the stabilization of self organised leucogranite networks implications for melt segregation and far field melt transfer in the continental crust abstract net structured leucocratic vein systems are ubiquitous in high grade and migmatite terrains and are interpreted to represent interconnected former magma bearing structures that accommodated the migration of granitic magmas out of their anatectic source regions net structured leucogranite vein systems in high grade gneisses from the damara belt in namibia describe a size based hierarchy and spatial distribution that indicates self organisation of the magma transfer system the internal geometry and connectivity of the net structured leucogranites are controlled by variations in melt pressure whereas regional strains control the orientation of the leucogranites foliation parallel stromatic and shear band hosted granite veins accommodate transport at relatively low melt volumes and account for the metre scale segregation of melt close to the anatectic source during times of higher melt supply the formation of extensional fractures that cross cut stromatic and shear band hosted melt sheets at high angles is promoted extensional fracturing and associated dilatancy create gradients in magmastatic head that cause melt to be drained from pervasive stromatic and shear band hosted vein networks into spaced dilatant fractures this has the potential to initiate buoyancy driven far field melt transfer along suitably orientated extensional fractures as vertical dykes or self propagating hydrofractures our results suggest that melt transfer systems are able to adjust to variations in melt supply by forming conduits that accommodate varying melt volumes and will tend to develop towards a state of self organisation

effect of partial melting on rock deformation experimental and natural evidences on rocks of granitic compositions abstract deformation tests at constant strain rate 10 5 s 1 at 210 250 mpa confining pressure and at 560 900 c are performed on an aplite with varying water contents the mechanical behaviour is correlated with the microstructure after a stage of plastification depending on the temperature and on the water content the rock strength falls dramatically under such confining pressures before melting and before straining the pores of the wet rocks burst as the thermal expansion of water develops a local high pore pressure which causes cracking and fracturing in our opinion this pore bursting will increase the effects of thermal cracking due to the differential expansion of the minerals the rocks exhibit a uniform crack network with increasing temperature melting occurs in the cataclased rock the crack development and melting depend on the initial water content the loss of cohesion obtained either by cracking or by cracking and melting provokes a dramatic weakening axial shortening induces cracking parallel to 1 and melt transfer into extensional regions deformation is concentrated in dilatant shear bands at the highest temperature 900 c a melt film network is rapidly established and induces a very low flow stress melt effects in naturally deformed gneisses suggest that biotite breakdown furnishes a silicate fluid which induces hydraulic fracture and melt dispersion

on the rheology of partially molten synthetic granite abstract in an attempt to obviate some of the difficulties inherent in using natural rocks to study experimentally the rheology of partially molten granitic rocks we report some preliminary experiments using hot pressed synthetic aggregates with quartz as the solid phase and a quartz albite glass to form the melt phase undrained constant displacement rate and stress relaxation experiments were performed at 1100 c and 300 mpa total confining pressure using nominally 16 and 28 wt anhydrous melt and at 980 c with 12 wt of water saturated melt strain rate varies non linearly with stress corresponding to a stress exponent of 3 6 for the anhydrous melt tests and 1 9 with the wet melt strain rate is enhanced about 160 fold through doubling the melt fraction from 16 wt intracrystalline plasticity appears to contribute insignificantly to the observed deformation and the preservation of relatively equant grains implies a granular flow process microcracking occurs during isostatic hot pressing and also contributes to subsequent non isostatic deformation at high stresses and strain rates models of flow of partially molten rock that assume diffusive transfer accommodation of granular flow predict linear viscosity but only at lower strain rates than accessed experimentally it is suggested that the non linear granular flow observed in these experiments involved the episodic unsticking of sintered contacts between grains by a rate dependent cracking and or dislocation accommodation process

mapping the distribution of melt during anatexis at the source area of crustal granites by synchrotron μ xrf proyecto fapa universidad de los andes bogota colombia centro nacional de pesquisa em energia e materiais brazilian synchrotron light laboratory lnls proposal n xafs1 17105 cariparo cassa di risparmio di padova e rovigo project makearth european union s horizon 2020 research and innovation programme under the marie sklodowska curie grant agreement no 654606

granite ascent and emplacement during contractional deformation in convergent orogens based on a case study in the central maine belt of west central maine u s a it is proposed that crustal scale shear zone systems provide an eaective focussing mechanism for transfer of granite melt through the crust in convergent orogens during contractional deformation flow of melt in crustal materials at depths below the brittle plastic transition is coupled with plastic deformation of these materials the flow is driven by pressure gradients generated by buoyancy forces and tectonic stresses within the oblique reverse central maine belt shear zone system stromatic migmatite and concordant to weakly discordant irregular granite sheets occur in zones of higher strain which suggests percolative flow of melt to form the migmatite leuco somes and viscous flow of melt channelized in sheet like bodies possibly along fractures cyclic fluctuations of melt pressure may cause instantaneous changes in the eaective permeability of the flow network if self propa gating melt filled tensile and or dilatant shear fractures are produced due to melt enhanced embrittlement in homogeneous migmatite and schlieric granite occur in zones of lower strain which suggests migration of partially molten material through these zones en masse by granular flow and channelized flow of melt carrying entrained residue founded on the central maine belt case study we develop a model of melt extraction and ascent using the driving forces stress conditions and crustal rheologies in convergent especially transpressive orogens ascent of melt becomes inhibited with decreasing depth as the solidus is approached for intermedi ate a h2o muscovite dehydration melting the water saturated solidus occurs between 400 and 200 mpa near the brittle plastic transition during high t low p metamorphism where the balance of forces favors sub horizontal fracture propagation emplacement of melt may be accommodated by ductile flow and or stoping of wall rock and inflation may be accommodated by lifting of the roof at shallower crustal levels and or sink ing of the pluton floor the resultant plutons have sub horizontal tabular geometries with floors that slope down to the ascent conduits although these plutons may have locally discordant relations with country rock structures when viewed at the crustal scale granite ascent and emplacement in convergent orogens are syn tec tonic processes 1998 elsevier science ltd all rights reserved

a new magma chamber model based on structural studies in the oman ophiolite abstract structural mapping in the mafic ultramafic transition zone and in the overlying crustal section of the oman ophiolite has revealed the importance of magmatic flow in the formation of layering in the gabbros and the mechanical coupling between this flow and the asthenospheric flow of the underlying peridotites the crustal section near the spreading axis and in particular the magma chamber are fed by two independent melts a dominant gabbroic melt episodically injected from depth and a subordinate wehrlitic crystal mixture produced by compaction of the transition zone layering in the gabbros can be partly produced by tectonic transposition of the gabbroic and wehrlitic mixtures during magmatic flow whatever its origin the layering orientation in the newly created crust does not necessarily reflect its original attitude the final orientation of the layering is determined by the attitude of the magmatic flow plane at the time it was frozen a new magma chamber model is proposed which solves some of the physical difficulties of previous models and accounts for the seismic imaging of magma chambers beneath oceanic ridges

rheological transitions in progressive melting of rock and their geological constraints from the fuhu metatexite diatexite profile in guangdong province se china abstract integration of the published experimental data of partially melted amphibolite orthogneiss granite and aplite reveals the existence of three rapid strength drops of the rock assemblage at melt fraction around 7 21 and 41 respectively the first and the last drops are equivalent to the well known melt connectivity transition mct and solid to liquid transition slt the drop at melt fraction around 21 is newly identified and termed as the framework melting transition fmt the fmt is defined as the transition from eutectic quartz feldspars melting to refractory biotite melting the three rheological transitions are well constrained by the geological data from the fuhu profile in guangdong province se china this profile is a 15 m high cliff rocks exposed on the profile are zoned as mottled stripped narrow banded and wide banded migmatites and diatexitic granite from the top of the profile downwards the leucosome proportions of the zones measured on the outcrops combined with the experimental data of the partially melted rocks have significant implications for understanding the role of rheological transitions during crustal melting the mct which corresponds to the boundary between the mottled and the narrow banded migmatites suggests the segregation of melt within the partially melted system along with the compaction of matrix thus the mct is deemed to be the transition of the partially melted system from matrix supported melt stored in pore space to framework supported melt stored in foliation bedding space of protolith the fmt corresponding to the boundary between the narrow and the wide banded migmatites denotes the inception of melting of the solid framework mechanically the fmt can be regarded as the transition of the framework from compaction to fusion and geochemically the transition from eutectic melting of quartz feldspars to that of refractory biotite the increasing melt due to framework melting after the fmt is basically limited within the solid framework until the melt fraction exceeding the slt the slt is geologically constrained by the in situ metatexite diatexite transition that is also termed as magma interface mi the slt mi represents the upper limit of a crustal magma layer because of the downward increasing temperature and melt fraction there should be no consecutive layer of felsic rock existed in the space between the slt mi and the mafic lower crust except the isolated rock blocks within the magma layer

syntectonic anatexis and magmatism in a mid crustal transpressional shear zone an example from the hercynian rocks of the eastern pyrenees abstract hercynian metamorphism and magmatism in the cap de creus peninsula eastern pyrenees occurred contemporaneously with non coaxial deformation in a transpressive regime an example of this has been taken from a migmatite complex in the northern coast the studied area is formed by partially melted sillimanite schists together with two different suites of igneous rocks a calc alkaline magmatic sequence consisting of small granitoid bodies and later peraluminous leucogranites and pegmatites all these rocks occur within a ne sw to e w trending sub vertical high strain zone where a first schistosity is tightly folded and transposed the relations between folds and crenulation cleavage in the metasediments and deformational fabrics in the granitoids and migmatites provide good evidence for the penecontemporaneity of deformational processes magmatism and migmatization furthermore the analysis of cross cutting relationships between different granitoids as well as the observation of their different degrees of deformation verifies that magmatism in this area took place as synkinematic consecutive intrusions from the more basic magmas to the peraluminous acid dykes

contact partial melting of granitic country rock melt segregation and re injection as dikes into ferrar dolerite sills mcmurdo dry valleys antarctica numerous interconnected granitic dikes 530 cm in width and hundeds of meters in length cut ferrar dolerite sills of the mcmurdo dry valleys antarctica the source of the granitic dikes is partial melting of granitic country rock which took place in the crust at a depth of about 2 3 km adjacent to contacts with dolerite sills sustained flow of doleritic magma through the sill generated a partial melting front that propagated into the granitic country rock granitic partial melts segregated and collected at the contact in a melt rich nearly crystal free reservoir adjacent to the initial dolerite chilled margin this dolerite chilled margin was subsequently fractured open in the fashion of a trapdoor by the granitic melt evacuating the reservoir to form an extensive complex of granitic dikes within the dolerite sills at the time of dike injection the dolerite was nearly solidified unusually complete exposures allow the full physical and chemical processes of partial melting segregation and dike formation to be examined in great detail the compositions of the granitic dikes and the textures of partially melted granitic wall rock suggest that partial melting was characterized by disequilibrium mineral dissolution of dominantly quartz and alkali feldspar rather than by equilibrium melting it is also unlikely that melting occurred under water saturated conditions the protolith granite contains only 7 vol biotite and estimated contact temperatures of 900 9508c suggest that melting was possible in a dry system granite partial melting under closed conditions extended tens of meters away from the dolerite sill yet melt segregation occurred only over less than one half a meter from the dolerite chilled margin where the degree of partial melting was of the order of 50 vol this segregation distance is consistent with calculated length scales expected in a compaction driven process we suggest that the driving force for compaction was differential stress generated by a combination of volume expansion as a result of granite partial melting contraction during dolerite solidification and relaxation of the overpressure driving dolerite emplacement on a purely chemical basis the extent of melt segregation necessary under fractional and batch melting to match the rb concentrations between melt and parent rock is a maximum of 48 and 83 vol melt respectively

