a magnetic fabric study of the aigoual saint guiral liron granite pluton french massif central and relationships with its associated dikes 1 in the southeastern french massif central the aigoual saint guiral liron pluton consists of porphyritic and microgranitic types the latter is encountered within dikes forming the northern end of the pluton both types show prefull crystallization microstructures indicating weak subsolidus deformations an anisotropy of magnetic susceptibility ams study has been carried out to determine the granite fabric biotite local hornblende and small grains of magnetite are the main carriers of ams in both types porphyritic granite and dikes display different ams patterns related to magma dynamics and regional deformation recorded during crystallization in the porphyritic type the ams lineation is mainly consistent with the regional nw se to e w trending extensional event coeval with emplacement and crystallization of the pluton indicating an influence of regional tectonics on the linear fabric development the dome shaped foliation pattern of the saint guiral massif likely corresponds to internal deformation related processes within the pluton in the microgranite dike swarm the nne ssw trending lineations with shallow plunges record magmatic flow processes within dikes i e magma injection and filling of dikes from a probable source located southwestward regional tectonics played a significant role in the pluton geometry and fabric development for example the ne sw trend of the dikes suggests that extensional fractures took place in the same extensional strain field as elsewhere in the pluton different fabric development modes were therefore responsible for the contrasted fabric patterns between the microgranite and the porphyritic granite

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

emplacement and deformation of granites during transpression magnetic fabrics of the archean sparrow pluton slave province canada abstract the sparrow pluton is part of the prosperous suite of two mica granites that crop out within amphibolite grade meta greywackes of the southern yellowknife domain in the slave province of the canadian shield the magnetic susceptibility k and the anisotropy of magnetic susceptibility ams were used to systematically map the structural patterns in the pluton and to establish the relationship between plutonism and late archean tectonics in the region paramagnetic fe phyllosilicates biotite chlorite and very fine grained magnetite contribute to k and to the ams the magnetic foliation and the magnetic lineation are predominantly controlled by the biotite fabrics and their orientations are consistent with the regional d 2 strain field the horizontal magnetic lineations in the sparrow pluton suggest a horizontal stretching component associated with the regional d 2 event the zonation defined by k values is compatible with a fold pattern trending parallel to the regional f 2 folds and s 2 foliation and to the magnetic fabric trends in the pluton the intensities and symmetries of the ams also define map patterns that are consistent with d 2 deformation microstructural study indicates the pluton recorded d 2 strain as it crystallized and cooled from the solidus demonstrating syn d 2 emplacement the results indicate the pervasive structural patterns in the sparrow pluton are an integral part of the regional strain field and that they are kinematically consistent with a transpressive d 2 strain regime mapping the fabric patterns within syntectonic plutons provides a useful approach to the kinematic analysis of synemplacement deformation events in multiply deformed metamorphic terranes

pull apart emplacement of the margeride granitic complex french massif central implications for the late evolution of the variscan orogen a microstructural magnetic fabric and gravity study is performed on the carboniferous margeride granitic complex that crops out in the central part of the variscan french massif central this complex consists of three facies namely a main porphyritic monzogranite a two mica granite and late leucogranite dykes and stocks in spite of local variations the magnetic lineation mainly trends nw se with a shallow plunge throughout the complex the magnetic foliation pattern is more complex with various strikes and generally a moderate dip this fabric pattern complies with the late orogenic nw se regional extensional deformation already recognised in this part of the variscan belt new gravity measurements complete available data and are used to build up a gravity map and a cross section with which four gravity minima are identified three gravity minima are interpreted as extensional fractures consistent with a nw se maximum stretching the last gravity low corresponds to an extensional jog between the two westernmost fractures the structural and gravity features of the complex are used to propose a feeding and emplacement model controlled by the regional late orogenic extensional tectonics the margeride complex is interpreted as a kilometre scale laccolith like pluton emplaced in a transtensional setting controlled by a nw se opening direction such a model strengthens the relationships between pluton emplacement and late orogenic collapse of the variscan belt

reply to comment on interplay of deformation and magmatism in the pangong transpressional zone eastern ladakh india implications for remobilization of the trans himalayan magmatic arc and initiation of the karakoram fault abstract in the eastern part of ladakh the right lateral karakoram fault zone kfz bifurcates into two strands called the pangong strand and the tangtse strand these two strands bound a region called the pangong transpression zone ptz which consists of migmatitic dioritic gneiss calc silicates and the durbuk pluton a pluton of two mica leucogranite outcrop scale observations suggest pervasive migration of leucogranitic melt through the existing tectonic structures of the gneiss magnetic fabric from both the tectonized and undeformed parts of the durbuk pluton show parallelism with the tectonic fabric of the host gneiss which along with pervasive melt migration indicates syn kinematic relationship between deformation along the kfz leucogranite magmatism and emplacement of the durbuk pluton u pb geochronology of zircons from the dioritic gneiss yields a crystallization age of 63 6 1 5 ma and also shows younger zircon growth down to 13 ma which suggest arc magmatism at 65 ma followed by partial melting and leucogranite magmatism in the kfz till 13 ma one two mica leucogranite sample from the durbuk pluton gives a crystallization age of 22 7 0 5 ma as the durbuk pluton is syn tectonic with deformation along kfz it is inferred that the kfz initiated at least 23 ma ago

solving a cold case new occurrences reinforce juvenile callianassids as the ophiomorpha puerilis tracemakers abstract the ichnotaxon ophiomorpha puerilis was erected based on material from late pleistocene shallow marine siliciclastic deposits of southeastern brazil these tiny burrows with a distinctive lining of cylindrical pellets having rounded ends were originally interpreted as burrows of juvenile callianassid shrimp with polychaetes also considered as a possible tracemaker recent discoveries of o puerilis in late pleistocene shallow marine carbonates from two localities in the bahamas and from the miami limestone of south florida described herein have expanded significantly the geographic range of the ichnotaxon and provided numerous well preserved specimens for detailed structural analysis of its burrow form and pellets the new information strengthens the interpretation of juvenile callianassids as the tracemakers resolving the cold case of the burrow s tracemaker microscopic analyses revealed that the pellets of o puerilis are constructional not fecal furthermore larger forms of ophiomorpha are common and occur in close association with o puerilis at each locality these new data allowed close comparison of o puerilis pellets with those of sergio mirim a modern callianassid from southeastern brazilian beaches ophiomorpha nodosa from brazilian pleistocene deposits and fossil polychaete burrows filled with fecal pellets as described in the literature the combined evidence allows us to exclude polychaetes as potential o puerilis tracemakers rather o puerilis records the settling and initial burrowing behavior of callianassid decapodids the characteristics of an ophiomorpha ichnofabric with the addition of o puerilis also is described and explored an emended diagnosis for the o puerilis ichnotaxon is provided based on the new structural data for this burrow

heterogeneous brittle ductile deformation at shallow crustal levels under high thermal conditions the case of a synkinematic contact aureole in the inner northern apennines southeastern elba island italy abstract we present an example of interaction between magmatism and tectonics at shallow crustal levels in the late miocene the metamorphic units of the eastern elba island northern apennines were intruded at very shallow crustal levels by a large pluton 60 km 2 with the development of an hectometre sized contact aureole defined by growth of low pressure high temperature mineral assemblages p max max 650 c structural data show that the contact aureole is associated with a km sized antiform of the foliation and by several metre to decametre thick high strain domains consisting of strongly foliated rocks containing synkinematic ht lp mineral assemblages and ductile shear zones of variable thickness these shear zones are characterized by a mylonitic foliation variably overprinted by cataclasis quartz microfabrics indicate that the dynamic crystallization processes progressively changed from grain boundary migration associated with the thermal peak of contact metamorphism to subgrain rotation and bulging recrystallization the latter mostly associated with the cataclastic overprint these transitions of recrystallization mechanisms in quartz are related to a progressive decrease of temperature during deformation deformation accompanied the development and cooling of the contact aureole which recorded the switch from high temperature ductile to low temperature brittle conditions the geometry of the studied deformation structures is consistent with the constraints of the regional tectonic evolution and its local interaction with the localized and transient thermal anomaly related to the coeval emplacement of igneous rocks

microstructure and magnetic susceptibility applied to emplacement kinematics of granites the example of the foix pluton french pyrenees abstract the variscan foix granite 40 km 2 central pyrenees was subjected to detailed microstructural magnetic susceptibility and anisotropy studies magnetic susceptibility is shown to be of dominant paramagnetic origin its magnitudes clearly define a zoning which compares with the petrographic zoning and reveals that the pluton is the southern remnant of a normally zoned pluton truncated during alpine tectonics magnetic susceptibility anisotropy characterizes the planar and linear preferred orientations of the main iron bearing silicates namely biotite and accessory amphibole it is argued that these fabrics also reflect the flow pattern of the granite microstructural observations aid in distinguishing the magmatic and late magmatic fabric signatures main body from the post magmatic solid state signature leucogranite in order to account for the consistently subhorizontal and ne sw directed magmatic lineations in the northern sector of the foix granite an oblique intrusion is proposed it may be coeval with the early variscan regional sw trending shearing event steepening of the structures in at least part of the southern sector may be coeval with the late development of upright folds and vertical cleavage in the country rocks the utility of combined microstructural and magnetic susceptibility studies is demonstrated as an aid in the structural interpretation of granite intrusions which act as kinematic markers of their host terranes

fracture controlled magma conduits in an obliquely convergent continental magmatic arc magnetic fabric patterns of two mid cretaceous nested plutons 102 1 and 96 3 ma in the central sierra nevada batholith provide evidence that felsic magma emplacement and ascent occurred via north trending steeply dipping planar fracture conduits oriented obliquely to the arc u pb geochronology data indicate that emplacement of the plutons was separated by 2 to 10 m y and that they were emplaced in part via the same conduit magnetic fabrics in the younger pluton are related to its final emplacement which was strongly influenced by a system of host rock joints formation of the north trending conduits at 100 ma can be related to a small arc parallel dextral shear component that produced tension fractures and that was associated with high angle oblique convergence by 90 ma convergence had become sufficiently oblique for the development of nearly arc parallel structures which were then favored as magma conduits

