k feldspar megacrysts in granites phenocrysts not porphyroblasts abstract k feldspar megacrysts in granitoid plutons have been interpreted as either phenocrysts or porphyroblasts most of the microstructural mineralogical and chemical evidence e g shape alignment concentration ba content zoning inclusions and twinning favours a phenocryst origin the main features that have been used to support a porphyroblast origin are occurrence of megacrysts 1 across aplite vein boundaries 2 in country rocks and 3 in or across boundaries of microgranitoid enclaves mafic inclusions however these features can be explained by the phenocryst hypothesis in particular megacrysts in microgranitoid enclaves can be explained by growth or mixing in magma before a globule of that magma or a fragment of the resulting igneous rock was incorporated as an enclave all available evidence favours or is consistent with a phenocryst origin for k feldspar megacrysts in granitoid rocks and their enclaves the large size of the megacrysts is evidently due to nucleation difficulties for k feldspar in granitic melts though k feldspar is commonly the last mineral to begin crystallizing in granitic magmas abundant melt is still present at that stage allowing sufficient space for the megacrysts to grow the reason for the common lack of megacrysts in volcanic rocks may be that the phenocrysts do not grow large enough to be called megacrysts until the magma contains such a high proportion of crystals that it cannot erupt

structures on interfaces of mingled magmas stewart island new zealand abstract strain analysis of magmatic rocks has been attempted using the shapes of enclaves of contrasting magmas and analysis of mineral fabrics in composite plutonic rocks of the anglem complex stewart island new zealand interfaces between different magma types are deformed into fold like patterns which have the potential to provide new data on strain in magmatic processes the fold forms have shorter wavelength and higher amplitude on interfaces at a high angle to layering whereas fold forms are either absent or of low amplitude on interfaces parallel to layering the fold forms may be amplified de amplified irregularities or buckle folds and in either case they indicate shortening perpendicular to rock layering whole rock fabrics of the plagioclase hornblende biotite rocks analysed by shape preferred orientation and centre to centre methods record less intense alignment and strain than predicted by free rotation of particles in viscous media the inhibition of crystal rotation at high crystal concentrations and the growth of late poorly aligned crystals present difficulties for calibrating whole rock fabrics with the strain incurred by magmatic flow

cretaceous deformation in the western foothills of the sierra nevada california deformation of metamorphic rocks the tonalite of blue canyon several bodies of granite and granodiorite and the leucotonalite of ward mountain within an area of about 600 km 2 in the western foothills of the sierra nevada just south of the south end of the western metamorphic belt is attributed to emplacement of the leucotonalite in a nearly solid state the east flanks of two plutons of leucotonalite of ward mountain in the west central part of the deformed area dip gently beneath the area of deformed rocks whereas their west flanks are vertical or dip steeply east cata clastic planar and linear structures in the metamorphic rocks and in the tonalite of blue canyon form coherent and related patterns the planar structures generally strike parallel to contacts with the leucotonalite and dip outward between the two plutons of leucotonalite they form a synform lineations generally plunge outward from the leucotonalite but trend parallel to contacts within the synform heat and possibly volatiles that accompanied emplacement of the rising and westward moving mass of leucotonalite may have increased the susceptibility of the overlying rocks to attenuate normal to the planar structures and to stretch in the direction of the linear structures isotopic u pb and k ar determinations indicate that the age of the tonalite of blue canyon is about 114 m y and that the age of the leucotonalite of ward mountain coincides with the time of deformation at about 113 m y ago the isotopic age of the granodiorite of knowles which truncates cataclastic structures in the tonalite of blue canyon and the leucotonalite of ward mountain is 110 m y

neoglaciation and an early little ice age in western norway lichenometric evidence from the sandane area moraine sequences protalus ramparts rock glaciers and various slope deposits in seven separate glacier basins provide lichenometric ages for glacier retreat in an upland area of sogn og fjordane southern norway geomorphological mapping relative dating based on section rhizocarpon size frequency distributions observations on vegetation cover and numeric dating based on a regional lichen dating curve for section rhizocarpon place moraines into three groups stage 1 moraines of likely preboreal or younger dryas age stage 2 moraines of pre or early little ice age but post preboreal age thirteenth fourteenth centuries and stage 3 moraines of fifteenth century age and younger the occurrence of thirteenth sixteenth century pre or early little ice age moraines at low altitudes in the sandane area is thought to relate to greater availability of moisture and to the capture of wind drifted snow these moraines are some of the oldest little ice age moraines dated by lichenometry in southern n

