probable burial diagenetic and provenance effects on dakota group clay mineralogy denver basin abstract illite smectites in cored dakota group cretaceous shales and bentonites of the northern denver basin identified using a modification of reynolds and hower s 1970 x ray diffraction criteria show decreasing sample sample expandability ranges lower modal expandability and a change from random to ordered mixed layering with increasing burial depths and temperatures these are results characteristic of burial diagenesis as described by perry and hower 1970 ordered illite smectites from low temperature wells and much of the kaolinite chlorite vermiculite and discrete illite from all wells are interpreted as detrital episodic but frequent admixture of highly expandable bentonitic illite smectite with detrital clays is reflected by fluctuating expandabilities within individual cores and the lack of samples containing both highly expandable illite smectite and high proportions of other clay minerals differential diagenesis and or differential sedimentation rates do not satisfactorily account for lower modal expandabilities and increased proportions of ordered illite smectite observed in shales from d and j sand stones compared with those from huntsman and skull creek shales of equivalent temperatures instead they are attributed to provenance differences which gave lower expandability illite smectites and a head start on diagenetic trends to sand associated shales eastern and western provenances identified from heavy mineral studies e g mackenzie and poole 1962 for d and j sands were not matched by similar clay mineral provenances affecting shales however decreasing proportions of kaolinite chlorite vermiculite encountered from northeastern to southeastern d locales are interpreted as the results of differing sources

the influence of melting and melt drainage on crustal rheology during orogenesis partial melting significantly weakens crustal rocks by introducing a low viscosity liquid phase however near concomitant melt drainage can remove this weak phase potentially reversing the rheological effects such that the strength of a specific lithology depends on when the prograde pressure temperature path intersects a melting reaction how much melt is produced and how long this melt is retained before it is lost phase equilibria and mixed rheology modeling of typical metapelite and metagreywacke compositions indicate that these rocks undergo continuous but pulsed melt production during prograde metamorphism depending on whether melt removal is continuous or episodic and assuming geological strain rates the lithologies can retain a very low strength less than 1 mpa or transiently strengthen to 5 mpa following melt loss lithologies undergoing episodic melt loss can therefore cycle between being relatively weak and relatively strong components within a composite crustal section melt production retention and weakening in the middle to lower crust as a whole is more sustained during heating and melt production consistent with geodynamic inferences of weak melt bearing lower crust however the long term consequence of melting and melt loss is a 50 400 increase in the strength of residual lithologies the strengthening is more pronounced in metapelite than metagreywacke and is achieved through a combination of dehydration and the removal of the weak mica framework coupled to increased proportions of strong feldspars and garnet despite prolonged weakness melting and melt loss therefore ultimately result in a dry and elastic lower crust

ductile fractures and magma migration from source mechanisms proposed to explain effi cient melt transport away from hot ductile source regions are problematic brittle elastic fracturing is a well known mechanism that allows fast magma migration as dikes through cold crust ductile fractures have been propo sed as an alternative for ductile environments where brittle elastic diking is inhibited ductile fracturing results from rock creep and growth of microscale voids that become interconnected leading to rock failure in this paper we present observations and numerical models supporting the hypothesis that ductile fracture controls early steps in magma migration we postulate that once developed ductile fracture dikes may reach a critical length where magma stresses at dike tips overcome fracture toughness and lead to brittle elastic diking which subsequently controls magma migration

partial melting of metagreywackes part ii compositions of minerals and melts a series of experiments on the fluid absent melting of a quartz rich aluminous metagreywacke has been carried out in this paper we report the chemical composition of the phases present in the experimental charges as determined by electron microprobe this analytical work includes biotite plagioclase orthopyroxene garnet cordierite hercynite staurolite gedrite oxide and glass over the range 100 1000 mpa 780 1025 c biotites are na and mg rich with ti contents increasing with temperature the compositions of plagioclase range from an17 to an35 with a significant orthoclase component and are always different from the starting minerals at high temperature plagioclase crystals correspond to ternary feldspars with or contents in the range 11 20 mol garnets are almandine pyrope grossular spessartine solid solutions with a regular and significant increase of the grossular content with pressure all glasses are silicic sio2 67 6 74 4 wt peraluminous and leucocratic feo mgo 0 9 2 9 wt with a bulk composition close to that of peraluminous leucogranites even for degrees of melting as high as 60 vol with increasing pressure sio2 contents decrease while k2o increases at any pressure the melt compositions are more potassic than the water saturated granitic minima the h2o contents estimated by mass balance are in the range 2 5 5 6 wt these values are higher than those predicted by thermodynamic models modal compositions were estimated by mass balance calculations and by image processing of the sem photographs the positions of the 20 to 70 isotects curves of equal proportion of melt have been located in the pressure temperature space between 100 mpa and 1000 mpa with increasing pressure the isotects shift toward lower temperature between 100 and 200 mpa then bend back toward higher temperature the melting interval increases with pressure the difference in temperature between the 20 and the 70 isotects is 40 c at 100 mpa and 150 c at 800 mpa the position of the isotects is interpreted in terms of both the solubility of water in the melt and the nature of the reactions involved in the melting process a comparison with other partial melting experiments suggests that pelites are the most fertile source rocks above 800 mpa the difference in fertility between pelites and greywackes decreases with decreasing pressure a review of the glass compositions obtained in experimental studies demonstrates that partial melting of fertile rock types in the crust greywackes pelites or orthogneisses produces only peraluminous leucogranites more mafic granitic compositions such as the various types of calk alkaline rocks or mafic s type rocks have never been obtained during partial melting experiments thus only peraluminous leucogranites may correspond to liquids directly formed by partial melting of metasediments other types of granites involve other components or processes such as restite unmixing from the source region and or interaction with mafic mantle derived materials

relationship between thermal maturation gradients geothermal gradients and estimates of the thickness of the eroded foreland section southern alberta plains canada abstract analysis of post laramide tertiary uplift and erosion in the southern alberta plains indicates that the greatest erosion occurred in regions where the youngest stratigraphic units are preserved this is consistent with geological structure and the few preserved stratigraphic constraints on erosional history throughout this region erosion is pervasive and the uplift history is commonly constrained by coalification data the analysis of coalification erosion and paleogeothermics are interrelated and knowledge of them is important to understand hydrocarbon generation and tectonic history several independent attempts to analyse coalification erosion and paleogeothermics in this area have given different results the most striking differences are those between estimates derived from the analysis of well profile coalification gradient and those determined using a commonly accepted relationship between the amount of eroded section and the equilibrium moisture content of near surface coals the match between present and paleogeothermal gradient fields is better when the latter technique is used correlation is expected between the late orogenic and present geothermal gradient fields because the hydrodynamically controlled advective heat flow pattern that now dominates geothermal gradients in the mesozoic and tertiary foreland succession was initiated by the growth of topography in the west throughout cordilleran orogeny well profile coalification gradients have significant though commonly unacknowledged uncertainties these uncertainties are propagated in erosion and paleogeothermal gradient calculations ideally the relationship between erosion estimates using well profile coalification gradients and near surface coal properties can be compared unfortunately the uncertainties in well profile coalification gradients prevent this

modelling granite migration by mesoscale pervasive flow abstract mesoscale pervasive magma migration leads to granite injection complexes common in hot crustal terranes pervasive migration is limited by magma freezing when intruding cold country rock here we explore numerically the feedback mechanism between magma intrusion and heating of the country rock which allows younger intrusive batches to reach increasingly shallower cooler levels this process relies on the higher solidus temperature of a rock compared to that of its melt once melt is segregated we define the free ride layer as the region above the melt source where magma may freely migrate because rock temperature is above melt solidus the top of the free ride layer which corresponds to the melt solidus t s isotherm is at the limiting depth z s after magma passes through the free ride layer the magma front is always at the limiting depth we modeled the thickening and heating of the crust above the source as melt at its liquidus t l intrudes it pervasively from below we found that a magma quickly warms crust below z s to about t l forming a step in temperature at z s b the front z s moves up through the crust as more magma is intruded c as magma is emplaced at the front a mingled layer of about half magma half crust forms below it so that the total rise of the front corresponds approximately to half of the thickness of magma added to the free ride layer d the rate of rise of the front depends on the temperature difference between crust and t l and slows down as the magma front rises e for most reasonable intrusion rates and volumes the crust above z s feels little influence of the intrusion because the diffusion time scale is much smaller than the rise rate of the front in summary pervasive migration is an efficient way of heating the lower to middle crust and can result in an injection complex several kilometers thick consisting of about half magma and half original crust

chemical models of vitrinite reflectance evolution a global kinetic model of vitrinite reflectance evolution is developed to illustrate a new approach to vitrinite reflectance modelling the method utilizes quantitative pyrolysisgas chromatographic data from isolated vitrinite kerogens to derive the concentrations of structurally specific moieties alkylphenol precursors in vitrinite kerogens as a function of rank this data set is used to calibrate a gaussian distributed activation energy model for phenol precursor loss from vitrinites using published burial histories phenol yield is then correlated with vitrinite reflectance the predictive vitrinite reflectance model based on this phenol system is tested against a well from the us gulf coast area the results being compared with a lopatin model of the same well this type of vitrinite reflectance model is numerically compatible with current generation kinetic models of hydrocarbon production from source rock kerogens and has a better heating rate independence than lopatin s method

pervasive granitoid magma transfer through the lower middle crust during non coaxial compressional deformation granitic magmas migrated through early proterozoic middle lower crust at mt hay central australia via a diverse network of narrow structurally controlled channelways during a period of progressive w sw directed thrusting d1a d1d they utilized existing folds boudins and shear zones or created new channels by magmatic fracture either parallel to layering or rarely in irregular arrays the magmas rose obliquely parallel to the plunging 50 60 regional elongation direction which was defined by coaxial folds boudin necks and a strong mineral elongation lineation megacrystic charnockitic magmas migrated through metre scale conduits during d1a d1b but leucosomes were generally restricted to smaller centimetre scale structures that existed throughout the entire deformation history thus d1a d1b leucosomes were potential feeders of in situ partial melts to the adjacent larger conduits of charnockite magma thereby providing a pervasive interconnected network that allowed efficient migration of all magma types during the early stages of thrusting the upper middle crust of the anmatjira reynolds range area contains abundant megacrystic granitoid sheets that are of similar age and geochemistry to those at mt hay they are considered to have formed as syntectonic intrusions emplaced during w sw directed thrusting as at mt hay suggesting that granitic magmas formed near the base of the continental crust passed through the mid lower crustal level 25 30 km exposed at mt hay and accumulated in batholithic proportions at shallower crustal levels 12 20 km such as the anmatjira reynolds range area the observations imply that granitoid magmas in the deep crust are capable of pervasive migration through the crust during major compressive noncoaxial shear deformation localization of magmas by sequentially developed narrow compressive structures suggests that dilatancy followed successive foliation forming events a situation that can occur during steady state deformation if the effective confining pressures are low which would be a result of high and possibly variable rates of magma influx the inferred rapid melt segregation and migration during deformation suggest that large chambers do not form until magma reaches neutral buoyancy in the middle to upper continental crust