magnetic fabric of the barrington passage pluton meguma terrane nova scotia a two stage fabric history of syntectonic emplacement abstract structural analysis and the anisotropy of magnetic susceptibility ams are used to document the internal magmatic to high temperature subsolidus fabrics of the tonalitic late devonian barrington passage pluton the ams fabric orientations compare favorably with mesoscopic scale fabrics in general the k1 k2 principal plane of the ams is close to the observed mineral foliation defined by biotite and plagioclase and the k1 axis is aligned parallel to a mineral lineation defined by the same minerals and to a locally developed weak extension lineation defined by quartz measurement of the anisotropy of anhysteretic remanence aar and image analysis of biotite preferred orientations confirm that the orientation of the ams is principally controlled by biotite locally anomalous ams orientations are attributed to the influence of fine grained magnetite crystals the presence of which is revealed by measurements of hysteresis and coercivity properties a two stage fabric history is revealed first horizontal fabrics were formed foliation compositional banding during emplacement of a laccolith like pluton the second stage involved synmagmatic folding of the horizontal foliation and banding in response to regional contraction associated with the acadian orogeny with development of a lineation that records stretching parallel to the fold axis the results demonstrate that the barrington passage pluton was emplaced during the main phase of the acadian orogeny a model is proposed that depicts the barrington passage pluton as the folded base of a larger syntectonic pluton that is now largely eroded off

magnetic fabric and microstructural evidence for a tectono thermal overprint of the early proterozoic murray pluton central ontario canada abstract the 2 38 ga old murray granite pluton intruded the southern footwall of the sudbury igneous complex and was subjected to repeated ductile deformation its nw and se domains display differences in strain state ams signature and the nature and distribution of fe oxide minerals the magnetic foliation is parallel to the visible foliation in the nw domain but discordant to it in the se domain microstructural data show that the magnetic fabric in the nw domain coincides with a foliation formed at high temperature probably in response to thermal softening during the emplacement of the adjacent sudbury igneous complex this tectono thermal overprint affected pre existing shape fabrics and was facilitated by incipient melting of the granite near the intrusive contact with the sudbury igneous complex rocks of the se domain are only partially overprinted and two mineral subfabrics are preserved prolate susceptibility ellipsoids and clusters of maximum susceptibility directions at the intersections of the two planar fabrics suggest oblique superposition of strain increments increases in bulk magnetic susceptibility and magnetic anisotropy degree towards the intrusive contact with the sudbury igneous complex can be explained by respective increases in the proportion of magnetite over ilmenite and strain intensity in the murray pluton

magnetic fabrics and strain in pencil structures of the knobs formation valley and ridge province us appalachians pencil structures which are found in weakly deformed mudrocks reflect the bedding cleavage intersection in weak to moderatelycleaved rocks their presence indicates conditions where bedding and cleavage fabrics are approximately equal in intensity we have determined the anisotropy of magnetic susceptibility ams in pencil structures from a sequence of mudstones of the ordovician knobs formation in the valley and ridge province of the us appalachians magnetic mineralogy was determined by x ray analysis and lowtemperature susceptibility measurements distribution of the magnetic ellipsoid axes is consistent with the incipient tectonic fabric of the pencil mudstones the maximum susceptibility axes parallel the pencils long axes while the minimum axes of susceptibility are normal to the primary sedimentary fabric independent strain quantification permits a correlation between magnetic fabric and tectonic strain an exponential relationship between the ams shape parameter t and tectonic shortening has been found for the interval of 10 25 shortening shortening 17 p exp t this relationship appears to be supported by tectonic strains up to 40 the t parameter t lnf 2 lnl lnl lnf where l lineation is kmax kint and f foliation is kint kmin describes the shape of the magnetic susceptibility ellipsoid which appears more sensitive to strain than past correlation attempts with the magnetic intensity parameter p or p 0 whereas this correlation between strain and ams is only valid within a restricted window of strain 10 40 shortening it establishes the magnitude and directions of tectonic strain in weakly deformed clay rich rocks where strain indicators are otherwise lacking or are poorly developed q 2003 published by elsevier science ltd

middle and late albian geography oceanography and climate and the setting of the kirchrode i and ii borehole sites abstract the paper reviews the literature on the geography oceanography and climate belts during the middle and late albian emphasis is placed on the northern hemisphere and the lower saxony basin the middle and late albian represents a time with a greenhouse climate the n s temperature gradient and the temperature gradient between the shallow and deep waters of the oceans were lower than at present meaning higher temperatures especially at middle and high latitudes a more sluggish ocean circulation than today and the absence of polar ice caps warming from the early to late albian is documented in the marine sediments by oxygen isotope studies and the poleward expansion of rudist dominated carbonate platforms in the terrigenous sediments of the northern hemisphere it is documented by northward migration of low latitude relatively arid flora the opening north atlantic was still narrow at the beginning of the albian it widened and deepened through the albian a shallow seaway between the south atlantic and the western tethys developed during the late albian wide shelf seas existed on the continental plates with rising sea level the basins of the western epicontinental seas of eurasia became increasingly connected and sedimentation gradually became more calcareous nevertheless these basins received a large clastic input from the land documenting the weathering conditions on the surrounding land masses they received also a considerable biogenic particle flux from the surface waters documenting productivity of the marine plankton because of these different origins of the sediment components as well as the connections with neighbouring seas the sediments in these shelf basins were expected to document changes in climate as well as palaeo oceanographic changes earlier interpretations based on ammonite studies that indicate changing connections between the arctic ocean and the tethys during the albian can thus be tested the lower saxony basin was a shelf sea in the southern part of the warm humid climate belt at mid latitudes in the northern hemisphere in which thick deposits of hemipelagic sediments accumulated mapping previous to our study indicated that a complete undisturbed albian basinal sequence ca 400 m thick is present below a thin quaternary cover in a sub basin between the nne ssw trending benthe and lehrte salt structures in the central part of the lower saxony basin the boreholes at the kirchrode i and ii sites 52 22 35 n 9 49 87 e and 52 22 16 n 9 49 12 e respectively in hannover were drilled into this sub basin the high sedimentation rates known for the albian of the lower saxony basin are ideal for studying climatic changes with a cyclicity of a few ten thousand to a few hundred thousand years milankovitch cyclicity

reply to comment on magnetic fabrics crystallographic preferred orientation and strain of progressively deformed metamorphosed pelites in the helvetic zone of the central alps quartenschiefer formation by carl richter lothar ratschbacher and wolfgang frisch

regional scale strain variations in banded iron formations of eastern india results from anisotropy of magnetic susceptibility studies anisotropy of magnetic susceptibility ams data are used as a tool to determine strain variations in different parts of the banded iron formations bifs of the bonai synclinorium eastern india ams data of 88 cylindrical cores drilled from 29 samples collected from the limb and hinge parts of mesoscopic scale folds as well as different parts of the entire synclinorium are presented it is found that the samples from limbs of small scale folds and also from limbs of the regional scale synclinorium have higher degrees of anisotropy than the hinges this is inferred to indicate that the limbs accommodated higher strain than the hinges ams orientation data are analysed in conjunction with field data it is concluded that the magnetic fabric developed in the limbs as well as hinges of the bifs of the study area is related to deformation and is not a manifestation of sedimentary fabric

an archean metamorphic core complex in the southern slave province basement cover structural relations between the sleepy dragon complex and the yellowknife supergroup archean rocks in the fenton lake brown lake area southern slave province are subdivided into two lithotectonic domains a supracrustal domain which consists mainly of the archean yellowknife supergroup and a gneiss granite domain the latter is composed of gneissic and metaigneous rocks of the sleepy dragon complex determined to be basement to the yellowknife supergroup and granite plutons including the 2641 3 5 ma suse lake granite and the 2583 5 1 ma morose granite volcanic rocks of the cameron river belt and greywacke mudstone turbiditic metasedimentary rocks of the burwash formation constitute the supracrustal domain a late archean amphibolite to greenschist facies ductile to local brittle high strain zone separates the domains kinematic indicators demonstrate that the zone experienced two kinematically opposed episodes of displacement the older episode involved pre to synthermal peak thrusting of the supracrustal rocks over the gneiss granite domain thrusting is kinematically an

strain and fabric analyses based on porphyroclast interaction abstract two dimensional computer models of the interaction of elliptical clasts in a variety of kinematic conditions are used to study how clast imbrication and shape fabric development relate to strain and strain history the models provide templates for a known clast density and clast ellipticity that correlate clast imbrication angle of collision and clast shape fabric to strain and kinematics of deformed rocks modeling also shows that the mode of clast interaction plays a significant role in the accumulation of imbricated clasts and the development of shape fabric upon collision between clasts the trains formed can remain fixed or rotate if they rotate imbricated clasts can become independent when they are no longer forced together by the flow based upon the mode of clast and train rotation using the march rotation of passive lines and the jeffery rotation of rigid particles as end members three models are defined in an attempt to simulate the conditions of clast interaction under varying conditions the march fixed train march rotating train and jeffery rotating train models simulate solid state intermediate and magmatic conditions respectively modeling shows that the two march models produce similar results but the jeffery model of train rotation always produces a lower proportion of imbricated clasts and a much weaker shape fabric application of the modeling to the study of a syntectonic granite in the sierra nevada suggests that deformation was dominated by simple shear some k feldspar imbrication and fabric development took place initially in the magmatic stage and culminated in the solid state to produce a large proportion of imbricated k feldspar porphyroclasts which define a strong shape fabric this type of analysis provides a rationale to determine syn vs post emplacement deformation in the granite