glacier reconstruction and mass balance modelling as a geomorphic and palaeoclimatic tool the reconstruction of former mountain glaciers has long been used to examine the implications of rapid climate shifts for example at the last glacial interglacial transition and for evaluating asynchronous behaviour of mountain glaciers compared with mid latitude ice sheets during the late quaternary glacier reconstruction has also been used as a source of palaeoclimatic information based on the recognition of empirical relationships between glaciers and climate this paper reviews the application and implications of a recently revised method of glacier reconstruction carr and coleman 2007 based around glaciological principles of mass balance this study examines how this approach can be used to test geomorphological interpretations of former mountain glaciation and also to infer precipitation fields at sites of former glaciation sites of younger dryas niche and icefield glaciation in the british isles demonstrate how this method can verify interpretations of marginal glaciation and begin to understand the different behaviour of outlet glaciers within the same environmental regime examination of a site of former niche glaciation in southern africa demonstrates how glacier reconstruction may be used to infer annual and seasonal precipitation values and strongly supports the idea that winter precipitation in lesotho and se south africa was substantially greater than present day values during the last glacial cycle copyright 2010 john wiley sons ltd

younger dryas and holocene glacier fluctuations and equilibrium line altitude variations in the jostedalsbre region western norway reconstructed younger dryas 11000 10000 y bp valley and cirque glaciers west of the jostedalsbre ice cap suggest an equilibrium line altitude ela depression of 450 50 m compared to the present level the mid preboreal 9500 200 y bp deglaciation was characterized by vertical wastage indicating that the ela was above the summit plateaus during the erdalen event 9100 200 y bp marginal moraines were formed up to 1 km beyond the little ice age lia moraines which lie in front of the present valley outlet glaciers of the jostedalsbre ice cap the average ela lowering during this event is calculated to 325 m below the modern level lithostratigraphic and paleobotanical studies show that the hypsithermal ca 8000 6000 y bp ela was about 450 m higher than at present as a result jostedalsbreen probably disappeared entirely during that period the glacier reformed about 5300 y bp the ela intersected the modern mean equilibrium line altitude five times from ca 2600 y bp to the present the outlet valley glaciers reached their maximum neoglacial extent during the lia in the mid 18th century when the ela was depressed 100 150 m below the present level

plateau icefields as contributing areas to valley glaciers and the potential impact on reconstructed elas a case study from the lyngen alps north norway

equilibrium line altitudes on reconstructed lgm glaciers of the northwest barguzinsky ridge northern baikal russia abstract the spatial extent of the last glacial maximum lgm glaciers mis 2 in the northwest of the barguzinsky ridge has previously been mapped geographical information system gis computing of the glaciers quantitative parameters allowed us to use various methods to evaluate the former equilibrium line altitudes elas for the 10 largest glaciers elas on reconstructed glaciers were calculated using four common methods 1 the median elevation of glaciers meg 2 the toe to headwall altitude ratio thar 3 the accumulation area ratio aar and 4 gefer s method the results suggest that the mean macroclimatic lgm background ela for the area studied was about 1200 145 m above present sea level and the mean ela depression relative to modern conditions was about 1100 m tentative estimates suggest that the reconstructed glaciers could have existed in a drier about 1 5 times drier than present environment if the mean summer air temperature was about 8 9 c lower than present day

structural pattern and ascent model in the central extremadura batholith hercynian belt spain abstract the central extremadura batholith constitutes an important alignment of plutonic rocks occupying part of the internal zones of the iberian hercynian belt it comprises 13 plutons and numerous minor intrusions and covers a wide compositional range from quartz diorites to alkali feldspar granites structural study of the individual plutons reveals that their internal structural patterns may be correlated correlation between the different structural patterns in the plutons and interpretation of the superimposed deformation in the metasedimentary host rocks indicate that the plutons were emplaced and deformed in an e w dextral intracontinental shear zone developed during the second deformation phase 302 320 ma a qualitative ascent model has been established as follows 1 development of extensional fractures at 45 to the e w dextral shear zone 2 intrusion of granitic magmas along these fractures and 3 rotation of the earlier intrusions in a dextral sense inducing antithetic shear zones n s sinistral and a transverse shortening perpendicular to the major axis of the earlier deformed plutons as well as the forced emplacement of the later plutons

deformation of incompletely crystallized magma systems granitic gneisses and their tectonic implications certain textures in two feldspar calc alkaline granitic gneisses have been identified as indicators of the presence of intercrystalline melt during deformation of crystal melt mushes fluid relocation or fracting is to be expected in an incompletely crystallized magmatic system as deviatoric stresses are applied to it relocation of late stage fluids capable of crystallizing k feldspar quartz microaplite and myrmekite to low pressure zones such as the pressure shadow region around earlier crystals occurs within some developing mylonitic gneiss fabrics and results in a distinctive assemblage of textures strain in these rocks is expressed by various brittle and ductile features and by fluid relocation textures the petrogenesis of these particular gneisses is therefore both magmatic and metamorphic contrasting with gneiss forming processes that had no participating magmatic component migmatitic complexes evolving by partial anatexis of non magmatic rocks in a tectonically active environment are not

