theoretical models of magnetic anisotropy to strain relationship revisited abstract mathematical modelling of the relationships between the low field magnetic anisotropy and strain are redeveloped and the calculated data are compared with the degree of anisotropy for various rock types it is found that the degree of anisotropy for realistic strain magnitudes is unrealistically high in the passive model the ductile model for which the degree of anisotropy depends on the magnetic grain the matrix viscosity ratio becomes realistic at high viscosity contrasts in the line plane model the theoretical degree of anisotropy corresponds well to the natural degree of anisotropy for rocks in which the carrier of magnetic anisotropy is either magnetite or phyllosilicate minerals by contrast in the case of haematite and pyrrhotite the modelled degree of anisotropy is much higher than the natural values in the viscous model the calculated degree of anisotropy corresponds well to that measured in sedimentary and volcanic rocks in the models imposing pure shear strain the natural logarithm of the degree of anisotropy to natural strain relationship can be approximately represented by a straight line at least for low to intermediate strains the proportionality constant varies according to the specific model and the specific carrier of the anisotropy of magnetic susceptibility

links between southwestern tropical indian ocean sst and precipitation over southeastern africa over the last 17 kyr abstract time series of mg ca ba ca and 18o analyzed in tests of surface dwelling planktonic foraminifer globigerinoides ruber from two marine sediment cores recovered in the mozambique channel off the zambezi river southwestern tropical indian ocean reveal climate variability over the last 17 kyr analysis of samples collected from the water column of the mozambique channel validates that mg ca in g ruber reflects calcification temperatures at 0 30 m water depth and that the surface water of the southwestern indian ocean is very sensitive to dissolved ba input from adjacent rivers foraminiferal ba ca and mg ca time series are used to reconstruct hydrological and thermal changes over southeastern african and southwestern tropical oceans the mg ca based sea surface temperature sst estimates indicate that the thermal evolution of the tropical southwestern indian ocean followed within age model uncertainties climate changes over antarctica the trend of the sst record is marked by a gradual warming from 24 7 0 6 c at 17 0 0 2 kyr bp to 26 4 0 3 c at 10 11 kyr bp interrupted by two prominent coolings of 1 5 0 2 c and 1 c centered at 15 0 1 kyr bp and 13 4 0 2 kyr bp respectively declining ssts in the early holocene reach their minimum 25 c at 8 7 0 2 kyr bp and give way to stable thermal conditions over the middle and late holocene the ba ca record indicates that the zambezi basin experienced relatively wet conditions during the early phase of the last deglaciation bolling allerod and the early holocene these wet phases coincide with an increase of sst in the mozambique channel in contrast relatively dry conditions throughout the middle and late holocene epoch are accompanied by relatively cold mozambique channel surface water these shifts likely reflect a response to meridional shifts of the austral westerlies and subtropical front these hypothesized shifts would have modulated the advection of cold southern ocean water into the mozambique channel changes in sst in the mozambique channel and possible resultant changes in the zonal gradient in the tropical indian ocean in turn had a strong impact on the precipitation over southeastern africa

magnetic fabric in the malanjkhand granite central india implications for regional tectonics and proterozoic suturing of the indian shield abstract in this paper field microstructural and anisotropy of magnetic susceptibility ams data are presented from the 2 48 ga malanjkhand granite and adjacent gneiss with an aim to evaluate the time relationship between fabric development in the granite and regional tectonics the central indian suture cis that demarcates the southern margin of the ne sw to ene wsw trending central indian tectonic zone citz and is a consequence of the accretion between the northern and southern indian shields lies to the north of the granite the northern margin of the granite that has proximity to the cis is mylonitized and shows a dextral top to the ne sense of shear field and magnetic foliation in the gneiss are parallel to each other as well as to the field foliation in the western and northwestern margin of the granite also the field fabrics in the granite and gneiss curve clockwise into the cis the magnetic foliation trajectories curve from a ns orientation in areas remote from the cis to a ne sw orientation in parts that are proximal to the cis in the north the granite shows synmagmatic deformation fabrics such as preferentially oriented zoned feldspar phenocrysts as well as evidence of high t solid state deformation fabric such as chessboard pattern in quartz magnetic anisotropy increases towards the cis which is inferred to support synmagmatic deformation it is concluded that the tectonic evolution of the citz and emplacement fabric development in the malanjkhand granite were synchronous phenomena wnw ese directed convergence led to transpression which is inferred to be responsible for the emplacement of the granite it is concluded that in the malanjkhand granite the development of syndeformational emplacement fabrics to syntectonic cooling was a continuum and the suturing of the northern and southern indian shields along the cis took place during the palaeoproterozoic period thus the study provides an insight into the amalgamation and stabilization of the indian shield during the late archaean palaeoproterozoic time

models of magnetic anisotropy variations in sedimentary thrust sheets abstract magnetic anisotropy variation in sedimentary thrust sheets was modelled through the extension of strain models in thrust sheets coward and kim 1981 sanderson 1982 using the empirical relationship between the magnetic anisotropy and strain and respecting the pre deformational anisotropy of sedimentary rocks in thrust sheets deformed by simple shear and lateral lengthening the magnetic foliations remain near the bedding while in thrust sheets deformed by simple shear and lateral shortening the magnetic foliation may deviate strongly from the bedding even creating a girdle pattern in its poles

