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

distinguishing diapirs from inflated plutons an integrated rock magnetic fabric and structural study on the roundstone pluton western ireland granitoid plutons account for much of the continental crust and are critical in the generation of several economic resources despite over a century of research the fundamental process by which large felsic bodies intrude remains controversial two contrasting models persist 1 mass ascent and subsequent cooling of magma diapirism 2 sheet ascent and subsequent emplacement laccoliths the latter hypothesis is different from the former as distinct ascent and emplacement processes must occur and be identifiable traditional field methods rarely allow this important distinction to be made we present field petrographic and anisotropy of magnetic susceptibility data from the roundstone pluton connemara western ireland which was previously considered a diapiric intrusion the new data reveal anomalous subvertical magmatic lineations in the core of this circular intrusion as well as a suite of magmatic and submagmatic fabrics that parallel nnw sse country rock faults and coeval g2 sheets within the pluton we deduce that these structures reflect a distinct centralized ascent process along a nnw sse conduit lateral emplacement and pluton inflation followed ultimately forming a punched laccolith we conclude that the combined application of the above techniques provides a unique insight into pluton architecture that removes ambiguity between contrasting diapiric and inflated pluton models supplementary material complete rock magnetic data tables and sample site coordinates irish grid are available at http www geolsoc org uk sup18837

melt extraction from crystal mushes numerical model of texture evolution and calibration of crystallinity ordering relationships abstract mechanical crystal melt interactions in magmatic systems by separation or accumulation of crystals or by extraction of interstitial melt are expected to modify the spatial distribution of crystals observed as phenocrysts in igneous rocks textural analysis of porphyritic products can thus provide a quantitative means of interpreting the magnitude of crystal accumulation or melt loss and reconstructing the initial crystal percentage at which the process occurred we present a new three dimensional numerical model that evaluates the effects of crystal accumulation or interstitial melt removal on the spatial distribution of crystals both processes lead to increasing apparent crystallinity but also to increasing spatial ordering expressed by the clustering index r the trend of progressive crystal packing deviates from a random texture trend produced by static crystal nucleation and growth and it is universal for any texture with straight log linear crystal size distribution for sparse crystal suspensions 5 vol crystals r 1 03 up to 97 melt can be extracted corresponding to a new crystallinity of 65 vol and r 1 32 when the rheological threshold of crystal interlocking is reached for initially crystal rich suspensions the compaction path is shorter this is because the initial crystal population is more aggregated and it reaches the limit of interlocking sooner crystal suspensions with 35 vol crystals cannot be compacted without mechanical failure these results illustrate that the onset of the rheological threshold of magma immobility strongly depends on the spatial configuration of crystals in the mush the primary rigid percolation threshold 35 vol crystals corresponds to touching or interlocking crystal framework produced by in situ closed system crystallization whereas the secondary rigid percolation threshold 35 to 75 vol crystals can be reached by compaction which is particularly spatially efficient when acting on sparse crystal suspensions illustrative quantitative evaluation of the crystallinity clustering relationships to representative porphyritic granites from a single intrusive unit of the krkonose jizera pluton central europe reveals a single crystal accumulation path starting at low initial crystallinity 5 7 vol k feldspar phenocrysts with 24 84 melt extracted leading to the observed crystallinity of 9 26 vol by contrast a camptonite dyke from the ceske st edoho i volcanic province has experienced the onset of crystal accumulation later 18 vol amphibole crystals and lost 23 interstitial melt only the combination of modal and clustering analysis offers a sensitive tool for identifying differentiation processes in natural magma chambers and here it illustrates examples of mechanically dominated open system vs in situ nearly closed system crystallization from two contrasting magmatic settings

magnetic fabric and 3d geometry of the hombreiro sta eulaliapluton implications for the variscan structures of eastern galicia nw spain abstract in this paper the internal structure and 3d geometry of the hombreiro sta eulalia granitic pluton hercynian belt nwspain are described characterization of the internal structure was performed from surface data based on microstructural analysis and anisotropy of magnetic susceptibility studies the geometrical features of the pluton morphology at depth were derived from gravity data the pluton is made up of paramagnetic granites and leucogranites k values ranging between 1 1 and 13 3 10 5 si with well developed magnetic fabrics anisotropy degree p 1 05 for 78 of the sampling localities the results obtained enable us to depict a flat lying magnetic structure with associated n120 e trending magnetic lineations the gravity survey corroborates the subhorizontal laminar geometry of the pluton which has an estimated thickness of 2 km and an almost planar floor the 3d morphology is elongate at depth parallel to the linear internal fabric this would imply that magma emplacement took place along this preferential direction whereas the deepest zones of the pluton trend wnw ese elongate parallel to regional 1 it is almost rootless we present data showing that the hombreiro sta eulalia pluton emplacement was closely related spatially and chronologically along with other granitoid plutons from the lugo dome with two major structures of eastern galicia the basal shear zone of the mondonedo nappe and the extensional vivero fault

linking microcracks and mineral zoning of detachment exhumed granites to their tectonomagmatic history evidence from the salihli and turgutlu plutons in western turkey menderes massif abstract the menderes massif western turkey is a metamorphic core complex that displays linked syntectonic plutonism and detachment faulting fabrics in s type peraluminous granites salihli and turgutlu in the detachment alasehir footwall change from isotropic to protomylonitic to mylonitic towards the structure samples from the isotropic and protomylonitic zones were imaged in transmitted light cathodoluminescence cl backscattered bse and secondary electrons se and show that these rocks contain abundant microcracks and that plagioclase grains have zoning consistent with magma mixing the granites contain fluid inclusion planes fips myrmekite replacing plagioclase and the removal of blue luminescence in k feldspar along microcracks and grain boundaries calcite and hydrous minerals commonly fill microcracks the samples record features that formed due to 1 magma crystallization and ductile deformation fips mineral zoning 2 changes in p and or t impingement and stress induced microcracks in protomylonitic rocks and 3 differences in intrinsic mineral properties radial cleavage blunted and deflected microcracks overprinted microcracks indicate exhumation during pulses the middle miocene ages of these granites reported elsewhere are similar to those from large scale extensional structures in greece s cycladic massif the menderes and cycladic core complexes may have developed simultaneously due to the widespread intrusion of subduction related granitoids

