slip system domains 2 kinematic aspects of fabric development in polycrystalline aggregates abstract in the first paper of the present series cobbold and gapais 1986 we develop theoretical models of plane strain domainal deformation by slip along inextensible and indestructible fibres for such extreme mechanical conditions we show that deformation is largely controlled by kinematic factors we use our models to explain domainal patterns of natural slip systems including bedding and foliation planes faults ductile shear zones and lattice planes the present paper focusses on kinematic aspects of fabric development in polycrystalline aggregates a three dimensional kinematic model is developed it reveals that common quartz fabrics may develop domainally by reorientation and selection of inextensible slip directions a axes or slip planes with initially random orientation stable orientations of slip directions are close to both surfaces of no finite extension and orientations of large amount of shear we explain 1 1 common patterns of quartz a and c axis fabrics e g small circles and crossed girdles 2 2 characteristic differences between fabric patterns according to the shape of the finite strain ellipsoid 3 3 development of asymmetric fabrics during non coaxial deformation histories this last process involves selective destruction or replacement of certain orientation domains so that a preferred orientation of slip lines develops close to the bulk shear direction rotation recrystallization is shown to be an efficient natural selection mechanism the models also account for many microstructural features found in oriented polycrystalline rocks especially 1 1 alternating band like or kink like domains of twinned preferred orientations 2 2 individual grains or clusters of grains with retort like shapes and extensive recrystallisation at boundaries 3 3 small scale shear bands formed by strain partitioning and shear localization

near surface deformation in the new madrid seismic zone as imaged by high resolution sh wave seismic methods over 1 5 kilometers of high resolution sh wave refraction and reflection profiles have been performed in the madrid bend area of northwestern tennessee approximately 8 km north of tiptonville tennessee to establish the existence of neo tectonic near surface deformation the specific area was chosen because of the access it provided to the tiptonville dome a holocene flexure and the trend of contemporary seismicity within the new madrid seismic zone nmsz we believed the highest likelihood of near surface deformation to be over these features partially reversed refraction reflection walk away tests and common depth point cdp seismic profiling using the non traditional sh wave method have traced antiformal flexure and numerous faults into the late eocene and holocene sediments of the tiptonville dome province of the lake county uplift lcu vertical displacements exhibited across the faults range from approximately 3 to 30 m these structures have been interpreted to be neo tectonic features associated with tensional stresses across the tiptonville dome

elevated lateral stress in unlithified sediment midcontinent united states geotechnical and geophysical indicators for a tectonic origin abstract indirect and direct geotechnical measurements revealed the presence of high lateral earth pressure ko in shallow unlithified sediment at a site in the northernmost mississippi embayment region of the central united states results from pile load and pressuremeter tests showed maximum ko values greater than 10 however the complex geologic environment of the midcontinent made defining an origin for the anomalous ko based solely on these measurements equivocal although in situ sediment characteristics indicated that indirect tectonic or nontectonic geologic mechanisms that include transient overburden loads e g fluvial deposition erosion glacial advance retreat and dynamic shear loads e g earthquakes were not the dominant cause they were unable to provide indicators for a direct tectonic generation localized stresses induced anthropogenically by the geotechnical field tests were also considered but ruled out as the primary origin a high resolution shear wave sh reflection image of geologic structure in the immediate vicinity of the test site revealed compression style neotectonism and suggested that the elevated stress was a tectonic manifestation post paleozoic reflectors exhibit a tertiary structural inversion as evidenced by post cretaceous fault displacement and pronounced positive folds in the hanging wall of the interpreted faults the latest stratigraphic extent of the stress effects i e all measurements were in the late cretaceous to tertiary mcnairy formation as well as the relationship of stress orientation with the orientation of local structure and regional stress remain unknown these are the subjects of ongoing studies

laccolithic as opposed to cauldron subsidence emplacement of the eastern mourne pluton n ireland evidence from anisotropy of magnetic susceptibility the structural evolution and emplacement of the eastern mourne pluton was investigated using anisotropy of magnetic susceptibility ams measurements carried out on 112 oriented block samples and structural data from the host rocks from these new data cauldron subsidence as the emplacement mechanism is disputed and evidence for an alternative laccolithic style model involving inflation is presented this includes deflection and uplift of host rock bedding close to contacts and the magnetic fabric pattern which has a gentle dome geometry even close to contacts the magnetic lineations usually plunge down dip near the external margins but otherwise have a general ssw nne trend that diverges northward this suggests a northward directed inflow direction the model for the emplacement of the eastern mourne pluton is a laterally fed laccolith emplaced south to north the eastern margin is interpreted as a faulted contact facilitating the inflation of an asymmetrical breached laccolith

structure emplacement and tectonic setting of late devonian granitoid plutons in the tepla barrandian unit bohemian massif the st novice and cista granodiorite tonalite plutons are small 27 and 38 km2 respectively intrusions that are largely discordant to regional ductile structures in the center of the upper crustal tepla barrandian unit bohemian massif their whole rock and trace element compositions are consistent with medium k calc alkaline magma generated above a subducted slab in a continental margin arc setting the u pb zircon age of the st novice pluton newly determined at 375 2 ma using the laser ablation icp ms technique is within the error of the previously published pb pb age of 373 1 ma for the cista pluton the two plutons also share other characteristics that are typical of concentrically expanded plutons ceps such as elliptical cross section in plan view steep contacts inferred downward narrowing conical shape faint normal zoning and margin parallel magmatic foliation decoupled from the regional host rock structures we interpret the st novice and cista plutons as representing the initial late devonian stage of much more voluminous early carboniferous arc related plutonism represented most typically by the central bohemian plutonic complex in the upper crust of the central bohemian massif these two plutons are important tectonic elements in that they indicate an overall shift of the arc related plutonic activity from the nw to the se accompanied with a general compositional trend of the magmas from medium k calc alkaline to shoshonitic ultrapotassic such a pattern is compatible with se directed subduction of the saxothuringian ocean beneath the tepla barrandian overriding plate as a cause of arc related magmatism in this part of the bohemian massif

quaternary grabens in southernmost illinois deformation near an active intraplate seismic zone abstract narrow grabens displace quaternary sediments near the northern edge of the mississippi embayment in extreme southern illinois east central united states grabens are part of the fluorspar area fault complex fafc which has been recurrently active throughout phanerozoic time the fafc strikes directly toward the new madrid seismic zone nmsz scene of some of the largest intra plate earthquakes in history the nmsz and fafc share origin in a failed cambrian rift reelfoot rift every major fault zone of the fafc in illinois exhibits quaternary displacement the structures appear to be strike slip pull apart grabens but the magnitude and direction of horizontal slip and their relationship to the current stress field are unknown upper tertiary strata are vertically displaced more than 100 m illinoian and older pleistocene strata 10 to 30 m and wisconsinan deposits 1 m or less no holocene deformation has been observed average vertical slip rates are estimated at 0 01 to 0 03 mm year and recurrence intervals for earthquakes of magnitude 6 to 7 are on the order of 10 000s of years for any given fault previous authors remarked that the small amount of surface deformation in the new madrid area implies that the nmsz is a young feature our findings show that tectonic activity has shifted around throughout the quaternary in the central mississippi valley in addition to the nmsz and southern illinois the wabash valley illinois indiana benton hills missouri crowley s ridge arkansas missouri and possibly other sites have experienced quaternary tectonism the nmsz may be only the latest manifestation of seismicity in an intensely fractured intra plate region

fabric transitions in the saxony granulite terrain abstract quartz fabric transitions reported from the saxony granulite terrain and from the nearby ore mountains are interesting because of the changes in the pattern types and the variation in the opening angles of the fabric skeletons a short summary is presented of salient features in research documented in the east german literature between 1961 and 1978 the changes in fabric skeleton with decreasing metamorphic grade are proposed as mainly consequent to the deactivation of prism c glide systems as temperature decreases fabrics indicative of the appearance of the c burgers vector might be diagnostic for deformation in regimes of comparatively high temperatures or low strainrates or for deformation under conditions such that there is a relatively high kinetically effective hydroxyl content in the quartz structure

deformation of partially molten granite a review and comparison of experimental and natural case studies experimental and natural investigations of partially molten granite are compared and reviewed experiments suggest that deformation of partially molten granite with low viscosity melt 104 pa s exhibits a rheological critical melt percentage rcmp in case of high viscosity melts 108 pa s however the relationship between melt fraction and log viscosity of the partially molten granite may be linear considerations about viscosity rheological thresholds and segregation of natural melts suggest that low viscosity melt experiments simulate natural conditions more realistically therefore an rcmp is to be expected under natural conditions both diffusion creep and dislocation creep may occur under natural conditions whereas cataclastic flow is only observed under experimental conditions a melt induced transition from dislocation creep to diffusion creep occurs under experimental and natural conditions melt topology is controlled by the magnitude of differential stress under experimental conditions if differential stress is higher than 100 150 mpa melt pockets are elongate and oriented at a low angle to the maximum compressive stress in contrast in nature melt pockets tend to be oriented subparallel to the foliation plane i e presumably at a high angle to the maximum compressive stress

simple shear deformation and quartz crystallographic fabrics a possible natural example from the torridon area of nw scotland ln this paper the microstructures and crystallographic fabrics of a 30 cm wide deformed quartz vein from the torridon area of nw scotland are described the vein which lies along a joint separating two blocks of proterozoic gneiss was deformed by crystal plastic processes when the rigid joint blocks moved in opposite directions parallel to the vein margins mylonitic foliation within this quartzose ductile shear zone locally displays the classic orientation variation expected for heterogeneous simple shear deformation in thin section the vein is a mylonite composed of dynamically recrystallized elongate quartz grains aligned oblique to the mylonitic foliation fabrics within the central part of the vein have been examined by optical and x ray texture goniometry methods together with orientation distribution function odf analysis the a axis fabric consists of a dominant single point maximum orientated within the xz plane at 9 to the lineation x this point maximum occupies a pole position to the corresponding single girdle c axis fabric for individual positions on the c axis fabric skeleton the orientations of potential crystallographic slip systems slip plane and direction relative to shear zone co ordinates have been calculated by odf analysis the calculation of relative resolved shear stresses schmidfactors for the potential slip systems assuming a simple shear kinematic framework reveals an elegantly simple relationship between individual grain c axis orientation and correspond ing orientations of potential slip systems these results are readily interpreted in terms of bulk simple shear deformation