late glacial cirque glaciation in parts of western norway younger dryas cirque glaciers are known to have existed beyond the scandinavian ice sheet in parts of western norway at krakenes on the outermost coast a cirque glacier formed and subsequently wasted away during the younger dryas no glacier existed there during the allerod large cirque moraines some with marine deltas and associated fans extend into the western part of sykkylvsfjorden comparison with existing late glacial sea level curves shows that the uppermost marine sediment in these features was deposited well above younger dryas sea level demonstrating that the cirques were occupied by glaciers before the younger dryas during the younger dryas the cirque glaciers expanded and some advanced across the deltas depositing till and supplying the sediment to form lower level fans and deltas controlled by younger dryas sea level the extent of the younger dryas advance of some of the glaciers was at least in part controlled by grounding on material deposited before the younger dryas the depositional history of the glacial marine deposits in the sykkylven area indicates that cirque glaciers existed throughout late glacial time and only expanded during the younger dryas the sediment sequence in glacial lakes beyond cirque moraines and reconstructions of glacier equilibrium lines indicate that this was true for most cirques in western norway only on the outermost coast were new glaciers formed in response to younger dryas climate cooling 1998 john wiley sons ltd

the guitiriz granite variscan belt of northern spain extension controlled emplacement of magma during tectonic escape abstract the ollo de sapo domain of the northern part of the variscan belt of spain contains precambrian and ordovician metamorphic rocks intruded by the guitiriz granite the domain is bounded by two n s transcurrent shear zones detailed structural and anisotropy of magnetic susceptibility studies of the guitiriz pluton reveal a syntectonic emplacement relative to movement on the two n s trending bounding shear zones characterized by 1 development of n s trending structural and magnetic fabrics 2 concordant structures in granites and country rocks and 3 development of shear zones along the east and west granite margins gravity data show two roots trending 110 e extending down to 4 5 km from an otherwise thin

oblique diapirism the criffel granodiorite granite zoned pluton southwest scotland abstract strain trajectories strain gradients and quartz c fabrics have been used to propose an emplacement history of the criffel zoned pluton strain has been estimated from the microdioritic xenoliths included in the outer granodiorite textural criteria have been used to complete the pattern of strain variations throughout the pluton strain gradients are found to be related to the granodiorite granite boundary zone with highest strain towards the northeast side of the pluton giving an asymmetric horseshoe pattern quartz c fabrics allow two strain histories to be distinguished within the pluton an early coaxial flattening in the granodiorite followed by a non coaxial deformation in the granite and the adjacent granodiorite these features are interpreted as the result of an oblique diapiric intrusion of the inner granite into the partially emplaced and crystallized granodiorite

changes in glacier extent on north novaya zemlya in the twentieth century glacier retreat on north novaya zemlya for the past century was documented by registering glacier terminus positions from expedition and topographic maps and remotely sensed images recession of tidewater calving glaciers on north novaya zemlya in the first half of the twentieth century was relatively rapid 300 m yr 1 consistent with post little ice age warming documented by a 122 year instrumental record from malye karmakuly the glaciers completed 75 to 100 of the net twentieth century retreat by 1952 between 1964 and 1993 half of the studied glaciers were stable the remainder retreated modest distances of 0 75 elevated sst in the barents sea appear to reflect increased advecti

c slip in quartz from subsolidus deformed granite abstract the slip behaviour of quartz from a granite and granitic veins during subsolidus high temperature conditions 700 800 c of deformation is studied by lattice preferred orientation lpo and microstructural techniques lpos with a point maximum of c axes parallel to the shear direction which is close to the stretching lineation are presented and interpreted with the aid of light and electron microscopy in terms of c as the dominant slip direction during plastic deformation microscopy of such samples reveals the presence of 0001 tilt boundaries and free 0001 burgers vector dislocations in edge orientations a change in lpo in a decreasing temperature environment from c axes parallel to the shear direction to c axes normal to the shear direction documents a fabric transition from the rare c slip to the more common a slip fabric it is concluded that conditions of high temperature and partial pressure of water are required to initiate dominant c slip during deformation at geological strain rates