multiple injections of magmas along a hercynian mid crustal shear zone sila massif calabria italy abstract syn tectonic late hercynian granitoids emplaced at mid crustal level through multiple dyke injections are well exposed in a 1 km long section in the southern sila massif calabria italy the fieldwork study permitted us to reconstruct the following order of emplacement i granodiorites with euhedral kfs megacrystals grd1 in the main text and heterogranular granodiorites with coarse rounded pl and kfs in a fine grained biotite rich matrix grd2 ii granodiorites with a nearly homogeneous grain size grd3 iii tonalite and iv granite both in the wall rock represented by migmatitic paragneisses and in the deformed granitoids the foliation attitude is substantially homogeneous striking about n140 with a dip of 50 60 to the ne the magmatic lineation is defined by the preferred alignment of euhedral feldspars parallel to the mineral lineation observed in the host rocks micro and meso structural analyses indicate that foliation evolved from melt present to solid state conditions feldspar tiling s c structures type structures c axis quartz orientations commonly suggest a top to the west sense of shear during magma injection and deformation under decreasing temperatures age of magma emplacement is constrained by u pb datings at 304 300 ma coeval with the regional metamorphic peak foliated granitoids and wall rock are intruded by poorly foliated hbl gabbro and finally by undeformed leucogranite pegmatite and felsic porphyritic dykes new u pb datings of the last intrusion event indicate an age of emplacement of 281 8 ma providing a minimum estimate for the end of the shear strain at mid crustal level

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

estimation of modified fluid factor and dry fracture weaknesses using azimuthal elastic impedance abstractwe consider the problem of fluid identification and fracture detection in unconventional reservoir tight gas sand and shale gas characterization we begin with a simplification of the stiffness parameters and the derivation of a linearized reflection coefficient and azimuthal elastic impedance ei the accuracy of the simplification is confirmed in application to gas bearing fractured rocks with low porosity and small fracture density we have developed a modified fluid factor that is more sensitive to fluid type and less influenced by porosity a two step inversion workflow is evaluated based on the derived linearized reflection coefficient and azimuthal ei including 1 a damped least squares inversion for azimuthal ei constrained by an initial model and 2 a bayesian markov chain monte carlo inversion for the modified fluid factor and dry fracture weaknesses stability and accuracy are examined with synthetic data from which we conclude that the modified fluid factor and dry fracture we

microstructures of melt bearing regional metamorphic rocks the most reliable microstructural criterion for the former presence of felsic melt in regional migmatites is a three mineral quartz k feldspar and sodic plagioclase aggregate in veinlets several other criteria are potentially reliable namely 1 euhedral crystals of feldspar precipitated from liquid or peritectic minerals e g garnet cordierite orthopyroxene k feldspar lining felsic protoleucosomes 2 inclusionfree euhedral overgrowths of feldspar precipitated from liquid or peritectic minerals e g garnet cordierite orthopyroxene k feldspar on residual grains of the same minerals with abundant inclusions in the mesosome 3 aligned euhedral feldspar crystals 4 simple twinning in k feldspar 5 dihedral angles of 60 subtended where a grain of feldspar and or quartz inferred to have pseudomorphed former melt meets two grains of other minerals 6 cuspate volumes of quartz k feldspar or sodic plagioclase especially where surrounded by grains inferred to have been residual during melting 7 veinlets of inferred former melt now mineral pseudomorphs consisting of one of quartz k feldspar or sodic plagioclase preferably though less commonly involving two or three of these minerals along grain boundaries or along inferred former intragranular fractures 8 biotite pseudomorphed by feldspar 9 veinlets of plagioclase that is more sodic than plagioclase grains in the adjacent rock 10 plagioclase with oscillatory zoning 11 microgranophyric intergrowths of quartz and alkali feldspar in patches or veinlets between primary grains 12 symplectic replacement aggregates that can be explained by reactions between peritectic grains and cooling melt and 13 melanosome patches and layers from which leucosome has been extracted however all these criteria must be interpreted with care some other proposed criteria are questionable for example 1 random mineral distributions 2 grain size increase 3 interstitial grains 4 corroded relics of inferred reactant mineral grains surrounded by areas of quartz k feldspar or sodic plagioclase 5 projections into a mineral grain 6 lobes of myrmekite and 7 plagioclase rims with a constant sodic composition occurring on plagioclase cores that are more calcic and or of variable composition

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

multistage emplacement of the mount givens pluton central sierra nevada batholith california the ca 90 ma mount givens pluton is one of the largest granodioritic to granitic intrusions in the sierra nevada batholith of california emplacement of the pluton occurred during a critical time in the tectonic evolution of the central sierra nevada magmatic arc marked by a transition from regional contraction to dextral transcurrent shear a model for the emplacement of the intrusion is developed based on detailed mapping of the pluton and its wall rocks and characterization of its internal structure by measurements of the anisotropy of magnetic susceptibility ams at 351 stations one of the key results of the study is documentation of a strong correlation between petrologic and structural fabrics in the pluton and determination that these fabrics reflect internal magma chamber dynamics more than regional tectonic strain the 80 km long 15 30 km wide pluton crystallized from a multiphase three segment magma chamber marked by a bulbous northern lobe and linear central and southern segments the pluton is interpreted to be tabular in shape with a thickness of 5 km most of the space for the pluton was created by piecemeal block downdrop of the magma chamber floor along three principal fracture sets the most important of which were steeply dipping northwest trending fractures formed parallel to the structural grain of the arc and vertical north trending extension fractures formed in response to a component of arc parallel dextral shear some of these fractures acted as magma conduits episodically filling the pluton as source rocks became depleted in melt an initial voluminous intrusive event stage 1 quickly filled the southern chamber with granodiorite magma but only partially filled the northern and central chambers stage 2 magmatism involved underplating of megacrystic granite in the northern chamber and lateral flow of a large batch of this magma from the northern to the central chamber the latter delineated by a 20 km long belt of megacrystic granite containing subhorizontal magnetic lineations that connects the pluton segments floor downdrop eventually ceased to be an effective space making process in the northern lobe and renewed magmatism stage 3 led to expansion and doming of the chamber as the northern lobe cooled a ring fault ruptured within the viscoelastic stage 1 2 carapace allowing ring dike intrusion stage 4 and sinking of a central flap of consolidated material the temporal and spatial variations in emplacement mechanisms demonstrated for the mount givens pluton i e fracture generation floor downdrop underplating inflation ring diking suggest that end member models e g fracture vs diapir are oversimplifications of the pluton assembly process