tertiary and quaternary tectonic faulting in southernmost illinois abstract tertiary and or quaternary tectonic faulting is documented in three areas of southernmost illinois the fluorspar area fault complex fafc in pope and massac counties the ste genevieve fault zone sgfz in alexander and union counties and the commerce fault zone cfz in alexander county in the fafc faults that strike ne and nne displace mounds gravel late miocene to early pleistocene and locally the metropolis terrace gravel pleistocene pre woodfordian no woodfordian or younger deposits are deformed faults typically outline narrow linear grabens that formed under tension with a component of strike slip north south to nw trending vertical faults near the southeast end of the sgfz displace eocene sediments again faults outline narrow grabens and show indications of strike slip deformed quaternary sediments have not been observed the cfz which trends northeast displaces mounds gravel in illinois and units as young as peoria silt woodfordian in missouri quaternary movement has been interpreted as right lateral strike slip the cfz coincides with a subtle gravity and magnetic lineament and seems to reflect a major feature in the basement surface expression in illinois is subtle but mafic and ultramafic intrusions hydrothermal alteration and small faults align with the commerce geophysical lineament earthquake foci in missouri and illinois lie on or close to the cfz some focal mechanisms fit the fault trend among these structures only the cfz exhibits slip that conforms to the current stress field principal compressive stress axis e w to ene wsw possibly the stress field changed during neogene time alternatively high fluid pressures or local stress concentrations may have induced slip on less favorably oriented fractures tighter constraints are needed on timing magnitude and direction of neogene displacement

rheology and microstructure of experimentally deformed plagioclase suspensions we present the result of the first deformation experiments at high temperatures and high pressures on synthetic magmatic suspensions of strongly anisometric particles the results highlight the interplay between the rheological response and the development of microstructures and they demonstrate the critical importance of the shape of crystals on the mechanical behaviour of magmas plagioclase suspensions with two crystal fractions 0 38 and 0 52 were deformed both in compression and in torsion in a paterson apparatus with increasing crystal fraction the rheological behaviour of the magmatic suspension evolves from nearly steady state flow to shear weakening this change being correlated with a microstructural evolution from a pervasive strain to a strain partitioning fabric magmatic suspensions of plagioclase have viscosities approximately five orders of magnitude higher than suspensions of equivalent crystallinities made of isometric particles such as quartz

caledonian plutonism and major lineaments in the sw scottish highlands within the sw grampian highlands several ne sw trending shear zones and faults related to the caledonian transpressional collision are recognized as being distinct from an intersect ing set of nw se trending pre caledonian crustal lineaments which were reactivated during caledonian orogenesis the geochemical and isotopic characteristics of the 425 400 ma granitoids of this region show that they were derived by anatexis of the lower crust associated with a mantle component which provided an influx of mantle heat and or metasomatic fluids their spatial distribution suggests a close genetic relationship with caledonian shear zones having made the fundamental distinction between ascent transport and emplacement arrival configurations possible for granitoid magmas new data are presented for these plutons which show that i a common modal sequence of intrusive phases can be recognized ii these phases are all sited at shear zone or lineament intersections where transtensional zones allowed and facilitated ascent iii emplacement was often by a process of localized in situ ballooning the existence of such lineaments in these orientations in the sw highlands may indicate that the structure of the lower crust can be regarded as a series of blocks bounded by intersecting ductile zones of high strain the establishment of such a pattern of structural interactions within the lower crust could provide a mechanistic framework within which the location of anatectic zones siting and ascent pathways and any subsequent emplacement phenomena can be explained in orogenic belts

quantification of magnetic coercivity components by the analysis of acquisition curves of isothermal remanent magnetisation abstract a new method of analysing isothermal remanent magnetisation irm acquisition curves based on cumulative log gaussian analysis robertson and france phys earth planet inter 82 1994 223 234 is proposed it is based on the curve fitting of the irm acquisition curve versus the logarithm of the applied field with i the acquisition curve on a linear scale ii the acquisition curve expressed as a gradient and iii the acquisition curve on a probability scale even when a sample is not saturated its magnetic properties can be defined although with less certainty the number of magnetic components required for an optimal fit to a measured irm acquisition curve is evaluated statistically the method discriminates on the basis of different mineral coercivity therefore additional rock magnetic tests are still required to separate minerals with similar coercivities

shape anisotropy versus magnetic interactions of magnetite grains experiments and application to ams in granitic rocks the magnetic fabric of ferromagnetic granitic rocks results from both the shape preferred orientation of individual magnetite grains and their distribution anisotropy through magnetic interactions between neighbouring grains measurement of the low field magnetic anisotropy of single multi domain magnetite grains shows a linear correlation between their magnetic anisotropy degree and their aspect ratio interactions between two elongated grains were studied experimentally using two types of grain arrangement an aligned configuration and a side by side configuration for a distance between the grain centers equal to approximately twice the average grain size the magnetic susceptibility and its anisotropy are enhanced in both configurations and the direction of kmax the easiest magnetization axis is stable in the aligned configuration whereas it rotates toward an orthogonal direction in the side by side configuration depending on the distribution of the interacting magnetite grains magnetic interactions may therefore either increase the whole rock anisotropy magnitude or reduce it as in the given example of the granitic rocks from madagascar

ascent of a granitoid diapir in a temperature varying medium a relationship for the ascent velocity of a granitoid diapir is derived and used in conjunction with a crustal heat flow model which incorporates a depth dependent temperature to predict emplacement histories ascent rate is strongly dependent on the width of a deformation layer of variable viscosity that is formed by the transfer of heat to the country rock and on the buoyancy force which propels the diapir through it ascent velocity is described by the expression u 2 gd3z 0r where is the density contrast between diapir and country rock g is gravitational acceleration d is the deformation zone width z is a parameter which describes the increase in viscosity across the zone 0 is the country rock viscosity at the contact and r is the diapir radius the width of the deformation zone as dictated by the temperature distribution and rheological function is the point at which the viscosity increases by a factor f from the contact value although ascent rates vary with choice of this parameter ascent distances are not strongly dependent on f results of simulations which incorporate a spectrum of input parameters reveal that ascent distance is strongly dependent on both the rheology and ambient temperature of the encompassing rock but only weakly dependent on the initial diapir temperature ascent velocity varies with the diapir size with larger bodies moving more slowly and ascending for longer periods relative to smaller plutons as a result of the proportionately larger amount of thermal energy available for ascent larger bodies will rise greater distances than smaller diapirs however the additional ascent appears nominal relative to the contrast in available energy modeling diapirs using a no slip boundary condition decreases ascent velocity by a factor of about 3 relative to results incorporating a stress free boundary condition the time scale of granitoid diapirism over crustal distances cannot be less than 104 years due to the rate limiting effect of thermal conduction above the body and not greater than 105 years reflecting solidification times of kilometer sized plutons a consequence of ascent by a deformation zone mechanism is the generation following emplacement of a mechanically weakened crust which extends from beneath the diapir to near the source perhaps explaining the relatively common occurrence of synmagmatic to postmagmatic mafic dikes within granites believed to be derived from interaction of basalt with the lower crust

the mechanism of flow and fabric development in mechanically anisotropic trachyte lava anisotropy of magnetic susceptibility ams and electron back scattered diffraction ebsd of magnetite and sanidine fabrics throughout an eroded trachyte lava dome in tertiary volcanic province of the nw czech republic revealed two fabric types the high degree of ams fabric is associated with sanidine textural domains similar to normal kink bands type i fabric and occupies the whole body except the sw margin folded fabric and low anisotropy of ams also in the sw margin reveals sanidine alignment domains resembling reverse kink bands type ii fabric the flow of trachyte lava occurred via simultaneous slip of sanidine crystals along their 010 planes and also by readjustment of the textural domain boundaries according to the fibre slip theory this microfabric study suggests that the type ii fabrics resulted from collapse of vertically anisotropic trachyte crystal mush above the feeding conduit type i fabric is interpreted to originate from type ii fabrics by further stretching of highly attenuated fold limbs asymmetric type i fabrics along margins of the dome are related to outflow of trachyte lava away from the conduit region due to divergent flow the trachyte fabric zonality is interpreted to reflect the process of successive emplacement of progressively rotated trachyte lava lobes within a lava dome that locally preserves the collapsed and folded vertical fabrics

deformation of incompletely crystallized magma systems granitic gneisses and their tectonic implications certain textures in two feldspar calc alkaline granitic gneisses have been identified as indicators of the presence of intercrystalline melt during deformation of crystal melt mushes fluid relocation or fracting is to be expected in an incompletely crystallized magmatic system as deviatoric stresses are applied to it relocation of late stage fluids capable of crystallizing k feldspar quartz microaplite and myrmekite to low pressure zones such as the pressure shadow region around earlier crystals occurs within some developing mylonitic gneiss fabrics and results in a distinctive assemblage of textures strain in these rocks is expressed by various brittle and ductile features and by fluid relocation textures the petrogenesis of these particular gneisses is therefore both magmatic and metamorphic contrasting with gneiss forming processes that had no participating magmatic component migmatitic complexes evolving by partial anatexis of non magmatic rocks in a tectonically active environment are not