the miocene climatic optimum evidence from ectothermic vertebrates of central europe abstract data sets of central european temporal distributions of thermophilic ectothermic vertebrates channidae varanidae chamaeleonidae cordylidae tomistomidae alligatoridae giant turtles and of north alpine foreland basin nafb distributions of ectothermic vertebrates adapted to dryer habitats albanerpeton inexpectatum salamandra sansaniensis bufo cf viridis chamaeleo caroliquarti gekkonidae varanus hofmanni bransateryx sp are analysed two main migration events of thermophilic ectotherms at 20 ma and 18 ma in the lower miocene are discerned they indicate the beginning of the miocene climatic optimum in central europe 42 45 n palaeolatitude with a lower limit of the mean annual temperature mat of 17 4 c derived from the minimal mat of their extant relatives furthermore additional palaeobotanical data and records of bauxite point to a mat of 22 c this warm and humid optimum peaked at 18 16 5 ma ottnangian karpatian and is confirmed by the coexistence of all investigated thermophilic taxa the following period early badenian is characterised by probably unchanged temperatures but a seasonality in precipitation with dry periods up to six months two major seasonal phases between 16 3 and 15 7 ma earliest early badenian and between 14 7 and 14 5 ma early middle badenian transition are indicated by an immigration of dry adapted taxa from the surrounding karst plateau to the nafb it is presumed that the tectonical reorganisation of the central paratethys realm had considerable influence on this regional humidity pattern the warm period ended abruptly between 14 0 and 13 5 ma middle late badenian transition with major regional extinction events of most of the thermophilic groups in central europe and a drop of the mat of probably more than 7 c to temperatures around 14 8 15 7 c this drop can be attributed predominantly to a decrease of more than 11 c of the minimum cold months temperature this temperature decrease marked the beginning of a climatic zonation of the european continent and is also evidenced by a progressively southward disappearance of the crocodile diplocynodon from 38 45 n palaeolatitude to 30 37 n during the middle and earliest late miocene the results correlate well with palaeobotanical data from the mid latitudes of europe and north america and the deep sea temperature curve generated from oxygen isotope ratios

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

production of subtidal tubular and surficial tempestites by hurricane kate caicos platform british west indies abstract storm infilling of deep open callianassa burrows with molluscan to peloidal packstone was the dominant style of preservable sedimentation produced by the passage of hurricane kate across caicos platform british west indies on 18 november 1985 this moderate hurricane was the first to affect an actively studied portion of the carbonate platform environments of the south florida bahama region in 19 years a time during which many of our concepts of storm sedimentation have evolved prior to hurricane kate much of the shallow platform interior peloidal packstone to grapestone grainstone had a sparse seagrass cover and a highly irregular bottom caused by abundant callianassa mounds hurricane kate flattened the mounded bottom of the platform interior and caused minor smothering and erosion of the seagrass beds a thin surficial tempestite though deposited over much of the platform was difficult to identify because it lacked a coarse base instead much of the reworked surface sediment poured down the large callianassa burrow entrances and filled the vast burrow networks with either a coarse molluscan packstone or peloidal skeletal packstone storm burrow filling tubular tempestites effectively removed the coarse fraction from contributing to a surficial storm layer ten percent of the upper 75 cm of platform interior sediment consists of tubular tempestites from hurricane kate

kinematic evolution of the mbakop pan african granitoids western cameroon domain an integrated ams and ebsd approach abstract this study integrates anisotropy of magnetic susceptibility microstructural and crystallographic preferred orientation cpo data from the mbakop granitic pluton mgp pan african age in order to decipher its kinematic evolution the mgp lies close to ne sw branch of central cameroon shear zone ccsz and is emplaced in gneissic basement high mean magnetic susceptibility and presence of multi domain magnetite are recorded quartz cpo measured using electron backscatter diffraction reveals dominance of rhomb prism and prism slip in different samples which is consistent with microstructures developed under upper greenschist amphibolite facies conditions quartz cpo along with other kinematic indicators feldspar porphyroclasts mineral fish indicate non coaxial deformation was important during tectonic evolution of the mgp contrasting sense of shear is recorded implying multi stage mylonitization in the western cameroon domain top towards south sense of shear is related to regional d 2 deformation 613 585 ma while top towards north is related to d 3 585 540 ma the magnetic fabric in mgp records d 3 the obliquity between mean orientation of magnetic foliation n12 e and the ne sw ccsz branch n48 e gives kinematic vorticity number of 0 95 this indicates dominantly simple shear with a minor pure shear component it is concluded that regional transpression was important during mgp emplacement

occurrence of bioglyphs on ocypode crab burrows in a modern sandy beach and its palaeoenvironmental implications abstract the ichnological term bioglyph covers biogenic sculpture on burrow walls bioglyphs in the burrows of ocypodid crabs were studied in a modern unconsolidated sandy substrate looseground on irino coast southwestern japan they are seen exclusively on sides and roof of the burrow and are characteristically seen near the distal end of the burrow moist sandy substrate where sand particles are bound together by surface tension of interstitially suspended water might allow the production of such bioglyphs although bioglyphs are only partially developed in such burrows those interpreted to have formed in semi consolidated substrates firmground are known to be sculptured over the entire burrow surface such difference in the modes of bioglyph occurrence can be used as a criterion to reconstruct the substrate consistency in the rock record

middle and late jurassic roots of brachyuran crabs palaeoenvironmental distribution during their early evolution abstract knowledge of early mesozoic crabs is still rudimentary mainly due to the poor preservational potential of crustacean decapods fossil evidence suggests that the family prosopidae is ancestral to all other brachyurans including podotremata with a very close phylogenetic relationship to homolodromiidae dromiidae homolidae latreillidae dynomenidae xanthidae cyclodorippoidea and calappoidea prosopidae is an extinct family consisting mostly of mesozoic species almost exclusively known by their carapaces this family appeared in the late early jurassic late pliensbachian and disappeared at the end of the danian the early jurassic pliensbachian oldest crab species eocarcinus praecursor withers is transitional in many of its observable traits between the macruran glypheoidea middle triassic pseudopemphix and the early brachyuran prosopids especially the earliest known species eoprosopon klugi forster late pliensbachian middle jurassic prosopids lived in shallow sea soft bottom environments the oldest known prosopid species lived on a silty sea floor as did the first known crab late early pliensbachian and their presumed ancestors pemphicidae were probably also shallow water organisms middle jurassic prosopids lived both in shallow warm waters within organic buildups shelly accumulations and on silty sea floors during the bajocian bathonian as illustrated by a new example from central poland prosopids had an evolutionary climax during the late jurassic and were widely distributed in sponge microbial oxfordian buildups and coral reef kimmeridgian tithonian environments of europe pithonoton coelopus longodromites prosopon nodoprosopon lecythocaris glaessneropsis when biohermal and reef facies retreated at the end of the jurassic favourable conditions for prosopid crabs diminished and cretaceous prosopids are rare and spatially dispersed their closely related descendants the homolodromiids preferentially inhabited soft muddy bottoms in deeper colder waters as is well documented by cenozoic and recent occurrences

dextral transpression and late eocene magmatism in the trans himalayan ladakh batholith north india implications for tectono magmatic evolution of the indo eurasian collisional arc the trans himalayan ladakh batholith is a result of arc magmatism caused by the northward subduction of the tethyan oceanic lithosphere below the edge of the eurasian plate the batholith dominantly consists of calc alkaline i type granitoids which are ferromagnetic in nature with the presence of magnetite as the principal carrier of magnetic susceptibility the mesoscopic and magnetic fabric are concordant and generally vary from wnw ese to ene wsw for different intrusions of ferromagnetic granites in different parts of the batholith strike of magnetic fabric is roughly parallel with the regional trend of the ladakh batholith in the present study area and is orthogonal to the direction of india eurasia collision in khardungla and changla section the magnetic fabric is distributed in a sigmoidal manner it is inferred that this sigmoidal pattern is caused by shearing due to transpression induced by oblique convergence between the two plates u pb zircon geochronology of a rhyolite from the southern parts of the batholith gives a crystallization age of 71 7 0 6 ma coeval with 68 ma magmatism in the northern parts of the batholith the central part of the batholith is characterized by s type two mica granites which gives much younger age of magmatism at 35 5 0 5 ma the magnetic fabric of these two mica granites is at a high angle to the regional trend of the batholith it is proposed that these two mica granites were emplaced well after the cessation of subduction and arc magmatism along fractures that developed perpendicular to the regional strike of the batholith due to shearing

assessment of the relationship between emplacement of the algoman plutons and regional deformation in the rainy lake region ontario the algoman suite of granites and granodiorites located within the rainy lake region of the superior province intruded the wabigoon quetico subprovince boundary about 2686 ma deformation occurred during the late archean collision between the wabigoon and wawa volcanic arcs the algoman plutons are the youngest rocks in the region their apparent lack of macroscopic deformation fabrics has led previous researchers to use their age as a constraint for the cessation of regional deformation however contrasting competence between the relatively rigid granites and surrounding volcanic and metasedimentary rocks suggests that obvious deformation fabrics may not be observed in the plutons even if they were present during deformation a field anisotropy of magnetic susceptibility ams gravity inversion model and microstructural study were undertaken on two neighboring algoman plutons to determine their emplacement history relative to the regional deformation there is a steep macroscopic foliation in the adjacent rocks and in parts of the plutons the magnetic foliation is very strong and roughly coincident with the field foliations the gravity inversion models indicate that the plutons are relatively shallow 1 km and 4 5 km at their deepest points and their shapes are consistent with emplacement during dextral transpression quartz microstructures such as undulose extinction and subgrain formation indicate that there was some solid state deformation accommodated by dislocation creep mechanisms the field ams gravity and microstructural evidence indicate that the plutons were most likely emplaced syntectonically thus the pluton age does not provide a conclusive constraint to the cessation of regional deformation