magnetic fabrics and microstructures of the post collisional aegirine augite syenite triunfo pluton northeast brazil abstract anisotropy of magnetic susceptibility ams and microstructures of the neoproterozoic triunfo alkaline pluton situated in northeast brazil have been investigated in order to characterize fabrics formed during its emplacement bulk magnetic susceptibility in the pluton varies between 0 15 10 3 and 25 10 t 3 si and the mean magnetic anisotropy ratio is around 1 04 aegirine augite and secondary magnetite are the main carriers of the magnetic susceptibility with the former controlling the directions of the anisotropy magnetic foliation and lineation are consistently oriented throughout the pluton foliation typically dips gently to the northeast and lineation plunges gently to the east these structures were mostly acquired at the magmatic and sub magmatic stages the shape of the magnetic ellipsoid is dominantly oblate a feature that may reflect either the uniaxial oblate ams ellipsoid of the aegirine augite crystals and or a vertical compaction of the magma in its final stages of crystallization the foliation pattern suggests the pluton has a tabular shape within the basement rocks magma emplacement is inferred to have occurred by its lateral migration along a flat lying crustal structure after fracture propagation and ascension of the magma from a lower crust mantle source late fine grained vertical dykes with the same mineral composition as the triunfo syenite cross cut the wall rocks of the pluton and close the alkaline magmatism in the area the ne trending alignment of alkaline plutons and the nne trending syenitic dykes indicate that the emplacement of such bodies occurred along a crustal extension event with a minimum compressive stress horizontal trending roughly e w

response of remanent magnetization to deformation in geological processes using 3d printed structures abstract palaeogeographic reconstructions and construction of apparent polar wander paths are dependent on having reliable palaeomagnetic directions the importance of inclination flattening in biasing the palaeomagnetic record has been debated for over 60 yrs correction for this effect often assumes that the palaeomagnetic vector deforms as a passive line in a novel approach using 3d printed analogue rocks we revisit the question of how a palaeomagnetic vector responds to deformation specifically compaction maghaemite nanoparticles were mixed in the printing resin with a concentration of 0 15 wt and five series of cylinders with 1 cm height and diameter were printed with porosities between 0 and 20 samples were given an anhysteretic remanent magnetization and were subjected subsequently to incremental compaction the magnetic fabric shows an initially weak compaction in the printing plane that becomes larger with increased compaction the palaeomagnetic inclination changes according to the strain that the sample undergoes and the amount of deflection is less than predicted by a passive line model of deformation our results demonstrate that using a single correction factor for inclination flattening is questionable and show the need for a method that considers how the rock deforms further we demonstrate the usefulness of 3d printed analogue rock which can inspire more realistic methods to correct for inclination flattening

magma flow paths and strain patterns in magma chambers growing by floor subsidence a model based on magnetic fabric study of shallow level plutons in the stiavnica volcano plutonic complex western carpathians the miocene stiavnica volcano plutonic complex western carpathians exposes two nearly coeval intra caldera plutons their roof basement of a stratovolcano and associated volcanic rocks the complex thus provides insights into mechanisms of magma chamber growth beneath large volcanoes as inferred from the anisotropy of magnetic susceptibility ams these plutons were emplaced through significantly different processes the diorite as a discordant stock with steep fabric and the granodiorite as a tabular bell jar pluton in detail we interpret that the latter was assembled in two stages first an upper layer intruded as a thin sill along a major subhorizontal basement cover detachment the subhorizontal magnetic fabric and strongly oblate ams ellipsoid in this layer record intrusive strain where the magma flow paths were subparallel to the pluton roof second in the lower layer of the pluton magnetic foliations dip moderately to the nw and wnw to vertical and are associated with down dip to subhorizontal lineations and prolate to weakly oblate shapes of the ams ellipsoids such a fabric pattern is compatible with piecemeal floor subsidence where magma flowed along multiple subsiding fault bounded blocks based on this case example we develop a conceptual model for magma flow paths and strain patterns for four main modes of floor subsidence 1 piston cauldron subsidence is characterized by convergent flow and radial principal stretching above the magma chamber floor 2 the piecemeal floor subsidence leads to steep to inclined magma flow paths in conduits along fault bounded blocks 3 asymmetric trapdoor subsidence produces first divergent flow paths near the conduit sides changing into convergent paths in the narrower space near the kinematic hinge and 4 symmetric cantilever funnel subsidence will lead to divergent flow from a central feeder and thus circumferential principal stretching of the magma if the growing pluton develops a two layer structure all the flow paths and associated strains are affected by the flat lying pluton roof and will convert into horizontal flattening as the roof is approached

constraint of the co2 rise by new atmospheric carbon isotopic measurements during the last deglaciation 1 the causes of the 80 ppmv increase of atmospheric carbon dioxide co2 during the last glacial interglacial climatic transition remain debated we analyzed the parallel evolution of co2 and its stable carbon isotopic ratio 13co2 in the european project for ice coring in antarctica epica dome c ice core to bring additional constraints agreeing well but largely improving the taylor dome ice core record of lower resolution our 13co2 record is characterized by a w shape with two negative 13co2 excursions of 0 5 during heinrich 1 and younger dryas events bracketing a positive 13co2 peak during the bolling allerod warm period the comparison with marine records and the outputs of two c cycle box models suggest that changes in southern ocean ventilation drove most of the co2 increase with additional contributions from marine productivity changes on the initial co2 rise and 13co2 decline and from rapid vegetation buildup during the co2 plateau of the bolling allerod