the anisotropy of magnetic susceptibility in biotite muscovite and chlorite single crystals the anisotropy of magnetic susceptibility ams of single crystals of biotite muscovite and chlorite has been measured in order to provide accurate values of the magnetic anisotropy properties for these common rock forming minerals the low field ams and the high field paramagnetic susceptibility are defined for the high field values it is necessary to combine the paramagnetic deviatoric tensor obtained from the high field torque magnetometer with the paramagnetic bulk susceptibility measured from magnetization curves of the crystals this leads to the full paramagnetic susceptibility ellipsoid due to the anisotropic distribution of iron cations in the silicate lattice the ellipsoid of paramagnetic susceptibility which was obtained for the three phyllosilicates is highly oblate in shape and the minimum susceptibility direction is subparallel to the crystallographic c axes the anisotropy of the susceptibility within the basal plane of the biotite has been evaluated and found to be isotropic within the accuracy of the instrumental measurements the degree of anisotropy of biotite and chlorite is compatible with previously reported values while for muscovite is smaller than previously published values the shape of the chlorite ams ellipsoid for all the samples is near perfect oblate in contrast with a wide distribution of oblate and prolate values reported in earlier studies reliable values are important for deriving models of the magnetic anisotropy where it reflects mineral fabrics and deformation of rocks d 2003 elsevier science b v all rights reserved

time resolved construction of a bimodal laccolith torres del paine patagonia abstract granitic and mafic magma pulses were sequentially accreted in the spectacularly exposed shallow crustal torres del paine laccolith in southern patagonia this 12 5 ma pluton forms a composite intrusion with a subvertical feeding system in the west and a laccolith in the east a key unknown in the formation of sill complexes is how individual magma pulses are assembled over time and the geometry and localization of their feeding system high resolution zircon ca id tims u pb dating shows that the laccolith grew first by under accretion of granitic sills over 90 30 ka linked to a sheet like feeding system followed by underplating of mafic sills after 20 ka of quiescence in the mafic sills complex individual sills were injected by over accretion during 41 11 ka our data show that successive granitic and mafic magmas emplacement generated a volume of 88 km3 in 162 11 ka

tectonic history of the illinois basin the illinois basin began as a failed rift that developed during breakup of a supercontinent approximately 550 ma a rift basin in the southernmost part of the present illinois basin subsided rapidly and filled with about 3 000 m of probable early and middle cambrian sediments by the late cambrian the rift bounding faults became inactive and a broad relatively slowly subsiding embayment extending well beyond the rift and open to the iapetus ocean persisted through most of the paleozoic era widespread deformation swept through the proto illinois basin beginning in the latest mississippian continuing to the end of the paleozoic era uplift of basement fault blocks resulted in the formation of many major folds and faults the timing of deformation and location of these structures in the forelands of the ouachita and alleghanian orogenic belts suggest that much of the deformation resulted from continental collision between north america and gondwana the associated compressional stress reactivated the ancient rift bounding faults upthrusting the northern edge of a crustal block approximately 1 000 m within the rift concurrently dikes radiometrically dated as early permian sills and explosion breccias formed in or adjacent to the reactivated rift subsequent extensional stress probably associated with breakup of pangea causedmore the crustal block within the rift to sink back to near its original position high angle northeast to east west trending normal faults with as much as 1 000 m of displacement formed in the southern part of the basin these faults displace some of the northwest trending early permian dikes structural closure of the southern end of the illinois basin was caused by uplift of the pascola arch sometime between the late pennsylvanian and late cretaceous less

multiple magmatic fabrics in the sazava pluton bohemian massif czech republic a result of superposition of wrench dominated regional transpression on final emplacement abstract the sazava pluton 354 ma of the central bohemian plutonic complex was emplaced syntectonically into the upper crustal neo proterozoic and lower paleozoic host rock along the se margin of the tepla barrandian zone bohemian massif czech republic the host rock is characterized by transpressional fabric dominated by steep se nw dipping foliations and subhorizontal ne sw stretching lineations associated with flattening to a plane strain ellipsoid the strain intensity degree of oblateness and temperature conditions of deformation increase in the host rock towards the pluton margin in the pluton quartz microfabric indicates progressive cooling of the syntectonically emplaced magma the ams method revealed multiple magmatic fabrics and lateral variations in the shapes of the ams ellipsoid and the magnetic fabric intensity in the pluton the central part of the pluton yields prolate shapes of the ams ellipsoid and a low degree of anisotropy with preserved steep magnetic lineations whereas along the pluton margins oblate ams ellipsoids are associated with a high degree of anisotropy we interpret the multiple fabrics and the partially decoupled fabric pattern between the host rock and the pluton as being a result of superposition of regional tectonic strain during highly oblique transpression on emplacement related intrusive strain where outer solidified and more rigid edges of the pluton enabled preservation of older steep fabrics in its interior

some remarks on fabric overprints and constrictional ams fabrics in igneous rocks during the ascent emplacement and post emplacement deformation of igneous rocks two or more phases of deformation that overprint each other are often depicted these overprints when magnetic minerals are present are recorded in magnetic fabric in this contribution overprints are studied by means of numerical modeling following several basic scenarios common to igneous rocks biotite and amphibole that occur often together in igneous rocks are considered as carriers of the anisotropy of magnetic susceptibility modeling shows that 1 a constrictional fabric with a low degree of anisotropy as commonly recorded in magmatic rocks may result from a deformation overprint and not necessarily from an extensional transtensional regime and 2 that the constrictional ams fabrics originates from orthogonal superimposition of a deformation event on an ams fabric inherited from earlier magma emplacement history therefore the interpretation of a constrictional fabric must be performed with caution numerical modeling may provide a suitable help in strengthening the interpretation of real magnetic fabric data

anisotropy of magnetic susceptibility in alkali feldspar and plagioclase feldspars are the most abundant rock forming minerals in the earth s crust but their magnetic properties have not been rigorously studied this work focuses on the intrinsic magnetic anisotropy of 31 feldspar samples with various chemical compositions because feldspar is often twinned or shows exsolution textures measurements were performed on twinned and exsolved samples as well as single crystals the anisotropy is controlled by the diamagnetic susceptibility and displays a consistent orientation of principal susceptibility axes the most negative or minimum susceptibility is parallel to 010 and the maximum least negative is close to the crystallographic 001 axis however the magnetic anisotropy is weak when compared to other rock forming minerals 1 53 10 9 m3 kg 1 at maximum therefore lower abundance minerals such as augite hornblende or biotite often dominate the bulk paramagnetic anisotropy of a rock ferromagnetic anisotropy is not significant in most samples in the few samples that do show ferromagnetic anisotropy the principal susceptibility directions of the ferromagnetic subfabric do not display a systematic orientation with respect to the feldspar lattice these results suggest that palaeointensity estimates of the geomagnetic field made on single crystals of feldspar will not be affected by a systematic orientation of the ferromagnetic inclusions within the feldspar lattice

interpreting magmatic fabric patterns in plutons abstract most plutons have widespread magmatic fabrics the interpretation of which remains controversial we propose a method to constrain likely causes of fabric patterns the application of which indicates the following 1 preserved fabric patterns often form after chamber construction and only rarely provide information about ascent or emplacement 2 fabrics are poor recorders of total strain and are easily reset preserving only the last increment of strain during crystallization 3 in magmatic systems mechanically decoupled from host rocks patterns may result from strain during internally driven flow filter pressing or porous flow in relatively static chambers or by final increments of strain during emplacement 4 with greater emplacement depths fabric patterns increasingly reflect strain caused by regional deformation and 5 given that magmatic fabrics are easily reset and reflect only the last increment of strain of comparatively weak materials they may provide a relatively direct record of paleostress in orogenic belts

emplacement and fabric forming conditions of the alous en tides granite eastern border of the tin seririne tin mersoi basin algeria magnetic and visible fabrics analysis abstract the alous en tides pluton intruded within one of the most important late panafrican n s shear zones the 7 30 shear zone in the southern hoggar shield a magnetic fabric study points out strong preferred orientations of the magnetite grains the orientation is coherent in the whole massif however it cannot be correlated with any of the visible structures in the field or in thin section strongly oriented magnetites are thus disseminated within all the rock the main rock forming minerals in this pluton were not preferably oriented during their crystallization showing that magma was emplaced without strongly oriented stresses magnetite orientations on the contrary reflect a strong stress field strike slip movements along the 7 30 shear zone probably generated local relative distension allowing pluton emplacement during the last magmatic phase they put the intrusion under the regional compressional stress field causing orientation of the magnetite the magnetic fabric then reveals the regional ene wsw stress field during late panafrican times in part of the pluton which was later affected by very intense solid state deformation during dextral movement the magnetic fabric remains mainly in connection with this initial magnetite fabric

k o ocr relationships in soil the relationships between k o and ocr are investigated for primary loading unloading reloading conditions the study reviews laboratory data from over 170 different soils and presents an approach common to clays silts and sands simple empirical methods for predicting k o for normally consolidated and overconsolidated soils are evaluated the validity of the methods is supported by statistical analyses on the basis of the findings only the effective stress friction angle o and prior stress history ocr and ocrmax are needed to predict approximate values of k o

a comparison of different magnetic methods for determining the relative grain size of magnetite in natural materials some results from lake sediments abstract a new rapid method for identifying relative grain size variations in magnetic involves the parameter anhysteretic susceptibility arm i e specific arm obtained in a 1 oe steady field which is particularly sensitive to the single domain sd and small pseudo single domain psd grains of the finer magnetite fraction a second parameter low field susceptibility is relatively more sensitive to the coarser magnetite fraction larger psd and smaller multidomain md grains we can then obtain a measure of the ratio of coarse to fine grain magnetite for large numbers of samples by plotting arversus a simple idealized model based on sized magnetite samples is proposed to explain the use of the armversus plot for detecting relative grain size changes in the magnetic content of natural materials the sediments of three lakes that contain magnetite or a similar magnetic carrier and have a wide range of values of arm and are used to test the model the model is used to interpret the magnetic variations observed and the interpretations are supported by high field hysteresis measurements of the same sediments the combination of the high field hysteresis method of day et al 1 and the arm vs method is a powerful technique allowing the rapid identification of both the relative grain size and domain state for large numbers of samples containing magnetite the armvs method should be used as an intial means of identifying distinct groups of samples the high field hysteresis method should then be applied to a few representative samples from each group to confirm the initial interpretation

