the results of x ray pole figure goniometry should show a qualitative relationship with ams this idea is tested on single phase deformed low grade pelites of the lower palaeozoic brabant massif belgium representing the southeastern part of the anglo brabant deformation belt for the vast majority of the samples investigated the different lf ams parameters suggest a paramagnetic control on lf ams different parameters of lf ams measured at 77 k low t lf ams and a comparison of these with the lf ams parameters indicate that lf ams is controlled virtually entirely by paramagnetic carriers high field torque magnetometry hf ams indicates further that ams is controlled entirely by paramagnetic carriers for the vast majority of the samples two apparent discrepancies are observed however these are 1 a frequent mismatch between the lf ams fabric on the one hand and the paramagnetic fabric indicated by low t lf ams and hf ams on the other hand and 2 a rather common mismatch between the preferred orientation of chlorite and white mica suggested by x ray pole figure goniometry on the one hand and the lf ams fabric low t lf ams fabric and hf ams paramagnetic fabric on the other hand these apparent discrepancies may partly be attributed to the composite nature of both the lf ams fabric and the paramagnetic susceptibility fabric the presence of different populations of paramagnetic carriers possibly in combination with minor traces of ferromagnetic s l carriers which are not picked up by the methods applied may explain some of the mismatches observed and are compatible with the basin evolution history of the brabant massif in addition it is possible that the low temperatures low t lf ams and high fields hf ams are capable of enhancing one of the paramagnetic phases thus leading to discrepancies between methods that define the mineral and the magnetic fabrics the results of this study show that even when the lf ams data suggest that the lf ams of a given pelitic rock in which phyllosilicates form the main paramagnetic carriers is controlled entirely by paramagnetic carriers alternative methods such as phyllosilicate x ray pole figure goniometry will not necessarily reflect the paramagnetic carrier orientation although a number of cases have successfully correlated lf ams with mineral fabric and occasionally even strain this study serves as an example for how methods to define mineral and magnetic fabrics can be sensitive in detecting different paramagnetic phases

ice microphysics observations in hurricane humberto comparison with non hurricane generated ice cloud layers abstract measurements are presented that were acquired from the national aeronautics and space administration nasa dc 8 aircraft during an intensive 3 day study of tropical storm hurricane humberto on 22 23 and 24 september 2001 particle size distributions particle image information vertical velocities and single and dual wavelength doppler radar observations were obtained during repeated sampling of the eyewall and outer eye regions eyewall sampling temperatures ranged from 22 to 57 c and peak updraft velocities from 4 to 15 m s 1 high concentrations of small ice particles in the order 50 cm 3 and above were observed within and around the updrafts aggregates some larger than 7 mm dominated the larger sizes the slope of the fitted exponential size distributions was distinctly different close to the eye than outside of that region even at low temperatures was characteristic of warm temperature growth 30 cm 1 close to the eye and characteristic of low temperature growth outsi

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