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

formation uplift and tectonic integration of a periadriatic intrusive complex pohorje slovenia as reflected in magnetic parameters and palaeomagnetic directions summary the periadriatic lineament is a 700 km long first order tectonic boundary in the alps along which several tertiary intrusions are located that were emplaced while tectonic processes were active the pohorje pluton is one of the periadriatic magmatic suites and comprises a pluton and a dacite stock that were emplaced at depths of about 10 and 2 km respectively oriented samples were collected from 33 sites in the magmatic and three in the surrounding metamorphic rocks and subjected them to standard palaeomagnetic and magnetic susceptibility anisotropy processing there is extreme variation in susceptibility although the magnetic mineral are always magnetite and in its anisotropy within the pluton lowest values are in the mafic members in the gabbro the oldest and in some lamprophyres the youngest member of the plutonic suite while the tonalite granodiorite exhibits extreme variation far exceeding those observed for other periadriatic plutons the abnormality of the pohorje pluton is attributed to the complex history that involves assimilation fractional crystallization stratification in the magma chamber incorporation of wall rocks variable degree of k metasomatism and hydrothermal alteration despite the above described heterogenities and sometimes very high degree of susceptibility anisotropy much higher that in the metamorphic samples in the acid member the palaeomagnetic directions observed for the pluton define three clear cut groups the directions show no dependence on the degree of magnetic susceptibility anisotropy in the order of crystallization they exhibit decreasing degree of clockwise declination deviation from north the dacite stock is characterized by counter clockwise rotated declinations as the pohorje pluton was uplifted very fast within the right lateral periadriatic shear zone system it is interpreted that the palaeomagnetic directions observed for the pluton are evidence for a clockwise rotation during exhumation the palaeomagnetic directions for the dacite which formed after the climax of the external forces fits the regional pattern of counter clockwise rotation observed in the neogene sediments around the pohorje pluton this shows that by the time of the dacite intrusion the pohorje pluton was already incorporated into the block that was driven by counter clockwise rotated adriatic microplate

deformation and metamorphism in the bard area of the sesia lanzo zone western alps during subduction and uplift the structure microstructure and petrology of a small area close to the village of bard in val d aosta italy has been studied in detail the area lies across the contact between the gneiss minuti gm and the eclogitic micaschist ems complexes of the lower element of the sesia portion of the sesia lanzo zone western alps both complexes have undergone high pressure metamorphism but the metamorphic assemblages indicate a sudden increase in pressure in going across the contact from the gm to the ems therefore we interpret the contact as a thrust dividing the lower element of the sesia into two sub elements this interpretation is supported by structural evidence the early alpine 90 70 ma metamorphic history is best preserved in the ems and is one of increasing pressure associated with thrusting the maximum p t recorded in the ems is 1500 mpa 15kbar and 550 c and in the gm is 1500 1300 mpa 15 13 kbar and 500 550 c we suggest that the rocks were probably in an active benioff zone during this time from then on the histories of the gm and ems are the same deformation continued and the thrust and thrust slices were folded during decreasing pressure we interpret the first postthrusting deformation in terms of uplift associated with continued shortening of the crust and underplating after the benioff zone had become inactive and a new benioff zone had developed further to the north west a still later deformation and the lepontine metamorphism 38 ma are related to continued uplift much of this deformation is characterized by structures indicative of vertical shortening and lateral spreading as the mountains rose above the general level of the surface

non scaled analogue modelling of ams development during viscous flow a simulation on diapir like structures development of magnetic fabric within a diapirically ascending columnar body was investigated using non scaled analogue model made of plaster of paris containing small amount of fine grained homogeneously mixed magnetite the apparatus for the modelling consists of a manual squeezer with calibrated spring and a perspex container set of weak coloured layers at the bottom of the container was forced to intrude overlying fine grained sand through a hole in a board attached to the squeezer the development of ams fabric is correlated with complex flow pattern indicated by coloured and originally horizontal plaster layers strongly constrictional and vertical fabric in the base and in the lower domain of the diapir resulting from convergent and upwards flows is overprinted by subhorizontal oblate fabrics due to vertical flattening and initial divergent flow in the apical parts the measured ams fabrics are compared with natural examples of magmatic stocks and dykes

pervasive horizontal fabric and rapid vertical extrusion lateral overturning and margin sub parallel flow of deep crustal migmatites northeastern bohemian massif abstract in the west sudetes northeastern bohemia massif geochronometry provides evidence for repeated episodes of rapid cooling that contrasts sharply with an absence of structural evidence for significant tectonic exhumation by crustal extension instead high grade assemblages of the orlica snieznik complex have a regional sub horizontal foliation and sub horizontal lineations that trend parallel to narrow sub vertical shear zones containing exhumed high pressure assemblages mesoscopic petrofabrics combined with anisotropy of magnetic susceptibility ams data from amphibolite facies to migmatitic meta sedimentary and meta igneous rocks reveal remarkably consistent average lineations that plunge shallowly to the ssw on both steep and sub horizontal nne trending planar fabrics the dominant ssw nne fabric orientation is parallel to the bohemia brunia suture which marks a major boundary along the eastern margin of the massif the shape of the ams ellipsoid is predominantly oblate revealing flattened fabrics with only local prolate ellipsoids we envisage that the continental brunian indentor operated as a rigid backstop and allowed the migmatized lower crustal orogenic root to be exhumed along the bohemian margin shortly following terminal arc collision sub vertical extrusion of the orogenic root was arrested in the mid crust where the lower ductile crust was laterally overturned at the base of rigid upper crustal blocks upon reaching the crustal high strength lid the exhumed ductile mass of continental material laterally spread sub parallel to the margin underwent subsequent supra barrovian metamorphism and quickly cooled the application of ams techniques to high grade metamorphic rocks in concert with macroscopic structural observations is a powerful approach for resolving the deformation history of a terrane where visible rock fabrics can be tenuous