experimental deformation of partially molten westerly granite under fluid absent conditions with implications for the extraction of granitic magmas the mechanical behavior of partially molten westerly granite was investigated in the temperature range 800 1100 c 250 mpa confining pressure by means of constant strain rate creep and stress relaxation tests the only water in the samples came from the breakdown of hydrous phases biotite minor chlorite and muscovite and alteration products of feldspars thus the amount of melt was controlled by the test temperature and ranged from 3 at 800 c to 50 at 1100 c over that temperature range strength decreased from 500 mpa to less than 1 mpa and a preliminary constitutive flow law for the partially molten rock was obtained to allow extrapolation to low strain rates the comparative viscosity of the melt alone was estimated at 950 and 1000 c from the distance it could be made to penetrate into a porous sand under a known pressure gradient under all conditions deformation of the matrix of solid grains was by brittle fracture only samples containing up to 10 vol melt failed with the formation of a shear fault zone at higher melt fractions melt filled pores collapsed by shear enhanced compaction squeezing the melt into axial cracks above 40 vol melt unfractured solid grains were carried about passively in the flowing liquid there was no evidence of a rheologically critical melt percentage in this system by analogy with the uniaxial compaction of water saturated soils a simple model is erected to describe a two stage process for the extraction of granitic melts from their protoliths with the aid of nonhydrostatic stress shear enhanced compaction is inferred to drive melt into a network of melt filled veins whereupon porous flow through the high permeability vein network allows rapid drainage of melt to higher crustal levels

from sediment to granite timescales of anatexis in the upper crust abstract granite formation is the culmination of a sequence of events initiated by prograde heating of the protolith and followed by formation of a grain boundary melt melt segregation into a vein network ascent of the melt through the network and finally crystallisation of the melt experimental constraints on the formation of a crustal melt from the incongruent melting of muscovite combined with geochemical studies of anatexis in the high himalaya allow the timescales required for each of these processes to be assessed discordant temperatures determined from monazite and zircon thermometry for himalayan anatectic granites indicate that at least for some intrusives the melt was undersaturated in lree implying that melts have probably been extracted in less than 10 ka experimental studies suggest that some himalayan melts are also undersaturated in zr implying segregation may have occurred within 100 years such short timescales confirm that deformation driven mechanisms are important in extracting these melts from their source the transport distances of himalayan granitic melts of 10 km may be achieved by the ascent of magma through dykes in about 1 day at such rates even the largest granite could theoretically be emplaced in 10 years crystallisation of himalayan melts involves much longer periods if emplaced as thin sheets 100 m wide a timescale of 500 years is required compared with 30 ka for single stage intrusion of the larger laccoliths for composite sheet complexes magma crystallisation rather than melt ascent comprises the rate determining step on the emplacement of the intrusion the overall timescales of melt segregation and emplacement for many orogenic granites are therefore less than 10 ka and possibly less than 1 ka in contrast the timescale required for prograde heating of the protolith is 1 ma since the melt production rate is determined by heat flow into the protolith and not by reaction kinetics for any geologically significant period we conclude that heat flow determined by both the mechanism of heating and the thermal diffusivities of crustal rocks provides the overall rate determining step of crustal anatexis

well wetted olivine grain boundaries in partially molten peridotite in the asthenosphere abstract pore morphology in partially molten peridotites strongly controls many physical properties of the earth s deep materials the dihedral angle of the olivine silicate melt system is a key factor in understanding the physical behavior of the upper mantle for a limited range of melt compositions previous studies of wetting behavior have determined dihedral angles of 30 50 however the dihedral angle of partially molten peridotites should be variable under a wide range of pressure and temperature conditions because wetting behavior depends strongly on liquid structure and composition the dihedral angles of olivine silicate melt in partially molten peridotite were determined at pressures of 1 to 7 gpa and temperatures between 1473 and 1993 k the dihedral angle decreased approaching 0 with increasing temperature which corresponds to completely wetted grain boundaries this angle variation probably depends on a decrease in the solid melt interfacial energy which is a product of large change in melt structure these results suggest that the presence of partial melt would have large influences on the physical properties of the upper mantle even if the melt fraction was very low if grain boundary diffusion creep dominates in the asthenosphere the shear strength of partially molten peridotites at asthenospheric pressure 3 gpa would be much lower than that predicted from experiments at relatively lower pressure 0 3 gpa because of the extremely low grain boundary contiguity

melt segregation and magma interactions during crustal melting breaking out of the matrix abstract differentiation of the continental crust begins with its partial melting the products of crustal melting are silicic hydrous h2o undersaturated granitic liquids that are generated within matrices of residual crystals crustal differentiation requires that felsic magmas form and escape from these solid residua an important question is whether granitic magmas collect into large batches within or near their sources which then give rise to ascent or alternatively bleed out of the sources in smaller streams or pulses we demonstrate that the physical reality is closer to the second alternative and thus question the validity of the concepts of magma segregation and source fertility as they are sometimes visualised granitic plutons contain chemically distinct sub populations formed by source level entrainment of the peritectic assemblages into the melts rapid evacuation at source levels and high ascent rates protect the magmas from wall rock interactions during their tenure at source depths and during their ascent through cool upper crust the existence of different types of granites and hence of clearly defined chemically different magmas within plutons dictates that felsic magmas must separate efficiently from their anatectic sources and must ascend to the sites of their emplacement with minimal chemical interaction with crust through which the magma must move exposed deep crustal sections are typically lithologically diverse with the more fertile rocks commonly forming discrete layers surrounded by rocks with contrasting compositions if the melts were required to segregate and accumulate into large volumes within their hot sources especially by slow gravity driven melt percolation it is very likely that they would be substantially modified by reaction with diverse source rocks thus the processes mooted to occur in melting assimilation storage and homogenisation mash or deep crustal hot dch zones would act to erase original compositional heterogeneities and produce larger batches of more homogeneous magma perhaps carrying evidence of extensive magma mixing from various lines of evidence we conclude that mash and dch zones may not exist and even if they do they cannot form the sources of most granitic magmas the intrinsic heterogeneity in crustal source rocks the likely occurrence of peritectic assemblage entrainment and the inefficiency of magma mixing decree that granitic rocks will retain source inherited chemical and isotopic heterogeneities rapid semi continuous and disequilibrium withdrawal of small magma batches from source rocks means that elements of whole rock trace element chemistry and accessory mineral chemistry will be decoupled from major element variations this also means that a large source with low nominal fertility due to low hydrous mineral content for example could still produce a substantial granitic pluton by additions of individually small increments of magma

comparison of sulfide oxidation in unweathered pyritic mine tailings tailings are a fine grained waste product produced during the metal recovery process tailings consist mostly of different silicates but also sulfides e g pyrite since 100 metal recovery is not possible freshly processed tailings are deposited in large impoundments if the mine tailings in the impoundments are exposed to water and oxygen the sulfides will oxidize and release acidity and metals such as fe cu zn and pb the sulfide mineral oxidation reactions are catalyzed by sulfur and iron oxidizing bacteria principally acidithiobacillus ferrooxidans that oxidize ferrous iron to ferric iron which then oxidizes pyrite when the leachate produced by this process discharges from the impoundment it is called acid mine drainage which may lead to the pollution of adjacent streams and lakes the intention with this thesis is to investigate and quantify mineral weathering processes and element release rates occurring in water saturated and soil covered sulfidic mine tailings the study was performed in different batch and column experiments in room temperature and in the laboratory the batch experiments were conducted for ca three months and investigated a microbial and abiotic sulfide oxidation in freshly processed tailings under oxic conditions at ph 2 3 and ph 8 b microbial oxidation of pure pyrite grains at ph 2 3 under different oxygen concentrations ranging from anoxic to oxic conditions the column experiments consisting of unoxidized tailings in water saturated columns were conducted for up to three years in these experiments an oxygen saturated solution was continually pumped into the column inlet and investigated a differences in oxidation rates between tailings of two different grain sizes b factors affecting element discharge rates acid neutralization and sulfide oxidation c the effect of ions released in a soil cover on release rates in the tailings sulfide oxidation processes within the batch experiments were limited by surface kinetics the microbial oxidation of pure pyrite at atmospheric conditions produced the most rapid rate while the microbial oxidation of pure pyrite at anoxic conditions was slower by 1 8 orders of magnitude microbial and abiotic oxidation of pyrite in freshly processed tailings resulted in pyrite oxidation rates that were intermediate between these two extremes the results from the microbial experiments with pure pyrite indicated a positive correlation between the concentration of dissolved oxygen ferric iron and bacterial cells at a total cell concentration 106 cells ml and a dissolved oxygen concentration 13 2 m which implies an interdependence of these factors the results from these batch experiments support the indirect mechanism for microbial oxidation by the ferric oxidation pathway pyrite oxidation rates estimated from the batch experiments may be comparable with oxidation rates in the unsaturated zone and at the groundwater table in a tailings impoundment acid neutralization reactions in the column experiments resulted in the release of base cations to the column leachate calcite was the most important neutralizing mineral despite that it was only present in minor amounts in the tailings it was confirmed that acidity forced the calcite dissolution element release rates in the column experiments were controlled by the availability of dissolved oxygen which was a function of the water flow rate into the column these column experiments also showed that the results are comparable with results from field studies justifying the use of column experiments to study processes within tailings impoundments

southern ocean jets and how to find them improving and comparing common jet detection methods this study undertakes a detailed comparison of different methods used for detecting and tracking oceanic jets in the southern ocean the methods under consideration are the gradient thresholding method the probability density function pdf method and the contour method some weaknesses of the gradient thresholding method are discussed and an enhancement the whose method based on techniques from signal processing is proposed the whose method is then compared to the other three methods quantitative comparison is undertaken using synthetic sea surface height fields the whose method and the contour method are found to perform well even in the presence of a strong eddy field in contrast the standard gradient thresholding and pdf methods only perform well in high signal to noise ratio situations the whose pdf and the contour methods are then applied to data from the eddy resolving ocean general circulation model for the earth simulator while the three methods are in broad agreement on the location of the main acc jets the nature of the jet fields they produce differ in particular the whose method reveals a fine scale jet field with complex braiding behavior it is argued that this fine scale jet field may affect the calculation of eddy diffusivities finally recommendations based on this study are made the whose and gradient thresholding methods are more suitable for the study of jets as localized strong currents useful for studies of tracer fluxes the contour and pdf methods are recommended for studies linking jets to hydrographic fronts