variscan dextral transpression in the french pyrenees new data from the pic des trois seigneurs granodiorite and its country rocks abstract new structural data from both the trois seigneurs granodiorite and its country rock lead to new conclusions about the variscan tectonic history of this part of the pyrenees sedimentary rocks of the massif that increase in metamorphic grade from north to south are imprinted by a single major deformation responsible for both the tight upright e w trending folds with vertical to steeply n dipping foliations and the gently w plunging stretching lineations syntectonic emplacement of the pic des trois seigneurs granodiorite is demonstrated by the parallelism between structures of the pluton as determined by magnetic fabric measurements and the foliations and lineations imprinted in the country rocks large deformation of the granodiorite magma during emplacement is indicated by strong anisotropy and ubiquitous magmatic microstructures the high thermal gradients of regional metamorphism which is also syntectonic are attributed to a large thermal aureole provided by deep seated magma reservoirs shear sense criteria in xz thin sections of the metasedimentary country rocks indicate a dextral sense of the non coaxial component of strain throughout the massif and regardless of metamorphic grade the overall structure of the massif is concluded to have derived from a major shearing event that is equated with the d 2 main phase observed in the entire variscan pyrenees as the e w oriented stretch and dextral shear cannot be separated from compressive structures generally considered to be characteristic of d 2 this phase is concluded as representing regional transpression

magnetic susceptibility of the mont louis andorra ilmenite type granite pyrenees a new tool for the petrographic characterization and regional mapping of zoned granite plutons we have observed remarkably consistent patterns of concentric zonation in the values of low field magnetic susceptibility measurements over the variscan age mont louis andorra granite pluton of the eastern pyrenees of andorra spain and france this zonation is a function of the rock petrology since a close correlation is shown between the petrographic nature as defined by chemical analysis and the magnetic susceptibility magnitude of the rocks it reflects the dominantly paramagnetic nature of the granite carried by fe bearing silicates and this is demonstrated by the fact that low field susceptibilities of representative specimens are almost equal to 1 their high field susceptibilities and 2 their calculated susceptibilities using fe contents assuming a null ferromagnetic contribution we conclude that this technique accurately reflects the modal abundances of ferromagnesian phases in rocks of the ilmenite series and that it represents a powerful and efficient tool for the reconnaissance surveying of petrological variations in granitoid plutons

structure magnetic fabric and emplacement of the archean lebel stock sw abitibi greenstone belt abstract the anisotropy of magnetic susceptibility ams has been determined in a suite of samples from the ca 2680 ma old sub circular syenitic lebel stock which is bound to the north by a major late archean shear zone larder lake cadillac deformation zone lcdz the ams defines a magnetic foliation which is parallel to a strong planar preferred mineral orientation fabric considered to have been acquired during flow of a crystalladen magma during emplacement the geometry of the foliation indicates that the stock has an horizontal dish shape at depth the syenites also contain a well defined magnetic lineation which consistently points toward the lcdz apart from localities in the south where it trends e w parallel to the stock s margin ams ellipsoids are dominantly of oblate type except in samples showing solid state strain and alteration overprints which often have plane to prolate ellipsoids the intensity of the magnetic fabric shows a weak spatial variation being strongest at the southern margin the magnetic and magmatic fabric pattern ams parameter variation and the sense of displacement of the western wall rocks are used to propose an emplacement mechanism involving southward migration of a relatively thin sheet of syenitic magma from a linear source corresponding to the present location of the lcdz

a multidisciplinary study of a syntectonic pluton close to a major lithospheric scale fault relationships between the montmarault granitic massif and the sillon houiller fault in the variscan french massif central 2 gravity aeromagnetic investigations and 3 d geologic modeling 1 new gravity and aeromagnetic investigations have been carried out to understand the emplacement mechanisms of a granitic pluton and the relationships with a nearby lithospheric scale fault this paper concerns the second part of a methodological multidisciplinary study and complements previous geochronologic and anisotropy of magnetic susceptibility ams studies on the same pluton in the northern part of the variscan french massif central fmc the montmarault massif crops out along the sillon houiller fault shf bouguer and aeromagnetic anomaly maps imply thickening of the pluton along the shf and suggest laccolitic spreading northwestward on the basis of petrophysical measurements direct two dimensional 2 d joint gravity and magnetic modeling has been performed along 10 cross sections in order to quantitatively constrain the 3 d pluton geometry and its relationships with surrounding geologic units these geophysical cross sections new structural information field and ams measurements and petrophysical data have been integrated into a regional 3 d geological and geophysical model altogether the results obtained from geochronology petromagnetic fabrics part 1 gravity and aeromagnetic investigations as well as 3 d modeling part 2 demonstrate that the montmarault pluton was emplaced during the namurian period along the shf our results further show that at that time in response to a nw se regional extension if the shf existed it behaved as a normal fault mylonites attesting for synmagmatic normal motion on the northeastern part of the montmarault pluton strengthen this tectonic scenario during the late carboniferous the fmc experienced ne sw extension along the shf by 80 km of brittle left lateral wrench offset this second tectonic event is well recorded in the stephanian coal basins which were formed along nw se listric brittle faults and constrain the present day shape of the montmarault pluton

stoped blocks in plutons paleo plumb bobs viscometers or chronometers abstract stoped blocks potentially provide information about paleohorizontal during emplacement of plutons and about the timing of and viscosities and kinematics during magmatic fabric formation in the mount stuart batholith washington we have examined magmatic fabrics patterns around stoped blocks in tonalite located near the pluton roof and completed 1 1 scale three dimensional mapping of fabric patterns around stoped blocks in diorite located 1000 m below the roof in both settings no structural record of magma ascent early emplacement or settling of the blocks is preserved instead fabric formation largely post dates the settling and trapping of stoped blocks two dimensional finite difference thermal modeling and calculations of sinking rates support short

high latitude albian climate variability palynological evidence for long term drying in a greenhouse world abstract detailed quaternary style quantitative spore pollen counts with a pollen sum based on total non angiosperm seed plants from a southern high palaeolatitude 60 65 terrestrial sequence in gippsland southeast australia has revealed strong vegetation and climate variability during the albian this variability is more pronounced than previously suggested in global early cretaceous vegetation and climate reconstructions the quantitative spore pollen record shows drying throughout the albian based on upward decreasing total ferns and variation in podocarp and total alisporites vitreisporites pollen this record suggests that although global climate during the albian is considered to have been warm stable and equable regional factors such as water availability and continentality were the main drivers of this vegetation change

magnetic fabrics crystallographic preferred orientation and strain of progressively metamorphosed pelites in the helvetic zone of the central alps quartenschiefer formation we investigate the relationships between the anisotropy of magnetic susceptibility ams mineral preferred orientation macroscopic structures and finite strain in a section of increasing metamorphism in the helvetic zone of the central alps switzerland the upper triassic quartenschiefer formation an initially hematite bearing red bed sedimentary rock can be traced from unmetamophosed shale to amphibolite facies schists the magnetic fabrics of 805 specimens agree well in orientation with the foliation normal to kmin kmax kint kmin are principal susceptibilities and the mineral stretching lineation parallel kmax in all metamorphic grades the maximum susceptibility axes are in an approximately n s orientation and were acquired during the miocene north directed nappe transport the effects of the tectonic position and the metamorphic grade on the ams ellipsoid suggests that deformation has a stronger influence on its shape than the metamorphic grade the identification and quantification of the sources of magnetic susceptibility was done with 1 a model calculation 2 the high field low field method and 3 low temperature heating curves the ams of low grade samples is dominated by the paramagnetic minerals mainly mica and the ams of higher susceptible medium grade samples by magnetite the paramagnetic dominated magnetic fabrics correlate well with mica 002 lattice preferred orientations obtained from x ray texture goniometry a one to one correlation between march strains and a magnetic parameter mi ln ki kmaxkintkmin is predicted by a numerical model and verified empirically the magnetic fabrics of well characterized samples can thus be used to quantify the degree of mica preferred orientation using relatively simple magnetic anisotropy equipment

mid pliocene warmth stronger greenhouse and stronger conveyor abstract three million years ago prior to the onset of northern hemisphere glaciation global mean temperatures may have been as much as 3 5 c warmer than at present we present evidence based on the carbon isotopic composition of marine organic matter that atmospheric co2 levels at this time were on average only about 35 higher than the preindustrial value of 280 ppm we also present carbon isotopic evidence for stronger thermohaline circulation in the atlantic ocean during the warmest intervals and propose that the north atlantic conveyor belt may act as a positive feedback to global warming by enhancing sea ice retreat and decreasing high latitude albedo based on our results it seems unlikely that the mid pliocene warm period was a doubled co2 world

magnetic anisotropy of some phyllosilicates magnetic susceptibility anisotropy of susceptibility and hysteresis of single microcrystals of chlorite biotite phlogopite muscovite zinnwaldite and fuchsite were measured in low and high magnetic fields with an alternating gradient force magnetometer micromag their properties are sufficient to account for the low field susceptibility ams of most micaceous rocks nearly all samples show some ferromagnetic contribution at low fields due to inclusions of pseudosingle domain and multidomain magnetite the paramagnetic contribution isolated at high fields usually exceeds the ferromagnetic contribution the paramagnetic susceptibility is intrinsic to the silicate lattice and agrees with values predicted from chemical composition within the limits of error the minimum susceptibility is nearly parallel to c another axis is parallel to b and the third susceptibility usually the maximum is close to a the paramagnetic susceptibility has a disk shaped magnitude ellipsoid with strong anisotropy p 2 the ferromagnetic contributions at low fields have more variably shaped ellipsoids with greater eccentricity p 5 the silicate lattice does not constrain their orientation our technique cannot determine the principal axes of the ferromagnetic component however its principal values usually correspond with the paramagnetic principal susceptibilities in order of magnitude thus the combined paramagnetic ferromagnetic anisotropy recognised in routine studies of ams should faithfully represent the petrofabric of most micaceous rocks nevertheless nearly 10 of our samples have incompatible anisotropy ellipsoids for the silicate host and magnetite inclusions these yield a net inverse ams that does not correctly represent the orientation of the silicate lattice therefore some caution is necessary in petrofabric ams studies of micaceous rocks