slaty cleavage development and magnetic anisotropy fabrics the shale to slate transition preserved in the ordovician martinsburg formation at the lehigh water gap pennsylvania provides an opportunity to study the relationship between magnetic anisotropy fabrics and the development of slaty cleavage our previous work has indicated that anisotropy of magnetic susceptibility ams does not record changes in finite strain associated with cleavage development in these rocks but instead measures the degree of dissolution and new growth of ehlorite additional ams data presented in this paper lend further support to this conclusion conversely anhysteretie remanent magnetization anisotropy arma which is not affected by paramagnetie ehlorite accurately reflects the strain induced rock fabrics associated with cleavage formation arma results show that magnetite dimensional orientations vary from bedding parallel in shale samples to cleavage parallel in samples with well developed slaty cleavage samples with weak and pencil cleavage display scattered arma orientations which lie in between bedding and cleavage these intermediate orientations may be due to either passive rotation of magnetite from bedding parallel to cleavage parallel or re crystallization of magnetite if rotation occurred grain rotation was highly heterogeneous in the samples with incipient cleavage the intermediate arma orientations may also reflect the varying contribution of two magnetite preferred orientations a depositional orientation parallel to bedding and a new growth orientation parallel to cleavage

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

the composition and evolution of an oligocene regolith on top of the sesia lanzo zone western alps an oligocene paleosurface regolith lies on top of the high pressure metamorphic rocks of the sesia lanzo zone near biella nw italy only the saprock the lowermost part in a regolith profile is preserved no evidence for any paleosoil can be observed field observations indicate that the regolith developed through in situ mechanical fracturing of the rocks of the sesia lanzo zone in a continental environment density estimations of the regolith and the underlying rocks of the sesia lanzo zone confirm the field observations and imply that a relatively small amount of alteration minerals was formed the main detected alteration phases are chlorite various carbonates quartz clay minerals fe oxides and fe hydroxides chlorite differing in chemistry and crystallographic ordering demonstrates different stages of alteration oxygen and carbon isotopic composition of carbonates suggests temperatures higher than surface conditions illite and chlorite thermometry indicates temperatures related to the anchizone 250 300 c these data are considered as a robust indication of the re burial of the regolith together with its substrate and its volcanic cover the burial is closely related to the tilting of the preserved stratigraphic sequence formed by the rocks of the sesia lanzo zone the regolith and the rocks of the biella volcanic suite lanza in schweiz miner petrogr mitt 57 281 290 1977 lanza in geologishe rundschau 68 83 92 1979 furthermore the burial is consistent with this sequence of subaerial rocks being very close to the intrusion depth of the valle del cervo pluton at the time of its emplacement 4 7 km zanoni et al in rend online sgi note brevi 1 199 202 2008 zanoni et al in int geol rev 52 1244 1267 2010 and references therein

seasonal and interannual variation in santa barbara basin water temperatures observed in sediment trap foraminiferal mg ca 1 we have generated a santa barbara basin sediment trap mg ca record to evaluate culture based calibration equations for the temperate subpolar planktonic foraminiferal species globigerina bulloides and neogloboquadrina pachyderma dextral g bulloides and n pachyderma mg ca are significantly correlated with seasonal variations in temperature of the near surface and subthermocline depths respectively the average deviation between mg based and 18o based temperature estimates is 0 6 c for g bulloides and 0 8 c for n pachyderma differences between mg derived temperatures and instrumental temperatures may be due to cleaning methods environmental factors such as seasonal variations in foraminiferal depth habitats or possible secondary effects on mg ca core top mg ca of both g bulloides and n pachyderma is in excellent agreement with average values from the sediment trap lending strong support for the interpretation of downcore mg ca from these species as annual average near surface and thermoclinal temperatures

core top calibration of mg ca in tropical foraminifera refining paleotemperature estimation 1 optimal use of mg ca as a paleotemperature proxy requires establishing calibrations for different species of foraminifera and quantifying the influence of dissolution to achieve this goal we have measured mg ca and 18o in a series of tropical and subtropical core tops including four depth transects the ceara rise the sierra leone rise and the rio grande plateau in the atlantic and the ontong java plateau in the pacific focusing on spinose mixed layer dwelling species globigerinoides ruber and globigerinoides sacculifer and nonspinose thermocline dwelling neogloboquadrina dutertrei shell mg ca in g sacculifer is 5 15 lower than in g ruber while n dutertrei mg ca is 49 55 lower than in g ruber this statistically significant offset has allowed us to establish different calibrations for each species multilinear regression analysis was used to develop calibration equations that include a correction term for the dissolution effect on mg ca in foraminiferal calcite presented in this paper are two sets of calibrations one set using core depth as a dissolution correction and another using co32 as a dissolution parameter the calibrations suggest that g ruber is the most accurate recorder of surface temperature while g sacculifer records temperatures below the surface at 20 30 m the depth habitat of n dutertrei is more uncertain owing to the wide range in habitat depths depending on hydrographic conditions but on average mg ca and 18o data suggest it is at 50 m of the three species n dutertrei is the most sensitive to dissolution up to 23 decrease in shell mg ca per km while g sacculifer is the most resistant

degree of magnetic anisotropy as a strain intensity gauge in ferromagnetic granites anisotropy of magnetic susceptibility data for a ferromagnetic granite godhra granite nw india are presented and it is shown that the degree of magnetic anisotropy p is not controlled by the mean susceptibility k m analyses carried out across a high strain zone lying between granite and adjacent gneiss show that p values are highest in samples that lie close to the contact and decrease away from it based on these results it is concluded that if p is not controlled by k m then the former can be used to gauge strain intensity variations in ferromagnetic granites