granitic magma transport by fracture propagation granitic magmas commonly ascend tens of kilometres from their source terranes to upper crustal emplacement levels or to the earth s surface apart from its obvious bearing on the interpretation of the geology and geochemistry of felsic igneous rocks the magma ascent mechanism critically affects any modelling of the metamorphic evolution of the upper lithosphere as well as its rheology we propose that in general granitic magmas ascend via propagating fractures as dykes in extremely short time periods long distance diapiric transport of granitoid magmas through crustal sections is not viable on thermal or mechanical grounds and there is an apparent total absence of field evidence for diapiric rise of such magmas even in supposed type localities neither the shapes nor internal or external characteristics of granitic plutons necessarily reveal anything about the transport of their precursor magmas these are purely arrival phenomena dictated by local structure kinematics and stress states based on existing numerical treatments of the problem we show that granitic magmas are apparently sufficiently inviscid to travel through fractures to high crustal levels without suffering thermal death by freezing for example a 2000 km3 granitic batholith can be inflated by a 1 km 3m 20 km deep dyke system in less than 900 years the model proposed has numerous far reaching petrological and rheological consequences some of which are outlined

petrogenesis of juvenile type birimian paleoproterozoic granitoids in central cote d ivoire west africa geochemistry and geochronology abstract the birimian paleoproterozoic granitoids of central cote d ivoire are associated either with greenstone belts or with basin sedimentary rocks field data indicate two stages of granitoid emplacement which according to singlezircon and monazite 207 pb 206 pb age determinations occurred within a short period of time the first generation of granitoids 2123 2108 ma intruded and metamorphosed the greenstone belts whereas the second generation 2108 2097 ma intruded and metamorphosed the sedimentary pile and subordinate andesitic volcanic rocks of the bandama basin unconformably overlying the greenstone belts geochemical and isotopic data show that the various granitoids belong to four magmatic groups 1 sodic calc alkaline nacg 2 potassic calc alkaline kcg 3 peraluminous alg and 4 alkaline alkg all the granitoids show juvenile features with mantle like low initial sr isotopic compositions 0 700 0 702 and positive epsilon nd values 1 5 2 7 these data indicate that a the nacg may have formed by partial melting of a garnet amphibolite crust b the kcg and alkg derived from partial melting of crustal mafic to intermediate metaigneous rocks and c the alg epsilon nd 1 5 represent infracrustal melting of young sialic igneous materials during a regional crustal shortening in a transcurrent tectonic context sm nd model ages 2 25 2 4 ga preclude the existence of an archean crust reworked in the birimian magmas an underplating model is discussed

evidence for reaction induced microfracturing in granulite facies migmatites water undersaturated partial melting at granulite facies conditions followed by accumulation and upward migration of the resulting granitic melt is one of the principle causes of crustal differentiation microfracturing caused by small positive volume changes associated with water undersaturated melting reactions may facilitate rapid extraction of melts from melting sites we have successfully imaged annealed microfractures in residual quartz from three granulite facies migmatites annealed microfractures have been discovered in 1 quartz inclusions in peritectic garnet 2 quartz inclusions in k feldspar and 3 quartz occurring as entrained grains in the latter oscillatory zoned quartz has overgrown fractures in the residual core indicating that fracturing occurred prior to melt crystallization and that postanatectic volume changes are not responsible for the observed fracturing fractures are generally 5 m wide are parallel sided and have low sinuosity crack densities are two to three times higher than experimental studies involving muscovite melting and approach theoretical interconnectivity thresholds for percolation implying that reaction induced microfracturing is a viable mechanism contributing to melt interconnectivity during anatexis under granulite facies conditions

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

granite rheology magma flow and melt migration granite magma rheology has long been studied by rock physicists petrologists and experimentalists new data on viscosity of dry and h 2 o bearing melts and glasses in a wide range of temperatures and h 2 o content changed drastically the general view on the arrhenian behaviour of granitic melts recent studies on the deformation of partially molten granite rocks at up to 50 vol of melting show the failure of the rcmp rheologically critical melt percentage concept for granites we present new direct measurements of melt migration from a combination of centrifuge experiments falling sphere viscometry of partially molten granites assisted by a centrifugal field and viscoelastic behaviour of partially molten granites in torsion oscillation apparatus the results suggest that the extrapolation of the einstein roscoe equation for the viscosity of partially molten rocks does not give adequate results for granites with 50 vol of melt phase rheology of granite magmas is very sensitive to chemical composition and viscosity of the melt phase adding h 2 o to partially molten granites results in a decrease in the viscosity of the melt phase as well as dissolution of quartz crystals in turn this produces more felsic and viscous melt thus these factors smear out the contrast between partially and completely molten granites and between anhydrous and h 2 o bearing magmas at moderate h 2 o contents 1 to 2 wt

rheology of granitic magmas during ascent and emplacement flow abstract considerable progress has been made over the past decade in under standing the static rheological properties of granitic magmas in the continental crust changes in h2o content co2 content and oxidation state of the interstitial melt phase have been identified as important compositional factors governing the rheodynamic behavior of the solid fluid mixture although the strengths of granitic magmas over the crystallization interval are still poorly constrained theoretical investigations suggest that during magma ascent yield strengths of the order of 9 kpa are required to com pletely retard the upward flow in meter wide conduits in low bagnold number magma suspensions with moderate crystal contents solidosities 0 1 0 3 viscous fluc tuations may lead to flow differentiation by shear enhanced diffusion ams and mi crostructural studies support the idea that granite plutons are intruded as crystal poor liquids 50 with fabric and foliation development restricted to the final stages of emplacement if so then these fabrics contain no information on the ascent verti cal transport history of the magma deformation of a magmatic mush during pluton emplacement can enhance significantly the pressure gradient in the melt resulting in a range of local macroscopic flow structures including layering crystal alignment and other mechanical instabilities such as shear zones as the suspension viscosity varies with stress rate it is not clear how the timing of proposed rheological transitions formulated from simple equations for static magma suspensions applies to mixtures undergoing shear new theories of magmas as multiphase flows are required if the full complexity of granitic magma rheology is to be resolved

structures and melt fractions as indicators of rheology in cordierite bearing migmatites of the bayerische wald variscan belt germany a melt but the degree of their shape preferred orientation increases the relation between melt volume fraction melt segregation and with increasing melt segregation and differential stress the mideformation mechanisms of minerals in migmatites and the concrostructures suggest that deformation mechanisms and hence the trolling effects of all these factors on the bulk mechanical behaviour bulk mechanical behaviour of migmatites change in space and time were investigated using rocks from the bayerische wald bohemian during partial melting the observed complex interplay of melt massif variscan belt germany biotite dehydration melting at volume fraction melt segregation bulk strength contrasts mechanical 800 850 c and 0 5 0 7 gpa was the migmatite forming process properties of different minerals and time cannot be described by a in this area four migmatite types were distinguished that alternate single flow law detailed mapping of migmatite areas along with on the scale of several decimetres to several tens of metres type microstructural observations deformation experiments considering mig1 is massive and undeformed types mig2 and mig3 are heterogeneous melt distribution and numerical models that integrate both stromatic leucosome mesosome interlayering but differ in the different flow laws for various stages of partial melting may serve degree of deformation type mig4 has an interlayering of meto derive quantitative models for the bulk mechanical behaviour of lanosome and leucosome and is strongly deformed melt volume crustal sections in the future fractions found by volume estimation of pure melt leucosomes on outcrop hand specimen and thin section scales are 20 40 vol and coincide fairly well with melt volume fractions produced in dehydration melting experiments with similar bulk compositions at the relevant pressure and temperature conditions 20 30 vol the degree of melt removal from mesosomes and melanosomes melt

role of melt in the formation of a deep crustal compressive shear zone the maclaren glacier metamorphic belt south central alaska the maclaren glacier metamorphic belt is an exhumed portion of a deep crustal shear zone where hot upper amphibolite facies rocks were emplaced over cooler lower grade rocks it is located in south central alaska within the collision zone between terranes previously accreted to north america and the wrangellia superterrane crosscutting relationships and orientations of thin granitoid sills within the hanging wall show that melt was repeatedly intruded into the shear zone during overall compression in addition a 1 km thick tonalite sill the valdez creek tonalite was emplaced into the shear zone while it was active this conclusion is based on the presence of a well developed foliation within the sill which is concordant to the fabric of the shear zone the alignment and tiling of plagioclase laths the presence of highly strained mafic enclaves within a matrix which shows no evidence of any subsolidus deformation and the preservation of a delicate magmatic texture which indicates that a magmatic fluid was still present after deformation in the sill had ceased a one dimensional thermal model for sill shaped plutons of varying thicknesses which are emplaced into country rocks at different initial temperatures indicates that melt can be present for long periods of time in the deep crust 1 m y an important factor controlling the length of time that a sill remains molten is the temperature of the surrounding rocks which in the lower crust can be as high as the solidus temperature of granitoid melts if the amount of time for melt to crystallize is sufficiently long potentially large amounts of strain will be accommodated by zones containing melt due to the low strength of melt compared to rock in the maclaren glacier metamorphic belt the amount of time needed for the valdez creek tonalite to fully crystallize is calculated to be about 90 000 years this is a minimum value since the original thickness of the sill is not known nevertheless using the 90 000 year value and assuming that the bulk of convergence between north america and wrangellia was concentrated within the valdez creek tonalite a displacement of at least 10 km could have been accommodated across the sill while melt was present

rheological properties of dome lavas case study of unzen volcano abstract transitions between effusive and explosive styles of lava dome eruptions are likely accompanied by changes in lava rheology the common presence of crystals in dome lavas produces a complex non newtonian rheology thus models of such complex rheology are essential for volcanic eruption models here we have measured the rheology of natural unzen lavas with a compressive uniaxial press operating at stresses between 1 and 70 mpa and temperatures between 940 and 1010 c crystal rich unzen lavas are characterised by two essential rheological features which produce non newtonian effects the first is an instantaneous response of the apparent viscosity to applied stress which requires that the magma be described as a visco elastic fluid that exhibits shear thinning the second effect takes the form of a time dependence of the viscosity at moderate to high stress 10 mpa in this regime the apparent viscosity slowly decreases as increasing fracturing of the phenocrysts and the groundmass occurs fragmentation of crystals and alignment of crystal fragments are observed to produce flow banding effects which in turn lower the apparent viscosity of natural dome lavas ultimately deformation may lead to complete rupture of the lava if the stress is sufficient cracking thus stands as an important process in natural dome lava rheology the ubiquitous non newtonian rheology of dome lavas observed experimentally here needs to be adequately treated in order to generate appropriate eruption models