experimental deformation of synthetic magnetite bearing calcite sandstones effects on remanence bulk magnetic properties and magnetic anisotropy we have quantified effects of experimental deformation on the magnetic properties of a set of synthetic calcite sandstone samples containing magnetite the deformation was carried out in a microcomputer controlled apparatus that adjusted the applied differential stress as needed to maintain a constant strain rate of 10 5 s 1 most samples were deformed under dry conditions but a few were deformed with a pore fluid present the samples deformed under dry conditions required substantially higher differential stresses macroscopically ductile shortening strains of up to 25 produced the following irreversible changes in magnetic properties 1 increased bulk coercivity remanence coercivity and mean anhysteretic remanence susceptibility 2 decreased mean low field susceptibility 3 decreases in the component of remanence parallel to shortening 4 smaller decreases for most samples in the component normal to shortening resulting in a net rotation of the remanence away from the shortening axis 5 larger decreases in the normal component in a few samples resulting in a net rotation of the remanence towards the shortening axis 6 increased magnetic anisotropy and 7 increased deformation of initial magnetic ellipsoids a comparison of data for samples deformed under dry and wet conditions higher and lower differential stresses respectively indicates that remanence reorientation and susceptibility anisotropy are controlled primarily by bulk strain i e rotation and displacement of particles whereas coercivity and anhysteretic anisotropy are controlled dominantly by microstrain or intragranular stress

shear criteria in granite and migmatite deformed in the magmatic and solid states microstructural criteria for the determination of the sense of shear in rocks homogeneously deformed in the partially melted state are similar to those which apply to solid state deformation sense of shear determination is either direct deduced from the sense of rotation of markers or indirect involving the obliquity between the shear and foliation planes or between the successive foliations imprinted at different stages of progressive deformation this study is a by product of the detailed structural and microstructural investigation of a high grade metamorphic rock pile variscan vosges massif france which underwent subhorizontal shearing during partial melting and further solidification depending on the rock chemistry on the position in the pile and the relative timing of progressive deformation layered migmatites and homogeneous granites were variously deformed in the partially melted and solid states the sense of shear obtained from these rock types using the criteria presented here consistently gives a top to sw direction

rapakivi texture an indication of the crystallization of hydrosilicates ii rapakivi granites have puzzled all who have seriously studied them typical rapakivi texture is a mixture of variously mantled non mantled or partly mantled concentrically zoned plastically distorted fragmented reaggregated large and small ovoids commonly they are potash feldspar often mantled by and having a variable content of plagioclase some display remarkable sphericity in form composition zoning sequence and crystallization pattern each ovoid reflects an individual development up to five concentric internal plagioclase rims have been observed and some ovoids may be isolated in autoliths and wall rocks anomalies and contradictions arise from any assumption of genesis from a cooling melt the recorded objective data imply that the magma from which rapakivi textures develop had similar diffusive and rheological properties to those of a partly dewatered macromolecular paste or a mixture of gelatinous hydrosilicates as indicated by deep oil wells this system is found at somewhat elevated temperatures at considerable depths within accumulated sediments in addition to the very specific diffusive and rheological properties of such partly dewatered sediments the system has as its major components normal solvated macromolecules of mixed clays silica gels and hydrous ferromagnesian minerals which are characterised by distinctive particle sizes and geometric shapes platelets spheres and rods respectively thixotropic liquefaction and intrusion of such concentrated gelatinous magma or sediment paste introduces relative movement between the component macromolecules whereby they can reduce surface energy by interaction to assume a close packed condition and aggregate during laminar flow into macro accretions comprised essentially of their respective particle shapes syneresis of these precursor accretions desorbs ions including the small montmorillonite particles behaving as a colloidal electrolyte these diffuse from the illitic cores to form a montmorillonite rich rim which it is suggested crystallizes together with the illitic cores to form mantled or polymantled feldspar ovoids crystallization of the rapakivi massif is associated with strong temperature rise stemming from exothermic crystallization of the close packed metastable colloids this follows the development of the characteristic texture the rounded and rimmed precursor accretions are formed during earlier lower temperature episodes of thixotropic liquefaction which are isothermal the fluidity is an earlier event there is high temperature dependent on the rate of water loss but no molten stage forty six typical features of rapakivi texture are described and illustrated each of which is directly attributable to specific interactions in an alternately dynamic and static colloidal system individual correlation between each observed distinctive feature of the rapakivi texture and the well documented physico chemical process is complete for sediment derived granites therefore the rapakivi texture can confidently be assumed to be an indication of the crystallization of their sedimentary hydrosilicate precursors

rheology of crystal bearing silicate melts an experimental study at high viscosities the viscosity of partially crystallized mg3al2si3o12 melts has been measured under uniaxial compression in the interval 1010 1013 poise as a function of the volume fraction of crystals these inclusions are well rounded spherulites of aluminous enstatite having the same composition as the melt and whose growth rate is negligible at the temperature of the measurements the viscosity increases by less than 1 order of magnitude for crystal fractions of 40 vol and remains newtonian up to the maximum stress exerted namely 1 kbar the einstein roscoe equation 0 1 m n provides very good fits to the measurements only if either the m or n parameter is allowed to depend on temperature for modeling of magmatic processes however the widely recommended constant values m 0 6 and n 2 5 should be adequate the rheology changes abruptly when the clustered spherulites begin to oppose shear deformation at a crystal fraction of about 40 vol the viscosity becomes non newtonian with yield strengths of a few tens of bars at temperatures at which the viscosity of the melt is higher than 1010 poise as long as the crystal fraction remains lower than 70 vol the deformation proceeds in an irregular manner with a nonuniform distribution of crystals and melt the deformation becomes again regular at low stresses with lower melt fractions but samples undergo extensive fracturation along the direction of uniaxial stress similar rheology changes have been observed during the isothermal crystallization of li2si2o5 melts which produces small ellipsoidal inclusions these results suggest that the influence of solid suspensions on the rheology of magmas is primarily determined by the crystal fraction even though additional measurements would be useful to determine the possible influence of other factors such as the size distribution or the shape of the inclusions

flow direction and groundmass shear zones in dykes shimane peninsula japan the groundmass of andesitic dykes at sezaki southwest japan has trachytic texture and contains microscopic shear zones the shear zones comprise a conjugate pair formed by flattening of the solidifying dyke rock probably caused by the magma pressure of the still molten part of the dyke this pressure shortened the solidifying rock perpendicular to the dyke margins and caused it to extrude parallel to the magma flow direction the groundmass shears indicate that locally the magma flowed 60 upward in the dykes it is concluded that while groundmass shears are a useful indicator of flow direction in dykes phenocryst alignment in dykes is strongly influenced by magma pressure flattening and thus may be a poor indicator of flow direction

melt segregation structures in granitic plutons when melt fraction increases beyond a critical value migmatites behave as magmas conversely when melt fraction decreases crystallizing magmas form solid framework mushes and behave as solids the richness in preserved mesoscopic melt segregation structures in migmatites is not matched by melt segregation structures in granitic bodies this paper identifies melt segregation structures in granites and compares them to structures in migmatites the rarity of segregation structures in granites is a consequence of the solid framework mush allowing for cryptic melt extraction from its pores the relatively short duration of solidification of the mush and the fragile nature of the solid framework identifying segregation features in granitoids at outcrop scale provides the basis for understanding the physical processes that lead to chemical and mineralogical differentiation in granitic magmas

emplacement and fabric forming conditions of plutons from structural and magnetic fabric analysis a case study of the plana pluton central bulgaria abstract the relationship between intensity parameters such as the corrected anisotropy degree p and mean susceptibility km for plutons with similar magnetic mineralogy yields a criterion to determine the origin of their magnetic fabric for a same mineralogy the higher the p values for the same mean susceptibility km irrespective of its absolute value the higher tectonic effect was possible using this criterion comparison of the magnetic fabric of the upper cretaceous mid to shallow crustal level plana pluton with that of other small upper cretaceous plutonic bodies in sredna gora zone central and southeast bulgaria highlights the structural evolution of the plana pluton the central part of plana pluton and its southwest west and east margins have preserved their emplacement fabric along its northern contact the pluton is affected by the last movements within the okol shear zone where high temperature s l mylonites developed the fabric of the pluton at its southeastern border was disturbed during the intrusion of the neighboring gutsal pluton the similarity in the orientation of magmatic and magnetic structures preserved in the central and southern parts of the plana pluton and the transition from magmatic to high temperature superimposed foliations and lineations at its north contact point to a composite superimposed shear induced and emplacement related magmatic magnetic fabric nearly vertical orientation of magnetic and magmatic foliations and lineations from the undeformed parts of the pluton shows a process of vertical magma rising and emplacement the sub vertical high temperature solid state mylonitic foliation and dip parallel stretching lineation in the pluton along its northern contact reveals the transpression nature of the deformation in the vicinity of okol shear zone with a strong pure shear component the smooth transition between the deformed and undeformed parts of plana pluton reveals the syn kinematic character of the emplacement

intrusion of lamprophyre dyke and related deformation effects in the host rock salt a case study from the loule diapir portugal abstract a rock salt lamprophyre dyke contact zone sub vertical ne sw strike was investigated for its petrographic mechanic and physical properties by means of anisotropy of magnetic susceptibility ams and rock magnetic properties coupled with quantitative microstructural analysis and thermal mathematical modelling the quantitative microstructural analysis of halite texture and solid inclusions revealed good spatial correlation with ams and halite fabrics the fabrics of both lamprophyre and rock salt record the magmatic intrusion plastic flow and regional deformation characterized by a nw se trending steep foliation ams and microstructural analysis revealed two deformation fabrics in the rock salt 1 the deformation fabrics in rock salt on the nw side of the dyke are associated with high temperature and high fluid activity attributed to the dyke emplacement 2 on the opposite side of the dyke the emplacement related fabric is reworked by localized tectonic deformation the paleomagnetic results suggest significant rotation of the whole dyke probably during the diapir ascent and or the regional tertiary to quaternary deformation