microstructural controls and the role of graphite in matrix porphyroblast exchange during synkinematic andalusite growth in a granitoid aureole in the contact metamorphic aureole of the tinaroo batholith north queensland australia mylonitic rocks were metamorphosed during a regional folding crenulation event d2 synchronous with the emplacement of muscovite bearing granitoids prismatic and skeletal andalusite porphyoblasts grew in carbonaceous schists mainly from the dissolution of staurolite muscovite quartz and biotite played a dual role in this reaction acting in a catalytic capacity as well as reactants or products staurolite was replaced by coarse grained muscovite biotite whereas andalusite locally replaced quartz muscovite biotite with diffusion of h al si mg fe and k ionic species linking sites of dissolution and growth graphite contributed to the reaction mechanism in a number of ways accumulations of graphite in front of advancing andalusite crystal faces led to skeletal growth and the formation of chiastolite structure where incremental growth occurred on adjacent 110 faces with subsequent filling in and inclusion of graphite along the diagonal zones the presence of graphite in some layers in the schist matrix prevented recrystallization of strained muscovite grains the muscovite grains in these layers in contrast to adjacent thin non graphitic layers were preferentially replaced by quartz this resulted in muscovite depletion haloes in graphitic layers around andalusite porphyroblasts somewhat arcuate zones of graphite concentrated during dissolution of quartz along a crenulation cleavage occur on some andalusite faces reactivation of the mylonitic foliation during the formation of d2 crenulations led to a preferential dissolution of quartz in zones of progressive shearing localized near andalusite porphyroblasts and hence the accumulation of graphite lack of deflection of the pre existing mylonitic foliation and anastomosing of the axial planes of d2 crenulations around andalusite porphyroblasts demonstrate not only the timing of growth but also that growing porphyroblasts do not push aside existing foliations

calamity peak layered granite pegmatite complex black hills south dakota part i structure and emplacement the calamity peak pluton is a satellitic granite pegmatite intrusion located 2 km southwest of the main harney peak granite dome in the black hills south dakota many aspects of the structural development of the calamity peak pluton 1 km 2 mimic those of the larger harney peak dome 100 km 2 thus the model described here for the calamity peak pluton provides a general basis for evaluating the evolution of proterozoic granite pegmatite intrusives of the harney peak granite system the overall structure of the intrusive rocks at calamity peak is that of a dome as shown by the general geometry of the pluton contacts and by a domical pattern of internal textural layering textural layering is defined by alternating bands of pegmatite and fine grained granite 0 1 2 0 m thick fine grained layers are in turn banded on a scale of 2 20 mm owing to modal variations of tourmaline quartz and feldspars textural differentiation of at least some of these layers resulted from segregation of initially homogeneous magmas into pegmatitic upper and aplitic lower components during crystallization relationships between the pluton and regionally dipping schistose country rocks however do not support a simple domal structure schistosity conforms to the contact only along the southern margin of the pluton the side facing with the regional dip country rock schistosity is at a high angle to the contact at the apparent floor of the pluton which is exposed in the core of the dome and along the northern margin the side that opposes the regional dip in order to explain the structural observations it is inferred that the initial intrusive body at calamity peak consisted of a flat lying discordant sheet intruded into steeply dipping quartz mica schist country rock however an arcuate sheet concave downward cannot be ruled out new magma pulses possibly several thousands were successively emplaced along the hanging wall contact of earlier pulses as indicated by the upward truncation of early layers creating a composite layered pluton intrusions of individual magma pulses were localized in three major composite sheets which form structurally and chemically discrete portions of the pluton growth of the pluton proceeded by forcible distension and plastic deformation of overlying country rocks schistosity was molded into a conformable attitude in portions of the hanging wall and pre intrusive country rock lineations were deflected around the pluton the layered granite pegmatite series is crosscut by four successive stages of fracture filling bodies the orientations and compositions of these bodies record the late stages in the structural and fluid evolution of the plutonic system

climatic interpretation of alpine snowline variations on millennial time scales abstract the depression of snowlines or equilibrium line altitudes of alpine glaciers is often used by glacial geologists to infer variations in mass balance the climatic interpretation of snowline depression however is complicated by the number of factors that control glacier mass balance the simple lapse rate method of temperature interpretation ignores the effects of changes in radiation and snow accumulation the statistical approach to temperature interpretation which regresses precipitation and temperature against snowline altitude neglects the effect of radiation the most comprehensive approach for the climatic interpretation of snowline depression couples the heat and mass balances of a glacier surface a sensitivity analysis that utilizes the coupled heat and mass balance approach indicates that the 1000 m variation in snowline of alpine glaciers on glacial to interglacial time scales could be a result of significant changes in temperature and to a lesser extent changes in insolation snowline variations are sensitive only to relatively large changes in annual accumulation which should also be evident in other proxy records of moisture change the approaches outlined here provide glacial geologists with a summary of how various climatic forcings associated with glaciation may be quantified from snowline data