melt segregation in the continental crust distribution and movement of melt in anatectic rocks the grain and outcrop scale distribution of melt has been mapped in anatectic rocks from regional and contact metamorphic environments and used to infer melt movement paths at the grain scale anatectic melt is pervasively distributed in the grain boundaries and in small pools consequently most melt is located parallel to the principal fabric in the rock typically a foliation short branched arrays of linked melt bearing grain boundaries connect melt depleted parts of the matrix to diffuse zones of melt accumulation protoleucosomes where magmatic flow and alignment of euhedral crystals grown from the melt developed the distribution of melt leucosome and residual rocks normally melanocratic in outcrop provides different but complementary information the residual rocks show where the melt came from and the leucosomes preserve some of the channels through which the melt moved or sites where it pooled different stages of the melt segregation process are recorded in the leucosome melanosome arrays regions where melting and segregation had just begun when crystallization occurred are characterized by short arrays of thin branching leucosomes with little melanosome a more advanced stage of melting and segregation is marked by the development of residual rocks around extensive branched leucosome arrays generally oriented along the foliation or melting layer places where melting had stopped or slowed down before crystallization began are marked by a high ratio of melanosome to leucosome because most of the melt has drained away very few leucosomes remain to mark the melt escape path this is common in melt depleted granulite terranes many migmatites contain abundant leucosomes oriented parallel to the foliation mostly these represent places where foliation planes dilated and melt drained from the matrix via the branched grain boundary and larger branched melt channel leucosome arrays collected melt collected in the foliation planes was partially or fully expelled later when discordant leucosomes formed leucosomes or veins oriented at high angles to the foliation layering formed last and commonly lack melanocratic borders hence they were not involved in draining the matrix of the melting layer discordant leucosomes represent the channels through which melt flowed out of the melting layer

modelling of melt segregation processes by high temperature centrifuging of partially molten granites i melt extraction by compaction and deformation the present study deals with the experimental modelling of two different mechanisms of crystal melt segregation in crustal rocks 1 the buoyancy driven compaction of the crystal melt matrix and 2 melt filtering in a partially crystalline matrix due to differential stresses these two segregation mechanisms have differing relative efficiencies in the deformation of crustal rocks and result in different texture scales depending on melt fraction melt viscosity and tectonic stresses a centrifuge furnace has been used in the present study for the modelling of melt migration in partially molten granitic rocks samples of beauvoir granite massif central france with a grain size of 0 16 0 5 mm and dimensions of diameter 5 mm length 16 mm were used these samples had been pre fused at temperatures of 1000 1075 c yielding an initial average melt fraction of 45 50 volume per cent the centrifuging of partially melted samples during 6 hr at an acceleration of 1000g g is gravity results in a linear vertical distribution of melt over the length of the sample without the development of a compaction layer the gradient of the melt fraction melt migrates to the top of samples correlates with temperature 1075 c 7 volume per cent mm 1 1050 c 4 volume per cent mm 1 1000 c 1 5 volume per cent mm 1 the calculated rate of melt migration varies from 3x10 5 cm s 1 1075 c to 2x10 6 cm s 1 1000 c differential stresses of 0 7 1 4 mpa have been generated in the centrifuge by putting a piston weight 1 02 2 05 g diameter 4 5 mm on the top of the partially melted sample which is then centrifuged at 1000g the rate of melt squeezing from the sample in this case is about two orders of magnitude higher than that observed without the piston after centrifuging for 6 hr a compaction layer below the piston is formed with a thickness of 2 5 mm and a crystal fraction of 70 65 volume per cent further centrifuging 15 hr does not result in any increase of the compaction layer thickness or volume percentage of crystals in it the comparison of the two segregation mechanisms confirms the much greater efficiency of differential stress induced melt segregation and accumulation in veins and pockets than the compaction mechanism

bulk flow strength of forsterite enstatite composites as a function of forsterite content creep experiments have been conducted to investigate the effect of varying forsterite content vfo on the bulk flow strength of dry forsterite enstatite fo en aggregates in order to evaluate the applicability of existing theoretical models to two phase rocks as well as to understand the rheology of polyphase systems in general the experiments were performed at temperatures of 1423 1593 k stresses of 18 100 mpa oxygen fugacities of 10 14 10 2 5 mpa and 0 1 mpa total pressure the fine grained fo 10 17 mm en 14 31 mm composites of various fo volume fractions vfo 0 0 2 0 4 0 5 0 6 0 8 and 1 were synthesized by isostatically hot pressing in a gas medium apparatus at 1523 and 350 mpa our experiments show that flow strength contrasts between fo and en are in the range of 3 8 at the given experimental conditions with fo as the stronger phase the measured stress exponent n and activation energy q values of the fo en composites fall between those of the endmembers the n values show a nearly linear increase from 1 3 to 2 0 while the q values display a non linear increase from 472 to 584 kj mol with en volume fraction from 0 to 1 0 there is no clear dependence of creep rates on oxygen fugacity for the fo en composites the mechanical data and tem microstructural observations suggest no change in deformation mechanism of each phase when in the composites compared to when in a single phase aggregate the en deformed mainly by dislocation creep while the fo deformed by dislocation accommodated diffusion creep for our grain sizes and experimental conditions comparisons between the measured composite strengths and various theoretical models indicate that none of the existing theoretical models can give a precise predication over the entire vfo range from 0 to 1 however the theoretical models based on weak phase supported structures wps yield a good prediction for the flow strengths of the composites with vfo 0 6 no model gives a good prediction for the bulk strength of two phase composites in the transitional regime vfo 0 4 0 6 applications of the wps and sps based models in the transitional regime result in under and over estimations for the composite flow strength respectively thus the effect of rock microstructure should be taken into consideration in modeling the bulk flow strengths of the crust and upper mantle using laboratory determined flow laws of single phase aggregates d 2001 elsevier science b v all rights reserved

transition from dislocation creep to melt enhanced diffusion creep in fine grained granitic aggregates abstract sintered aggregates composed of quartz albite and microcline of two different grain sizes 2 10 and 10 50 m each with two different melt contents

water fluxed melting of the continental crust a review abstract water fluxed melting also known as fluid or water present melting is a fundamental process in the differentiation of continents but its importance has been underestimated in the past 20 years during which research efforts focused mostly on dehydration melting reactions involving hydrate phases in the absence of a separate aqueous phase the presence of a free aqueous phase in anatectic terranes influences all major physical and chemical aspects of the melting process from melt volumes viscosity and ability to segregate from rock pores to melt chemical and isotopic composition a review of the literature shows that melting due to the fluxing of aqueous fluids is a widespread process that can take place in diverse tectonic environments active tectono magmatic processes create conditions for the release of aqueous fluids and deformation driven transient high permeability channels capable of fluxing high temperature regions of the crust where they trigger voluminous melting water fluxed melting can be either congruent in regions at the water saturated solidus or incongruent at suprasolidus p t conditions incongruent melting reactions can give rise to peritectic hornblende or to nominally anhydrous minerals such as garnet sillimanite or orthopyroxene in this case the presence of an aqueous phase is indicated by a mismatch between the large melt fraction generated and the much smaller fractions predicted in its absence the relatively small volumes of aqueous fluids compared to that of rocks imply that melting reactions are generally rock buffered fluids tend to move upwards and down temperature however there are cases in which pressure gradients drive fluids up temperature potentially fluxing suprasolidus terranes crustal regions at conditions equivalent to the water saturated solidus represent a natural impediment to the up temperature migration of aqueous fluids because they are consumed in melting reactions in this case continued migration into supra solidus terranes take place through the migration of water rich melts thus melts become the transport agent of water into supra solidus terranes and responsible for water fluxed melting other processes such as the relatively rapid fluid migration through fractures also allow regional aqueous fluids to by pass the water saturated solidus fluid trap and trigger melting above solidus conditions when aqueous fluids or hydrous melts flux rocks at supra solidus conditions they equilibrate with the surroundings through further melting decreasing water activity and giving rise to undersaturated melts it is in these conditions that hornblende or anhydrous peritectic phases are stabilized unlike dehydration melting the melt fraction generated in this case is not limited by the water contained in hydrous minerals but by the volume of water added to the system unlike melting at the water saturated solidus these melts are capable of rising without freezing and do give rise to upper crustal granitic bodies

progressive adjustments of ascent and emplacement controls during incremental construction of the 3 1 ga heerenveen batholith south africa abstract the heerenveen batholith is part of a suite of areally extensive shallow crustal granitoid plutons intruded during the last regional phase of tectonism and nw se subhorizontal shortening recorded in the mesoarchean barberton granitoid greenstone terrain of south africa at 3 1 ga intrusive relationships allow at least four main successively emplaced intrusive stages to be distinguished each of these shows distinct geometries and intrusive styles that provide evidence for the progressive change of emplacement controls during the incremental construction of the heerenveen batholith the earliest sheet like granitoids intruded as foliation parallel sills along the shallowly dipping basement gneissosity emphasizing the role of favourably inclined pre existing wall rock anisotropies for granite emplacement during the early stages of pluton assembly continued sheeting and coalescence of sheets provided the thermal ground preparation that led to the formation of larger coherent magma bodies and the main phase of homogeneous commonly megacrystic granites these megacrystic granites form the central parts of the heerenveen batholith and are interpreted to represent steady state magma chambers the introduction of the rheologically weaker melt bodies into the shallow crust resulted in the nucleation of conjugate synmagmatic transpressive shear zones around the central granites the shear zones correspond to several km wide zones of shear zone parallel granite sheeting this stage marks a dramatic switch in emplacement styles while the initial stages of magma emplacement were largely determined by factors external to the magma most importantly the pre existing wall rock anisotropies subsequent stages are dominated by factors intrinsic to the magma namely strain localization and partitioning along melt bearing zones during syntectonic plutonism the associated melt transfer along these zones is independent of pre existing structures and mainly related to buoyancy and strain induced melt ascent the last granites of the heerenveen batholith are post tectonic they intrude as either plugs or stocks of seemingly random orientation but display a clear control by wall rock anisotropies where they are in contact with the country rocks on a regional scale the different phases of the heerenveen batholith describe an overall zonation of central homogeneous granites enveloped by composite sheeted and sheared margins this pattern is typical for most of the large 3 1 ga granite batholiths in the barberton granitoid greenstone terrain we suggest that the sequence of progressively changing emplacement controls and the formation of steady state magma chambers described here for the heerenveen batholith may be of wider application to other zoned and or incrementally assembled batholiths

geochronology and geochemistry of zircon from the northern western gneiss region insights into the caledonian tectonic history of western norway abstract the western gneiss region wgr of norway is divided by the more trondelag shear zone mtsz into a southern region that contains domains of caledonian ultrahigh pressure uhp metamorphic rocks 2 5 gpa and a northern area of similar caledonian aged rocks that record a maximum pressure reported thus far of 1 5 gpa although both regions contain similar lithologies primarily migmatitic quartzofeldspathic gneiss containing mafic lenses and structural relationship of basement rocks to infolded nappes this difference in maximum pressure implies a difference in tectonic history continental subduction south of the shear zone none to the north and raises questions about the role of the mtsz in the metamorphic history including exhumation of the wgr previous geochronology results indicated a difference in timing of peak metamorphism older in north younger in south in order to better understand the tectonic history of the northern wgr and the mtsz and in particular the late to post caledonian tectonic history u pb zircon geochronology and trace element abundances were obtained using the split stream laser ablation icpms technique from metabasaltic lenses and migmatitic quartzofeldspathic host rocks from the structurally lowest exposed region of the northern wgr roan peninsula basement as well as leucosomes from an intercalated portion of the seve nappe complex and a pegmatite in the mtsz zircon from roan gneiss and metabasite yield metamorphic ages of ca 410 406 ma and zircon from a variety of migmatite samples foliation parallel leucosome to dikes indicate melt crystallization at ca 410 to 405 ma the seve nappe leucosomes yield only early caledonian dates that cluster at ca 437 ma and ca 465 ma suggesting that the allochthons in this region did not experience or record the same scandian tectonic history as the basement rocks zircon from a weakly deformed pegmatite dike within the mtsz crystallized at ca 404 ma indicating that this shear zone was active during the end stages of high grade metamorphism in both the southern and northern wgr domains results of this study show that the northern and southern wgr experienced a coeval scandian metamorphic magmatic and deformation history despite a possible difference in maximum p t conditions