coalification in the northern wildhorn nappe and adjacent units western switzerland implications for tectonic burial histories abstract vitrinite reflectance of fourteen eocene coal samples from the northern wildhorn nappe in the kander valley have been analyzed and compared to nine agewise similar coals from adjacent tectonic units the degree of coalification decreases regularly from semi anthracite in the kander valley to lignite in the plateau molasse the degree of coalification in the tertiary coals appears to be solely dependent on their tectonic history and indicates and estimated 6 km of burial by higher pennine nappes for the kander valley the rank at this locality low volatile bituminous to semi anthracite is significantly higher than in the border chain at beatenberg high volatile a bituminous the latter locality therefore was never buried deeper than about 4 km a further decrease in rank is found in the subalpine flysch and molasse high volatile b bituminous which in turn is significantly more mature than lignites from the folded plateau molasse at linden two samples of dogger coal from the pennine prealpes medianes are medium to low volatile bituminous that is intermediate between the kander valley and beatenberg their rank however was achieved before their final emplacement north of the wildhorn nappe by comparing calculated tti time temperature indices values for time depth burial curves with measured vitrinite reflectances maximum burial temperatures were estimated for the various tectonic units for the wildhorn nappe 160 180 c were obtained in the kander valley and 100 130 c in the border chain as a result of tectonic burial due to the thrusting by the pennine prealps sedimentary burial led to temperatures of 100 120 c in the subalpine molasse below the border chain prior to its thrusting

the ascent of felsic magmas in dykes abstract the results of a thermal and fluid dynamical analysis are presented that allow geologists to estimate the critical dyke or fracture width w c necessary for the transport of felsic magma through the crust without control by solidification the principal geological variables required to estimate w c are the magmatic viscosity the density and temperature contrasts and t between magma and country rock and the height of ascent h the results show that for typical values of and and for transport distances of 20 to 30 km the critical dyke width is constrained to lie between about 2 and 20 m

the pangong injection complex indian karakoram a case of pervasive granite flowthrough hot viscous crust in the karakoram range of nw india the tangtse gorge cuts across deep crustal rock sexhumed by transpression along two strands of the dextral karakoram fault crustal leucogranitic magmas pervasively intruded amphibolites and migmatites in the form of sheets that locally coalesced and expanded to form kilometre scale plutons sheets resulted from slow seeping of granite into foliation planes magma wedging rather than from dyking driven by magma buoyancy and possibly syn intrusive tectonic deformation high temperature of the country rocks at the time of intrusion is inferred from similar crystallization ages of the intrusive leucogranite and in situ partial melt in the migmatites and reflected in the ductile structures developed whereas low country rock viscosity inhibited dyking high temperature freed the magma from the constraints of freezing and permitted pervasive intrusion the injection complex exposed along the tangtse gorge rather than representing the final emplacement structures represent transient structures of the granite pathways on their upward journey to build the karakoram batholith which crops out a few kilometres north at structurally shallower levels we suggest that pervasive magma flow is a transitional step between magma segregation at the source and later rise through cold crust and it may be one of several factors controlling whether dyking or diapirism becomes dominant during late ascent

the mechanism of ascent and emplacement of granite magma during transpression a syntectonic granite paradigm we propose a model for syntectonic ascent and emplacement of granite magma based on structural relations in part of the northern appalachians in the study area in western maine strain was distributed heterogeneously during devonian acadian transpression metasedimentary rocks migmatites at high grades record two contrasting types of finite strain in zones that alternate across strike rocks in both types of zones have a penetrative moderately to steeply ne plunging mineral elongation lineation defined by bladed muscovite fibrolite sillimanite at high grades in straight belts of enhanced deformation rocks have s l fabrics that record apparent flattening to plane strain apparent flattening zones afzs but rocks between these belts have l s fabrics that record apparent constriction apparent constriction zones aczs at metamorphic grades above the contemporary solidus rocks in afzs developed stromatic structure in migmatite which suggests that percolative flow of melt occurred along the evolving flattening fabric stromatic migmatites are intruded by concordant to weakly discordant m scale composite sheet like bodies of granite to suggest magma transport in planar conduits through the afz rocks inhomogeneous migmatite is found in the intervening aczs which suggests migration of partially molten material through these zones en masse probably by melt assisted granular flow inhomogeneous migmatites are intruded by irregular m scale bodies of granite that vary from elongate to sub circular in plan view and seem cylindrical in three dimensions these bodies apparently plunge to the northeast parallel to the regional mineral elongation lineation to suggest magma transport in pipe like conduits through the acz rocks we postulate that the form of magma ascent conduits was deformation controlled and was governed by the contemporaneous strain partitioning magma ascent in planar and pipe like conduits through migmatites is possible because oblique translation during contraction displaces isotherms upward in the orogenic crust to form a thermal antiform within this hot corridor it is the difference in temperature between melt producing reactions in the anatectic zone and the wet solidus for granite melt that enables magma to migrate pervasively up through the orogenic crust without congealing heat advected with the migrating melt promotes amplification of the thermal antiform in a feedback relation that extends the zone of plastic deformation and pervasive melt migration to shallower levels in the crust at the wet solidus we suggest melt flows obliquely toward axial culminations in the thermal antiform which are sites of melt accumulation and perturbations from which magma may escape to form plutons batches of melt that escape from these perturbations may be trapped by tectonic structures higher in the crust or ascent may become inhibited with decreasing depth by thermal arrest and solidification if the rate of arrival of subsequent melt batches exceeds the rate of crystallization at the site of pluton construction melt pressure ultimately may lead to sub horizontal magma fracture or viscous flow of wall rocks may allow lateral spreading the resultant plutons have sub horizontal tabular geometries with floors that slope down to the ascent conduit as the thermal antiform decays the height of sub solidus crust that separates the deepest part of the pluton from the anatectic zone increases consequently pluton inflation declines and solidification leads to infilling of the magma feeder channel to form a root zone that passes downward into migmatite which may explain the difficulty of determining precisely the floor to these deeper segments of large plutons using gravimetry

a review of the superior province of the canadian shield a product of archean accretion abstract the superior province consists of northern and southern high grade gneiss subprovinces and a central region of alternating granite greenstone and metasedimentary belts subprovinces are commonly fault bounded and display contrasting lithological assemblages metamorphic and structural styles geophysical characteristics and ages they are comparable to phanerozoic suspect terranes the middle and late archean rocks of the superior province are of mantle and juvenile crustal origin with little evidence of inheritance of components older than ca 3 1 ga high grade gneiss subprovinces are mainly deeper level equivalents of the supracrustal rich belts but one minnesota river valley is part of an older ca 3 6 ga terrane that was juxtaposed late in the tectonic history granite greenstone terranes are characterized by low grade volcano sedimentary sequences tholeiitic komatiitic submarine lava plain tholeiitic calc alkalic submarine to subaerial central complexes early platform type quartz arenite stromatolitic carbonate late timiskaming type shoshonitic alkalic volcanic fluvial sediment that range in age from ca 3 0 ga to 2 7 ga the volcanics represent oceanic island arc and continental arc volcanism the quartz arenite carbonate sequences deposition on relatively stable early formed ca 3 0 ga crust and the timiskaming type sequences deposition in pull apart basins developed along strike slip faults late archean ca 2 75 2 70 ga greenstone sequences occur throughout the superior province middle archean ca 3 0 2 8 ga sequences are common in northern and central superior province rare or absent in the south volcanism was accompanied by mafic to trondhjemitic plutonism the metasedimentary belts consist of variably metamorphosed volcanogenic turbidites with detrital zircons ranging in age from ca 3 0 ga to 2 7 ga the metasediments were deposited after major volcanism and probably represent accretionary prisms late archean orogenesis accompanied and followed by calc alkalic plutonism youngs southward from about 2 73 2 72 ga to 2 70 2 68 ga it involved large scale north south compression and dextral transpression and displays thin to thick skinned transitions the contemporaneity of events along the lengths of the belts and their southward younging coupled with the evidence of major compression are consistent with subduction driven oblique accretion of oceanic and continental volcanic arcs accretionary sedimentary wedges older microcontinental fragments etc in a convergent margin setting analogous to parts of the pacific rim differences eg abundance of komatiites and tonalitic plutonic suites are attributable to a hotter archean mantle

involvement of fluids in the metamorphic processes within different zones of the southern marginal zone of the limpopo complex south africa an oxygen isotope perspective abstract we present oxygen isotope data obtained by laser fluorination for three outcrops from the south marginal zone smz of the limpopo granulite complex south africa these outcrops are located within the granulite zone bandelierkop quarry on the retrograde anthophyllite in isograd manamead locality and within the zone of rehydrated granulite south of the retrograde isograd klipbank locality studied samples also include felsic granitoid rocks that occur as intrusive bodies veins and veinlets in the host tonalite gneisses or the metapelite the tonalite gneiss tg and the k feldspar rich segregations kfs g at klipbank have marginally different 18 whole rock wr values 7 9 and 7 3 correspondingly the kfs g may have formed by partial melting of the tg in the presence of external saline h 2 o co 2 fluid metapelites at manamead locality have 18 o values 9 5 10 3 lower than those at bandelierkop quarry 10 0 11 4 the two mineral oxygen isotope temperature estimates for metapelite minerals from manamead cluster around two values 620 30 and 730 40 c oxygen isotope temperature estimates for the metapelites from bandelierkop quarry define a narrow temperature range of 700 740 the oxygen isotope temperatures are in reasonable agreement with the results of classical geothermobarometry the 18 values of the whole rocks and individual constituent minerals of metapelites strongly negatively correlate with the rocks volatile content loi values this suggests that a fluid phase was involved in the hydration of metapelites in the vicinity of the regional anthophylite in isograd of the southern marginal zone the fluid may have been released during crystallization of leucogranite melt oxygen isotope and geochemical features of the leucogranite indicate genetic relation to the tonalitic baviaanskloof gneisses but do not support the formation of leucogranite via in situ partial melting of metapelites