u pb zircon and microfabric data of meta granitoids of western cameroon constraints on the timing of pluton emplacement and deformation in the pan african belt of central africa abstract striking characteristics of the western neoproterozoic belt of cameroon nfbc are the large volume of granitoids and crustal scale shear zones new structural and geochronological data from this area are provided to put constraints on the tectonic evolution of this segment of the belt and to make further correlations between major shear zones exposed on both sides of the atlantic ocean three different complexes have been identified in the study area the migmatitic complex of foumbot mcf the metagranitoid complex of bangwa bc and the batie pluton bp the mcf was intruded by the bc while the bp cuts through the bc u pb zircon dating of metaleucogranite and metagranodiorite of the bc yielded concordant to subconcordant ages of 638 2 ma and 637 5 ma respectively a concordant u pb zircon age of 602 1 4 ma has been obtained from porphyrogranite of the bp these ages are interpreted as emplacement ages continuous deformation from magmatic to solid state flow along the bp margins and the sub parallelism of the steep solid state foliation in the bp margins with the foliation in the surrounding bc and mfc suggest synkinematic emplacement of the bp along crustal scale nne to ene trending strike slip shear zones subhorizontal foliations in migmatitic gneiss xenoliths found in the bc suggest that the major transcurrent motion was preceded by thrusting the new data confirm previous assumptions that the western nfbc is equivalent to parts of the borborema province of brazil there are geochronological correlations between the studied meta granitoids and brasiliano pre to syn transcurrent granitoids of the borborema province

structural characterization of the misaje granitic pluton nw cameroon constraints from magnetic and field observations the misaje granitic pluton emplaced between 569 and 560 ma in an amphibolitic and gneissic host rock comprises four petrographic units namely biotite hornblende granite bhg granodiorite gd biotite granite bg and leucocratic granite lg four major tectonic events have been described in the studied area a d1 early tectonic event responsible of the e w flat foliation which has been progressively transposed by a d2 tectonic event a d2 event has developed heterogeneous simple shear in a dextral transpressive context with moderate to strong dipping ne sw striking foliation a d3 tectonic event has lead to a sinistral n s ductile shear characterized by n to ene striking foliation and e w strike slip shear corridors and a d4 tectonic event that developed n s dextral ductile strike slip deformation the magnetic study of the pluton based on the ams parameters reveals the coexistence of both paramagnetic dominated by iron bearing silicates 54 of sites and ferromagnetic due to the occurrence of psd and md grains of magnetite or other ferromagnetic minerals 46 of sites behaviors magnetic foliation shows best poles at 55 82 for the whole pluton 95 32 in bhg and 273 83 in bg and the magnetic lineation trends are mostly nne ssw with best lines at 210 8 198 19 and 36 3 respectively the trend of the magnetic lineation in bg indicates an s shape trajectory suggesting a sinistral sense of shear motion along discrete e w corridors situated at the northern and southern ends kinematic indicators in bg point to a sinistral sense of shear suggesting its emplacement during the d3 event the close relationship between k1 and k3 points to a syn kinematic emplacement and crystallization of the misaje granitic pluton during the pan african event and the tectonic evolution of the study area is considered to be coeval with the tectonic evolution of the trans saharan pan african belt of eastern nigeria

the passa tres lode gold deposit parana state brazil an example of structurally controlled mineralisation formed during magmatic hydrothermal transition and hosted within granite abstract the passa tres granite is a nne ssw elongated shape intrusion located in the parana state southern brazil this intrusion was emplaced within metapelites of the mesoproterozoic votuverava group which are part of the n040 e trending lancinha shear zone gold mineralisation within the passa tres granite is held by meter scale quartz veins forming orebodies with variable massive banded sheared and or brecciated internal textures structural data indicate the existence of two orthogonal directions of structures n s and e w dipping 60 75 w and 45 70 s respectively mineralised veins contain in addition to the quartz of the gangue and in chronological order fluorite pyrite chalcopyrite gold aikinite molybdenite muscovite carbonate and baryte gold occurs as native grains within fractures that affect pyrite commonly associated with chalcopyrite and aikinite quartz veins are sometimes bordered by aplitic dykes additionally some of the veins exhibit a thin margin of k feldspar minerals that could represent the early stage of vein formation these observations the presence of unidirectional solidification textures ust along with abundant expression of pegmatite rich pockets within granite that crops out close to the surface allow the reconstruction of the granite architecture in terms of late magmatic evolution magmatic hydrothermal transition and position of the cupola n s and e w systems are interpreted to be contemporaneous and conjugate normal displacements are predominant and main mineralised veins are essentially located within extensional pull apart structures the structural model suggests that the normal faults were initiated along former low angle planes associated with aplite and or early quartz veins that subsequently controlled the opening of the pull apart structures that represent the economic orebodies zircon from the granite and muscovite grains from mineralised veins were dated by u pb and ar ar methods respectively zircons from the main facies medium grained gem and microgranite gef provided undistinguishable ages which were pooled to give an age of 611 9 3 6 ma a less abundant leucocratic facies white granite geb yielded a significantly younger age of 592 8 7 1 ma muscovites from quartz veins gave ar ar ages of 612 9 2 to 608 8 2 ma transitional vein with a k feldspar border 611 7 2 to 608 8 2 ma mineralised veins and 608 4 2 ma barren quartz vein thus the passa tres granite and its gold mineralisation appear to represent a unique example of an intrusion related gold system in which the mineralisation concentrates in the core of the magmatic intrusion in the form of meter scale veins strongly controlled by tectonics