hydraulic and acoustic properties as a function of porosity in fontainebleau sandstone laboratory measurements have been made of the permeability k free porosity l compressional velocities vp or ve and compressional attenuations qp or qe in fontainebleau sandstone over a continuous range of porosities from 3 to 28 this large variation was achieved without any composition change fontainebleau sandstone is made of fine quartz grains with regular grain size 250 m permeability was measured with a falling head permeameter velocities and attenuations were obtained either through an ultrasonic experiment for frequencies around 500 khz or through a resonant bar technique experiment for frequencies around 5 khz and in both cases with varying water saturation the results show an excellent correlation between permeability k and total porosity for all our samples for low porosities 3 to 9 permeability in millidarcies is 2 75 10 5 7 33 while for high porosities 9 to 28 permeability k in millidarcies is given by 0 303 3 05 the correlation is also excellent between free porosity and total porosity on the other hand the correlation between acoustic properties and total porosity is not as clear as for hydraulic properties whatever the frequency 500 khz or 5 khz or the water saturation on the average velocity decreases and attenuation roughly increases with increasing total porosity velocity and attenuation values are related to the variation of grain contact structure and two samples with the same porosity and permeability may exhibit different velocities and attenuations the clear correlation between hydraulic properties and porosity is related to constant grain size while the lack of correlation for acoustic properties emphasizes the importance of the microstructure

magma ascent by porous flow porous flow of buoyant liquid through partially molten rock is regarded as the initial transport process leading to magma segregation in the mantle recent work has identified the importance of matrix deformation and compaction in this process we present finite difference calculations based on a generalized form of darcy s law that includes matrix deformation in two dimensional cartesian and cylindrical coordinates we emphasize the existence of solitary wave solutions called magmons these waves are regions of locally high porosity that ascend through regions of low uniform porosity they differ from diapirs where the liquid and matrix ascend together the one dimensional waves that were previously reported are found to be unstable in two dimensions breaking down to form two dimensional waves of circular cross section both the development of the instability and the form of the two dimensional waves are supported by theoretical analysis numerical experiments in which two dimensional waves collide show that the extent to which they are conserved after collision depends on the lateral offset of the waves the conservation can be very good in other cases larger waves appear to grow at the expense of smaller waves although the quantification of the relevant permeability and rheological parameters remains uncertain geophysically plausible estimates suggest wavelengths of kilometers and velocities of centimeters per year in our preliminary assessment of the relevance of these results to igneous processes we find that magmons are unlikely to be important in regions of broad upwelling such as beneath spreading centers here the transport of liquid adjusts to match the supply by melting and compaction processes are not important if liquid is supplied from below to a stable partially molten region of the asthenosphere it is expected to ascend in magmons this may occur beneath oceanic volcanic centers or in subcontinental mantle it is possible that magma ascent in magmons leads to spatial and temporal episodicity of volcanic activity if higher level processes do not obscure this influence the waveform of a magmon ascends faster than the liquid within the magmon so new liquid is taken in from above while original liquid is lost from below consequently magmons can mobilize small degrees of partial melt and deliver it rapidly to the surface

pervasive melt migration from migmatites to leucogranite in the shuswap metamorphic core complex canada control of regional deformation abstract the shuswap metamorphic core complex exhumed in the hinterland of the canadian cordillera displays a 15 km structural section from migmatites to leucogranite it comprises a lower unit dominated by anatectic migmatites exposed in the core of domes at higher structural level the transition from a middle amphibolite facies unit to an upper crustal unit is marked by a low angle detachment associated with the emplacement of laccoliths of leucogranite the amphibolite facies middle unit is permeated by a network of granitic veins feeding the laccoliths and structurally connected to the migmatites of the lower unit this paper describes the geometric textural and structural characteristics and the distribution of the granitic fraction at the outcrop scale in the amphibolite facies unit separating the migmatites from the leucogranite this analysis constrains the mechanisms of melt migration within a plurikilometer scale section across high grade rocks of the middle crust in fertile lithologies metapelites felsic amphibolites the granitic fraction in part generated in situ forms a diffuse network of concordant veins feeding discordant veins and structural sites such as the foliation shear zones and boudin necks discordant granitic veins are oriented perpendicular and to a lesser extent parallel to the mineral and stretching lineation in refractory lithologies the granitic fraction is dominantly intrusive and displays sharp contacts with the host rock however distribution of the granitic fraction shows the same characteristics as for fertile lithologies the melt fraction migrated through a network of fractures taking advantage of mechanical weaknesses such as the foliation plane or forming dikes oriented dominantly perpendicular to the regional stretching and mineral lineations these geometric and textural characteristics suggest that granite migration in these rocks is achieved dominantly by viscous flow of the melt solid through the solid matrix driven by its buoyancy and controlled by mechanical anisotropy of the rock and local dilation created by heterogeneous deformation the relationship between the regional fabric and the distribution of the granitic fraction indicates that regional deformation incremental and finite played a major role in providing pathways for melt migration the formation of laccoliths of leucogranite at higher structural levels suggests that upward melt migration led to accumulation of granitic magmas these observations are consistent with a model of pervasive melt migration through a network of interconnected concordant and discordant granitic veins feeding laccolithic plutons extracted from the dominantly solid matrix during vertical thinning and compaction at a regional scale the presence of both transposed and intact granitic networks indicate an overlap between deformation and granite migration as a continuum or in pulses the methodology and terminology proposed in this paper provide some insights on the behavior of the granitic fraction in the middle crust this approach should be applicable to other high grade terrains exhumed in the cores of orogenic belts

structural geometry lower crustal magmatic underplating and lithospheric stretching in the ivrea verbano zone northern italy abstract the ivrea verbano zone is believed to represent an up ended cross section through the lower continental crust as it existed at the end of the hercynian orogeny in the southern alps structurally oriented geological mapping has been carried out in the central and northern parts of the ivrea verbano zone a region some 30 km along strike the geology of the southern half of the zone is dominated by a large basic ultrabasic complex the mafic formation which is in contact with a strongly banded metasedimentary metabasic sequence to the north particular attention was paid to a the structural relationship between the rocks of the mafic formation and their envelope of high grade metasedimentary and metabasic rocks b the geometrical configuration throughout the ivrea verbano zone of high temperature shear zones which accommodated post hercynian crustal extension and c the geometry of late low temperature faulting the effects of which have been removed in order to produce a restoration of the structure as it existed during the post hercynian extensional phase the intrusion of large volumes of basic magma ca 50 of the outcrop area to form the rocks of the mafic formation appears to be coeval with the onset of extension ca 280 ma the main basic body has a laccolithic form which was originally more than 10 km thick overfolding developed at the northern margin of the laccolith and is interpreted in terms of the gravitational collapse of the hot immediately subsolidus or partially molten body incorporating its envelope of hot metasediments into a large originally recumbent fold a geometrical association with a high temperature low angle fault zone suggests that faulting was subsequently localized by the several km of uplift associated with the laccolithic intrusion the ivrea verbano zone may therefore demonstrate at least one particular geometry of lower crustal magmatic underplating which may aid in the interpretation of present day deep seismic profiles it also demonstrates the geometry of a network of conjugate high temperature low angle shear zones in a well layered lower crustal section

effect of finite deformation and deformation rate on partial melting and crystallization in metapelites 1 strain and strain rate partitioning in partially molten rocks are two of the important mechanisms that govern the process of coupling and or decoupling of the partially molten lithosphere consequently the proportion of partial melt and crystals and their network in partially molten rocks influence the degree of the partitioning along with the bulk rheology of the system this study explores the possible role of finite strain and strain rate on the rate and volume of partial melting and crystallization in a metapelitic system undergoing deformation cylinders of synthetic quartz muscovite aggregate 7 3 volume ratio were deformed in torsion at 750 c 300 mpa and constant shear strain rate 3 1 0 4 s 1 for finite shear strains g 1 15 the deformed samples were studied along the longitudinal tangential lt and axial la sections to obtain the data along a range of strain rates for a given finite strain and vice versa the results showed that deformation plays an important role on the kinetics of partial melting and crystallization with increasing strain rate amount and rate of crystallization comprise the volumetrically dominant process compared to partial melting at a given finite strain in contrast when the strain rate is constant partial melting is the dominant process over crystallization up to moderate strain g 5 the dominant process reverses at higher strain and the system shows more crystallization than partial melting application of the experimental data to geological systems implies that for metapelites a significant amount 20 of partial melt can generate at high strain rate and moderate strain g 7 but at high strain g 15 the system is melt depleted under such conditions decoupling should take place in brittle ductile mode on the other hand rocks undergoing deformation with low strain rates and strain g 3 contain more than 25 partial melt which can act as a major decoupling agent by localizing ductile shear zones

constraints on melting and magma production in the crust major intrusions of granitic rocks are found in several tectonic settings and in all cases crustal melts may contribute to the volumes of granitic magma high grade metamorphism and partial melting of the crust take place predominantly under fluid absent conditions we present a model for calculating the amounts of melt that may be formed by fluid absent breakdown of micas and amphiboles in common crustal rock types pelitic quartzofeldspathic intermediate and mafic melt proportions depend mainly on the kind of source rock the pressure at which melting takes place the temperature and the hydrous mineral h2o content of the source as a consequence of the pressure dependence of water solubility in silicate melts any given source rock will produce more melt by a given fluid absent reaction at lower pressure at a given pressure higher temperature reactions can produce more melt from a given source rock based on a survey of the compositions of common rock types we show that the amounts of melt can vary from 50vol thus crustal rocks vary widely in their fertility as magma sources depending on the types and amounts of hydrous phases they contain in general muscovite breakdown in pelites will yield only small quantities of melt and lead to migmatite formation biotite breakdown in pelites occurs at higher temperature and because most high grade pelites below granulite grade are biotite rich can yield up to about 50 vol of granitoid melt rocks of intermediate composition and hornblende rich mafic rocks are potentially highly fertile magma sources also provided that the high temperatures necessary for biotite and hornblende breakdown are realized pyroxene rich mafic rocks and quartzofeldspathic rocks are much less potentially fertile data suggest that mechanisms exist for the efficient segregation of melt and restite in systems with 30and probably 20vol melt the pressure temperature history of a region can greatly influence crustal source fertility through its control over the occurrence of subsolidus dehydration and melting equilibria