overprinting of magnetic fabrics in granites by small strains numerical modelling abstract the anisotropy of magnetic susceptibility ams is used to determine weakly defined mineral preferred orientation fabrics in granites however the effects of small strains superimposed on the low intensity ams fabrics typical of these rocks is not well understood numerical simulations are presented which investigate the effects of small superimposed strains on the shapes magnitudes and orientations of pre existing ams fabrics which are similar to those reported in the literature for undeformed granites a computer generated biotite petrofabric is subjected to progressive strain using march s strain response model for pure shear plane strain axially symmetric shortening and simple shear regimes results indicate that a pre existing ams fabric might be significantly modified or overprinted by small strains 10 15 strain in the pure shear and axially symmetric shortening regimes 0 5 1 0 for simple shear a new ams fabric may develop with an orientation similar to that expected for shearing of an initially isotropic petrofabric at low strains the evolution of the shape of the ams ellipsoid depends strongly on the orientation of the initial petrofabric with respect to the strain framework the ams ellipsoid may evolve towards either oblate or prolate shapes and the evolution in the ellipsoid shape may be reversed during progressive strain this modelling suggests that small strains affecting a pluton following its emplacement could mask ams fabrics developed earlier the results also suggest that in simple shear the orientation of the ams ellipsoid may serve as a shear sense indicator for small strains even if the earlier fabric is not isotropic

using pluton ages to date regional deformations problems with commonly used criteria studies of pretectonic plutons in the foothills terrane central sierra nevada california along with a review of studies on syntectonic and post tectonic plutons indicate that no single criterion can establish the relative timing of pluton emplacement and regional deformation criteria most often used are whether a pluton is deformed cuts regional structures or is associated with porphyroblasts that postdate regional structures however all three types of plutons may 1 appear deformed or nondeformed 2 have contacts that appear to cut structures in the wall rocks and 3 have porphyroblasts in their aureoles that display varied timing relations the ambiguity of these criteria emphasize the need for careful studies of the structures present throughout the pluton and surrounding wall rock with particular attention paid to regions where the pluton contact is at high angles to regional structures porphyroblast cleavage relations are an important tool in this regard but also must be used with caution

zoning patterns and petrologic processes in peraluminous magma chambers hall canyon pluton panamint mountains california zoning patterns of mineral rock and isotopic compositions in the hall canyon pluton in southeastern california are used to determine and discuss the petrologic processes that operate in magma chambers that solidify to form peraluminous plutons the pluton is biotite muscovite granodiorite at lower levels and grades to a 150 m thick upper zone of muscovite granite capped by a 10 to 20 m thick zone of pegmatite aplite and quartz veins at the roof of the pluton mineral and whole rock compositions are essentially homogeneous in the 600 m of exposed lower zone whereas the thinner upper zone roof zone is systematically zoned to more evolved compositions roofward compositions of garnet plagioclase and muscovite in the upper zone roof zone track bulk rock compositions and in the case of muscovite range beyond those that have generally been considered magmatic suggesting that compositional criteria for distinguishing magmatic from secondary muscovite cannot be drawn without consideration of bulk rock composition initial nd values of 18 to 19 for the pluton indicate that the magma sources were entirely intracrustal and lower proterozoic in age the lower zone could represent melt formed by dehydration melting of a biotite rich metaigneous or metapsammitic source rock upper zone roof zone rocks are too evolved to have been unmodified crustal melts even the least evolved was a product of fractional crystallization and further in situ fractionation of the upper zone roof zone produced compositional zoning that defines whole rock sr and nd isochron ages of ca 72 ma slight differences in initial isotopic ratios indicate that lower zone magma and magma parental to the upper zone roof zone were derived from different source rocks and remained separate during most of the subsequent fractionation of the upper zone roof zone melt separation was inefficient leaving behind melt rich mushes that formed rocks that do not bear strong chemical signatures of being cumulate rocks we suggest that the upper zone roof zone was static while it fractionated by loss of residual liquid upward whereas the thicker lower zone may have been capable of convection that stirred the magma as it crystallized preventing it from becoming zoned late in the crystallization of the pluton meter scale layering of the granite formed when biotite muscovite granitic magma was injected as sills into the partly crystalline margin of the chamber near the upper zone lower zone boundary we suggest that peraluminous plutons are more heterogeneous isotopically and usually have less regular zoning patterns than metaluminous plutons because the small effective heights of the magma bodies inhibit convection this results in part from the sill like form of many peraluminous plutons but also from melt production rates in zones of purely intracrustal melting that are so low that there is significant cooling of magma in a chamber between arrival of successive melt batches if resident magma has crystallized to the point of lock up it cannot mix with new arrivals and does not contribute to the height of magma capable of convection systems in which melting is largely the result of advection of heat by mantle derived basalt might be expected to have larger magma supply rates because the volume of partial melt produced is not so strictly limited by the abundance of hydrous phases and by the approach of quartz and feldspar to cotectic proportions in the source and because some of the mafic magma is incorporated into the chamber convection would be favored by the resulting greater thickness of magma capable of flow

kinematics of compressional fold development in convergent wrench terranes abstract kinematic models are presented for compressional fold development in wrench and convergent wrench terranes that relate fold shortening axial rotation and axial extension fold shortening may be derived from final fold geometry existing fold geometry and axial orientation two readily measurable quantities provide the data needed to determine the relative components of shearing and convergence within the fold system analyses utilizing these kinematic models indicate that folds developed in sedimentary rocks in the wrench borderlands of both the rineonada and san andreas wrench faults in central california are the product of strongly convergent wrenching the axes of these folds have been rotated no more than a few degrees during the course of their development in contrast folds developed in the alpine schists along the alpine fault in new zealand and in pleistocene sediments along the southern limit of the san andreas fault suggest an almost pure wrench setting and large 25 axial rotations significant axial extension is inherent in wrench related compressional folds this axial extension is commonly manifest in the form of normal and strike slip faults that are internal to the folds and trend at high angles to the fold axes the relative amount of axial extension diminishes as the degree of convergence increases this axial extension and the associated extensional features can be a diagnostic indication of the influence of wrenching

petrology and li be b geochemistry of muscovite biotite granite and associated pegmatite near yellowknife canada prosperous granite rb sr 2520 25 ma occurs as several plutons 1 380 km2 outcrop area in a thick succession of metamorphosed greywacke mudstone of the yellowknife supergroup the average mineral content of the sparrow pluton in vol is quartz 32 plagioclase 31 k feldspar 24 muscovite 9 biotite 3 and apatite 1 average trace element concentrations in ppm are li 140 be 4 b 28 zn 47 rb 250 sr 76 zr 75 and ba 360 the central portion of the pluton is slightly richer in k sr and ba than the margin li is concentrated in mica li in biotite li in muscovite 4 7 and be and b in muscovite and plagioclase countless pegmatite dikes occur in the sparrow pluton and in schist hornfels to the east the outer limit is marked by the cordierite isograd 9 km from the granite contact dikes vary greatly in size 1 km to a few cm in length in mineral content quartz albite k feldspar muscovite tourmaline beryl spodumene in major element composition especially the na k ratio and in trace element content li 18 5000 ppm be 5 260 ppm b 20 150 ppm compared with prosperous granite the pegmatite bodies are richer in p and rb and poorer in ti fe mg zr and ba dikes rich in tourmaline beryl and spodumene occur in overlapping zones situated progressively farther from the centre of the sparrow pluton the composition of tourmaline is related to host rock the highest concentrations of fe and zn occur in crystals from pegmetite and the highest concentrations of mg and v occur in crystals from tourmalinized schist while those from granite and quartz veins occupy on intermediate position complex compositional zoning is present in some tourmaline crystals in pegmatite estimates of temperature 500 600 c and pressure 2 4 kb of granite emplacement based on the distribution of andalusite and sillimanite in the contact rocks suggest that the final stage of granite emplacement occurred at sub solidus conditions a vaportransport model is proposed to explain the widespread distribution of the pegmatite dikes and their extreme compositional variability some of the pegmatite constituents including li be and b were possibly derived from yellowknife graywacke and mudstone

in situ evidence for the nature of the seismic layer 2 3 boundary in oceanic crust the igneous oceanic crust is typically thought of as comprising two layers an upper crust seismic layer 2 characterized by a rapid increase in seismic velocity with depth and a thicker lower crust seismic layer 3 which is distinguished from layer 2 by both a higher p wave velocity 6 69 0 26 km s l and a much smaller vertical velocity gradient 1 8 km continuous hole drilled into the oceanic crust11 13 and find that at this location the seismic layer 2 3 boundary lies within the sheeted dyke complex where it is associated with gradual downhole changes in crustal porosity and alteration not a litho logical transition from sheeted dykes to gabbro

gravity inversion ams and geochronological investigations of syntectonic granitic plutons in the southern part of the variscan french massif central magnetic fabric analyses gravity inversion associated with chemical u th pb dating and structural observations are carried out to elucidate relationships between faulting and magmatic processes this multidisciplinary study has been undertaken on late carboniferous plutons situated in the southern part of the variscan french massif central fmc the glenat omps and boisset plutons crop out on both sides of the crustal scale sillon houiller fault shf the anisotropy of magnetic susceptibility ams measurements and structural observations show that i the plutons acquired their final structure during the magma crystallization and record a nw se maximum stretching trend ii in the boisset pluton post magmatic fabrics predominate with a nnw sse trending lineation the structural pattern deduced from the ams study is thus consistent with the nw se late orogenic extensional tectonic regime that has been documented in other parts of the fmc during late carboniferous the 3d geological modelling refined by 3d gravity inversion does not show any evidence of rooting of the granites along the shf therefore despite the apparent cartographic relationship between the shf and the three plutons our study does not support a genetic link between fault and plutons it also questions the existence of the shf in this part of the massif central at the time of pluton emplacement and emphasises the dominant role of the regional tectonic framework rather than local faulting as a factor controlling pluton emplacement