diapiric ascent of magmas through power law crust and mantle there has never been a convincing explanation of the way in which diapirs of molten granite can effectively rise through mantle and crust we argue here that this is mainly because the country rocks have previously been assumed to be newtonian and we show that granitoid diapirs rising through thermally graded power law crust may indeed rise to shallow crustal levels while still molten the ascent velocity of diapirs is calculated through an equation with the form of the hadamard rybczynski equation for the rise of spheres through newtonian ambient fluids this well known equation is corrected by factors dependent on the power law exponent n of the ambient fluid and the viscosity contrast between the drop and the ambient fluid these correction factors were derived from results reported in the fluid mechanical and chemical engineering literature for the ascent of newtonian drops through power law fluids the equation allows calculation of the ascent rates of diapirs by direct application of rheological parameters of rocks the velocity equation is numerically integrated for the ascent of diapirs through a lithosphere in which the temperature increases with depth the depth of solidification of the diapir is systematically studied as a function of the geothermal gradient buoyancy of the body solidus temperature of the magma and rheological parameters of the wall rock the results show that when the wall rock behaves as a power law fluid the diapir s ascent rate increases without a similar increase in the rate of heat loss in this way diapirs rising at 10 to 102 m yr can ascend into the middle or upper crust before solidification strain rate softening rather than thermal softening is the mechanism that allows diapirism to occur at such rates the thermal energy of the diapir is used to soften the country rock only at late stages of ascent the transport of magmas through the lower crust and mantle as diapirs is shown to be as effective as magmatic ascent through fractures

direct observation of deformation processes in crystal mushes isothermal microstructural development in deforming melt bearing crystal mushes is studied using synkinematic microscopy and a polyphase thiocyanate system the aim of the work is to contribute to the basis for understanding the origin of microstructures in rocks which have undergone melt present deformation during high strain rate pure shearing experiments microstructures indicating crystal plasticity and dynamic recrystallization are observed during low strain rate pure shearing experiments a pressure solution like process called contact melting is active resulting in optically strain free crystals crystal boundary sliding is active in both regimes framework scale processes such as filter pressing grain flow and development of a micro shear zone are illustrated some of these processes are cryptic microstructurally and may be difficult or impossible to recognize in rocks the validity of the experimental system as an analog for magmatic systems is discussed we conclude that the experiments can serve as a source of ideas to test against the evidence from rocks but that no direct analogy to the behavior of natural crystal mushes has been or will readily be established

the effect of dynamic loading on lateral stress in sand this paper presents the results of a laboratory study on the lateral stress in a vibrated sand no 3 ottawa sand was tested on a snaking table providing vertical vibration and at rest lateral stress was measured using a modified oedometer ring the test results show that the lateral stress in normally consolidated sand increases with vibration time the magnitude of the increase in lateral stress is related to the density of sand and the intensity of vibration for overconsolidated sand with a high coefficient of earth pressure at rest the lateral stress decreases with vibration time stress paths of a tested specimen are also presented in this paper key words sand coefficient of earth pressure at rest lateral stress vibration overconsolidation ratio stress path

rapid remobilization of magmatic crystals kept in cold storage we lack thermal histories for magma reservoirs but here the magma under mount hood oregon usa is shown to have been too cold to mobilize for most of the time it has been stored which implies that magma mobilizes at which point it can be imaged geophysically very quickly prior to eruption this paper presents a novel approach to constraining the thermal history of the subsurface magma bodies that feed eruptions by combining temporal information from a variety of sources kari cooper and adam kent combine timescales derived from uranium series disequilibria textural information and trace element zoning in crystals they show that at mount hood oregon only a small fraction of the total storage duration has been spent at temperatures above the critical crystallinity the point at which magma is easily mobilized they conclude that largely liquid bodies that could be imaged geophysically will be ephemeral features and therefore their detection could indicate imminent eruption the processes involved in the formation and storage of magma within the earth s upper crust are of fundamental importance to volcanology many volcanic eruptions including some of the largest result from the eruption of components stored for tens to hundreds of thousands of years before eruption1 2 3 although the physical conditions of magma storage and remobilization are of paramount importance for understanding volcanic processes they remain relatively poorly known4 5 eruptions of crystal rich magma are often suggested to require the mobilization of magma stored at near solidus conditions6 7 8 however accumulation of significant eruptible magma volumes has also been argued to require extended storage of magma at higher temperatures7 8 9 what has been lacking in this debate is clear observational evidence linking the thermal and therefore physical conditions within a magma reservoir to timescales of storage that is thermal histories here we present a method of constraining such thermal histories by combining timescales derived from uranium series disequilibria crystal sizes and trace element zoning in crystals at mount hood oregon usa only a small fraction of the total magma storage duration at most 12 per cent and probably much less than 1 per cent has been spent at temperatures above the critical crystallinity 40 50 per cent at which magma is easily mobilized partial data sets for other volcanoes also suggest that similar conditions of magma storage are widespread and therefore that rapid mobilization of magmas stored at near solidus temperatures is common magma storage at low temperatures indicates that although thermobarometry calculations based on mineral compositions may record the conditions of crystallization they are unlikely to reflect the conditions of most of the time that the magma is stored our results also suggest that largely liquid magma bodies that can be imaged geophysically will be ephemeral features and therefore their detection could indicate imminent eruption

timing of incremental pluton construction and magmatic activity in a back arc setting revealed by id tims u pb and hf isotopes on complex zircon grains abstract the lifetimes and thermal histories of upper crustal plutons are increasingly determined using geochronology but complex growth of datable minerals in magmas impedes simple age interpretations careful field observation helps constrain zircon u pb dates in terms of timing of magma injection for example because relative ages of successive magma pulses must be honored we use id tims u pb zircon geochronology and field geology to construct timescales of incremental pluton assembly in the st jean du doigt sjdd bimodal layered intrusion brittany france field evidence suggests that early pulses were injected into a cold environment with little supersolidus interaction among successive magma pulses later injections occurred in a progressively hotter environment with protracted mafic and felsic magma interaction zircon dates show that early activity ca 347 ma predates the thermally mature episode by about 1 ma which terminated at ca 345 ma dates from samples displaying core rim zircon overgrowths span about 5 ma 351 346 ma which we interpret to represent two distinct crystallization events hf isotopic data from cores and rims are homogeneous precluding zircon inheritance from basement rocks these textures and dates could instead reflect zircon saturation fluctuations at the emplacement depth or antecrystic zircon grains recording pre emplacement magmatic growth

four magmatic fabrics in the tuolumne batholith central sierra nevada california usa implications for interpreting fabric patterns in plutons and evolution of magma chambers in the upper crust for the first time four distinct magmatic fabrics are documented in a composite plutonic body the tuolumne batholith central sierra nevada california usa one type of fabric was formed by strain caused by highly localized magma flow type 1 whereas the other three chamber wide fabrics recorded strain increments during boundary processes along batholith margins type 2 superimposed by increments of heterogeneous regional tectonic strain types 3 and 4 our present work indicates that in contrast to studies that consider magmatic fabrics to be simple structures formed by a single process magmatic lineations and foliations in plutons may reflect accumulated finite strain and form as composite structures recording multiple strain increments in relatively static actively deforming and rheologically complex crystal mushes at lower melt percentages we demonstrate that multiple magmatic fabrics in a single batholith may record remarkably different processes and thus preserve a temporal record of strain in the batholith from strain during internal chamber processes to postem placement regional tectonic strain however it may be commonly very problematic to infer the exact nature of flow or even fabric forming process from the preserved rock record our study also exemplifies how examination of magmatic fabric patterns in plutons complemented with geochronology may provide crucial constraints on the interplay among successive magma emplacement fabric preservation temporal evolution of strain fields in a crystallizing magma chamber and the development of crystal mush zones

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

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

magnetic fabric in the biella and traversella stocks periadriatic line implications for the mode of emplacement abstract the biella and traversella stocks forming part of the intrusions along the periadriatic line intruded into the sesia lanzo zone italian western alps 30 ma ago samples were collected from 12 localities in the traversella massif diorites and 22 in the biella massif granites syenites monzonites in most localities the fabric is primarily planar with a distinct foliation of intermediate to subvertical dip the magnetic lineation is less developed its plunge is very variable marking a girdle pattern the mean foliations and lineations per locality are scattered this is probably due to the fact that the outcropping parts of the two stocks are summital i e nearer the roof and hence the magma movements may have been less regular in the structurally deepest part of the biella massif the magnetic foliation dips regularly to the northwest its direction could reflect the pattern of the deep fractures along which the magma rose the classic models of owens to describe the process of magnetic mineral orientation do not apply to the features of these two stocks a new model has been constructed to take account of the differences in viscosity contrast between the magnetic mineral crystals and the matrix referred to as the ductile model it offers a suitable representation of the typical situation of crystal mushes and is the most appropriate for the biella and traversella stocks