diapirism during regional compression the structural pattern in the chibougamau region of the archean abitibi belt quebec the major fold pattern of the chibougamau region in the archean abitibi belt quebec is the result of two fold phases the principal f1 synclines first formed as subsiding fault troughs and were shortened in ns direction and molded around volcanic centers that had been consolidated by large synvolcanic plutons they have a general easterly direction but curve locally to the ne or se n trending f1 folds are locally present in the anticlinoria and are thought to have been produced by the upwelling of basement gneiss and or synvolcanic plutons the f2 folds have rather regular easterly trends their axial plane schistosity s2 is the predominant planar fabric element basin margin faults were transformed into east trending thrust faults during the f1 and f2 folding

early holocene glacier fluctuations of northern grovabreen western norway marginal moraines on the northern side of grovabreen a plateau glacier in inner sunnfjord western norway have been mapped and morphostratigraphically correlated with the erdalen event and possibly the finse event and the little ice age schmidt hammer exposure age dating was used to evaluate the age of the most distinct marginal moraines by measuring the degree of surface weathering on boulders the lithostratigraphy of lake sediments was analysed in a core from dalevatnet in order to correlate this stratigraphy with the marginal moraines in the catchment area of the lake and reconstruct the early holocene history of grovabreen the lake catchment was deglaciated at 10 750 cal yr bp two readvances of an outlet glacier in fagredalen were dated to between 10 340 and 9960 cal yr bp correlated with the two peaked erdalen event a readvance shortly after 8450 cal yr bp can most probably be correlated with the 8200 cal yr bp finse event

evidence of syndeformational contact metamorphism from porphyroblast matrix microstructural relationships abstract cordierite porphyroblasts in three high level contact metamorphic aureoles in southeast australia show microstructural evidence of having grown during the development of a crenulation foliation the evidence includes curvature of straight inclusion trails into crenulated matrix folia and deflection of matrix foliations including micaceous crenulation folia axial surfaces around porphyroblasts in some rocks coarsening has obliterated evidence of crenulations in the matrix owing to heating having outlasted deformation the crenulations are confined to the contact aureoles of granitoid plutons that have not undergone penetrative post intrusion deformation therefore the crenulations appear to have resulted from local deformation caused by the intrusion

ams record of brittle dilation viscous stretching and gravity driven magma ascent in area of magma rich crustal extension vosges mts ne france orogenic compression related fabrics 340 335 ma were reworked during regional extensional deformation 328 325 ma in a large anatectic crustal domain of the central vosges ne france the extension was first accommodated by brittle dilation affecting vertically anisotropic high grade rocks associated with emplacement of subvertical granitic sheets the ams fabric of granitoids is consistent with highly partitioned transtensional deformation marked by alternations of flat and steep foliations and development of orthogonal lineations this deformation passes to top to the southwest ductile shearing expressed in southerly migmatitic middle crust the ams fabric revealed moderately west dipping foliations bearing subhorizontal nnw sse trending lineations and predominantly plane strain to prolate shapes this fabric pattern is interpreted as a viscous response of stretched partially molten crust during continuous ductile extension vertical ascent of voluminous granites and stoping of the upper crust occurs further south this gravity ascent triggered by extension leads to development of south dipping ams foliations south plunging lineations and oblate fabrics in various crustal granites vertical shortening related to ascent of these 325 ma granitoids and persistent n s stretching is responsible for reworking and remelting of originally vertical compression related fabric in roof supracrustal granites 340 ma and development of highly prolate fabrics in these rocks this work shows that the finite shape of ams fabric ellipsoid is highly sensitive to both strain regime and superpositions of orthogonal deformation events

shear criteria in granite and migmatite deformed in the magmatic and solid states microstructural criteria for the determination of the sense of shear in rocks homogeneously deformed in the partially melted state are similar to those which apply to solid state deformation sense of shear determination is either direct deduced from the sense of rotation of markers or indirect involving the obliquity between the shear and foliation planes or between the successive foliations imprinted at different stages of progressive deformation this study is a by product of the detailed structural and microstructural investigation of a high grade metamorphic rock pile variscan vosges massif france which underwent subhorizontal shearing during partial melting and further solidification depending on the rock chemistry on the position in the pile and the relative timing of progressive deformation layered migmatites and homogeneous granites were variously deformed in the partially melted and solid states the sense of shear obtained from these rock types using the criteria presented here consistently gives a top to sw direction

pressure solution structures in a granite abstract syntectonic two mica granites in northwest spain have suffered regional late variscan shear deformation the deformed corcoesto granite shows a marked planar and linear fabric resulting from ductile behaviour and contains quartz veins at about 60 to the foliation offsets of these quartz veins along shear planes are commonly contrary to the general sense of shear and thus provide evidence for pressure solution processes