microstructural evidence for magma confluence and reusage of magma pathways implications for magma hybridization karakoram shear zone in nw india in the karakoram shear zone ladakh nw india miocene leucogranitic dykes form an extensive varied and complex network linking an anatectic terrane exposed in the pangong range with leucogranites of the karakoram batholith mineral paragenesis of the heterogeneous anatectic source rocks suggests melting has resulted from water influx into rocks at upper amphibolite facies conditions and microstructures suggest anatexis was contemporaneous with shearing the network is characterized by continuous and interconnected dykes with only rare cross cutting relationships forming swarms and chaotic injection complexes where magmatic rocks cover up to 50 of the outcrop area despite this volume of magma the system did not lose continuity suggesting that it did not flow en masse and that the magma network was not all liquid simultaneously leucogranites in this network including leucosomes in migmatites carry an isotopic signature intermediate between the two main anatectic rocks in the source suggesting efficient homogenization of the magmatic products here we describe a number of microscopic features of these magmatic rocks which suggests that several pulses of magma used the same pathways giving rise to textural and chemical disequilibrium features these include i narrow tortuous corridors of fine grained minerals cutting across or lining the boundaries of larger grains interpreted to be remnants of magma filled cracks cutting across a pre existing magmatic rock ii corrosion of early formed grains at the contact with fine grained material iii compositional zoning of early formed plagioclase and k feldspar grains and quartz overgrowths documented by cathodoluminescence imaging iv incipient development of rapakivi and anti rapakivi textures and iv different crystallographic preferred orientation of early formed quartz and fine grained quartz mapping of the fine grained corridors interpreted to represent late melt channels reveal an interlinked network broadly following the s c fabric defined by pre existing magmatic grains we conclude that early formed dykes provided a pathway exploited intermittently or continuously by new magma batches new influxes of magma opened narrow channels and migrated through a microscopic network following predominantly grain boundaries along an s c fabric related to syn magmatic shearing a mixed isotopic signature resulted not from the mixing of magmas but from the micro scale interaction between new magma batches and previously crystallized magmatic rocks through local equilibration

thermal diagenesis in the swiss molasse basin implications for oil generation clay mineral transformations during burial are indicators of the degree of diagenesis of sediments diagenetic zonations in numerous wells of the swiss molasse basin are defined by the disappearance of smectite and or the appearance of either corrensite or irregular 2 1 mixed layers the maximum level attained in the thickest molasse sections corresponds to organic matter maturation suitable for hydrocarbon generation reconstructed on the basis of the clay mineral transformation data a burial history of the basin is proposed

zooarchaeology of the layers from dorochivtsy iii ukraine palaeolithic archaeological sites of the western ukraine are clustered along the prut and dniester rivers different sites provided data enabling reconstruction of the paleoenvironment chronology and cultures of human group during the upper paleolithic notably molodova v during the second part of the pleniglacial between 23 000 and 20 000 years bp palaeoclimatic variations took place the intensification of cold and arid conditions is liable to force human groups to adapt to a changing environment little is known about this period with only a few assemblages ongoing excavations continue to provide new data the archaeological site of dorochivtsy iii has an important sequence stratigraphy with several archaeological layers among the seven upper palaeolithic layers layers 6 5 4 and 3 testify to activities of a human group during the upper pleniglacial we studied the faunal assemblages applying zooarchaeological methods identifying mammoth mammuthus primigenius reindeer rangifer tarandus horse equus sp and fox alopex lagopus vulpes vulpes the gravettian layers 3 4 5 have anthropogenic clues in connection with subsistence activities oriented on reindeer then horses and finally fox concerning mammoths we cannot define the modes of acquisition and use these occupations have been interpreted as recurrent hunting occupations linked to procurement of local flint and lithic production for butchering activities layer 6 dated to 22 330 100 bp is remarkable because of previously unseen practises the lithic assemblage combined with bone industry and engraved tusk is a novel set of cultural elements in this area called ancient epigravettian this layer testifies to the diversity of human activities during the upper pleniglacial and to the particular status of mammoth ivory as an artistic medium palynological data and taphonomic observations on bones indicate the persistence of relatively moist conditions during some periods which could favour the movement of human groups although little is known about the upper pleniglacial period dorochivtsy iii testifies to the continuity of a large exploitation of the territory of the dniester valley

magma accumulation and segregation during regional scale folding the holland s dome granite injection complex damara belt namibia abstract the regional scale upright fold of the holland s dome in the damara belt of central namibia contains a kilometre scale network of intrusive highly fractionated uraniferous leucogranites three broadly orthogonal and intersecting sets of leucogranite sheets that intruded parallel and at right angles to the axial plane of the first order fold can be distinguished the granites are internally sheeted and illustrate the growth of the injection complex through the successive addition of thousands of smaller magma batches spatial and timing relationships point to a stepwise evolution of the injection complex early dilatancy driven segregation and accumulation of granitic magmas in the core of the fold above a basal detachment was followed by compaction driven segregation of a melt phase during fold tightening the intersecting leucogranite sets provide a suitably organized permeability structure for melt segregation while the successive injection of magma batches ensures compatibility between regional strain rates during folding and the rates of magma segregation the three dimensional network of melt bearing structures further assisted regional shortening past the lock up of the fold the holland s dome injection complex illustrates the geometric complexity of magma transfer pathways and the significance of regional scale folding for the accumulation segregation and fractionation of granitic magmas in suprasolidus crust

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

contrasting thermal evolution of thrust systems an analytical and modeling approach in the front of the western alps in foreland fold and thrust belts the study of the maturity of the organic matter and kinematic and thermal modeling techniques is useful in unraveling the thermal history and maturation of source rocks the case study presented here is the classical example the western alps this work evidences that contrasting thermal evolutions can develop in relatively closely adjacent areas of the same thrust belt analytical results show that the mesozoic rocks have undergone a wide range of temperatures up to 250c locally the higher temperature values are associated with the tectonic emplacement of early widespread allochthonous nappes that were emplaced obliquely in the northern part of the area prior to the thrust tectonics of the subalpine chains folding and offsets of the isomaturity surfaces are observed which implies that in some parts of the thrust belt the thermal peak was reached before fold and thrust deformation erosion rates vary greatly along the thrust front extensive erosion probably more than 4 km 2 5 mi of sediments from the tertiary and the prealpine nappes occurred in the north of the area studied along the bornes transect away from the area of influence of the prealpine nappes numerical modeling shows differences in the timing of maturation of the source rocks according to the area considered maturation was attained either early before thrust tectonics most of the vercors area or during the deposition of the syntectonic flexural series preceding thrust tectonics molasse basin or else during thrust tectonics most of the chartreuse area

the ti saturation surface for low to medium pressure metapelitic biotites implications for geothermometry and ti substitution mechanisms the ti content of biotite can serve as a geothermometer for graphitic peraluminous metapelites that contain ilmenite or rutile and have equilibrated at roughly 4 6 kbar the relationship between ti content temperature and mg mg fe value was calibrated empirically using an extensive natural biotite data set 529 samples from western maine and south central massachusetts in combination with the petrogenetic grid of spear et al 1999 the calculated ti saturation surface is curved such that for a given mg mg fe value ti concentration increases as a function of temperature in a nonlinear fashion and for a given temperature ti concentrations decrease with an increase in mg mg fe the fit to the ti saturation surface can be reformulated as the geothermometric expression t ln ti a c x mg 3 b 0 333 in which t is temperature in degrees celsius ti is the number of atoms per formula unit apfu normalized on the basis of 22 o atoms x mg is mg mg fe a 2 3594 b 4 6482 10 9 and c 1 7283 the calibration range for this expression is x mg 0 275 1 000 ti 0 04 0 60 apfu and t 480 800 c precision of the ti in biotite geothermometer is estimated to be 24 c at the lower temperature range and improves to 12 c at higher temperatures application of the ti in biotite geothermometer to ilmenite or rutile bearing graphitic peraluminous metapelites equilibrated at 3 6 kbar is generally consistent with independent temperature determinations but with some deviations that represent local reequilibration consequently the ti systematics in biotite can also serve as the basis of a very sensitive indicator of chemical equilibrium or lack thereof application of the geothermometer to metapelites not containing the requisite mineral assemblages can lead to minor to significant errors in estimated temperatures biotite ti substitution mechanisms are controlled by several factors based on the biotite calibration data set magnesian biotites x mg 0 65 incorporate ti in accordance with the exchange vector tial2r 1si 2 where r is the sum of the divalent cations mg fe mn this substitution mechanism is primarily a response to misfit of the octahedral and tetrahedral layers in magnesian biotites intermediate biotites x mg 0 65 particularly at higher temperatures exhibit enhanced ti concentrations most consistent with the ti deprotonation tio2r 1 oh 2 exchange vector dominance of ti deprotonation substitution is largely a function of reduction of h2o activity at higher metamorphic grades supplementary biotite data from metaluminous amphibolites and mafic granulites metamorphosed isothermally with variable h2o activities reveal that low al biotite incorporates significantly higher concentrations of ti relative to peraluminous biotite as a result of a combination of the exchange vectors tio2r 1 oh 2 and rsial 2 substituting in roughly an 8 1 ratio

time and temperature in petroleum formation application of lopatin s method to petroleum exploration n v lopatin in the soviet union has developed a method for taking both time and temperature into account as factors in thermal maturation of kerogen lopatin s time temperature index of maturity tti values correlate with the thermal regimes corresponding to generation and preservation of hydrocarbons because such information is potentially of great interest for oil exploration a calibration and evaluation have been made of lopatin s method within the limitations of the data presently available the following statements can be made 1 the rate of the chemical reactions involved in thermal maturation of organic material appears to double with every 10 c 18 f rise in temperature 2 threshold values of lopatin s time temperature index of maturity tti are 15 onset of oil generation 75 peak oil generation 160 end oil generation 500 40 oil preservation deadline 1 000 50 oil preservation deadline 1 500 wet gas preservation deadline 65 000 dry gas preservation deadline 3 tti values calculated from lopatin reconstructions consistently agree with other maturation parameters commonly used by petroleum geochemists potential applications of lopatin s method for oil exploration include timing of oil generation calculation of volume of hydrocarbons generated within a basin and determination of economic deadlines