the pan african toro complex northern nigeria magmatic interactions and structures in a bimodal intrusion the toro complex is one of the pan african older granites of nigeria first described as a reversely zoned pluton made of a central dioritic mass surrounded by a broad granitic rim it has been thoroughly reinvestigated both from the petrographic and structural points of view with the help of systematic anisotropy of magnetic susceptibility ams measurements the granite main body is a hornblende biotite porphyritic monzogranite characterized by an early submagmatic fabric displaying a concentric pattern of foliations and west plunging lineations stage 1 this fabric is overprinted by a later one due to solid state strain along north south subvertical dextral shear zones stage 2 in the vicinity of the diorite an evengrained granite displays magmatic structures that are contemporaneous with this strike slip event the diorite granite contact is a complex zone where field petrographic and geochemical data enable recognition of the effects of mixing and mingling between a mafic and a felsic magma tonalites cropping out within this contact zone are interpreted as hybrid rocks the reverse zonation of the diorite itself is also the result of some hybridization process magmatic interactions mainly resulted from in situ infiltration of granitic liquid into the dioritic mass the detailed history of this bimodal intrusion began with the emplacement of the granitic magma acquiring a first stage fabric before full crystallization of the granitic core intrusion of the dioritic magma permitted reheating of the granitic magma that then crystallized with specific structural characters the second stage structures whether characterized by magmatic fabric near the diorite or by solid state strain features in north south shear zones elsewhere in the granite are related to late pan african dextral strike slip tectonics in the basement of northern nigeria the bimodal toro complex is therefore considered as a late pan african syntectonic pluton

significance of a hiatus in down temperature fabric development within syn tectonic quartz diorite complexes channel islands uk detailed fabric development histories have been deduced for neoproterozoic foliated quartz diorite complexes of the channel islands uk the plutons were emplaced during regional d2 deformation magmatic fabrics formed at low crystal contents pre rheologically critical melt percent are only locally preserved due to overprinting by solid state deformation which occurred at moderate temperatures 400 550 c this is demonstrated by brittle microcracking of plagioclase and amphibole with only local ductile bending and dynamic recrystallization marginal recrystallization and myrmekite development on alkali feldspar ductile deformation of quartz to form types 2 3 ribbons quartz recrystallization by sub grain rotation associated with a slip but not c slip biotite recrystallization within micro shears and variable amphibole recrystallization the deformation histories display a distinct division between magmatic state and moderate temperature solid state deformation features with little evidence for intervening high temperature solid state fabrics this contrasts with criteria widely considered diagnostic of syn tectonic plutons which envisage development of a continuum of magmatic through high temperature solid state deformation fabrics however we consider the plutons syn tectonic and attribute the hiatus to contrasting strain and pluton cooling rates length and nature of deformation events and host rock ambient temperatures intermediate magmas emplaced at moderate to shallow levels in the crust may be more prone to develop such apparently punctuated deformation histories than sio 2 richer granitoids

evidence of an early ns magmatic event in the paleoproterozoic teofilndia granitoids so francisco craton brazil a combined microstructural and magnetic fabric study abstract the teofil ndia area south of the serrinha block sao francisco craton ne brazil marks a region where the boundary between the serrinha block and the itabuna salvador curaca belt rotates from ns to ew the granitoids of teofil ndia are made of granodiorites and trondjhemites dated at 2 13 ga to the south and west they are hosted by biotite bearing basement orthogneiss an oriented sampling of 157 sites covering 220 km2 was subjected to a systematic microstructural and magnetic fabric study complemented by pressure determinations using the al in hornblende barometer the highly variable magnetic susceptibilities from 50 to 21 000 si reflect both the variable primary magnetite content of these rocks and the variable intensity of the late hydrothermalism that is responsible for gold mineralization hosted by the metabasalts in the north of the area three main types of microstructures have been distinguished along with some transitions magmatic high temperature gneissic and fluid present low temperature high stress mylonitic combined microstructural and magnetic fabric data reveal that a ns trending primary magmatic structure has been locally shielded from two subsequent ew trending ht gneissic and low t mylonitic events our tectonic reconstruction proposes that the preserved ns magmatic lineations were formed in a submeridian magmatic arc parallel to the western border of serrinha block and along which an oblique convergence took place the subsequent ew trending events are equated with i the already identified ew compression that accreted the serrinha block to the craton and ii the late event that we correlate with ore deposits in the metabasalts dated between 2 08 and 2 03 ga

emplacement of the arzachena pluton corsica sardinia batholith and the geodynamics of incoming pangaea abstract the assembly of the corsica sardinia batholith c sb coincides with final shaping of the variscan belt and represents a key structure to unravel the feedbacks between partial melting rheology and the evolution of collisional orogens this paper presents a model for the genesis of the arzachena pluton azn one of the major calc alkaline massifs of the c sb based on u pb zircon dating thermobarometry and structural analysis major and trace element compositions indicate that azn has hybrid characteristics between that of typical s and i type granites that could be explained in terms of incremental melting of a heterogeneous crustal source made of metatexites and ordovician calc alkaline granitoids growth of the pluton started around 320 315 ma with the emplacement at middle crustal level 0 37 0 4 gpa of granodioritic melts within narrow conjugate nw se sinistral and e w dextral shear zones the main growth stage 311 6 4 ma is marked by emplacement of large volumes of monzogranitic melts that induced a local decrease of the crustal strength expressed by horizontal channel flow driven by the gravity finally 307 6 3 5 ma leucogranites emplaced within radial and peripheral dilatant fractures developed during the cooling of the main body the transition from magmatic to sub magmatic and ht solid state fabric observed throughout azn indicates that deformation plays a non trivial role during the growth of the magmatic system restoring the position of the corsica sardinia block to early permian coordinates allow to recast the birth of the c sb in a consistent geodynamic framework that conciliates the development of conjugates strike slip structures the oroclinal bending of the chain and the thermal relaxation this study indicates that the c sb had an active role during post orogenic extension rather than being just a consequence of it