kinematic analysis using ams data from a deformed granitoid abstract this study highlights the usefulness of anisotropy of magnetic susceptibility data from a deformed granitoid in deciphering its kinematic evolution vis a vis shear zone data are presented from the chakradharpur granitoid ckpg that lies to the north of the northerly dipping ene wsw striking singhbhum shear zone ssz eastern india whilst the foliation recorded in the field in some parts of the granitoid is parallel to the ssz the magnetic foliation is n54 e 90 mean orientation it is suggested that the magnetic fabric provides a window into an evolutionary stage prior to the final shearing thrusting event the evidence of which is preserved on the mesoscopic scale it is envisaged that during the initial stages of deformation there was simple shear along the evolving ssz that resulted in sinistral strike slip movement the vorticity axis at this stage was steeply plunging and sense of rotation was anticlockwise space was generated in a direction n25 e perpendicular to maximum instantaneous stretching axis into which ckpg emplaced synchronously with regional deformation and evolving ssz with continued deformation there was thrusting along the ssz the vorticity axis flipped to a sub horizontal orientation thus leading to the development of down dip stretching lineations and sheath folds within the ssz however at the same time the vorticity axis responsible for fabric evolution within the syntectonically crystallizing cooling ckpg was steeply plunging with clockwise rotation the magnetic foliation mean orientation n54 e 90 developed during the final stage of syntectonic crystallization however deformation in the region and thrusting along the ssz continued even after the ckpg had fully crystallized and solidified which led to the development of the ene wsw striking mesoscopic foliation that is parallel with the ssz we propose that the angle between the magnetic foliation and the ssz foliation recorded in the field enables to decipher the kinematic vorticity number of flow responsible for fabric evolution of the ckpg it is concluded that transpression was an important mechanism and during regional deformation whilst the ssz developed structures by dominantly simple shear the ckpg underwent dominantly pure shear

accretion of the archean slave province continental rift models have long been applied to the archean slave province of northwestern canada a reassessment of these models shows them to be incompatible with observed geological relations and suggests that contractional tectonic models may be more appropriate than extensional ones regions composed of different rock suites e g orthogneisses vs mafic volcanics are separated by high strain zones recording large displacements it is proposed that the high strain zones separate four distinct terranes that have been juxtaposed during collisional orogenesis from west to east these include the anton terrane interpreted as an archean microcontinent the sleepy dragon terrane possibly an exhumed more eastern part of the anton terrane the contwoyto terrane a westward verging fold and thrust belt containing tectonic slivers of greenstone volcanics and the hackett river volcanic terrane interpreted as an archean island arc the contwoyto and hackett river terranes represent a paired accretionary prism and island arc system that formed above an east dipping subduction zone these collided with the anton microcontinent producing a basement nappe expressed as the sleepy dragon terrane during the main accretion event within the slave province the whole tectonic assemblage was intruded by late kinematic to postkinematic granitoids

the montagne noire migmatitic dome emplacement french massif central new insights from petrofabric and ams studies in the southern french massif central the montagne noire axial zone is a ne sw elongated granite migmatite dome emplaced within visean south verging recumbent folds and intruded by syn to late migmatization granitoids the tectonic setting of this dome is still disputed thus several models have been proposed in order to better understand the emplacement mechanism of this dome petrofabric and anisotropy of magnetic susceptibility ams studies have been carried out in the granites and migmatites that form the dome core magmatic texture and to a lesser extent weak solid state texture are dominant as a paramagnetic mineral biotite is the main carrier of the magnetic susceptibility on the basis of 135 ams sites the magnetic fabrics appear as independent of the lithology but related to the dome architecture coupling our results with previous structural and geochronological studies allows us to propose a new emplacement model between 340 325 ma the palaeozoic series underwent a compressional deformation represented by nappes and recumbent folds involving the thermal event leading to partial melting until 325 310 ma the dome emplacement was assisted by diapiric processes an extensional event took place at 300 ma after the emplacement of the late to post migmatitic granitic plutons in the northeast side of the dome a brittle normal dextral faulting controlled the opening of the graissessac coal basin

composite magnetic fabrics from s c mylonites magnetic anisotropy data are presented for samples of s c mylonites from a shear zone developed in the veiga granodiorite a late kinematic pluton located in the northern part of the iberian variscan belt spain the magnetic susceptibility is geometrically represented by an ellipsoid whose principal axes k 2 kint 1 kmi often show a one to one correlation with the principal directions x y and 2 f finite strain we report an exception to this rule since our results reflect composite magnetic fabrics arising from the contribution of both the c and s structures the magnetic foliation defined as the plane normal to k i shows an intermediate orientation between the c and s planes and rotates towards the orientation of the c planes as finite strain increases the magnetic lineation parallel to k and the stretching lineation present a similar trend but different values of plunge copyright 0 1996 elsevier science ltd

psilonichnus upsilon frey curran and pemberton 1984 burrows and their environmental significance in transgressive albian lower cretaceous sands of glanow stroniczki cracow upland southern poland abstract a considerable upper albian sand lithosome developed on the external margin of the albian epicontinental sea in the polish jura chain miechow synclinorium southern poland is recognized as a shallowing up sequence within the generally transgressive albian sands in particular burrows described as the ichnospecies psilonichnus upsilon frey curran and pemberton 1984 have a particular ecologic and sedimentological significance and constitute the primary focus of this paper in the glanow stroniczki section cracow upland southern poland such burrows seem to be a crucial tool in the interpretation of basin bathymetry indicating a foreshore to backshore beach facies and probably recording a temporary break in sedimentation they were infilled by sand with pebbles or pebble material potentially during hurricane or strong storm action lithification of the burrow infillings and their enveloping concretionary halos should have progressed in a beachrock mode the glanow horst composed of jurassic biohermal limestones was likely an emerged element that neigboured or was surrounded by a beach with active fauna the psilonichnus upsilon burrows in glanow stroniczki closely resemble burrows of the modern ghost crab ocypode in modern settings representatives of ocypode are encountered in extremely shallow marine foreshore intratidal and backshore supratidal to dune environments the ichnological data from glanow stroniczki suggests that fauna behaviorally similar to ocypode may have occupied the beach backshore and to a lesser extent the foreshore zone near the emerged glanow horst

magnetic fabrics in the cabanas granite ne brazil interplay between emplacement and regional fabrics in a dextral transpressive regime the late neoproterozoic cabanas granite northeastern brazil is a tabular body that was emplaced south of the dextral east pernambuco shear zone system anisotropy of magnetic susceptibility ams measurements reveal that the cabanas granite has fabric patterns more complex than usually reported in plutons intruded in similar settings most structures have ew to ene trending magnetic lineations consistent with the overall regional structural direction in the north these structures parallel the mylonitic fabric encountered in shear zones that bound or cross cut the pluton in the central and southern portions of the pluton magnetic foliation trajectories the overall banded disposition of the iso susceptibility lines and shape parameters of the ams ellipsoids suggest that the cabanas granite was subjected to ene trending folding along with its underlying and enclosing country rocks it is concluded that emplacement took place during regional dextral transpression a secondary but well developed family of structures consists of n to nw plunging lineations which is interpreted to represent the trace of the vertical conduits that fed the pluton this study emphasizes the utility of the ams to unravel both the internal structure of low anisotropy plutons and the interplay between emplacement and regional straining during magma crystallization

geology and gravity modeling of the logrosan sn w ore deposits central iberian zone spain abstract sn w granite hosted ore deposits are characterized by the occurrence of pegmatites stockworks and quartz veins within a granitic cupola and its surrounding host rocks a regional exploration tool for these deposits consists of targeting syn to late orogenic specialized s type hidden shallow granites by geophysical methods however gravity as a tool for brownfield type exploration in a mature granite related ore setting has not been widely used the logrosan area central iberian zone provides a perfect case scenario with sn w endo and exogranitic ore deposits within a relatively small scale realm we suggest that the understanding of the subsurface of the logrosan area provides a key tool to develop a more comprehensive geological and metallogenic model for the ore deposits in addition a better explanation for the mineral evolution and the sn w ore precipitation can be achieved by comparing the chemical and textural features of ores from several of the logrosan deposits field gravity and geologic data allowed the modeling of the hidden granite bodies combining this information with detailed mineralogical geochemical data and ore deposit modeling has allowed a definition of targets for probable new sn w deposits all within a few kilometers of the main intrusion center

magnetic fabrics in the holum granite vest agder southernmost norway implications for the late evolution of the sveconorwegian grenvillian orogen of sw scandinavia abstract the holum granite vest agder southernmost norway has been considered to be the oldest 980 ma undeformed post tectonic pluton of a late sveconorwegian granitoid series that form two belts in southern norway and sw sweden an integrated structural study of this granite pluton based on a survey of its anisotropy of low field magnetic susceptibility ams complemented by microstructural observations optical microscopy and rock magnetism investigations including measurements of partial anhysteretic remanent magnetization and its anisotropy paarm is presented here the magnetic susceptibility and the ams of the holum granite are carried by large magnetite grains coaxiality between the magnetite controlled ams fabric and the rock fabric is verified which allows the use of the former as a proxy for the latter microstructural evidence of a deformation continuum in the granite from magmatic to solid state and homogeneity and continuity of the ams fabrics across the pluton demonstrate that the holum granite is not post tectonic but that it was emplaced in a tectonic strain field a model of emplacement and deformation during the last sveconorwegian regional folding phase evidenced in the country rocks of the pluton is proposed