vitrinite reflectance and shear induced graphitization in orogenic belts a case study from the kandersteg area helvetic alps switzerland vitrinite reflectance vr is an important indicator of incipient metamorphism and it is generally assumed that temperature and to a lesser degree time are the two main variables the role of stress in vr is controversial and will be addressed in this study in the kandersteg area north of lake oeschinen four different helvetic tectonic units are present comprising mainly limestones marls and greywackes of mesozoic and lower tertiary age vr rr rmax rmin and illite crystallinity ic were determined from a very steep section at elevations between 1700 and 2900 m a s l in general rr rmax and ic increase from tectonically higher to lower units i e from upper diagenetic 2 3 to 4 5 rr to upper anchizonal conditions 3 4 to 5 6 rmax several samples contain in addition to coaly fragments abundant semigraphitized and graphitized particles that are believed to be of authigenic origin transitional matter showsrmax values ranging from 7 to about 11 and rmin of 1 3 3 4 optical graphite showsrmax of about 15 16 and rmin of 1 6 1 8 there is good textural evidence that tectonic deformation has played a major role in the development of these strongly coalified particles the first tiny needle like crystals of graphitic material occur within narrow shear zones transecting the rock matrix the beginning of graphite formation parallels the onset of plastic deformation and dynamic recrystallization of quartz elevated vitrinite reflectance rmax and bireflectance values are found near thrust planes where simple optical observation on quartz grain morphology indicates an increase in strain intensity it appears that frictional heating associated with thin shear zones may have been responsible for the formation of authigenic graphite in the kandersteg samples

giant granulite terranes of northeastern superior province the ashuanipi complex and minto block the ashuanipi complex and minto block of the superior province are large regions that have been classified as high grade gneiss terranes on the basis of the presence of orthopyroxene bearing units like the granite greenstone and metasedimentary subprovinces of the southern superior province the two terranes consist predominantly of intrusive rocks but are distinguished by their primary magmatic orthopyroxene both high grade and gneiss are misnomers because granulite facies gneisses are only sparingly present and the regions consist dominantly of massive unmetamorphosed plutonic rock the ashuanipi complex consists of a deformed metamorphosed package of metasedimentary rocks and primitive early tonalite cut by widespread orthopyroxene garnet granodiorite diatexite as well as plutons of tonalite granite and syenite based on its lithological and chronological similarity and on strike position the complex appears to be the continuation of metasedimentary subprovinces such as the quetico its evolution involved deposition of immature greywacke in an accretionary prism early arc tonalitic magmatism and deformation followed by widespread intracrustal magmatism in the period 2700 2670 ma both metamorphic and igneous rocks record equilibration under granulite facies conditions 700 835 c 0 35 0 65 gpa a 0 3 and indicate exposure levels of 20 km the minto block at the latitude of leaf river consists of several north northwest trending domains of similar scale and diversity to the east trending subprovinces of the southern superior province the central goudalie domain is dominantly amphibolite facies tonalitic rocks including some with ages 3 ga with small belts of volcanic and sedimentary origin lake minto domain contains poorly preserved supracrustal remnants in a plutonic complex comprising hornblende granodiorite clinopyroxene orthopyroxene granodiorite orthopyroxene biotite diatexite and granite the hornblende granodiorite suite constitutes most of the utsalik and tikkerutuk domains and is thought to represent continental arc magmatism on the basis of their distinct aeromagnetic and lithological character two additional domains are evident north of the leaf river area the inukjuak domain in the west and the douglas harbour domain in the east the northerly grain of the minto block appears to have been established in situ with respect to the easterly belts of the southern superior province i e no large scale block rotation during the same interval of time 3 0 2 7 ga modification of the tectonic framework for the superior province is required to explain minto arc magmatism in the interval 2730 2690 ma ago a continental magmatic arc built the berens river and bienville subprovinces and minto block on the southern and eastern edges respectively of a northern protocratonic foundation in the same period primitive volcanic arcs and accretionary prisms developed outboard on oceanic crust and were accreted to form a southern tectonic regime

valid garnet biotite gb geothermometry and garnet aluminum silicate plagioclase quartz gasp geobarometry in metapelitic rocks abstract at present there are many calibrations of both the garnet biotite gb thermometer and the garnet aluminum silicate plagioclase quartz gasp barometer that may confuse geologists in choosing a reliable thermometer and or barometer to test the accuracy of the gb thermometers we have applied the various gb thermometers to reproduce the experimental data and data from natural metapelitic rocks of various prograde sequences inverted metamorphic zones and thermal contact aureoles we have concluded that the four gb thermometers perchuk l l lavrent eva i v 1983 experimental investigation of exchange equilibria in the system cordierite garnet biotite in saxena s k ed kinetics and equilibrium in mineral reactions springer verlag new york berlin heidelberg pp 199 239 kleemann u reinhardt j 1994 garnet biotite thermometry revised the effect of alvi and ti in biotite european journal of mineralogy 6 925 941 holdaway m j 2000 application of new experimental and garnet margules data to the garnet biotite geothermometer american mineralogist 85 881 892 model 6av kaneko y miyano t 2004 recalibration of mutually consistent garnet biotite and garnet cordierite geothermometers lithos 73 255 269 model b are the most valid and reliable of this kind of thermometer more specifically we prefer the holdaway holdaway m j 2000 application of new experimental and garnet margules data to the garnet biotite geothermometer american mineralogist 85 881 892 and the kleemann and reinhardt kleemann u reinhardt j 1994 garnet biotite thermometry revised the effect of alvi and ti in biotite european journal of mineralogy 6 925 941 calibrations due to their small errors in reproducing the experimental temperatures and good accuracy in successfully discerning the systematic temperature changes of the different sequences in addition after applying the gasp barometer to 335 natural metapelitic samples containing one kind of aluminosilicate and 33 natural metapelitic samples containing two kinds of aluminosilicate as well as to rocks in limited geographic areas and thermal contact aureoles we propose that the calibrations of holdaway holdaway m j 2001 recalibration of the gasp geobarometer in light of recent garnet and plagioclase activity models and versions of the garnet biotite geothermometer american mineralogist 86 1117 1129 and newton and haselton newton r c haselton h t 1981 thermodynamics of the garnet plagioclase al2sio5 quartz geobarometer in newton r c navrotsky a wood b j eds thermodynamics of minerals and melts new york springer verlag 131 147 based on kleemann and reinhardt s kleemann u reinhardt j 1994 garnet biotite thermometry revised the effect of alvi and ti in biotite european journal of mineralogy 6 925 941 thermometer are the most valid gasp barometers other gb thermometers and gasp barometers are not recommended

the influence of source rock type chemical weathering and sorting on the geochemistry of clastic sediments from the quetico metasedimentary belt superior province canada abstract the geochemistry of clastic sediments is controlled by at least four factors source rock composition weathering of the source rocks sorting of the weathered detritus and post depositional alteration during diagenesis and metamorphism in order to evaluate the relative importance of these factors major trace and rare earth element contents were determined for distal and proximal clastic turbidites from the archaean quetico metasedimentary belt the degree of metamorphism of the samples ranges from middle greenschist to upper amphibolite facies simple mixing of archaean mafic and acidic rocks of similar composition to those found in the adjacent granite greenstone terrains will account for the tio2 feot mgo cr sc y and hree contents of the clastic turbidites the metasediments are enriched in lree relative to the mafic acidic rock mixing line indicating that the acidic source was enriched in the lree compared to archaean terrains from other parts of the world some quetico turbidites have an additional fe rich source component possibly a chemical sediment incorporated at the time of turbidite slumping cao na2o k2o rb and sr form trends on bivariant plots that are oblique to the mafic acidic rock mixing line and hence cannot be accounted for by simple mixing of the source rocks chemical weathering of feldspars prior to deposition can account for cao na2o k2o rb and sr trends since cao na2o and sr are lost to the weathering solutions and k2o and rb are retained on the product clays the higher na 2 o cao k 2 o na 2 o rb k 2 o and sr cao ratios but lower cao content of the distal samples suggest that they were derived from a bulk sediment that had experienced a greater degree of chemical weathering than the proximal sediments sorting is the factor that most strongly influences the composition of individual samples within the proximal sample group the coarse grained metagraywackes with their higher quartz feldspar and heavy mineral contents are enriched in sio2 cao na2o sr lree zr and hf relative to the fine grained clay rich metapelites metapelites are enriched in tio2 al2o3 feot mgo k2o cr zn sc y hree cs and rb as a result of their higher clay contents thus the use of clastic sediment compositions in determining average crustal compositions e g for the ree can only give satisfactory results when all grain size fractions are sampled in their correct relative proportions the chemical differences observed between the high and low grade samples can be accounted for by source rock type chemical weathering of the source rocks or sorting post depositional element mobility does not appear to be an important factor in determining the composition of the quetico metasediments

large scale melt depletion in granulite terranes an example from the archean ashuanipi subprovince of quebec this study uses field petrographic and geochemical methods to estimate how much granitic melt was formed and extracted from a granulite facies terrane and to determine what the grain and outcrop scale melt flow paths were during the melt segregation process the ashuanipi subprovince located in the north eastern superior province of quebec is a large 90 000 km2 metasedimentary terrane in which 85 of the metasediments are of metagreywacke composition that was metamorphosed at mid crustal conditions 820 900 c and 6 7 kbar in a late archean dextral transpressive orogen decrease in modal biotite and quartz as orthopyroxene and plagioclase contents increase together with preserved former melt textures indicate that anatexis was by the biotite dehydration reaction biotite quartz plagioclase melt orthopyroxene oxides using melt orthopyroxene ratios for this reaction derived from experimental studies the modal orthopyroxene contents indicate that the metagreywacke rocks underwent an average of 31 vol partial melting the metagreywackes are enriched in mgo cao and feot and depleted in sio2 k2o rb cs and u have lower rb sr higher rb cs and th u ratios and positive eu anomalies compared to their likely protolith these compositions are modelled by the extraction of between 20 and 40 wt granitic melt from typical archean low grade metagreywackes a simple mass balance indicates that about 640 000 km3 of granitic melt was extracted from the depleted granulites the distribution of relict melt at thin section and outcrop scales indicates that in layers without leucosomes melt extraction occurred by a pervasive grain boundary porous flow from the site of melting across the layers and into bedding planes between adjacent layers in other rocks pervasive grain boundary flow of melt occurred along the layers for a few to tens of centimetres followed by channelled flow of melt in a network of short interconnected and structurally controlled conduits visible as the net like array of leucosomes in some outcrops the leucosomes contain very little residual material 5 biotite orthopyroxene indicating that the melt fraction was well separated from the residuum left in situ as melt depleted granulite only 1 3 vol percentage melt remained in the melt depleted granulites hence the extraction of melt generated by biotite dehydration melting in these granulites was virtually complete under conditions of natural melting and strain rates in a contractional orogen