bursting the bubble of ballooning plutons a return to nested diapirs emplaced by multiple processes a popular model for the emplacement of roughly spherical plutons is that of ballooning or in situ inflation of a magma chamber in a common version of this model magma ascends until loss of heat or buoyancy causes the outermost magma to crystallize and cease ascent while the hotter tail of magma continues to rise and expand the already crystallized outer margin this expansion forms a concentric gneissic to mylonitic foliation and flattening type strain in the outer margin of the pluton by means of subsolidus deformation and pushes aside the surrounding country rock to form a dynamothermal aureole that postdates regional structures our reexamination of three supposedly ballooned plutons ardara ireland cannibal creek australia papoose flat california and evaluation of published descriptions of many others indicate that this model is largely incorrect deflections of country rock structures strains and porphyroblast matrix relationships indicate that only minor to moderate expansion usually 30 or less occurred during emplacement that other emplacement mechanisms must have occurred and that regional deformation continued during and after emplacement internal structures indicate that when magma chamber expansion did occur it did so by flow of magma that magmatic foliations and lineations formed late in the magma chamber evolution that enclave shapes are neither good strain markers nor indicators of the magnitude of expansion and that only minor internal subsolidus deformation results from emplacement this study indicates that many plutons previously interpreted as post tectonic ballooning plutons are better viewed as syntectonic nested diapirs emplaced by a variety of country rock material transfer processes this nested diapir model implies that magma ascent may occur by rise of large magma batches instead of transport in dikes followed by ballooning that magma chamber dynamics differ from that in the ballooning model and that normally zoned plutons may form by intrusion of several pulses of magma rather than by in situ crystal fractionation from a single parent melt

noncoaxial k feldspar and ams subfabrics in the land s end granite cornwall evidence of magmatic fabric decoupling during late deformation and matrix crystallization 1 a comparative study of the anisotropy of magnetic susceptibility ams and k feldspar phenocryst fabrics in the land s end granite demonstrates that the ams fabric predominantly reflects late magmatic deformation tensor analysis of the k feldspar fabric shows a complex pattern characterized by meter scale variations in orientation symmetry and intensity mainly related to heterogeneous flow of the phenocryst rich magma during emplacement in contrast the ams fabric is predominantly homogenous subhorizontal and oblate and is stable at the pluton scale quantitative microstructural analysis suggests that the ams fabric is controlled by deformation of the partially crystallized matrix resulting from the combined effects of late internal adjustment within the pluton and regional deformation a general model of fabric development associated with a vertical pure shear overprint on a variable vertical fabric is evaluated by numerical modeling the study demonstrates how the memory of different fabric elements may be dependent upon their grain size crystallization sequence and recorded previous strain

effects of magnetic interactions in anisotropy of magnetic susceptibility models experiments and implications for igneous rock fabrics quantification besides granites of the ilmenite series in which the anisotropy of magnetic susceptibility ams is mainly controlled by paramagnetic minerals the ams of igneous rocks is commonly interpreted as the result of the shape preferred orientation of unequant ferromagnetic grains in a few instances the anisotropy due to the distribution of ferromagnetic grains irrespective of their shape has also been proposed as an important ams source former analytical models that consider infinite geometry of identical and uniformly magnetized and coaxial particles confirm that shape fabric may be overcome by dipolar contributions if neighboring grains are close enough to each other to magnetically interact on these bases we present and experimentally validate a two grain macroscopic numerical model in which each grain carries its own magnetic anisotropy volume orientation and location in space compared with analytical predictions and available experiments our results allow to list and quantify the factors that affect the effects of magnetic interactions in particular we discuss the effects of i the infinite geometry used in the analytical models ii the intrinsic shape anisotropy of the grains iii the relative orientation in space of the grains and iv the spatial distribution of grains with a particular focus on the inter grain distance distribution using documented case studies these findings are summarized and discussed in the framework of the generalized total ams tensor recently introduced by canon tapia canon tapia e 2001 factors affecting the relative importance of shape and distribution anisotropy in rocks theory and experiments tectonophysics 340 117 131 the most important result of our work is that analytical models far overestimate the role of magnetic interaction in rock fabric quantification considering natural rocks as an assemblage of interacting and non interacting grains and that the effects of interaction are reduced by i the finite geometry of the interacting clusters ii the relative orientation between interacting grains iii their heterogeneity in orientation shape and bulk susceptibility and iv their inter distance distribution we reconcile analytical models and experiments with real case studies that minimize the role of magnetic interaction onto the measured ams limitations of our results are discussed and guidelines are provided for the use of ams in geological interpretation of igneous rock fabrics where magnetic interactions are likely to occur

textural evidence for dilatant shear thickening rheology of magma at high crystal concentrations investigation of the rheology of magmas at high crystal concentrations by experimental means has proved problematic an alternative approach is to study textures of igneous rocks that not only preserve evidence of the kinematics of magma flow such as flow direction but can also preserve evidence of rheology flow textures in multiply intruded trachyte dykes on fraser island eastern australia record evidence of dilatant flow during solidification this conclusion is reached by interpretation of microscopic ductile shear zones that disrupt the groundmass of aligned feldspar laths detailed three dimensional investigation demonstrates that the dihedral angle between conjugate micro shear zones is approximately 65 this conjugate angle is equivalent to that observed in dilatant granular materials such as sand dilatant behaviour is synonymous with shear thickening rheology indicating that the magma flow is time dependent and resists high flow rates some of the dykes contain autobrecciation fragments that may represent localities where the ductile flow rate threshold was exceeded newtonian or pseudoplastic shear thinning rheology of crystal poor magmas must progressively give way to shear thickening rheology during cooling and increasing crystal concentration

structure emplacement and lateral expansion of the san jose tonalite pluton peninsular ranges batholith baja california mexico abstract the 108 km2 san jose pluton forms part of the jurassic to cretaceous peninsular ranges batholith of northern baja california mexico the pluton was formed by three nested southward migrating intrusive pulses and the internal contacts between them indicate juxtaposition while the adjoining pulses were magmas shrimp u pb zircon data indicate that the entire pluton was emplaced in less than 4 4 m y ages of the individual pulses cannot be separated at the 95 confidence interval owing primarily to low uranium content of zircon detailed structural data and geologic mapping are consistent with a component of asymmetrical lateral expansion at the site of emplacement the direction of maximum lateral expansion may have been controlled by thermal compositional and resulting rheological gradients in the surrounding wall rocks a carapace of predominantly solid state deformation marks the northern two thirds of the pluton and the early stages of this fabric may have formed in the presence of a small amount of melt lack of evidence for syn to post emplacement regional ductile deformation around the pluton suggests that this carapace was deformed during the lateral expansion of the pluton

mineral magnetic properties of artificial samples systematically mixed from haematite and magnetite summary detailed rock magnetic investigations were carried out on a set of samples with defined ratios of haematite and magnetite the measured parameters provide a reference for interpreting common rock magnetic parameters in investigations of sediments the contribution of haematite to the magnetic fraction must exceed 95 wt of the magnetic fraction when mixed with magnetite in order to visibly influence grain size and coercitivity indicative magnetic parameters coercivity of remanence bcr and coercive force bc do not change in the same way with increasing haematite content which results in a peak bcr bc value at around 99 5 wt haematite variations in haematite content can be ignored when interpreting most rock magnetic parameters especially grain size indicative parameters for samples where haematite contents range from 0 to 98 wt the s ratio is still the most sensitive parameter for estimating the relative amount of haematite in magnetite haematite mixtures a combination of s ratio the saturation isothermal remanent magnetization divided by the low field magnetic susceptibility sirm lf and bcr is the most effective way to identify haematite in natural samples our results agree with literature data and fill the gap between results obtained either from pure magnetite or haematite with comparable grain sizes

theory and application of the day plot mrs ms versus hcr hc 2 application to data for rocks sediments and soils 1 new theoretical curves relating the hysteresis parameters mrs ms and hcr hc for single domain sd superparamagnetic sp pseudo single domain psd and multidomain md grains and their mixtures are applied to published data for natural materials the day plot of mrs ms versus hcr hc has been used to crudely classify samples into box like sd psd and md or sometimes incorrectly md sp regions with arbitrary boundaries new type curves for md psd sd md and sd sp grains and mixtures permit more subtle and precise modeling the predicted md trend and its junction with the psd trend are observed in two data sets for magnetite spherules from carbonate rocks and for temperature varying hysteresis results spanning the verwey transition the latter data are the basis of a suggested new method for pinpointing the psd md threshold size selected data for pottery clays soils and paleosols generally follow sd md type curves and indicate intermediate size psd magnetite with narrow to broad size distributions a lake sediment section with known grain size progression tracks in the predicted sense along the sd md trend selected data for glaciomarine and pelagic sediments are also generally compatible with sd md trends examples of remagnetized carbonate rocks submarine basaltic glasses and glassy rims of pillow basalts all follow predicted sp sd or sp psd mixing curves with a large range in volume fraction of sp grains 0 75 but a narrow range of sp particle sizes 10 2 nm larger sp grains spanning the range to sd size 25 30 nm are absent for unknown reasons oceanic dolerites gabbros and serpentinized peridotites in some cases fall in a novel region of the day plot parallel to but below magnetite sd md mixing curves

partial melt topology in statically and dynamically recrystallized granite microstructures of the murray granite pluton central ontario canada show evidence of both static and dynamic crystallization subsequent to partial melting backscattered electron analyses reveal interstitial k feldspar and plagioclase at triple junctions of strain free isometric quartz grains the geometry of the quartz feldspar boundaries mimics the original topology of the quartz melt contacts during crystallization this conclusion is suggested by the occurrence of both rounded and planar faces of quartz grains and by low 27 dihedral angles of quartz quartz feldspar boundaries similar to dihedral angles in experimentally crystallized quartz quartz silicic melt systems in contrast feldspar seams in deformed granites have high axial ratios are usually elongated perpendicular to the foliation plane and are located preferentially along individual grain boundaries quartz grains are dynamically recrystallized and occasionally transected by feldspar seams indicating that fracturing occurred in the presence of melt during crystal plastic deformation of quartz the subparallel orientation in quartz grains of intragranular feldspar bearing fractures and interstitial feldspar seams suggests that these features originated as intragranular and intergranular fractures respectively partial melt topology was therefore controlled by intergranular and occasionally by intragranular fracturing