tracing the magmatic hydrothermal transition in regional low strain zones the role of magma dynamics in strain localization at pluton roof implications for intrusion related gold deposits structural controls are critical during magmatic to hydrothermal transition in the formation of intrusion related gold deposits they may explain why only some parts of intrusions are mineralized and why only very few intrusions host large deposits moreover most of these gold deposits postdate peak regional metamorphism and were formed in zones of relatively low strain indeed the efficiency of structural gold traps is highest along favourably oriented intrusion host rock contacts where mechanical instability maintains high permeability in the cracked thermal aureole this may be reinforced by melt injections from an underlying root zone we present a structural analysis of the deformation features of a granite pluton roof large scale dykes and a network of gold veins are intensively developed in this roof recording a succession of mechanical instabilities our gravity survey underlines the presence of a pluton feeder zone located just beneath the mineralized network it is argued that interferences between regional stress and melt injection in the feeder zone favoured the development of the network by strain located close to the granite roof this stresses the role of mechanical instabilities triggered by the combined effects of regional stress and melt dynamics in determining the location and size of this type of gold deposit

tonalite sill emplacement at an oblique plate boundary northeastern margin of the bohemian massif abstract a tonalitic sill has been examined at the variscan transpressive boundary of the lugian and silesian plates at the ne margin of the bohemian massif a structural petrological and geochronological study reveals that it was emplaced syn tectonically with major ductile shearing in lower crustal rocks magmatic and pre rheological critical melt percentage rcmp fabrics are concordant with the hanging wall structures but discordant with those of the footwall the ams study shows the predominance of flattening strain at the margins and plane strain fabrics in the core numerical modelling of ams fabrics is in good agreement with the hypothesis of magma flow and deformation in oblique transpression a tectonic model was developed explaining emplacement and syn tectonic deformation of progressively cooled tonalitic intrusion

internal fabric and strike slip emplacement of the pan african granite of solli hills northern nigeria the solli hills pluton 250 km2 in northern nigeria is an example of a pan african granite emplaced circa 580 ma ago in the jos adamawa block its micro structures and internal fabrics have been studied in order to help constrain the kinematics of the pan african orogeny in this block we used field observations and measurements petrographic examinations and measurements of the magnetic susceptibility and anisotropy of magnetic susceptibility of 124 regularly spaced stations most samples are ferromagnetic i e belong to the magnetite series granites and present predominantly magmatic microstructures particularly remarkable are the asymmetrical zoning of the petrographic types the susceptibility magnitudes and the planar linear magnetic fabrics the magnetic foliations and lineations are very consistent in the pluton around n 20 e 60 w and n 205 e 10 respectively field and microscopic observations reveal that deformation occurred everywhere in the pluton and immediate country rock envelope during a dextral strike slip synplutonic episode it is suggested that the solli hills pluton was emplaced in a late pan african dextral tear fault system the striking fabric asymmetry of the pluton strongly suggests a shear zone termination emplacement model

a review of mesoscopic magmatic structures and their potential for evaluating the hypersolidus evolution of intrusive complexes abstract the perception that plutonic bodies are structurally simple is disappearing with the recognition of an array of magmatic structures useful for constraining hypersolidus temporal histories evolving rheologies strain fields flow directions growth and cooling patterns tilting and syn emplacement tectonism these histories provide a powerful means of testing an array of growth emplacement chamber evolution and tectonic models important points include that 1 many structures form in hydrogranular or congested magma slurries during magma mush avalanching local convection and late hypersolidus strain challenging the notion that magmas must have 55 crystals to convect fractionate and form compositional diversity in upper crustal magma chambers 2 magmatic fabrics reflect transient strain in these slurries rather than flow directly the latter must be inferred by linking geometries with temporal and kinematic information 3 caution is needed when using anisotropy of magnetic susceptibility and similar quantitative tools that characterize through a single ellipsoid preferred orientations of mineral grains given the increasing recognition of multiple fabrics in plutons and 4 that future studies are particularly needed in plutons focusing on the distribution and styles of compositionally defined structures magmatic folding shear zones and faults multiple fabrics and of the physical chemical behaviors in hydrogranular slurries

intrusion within a transtensional tectonic domain the cista granodiorite bohemian massif structure and rheological modelling abstract the cista granodiorite stock which intrudes the tis granite laccolith and their neoproterozoic country rocks of the tepla barrandian zone were studied by means of structural analysis and anisotropy of magnetic susceptibility the rocks were dated by the pb pb evaporation on zircons determining the age of the cista granodiorite and tis granite at 373 ma and 504 ma respectively the structures in the country rocks are characterised by an axial cleavage dipping to the northwest and overprinting the folded bedding s1 cleavage bears ne sw trending mineral lineations which plunge to the northeast or southwest at shallow angles the cleavage is deformed by d2 kink bands which indicate a vertical shortening and a nw se stretching both the cista granodiorite stock and the tis granite are deformed by a sinistral transtensional shear zone the geometry of this zone is compatible with the d2 brittle ductile extensional kink bands developed in the metasediments according to microstructures in the granitoids affected by the shear zone we show that the tis granite was deformed in solid state at high temperatures whilst the cista granodiorite developed both the magmatic and high temperature solid state deformation fabric during its syntectonic cooling numerical thermal and rheological modelling of the cista granodiorite intrusion suggests that it caused an important weakening of the crust at the site of emplacement which in combination with regional transtension explains that it became the site of a ductile shear zone

jurassic barrovian metamorphism in a western u s cordilleran metamorphic core complex funeral mountains california large magnitude retroarc shortening of cretaceous age is well documented in the sevier orogenic belt of the western united states and has been associated with eastward franciscan subduction that began in the middle late jurassic but evidence for major late jurassic retroarc shortening has been lacking here we report new lu hf garnet geochronology pressure temperature p t paths and 40 ar 39 ar thermochronology data that document tectonic burial of late jurassic age in a barrovian metamorphic terrain the funeral mountains metamorphic core complex california located in the hinterland of the sevier orogenic belt the p t paths determined from growth zoned garnets in upper greenschist facies pelitic schist show steep p t trajectories consistent with metamorphism during thrust loading the age of thrust loading is constrained by a five point lu hf garnet isochron to be 158 2 2 6 ma 2 partial exhumation recorded in 146 153 ma 40 ar 39 ar muscovite cooling ages closely followed garnet growth late jurassic barrovian metamorphism has not been previously recognized in cordilleran metamorphic core complexes possibly due to being obscured by late cretaceous to tertiary deformation magmatism and metamorphism this study finds that the period of large magnitude crustal shortening in the retroarc extended into the late jurassic and may have closely followed the formation of the coherent orogenic system associated with east dipping franciscan subduction