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

constraints on geological strain rates arguments from finite strain states of naturally deformed rocks a summary of known finite strain states is presented longitudinal strains 1 e as measured in many rocks often range from 1 to 40 and 1 to 0 025 the time span available to produce such measureable strains in young orogenic zones seems to be less than 10 m y possibly less than 1 m y which constrains conventional strain rates into the range of 10 sup 13 s sup 1 to 10 sup 15 s sup 1 for both pure and simple shear the most efficient way and much less efficient way to accumulate incremental strains respectively the ellipticity of the finite strain ellipse increases in a nonlinear manner finite strain variations in adjacent layers which give rise to features such as cleavage refraction arise with only slight differences in the strain rates within these layers

magnetic fabric and emplacement of the post collisional pomovaara granite complex in northern fennoscandia abstract the proterozoic pomovaara granite complex in northern finland comprises three separate highly magnetic granite stocks they are discordant apparently unfoliated and according to isotope data a significant archaean component characterizes the source of these granites the three stocks are aligned in an array parallel to major trans crustal faults as interpreted from both aeromagnetic and gravity data their younger age of 1 8 ga compared to the main tectonic events at 1 9 ga in northern fennoscandia indicates their post collisional nature with respect to these events the anisotropy of magnetic susceptibility ams was studied together with magnetic gravity and geological data in order to assess the emplacement mechanisms of the pomovaara granite complex and the possible tectonic control of fault systems on the ascent and emplacement of granitic magma the orientation of magnetic fabrics within the granite stocks indicates that the direction of the original magma upwelling was from the sw parallel to the major fault zones that controlled at the crustal scale the ascent of granite magmas the predominant nw se orientations of the minimum magnetic axes of the magnetic ellipsoid and the elongate shapes of the stocks indicate compression normal to the deep fault trend during the crystallization of the granite magma

the structure and dynamics of the thin near bed layer in a complex marine environment a case study in beatrix bay new zealand abstract the 1 3 cm thick near bed layer at the interface between sea water and the sea bed was studied using two acoustic doppler velocimeter adv deployments in beatrix bay new zealand which relate to late autumn and early winter conditions the data strongly support the multi mechanism nature of the near bed layer and show that the turbulent stresses and energy may be non zero even at nearly zero or zero mean velocities the turbulent fluctuations in the near bed layer are highly intermittent and consist of two components 1 low energy background fluctuations and 2 relatively rare high energy events hee the structure dynamics and influence of these components on bed erosion particle aggregation and re suspension are significantly different our results suggest that the revealed high energy events are the main contributors to bed erosion and sediment re suspension the estimates of the local reynolds number and other turbulence parameters show that hee may change the near bed flow regime from viscous or transitional at low energy background conditions to fully turbulent during the high energy events although the physical origin of hee is not yet clear most probably they are generated by intermittent highly energetic internal waves or near bed convective mixing or both these results provide a base for future research in this complex near bed region

intracrystalline deformation and nanotectonic processes in magnetite from a naturally deformed rock abstract although experimental studies have shown dislocation creep to be an important deformation mechanism in magnetite at medium to high temperature evidence of intracrystalline deformation in magnetite remains to be established in natural tectonically deformed rocks in this study we investigate intracrystalline deformation features and nanostructures in elongated magnetite from a naturally deformed rock mylonitized mica schist deformed in a large scale shear zone of the seve nappe swedish caledonides the magnetite grains have very high aspect ratios up to 10 40 that result in very high degree of magnetic anisotropy in the rock we show low and high angle grain boundaries lagb and hagb in magnetite using a combination of electron backscatter diffraction and high resolution transmission electron microscopy hrtem analysis hrtem studies on lamellae excavated perpendicular to the lagb and hagb reveal translational and rotational moire fringes respectively dislocations slip bands stacking faults twins and recrystallized domains are observed in the vicinity of the grain boundaries thus providing unequivocal evidence of intracrystalline deformation of magnetite our study also reveals the presence of biotite inclusions intergrown epitaxially with magnetite that show no evidence of lattice defects thus suggesting that the intracrystalline deformation of magnetite took place under wet conditions the movement at the grain boundaries is interpreted as a response to regional tectonics with a top to nw transport direction it is established that at the nanoscale the lagb and hagb were favourably oriented to accommodate strain dominantly by translation and rotation respectively thus the nanotectonic processes are consistent with the regional tectonic reference frame the importance of evaluating ductile behaviour of magnetite from deformed polymineralic rocks in petrofabric analysis and modeling the relation between strain and rock magnetic anisotropy is discussed