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

the original swiss flysch a reappraisal of the type deposits in the swiss prealps abstract the flysch sequences of the swiss prealps alpine front ranges are described and interpreted in the light of a decade of study by a group research project at fribourg the geographical and geological settings are illustrated the stratigraphy and sedimentology the sedimentary petrography and the geodynamic setting are discussed correlations within and outside the prealps as well as outstanding problems are treated the flysch units and sequences covered are the gurnigel flysch the medianes flysch helminthoid flysch fouyet manche and mocausa flysch hundsruck flysch niesen flysch and the ultrahelvetic flysch the data from clast framework grain and heavy mineral analysis from micropalaeontology from facies analysis palaeocurrent measurements and stratigraphy allow the interpretation of sedimentary environments source terranes and depositional models in all cases flysch deposits are deep marine detrital accumulations and source areas were undergoing active tectonics individual models are based on the deep sea fan concept but interpretations tend to show significant modifications with respect to simple fan characteristics these departures are to some extent due to available grain size to active structuring of basins or to minor controls such as eustatic variations or climatic influence the integration of sedimentological data with stratigraphy and regional structure furnishes palinspastic reconstructions in map view these provide insights on the palaeogeography of the western alps from mid cretaceous to oligocene and give a picture of the evolution of the western mediterranean tethys during the same period the relationship between flysch deposition and alpine mountain building is confirmed while constraints on basin evolution are established

first u pb zircon ages of granitoid plutons from the la grande greenstone belt james bay area new quebec zircon ages from three granitoid plutons are the first to be reported from the la grande greenstone belt two of the dated samples are from highly tectonized early tectonic plutons that at the present level of erosion are just outside the greenstone belt proper their zircon ages of ca 2740 ma are emplacement ages or alternatively represent the age of maximum deformation of the greenstone belt the third sample is from a mildly deformed late tectonic pluton within the greenstone belt its zircon age of ca 2670 ma probably represents the emplacement age the above dates and the relationships of the dated plutons to the greenstone belt as a whole suggest that the bulk of the volcanism in the la grande belt is older than 2 7 ga this limiting age indicates that the age of the la grande supracrustals is similar to those of the other greenstone belts in the superior province

migmatites formed by water fluxed partial melting of a leucogranodiorite protolith microstructures in the residual rocks and source of the fluid abstract the opatica subprovince in the canadian shield is a late archaean 2761 2702 ma plutonic arc formed above a north dipping subduction zone anatexis 2690 2677 ma of leucogranodiorite and leucotonalite orthogneisses in the opatica generated migmatites in an area of north vergent back thrusts visible at the surface and in l ithoprobe seismic profile 48 schollen diatexite migmatites occur in the thrusts and metatexite migmatites between them the modal mineralogy microstructure and whole rock major trace and oxygen isotope compositions of the protolith and migmatites were investigated to 1 determine the melting reaction 2 find microstructural criteria for identifying residual rocks in leucocratic systems where there is no melanosome and 3 to determine the source of the fluid involved in anatexis partial melting of the protolith did not change the mineral assemblage but the abundance of quartz and microcline both declined and plagioclase and biotite increased in the residual rocks quartz plagioclase and microcline show evidence for dissolution and biotite does not thus water fluxed melting of quartz plagioclase microcline occurred a mass balance indicates 25 30 partial melting the melting reaction consumed the microcline and created essentially monomineralic domains of plagioclase extraction of 80 90 of the melt left a thin film of melt on the grain boundaries and crystallization of these in the plagioclase domains created diagnostic microstructures microcline fills the last remaining pore space and forms high aspect ratio crystals between plagioclases or triangular crystals at grain junctions quartz shows a range of morphologies from high aspect ratio films through the string of beads to isolated rounded grains as the microstructure progressively equilibrated after crystallisation most accessory phases including zircon remained in the residuum however almost all the schollen migmatites have high contents of th u nb ta and ree relative to the protolith due to contamination by accessory phases derived from mafic rocks disaggregation of the mafic rocks may have been facilitated by the high strain in the back thrusts where the schollen diatexites formed average whole rock 18 o for the protolith and migmatites are similar ca 8 2 and the small difference between melt rich 8 6 and residuum rich rocks 8 0 is consistent with fractionation thus the fluid that caused melting was probably of metamorphic origin with 18 o similar to the protolith the seismic profile shows several reflectors extending to a present depth of 20 km ca 40 km in the late archaean under the migmatites these are the paths along which the metamorphic fluid migrated and generated the migmatites now at the surface a new type of neosome reported in this study may have formed along fractures that the fluids migrated along however these are peripheral pathways in the metatexites adjacent to the back thrusts and schollen diatexites

geothermal gradients in the hinton area of west central alberta temperature data from petroleum exploration well logs of 3360 wells in a region of west central alberta are used to estimate thermal gradients a relatively high geothermal gradient 36 c km of oblong shape located near hinton is observed the axis of the anomaly strikes approximately southwest northeast and passes through the miette hot springs area it appears that water is heated at depth in the rocky mountain disturbed region and travels eastward and toward the surface along fault planes

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

coalification shale diagenesis and thermal modelling in the alpine foreland basin the western molasse basin switzerland france abstract the analysis of coalification and shale diagenesis in oligocene and lower miocene sediments in the western part of the molasse basin western switzerland and haute savoie france shows a close relationship between the very low temperature metamorphism in the foreland and the tectonic history in the orogenic belt the degree of thermal maturation generally increases towards the alpine front isomaturity lines however run slightly oblique to today s alpine front this is probably due to the tectonic burying under the alpine nappes in early miocene time second order variations of the coalification pattern are explained as resulting from a regional discharge of warm fluids controlled by tectonic structures

u pb geochronology of the opatica tonalite gneiss belt and its relationship to the abitibi greenstone belt superior province quebec u pb ages for zircon monazite and titanite from samples collected from two transects across the opatica tonalite gneiss belt in the superior province of quebec indicate that the belt contains rocks that are significantly older than those in the adjacent low grade northern abitibi belt tonalite and tonalite gneiss which make up most of the belt formed over an interval of 100 ma from pre 2800 to 2702 ma five samples have ages of ca 2807 13 2773 23 and 2702 3 ma zircon growth at 2718 2721 ma in the two oldest samples may record an early period of high grade metamorphism in the belt hornblende diorite monzodiorite and tonalite plutons were intruded at 2693 2696 ma particularly along the southern boundary with the abitibi belt these include the canet pluton at ma the lac ouescapis pluton at 2693 2 ma and the barlow pluton at 2696 3 ma pink granite plutons and dykes are the youngest intrusive rocks in the belt three samples have yielded zircon ages of 2690 2 and 2686 4 ma

thermo tectonic evolution of an archean accretionary complex u pb geochronological constraints on granulites from the quetico subprovince ontario canada abstract u pb geochronological data have been obtained for a granulite zone in the quetico subprovince an archean accretionary complex of the superior province north of manitouwadge ontario canada this granulite zone represents the culmination of a low pressure high temperature regional metamorphism in the quetico subprovince and an apparent continuation of a northward increase in metamorphic grade in the wawa subprovince and across the quetico wawa boundary a u pb zircon age of 2666 1 ma from a concordant magnetite bearing granitic pegmatite in the quetico granulite zone is consistent with the inferred timing of regional metamorphism in amphibolite facies zones 2671 2665 ma and indicates that the low pressure high temperature metamorphism in the quetico subprovince commenced during the main compressional deformation titanite in a calc silicate rock from low leucosome fraction layered migmatites that might represent incipient melting gave a 207pb 206pb age of 2658 1 ma the timing of the granulite facies metamorphism is constrained by u pb zircon ages of 2650 2 and 2651 3 ma from mafic granulite and garnet bearing tonalitic leucosome respectively that are similar to reported u pb ages for mafic granulites in the upper levels of the kapuskasing structural zone the present u pb data suggest a diachronous development of peak metamorphic conditions of the regional metamorphism in the quetico and wawa subprovinces this diachronous development and the zonal distribution of the regional metamorphism are probably related to oblique collision at a convergent plate margin and differential rates of erosional uplift away from the quetico wawa boundary

warm fluid migration along tectonic melanges in the kodiak accretionary complex alaska analyses of methane water fluid inclusions from syntectonic quartz veins in melange boudins of the kodiak accretionary complex alaska indicate fluid temperatures ranging from 215 to 290 c at depths between 10 and 14 km these fluid temperatures are significantly higher than those predicted by conductive heat flow models of subduction zones given the available geological constraints this discrepancy is interpreted as the result of migration of warm fluids from deeper structural levels along active fault zones during subduction related underthrusting of these units this interpretation requires more careful consideration of how migrating fluids affect the general thermal structure of subduction zones

formation and evolution of granite magmas during crustal reworking the significance of diatexites taylor mclennan 1985 the physical processes ina continuous section through reworked archaean crust records the volved particularly how granite magma is formed remain generation of granitic magma and its subsequent development in the controversial miller et al 1988 white chappell opatica subprovince in the canadian shield there the transition 1990 a partially melted source can form a granitic from palaeosome to granite was a closed system process through magma only if large volumes of melt are separated from intermediate stages of patch migmatite and diatexite the average most of their residuum understanding this process is degree of partial melting was less than 30 but the melt crucial to determining how crustal recycling and differfraction was redistributed within individual diatexite layers during entiation occurs for example melt residuum separation deformation regions that lost melt became residual diatexites could be a nearly perfect single stage process at the enriched in tio2 feot mgo cao sc cr co sr rare earth site of partial melting as described for leucosomes in elements ree and high field strength elements hsfe melt metatexite migmatites wickham 1987a sawyer 1991 accumulated to create diatexite magmas enriched in large ion 1994 brown et al 1995 alternatively the separation lithophile elements lile but contaminated with residuum macould be an imperfect multi stage process that yields a terial such diatexite magmas are parental to granites found at magma with a large residual component as is observed higher crustal levels in the terrane flow of the diatexite magma in in diatexite migmatites bea 1991 greenfield et al response to deformation separated some of its residuum into schlieren 1996 sawyer 1996 the metatexite model necessarily parautochthonous plutons were created where ascending granitic produces leucocratic residuum free granites such as magma locally ponded below impermeable layers and structures those described by le fort 1981 and montel et al magma left the anatectic region in dykes and lost its remaining residuum as it crystallized consequently the allochthonous granite 1991 and maximizes the geochemical signature of magmas that rose through 20 km of crust to feed the highest level crustal differentiation in contrast the diatexite model plutons in this region are highly fractionated and essentially free of can produce residuum rich granites and so reduce the residuum geochemical effect of crustal differentiation as chappell 1996 noted how anatectic magmas formed in the deeper crust evolve to the granitic magmas emplaced in the upper crust is also poorly known because few crustal sections