age and origin of the well preserved organic matter in internal sediments from the silesian cracow lead zinc deposits southern poland the molecular and petrographic characteristics of organic matter in internal sediments from the mississippi valley type lead zinc deposits in southern poland reveal immature and well preserved organic matter huminite reflectance values of organic matter in all internal sediments are low with a mean value of 0 29 corresponding to a lignite range of coalification most organic compounds in the organic matter e g cadalene retene simonellite perylene and sitosterol and its transformation products stigmastanol and stigmasta 3 5 dien one as well as lignin degradation compound products e g benzoic acid vanillin 4 benzaldehyde benzenedicarboxilic acids and hydroxybenzoic acids are of terrestrial origin monosaccharides with dominant and glucose were identified as possible remnants of cellulose degradation products suggesting an excellent state of organic matter preservation given that monosaccharides are preserved only under conditions of limited oxygen after sedimentation resulting from the rapid accumulation of internal sediments in meteoric paleokarst cavities followed by insignificant diagenesis petrologic and palynological data on internal sediments clearly indicate a middle triassic age for organic matter and for the development of a triassic meteoric karst system immediately after anisian carbonate sedimentation

fabric development in syn tectonic intrusive sheets as a consequence of melt dominated flow and thermal softening of the crust the temperature dependence of ductile deformational processes suggests that the thermal anomaly associated with a cooling syn tectonic intrusion will produce a crustal low viscosity horizon that will concentrate deformation in the vicinity of the pluton during cooling this effect should be most prominent when magma is present but should also occur after solidification of the magma when flow is by solid state processes this paper evaluates this hypothesis for sheet like intrusions using one dimensional time dependent thermal models and accompanying predictions of viscosity vs time history based on experimental flow laws these models predict that for systems with an initial normal geothermal gradient e g extensional systems strike slip systems or thrust systems with low displacement rates the base of a large plutonic sheet cools more slowly than the top and fabric development should be most pronounced on the floor of the pluton in contrast in megathrust systems where displacements are sufficiently rapid to produce temperature inversions cooling is also upside down and fabric development should preferentially occur along the top of plutonic sheets moreover when a pluton is emplaced within a zone of inverted isotherms the heat may be trapped within the inversion a natural system characterized by this history should show a sharp thermal front coincident with the top of a paleo temperature inversion if a pluton is weaker than its country rock it will form a weak horizon in the crust throughout its cooling history and the plutonic sheet should take up the bulk of the deformation throughout its cooling history if a pluton is stronger than its country rock under conditions of solid state flow however models predict a two phase deformational history prior to solidification the deformation should be concentrated in the pluton with the magma representing a weak horizon in the crust but upon crystallization the pluton should become relatively rigid with respect to its country rock and deformation should be concentrated in the wall rocks these two cases predict markedly different structural histories and the history could easily be misinterpreted in the first case static mineral growth might be prominent in the wall rocks and these textures could be misinterpreted as evidence for post tectonic emplacement in the second case the extensive high t deformation of the wall rocks could be readily ascribed to non tectonic emplacement related deformation rather than a consequence of syn tectonic emplacement the model predictions are tested with three examples of well exposed plutonic sheets a neogene extensional system in death valley california and two megathrust systems in southern alaska border ranges fault system and mclaren metamorphic belt structural observations from these systems are broadly consistent with the model predictions and lend support to first order characteristics of the models nonetheless more sophisticated 2 d models of the coupled thermal mechanical system are needed to thoroughly test the hypothesis

composite magnetic anisotropy fabrics experiments numerical models and implications for the quantification of rock fabrics housen b a richter c and van der pluijm b a 1993 composite magnetic anisotropy fabrics experiments numerical models and implications for the quantification of rock fabrics tectonophysics 220 1 12 magnetic fabrics from rocks with multiple mineral preferred orientations may have anisotropy ellipsoids whose shape and orientation arise from the addition of two or more component fabrics our numerical models and experiments demonstrate that such composite magnetic fabrics do not directly reflect the shapes and or orientations of the individual mineral fabrics and we provide criteria for the recognition and interpretation of composite fabrics in natural rocks these criteria include 1 the orientation of the maximum susceptibility axis is located at the intersection of two planar fabrics and 2 the shape of the susceptibility ellipsoid changes from oblate to prolate and the degree of anisotropy decreases as the relative intensity of two planar component fabrics becomes equal and as the angle between the planar fabrics increases composite magnetic fabrics are observed in the shales and slates of the martinsburg formation lehigh gap pennsylvania modeling of the ams anisotropy of magnetic susceptibility and arma anhysteretic remanent magnetization anisotropy behavior constrains the relative degree of anisotropy of the bedding parallel and cleavage parallel fabrics in particular arma model results allow a good estimate of magnetite fabric strength we conclude that in the presence of composite magnetic fabrics quantitative measures of finite strain in deformed rocks are limited by the ability to accurately determine the degree of anisotropy and relative susceptibility of each component fabric such determinations require knowledge of the mineral s that are responsible for the measured magnetic fabric and their behavior during deformation

the effects of callianassa bioturbation on the preservation of carbonate grains in davies reef lagoon great barrier reef australia abstract coring air life excavation and tracer sediment experiments in the lagoon floor sediments of davies reef revealed that callianassid shrimp had produced during their feeding a 5 60 cm thick surface layer of moderately to poorly sorted gravel free sediment above very poorly sorted gravelrich sediment the subsurface gravel is epilithic in origin close to reef framework but consists predominantly of infaunal molluscs through most of the lagoon these infaunal skeletons tend to be buried rapidly in a well preserved state escaping the microboring that attacks all grains on the surface two geologically significant points emerge first the surface layer will not get preserved in its present form and any analyses of surface samples can give a false impression of the accumulating sedimen pile and the prevailing hydraulic regime and second the combination of continuous fine sediment recycling and surface microboring can lead to a bias in the fossil reefal limestone record with epilithic organisms seemingly subordinate to infaunal molluscs

evidence for archean ocean opening and closing in the southern slave province archean mafic volcanic and plutonic rocks of the cameron and beaulieu river greenstone belts outcrop in the southern slave structural province of the canadian shield lower portions of the greenstone belts have ophiolitic characteristics but young felsic units may represent superimposed arc magmatism the greenstone belts are separated from older circa 2 7 3 2 ga quartzo feldspathic gneisses of the sleepy dragon complex by a regional decollement zone patterson lake structural complex consisting of deformed mafic volcanic rocks thin slivers of gneiss ultramafic rocks and banded iron formation mixed in a highly deformed phyllonitic and phacoidally cleaved metapelitic matrix high synmetamorphic strains are indicated by abundant intrafolial folds transposed layering rare sheath folds and by the parallelism of elongated primary features and metamorphic mineral lineations the patterson lake structural complex is similar to melanges of phanerozoic mountain belts adjacent quartzo feldspathic gneisses are strongly mylonitized the melange and deeper mylonites formed when the greenstone belts were emplaced as thrust sheets wildflysch shed from tips of emergent thrusts was in part incorporated into the basal melange as the allochthon overrode its own detritus continued compression involved the basement in the deformation uplifting the sleepy dragon complex in a structural culmination mantled by the imbricated greenstone stack late granodioritic to granitic intrusions formed regional thermal aureoles which overprint earlier metamorphic fabrics

ghost shrimps decapoda axiidea callianassidae as producers of an upper miocene trace fossil association from sublittoral deposits of lake pannon vienna basin slovakia numerous trace fossils are described from the late miocene sediments of the bzenec formation exposed at the gbely section the vienna basin slovakia during deposition of the sediments the area was part of the large long lived brackish to freshwater lake pannon most of the trace fossils are attributed herein to egbellichnus jordidegiberti igen et ispec nov and are interpreted as burrows produced by decapod crustaceans specifically by a ghost shrimp of the family callianassidae this interpretation is based on two independent lines of evidence environmental requirements of large bioturbators and the burrow morphology itself the new ichnotaxon is distinguished from other related ichnotaxa by a combination of typically inclined roughly at an angle of 45 cylindrical burrows absence of lining and tunnels making loops or bends at approximately right angles the burrow systems at gbely document the survival of ghost shrimp long after the closure of all seaways and the origin of lake pannon as today no ghost shrimp are known from long lived brackish lakes egbellichnus from gbely is the only although indirect record of ghost shrimp from a brackish lake environment reported so far

structural patterns and tectonic evolution of supracrustal domains in the archean slave province canada a new plate tectonic model accounts for lithological relations and regional structural patterns in late archean supracrustal domains of the slave province multiple dykes and pillowed mafic flows most common in the western part of the province suggest sea floor spreading the mafic volcanics lying in narrow homoclinal belts stratigraphically below more extensive turbidites are viewed as megaxenolithic remnants of oceanic crust preserved on the periphery of granitoid plutons and blocks of sialic crust closure of an oceanic basin was marked by emplacement of the granitoid plutons and coeval felsic volcanics the latter predominating over mafic volcanics in northeastern domains the felsic calc alkaline magmas may have risen from a shallow dipping subduction zone westerly verging folds westerly convex fold arcs and inclinations of later foliations particularly in lower level rocks of higher metamorphic grade are in accord with underthrusting to the east the zone of underthrusting shifted progressi

syn acadian emplacement model for the south mountain batholith meguma terrane nova scotia magnetic fabric and structural analyses the anisotropy of magnetic susceptibility and the structural geology of the late devonian south mountain batholith meguma terrane nova scotia are used to characterize its emplacement and structural evolution the south mountain batholith is the largest peraluminous granitoid complex within the appalachian orogen it is a composite batholith made up of stage 1 granodiorites and monzogranites and stage 2 leucomonzogranites and leucogranites the anisotropy of magnetic susceptibility was used to map the biotite petrofabric at the scale of the batholith the biotite fabric pattern is similar to the pattern of folding and shearing of the feldspar megacryst foliation documented at the outcrop scale in the stage 1 plutons the magnetic foliation is deformed into a girdle about the horizontal northeast southwest trending magnetic lineation which is parallel to regional fold axes and extension lineations in the country rocks in the stage 2 plutons a horizontal northeast southwest to east west trending magnetic lineation is also present but the horizontal orientation of the magnetic foliation is widely preserved the folding and shearing of the foliations and the horizontal northeast southwest trending lineation that is pervasive throughout the south mountain batholith are interpreted to record acadian tectonic deformation of the plutons as they crystallized acadian deformation continued during the latest stages of crystallization resulting in the localization of mineral deposits and greisens along shear zones faults and joints a model is presented for the syntectonic emplacement of the south mountain batholith as a laccolithic complex