calibration of mg ca thermometry in planktonic foraminifera from a sediment trap time series 1 paired mg ca and 18o measurements on planktonic foraminiferal species g ruber white g ruber pink g sacculifer g conglobatus g aequilateralis o universa n dutertrei p obliquiloculata g inflata g truncatulinoides g hirsuta and g crassaformis from a 6 year sediment trap time series in the sargasso sea were used to define the sensitivity of foraminiferal mg ca to calcification temperature habitat depths and calcification temperatures were estimated from comparison of 18o of foraminifera with equilibrium calcite based on historical temperature and salinity data when considered together mg ca mmol mol of all species except two show a significant r 0 93 relationship with temperature t c of the form mg ca 0 38 0 02 exp 0 090 0 003 t equivalent to a 9 0 0 3 change in mg ca for a 1 c change in temperature small differences exist in calibrations between species and between different size fractions of the same species o universa and g aequilateralis have higher mg ca than other species and in general data can be best described with the same temperature sensitivity for all species and pre exponential constants in the sequence o universa g aequilateralis g bulloides g ruber g sacculifer other species this approach gives an accuracy of 1 2 c in the estimation of calcification temperature the 9 sensitivity to temperature is similar to published studies from culture and core top calibrations but differences exist from some literature values of pre exponential constants different cleaning methodologies and artefacts of core top dissolution are probably implicated and perhaps environmental factors yet understood planktonic foraminiferal mg ca temperature estimates can be used for reconstructing surface temperatures and mixed and thermocline temperatures using g ruber pink g ruber white g sacculifer n dutertrei p obliquiloculata etc the existence of a single mg thermometry equation is valuable for extinct species although use of species specific equations will where statistically significant provide more accurate evaluation of mg ca paleotemperature

high temperature magnetic fabric development from plastically deformed magnetite in experimental shear zones summary magnetic fabric development has been studied in synthetic magnetite silicate aggregates in a series of high temperature simple shear deformation experiments samples composed of magnetite grains with a nominal size of 20 40 m dispersed at 3 wt in a matrix of plagioclase were deformed between 1000 and 1200 c with a confining pressure of 300 mpa shear stresses in the range 10 130 mpa and shear strains up to 3 we determined that both magnetite and plagioclase were deformed plastically at these conditions an oblate magnetic fabric ellipsoid develops subparallel to the shear plane and the degree of ams rapidly increases with strain up to a value of 2 5 theoretical strain response models of magnetic fabric development were applied to the data to obtain estimated magnetite strains the shape preferred orientation of magnetite grains after deformation determined from reflected light image analysis was used to calculate independent magnetite strain estimates these results were then compared with strains estimated from theoretical magnetic anisotropy development both strain estimation methods indicate strain partitioning between magnetite and the plagioclase matrix and the results are used to determine approximate viscosity ratios between the two phases at the experimental conditions

northern and southern hemisphere controls on seasonal sea surface temperatures in the indian ocean during the last deglaciation 37 are consistently warmer than those derived from mg ca by 2 3 c except for the heinrich event 1 in addition the initial timing for the deglacial warming of alkenone sst started at 15 6 ka which lags behind that of mg ca temperatures by 2 5 kyr we argue that the discrepancy between the two sst proxies reflects seasonal differences between summer and winter rather than postdepositional processes or sedimentary biases the u k 37 sst record clearly mimics the deglacial sst trend recorded in the north atlantic region for the earlier part of the termination indicating that the early deglacial warming trend attributed to local summer temperatures was likely mediated by changes in the atlantic meridional overturning circulation at the onset of the deglaciation in contrast the glacial to interglacialsstpatternrecordedbyg rubermg ca probably reflectscoldseasonssts this indicates that the cold season ssts was likely mediated by climate changes in the southern hemisphere as it closely tracks the antarctic timing of deglaciation therefore our study reveals that the tropical southwestern indian ocean seasonal sst was closely linked to climate changes occurring in both hemispheres the austral summer and winter recorded by each proxy is further supported with seasonal sst trends modeled by atmosphere ocean general circulation models for our core site our interpretation that the alkenone and mg ca ssts are seasonally biased may also explain similar proxy mismatches observed in other tropical regions at the onset of the last termination

the chinamora batholith zimbabwe structure and emplacement related magnetic rock fabric abstract the origin of dome and keel structural geometries in archean granite greenstone terrains appears to lack any modern analogues and is still poorly understood the formation of these geometries is investigated using structural and anisotropy of magnetic susceptibility ams data for the chinamora batholith in zimbabwe the roughly circular shaped batholith is surrounded by ca 2 72 2 64 ga greenstones the batholith granitoid suites have been divided on the basis of their ages and fabric relationships into four distinct units i banded basement gneisses ii granodioritic gneisses iii equigranular granites and iv central porphyritic granites in the gneissic granites a partial girdle n s of poles to the magnetic foliation is developed that has been folded around a consistent flat lying magnetic lineation plunging at shallow angles to the e or w in the equigranular granites the magnetic lineation generally plunges to the nw the magnetic foliation has a variable strike no clear trends can be distinguished the ams measurements of the porphyritic granite revealed a nw se striking foliation and showed subhorizontal magnetic lineations the magnetic foliation is subparallel to the macroscopic foliation wall rocks are moderately inclined and show radial or concentric lineations triaxial strain ellipsoids and kinematics that demonstrate off the dome sliding and coeval pluton expansion the results of the observations do not point to a single emplacement process neither the observed structural data nor the magnetic fabric support a model envisaging spherically ballooning it is argued that pluton diapirism played a major part in the formation of the fabrics in the gneisses whereas the fabrics in the porphyritic granites reflect emplacement as laccolith like sheets