non linear feedback loops in the rheology of cooling crystallizing felsic magma and heating melting felsic rock at least six major parameters control the rheology of partially molten systems melt content rate of melt production reaction to strain of the solid component reaction to strain of the molten component temperature and chemical composition of the source rocks we examine their interactions to understand the rheology of partially molten rocks and partly crystallised magmas this paper especially focuses on the rheology in the transitional domains between two pairs of thresholds that bracket a transitional regime between a solid state and a fluid behaviour during melting and crystallisation respectively we review related information and point out non linear effects that develop during heating of melting rocks and cooling of crystallising magmas owing to the non linear interactions positive or negative feedback loops accelerate or damp the system melt in migmatite experiences shear softening which along with strain partitioning facilitates melt segregation conversely the augmenting number of rigid crystals during cooling increases the suspension viscosity shear hardening which soon inhibits magma movement those effects reinforce the asymmetry between solid to melt and melt to solid transitions they severely contradict the concept of one rheological critical melt percentage valid for both melting and crystallisation transitions fabric acquisition competes with nucleation and crystal growth thus leading to hysteresis of the stress stain rate curves implications to field observations include horizontal magma segregation magma extraction and successive magma intrusions

the sphene centered ocellar texture an effect of grain supported flow and melt migration in a hyperdense magma mush abstractthe sphene centered ocellar texture consists of leucocratic ocelli with sphene titanite crystals at the center enclosed in a biotite rich matrix this texture has been recognized worldwide in hybrid intermediate rocks on the basis of structural petrological and geochronological data from selected outcrops of the variscan ribadelago pluton nw iberian massif we propose that the ocelli were formed by migration and accumulation of a residual melt through a plagioclase and biotite dominated crystalline framework at the late stage of crystallization the magma acted as a hyperdense suspension and reacted to the pressure gradient caused by the regional stress field entering the domain of grain supported flow microstructures reveal that aligned crystal domains arose in the crystal framework from the shearing and compaction of the crystal mush and behaved as magmatic microshears relative displacement of adjacent crystal clusters along these microshears corresponded to the onset of reynolds di

contrasted tectonic styles for the paleoproterozoic evolution of the north china craton evidence for a 2 1 ga thermal and tectonic event in the fuping massif structural analysis along with 40ar 39ar and u pb datings in the fuping massif provide new insight into the evolution of the eastern part of the trans north china belt north china craton from 2 7 ga to 1 8 ga d1 is responsible for the development of a dome and basin structure coeval with crustal melting giving rise to migmatite and nanying gneissic granites at 2 1 ga this dome and basin architecture resulted from the interference between a n s compression of a weak ductile crust and gravity driven vertical flow in a high thermal regime the next events involved flat lying ductile thrusting d2 and normal faulting d3 dated at around 1880 ma and 1830 ma respectively the d2 and d3 events belong to the trans north china orogeny that results in the final amalgamation of the north china craton the d1 deformation is considered as evidence for an earlier orogen developed around 2 1 ga prior to the trans north china orogeny the change in the deformation style between the 2 1 ga and 1 8 ga could be viewed as a consequence of the cooling of the continental crust in the north china craton

tectonic rotations and internal structure of eocene plutons in chuquicamata northern chile abstract a paleomagnetic and ams study on eocene plutonic complexes in the calama area northern chile reveals high temperature high coercivity magnetizations of dominantly thermoremanent origin and magnetic fabrics controlled by magnetite the paleomagnetic results indicate that 43 ma plutons underwent clockwise tectonic rotation whereas adjacent 39 ma plutons did not undergo discernible rotation this points to a middle eocene age for the younger tectonic rotations associated with the central andean rotation pattern in the chuquicamata calama area the petrofabric in these rocks formed under conditions ranging from purely magmatic i e before full crystallization to low temperature solid state deformation ams and paleomagnetism suggest that the plutonic bodies were formed by progressive amalgamation of subvertical magma sheets spanning multiple magnetic polarity chrons the parallelism between magmatic and tectonic foliations suggests that regional tectonic stress controlled ascent emplacement and rock deformation during cooling in this context we suggest that magma ascent and emplacement in the upper crust likely exploited mesozoic structures which were locally reactivated in the eocene

evaluation of multiple emplacement mechanisms the huichizi granite pluton qinling orogenic belt central china three end member granite emplacement mechanisms host rock ductile shortening hrds host rock rigid displacement hrrd and magmatic absorption ma are identified in this study of the huichizi pluton the internal fabrics are mainly flattening typesona 0 4 0 9u and strain is highoesa 1 0 0 6u near the boundaries and lowoesa 0 7 0 30u toward the central parts of the pluton in the 1 5 km wide contact aureole extension e is measured in syn emplacement deformed veins and the calculated average shortening normal to the sides and tips of the pluton are 1 14 km and 0 74 km respectively from this we conclude that the hrds produced only about 20 space for the present volume of the pluton the regional hrrd derived from the uplift by about 8 km of the qinling group in a flower structure contributed 19 032 space ms including stoping and material transfer processes yielded another 37 space of this stoping contributed a minimum of 1 space estimated from the surface area of 2 8 km 2 covered by xenoliths transfer processes provided about 36 of the needed space deduced from the average 64 36 ratio of hybridization of mantle derived to crustal qinling group derived magma the three mechanisms may act nearly simultaneously as a multiple emplacement mechanism this situation may apply to many other plutons as well 2000 elsevier science ltd all rights reserved

shearing of magma along a high grade shear zone evolution of microstructures during the transition from magmatic to solid state flow abstract syntectonic plutons may record short lived geological events related to crustal melting and deformation of the continental crust therefore interpretation of microstructure and orientation of fabrics is critical in order to constrain space time temperature deformation relationships during pluton crystallization here we describe the transition from magmatic to solid state deformation in the late variscan diorite granite suite dgs emplaced along the santa lucia shear zone the systematic collection of meso microstructural and quartz axis data allow us to examine the spatial distribution and the mode of superposition of different fabrics we identify three magmatic microfabric types thought to reflect the microstructural evolution at decreasing melt content during pluton crystallization our data suggest that diffusion creep dislocation creep and grain scale fracturing cooperated in accommodating the shearing of the partially molten quartzofeldspathic aggregate we suggest that the switch from upward to horizontal magmatic flow occurred at melt fractions gt 0 40 and that most of the hypersolidus fabrics formed during horizontal flow reflecting the stress field imposed by the shear zone and preserving no memory of the ascent stage