bone density and long bone representation in archaeological faunas comparing results from ct and photon densitometry abstract research into animal bone density has provided the foundation for the assessment of post depositional destruction of archaeological faunal assemblages this paper presents bone mineral density values for caprid long bones as determined by computed tomography ct unlike photon densitometry the technique employed in previous archaeological studies of bone density ct provides precise assessments of the cross sectional area of scan sites researchers using photon densitometry have been unable to factor out the marrow cavity in their determination of cross sectional area thereby significantly underestimating the density of long bone shafts the density values obtained by ct are much higher particularly for middle shaft portions than those presented in previous studies and are more consistent with existing data on the material properties of bone for two archaeological faunal assemblages that have been subject to post depositional attrition the ct density values show a much stronger correlation with long bone portion survival than those provided by photon densitometry given such advantages over photon densitometry ct is a promising method for future archaeological investigations into bone density

partial melting of aluminous metagreywackes in the northern sierra de comechingones central argentina we describe a suite of metamorphic and migmatitic rocks from the represent the source regions of anatectic magmas e g brown 1994 sawyer 1998 even though sawyer sierra de comechingones sierras pampeanas of central argentina that include unmelted gneisses migmatites and refractory granulites 1996 showed that diatexite migmatites have rheological and chemical properties that suggest that they are the gneisses are aluminous greywackes metamorphosed in the amphibolite grade and are likely to have been the protoliths for the parental to granite magmas it is also known that granulites depleted in incompatible major and trace higher grade migmatites and granulites mineralogical characteristics and major and trace element compositions show that metatexite elements are present in the lower continental crust e g lambert heier 1968 these rocks have been migmatites diatexite migmatites and granulites are all melt depleted rocks the migmatites both metatexites and diatexites have underinterpreted as refractory residues of partial melting complementary to granitic magmas e g clemens 1990 gone h2o fluxed melting and lost 20 melt whereas the granulites have lost as much as 60 melt formed chiefly by vielzeuf et al 1990 and there is ample theoretical and experimental evidence that supports this concept dehydration melting of biotite the granulites are rocks from which essentially all the granitic components have been extracted whereas e g brown fyfe 1970 thompson 1982 vielzeuf holloway 1988 patino douce johnston 1991 the migmatites cooled and solidified while still retaining a granitic fraction the only evidence for the presence of melt in the study patino douce beard 1995 it is thus possible that the source regions of some granitic magmas could area apart from migmatitic leucosomes are dikes and sills of leucogranite rich in cumulate k feldspar these leucogranite bodies consist of a wide spectrum of migmatites and meltdepleted granulites may represent the pathways along which melt was drained from the exposed rocks our study shows that in the sierra de comechingones in this paper we focus on a suite of metamorphic and migmatitic rocks from the sierras pampeanas of both migmatites and granulites represent source regions of anatectic magmas which were frozen in at different stages of development argentina the rocks in the study area include unmelted gneisses migmatites and refractory granulites we describe the fabrics mineral assemblages and field relations of the various rock types and present data

geological evolution of the manitouwadge greenstone belt and wawa quetico subprovince boundary superior province ontario constrained by u pb zircon dates of supracrustal and plutonic rocks fifty million years of archean evolution is recorded in the manitouwadge greenstone belt and the wawa quetico boundary region from ca 2720 ma volcanism and subvolcanic plutonism associated with m

multi stage melting in the lower crust of the serre southern italy the lower crustal section exposed in the serre southern italy consists part of the section the most depleted metagreywackes underwent melt extraction of about 9 13 vol the two stage melting mainly of al rich metasediments which underwent granulite facies metamorphism partial melting and melt extraction the paper occurred during the prograde metamorphism and continued during the isothermal decompression considers the formation of melts in metapelites and metagreywackes leucosomes and host rocks have been studied to investigate the melting process biotite rich and biotite free melanosomes with scarce felsic components are present the biotite rich types are widespread in the upper part of the section and the two types may occur side

large volumes of anatectic melt retained in granulite facies migmatites an injection complex in northern quebec abstract the opinaca subprovince in the superior province of northern quebec is a metasedimentary belt characterized by metagreywacke rocks that record a late archean granulite facies metamorphism and contains abundant thin veins of leucogranite regional scale study of this subprovince provides insight to the net budget of anatectic melt loss versus accumulation in the lower middle continental crust during anatexis a petrological study indicates that the metagreywackes partially melted at 820 c and 7 kbar and generated 1 from the metamorphic peak at 2666 ma to the granite solidus at 2636 ma the large discrepancy about 50 between the volume of anatectic melt produced locally in situ and the observed volume of leucogranite in the terrain indicates that anatectic melt accumulated in the opinaca subprovince it is an injection complex this finding that granulite facies terranes can be enriched in melt contrasts with the general view that granulite terranes are melt depleted the presence of an injection complex in the deep crust has several broad implications for the continental crust 1 h 2 o released as the injected melt crystallized rehydrated the adjacent granulite facies rocks which is evident from orthopyroxene replaced by amphibole and biotite consequently these deep rocks would be more fertile in a subsequent anatectic event than non rehydrated residuum 2 the retention of voluminous leucogranite in the injection complex has thermal consequences for the crust first the bulk composition of the crust containing the injection complex is necessarily more felsic thus the budget of heat producing elements th u and k is locally enhanced and radiogenic heat production is higher secondly latent heat of crystallization is released at a deeper level where the leucogranite solidifies the combined effect of both maintains the lower crust several tens of degrees warmer for longer period of time

mesoscale pervasive felsic magma migration alternatives to dyking abstract this paper reviews the literature on dyking as a mechanism of felsic magma extraction from a source and transport to shallower crustal levels and review the recent literature suggesting a range of alternative mechanisms of magma migration in hot crustal zones which produce mesoscale pervasive granite sheet intrusions recent papers have strongly favoured dyking as the main mechanism controlling magma migration however the initiation of dykes from a felsic magma source is fraught with difficulties even when magma is immediately available for transportation as in magma chambers within a partially molten source magma may reside in a range of structures with a wide range of shapes sizes and degrees of connectivity whereas the growth of individual dykes within a partially molten zone and the self propagation of large dykes into subsolidus crust have both been studied in some detail little attention has been given to the crucial intermediate step of the growth of a dyke network capable of producing wide crustal scale dykes the rarity of granite dyke swarms suggests that if dyking is the preferred mechanism of magma transport felsic magma sources produce only few major transporting dykes during their lifetime alternatively dyking is not an important mechanism the parameters controlling the volume of the catchment drained by one such dyke as well as other basic geometrical parameters controlling the structure of the dyke network within the source are unknown the ability of dyking to drain a partially molten source depends crucially on these variables and particularly on the horizontal permeability of the source the slow velocity of viscous felsic magmas traveling in rock pores implies that magma drained during dyking is mostly that previously extracted from the pores and resident in irregular magma bodies or dyke networks the observation that large volumes of buoyant magma are commonly present in migmatite zones and that dyking in these zones plays a secondary role suggest that dyking is inefficient and is able to extract only a fraction of the total melt available in the source in support of this conclusion recent detailed studies of exhumed hot crustal zones have revealed a range of alternative migration mechanisms characterized by mesoscale pervasive magma flow outcrop scale as opposed to porous flow pervasive migration gives rise to magma sheets preferentially emplaced parallel to high permeability zones such as foliation or bedding planes apart from local dyking three alternative mechanisms have been proposed to account for pervasive migration of magmas namely tectonic pumping magma wedging into low viscosity rocks and volatile driven intrusion because of their unfocused pervasive character these mechanisms are restricted to hot crust where magmas are not exposed to rapid freezing a model is proposed whereby heat advected with the magma pushes crustal geotherms upwards allowing pervasive magma migration to shallower depths

geothermal gradients hydrodynamics and hydrocarbon occurrences alberta canada using coal rank data and the demonstrated genetic link between the present hydrodynamic regime and geothermal gradient pattern it is possible to reconstruct the geothermal history of alberta over the past 60 m y palinspastic adjustment for tectonic compression caused by the major laramide thrusting shows that the predeformation isoreflectance lines increased logarithmically with depth in the late paleocene the geothermal gradient was about 23 c km 1 25 f 100 ft in the eastern alberta plains compared to about 30 c km 1 65 f 100 ft in the western alberta plains a regional trend opposite to the post laramide trends reconstruction of the early eocene surface indicates western uplands with geothermal gradients as low as 21 c km 1 15 f 00 ft and eastern lowlands with geothermal gradients of 27 c km 1 5 f 100 ft compared to the present situation this represents an enhanced topographic surface and a subdued geothermal gradient pattern the genetic relations of topography water table elevation hydrodynamic regime and geothermal gradient pattern in both the early eocene and the present conform to a model developed for any compacted sedimentary basin with subaerial relief in this model on a regional scale high topographic areas have high water table elevations with correspondingly high potentiometric surfaces these areas control the regional recharge of cold meteoric water and hence have low geothermal gradients areas of medium elevation exhibit regional lateral flow and intermediate geothermal gradients regional topographic lows correspond with low potentiometric surfaces and the regional discharge of warm formation waters from deep in the basin results in high geothermal gradients local topographic featur s cause perturbations in this picture study of both the regional pattern and fine detail of the early eocene and present topographic surfaces and geothermal gradient patterns shows the validity of the model the result of the second laramide orogenic pulse was therefore to reverse the geothermal gradient pattern resulting mainly from compaction flow and to impose a topographically controlled hydrodynamic regime with flow in the same direction but with a 9 c km 0 5 f 100 ft decreased geothermal gradient in western alberta and a 4 c km 0 2 f 100 ft increased geothermal gradient in eastern alberta as erosion proceeded during the tertiary the entire alberta basin warmed up until the present temperature regime was attained study of some major hydrocarbon occurrences shows a genetic link between the hydrocarbon occurrence and the present fluid regime which itself is controlled by the present topography for at least the significant upper cretaceous shallow gas reserves in southeastern alberta however their position may already have been determined as early as the beginning of the eocene by the topographic surface at that time therefore the extent to which the present topographic surface is responsible for hydrocarbon accumulation through gravity induced cross formational flow remains unknown because this process was operative as long ago as the early eocene what does not ap ear to be in doubt is the fact that gravity induced cross formational flow does control the hydrodynamic regime which in turn influences the geothermal gradient pattern and the accumulation of hydrocarbons