magnetic fabric of late jurassic arc plutons and kinematics of terrane accretion in the blue mountains northeastern oregon abstract the blue mountains province of northeastern oregon western idaho and southeastern washington usa consists of the amalgamated wallowa distal island arc baker melange bearing accretionary wedge forearc and olds ferry fringing island arc terranes anisotropy of magnetic susceptibility ams and particularly the orientation of magnetic lineations in middle to late jurassic diorite tonalite granodiorite plutons intruding the baker terrane indicate a change in tectonic regime from flattening with principal stretching at a high angle to the local orientation of the terrane boundaries at around 160 ma to constriction with boundary subparallel subhorizontal stretching at ca 146 ma the former magnetic fabric is compatible with magnetic lineations recording strain related to top to the southwest back thrusting onto the olds ferry arc in contrast the 146 ma boundary parallel stretching may record strain partitioning whereby a part of the baker terrane was extruded laterally parallel to terrane boundaries after the terrane collision after restoration for the clockwise post mid cretaceous terrane rotation the 160 ma restored principal stretching directions are compatible with the overall left oblique subduction and convergence of the wallowa distal and olds ferry fringing arc terranes magnetic fabric data from the plutons thus support the interpretation that the early displacement of the blue mountains superterrane and perhaps also its possible correlative intermontane superterrane of the canadian cordillera was southward along the truncated north american continental margin during the late middle jurassic

deformation and magnetic fabrics in ductile shear zones a review abstract the anisotropy of magnetic susceptibility ams is a well established petrofabric tool for indicating relative strain and microstructural character and has been validated on various rock types and different structural settings the magnetic susceptibility of a rock k depends primarily on the nature and abundance of magnetic minerals the physical arrangement and lattice preferred orientation of these magnetic minerals give rise to magnetic anisotropy the ams scalar parameters most commonly used to constrain strain include the corrected degree of anisotropy p 1 a proxy for fabric intensity and the shape factor 1 t 1 an indicator of the magnetic fabric symmetry prolate vs oblate a number of studies have shown that a positive correlation generally exists between p and strain thus the ams shows a great potential as a tool for examining deformation in geologic structures characterized by large strain gradients such as shear zones however a number of caveats exist i the increase of p with strain cannot be solely attributed to deformation because p also increases with k regardless of deformation ii strain across shear zones is typically heterogeneous and is often localized in units of different lithology thus making the separation of the lithological and strain controls on ams difficult also deformation is commonly accompanied by mineral segregation or fluid rock interaction that induces changes in magnetic mineralogy iii even if the undeformed lithology was uniform across a shear zone variations in strain rate or temperature may result in different deformation mechanisms hence the relationship between p and strain depends strongly on both the mineral carriers of ams and on deformation mechanisms and iv the ams is unable to resolve composite fabrics such as those resulting from s c structures where minerals on the c and s planes respectively contribute to ams

anisotropy of magnetic susceptibility as a strain gauge in the flamanville granite nw france the relationship between strain and anisotropy of magnetic susceptibility ams has been investigated in the carboniferous flamanville granite in the armorican massif nw france we measured the axial ratios of elliptical inclusions and the orientation of cleavage planes at eight sites around the granite margin measurements of ams were made on 73 specimens using a schonstedt spinner magnetometer ams measurements are shown to provide accurate predictions of cleavage and lineation direction even where these structures are difficult to measure in the field the strain and ams ellipsoids show similar regional variations in shape and intensity and a good correlation between the lengths of the principal axes finally our data are consistent with the hypothesis that the flamanville granite was syntectonically emplaced during the late stages of the hercynian orogeny

magnetic fabric and rheology of co mingled magmas in the nasavrky plutonic complex e bohemia implications for intrusive strain regime and emplacement mechanism abstract the fabrics of mafic microgranular enclaves mme and of the host granodiorite of the old granodiorite intrusion of the nasavrky plutonic complex e bohemia were investigated by means of magnetic anisotropy the magnetic fabric in mme is oriented coaxially with the magnetic fabric of the host granodiorite which is undoubtedly magmatic intrusive in origin consequently the magnetic fabric in mme originated during the same process as the magnetic fabric in granodiorite i e during the granodiorite emplacement in addition also the degree of anisotropy and the shapes of susceptibility ellipsoids are very similar in mme and in granodiorite which probably indicates that the mme had probably a similar viscosity to that of granodiorite and behaved as passive markers whose shapes resembled those of the intrusive strain ellipsoids petrological and geochemical approaches coupled with rheological modelling allow the prediction of the physical states of magmas and of the development of their internal fabrics observed fabrics were compared to the results of numerical modelling of multiparticle systems slowly moving in viscous fluid the steep magnetic foliations and almost vertical magnetic lineations suggest that today s erosion level represents a relatively deep intrusive level where magma flowed vertically and its intrusion was controlled by the shape of the feeder zone used for magma ascension

the pombal granite pluton magnetic fabric emplacement and relationships with the brasiliano strike slip setting of ne brazil paraiba state abstract the pombal pluton 500 km 2 a suite of diorite syenite and porphyritic granite bodies is here used to constrain kinematics of brasiliano age tectonic episodes in northeast brazil the pluton intrudes high grade to migmatitic gneiss forming the western basement of the serido belt and is located at the intersection between two sets of continental scale dextral strike slip shear zones the northern set of shear zone strikes ne sw and branches southwards into the e w patos mega shear zone a detailed microstructural and low field magnetic susceptibility study was performed to unravel the relationships between solid state deformation in the country rocks and magma emplacement porphyritic granite and syenite have quite high magnetic susceptibilities 10 3 10 2 si units indicative of magnetite as the principal carrier of susceptibility the magnetic fabric is remarkably homogeneous in orientation throughout the pluton it is characterized by a shape preferred alignment of magnetite itself parallel to the shape fabric of mainly biotite amphibole i e to the magmatic fabric even close to the contact with the high temperature mylonites of the patos shear zone south of pombal no imprint of the e w trending structures is observed in the fabrics of either the granite or the host rocks granite emplacement and its internal fabric development is concluded to be independent of the movement of the patos shear zone in the southwestern border of the pluton a low dip foliation bearing a ne sw striking lineation is shared in both the magmatic fabric of the pluton and the solid state fabric farther to the north approaching the ne sw strike slip shear zone the magmatic fabric is characterized by a steeply dipping ne striking foliation carrying a subhorizontal lineation transition from low to steep dips of the planar fabrics is progressive two models are proposed for emplacement of the pombal pluton one considers magma injection during an early episode of tangential tectonics responsible for the gently dipping foliations evolving later to strike slip deformation the other model considers that the pluton was emplaced in a pull apart domain developed in the overlapping sector of a right hand en echelon system of a dextral shear zone compatibility of these models with the tectonic evolution of the serido belt is discussed