magnetic fabric and microstructures of late paleozoic granitoids from the north patagonian massif evidence of a collision between patagonia and gondwana abstract widespread late paleozoic magmatism in northern patagonia is a target to test hypotheses on the long standing question over the origin of patagonia in recent years a dispute over whether it is an accreted crustal block that collided with gondwana in paleozoic times or an autochthonous part of south america has taken place as part of a multidisciplinary study an integrated microstructural and magnetic fabric study was carried out on the late carboniferous yaminue complex and the early permian navarrete plutonic complex both exposed in the northeastern corner of the north patagonian massif 40 5 s 67 0 w other investigated units are the late carboniferous tardugno granodiorite the newly defined cabeza de vaca granite and the late permian san martin pluton over 300 oriented cores from 60 sites were collected for anisotropy of magnetic susceptibility ams measurements a systematic analysis of around 100 petrographic thin sections was performed to characterize the microstructures of the different magmatic units microstructures in the yaminue complex are indicative of a transition from magmatic to solid state deformation microstructures of the orthogneiss of tonalitic composition suggest an early stage in the emplacement history of this complex the cabeza de vaca granite intrusive in yaminue complex is the most evolved unit and records less intense high temperature solid state deformation which suggests that the stress field that controlled the emplacement of the yaminue complex outlasted it according to petrologic and structural considerations the navarrete plutonic complex has been subdivided into three facies i e robaina guanacos and aranda respectively microstructures of the navarrete plutonic complex are mostly magmatic to submagmatic versus the solid state fabric that characterizes the robaina facies at the contact with the yaminue complex combined analyses of ams and microstructural data lead us to suggest that the yaminue complex cabeza de vaca granite and possibly tardugno granodiorite were intruded during a major compressional event associated with top to the ssw thrusting this event is most likely related to a frontal collision of the north patagonian massif and the southwestern gondwana margin at around 300 ma the navarrete plutonic complex and san martin pluton were emplaced after that tectonic event which must have ended by 281 ma previous magmatic geochronological and paleomagnetic data that suggest close connection of the north patagonian massif with the south american gondwana blocks during the paleozoic can be reconciled with a late paleozoic collision by a model of a para autochthonous north patagonian massif that rifted away from gondwana after the ordovician and collided again in the late carboniferous early permian

a new metamorphic constraint for the eburnean orogeny from paleoproterozoic formations of the man shield aribinda and tampelga countries burkina faso abstract progressive metamorphic zones developed in pelites around the aribinda granite burkina faso indicate contact metamorphism at 5 6 kbar biotite chloritoid staurolite kyanite zones are distributed concentrically around the aribinda pluton on its northern margin but are displaced by later thrust faults in the south of the aribinda area and in the nearly tampelga area these metamorphic and structural characteristics provide new constraints for the geodynamical evolution of the eburnean orogeny in the north part of the baoule mossi domain they show the leading part of the granitoid emplacement in the thermic structuration of the greenstone belts and the post metamorphic character of the tangential tectonic in burkina faso the eburnean orogeny underwent 1 initial greenschist facies metamorphism 2 emplacement of granitoids at mid deep crustal levels leading to unusual medium pressure metamorphism 3 later thrusting

magmatic structures and kinematics emplacement of the variscan granites from central portugal serra da estrela and castro daire areas abstract the late d3 variscan granites which represent the most important volume of granites of central portugal are studied here for their magmatic and solid state fabrics by means of the anisotropy of magnetic susceptibility ams technique in a 5000 km 2 area located between guarda and castro daire including the serra da estrela region two main directions n150e and n20e of stretching lineations are found indicating that the emplacement of these late kinematic granitoids was tectonically controlled a three stage model is proposed in which a openings along n150 striking dextral strike slip faults allow the first granitic magmas to be emplaced in the upper crust of palaeozoic metasediments and syn d3 granitoids b openings along n20 striking possibly sinistral strike slip faults conjugates to the prior strike slip faults and allow the enlargement of the granitic plutons and c the final emplacement of this huge volume of granitic rocks was mainly controlled by the magma pressure which explains the rarity of structures related to this stage of granites emplacement in the country rocks this structural study of granitic rocks yields new constraints on the tectonic evolution of this part of the variscan orogenic belt at c 300 ma

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

on thrusting regional unconformities and exhumation of high grade greenstones in neoarchean orogens the case of the waroonga shear zone yilgarn craton abstract during the neoarchean the dominant tectonic style progressively changed from an episodic overturn stagnant lid regime to modern style plate tectonics the neoarchean strengthening of continental lithosphere changed the style of deformation of orogenic belts the case study presented here provides insights into how such transition in tectonic style occurred a matter that is generally controversial we present structural and metamorphic data from the c 2660 ma waroonga shear zone wsz in the neoarchean yilgarn orogen western australia the wsz contains a syntectonic pluton and older high grade greenstones the tectonic fabric in the pluton developed during melt present thrusting followed by syn cooling wrench dominated transpression mafic greenstones preserve three metamorphic assemblages the m1 assemblage grt cpx qtz records peak p t conditions of 12 1 kbar and 800 50 c followed by isothermal decompression to 9 kbar m2 these anhydrous assemblages might predate the wsz greenstones then underwent decompression at c 2660 ma 3 4 kbar 600 650 c defined by the amphibole rich m3 assemblage synkinematic with the tectonic fabric in the wsz we show that shearing along the wsz exhumed these greenstones by at least 10 km inducing major uplift and erosion archean accretionary orogens developed on weak lithosphere where deformation suppressed crustal thickening orogenic relief and synorogenic exhumation of orogenic roots however our study indicates a genetic link between i strain localization along contractional structures inducing large scale uplift ii exhumation of high grade greenstones iii development of inverse metamorphic gradients iv establishment of a regional unconformity with clastic sediments fed by the uplifted terrane v incorporation of portions of the newly formed orogenic basins into the footwall of the wsz these features imply that the yilgarn orogenic lithosphere at c 2660 ma was stiff enough to allow tectonic processes analogous to those that dominate modern style orogenic belts representing an intermediate stage between archean and modern type orogens