fluids p t paths and the fates of anatectic melts in the earth s crust this paper presents a model for the longevity and physical behaviour of anatectic melts in the earth s crust it is assumed that a thermal anomaly has caused partial fusion of biotite plagioclase quartz rocks to produce a granitic melt and restitic solids the focus is on the potential chemical and physical outcomes as a function of the various p t fluid conditions rocks undergoing fluid present melting will sustain an increase in bulk density and will become more gravitationally stable diapiric up welling of such material should not occur in fluid absent melting the bulk density will decrease and foster gravitational instability stresses in the surrounding rocks could however lead to fracture and rapid evacuation of the melt with excess fluid and without melt segregation isobaric cooling will cause immediate freezing if t rises above the biotite quartz melting reaction freezing will still occur at the original reaction t diapiric up welling should not occur biotite bearing diatexites might be formed by large degrees of fusion but magma ascent is unlikely in isothermal decompression immediate freezing will ensue and the migmatite should contain orthopyroxene rather than biotite with excess fluid and melt segregation cooling will induce freezing at the fluid saturated granite solidus magma ascent could however occur even for xflh2o 1 in isothermal decompression melt will persist to the granite solidus for the imposed xflh2o limited magma ascent could occur all granites should contain primary igneous biotite for fluid deficient rocks without melt segregation freezing will occur at the t of the original melting if the reaction is overstepped solidification will occur at the original xflh2o magma formation is unlikely migmatites should contain either pyroxene retrogressed to biotite or biotite alone on decompression immediate freezing is likely if t remains at the biotite quartz reaction for higher t melt will survive decompression and freeze at the fluid saturated solidus for some increased xflh2o magma ascent is possible and the melt will freeze very close to the wet granite solidus in fluid deficient rocks with melt segregation cooling and crystallization will cause fluid saturation in situ segregated melt will freeze at the original xflh2o melt ascent will however cause exsolution of a co2 rich fluid with fluid escape melt will freeze close to the wet granite solidus an increase in melt proportion may accompany magma ascent or source up welling any low p granite intrusion should be charnockitic for fluid absent rocks without melt segregation freezing will occur on cooling to the t of the original reaction only transitory migmatites could be formed but melt will survive decompression almost to the h2o saturated granite solidus the rocks will reveal former melt presence only in the existence of veins of coarse retrograde biotite with isothermal decompression further melting may occur forming an orthopyroxene bearing granulite facies migmatite in fluid absent situations with melt segregation magma could be efficiently transported to higher crustal levels if the melt proportion were insufficient for magma formation granulite facies migmatites would result ascending melt would progressively dissolve any entrained restite the granites produced should be charnockitic to aid in interpretation of the modelling results we suggest that it may be slightly more common for the highest grade metamorphic terranes to exhibit isobaric cooling paths that fluid present anatexis is normally limited to the shallower parts of the crust and that fluid absent reactions are more likely at greater depths we conclude that the best models for natural fluid present anatexis are those dealing with essentially pure h2o fluid and that fluid deficient conditions will dominate over fluid excess we also believe that it is common for melts to be physically segregated on scales larger than the diffusion paths of many elements

strain distribution across a partially molten middle crust insights from the ams mapping of the carlos chagas anatexite aracuai belt east brazil abstract the easternmost part of the neoproterozoic aracuai belt comprises an anatectic domain that involves anatexites the carlos chagas unit leucogranites and migmatitic granulites that display a well developed fabric microstructural observations support that the deformation occurred in the magmatic to submagmatic state structural mapping integrating field and anisotropy of magnetic susceptibility ams revealed a complex 3d structure the northern domain displays gently dipping foliations bearing a nw trending lineation southward the lineation trend progressively rotates to ew then sw and the foliation is gently folded the eastern domain displays e w and ne sw trending foliations with moderate to steeply dips bearing a dominantly ns trending lineation magnetic mineralogy investigation suggests biotite as the main carrier of the magnetic susceptibility in the anatexites and ferromagnetic minerals in the granulites crystallographic preferred orientation cpo measurements using the electron backscatter diffraction ebsd technique suggest that the magnetic fabric comes from the crystalline anisotropy of biotite and feldspar grains especially the delineation of several structural domains with contrasted flow fabric suggests a 3d flow field involving westward thrusting orthogonal to the belt northwestward orogen oblique escape tectonics and ns orogen parallel flow this complex deformation pattern may be due to interplay of collision driven and gravity driven deformations

fabric evidence for granodiorite emplacement with extensional shear zones in the variscan gredos massif spanish central system abstract three granitoid bodies in the central part of the gredos massif spanish central system batholith are tabular around 1 km in thickness and intruded into a migmatitic middle crust during the d3 deformation phase of the variscan orogeny petrologically they are composed of bt granodiorite and crd monzogranite and they show varying abundance of large cm scale feldspar megacrysts a detailed study of the shape preferred orientation spo magmatic fabric defined by these megacrysts together with a kinematic analysis of the structures due to interactions between them and the measurement of quartz c axis fabrics in migmatites and granitoids suggests that granitic magma and country rocks were mechanically coupled during deformation the emplacement took place along large scale extensional shear zones active during the first stages of the d3 phase the shape of the spo ellipsoids varies from constrictional at the centre of the granitic bodies to flattening or even oblate at their external contacts with the migmatitic host rocks the favoured interpretation of this spatial fabric variation is the overprinting of the emplacement fabrics by a constrictional tectonic regime associated with the growth of tabular magma chambers along extensional detachments followed by shear zone development commonly at the top of the granitic bodies the entire structure was later folded during the last stages of the d3 phase

melt enhanced deformation a major tectonic process convergent tectonics between continental crustal blocks result in deep burial and anatexis of supracrustal rocks anatectic and or mantle derived melts combine to form a melt weakened zone in the thickened lower crust the accumulation of melt eventually leads to crustal failure along melt lubricated shear zones rapid 1 mm yr vertical component movements of large crustal blocks result we refer to these crustal displacements as tectonic surges the melt lubricated shears are characterized by the close association of sheared country rocks with foliated or massive igneous sills and plutons rocks that formed at different crustal levels are juxtaposed across these shear zones one result of surges with large lateral component of movement is metamorphic inversion with high pressure and high temperature metamorphic rocks structurally over lower pressure and temperature assemblages large and rapid vertical surges may displace crust containing abundant melt and may result in high t p including granulite facies metamorphism and preservation of metamorphic textures caused by rapid decompression

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

rheological transitions and the progress of melting of crustal rocks abstract high grade igneous and metamorphic systems which possess a variable percentage of melt may undergo a transition between crystal supported and fully fluid behavior the melt fraction interval over which this transition occurs is not well constrained we have conducted six series of numerical simulations of crustal melting using melt fraction intervals between 0 05 to 0 15 for this mechanical transition the results of these simulations demonstrate the dependence of convection and progress of melting on the rheological transition between solid and melt convective heat flux varied by a factor of 8 over the duration of the simulations 160 yr and the mass of melt produced varied by nearly a factor of 4 the onset of convection in simulations with the most gradual rheological transition was suppressed convective heat flux and progress of melting were more sensitive to the melt fraction interval for the rheological transition than to the composition of a range of crustal protoliths the rheological transition between solid and melt may be one of the dominant factors controlling the thermal evolution of high grade crustal rocks

timing and duration of melting in the mid orogenic crust constraints from u pb shrimp data muskoka and shawanaga domains grenville province ontario the central gneiss belt in the grenville province ontario exposes metaplutonic rocks orthogneisses and minor paragneisses that were deformed and metamorphosed at crustal depths of 20 35 km during the mesoproterozoic grenvillian orogeny we present sensitive high resolution ion microprobe shrimp u pb zircon data from eight samples of migmatitic orthogneiss granite and pegmatite from the muskoka and shawanaga domains that constrain the age and duration of partial melting in the mid orogenic crust our results support earlier interpretations that the protoliths to these migmatitic orthogneisses formed at ca 1450 ma emplacement and crystallization of granite and pegmatite in the shawanaga domain took place at ca 1089 ma apparently coevally with deformation and high grade metamorphism leucosomes in the muskoka and shawanaga domains yield ages of 1067 and 1047 ma respectively interpreted as the ages of melt crystallization the geochronological data and field observations suggest that melt was pr

modeling dynamic fracture in granite under in situ conditions at high temperatures and pressures abstract reproducing the in situ mechanical response of granite at a depth of a few kilometer under dynamic loading presents significant challenges we have developed and calibrated a new thermo mechanical model for granite using extensive experimental data from both quasi static and dynamic test data the model includes parameters which can be calibrated for a specific geologic setting using the model developed we have performed a series of 2d and 3d simulations to evaluate effects of in situ stress and temperature on the extent of damage surrounding underground explosions we compare our results with available data for cavity size plastic zone and peak velocity attenuation with range in granite

towards an improved understanding of the mechanical properties and rheology of the lithosphere an introductory article to rock deformation from field experiments and theory a volume in honour of ernie rutter ernie rutter s influential contribution to our understanding of rock deformation spans the whole continental crust from deformation just under the grass e g rutter green 2011 to melt migration in the lower crust e g rutter neumann 1995 ernie has also worked on many aspects of the deformation of oceanic crust rutter brodie 1988 however here we reflect on the wide range of deformation conditions ernie has studied by presenting key aspects of the strength and rheology of the continental lithosphere as we understand it today with the aim of providing the context for the contributions included within this volume the continental crust forms just over a third of the earth s surface and it is different from the crust of any other planet in our solar system it is rich in those elements that partition in a silicate melt and its formation and evolution determined the composition of the mantle and that of the atmosphere hawkesworth 2006 thanks to its physical and chemical fingerprint the earth s crust has sustained life uninterrupted for 3 8 ga and it is the source of major natural resources such as hydrocarbons and mineral deposits and others such as geothermal energy the continental crust is less dense than its oceanic counterpart and is therefore more buoyant it forms a substantial part of the cold thermal layer of the earth and its rheology from greek r1v rhe flow and logia logia study the study of the flow of matter is a key factor controlling plate tectonic processes at the earth s surface and in its interior davies 2011 beneath the continental crust lies the lithospheric mantle and together they form the continental lithosphere considerable variations in structure thickness and composition of the continental lithosphere mean that despite its importance we currently have limited understanding of the rheology of this complex system thatcher pollitz 2008 significant advances in our knowledge of continental rheology have been possible through