a new approach to modeling perpendicular fabrics in porphyritic plutonic rocks using the finite element method a growing body of field evidence indicates that hypersolidus fabrics preserved in syntectonic plutons are likely to have formed in highly crystallized rigid sponge magma this paper demonstrates that such magma could be idealized as a rheological solid and that the development of non coaxial fabrics in plutonic rocks can very conveniently be modeled in the framework of solid mechanics using the finite element method fem we modeled two strain regimes of small magnitudes plane strain horizontal simple shear with the shear strain of up to 0 30 and plane strain pure shear of up to 15 shortening superposed onto vertically oriented and variously spaced elastic phenocrysts set in the viscoelastic matrix in the simple shear regime the phenocrysts slightly rotate toward the shear plane while the principal strain directions in the matrix are instantaneously oriented at an angle of about 45 or less to the phenocryst fabric simple shear thus can only lead to the formation of oblique phenocryst and matrix fabrics by contrast the vertical phenocryst fabric is maintained in the pure shear regime and a new horizontal fabric can develop almost instantaneously in the matrix even for small amounts of superposed shortening 5 shortening after 10 ky in our model we conclude that such a mechanism can easily produce perpendicular hypersolidus fabrics in plutonic rocks and that only a very short time span first thousands of years is required to develop magmatic fabric in a pluton for normal rates 10 15 to 10 13 s 1 of tectonic deformation

the las chacras potrerillos batholith pampean ranges argentina structural evidences emplacement and timing of the intrusion within the southern part of the sierra pampeanas the sierra de san luis argentina a series of extensive intrusive bodies are regarded to post date the famatinian cycle but were emplaced during the achalian a period of heterogeneous deformation along crustal scale fault zones the largest of those is the las chacras potrerillos batholith that is situated at the northern end of the transpressive sinistral guzman shear zone this composite pluton exhibits three sub domains that comprise two granitoid sub units each the southern potrerillos stock muscovite bearing red granite and biotite bearing red granite and the central biotite porphyritic granite and giant porphyritic granite and northern domain equigranular granite and porphyritic granite of the las chacras stock the crystallisation ages of the biotite porphyritic granite is around 381 ma u pb on zircons and pb pb on sphene while the host rock was already cooled below 350 c at 420 ma thermal modelling approaches favour a pulsed intrusion with a duration of 1 5 ma the emplacement was followed by rapid cooling below the muscovite cooling temperature biotite cooling ages in different sub units reflect either a long lasting cooling history of approximately 30 ma which is supported by the modelling or a reheating effect at around 350 ma devonian age determinations on the fault rocks and granitoids point to a syn tectonic emplacement of the batholith the pluton is interpreted to be positioned at the crossover of sinistral shear zones the origin of this nne directed extensional setting in a transpressive regime seems to be related to the transfer of displacement along a secondary set of nnw trending sinistral faults the final emplacement is due to a subsequent ballooning of the batholith following the direction of space creation this model is based on the relative timing of the emplacement sequence and macroscopically visible planar fabrics in the field as well as magnetic fabric data our results indicate that the emplacement is syn kinematic with respect to the achalian deformation event

shear zones and magma ascent a model based on a review of the tertiary magmatism in the alps 1 the alpine oligocene plutons are spatially and temporally associated with the activity of the periadriatic fault system pfs an orogen parallel crustal scale transpressive mylonitic belt excellent three dimensional exposure combined with a wealth of structural seismic petrological geochronological geochemical and paleomagnetic data collected over the last decades help to constrain the relationships between deformation ascent and emplacement of the plutons magmas were channeled from the base of the thickened continental crust into the narrow mylonitic belt of the periadriatic fault system which was used as ascent pathway to cover vertical lengths of 20 to 40 km therefore the linear alignment of the plutons at the surface is not the expression of a linear source region at depth ascent of the melts is controlled by the mylonitic foliation of the pfs which forms the only steep anisotropy continuously traversing the entire alpine crust in contrast the flow direction is not influenced by the specific kinematics of the faults final emplacement of the plutons occurred by extrusion from the periadriatic fault system into the adjacent country rocks the transition from ascent to final emplacement is favored by partitioning of transpressive deformation

the emplacement of the rieserferner pluton eastern alps tyrol constraints from field observations magnetic fabrics and microstructures abstract within the alpine chain several tertiary intrusions e g bergell adamello intruded along the periadriatic lineament this study attempts to show how the rieserferner pluton vedrette di ries is related to the defereggen antholz vals dav line for a survey of the fabric pattern over the pluton the anisotropy of the magnetic susceptibility ams was determined on nearly 170 samples low bulk susceptibilities of k vol 6 si and a total degree of anisotropy p