evidence for deformation induced k feldspar replacement by myrmekite several examples of deformation induced myrmekite have been found in two amphibolite facies mylonites derived from granitic protoliths namely a muscovite poor s c mylonite and a single foliation muscovite poor mylonitic gneiss back scattered sem and conventional optical microscopy show that in both rock types syntectonic myrmekitic intergrowths of oligoclase and quartz formed on the two sides of k feldspar grains that faced the local inferred incremental shortening direction for the mylonite myrmekite does not occur on the two ends of the grain that faced the incremental stretching direction the replacement of k feldspar by plagioclase and quartz results in a volume decrease and is favoured on high normal stress sites around the grains we suggest that the ambient temperature pressure and chemical activities were such that the replacement reaction was favoured but the addition of extra strain energy along the high pressure sides of the grains localized the reaction at these sites this energy could arise from elastic strain or strain associated with tangled dislocations or twin boundaries the relative roles of stress and strain energy concentrations in driving the replacement reaction are not known but both were probably important

aureole deformation by flattening around a diapir during in situ ballooning the cannibal creek granite the cannibal creek granite a foliated pluton within a strongly deformed aureole shows several diagnostic features of a diapir the intensity of the aureole deformation diminished away from the contact the aureole foliation is continuous with that of the granite and forms closed elliptical trend lines and the contact metamorphic minerals are synkinematic with regard to the aureole foliation the pluton deformed its aureole in three stages involving initially brittle then ductile and finally brittle deformation styles initial intrusion of a low strength magma stoped kinked and flexed aside its overburden crystallization of the magma prevented further rise and it ballooned and deformed its aureole evidently entirely by ductile bulk shortening perpendicular to the contact this the major stage of aureole deformation records no evidence of vertical movement of the pluton or of progressive simple shear along its margin during this stage the magma may have been theologically a high strength bing

a magnetic fabric study of the shap region in the english lake district abstract the magnetic susceptibility anisotropy technique was applied to 50 sites comprising 280 core samples from the shap granite and the surrounding country rocks from both within and outside the thermal aureole the magnetic fabrics of individual cores from the granite pluton indicate preferred orientations of non equi dimensional magnetite grains this fabric developed during the slow ascent and consequent cooling of the magma the sites from the metamorphic rocks from the immediate contact with the shap granite show weak axial shortening directions which are subnormal to the granite contact core samples from the surrounding ordovician and silurian rocks within the thermal metamorphic aureole but further from the granite have oblate magnetic fabric ellipsoids with subvertical magnetic foliations trending approximately ne sw parallel to the regional caledonian cleavage planes this suggests that the magnetic fabric observed in the granite is primary with respect to the time of emplacement of the magma and that this emplacement post dates the main compressive phase of the caledonian orogeny the effect of the granite on the country rock is mainly thermal metamorphism with mechanical deformation limited to a very narrow strip around the granite

characteristics and mode of emplacement of gneiss domes and plutonic domes in central eastern pyrenees abstract gneiss domes and plutonic granitoid domes make up almost 50 of the pre hercynian terrains in the central and eastern pyrenees from a structural study of the shape and internal structure of the domes and of their relationships with the enclosing rocks it can be shown that both types of domes were emplaced diapirically during the major regional deformation phase and the peak of regional metamorphism the study also shows that the internal structure the overall shape and general behaviour relative to the host rocks are similar for plutonic domes and for gneiss domes this appears to be in good agreement with h ramberg s 1967 gravity deformation and the earth s crust academic press london 1970 model studies in relation to intrusion of plutonic bodies in mechanisms of igneous intrusion edited by newall g rast n geol j spec issue 2 261 286 model studies showing that dome or mushroom like structures similar to those observed develop when there is a small viscosity ratio between the rising body and its enclosing medium this implies a high crystal content for the granitoid magma this crystal content has been estimated by i calculating the viscosity and density in natural conditions from petrological data for the magma considered as a suspension using the model and program of j p carron et al 1978 bull soc geol fr 20 739 744 ii using the recent results of experimental deformation of partially melted granites of i van der molen m s paterson 1979 contr miner petrol 70 299 318 and ii comparing the preceding results with the data obtained by deformation experiments on rocks similar to those enclosing the domes the minimum crystal content for the development of a dome like structure has been thus estimated to about 70 i e a value very close to that estimated by van der molen paterson 1979 to be the critical value separating the granular framework flow from suspension like behaviour the effect of small variations in the viscosity of the rising body are then simulated by centrifuge experiments these small variations appear to exert a strong control on the shape and rate of rise of the domes they are thought to be sufficient to account for the variations in shape and structure and the level of emplacement of the different types of gneissic and plutonic domes finally more complex experiments with models built in order to simulate as closely as possible the natural structural evolution of the region as deduced from petrological and structural data are reported their implications for the regional interpretation of the relationships between gneissic and plutonic domes is then discussed