spatial distribution of melt bearing structures in anatectic rocks from southern brittany france implications for melt transfer at grain to orogen scale abstract in this study we present quantitative spatial information on the one and two dimensional distribution of inferred melt bearing structures in anatectic supracrustal rocks of the southern brittany migmatite belt south of the transcurrent south armorican shear zone sasz based on these data we infer the mechanism of melt extraction from partially molten crust former melt bearing structures include foliation parallel leucosomes and cross cutting granitic leucosomes that infill inter boudin partitions and extensional shear surfaces as well as discordant dykes of granite petrographic i e mineralogical and microstructural continuity of granite from structure to structure suggests that they once formed a continuous melt bearing network measurements along one dimensional line traverses perpendicular to layering of stromatic migmatite exposed in clean sub horizontal outcrop surfaces provide information about thickness and spacing distributions of foliation parallel leucosomes most leucosome thicknesses fall in the range of 1 10 mm with upper limits around 20 30 mm the number of thicker layers decreases abruptly with increasing thickness which is inconsistent with scale invariance this suggests that leucosome formation was controlled by short range melt movement along grain boundaries to form melt rich layers constrained by pre existing compositional layering spacing distributions also are not scale invariant however the large percentage of leucosomes 40 60 in these line traverses suggests that spacing distributions may be controlled in part by impingement of leucosomes making it difficult to derive genetic information from these data qualitative observation of inferred melt bearing structures in mutually perpendicular two dimensional exposures from the same outcrop reveals anisotropy of the leucosome network related to a well developed sub horizontal quartz feldspar lineation reflecting stretching associated with transcurrent movement along the sasz analysis of these two dimensional distributions using the box counting method corroborates the observed anisotropy but indicates that leucosome morphology and perhaps distribution is not scale invariant the applicability of the box counting method or of fractal analysis to understanding melt movement in migmatites is discussed in light of these results based on the anisotropy of melt bearing structures we infer that melt movement in structures now represented by layer parallel leucosomes was primarily sub horizontal these layers fed steeply dipping structures now represented by cross cutting leucosomes in particular those developed at inter boudin partitions and granite dykes the formation and orientation of these steeply dipping structures was in part controlled by far field stresses related to dextral displacement along the sasz melt extraction is inferred to have occurred along these steeply dipping structures extracted melt accumulated in plutons at higher crustal levels such as the quiberon sarzeau and guerande granites

a granite gabbro complex from madagascar constraints on melting of the lower crust the ranomandry complex is a neoproterozoic nested intrusion from central madagascar composed of a gabbroic core within a coeval peraluminous granite ring intruding pelitic metasediments although xenocryst entrainment and magma mixing have both contributed to marginal phases of the granite the primary melt is characterised by steep lree hree ratios and negligible or slightly positive eu anomalies both isotopic and trace element systematics preclude an origin from either partial melting of the metapelitic country rock or from fractional crystallisation of the gabbroic magma however trace element modelling suggests an origin from the dehydration melting of a plagioclase poor garnet bearing metagreywacke at temperatures of 850 900 c and at lower crustal pressures 10 kbar melting of an enriched subcontinental mantle generated gabbroic magmas that caused advective heating and anatexis at the base of thickened continental crust during their ascent transport of the resulting granite magma was facilitated by the pre existing plumbing system that overcame thermal and mechanical problems associated with both diapirism and self propagating dykes as mechanisms for long distance transport of granite magmas the nested geometry of the intrusions is an indication of a structurally homogeneous lower crust that contains no pre existing shear zones or fault systems

use of microgranitoid enclaves as solid state strain markers in deformed granitic rock an evaluation microgranitoid enclaves are common in many plutons and are potentially valuable as solid state strain markers in tectonically deformed granitoids we consider the parameters necessary to assess enclaves as two dimensional strain markers these include i their primary shapes ii differences in rheology between enclave and host granitoid iii the magmatic shape fabric ellipse of enclave populations iv the maximum fluctuation of enclave long axes developed during magmatic processes v the angle between the magmatic shape fabric ellipse and tectonic strain ellipse at the onset of tectonic deformation and vi the type of strain path undergone by the markers enclave populations show characteristic magmatic distributions as shown by plots of the magmatic shape fabric ellipse vs enclave axial fluctuation from several plutons in the sierra nevada california and in the adamello massif italy the plots of tectonically undeformed and deformed enclaves show nearly complete overlap creating substantial uncertainties in separating magmatic strain from tectonic strain if only the final enclave axial ratio is considered enclave host strength differences have been modeled using published mineral deformation data and theoretical approaches to simulate deformation of aggregates results indicate very similar flow properties of enclaves and felsic host between 500 and 800 c and possibly at lower temperatures as well provided that biotite bearing enclave and host compositions are present two dimensional strain modeling of the enclave populations indicates that values of the total shape fabric ellipse as determined from field measurements can be close to the true tectonic strain under some circumstances but most commonly the former substantially over or underestimates the latter if the parameters i v are assessed at each strain site however and each measured surface subsequently modeled using those parameters over and underestimates of solid state strain can be greatly reduced or eliminated and reasonable values for two dimensional tectonic strain of the granitoid and its enclaves can be obtained

primary crustal melt compositions insights into the controls mechanisms and timing of generation from kinetics experiments and melt inclusions abstract we explore the controls mechanisms and timing of generation of primary melts and their compositions and show that the novel studies of melt inclusions in migmatites can provide important insights into the processes of crustal anatexis of a particular rock partial melting in the source region of granites is dependent on five main processes i supply of heat ii mineral melt interface reactions associated with the detachment and supply of mineral components to the melt iii diffusion in the melt iv diffusion in minerals and v recrystallization of minerals as the kinetics of these several processes vary over several orders of magnitude it is essential to evaluate in nature which of these processes control the rate of melting the composition of melts and the extent to which residue melt chemical equilibrium is attained under different circumstances to shed light on these issues we combine data from experimental and melt inclusion studies first data from an extensive experimental program on the kinetics of melting of crustal protoliths and diffusion in granite melt are used to set up the necessary framework that describes how primary melt compositions are established during crustal anatexis then we use this reference frame and compare compositional trends from experiments with the composition of melt inclusions analyzed in particular migmatites we show that for the case of el hoyazo anatectic enclaves in lavas the composition of glassy melt inclusions provides important information on the nature and mechanisms of anatexis during the prograde suprasolidus history of these rocks including melting temperatures and reactions and extent of melt interconnection melt homogenization and melt residue equilibrium compositional trends in several of the rehomogenized melt inclusions in garnet from migmatites granulites in anatectic terranes are consistent with diffusion in melt controlled melting though trace element compositions of melt inclusions and coexisting minerals are necessary to provide further clues on the nature of anatexis in these particular rocks

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

the mode of deformation in the orogenic mid crust revealed by seismic attribute analysis 1 the processes and the structures within the middle and the lower crust are intimately related to the evolution of orogenies but more detailed knowledge is needed of these deep crustal processes seismic reflection data chiefly displayed in amplitude are commonly used to interpret deep crustal structures the strongest amplitude events are probably related to lithological changes and do not necessarily correspond to geological structures tectonic boundaries or deformation fabrics furthermore the detailed structures and the strain distribution between the interpreted structural boundaries remain obscure here we show an example of how seismic attributes combined with the seismic facies interpretation technique can be used to enhance 2d seismic reflection data from the palaeoproterozoic svecofennian crust of southern finland to reveal unprecedentedly detailed information about the deformation fabrics within the mid crust of a collisional orogen the images are plausibly interpreted to show that the extension lateral flow of the orogenic middle and lower crust was mainly accommodated by kilometer scale s c structures the structures form penetrative deformation fabrics which are correlated with outcrop observations the successful enhancement of the seismic data confirms the ductile extension affecting hot orogenic crust and gives new information about the strain distribution of the regional syn to late orogenic deformation the seismic attribute method and the seismic facies interpretational approach described in this paper should be applicable to other seismic datasets from the crystalline basement

fluid absent melting behavior of a two mica metapelite experimental constraints on the origin of black hills granite we have studied experimentally the vapor absent melting behavior introduction of a proterozoic metapelite hp 60 1 from the black hills south peraluminous leucogranites such as the miocene granites dakota to assess whether the high do tourmaline bearing granites of the himalaya and tourmaline granites of the harney of the harney peak suite resulted from muscovite dominated depeak suite in south dakota are widely considered to be hydration melting at 10 kbar samples were sealed with no added the product of muscovite dehydration melting yet few h2o in gold capsules then run in a 0 5 inch 1 27 cm pistonexperimental studies of muscovite dehydration melting cylinder apparatus over the temperature interval 812 975 c reactions have been performed because the low temexperiments were conducted at 10 kbar to allow comparison with peratures of the reactions hinder the approach to equiother metapelite melting studies mass balance calculations imply librium in addition melt fractions generated are typically the melting reaction muscovite biotite plagioclase quartz low resulting in small melt pockets which are very difficult melt alkali feldspar aluminosilicate garnet until to analyze with the electron microprobe in this study muscovite is exhausted 812 c then the reaction biotite we assess the possible genetic relationship between the plagioclase quartz alkali feldspar aluminosilicate tourmaline bearing granites of the harney peak suite melt garnet the inferred muscovite reaction is completed below and the aluminous metasediments these granites intrude 812 c and produces 1 2 wt melt melt production of the although the attempt to investigate the muscovite decontinuous biotite reaction increases steadily with rising temperature hydration melting reaction was hindered by the surto 32 wt in our highest temperature run the low melt prisingly low melt productivity we were able to infer a productivity of the muscovite reaction at 10 kbar suggests that balanced reaction illuminating the dominantly peritectic melting at lower pressures may be necessary to generate mobile melt nature of fluid absent muscovite breakdown under the fractions by muscovite dominated reactions in our starting material conditions investigated in addition melts of hp 60 1 are considerably more mafic than isotopic and trace element studies indicate a genetic the tourmaline bearing granites with average combined tio2 relationship between s type granites and aluminous metamgo feo contents of 1 85 wt and 0 84 wt respectively sediments in the black hills of south dakota where the in particular melts of hp 60 1 are enriched in ti and would harney peak granite hpg intruded proterozoic and probably stabilize biotite rather than tourmaline upon cooling archean schists and metagreywackes undergoing regional arguing against hp 60 1 as a potential source rock for the metamorphism the timing and mode of emplacement of tourmaline granites the hpg and the deformation and regional metamorphic

synmagmatic deformation in the underplated igneous complex of the ivrea verbano zone the ivrea verbano zone northern italy contains an igneous complex up to 10 km thick that is thought to have been intruded near the interface between the continental crust and mantle during the late paleozoic new data indicate that this complex is pervasively deformed and concentrically foliated widespread deformation under hypersolidus conditions is indicated by growth of undeformed poikilitic phases across the foliation and segregation of late stage melts into high temperature faults and pressure shadows of boudins the presence of analogous features in ophiolitic gabbros suggests that emplacement of the ivrea verbano zone plutonic rocks involved large scale flow of crystal mush in a dynamic and possibly extensional tectonic environment