the geochemical signature of a felsic injection complex in the continental crust opinaca subprovince quebec abstract the archean opinaca subprovince of the superior province in northern quebec is an injection complex consisting of lower granulite facies metasedimentary terrane that was pervasively injected with a large volume of leucogranitic melt which forms innumerable thin dykes and veins the typical microstructure of most leucogranites can be divided into two groups 1 one has an open framework constructed of k feldspar crystals in which the interstices are filled with albite rich plagioclase and quartz and 2 a microstructure defined by a framework of albite rich plagioclase crystals in which the interstices are filled by quartz and in some cases small pink garnets however pegmatitic and aplitic textures also occur the leucogranites that form the injection complex are all sio 2 rich above 70 wt and have low feo t mgo tio 2 contents compared to granitic melts obtained from partial melting experiments the mafic minerals were fractionated from the magma before its emplacement into the injection complex as leucogranite the leucogranites form a coherent trend on major element diagrams that is best explained by the removal of a cumulate dominated by k feldspar from a granitic initial melt composition the cumulate rocks are enriched in k 2 o whereas the residual melts are richer in sio 2 and na 2 o based on these results leucogranites with a k feldspar framework are interpreted as cumulate rocks this indicates that the early crystallising calcic plagioclase had already been fractionated from the magma before its injection into the complex the leucogranites have rare earth element ree patterns typical of feldspar accumulation the residual melts extracted after the k feldspar framework developed are those that have the framework of albite rich plagioclase these have ree patterns typical of highly evolved melts from which accessory minerals have also been fractionated the highly evolved nature of the leucogranites that were injected into granulite facies host rocks in the opinaca subprovince has several important implications for crustal evolution 1 the large volume of evolved melts emplaced at depth released a significant amount of h 2 o into the adjacent crust thus injection complexes should be considered as a potentially important source of h 2 o in the middle crust that is capable of rehydrating the granulite terranes into which they are injected 2 a corollary of the evolved nature of the leucogranite in the injection complex is that there should be evidence of accumulation of the early fractionated material still deeper in the crust 3 these findings are natural examples that corroborate predictions from numerical modelling which suggest that the whole process from melting to crystallisation of leucogranite can be confined to deep levels of the crust below or close to the solidus this has important impact on our general view of the transfer of leucogranites in the continental crust which is the main mechanism of crustal differentiation

stepwise accumulation and ascent of magmas one of the currently popular theories on magma ascent is that it mainly occurs by propagating hydrofractures dykes and that magma viscosity is the primary rate controlling factor this theory is based on mathematical models for single hydrofractures under idealised conditions we simulated magma ascent with air ascending through gelatine and observed that the air ascended in batches following paths made by their predecessors multiple batches accumulate at obstacles along the path although magma viscosity may control ascent rate during movement obstacles ultimately control the size and average ascent velocity of ascending batches we propose that step wise movement of magma batches is the mechanism of primary accumulation and ascent from the partially molten source rock of a magma to its first emplacement site and therefore the main ascent mechanism for granitic magmas classical dyking is the mechanism for secondary ascent from a magma chamber

temperatures of granulite facies metamorphism constraints from experimental phase equilibria and thermobarometry corrected for retrograde exchange this study assesses temperatures of formation of common granulites by combining experimental constraints on the p t stability of granulite facies mineral associations with a garnet orthopyroxene grt opx thermobarometry scheme based on al solubility in opx corrected for late fe mg exchange we applied this scheme to 414 granulites of mafic intermediate and aluminous bulk compositions our findings suggest that granulites are much hotter than traditionally assumed and that the p t conditions of the amphibolite granulite transition portrayed in current petrology textbooks are significant underestimates by over 100 c for aluminous and intermediate granulites mean corrected temperatures based on our method are 890 17 and 841 11 c respectively uncertainties reported as 95 confidence limits on the mean consistent with minimum temperatures for orthopyroxene production by fluid absent partial melting in these bulk compositions in contrast mean temperatures based on grt opx fe mg exchange equilibria using the same thermodynamic data are 732 22 and 723 11 c respectively well below the minimum temperatures for opx stability for mafic granulites the mean corrected temperature using our method is 816 12 c similar to the mean temperature of 793 13 c from fe mg exchange reasons for the differences between the mafic granulites and aluminous intermediate granulites are unclear but may be due to the lower al concentrations in opx in the mafic rocks and possible deficiencies in the thermodynamic modelling of these low concentrations we discuss a number of well known granulite terrains in the context of our findings including the adirondacks the acadian granulites of new england the incipient charnockites of southern india and sri lanka and the kerala khondalite belt our findings carry implications for thermotectonic models of granulite formation a computer program to perform our thermobarometry calculations rclc is available from the journal of petrology website at http www petrology oupjournals org or from the authors at http www geo ucalgary ca pattison drm pattison rclc htm

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

linking the northern alps with their foreland the latest exhumation history resolved by low temperature thermochronology the evolution of the central alpine deformation front subalpine molasse and its undeformed foreland is recently debated because of their role for deciphering the late orogenic evolution of the alps its latest exhumation history is poorly understood due to the lack of late miocene to pliocene sediments we constrain the late miocene to pliocene history of this transitional zone with apatite fission track and u th he data we used laser ablation inductively coupled mass spectrometry for apatite fission track dating and compare this method with previously published and unpublished external detector method fission track data two investigated sections across tectonic slices show that the subalpine molasse was tectonically active after the onset of folding of the jura mountains this is much younger than hitherto assumed thrusting occurred at 10 8 6 5 ma and potentially thereafter this is contemporaneous with reported exhumation of the external crystalline massifs in the central alps the jura mountains and the subalpine molasse used the same detachments as the external crystalline massifs and are therefore kinematically coupled estimates on the amount of shortening and thrust displacement corroborate this idea we argue that the tectonic signal is related to active shortening during the late stage of orogenesis

ultrahigh metamorphic temperatures over 1050 c recorded by fe ti oxides and implications for paleoproterozoic magma induced crustal thermal perturbation in jining area north china craton abstract a pseudobrookite approximately mg0 04fe2 0 85ca0 01al0 05fe3 0 16ti1 89o5 was discovered in fe ti oxide intergrowths in a spinel garnet bearing granulite from the xuwujia paleoproterozoic ultrahigh temperature uht metamorphic region within the khondalite belt of the north china craton the presence of this pseudobrookite indicates a peak temperature possibly over 1120 c when compared with experimental data ferric pseudobrookite grains fe3 up to 0 58 per formula unit from the same granulite outcrop record retrograde temperatures as low as 940 c titanomagnetite and ilmenite intergrowths that resulted from reduction exsolution which was buffered by the decomposition of high ti pseudobrookite grains recorded a post peak temperature up to 1050 c the thermal gradient 100 c kbar required to generate the uht metamorphic bodies in an area over 10 000 km2 around the jining area was modeled by the finite element method the thermal modeling results show that 1 lithospheric thermal erosion induced by a mantle plume with potential temperature of 1550 c could not have provided enough thermal perturbation to allow the observed uht metamorphism 2 underplating at the scale of even the largest known horizontal magma intrusion on earth would not be able to elevate the geotherm to the gradients required for the observed uht metamorphism and 3 intraplating of dykes and intrusions at the depth of this uht metamorphism was able to increase the local temperature field to the required gradients these modeling results suggest that a modern back arc may not be able to provide sufficient heat at the middle crust level for uht metamorphism the uht metamorphism in the study area was probably accompanied by an orogeny plume interaction event which simultaneously supplied heat through thermal erosion magma underplating and magma intraplating

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

melt production during granulite facies anatexis experimental data from primitive metasedimentary protoliths we conducted fluid absent partial melting experiments at 0 5 and 1 0 gpa in the temperature range 750 to 1000 c to investigate the influence of bulk rock mg 100mg mg fe and the effects of additional tio2 on the granulite grade anatectic evolution of relatively magnesian metapelites and metagreywackes in these experiments melting began between 780 and 830 c by the incongruent breakdown of biotite to produce quartz saturated granulite facies residual mineral assemblages in equilibrium with h2o undersaturated granitic melt the glass quenched melt compositions produced in this study vary little generally the glasses have compositions similar to those of many natural strongly peraluminous leucogranites the solidus temperatures in both rock types increase with increasing mg but are unaffected by the presence or absence of a tio2 component at 0 5 gpa the metapelites melted at temperatures up to 50 c lower than the equivalent metagreywackes but at 1 gpa there was no discernible difference this study suggests that the fluid absent solidus has a steep positive dp dt slope in metapelites and steep negative dp dt slope in metagreywackes the pattern of melt production with increasing temperature is strongly controlled by the upper limit of biotite stability in tio2 free compositions this was found to increase by 15 to 20 c in the metapelites and by 30 to 40 c in the metagreywackes as a function of increasing mg from 49 to 81 the presence of a tio2 component increases the upper limit of biotite stability by 50 c in the metapelites and by 80 c in the metagreywackes over that observed in the equivalent tio2 free compositions in consequence in the tio2 free samples large pulses of melt up to 35 wt are produced over narrow temperature ranges as little as 15 c in these experiments between 830 and 875 c in the tio2 bearing samples the major pulse of melt production occurs more gradually between 830 and 900 c

thermal buffering effects at the solidus implications for the equilibration of partially melted metamorphic rocks abstract a simple thermal model is used to investigate to what extent buffering effects of latent heat of fusion may prolong the thermal evolution of a one dimensional statically cooling partially or completely melted heat source for a melting model appropriate for crustal rocks the time of cooling of rocks through the solidus may be about tripled by this process depending on the melting model cooling may halt completely near the solidus for time spans comparable to the thermal time constant of the heat source in order to test the influence of this buffering effect on the equilibration of partially melted metamorphic rocks these thermal model results are coupled with a simple diffusion model that relates the degree of equilibration of a simple assemblage to temperature and cooling rate it is shown that for a broad range of initial heat source temperatures freezing of selected mineral equilibria may occur in a comparably narrow temperature range at and around the solidus the calculations may have some relevance to low p high t metamorphic terranes in as much as they may provide an explanation for the widely observed equilibration and partial re equilibration of rocks near the crystallisation temperatures of partial melts