strain pattern in the aar granite central alps orthogneiss developed by bulk inhomogeneous flattening the central part of the aar granite aar valley shows lens shaped domains of low strain separated by anastomosing domains of high strain a comparable pattern is found on all scales of observation deformation gradients are outlined by a gradual change from isotropic granite to orthogneiss and locally ultramylonites ultramylonites are concentrated within conjugate ductile shear zones where moderate the strain is concentrated in very narrow small scale faults which affect relatively undeformed granite within foliated domains finite strain measurements on deformed xenoliths indicate that i strain intensity increases gradually with grain size reduction and ii finite strain ellipsoids are of flattening type irrespective of the degree of mylonitization the pattern of small scale faulting the trends of the regional foliation and the orientation of ductile shear zones are consistent with a bulk strain field of flattening type throughout progressive deformation

origin of sierra nevadan granite evidence from small scale composite dikes composite dikes at hell hole meadow in the central sierra nevada contain hybrids created by small scale mixing of andesitic and rhyolitic magmas early rhyolitic injections had partially solidified when subsequent andesitic magmas arrived and mixed with small increments of remnant rhyolitic magma in major element chemistry the hybrid rocks define linear mgo variation diagrams that closely resemble those for the half dome mt givens and eagle peak granodiorites the patterns suggest that mixing of mafic and felsic magmas has been important in the evolution of these plutons

latest pleistocene and holocene alpine glacier fluctuations in scandinavia abstract during the early holocene abrupt decadal to centennial scale climate variations caused significant glacier variations in norway increased freshwater inflow to the north atlantic and arctic oceans has been suggested as one of the most likely mechanisms to explain the abrupt and significant lateglacial and early holocene climatic events in nw europe the largest early holocene glacier readvances occurred 11 200 10 500 10 100 9700 9200 and 8400 8000 cal yr bp the studied norwegian glaciers apparently melted away at least once during the early mid holocene the period with the most contracted glaciers in scandinavia was between 6600 and 6000 cal yr bp subsequent to 6000 cal yr bp the glaciers started to advance and the most extensive glaciers existed at about 5600 4400 3300 2300 1600 cal yr bp and during the little ice age times with overall less glacier activity were apparently around 5000 4000 3000 2000 and 1200 cal yr bp it has been proposed that several glacier advances occurred in scandinavia including northern sweden at 8500 7900 7400 7200 6300 6100 5900 5800 5600 5300 5100 4800 4600 4200 3400 3200 3000 2800 2700 2000 1900 1600 1200 1000 and 700 200 cal yr bp glaciers in northern sweden probably reached their greatest little ice age extent between the 17th and the beginning of the 18th centuries evidence for early holocene glacier advances in northern scandinavia however has been questioned by more recent multi disciplinary studies the early to mid holocene glacier episodes in northern sweden may therefore be questioned most norwegian glaciers attained their maximum little ice age extent during the mid 18th century cumulative glacier length variations in southern norway based on marginal moraines dated by lichenometry and historic evidence show an overall retreat from the mid 18th century until the 1930s 40s subsequently most norwegian glaciers retreated significantly maritime outlet glaciers with short frontal time lags 15 20 years continued their retreat to the 1970s and 1980s however maritime glaciers started to advance as a response to higher winter accumulation during the first part of the 1990s after 2000 several of the observed glaciers have retreated remarkably fast annual frontal retreat 100 m mainly due to high summer temperatures the general glacier retreat during the early holocene and the neoglacial advances after 6000 cal yr bp are in line with orbital forcing due to the decrease of northern hemisphere summer solar insolation and the increase in winter insolation in addition regional weather modes such as the north atlantic oscillation nao and the arctic oscillation ao play a significant role with respect to decadal and multi decadal climate variability

deformation of granitic rocks across the brittle ductile transition abstract a microstructural analysis has been carried out on mylonites and mylonitic gneisses of the eastern peninsular ranges mylonite zone which were formed over a range of metamorphic conditions from lower greenschist to amphibolite facies composite planar fabrics in the form of c and s planes are found at all metamorphic grades fractured feldspars kinked biotites and ductile deformation of quartz characterize the lower greenschist facies mylonites at mid upper greenschist grade orthoclase grains show dynamic recrystallization textures whereas plagioclase exhibits low temperature plasticity with only minor recovery biotite ribbons form by progressive rotation and coalescence of kink band segments to produce chevron fold patterns at epidote amphibolite grade and above recovery processes and annealing recrystallization predominate in all minerals residual orthoclase porphyroclasts show strain related myrmekite formation along those sides of the grains that face the instantaneous shortening direction myrmekite formation due to replacement reactions cannot explain this geometry it is proposed that the myrmekites formed due to a combination of exsolution replacement and strain enhanced diffusion