a review of criteria for the identification of magmatic and tectonic foliations in granitoids abstract foliations in granitoids can form by magmatic flow submagmatic flow high temperature solid state deformation and moderate to low temperature solid state deformation a review of previous work suggests that no single criterion can consistently distinguish foliations in granitoids formed by flow during ascent diapiric emplacement and expansion emplacement during regional deformation or regional deformation post dating emplacement however a magmatic origin is favoured for foliations defined by the alignment of igneous commonly euhedral minerals particularly where the foliation is parallel to internal or external pluton contacts foliations formed during expansion or ballooning of diapirs may be strictly magmatic in origin although some studies suggest that solid state deformation also may occur if so we would hope to find evidence of deformation of crystal melt systems and that the solid state deformation occurred at high temperatures the inference of syntectonic foliations is most convincing where magmatic and high temperature solid state foliations are subparallel these foliations are continuous with regionally developed foliations in the wall rocks synkinematic porphyroblasts are present in the wallrocks and igneous minerals have the same age as metamorphic minerals associated with the regional cleavage a strictly tectonic origin for foliations in granitoids is favoured when the foliation is defined by metamorphic minerals no alignment of igneous minerals occurs the foliation is locally at high angles to pluton wallrock contacts and the foliation is continuous with a regionally developed cleavage

tabular intrusion and folding of the late archaean murehwa granite zimbabwe during regional shortening the murehwa granite belongs to the late archaean chilimanzi suite of granites that occupy more than 50 of the zimbabwe craton the granite has compositional layers on metre to tens of metre scales with generally shallow dips and dip directions towards the centre of the granite near its margins the layering is systematically folded about sub horizontal east west axes microcline phenocrysts are generally strongly aligned parallel to the layering but locally crosscut the layering because they are axial planar to the folds crystals are not significantly deformed fabrics are thus magmatic the granite was intruded in a tabular sheet that may have been only about 6 km thick and fed by dykes contrary to previous concepts of diapirism ballooning for some archaean granites of the zimbabwe craton the systematic orientation of magmatic folds and axial planar fabrics demonstrate that the granite was intruded during regional north south shortening this shortening is consistent with the orientation of cratonic scale fractures that were intruded by the great dyke within 25 ma of the intrusion of the murehwa granite the granite may have intruded in a relatively short interval of less than 1 26 ma within the longer duration of the entire chilimanzi granite event

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

granite emplacement and its relation with regional deformation in the aravalli mountain belt india inferences from magnetic fabric abstract this contribution presents field microstructural and anisotropy of magnetic susceptibility ams data from the godhra granite a ca 1 ga pluton at the southern margin of the aravalli mountain belt western india that lies near the central indian tectonic zone citz the northern and southern margins of the granite are high strain zones with north dipping e w striking foliations and nw plunging stretching lineations the presence of preferentially oriented feldspars suggests that the granite was subjected to magmatic deformation during its emplacement high temperature solid state deformation fabrics are recorded from microstructural studies which imply that the granite is deformed ams data show magnetic foliations and magnetic lineations in the granite with orientations similar to the field data the magnetic foliation in the granite is parallel to the d 3 foliation in the gneissic host rock both the stretching lineations and the magnetic lineations at the granite margin high strain zones are parallel with the axes of d 3 reclined folds in the gneiss therefore the emplacement of the godhra granite is inferred to have taken place syntectonically while the gneiss was undergoing the d 3 phase of deformation the orientation and character of these lineations and the vergence of the d 3 folds imply oblique simple shear which is inferred to have controlled the emplacement of the granite the magnetic fabric data are compared with the regional structural trends of the metasedimentary rocks of the southern aravalli region and the available geochronological data from rocks of the southern aravalli region are summarised based on this information it is suggested that the emplacement of godhra granite deformation of the southern parts of aravalli mountain belt and tectonothermal events along the citz and rodinia supercontinent assembly were related events

emplacement modes of the ladinian plutonic rocks of the dolomites insights from anisotropy of magnetic susceptibility abstract in the dolomites eastern southern alps italy a diffuse middle triassic igneous activity is now present mostly as lava flow and pyroclastic successions with rare shallow depth intrusive bodies cropping out at predazzo monzoni and cima pape areas in this work the emplacement modes of the predazzo and monzoni bodies were investigated by means of petrographic and anisotropy of magnetic susceptibility ams data coupled with a field geological study the presence of intrusive rocks in between these two bodies and the continuity of the metamorphic aureola from west of the predazzo to east of the monzoni body suggest that they are parts of a 20 km wide sw ne oriented continuous pluton sub parallel to ladinian strike slip faults ams and petrographic data from the predazzo body are consistent with a multistage ring dyke emplacement mode with areas of upward flow of the magma located in the nw and ese part of the intrusion whereas in the southern sector of the pluton our data suggest prevalently horizontal flows in general the predazzo sheets indicate either upward magma flow or along strike lateral magma transport and the round shape suggests no influence of ladinian tectonic structures on the contrary the ene wsw elongated shape of the monzoni body was controlled by the occurrence of strike slip faults associated with ladinian tectonics the feeder being likely located at the ne edge of the body however the absence of deformation at the field and micro scale is consistent with a post ladinian tectonics timing of emplacement as for the predazzo pluton

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

timing and nature of magmatic fabrics from structural relations around stoped blocks abstract structural relations around several large 100 m stoped blocks in the granodiorite of castle creek sierra nevada california suggest that magmatic fabrics formed as or after the space making phase of pluton emplacement had ended the stoped granite blocks are approximately 360 m below the exposed pluton roof magmatic foliations in granodiorite surrounding the blocks commonly follow km scale orientation trends to within 1 m of block contacts where they become deflected parallel to the block boundaries locally undeflected foliations occur within a few centimeters of block contacts mafic enclave fabric ellipsoid intensities 0 2 we draw the following conclusions concerning magmatic fabrics in the granodiorite of castle creek 1 magmatic fabrics formed during and or after the latest stages of pluton emplacement and thus contain little or no information about space making processes 2 magmatic fabrics had poor strain memory and 3 during magmatic fabric formation pluton strains were partially decoupled from host rock strains published data from other plutons indicate that these relationships may be common particularly in the brittle upper crust it follows from these conclusions that even in the best case magmatic fabrics contain only qualitative information about pluton emplacement mechanisms regional tectonics and internal magma chamber processes interpretations of magmatic fabrics must be corroborated by evaluating causes kinematics and magnitudes of syn emplacement host rock deformation in the worst case the causes of magmatic fabrics cannot be uniquely determined

assessment of petrophysical surface data of the harsit granitoid in trabzon in northeastern turkey the harsit granitoid in northeastern turkey comprises four separate granite units that are apparently unfoliated the harsit granitoid was investigated here by using microstructural petrofabric and anisotropy of magnetic susceptibility ams data the structural data of the granitoid were found to be highly compatible with the zonation recognized from ams measurements the orientation of magnetic fabrics within the granite units indicates that tectonic deformation might have occurred coevally with the magmatic emplacement of the intrusion when we evaluated the manners on the scale of the pluton that the disruption took place in the form of uplifting probably related to a rapid migration of the volcanic front and the documented change from deep sea sedimentation predominant until late cretaceous to shallower environments during the paleocene the possible tectonic control of fault systems on the ascent and emplacement of the granitic magma in the study area however cannot be completely ruled out because the harsit granitoid is situated at or very near the naf systems in northern anatolia in any case the intrusion is clearly discordant to the regional deformational features formed during the collisional events between the eurasia and anatolia plates in northern turkey

composite magnetic fabrics and s c structure in granitic gneiss of cerro de los viejos la pampa province argentina the cerro los viejos gneiss in la pampa province argentina is a mylonitized granite which lies along the late paleozoic deformed boundary zone between the patagonia block and mainland gondwana to the north petrofabric and anisotropy of magnetic susceptibility ams analyses were compared for this body unexpectedly it was found that the kmin poles deviate from the poles of the main foliation s1 by about 25 similarly but not so noticeably the kmax poles trend ne sw with a near horizontal plunge whereas the principal lineation l1 plunges gently sw this unusual situation is attributed to the existence of superimposed fabrics arising from s c structures examination of oriented cores in a modified universal stage and of oriented thin sections revealed that the kmin poles are clearly associated with a younger but less obvious metamorphic c foliation s2 biotite and magnetite the main contributors to the ams response are distributed along both s1 and s2 the dominance of s2 in the ams anisotropy suggests that magnetite is preferentially distributed on s2

timing of plutonism deformation and metamorphism in the yellowknife domain slave province canada u pb zircon titanite and monazite ages for plutonic rocks are used to constrain the timing of post 2660 ma deformational and metamorphic events in the yellowknife domain southern slave province diorite and tonalite plutons of the defeat suite yield ages of 2628 3 and 2624 3 ma older than previous less precise estimates for this suite of ca 2618 2620 ma the defeat suite plutons crosscut and postdate upright f1 folds in turbidites of the ca 2680 2660 ma burwash formation d1 deformation is therefore bracketed between 2660 and 2630 ma the d1 event significantly predates deposition of polymict conglomerates of the jackson lake formation a second folding event f2 represented by northwest to north trending steeply plunging folds of bedding and d1 structures affected the area after intrusion of the hidden lake pluton at 2606 2 ma and synchronously with intrusion of the 2596 2 ma sparrow lake pluton a member of the two mica granite prosperous suite the time of initiation and the duratio