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

thrust related diapiric and extensional doming in a frontal orogenic wedge example of the montagne noire southern french hercynian belt abstract the montagne noire which is situated at the toe of the orogenic wedge of the french massif central south european variscides appears to be a well suited area for studying the origin and evolution of middle to upper crustal domes adjacent to foreland basins the data reported in the present paper show that the montagne noire dome is a particular type of basement involved frontal culmination in an orogenic wedge and foreland basin system this frontal culmination is characterized by a syn contractional ht decompression recorded by clockwise ptt paths and widespread strata overturning in thrust and fold structures which controlled the sedimentation in the adjacent foreland basin these unusual characteristics are interpreted to be a result of the succession of thrusting diapirism and extensional collapse antiformal stacking of syn metamorphic thrust sheets controlled the first stages of the foreland basin development diapirism was essentially responsible for the ht decompression and widespread strata overturning extensional doming was a result of late to post metamorphic collapse acting on the pre existing high amplitude dome diapirism and associated isothermal decompression metamorphism which constitute the essential difference between the montagne noire and ordinary frontal ridges in orogenic wedges were probably enhanced by a local partial melting of the upper to middle crust it is suggested that the occurrence of these phenomena in front of an orogenic wedge was related to local over thickening due to the superposition of an upper crustal antiformal stack on top of a lower crustal ramp anticline

modelling deformation of partially melted rock using a poroviscoelastic rheology with dynamic power law viscosity abstract a poroviscoelastic constitutive model is developed and used to study coupled rock deformation and fluid flow the model allows the relaxation of both shear and symmetric components of the effective stress experimental results are usually interpreted in terms of the power law viscous material however in this work the effect of strain damage on viscosity is considered by treating the viscosity as a dynamic time dependent parameter that varies proportionally to the second invariant of the strain rate healing is also taken into account so that the dynamic power law viscosity has a constant asymptotic at a given strain rate the theoretical model is implemented in a finite element fe formulation that couples fluid flow and mechanical equilibrium equations the fe method is applied to numerically study the triaxial compression of partially melted rocks at elevated pt conditions it is found that the numerically calculated stress strain curves demonstrate maxima similar to those observed in laboratory experiments also the computed pattern of melt redistribution and strain localization at the contact between the rock sample and a stiff spacer is qualitatively similar to the experimental observations the results also indicate that the matrix sensitivity to damage affects the scale of strain localization and melt redistribution

source controlled 87sr 86sr isotope variability in granitic magmas the inevitable consequence of mineral scale isotopic disequilibrium in the protolith abstract the broad sr isotopic variability exhibited by granitoid rocks is commonly interpreted to reflect the mixing of magmas from different sources however evidence from granites and migmatites indicates that melting and magma extraction from crustal sources can occur sufficiently rapidly that trace element and isotopic equilibration between liquid and residual phases is commonly not achieved additionally evidence from unmelted high grade metamorphic rocks indicates that major reactant minerals in the fluid absent melting process principally biotite and plagioclase do not always attain equilibrium during regional metamorphism when these two circumstances occur in combination the melt does not inherit its radiogenic isotopic signature from the bulk source in a simple way in such situations the isotopic composition of the melt will be dependent on the isotopic compositions of the reactant phases and the stoichiometry of the melting reaction this study has used information from experimental studies of fluid absent partial melting in metapelites and metagreywackes to investigate the consequences of sr isotopic disequilibrium between the reactant minerals for magma composition the study demonstrates that a range of isotopically distinct magmas can arise from progressive melting of a single source that is able to undergo melting through different reactions as temperature increases when translated to the typically layered sources constituted by sedimentary and volcano sedimentary rocks this process will produce magmas characterized by sr isotope variability that reflects the differences in melting reaction stoichiometry within the different layers even with no bulk rock isotopic variability between layers this study demonstrates that the sr isotope variability commonly observed within granitic suites as well as at the grain and sub grain scale within individual magmatic bodies can be primary reflecting differences in composition between magma batches produced from the progressive melting of a single source

deformational behaviour of migmatites and problems of structural analysis in migmatite terrains an understanding of the response of migmatites to deformation is crucial to an interpretation of their structures and in anatectic and intrusive migmatite terrains due consideration must be given to the modification of deformation processes imposed by melts in partially molten systems containing more than 30 melt the classical theories of fold formation are inapplicable the folds produced are of the viscous fold type their geometry is unpredictable and may mimic structures due to refolding this is particularly true at very high degrees of melting where flow of melt carrying rafts of solids begins failure to distinguish viscous folds from the products of refolding will lead to errors in interpreting the structural and metamorphic history of an area and to consequent misinterpretation of the true structural relations between geometrically complex high grade and more regularly deformed low grade areas

experimental deformation of partially melted granitic aggregates abstract the effects of varying amounts of partial melt on the deformation of granitic aggregates have been tested experimentally at conditions 900 c 1500 mpa 10 4 to 10 6 s where melt free samples deform by dislocation creep with microstructures approximately equivalent to those of upper greenschist facies experiments were performed on samples of various grain sizes including an aplite 150 m and sintered aggregates of quartz albitemicrocline 10 50 and 2 10 m water was added to the samples to obtain various amounts of melt 1 15 in the aplite 1 5 in the sintered aggregates optical and tem observations of the melt distribution in hydrostatically annealed samples show that the melt in the sintered aggregates is homogeneously distributed along an interconnected network of triple junction channels while the melt in the aplites is inhomogeneously distributed the effect of partial melt on deformation depends an melt amount and distribution grain size and strain rate for samples deformed with 1 melt all grain sizes exhibit microstructures indicative of dislocation creep for samples deformed with 3 5 melt the 150 m and 10 50 m grain size samples also exhibit dislocation creep microstructures but the 2 10 m grain size samples exhibit abundant tem scale evidence of dissolution precipitation and little evidence of dislocation activity suggesting a switch in deformation mechanism to predominantly melt enhanced diffusion creep at natural strain rates melt enhanced diffusion creep would predominate at larger grain sizes although probably not for most coarse grained granites the effects of melt percentage and strain rate have been studied for the 150 m aplites for samples with 5 and 10 melt deformation at 10 6 s squeezes excess melt out of the central compressed region allowing predominantly dislocation creep conversely deformation at 10 5 s produces considerable cataclasis presumably because the excess melt cannot flow laterally fast enough and a high pore fluid pressure results for samples with 15 melt deformation at both strain rates produces cataclasis presumably because the inhomogeneous melt distribution resulted in regions of decoupled grains which would produce high stress concentrations at point contacts at natural strain rates there should be little or no cataclasis if an equilibrium melt texture exists and if the melt can flow as fast as the imposed strain rate however if the melt is confined and cannot migrate a high pore fluid pressure should promote brittle deformation

a new mechanism of granite emplacement intrusion in active extensional shear zones one of the principal ways in which continental crust grows is by the incorporation from deeper within the earth of large volumes of granitic magma a space problem exists1 as to how these magmas are accommodated in the crust traditionally two main emplacement mechanisms have been emphasized forceful intrusion whereby buoyancy driven magmas physically push the crust aside creating granitic diapirs and balloons and passive emplacement characterized by replacive mechanisms such as cauldron subsidence and stoping although more recent work2 3 has demonstrated that space for granites may be created within bends and offsets of large transcurrent faults the simple view of either forceful or passive still fails to account for the intrusive mechanisms of many granites here we report the discovery of a new igneous intrusion mechanism in the superbly exposed proterozoic continental crust of south greenland we have observed that rapakivi granite was intruded as large scale sheets along ductile extensional shear zones that were active during emplacement in such a process the space problem seems to be simply resolved

shear rate dependent disequilibrium rheology and dynamics of basalt solidification magmas and lavas undergo a range of shear rates during transport and emplacement further transport of magma and lava occurs at subliquidus conditions where the melt crystallizes at varying temperature pressure and oxygen fugacity transport efficiency and eruption style are governed by magma rheology which evolves during cooling crystallization and degassing quantification of magma rheology rests almost exclusively on experimentation at constant temperature and shear rate we present the first study on the effect of shear rate on subliquidus basalt rheology at conditions relevant to lava flows and shallow magmatic systems the results reveal that basalts reach their rheologic death or cutoff temperature t cutoff i e the point at which the sample rheologically solidifies and flow stops at higher temperatures when flowing faster whereas crystallization is suppressed when the shear rate is low we explore the implications of shear enhanced crystallization for modeling and forecasting of lava flow hazards and our understanding of magma and lava transport storage systems plain language summary natural magmatic processes span several orders of magnitude in deformation rate the presented approach is the first to systematically document the resulting effects on the magma lava transport properties our paper presents an experimental study on the shear rate dependence of the crystallization solidification dynamics and rheology of basalts at experimental conditions that mimic the natural environment these were made possible through application of a newly developed experimental apparatus and method the measurements show that at a specific subliquidus temperature the so called rheological cutoff temperature the effective viscosity of basalts increases dramatically leading to solidification of the melt systematic investigation of this rheological cutoff shows a drastic previously unrecognized dependence on shear rate cooling rate and composition high deformation rates result in more intense crystallization at higher temperatures whereas crystallization is suppressed to lower temperatures in the absence of deformation the presented results open an entirely new field of studies in magma rheology and have important implications for the forecasting of natural hazards lava flow emplacement and the understanding of magma and lava storage and transport systems in general we discuss the implications of the experimental results for lava flow emplacement magma migration and for the computational modeling of lava flows for hazard assessment

timescales of melt generation and the thermal evolution of the himalayan metamorphic core everest region eastern nepal in the everest region of the nepalese himalaya 40ar 39ar and u pb geochronology provide evidence for a complex thermal history marked by multiple episodes of granite intrusion the oldest mobilized melt formed syn deformational granitic sills that have u pb crystallization ages of 21 33 0 03 and 21 80 0 05 ma preserved in these same granites is a record of earlier magmatic crystallization of xenotime zircon and monazite between ca 26 ma and ca 23 ma this pattern of accessory phase crystallization is interpreted to reflect incremental melting and crystallization in the source region of the sills before ultimate melt migration and provides the earliest evidence for anatexis in the everest region the beginning of crustal melting in the everest region predates the earliest known movement on both the main central thrust and the south tibetan fault systems but is temporally associated with the implied pressure decrease between eohimalayan and neohimalayan metamorphism

flow laws of multiphase materials and rocks from end member flow laws abstract rheological properties of polyphase rocks play an important role in the dynamics of the lithosphere and asthenosphere however flow laws for large portions of the polyphase rocks in the earth s crust and mantle have not been well determined an analysis based on the theory of mixtures has been made to calculate the general flow laws of coarse 5 m nearly equant grained aspect ratio 3 and massive polyphase rocks and materials for which only the flow laws and volume fractions of the constituents are taken into consideration in the modeling of the bulk rheology and effects of microstructure could be ignored the theoretical analysis is based on three assumptions 1 the polyphase composite and the monophase aggregates of its constituents obey the same kind of flow laws linear power or exponential 2 there is no change in the operative deformation mechanism of each phase when it is in the composite as compared to when it is in a monophase aggregate and 3 neither chemical metamorphic reactions take place among the constituent phases nor eutectic melting occurs due to the phase mixing the proposed iterative process allows to predict to the first approximation the flow laws for a large number of polyphase rocks in terms of the experimentally determined flow laws of a relatively small number of monomineralic aggregates applications of this approach to typical polyphase rocks such as granite diorite diabase aplite and websterite as well as to synthetic two phase materials such as forsterite enstatite mixtures and water ice ammonia dehydrate aggregates yield quite accurate approximations to the experimental values