magnetic fabrics and compositional evidence for the construction of the caleu pluton by multiple injections coastal range of central chile the caleu pluton which is located in the coastal range of central chile consists of three n s elongated lithologic zones which define an across pluton compositional variation characterized by a westward increase in sio2 content the gabbro diorite gdz tonalite tz and granodiorite gz zones a total of 547 cores were drilled at 68 sites within the different zones to carry out magnetic fabric and paleomagnetic studies the highest values of magnetic susceptibility and remanent magnetization are found in the gdz 0 04 0 1 si whereas the lowest values are observed in the gz 0 01 0 02 si this is consistent with the significant decrease in magnetite content from the gdz to the gz the dips of the magnetic foliation planes are steep within gdz and tz and shallower dips are observed in gz magnetic foliations along some borders of the pluton are parallel to the corresponding contacts the parallelism observed between the magnetic foliations and the contacts between zones suggests that these zones have recorded the same mechanism of emplacement at the magmatic state the peculiar foliation pattern observed in the central parts of tz and gz is attributed to a lobe like structure that was acquired during the late stages of emplacement and inflation the distinct compositional characteristics of these three zones were not acquired in situ rather they were emplaced successively from mafic to felsic from a subjacent stratified sill like magma reservoir which was filled after tilting of the host volcanic succession the rapid upward transport of these melts of different compositions up to a shallow depth is attested by both the equilibration pressure of late magmatic hornblende 200 mpa and the pressure of early magmatic epidote crystallization 500 600 mpa we conclude that space was created by lateral flow propagation in which the intrusion of later pulses pushed earlier ones away from the feeder system followed by roof lifting and possibly floor depression

wavelet transform a future of rock fabric analysis abstract although twenty years ago fabric was defined as the complete spatial and geometrical configuration of all those components that make up a deformed rock fabric was mainly synonymous with lattice preferred orientation very little attention has been paid to the multi scale geometrical and spatial relationships of the rock components fabric quantification in terms of size shape orientation and location at all scales is now performed in two dimensions using anisotropic wavelets as a first example the wavelets are applied to the famous colour plate of sander and the results compared to his axial distribution analysis applied to the k feldspars of a rock section from the sidobre granite pluton montagne noire france the wavelet analysis shows i alignment of grains resulting from mechanical interactions between grains and shows that shearing occurred within the crystalline frame ii preferred grain orientation the classical grain shape fabric parallel to the overall mineral lineation and iii small tensional domains elongate perpendicular to the lineation infilled by the residual melt just before total crystallisation attesting to the stretching nature of the mineral lineation the future of rock fabric analysis will come from new steps in understanding the processes acting during fabric development along with a further development of wavelet analysis using high resolution three dimensional fabric data

late magmatic healed fractures in granitoids and their influence on subsequent solid state deformation abstract late magmatic fractures developed during final stages of magma crystallization are recorded in many granitoid plutons by planar trails of magmatic biotite and or leucocratic veins but have not been previously described such biotite rich trails with lengths of a few centimetres to several tens of centimetres widths of a few millimetres and a variable orientation are ubiquitous in meta granitoids of the neves area tauern window eastern alps italy these pre alpine granitoids were metamorphosed to upper amphibolite facies and deformed during the alpine orogeny allowing the effect of planar healed magmatic fractures on the nucleation of subsequent solid state ductile shear zones to be directly assessed numerical models considering power law viscous materials predict that planar arrays of a weaker mineral e g biotite oriented at around 45 to the shortening direction should nucleate and localize viscous deformation however no discernible localization on the natural small scale biotite trails is observed even when they delineate planes that were well oriented for shear reactivation in contrast heterogeneous shear zones nucleated on larger scale 1 10 m long planar compositional or structural boundaries such as joints dykes quartz veins alteration layers surrounding veins and zones of magma mingling outlined by densely packed clusters of basic enclaves irrespective of their orientation relative to the imposed shortening direction clearly some crucial aspect is missing from purely viscous numerical models we propose that this missing aspect is the observed interplay between fracture and flow with new fractures developing and localizing shear at bulk strains too low for discernible localization to occur on the pre existing healed magmatic fractures natural granitoids have a truly elasto plasto viscous rheology even at low differential stress as in the neves example and for high grade metamorphic conditions considered as typical of wet ductile middle crust

magnetic susceptibility and partial anhysteretic remanence anisotropies in the magnetite bearing granite pluton of tourao ne brazil abstract rock magnetism and magnetic fabric studies were performed in the tourao granite western part of serido belt ne brazil this pluton 350 km2 is composed of k rich calc alkalic monzogranites and was emplaced between a set of ne and e trending dextral strike slip shear zones electronic and optical microscopy thermomagnetic curves hysteresis data and coercivity spectra revealed that magnetite fine and coarse grained is the unique ferromagnetic mineral in these rocks anisotropy of low field magnetic susceptibility ams was measured in 83 sites and for many sites from central and southern parts of the intrusive body a large scatter was noticed anisotropy of partial anhysteretic remanence paar was determined for 29 sites in the 0 50 mt paar0 50 and 19 sites in the 50 90 mt paar50 90 windows to isolate the fabric contribution of the remanence bearing grains magnetite in most sites ams is dominantly carried by magnetite whereas in some sites the paramagnetic contribution exceeds 60 of the bulk susceptibility the paar0 50 is assumed to be related to coarse grained early crystallized magnetites while the paar50 90 is interpreted as due to fine needle shaped magnetites hosted in biotites the combined analysis of these magnetic techniques permits interpretation in terms of fabric formation in the tourao granite and the inference that at least two successive kinematic events were recorded in this intrusive body devoid of any solid state deformation overprint the ams and paar0 50 fabrics for most of the sites correlate with the early nne trending magmatic fabric whereas paar50 90 reveals a different fabric probably related to late partitioning of magmatic straining along the e trending shear zones in the southern part of the body a completely different paar0 50 fabric is correlated with the late intrusion of charnockite stocks