seismic reflection images of shallow faulting northernmost mississippi embayment north of the new madrid seismic zone high resolution seismic reflection surveys document tectonic faults that displace pleistocene and older strata just beyond the northeast termination of the new madrid seismic zone at the northernmost extent of the mississippi embayment these faults which are part of the fluorspar area fault complex in southeastern illinois are directly in line with the northeast trending seismic zone the reflection data were acquired using an elastic weight drop source recorded to 500 msec by a 48 geophone array 24 fold with a 10 ft 3 0 m station interval recognizable reflections were recorded to about 200 msec 100 150 m the effects of multiple reflections numerous diffractions low apparent velocity i e steeply dipping noise and the relatively low frequency content of the recorded signal provided challenges for data processing and interpreting subtle fault offsets data processing steps that were critical to the detection of faults included residual statics post stack migration deconvolution and noise reduction filtering seismic migration was crucial for detecting and mitigating complex fault related diffraction patterns which produced an apparent folding of reflectors on unmigrated sections detected individual offsets of shallow reflectors range from 5 to 10 m for the top of paleozoic bedrock and younger strata the migrated sections generally indicate vertical to steeply dipping normal and reverse faults which in places outline small horsts and or grabens tilting or folding of stratal reflectors associated with faulting is also locally observed at one site the observed faulting is superimposed over a prominent antiformal structure which may itself be a product of the quaternary deformation that produced the steep normal and reverse faults our results suggest that faulting of the paleozoic bedrock and younger sediments of the northern mississippi embayment is more pervasive and less localized than previously thought

slip system domains i plane strain kinematics of arrays of coherent bands with twinned fibre orientations abstract slip system in rocks often occupy domains each of uniform slip system orientation examples are conjugate faults shear zones folded bedding and crystal lattices domainal behaviour in plane strain is modelled as simple shearing along inextensible fibres an array of alternating band domains with coherent boundaries can undergo a uniform bulk strain with local perturbations in the domains if 1 domain boundaries are planes of mirror symmetry with respect to fibre attitude and 2 domains have alternating fractional widths a and 1 a motion in the models is shown to be a combination of three independent modes plus a bulk rigid motion during mode 1 motion domain boundaries stretch but do not migrate during mode 2 they do not stretch but migrate by lateral translation during mode 3 they migrate by translation and rotation orientation distribution functions odfs are defined by assigning frequencies a and 1 a to orientations and changes in are shown to be due to mode 1 alone changes in a to mode 2 alone mode 3 has no effect on an odf combinations of modes 1 2 and 3 can be used to accommodate an imposed bulk motion two examples are discussed a bulk simple shear and a rigid motion large amounts of simple shear are possible if fibres are on average parallel to the imposed shear direction if modes 1 and 2 are operative the resulting odf has a maximum peak close to the shear direction this may explain the asymmetry of preferred lattice orientations and the occurrence of unique fault sets in rocks that have undergone a progressive simple shear

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

in defense of magmatic diapirs abstract diapirism as a crustal magma ascent mechanism has been recently criticized we contend that this reflects an overly simplistic view that diapirs must resemble modeled hot stokes diapirs and the perception that magma ascent in dikes is a more problem free mechanism for the construction of plutons we describe four cordilleran plutons that have characteristics much more compatible with diapirs than dike fed chambers these plutons were emplaced at depths ranging from 10 to 30 km and record different parts of diapiric ascent paths most ascended during complex visco elastic flow of host rock during regional deformation have narrow structural aureoles indicating power law behavior of host rock and were constructed of multiple batches of magma attributes enabling them to ascend greater distances than single hot stokes diapirs some features of these plutons are not typically attributed to diapirs and thus we introduce the term visco elastic diapir for bodies consisting of one or more batches of magma rising together with length to width ratios

an example of neotectonism in a continental interior thebes gap midcontinent united states abstract some of the most intense neotectonic activity known in the continental interior of north america has been recently discovered on a fault zone in the thebes gap area missouri and illinois this faulting almost assuredly was accompanied by large earthquakes the zone is located approximately 30 km north of the new madrid seismic zone and consists of complex north northeast to northeast striking steeply dipping faults that have had a long lived history of reactivation throughout most of the phanerozoic geophysical studies by others suggest that the faults are rooted in the deeply buried late proterozoic and early cambrian reelfoot rift system quaternary deposits are cut by at least four episodes of faulting two of which occurred during the holocene the overall style of neotectonic deformation is interpreted as right lateral strike slip faulting at many locations however near surface displacements have stepped from one fault strand to another and produced normal and oblique slip faults in areas of transtension and high angle reverse faults thrust faults and folds in areas of transpression there is evidence of reactivation of some near surface fault segments during the great 1811 1812 new madrid earthquakes quaternary faulting at thebes gap demonstrates that there are additional seismic source zones in the midcontinent u s other than new madrid and that even in the absence of plate margin orogenesis intense neotectonic activity does occur over long time periods along crustal weaknesses in continental interiors

a multi century sierra nevada snowpack reconstruction modeled using upper elevation coniferous tree rings california usa snowpack in the sierra nevada mountains accounts for around one third of california s water supply melting snow provides water into dry summer months characteristic of the region s mediterranean c

submagmatic microfractures in granites microstructures in hercynian granite plutons of the pyrenees indicate fracturing of plagioclase crystals in the presence of melt this is represented mainly by quartz and or feldspar that fills fractures electron microprobe analyses demonstrate that in compositional agreement with the rims of the zoned plagioclase the feldspar infillings are more sodic with decreasing melt fraction fracturing resulted from concentration of stress at contacts between grains while the granite was submagmatic i e when the melt was below the critical fraction for magmatic flow material compositionally far from eutectic is petrologically the best candictate to develop submagmatic fractures because during cooling the volume fraction of melt remains low for a large temperature range a strong tendency for microfractures to be oblique to flow foliation may constitute a new criterion for shear sense in magmas

magmatic diapirism of the fangshan pluton southwest of beijing china abstract diapirism as a crustal magma ascent and emplacement mechanism has been increasingly questioned due to lack of unambiguous natural examples in this paper we report the structure of the cretaceous fangshan pluton in the hinterland of the north china craton ca 40 km southwest of beijing china this pluton is a compositionally and texturally concentrically zoned granodiorite with an approximately circular shape our detailed structural and petrological investigations reveal a high temperature shear aureole with pluton side up kinematic indicators and a rim syncline around the pluton in addition an intensely deformed archean complex occurs at the northern and southern margins of the pluton requiring at least 4 km upward movement through the 4 5 km thick overlying cover sequence during magma ascent based on comparison of stratigraphic units inside and outside the aureole the bulk wall rock shortening by ductile flow is estimated to be about 4 km which is roughly the same as the radius of the pluton these features are consistent with results of numerous modeling studies and diagnostic criteria of magmatic diapirism indicating that the fangshan pluton is a magmatic diapir intruded into a ductile upper crust

status of the crustal stress in egypt as inferred from earthquake focal mechanisms and borehole breakouts abstract the recent stress field has been investigated by the analysis of the directions of maximum horizontal stress h as derived from earthquake focal mechanisms and borehole breakouts in egypt the results indicate that in the southern part of the gulf of suez the shallow borehole breakouts stress directions are not consistent with the deep earthquakes focal mechanisms stress directions analysis of 30 borehole breakouts measurements indicate wnw ese alignment of the maximum horizontal stress with a vector mean of 110 14 p e however the earthquake studies including orientation of p axes reflect ene wsw alignment of h with a vector mean of 66 30 thus the stress directions are not constant throughout the crust along the gulf of aqaba the southern part of the dead sea fault the focal mechanism solutions indicate that the maximum horizontal stress is presently nw se oriented corresponding to strike slip mechanism in concert with the geological evidence in northern egypt the nine earthquake focal mechanisms for the nile delta cairo bitter lakes region scatter in orientation varying from ne sw to nw se for h about 45 from these mechanisms indicate nw se 22 wnw ese 22 ene wsw and 11 ne sw alignment of the maximum horizontal stress while in southern egypt it is relatively uniform and aligned to nearly e w direction with a vector mean of 95 3

magnetic interactions at the origin of abnormal magnetic fabrics in lava flows a case study from kerguelen flood basalts summary anisotropy of low field magnetic susceptibility ams of basaltic lava flows can give some clues about post emplacement tilting occurring in volcanic sequences such a study has been carried out on a sequence of 19 successive lava flows from kerguelen archipelago surprisingly two different patterns were observed the first one herein called normal fabric is consistent with the lava flow direction inferred from geological observations whereas the second one observed for about 70 per cent of the analysed samples herein called abnormal fabric appears to be unrelated to the shear history of the lava flows during their emplacements these abnormal fabrics are not strictly inverse fabric but seem to have a more complex origin the unusual nature of these abnormal fabrics has been confirmed by lattice preferred orientation of plagioclases obtained from high resolution electron backscattered diffraction measurements the aim of this study is to propose a physical interpretation of these fabrics a first step in our understanding was to clearly identify the nature and the magnetic properties of thefe tioxidesassemblage thus wepresentacomprehensive rockmagneticanalysisrelying on low and high temperature thermomagnetic curves k t crossover diagrams first order

the misorientation index development of a new method for calculating the strength of lattice preferred orientation abstract using orientation data from experimentally deformed olivine we explore some practical problems with the j index a commonly applied measure of fabric strength we show that the j index is highly dependent on several factors including the number of discrete data in the orientation distribution function odf and arbitrary numerical parameters specified for its calculation because of this non uniqueness we conclude that the j index is difficult to interpret and should only be applied with caution as an alternative to the j index we propose a new measure of fabric strength that is based on the distribution of uncorrelated misorientation angles this m index is shown to be insensitive to the parameters specified for its calculation for typical deformed olivine samples we show that 150 discrete data are adequate to quantify fabric strength using the m index technique the m index correlates well with seismic anisotropy particularly for materials of the same fabric type therefore we conclude that the m index technique is well suited for the quantification of fabric strength and the comparison of like materials