maximum and minimum water contents of granitic melts generated in the crust a reevaluation and implications abstract recent results of studies aimed to determine the water solubilities and the liquidus temperatures in synthetic and natural granitic systems are used to constrain the minimum water contents of granitic melts generated in the crust as a function of pressure temperature melt composition and water activity it is concluded that melts generated in the crust at high temperature and low water activities such as a type granites contain higher water contents than previously assumed up to 20 at 800 900 c and 3 7 kbar as a consequence the melt fraction produced at a given amount of available water can be up to 20 lower the minimum water content of melts generated by partial melting of crustal protoliths especially quartzofeldspathic rocks can be predicted adequately from the liquidus curves in granitic systems this water content can be higher if the melt composition departs from a minimum or eutectic quartzofeldspathic composition melts generated from quartzofeldspathic rocks at low temperature 750 c and below are necessarily water rich 5 wt h 2 o and have approximately the same viscosity or even slightly lower viscosities than melts generated at higher temperatures viscosities in the range 10 4 3 10 5 4 pa s recent experimental data also show that the value of the positive d p d t slope of the liquidus curves for fixed water contents above 800 c is lower than predicted by previous models thus adiabatic decompression produces a higher amount of melt than previously assumed at high temperature the formation of melt by adiabatic decompression can be up to 50 higher than assumed

tectonic pumping of pervasive granitic melts finite element 2d models are used to study how tectonic stresses pump pervasive granitic melts within migmatites we start by assuming elliptical melt filled veins of different orientations interconnected by the assumption that they share the same pressure the melt is then redistributed in the vein array by the application of lateral compression or extension the effective permeability of vein networks is thought to be up to 13 orders of magnitude higher than the matrix permeability of 10 19 m2 this allows us to approximate pressure equilibration and neglect irreversible compaction in the matrix this simple configuration allows solution of constitutive equations for the equation of state in the viscoelastic matrix the melt in the vein array and the mechanical equilibrium along with force balance on the walls of the deforming veins a rectangular box is pressurized by a constant load applied to one side and continuously deformed by shift of another side with constant velocity new veins cannot initiate and pre existing veins cannot migrate bodily down pressure gradients however potential flaws are cut in line with the tip of every pre defined vein this means that veins not only close open and shear as they rotate but can also undergo limited propagation at rates dictated by the bulk deformation of the matrix we use constant viscosities s in the range 1017 1018 pa s deformation rates e vary between 10 10 and 10 9 s 1 and a total strain up to 4 5 isolated veins parallel and normal to 1 have melt pressures between p0 and p0 4 se the mean vein pressure differs from these extremes and is equilibrated by driving melt from shrinking veins into veins parallel to 1 which widen and lengthen the above assumptions result in an asymptotic pattern of stress distribution and the amount of melt redistributed at given strain approaching the kinematic limit with time this occurs whatever the viscosity of the matrix and the strain rate multilayered systems are modeled by pre defining a single vertical vein crossing the planar horizontal boundary between two uniform media compression parallel to the layering expels melt from the part of the vein in the more viscous layer to open and extend that part of the same vein in the less viscous layer melt moves in the opposite direction during lateral extension if sheet like bodies become sufficiently tall to become buoyant horizontal sheets resulting from lateral compression are likely to rise to higher crustal levels as diapirs while vertical sheets resulting from lateral extension are more likely to ascend as dikes

topological characterization of a polyphased gold bearing vein network abstract it is challenging to evaluate the connectivity of metal bearing hydrothermal vein systems i e the degree to which fractures or veins are connected within a network moreover many ancient ore bearing vein networks have been deformed and metamorphosed which hinders the reconstruction and quantification of their primary characteristics here we explore the reliability and limitations of the network distribution and topologic classification of vein terminations into i y and x nodes approaches to study deformed and metamorphosed mineral deposits we focus on the cheechoo gold deposit located in the eeyou istchee james bay area of quebec canada archean superior province this gold deposit shows a complex hydrothermal and magmatic polyphased gold bearing vein system hosted in a granodioritic tonalitic intrusion the cheechoo deposit is composed of quartz feldspar diopside qtz fsp di and quartz qtz veins that underwent ductile deformation and amphibolite facies metamorphism the high grade metamorphism led to the modification of vein shape relative position and spacing making these parameters unreliable for the characterization of the cheechoo vein system and similar metamorphosed networks however the number of veins per length unit and topology are reliable tools to characterize such networks in the gold bearing cheechoo system the gold mineralization appears to be mainly controlled by i the number of qtz and qtz fsp di veins per length unit and by ii the connectivity of these networks as shown by the increase of both parameters with the gold grade furthermore we introduce the y i ratio as a simple topological parameter to quantify the connectivity of two dimensional i y dominated systems this parameter is positively correlated with the number of connections per branch cb used to quantify network connectivity and ultimately represent the development of a fault or fracture zone

a review of the timing of coalification in the light of coal seam erosion clastic dykes and coal clasts abstract coal seam erosion clastic dykes penetrating coal seams and studies of coal clasts occurring in late paleozoic basins are used to demonstrate that coalification to the rank of subbituminous and bituminous coal occurred rapidly at shallow depth in some parts of the variscan orogen implying a precondition of high paleotemperatures for the coal basins the origin of clastic dykes particularly in the bolsovian westphalian c deposits of the plze and kladno rakovnik continental basins czech republic is shown to be a relevant factor in determining the timing of coalification pesek j 1978 erosion and clastic dikes in coal seams of the central bohemian basins and their significance for determination of plant substance coalification folia musei rerum naturalium bohemiae occidentalis geologica 12 1 34 is of the opinion that the 50 100 cm deep fractures filled with superposed clastics originated in fully ranked high volatile bituminous coal exposed during a hiatus between the early westphalian c early bolsovian and late westphalian d late asturian these dykes have either irregular shape or form conic bodies with sharp boundaries their filling does not show any signs of postsedimentary deformation coal clasts occurring in clastic sediments either close to or far above the roof of coal seams are a few millimetres up to several centimetres in size being subangular or angular however there also exist clasts of which one side is angular to subangular whereas the opposite side is markedly sharp in some basins coal clasts are embedded in units of the same age they are mostly of somewhat lower rank by 0 01 0 03 than the nearest coal seam whereas gayer r a pesek j s korova i valterova p 1996 coal clasts in the upper westphalian sequence of the south wales coal basin implication for the timing of maturation and fracture permeability in gayer r harris j eds coalbed methane and coal geology geological society special publication 109 pp 103 130 presumed in the south wales foreland basin a burial level of about 1 km with an elevated geothermal gradient 60 c km enhanced by hot fluids along thrusts resulting in rapid coalification to the bituminous coal rank no deep burial of organic matter could have occurred in the intramontane basins of the bohemian massif coalification of the late paleozoic seams must have proceeded at a very high rate the only logical reason leading to such rapid coalification of biomass could have been high value of geothermal gradient at least in the basins of the bohemian massif

an exposed hercynian deep crustal section in the sila massif of northern calabria mineral chemistry petrology and a p t path of granulite facies metapelitic migmatites and metabasites in the sila massif of northern calabria a continous section is exposed through a segment of a hercynian deep continental crust which has been interpreted by previous workers as a stack of basement nappes monte gariglione complex the section consists essentially of metapelitic migmatites and subordinate metabasites and marbles which were metamorphosed at medium pressure high temperature granulite facies conditions a continuous metamorphic gradient through the exposed segment can be deduced from the systematic change in the compositions of ferromagnesian minerals in divariant metapelitic assemblages this gradient is partly supported by conventional geothermobarometry and by applying the tweequ method however peak metamorphic conditions are better defined by dehydration melting reactions which reveal similar to4 kbar and 740 degreesc at the top and similar to6 kbar and 770 degreesc at the base of the section therefore the exposed rocks represent a former crustal depth range of similar to 14 21 km at the thermal peak of metamorphism the metamorphic evolution of the former deep crustal rocks has been reconstructed from reaction textures the prograde p t path took place in the stability field of sillimanite the retrograde path is characterized by a stage of isothermal uplift after peak metamorphism to mid crustal levels 10 15 km followed by near isobaric cooling to greenschist facies conditions the deep crustal section in northern calabria resembles that of the serre massif in southern calabria which represents the lowermost part of an exposed tilted cross section through the hercynian continental crust postkinematic mineral growth reaction textures and isotopic age constraints indicate that the thermal conditions in the calabrian crust during the hercynian orogeny were mainly controlled by advective heat input through magmatic intrusions as in southern calabria large granitic bodies were emplaced between the granulite facies lower crust monte gariglione complex and the amphibolite to greenschist facies upper crust during regional metamorphism

evolution of a palaeoproterozoic giant magmatic dome in the finnish svecofennian new insights from u pb geochronology abstract the svecofennian domain comprises a c 800 km by 800 km area in finland and sweden mainly composed of palaeoproterozoic granitoids schists and gneisses in the central part of the domain in western finland the vaasa complex hosts a sequence of high grade metamorphic rocks and granites formed by crustal anatexis during the culmination of the 1 9 ga svecofennian orogeny the vaasa complex consists of a c 8000 km 2 granitoid batholith surrounded by diatexitic and metatexitic migmatites as well as metasedimentary rocks in order to enhance the perception of the crystallisation history provenance and maximum sedimentation age of the protoliths involved nine granitoid xenolith pairs and a palaeosome neosome pair were collected from the main body of the vaasa batholith and surrounding rocks and zircon from them was u pb dated using the la mc icpms method the u pb zircon crystallisation ages of the granitoids are 1 88 1 87 ga which is in accordance with the few previous results from the vaasa region and confirms a relatively swift crystallisation of the granite core throughout the finnish part of the complex the samples from the central part of the batholith have younger zircon ages than those from batholith margin the inherited zircon age distribution pattern of the granitoids resembles that of the metasedimentary xenoliths our new comprehensive data combined with whole rock geochemistry from previous studies render an in situ origin of the vaasa granite probable the maximum sedimentation age of the supracrustal precursors of the vaasa complex is 1 92 ga some of the metasedimentary xenoliths from the vaasa complex host zircon that is coeval with their host granitoids and register incipient melting based on these 1 88 1 86 ga zircon grains the maximum sedimentation age would be deemed too young therefore our data calls for caution when determining maximum sedimentation ages of high grade metasedimentary rocks

p t conditions mechanism and timing of the localized melting of metapelites from the petronella shear zone and relationships with granite intrusions in the southern marginal zone of the limpopo belt south africa

petrogenesis of migmatites in maine usa possible source of peraluminous leucogranite in plutons high t low p facies series conditions during deformation within a devonian crustal scale shear zone system defined by kilometer scale straight belts of apparent flattening strain that anastomose around lozenges of apparent constrictional strain at upper amphibolite facies grade metapelites are partially melted the onset of which is introduction