shear wave splitting in quaternary sediments neotectonic implications in the central new madrid seismic zone determining the extent and location of surface near surface structural deformation in the new madrid seismic zone nmsz is very important for evaluating earthquake hazards a shallow shear wave splitting experiment located near the crest of the lake county uplift lcu in the central nmsz shows the presence of near surface azimuthal anisotropy believed to be associated with neotectonic deformation a shallow four component data set recorded using a hammer and mass source displayed abundant shallow reflection energy on records made with orthogonal source receiver orientations an indicator of shear wave splitting following rotation of the data matrix by 40 the s1 and s2 sections principal components of the data matrix were aligned with the natural coordinate system at orientations of n35 w and n55 e respectively a dynamic mis tie of 8 ms at a two way traveltime of 375 ms produced an average azimuthal anisotropy of 2 between the target reflector top of quaternary gravel at a depth of 35 m an

retrograde metamorphic reactions in deforming granites and the origin of flame perthite microprobe analyses of feldspars in granite mylonites containing flame perthite give compositions that invariably plot as three distinct clusters on a ternary feldspar diagram orthoclase or92 97 albite and oligoclase andesine the albite occurs as grains in the matrix as flame shaped lamellae in orthoclase and in patches within plagioclase grains we present a metamorphic model for albite flame growth in the k feldspar in these rocks that is related to reactions in plagioclase rather than alkali feldspar exsolution flame growth is attributed to replacement and results from a combination of two retrograde reactions and one exchange reaction under greenschist facies conditions reaction 1 is a continuous or discontinuous across the peristerite solvus reaction in plagioclase in which the an component forms epidote or zoisite most of the albite component liberated by reaction 1 stays to form albite in the host plagioclase but some na migrates to form the flames within the k feldspar reaction 2 is the exchange of k for na in k feldspar reaction 3 is the retrograde formation of muscovite as sericite and has all of the chemical components of a hydration reaction of k feldspar the si and al made available in the plagioclase from reaction 1 are combined with the k liberated from the k feldspar to produce muscovite in reaction 3 the muscovite forms in the plagioclase rather than the k feldspar as a result of the greater mobility of k relative to al the composition of the albite flames is controlled by both the peristerite and the alkali feldspar miscibility gaps and depends on the position of these solvi at the pressure and temperature that existed during the reaction using an initial plagioclase composition of an20 the total reaction can be summarized as 20 oligoclase 1 k feldspar 2 h2o 2 zoisite muscovite 2 quartz 15 albiteplagioclase 1 albiteflame this model does not require that any additional feldspar framework be accreted at replacement sites na and k are the only components that must migrate a significant distance e g from one grain to the next allowing al to remain within the altering plagioclase grain the resulting saussuritization is isovolumetric the temperature and extent of replacement depends on when and how much water infiltrates the rock the fugacity of the water and therefore the pressure of the fluid may have been significantly lower than lithostatic during flame growth

magnetic unmixing of first order reversal curve diagrams using principal component analysis we describe a quantitative magnetic unmixing method based on principal component analysis pca of first order reversal curve forc diagrams for pca we resample forc distributions on grids that capture diagnostic signatures of single domain sd pseudo single domain psd and multi domain md magnetite as well as of minerals such as hematite individual forc diagrams are recast as linear combinations of end member em forc diagrams located at user defined positions in pca space the em selection is guided by constraints derived from physical modeling and imposed by data scatter we investigate temporal variations of two ems in bulk north atlantic sediment cores collected from the rockall trough and the iberian continental margin sediments from each site contain a mixture of magnetosomes and granulometrically distinct detrital magnetite we also quantify the spatial variation of three em components a coarse silt sized md component a fine silt sized psd component and a mixed clay sized component containing both sd magnetite and hematite in surficial sediments along the flow path of the north atlantic deep water nadw these samples were separated into granulometric fractions which helped constrain em definition pca based unmixing reveals systematic variations in em relative abundance as a function of distance along nadw flow finally we apply pca to the combined dataset of rockall trough and nadw sediments which can be recast as a four em mixture providing enhanced discrimination between components our method forms the foundation of a general solution to the problem of unmixing multi component magnetic mixtures a fundamental task of rock magnetic studies this article is protected by copyright all rights reserved

controls on emplacement of the caledonian ross of mull granite nw scotland anisotropy of magnetic susceptibility and magmatic and regional structures abstract anisotropy of magnetic susceptibility ams was measured from 139 sites across the exposed portion of the caledonian ross of mull granite argyllshire nw scotland to investigate the internal architecture of the pluton field and petrographic observations support the results of the ams study and a complementary suite of rock magnetic experiments was used to quantify the magnetic mineralogy of the granite ams data reveal a fabric that records a partial tectonic overprint of an emplacement related magma inflow fabric the partially preserved inflow pattern indicates a south to north emplacement of subhorizontal sheets that coalesced to form a tabular pluton the ams data are remarkably consistent across the intrusion with clear north south strikes and trends dominating the magnetic foliation and lineation patterns respectively these ams fabrics are discordant to internal zonation in the granite in the southernmost part of the granite ams data are parallel to bedding cleavage orientations preserved in many large 100 m proterozoic moine blocks the scarcity of moine blocks in the northern part of the intrusion and the prevalence of randomly oriented stoped blocks suggest that this part of the intrusion is nearer to the ceiling of the pluton the partial tectonic overprint consistent with east west compression occurred during the latter stages of emplacement and mainly affected the younger granite facies rm2 while the oldest granite facies rm1 and certain magmatic structures diorite enclaves preserve the original emplacement fabric an alternative explanation interprets the magnetic lineations as an intersection fabric between a shallowly dipping emplacement fabric and a steep tectonic fabric we argue that emplacement was not associated with eastward orogenic collapse of the scandian moine nappes as proposed by previous workers but occurred either before orogenic collapse or during a period of compressional reactivation

multistage magma emplacement and progressive strain accumulation in the shallow level krkonose jizera plutonic complex bohemian massif 1 field relationships combined with new u pb zircon geochronology suggest that the shallow level krkonose jizera plutonic complex northern bohemian massif was assembled successively from bottom to top starting with emplacement of the separately evolved s type tanvald granite 317 3 2 1 ma followed by at least two voluminous batches of the i type porphyritic liberec 319 5 2 3 ma and jizera 320 1 3 0 ma and 319 3 3 7 ma granites the intrusive sequence was completed by uppermost minor intrusions of the equigranular harrachov 315 0 2 7 ma and krkonose granites the i type granites exhibit an unusually complex pattern of superposed feldspar phenocryst and magnetic fabrics as revealed from the anisotropy of magnetic susceptibility ams the outer liberec granite preserves margin parallel foliations and lineations interpreted to record emplacement related strain captured by cooling from the pluton floor and walls in contrast the inner jizera harrachov and krkonose granites were overprinted by synmagmatic strain resulting from dextral movements along regional strike slip faults cutting the opposite ends of the plutonic complex late stage felsic dikes in the liberec and jizera granites reorient from horizontal to vertical lineation perpendicular attitude in response to changing the least principal stress direction whereas mafic schlieren do not do so representing only randomly oriented small scale thermal mechanical instabilities in the phenocryst framework in general this case example challenges the common approach of inferring pluton wide magma flow from interpolated foliation lineation and schlieren patterns more likely magmatic fabrics in large plutons record complex temporal succession of superposed strains resulting from diverse processes at multiple scales

structural analysis of flow related textures in lavas abstract the textures of coherent volcanic rocks including lavas and volcanic intrusives commonly contain features that are attributed to flowage previous applications of structural analysis to volcanic rocks are expanded here to provide a framework for analysis textures defined as the crystallinity granularity and shapes and arrangements of the components crystals glass and voids of a rock together with structures defined as individual features composed of the disposition attitude arrangement or relative positions of the components of a rock are first described second the spatial fabrics shapes and arrangements of the components of a rock and the orientation of textures and structures are identified third textures structures and fabrics are placed in the spatial and temporal geological context finally detailed interpretations of the kinematics and rheology of structures and fabrics is made leading to an integrated flow history of the rock illustrative case studies include rhyolite from the basal part of the tertiary minyon falls dome northeastern new south wales australia which has a texture comprising planar domains of differing crystal abundance flow bands multiple folds of these domains relatively homogeneous crystal alignment parallel to the fold axes and microfolding of these domains in the zone of interaction between phenocrysts and matrix including retrorotation of phenocrysts on short limbs of inequant folds trachyte dykes on fraser island queensland australia have a texture comprising crystal alignment planar concentration domains banding two planar domains of crystal alignment interpreted to be conjugate shear zones phenocrysts influence the spacing and distribution of the domains and interacted with shear zones by undergoing small amounts of rotation the shear zones overprinted a homogeneous crystal alignment during the last stage of flow before solidification as a result of dilatant granular interactions lava from miocene submarine banded silicic mafic domes on katsurajima on the coast of the shimane peninsula southwestern japan has a texture comprising crystal alignment irregular domains interpreted as the result of quenching local internal deformation of crystals including brittle boudinage and elongate vesicles and amygdales dacite from the late stages of the 1991 1995 eruption of mount unzen in western kyushu japan has a texture comprising crystal alignment deformation of phenocrysts and their surrounding matrix producing voids by mechanical means with the possible involvement of vapour phases the pervasive mechanical failure of the flowing magma may have triggered frontal collapse and the ensuing pyroclastic eruptions a spectrum of increasingly intense flow related textures can be recognised from simple planar alignments of crystals and vesicles to overprinting effects and domainal textures such as banding and shear zones and deformed domains pervasive ductile tearing and ultimately brittle fracture record flow during the transition from ductile magma to brittle rock the development of these flow related textures is controlled by the interplay of driving forces magma pressure gravity and resisting forces viscosity where driving forces are strong flow related textures are well developed when viscous resistance exceeds the driving forces flow and the development of flow related textures ceases