crustal generation of the himalayan leucogranites abstract detailed studies of the himalayan two mica leucogranites such as the manaslu pluton indicate that they have very uniform mineralogical petrological and structural characteristics one can relate their occurrence to the thickest zones of the underlying tibetan slab in these zones migmatization attains its greatest development and vertical extension the granite is emplaced at first along the main disharmonic plane above the main central thrust mct at the top of the tibetan slab infrastructure ductile deformation of the granite is variable the granite being syn to late kinematic with regard to the functioning of the mct major elements are very homogeneous except for na and k implying that p t conditions of melting were relatively uniform the melted material was of a similar composition over a vast volume and the percentage of melting was small 10 15 trace elements are highly variable some are characteristic for very evolved material ta rb cs u or show the link with the tibetan slab ba sr whilst others are problematic th ree ree and th abundances being much less in the granite than in the tibetan slab imply that they have been extracted during one of the main stages of formation possibly by monazite radiogenic pb sr nd and stable o isotopes are consistent with the origin of the granite from the tibetan slab however the heterogeneous sr isotopic ratios make age dating difficult and imply poor mixing or little fluid interaction during its evolution h isotope data indicate that magmatic compositions of the main body of the manaslu granite have been preserved late or post magmatic alterations are extremely local in the main pluton to the north another belt of two mica granites occurs whose characteristics are very similar to the high himalaya belt they were probably generated in a similar way during this recent intracontinental evolution

horizontal and vertical transport of air over southern africa tropospheric air trajectories that occurred during the southern african fire atmosphere research initiative safari in august october 1992 are described in terms of a circulation classification scheme and the vertical stability of the atmosphere three major and frequently occurring stable discontinuities are found to control vertical transport of aerosols in the subtropical atmosphere at the end of the dry season of these the main subsidence induced feature is a spatially ubiquitous and temporally persistent absolutely stable layer at an altitude of about 5 km 3 5 km above the interior plateau elevation this effective obstacle to vertical mixing is observed to persist without break for up to 40 days below this feature an absolutely stable layer at 3 km 1 5 km above the surface prevails on and off at the top of the surface mixing layer for up to 7 days at a time being broken by the passage of regularly occurring westerly wave disturbances above the middle level discontinuity a further absolutely stable layer is frequently discerned at an altitude of about 8 km it is shown that five basic modes can be used to describe horizontal aerosol transportation fields over southern africa dominating these is the anticyclone mode which results in frequent recirculation at spatial scales varying from hundreds to thousands of kilometers in exiting the anticyclonic circulation transport on the northern periphery of the system is to the west over the atlantic ocean via a semistationary easterly wave over the western part of the subcontinent on the southern periphery wave perturbations in the westerly enhance transports which exit the subcontinent to the east into the indian ocean independently derived data suggest that during safari only 4 of the total transport of air from three locations south of 18 degrees 8 was into the atlantic ocean over 90 of the transport was into the indian ocean across 35 degrees e this result reflects circulation fields typical of the extremely dry conditions prevailing in 1992 the integrated effect of the control exerted by atmospheric stability on vertical mixing on the one hand and the nature of the horizontal circulation fields on the other is to produce a distinctive suite of transport patterns that go a long way to explain the observed high concentrations of tropospheric aerosols and trace gases observed over the subcontinent in winter and spring as well as over the tropical south atlantic and southwestern indian oceans

microgranitoid enclaves in granites globules of hybrid magma quenched in a plutonic environment microgranitoid enclaves autoliths cognate xenoliths mafic inclusions are common in high level granitoid plutons they have relatively fine grained igneous microgranitoid microstructures1 and many show evidence of having flowed in a magmatic condition2 these features counter interpretations that the enclaves represent transformed solid fragments of diverse wall rocks3 5 or restite6 11 an alternative interpretation is that the enclaves represent globules of mafic magma that have mingled commingled and quenched in the granitoid host magma12 16 a detailed review of the literature occurrence morphology and composition of micro granitoid enclaves strongly supports this view hut indicates that the enclave magmas range in composition from mafic to felsic and that magma mixing may be involved in their formation17 i summarize here the main features of microgranitoid enclaves and briefly outline the possible processes leading to their incorporation as magma globules in the host granitoid

holocene cirque glacier activity in western spitsbergen svalbard sediment records from proglacial linnevatnet holocene glacial variations of a presently ice free cirque in western spitsbergen are inferred from sediment records from the proglacial lake linnevatnet glaciation is indicated in the core records by increased intensity of laminae derived from the cirque inflow and by increase in sediment accumulation rate radiocarbon ages on terrestrial plant macrofossils limit the onset of glaciation in the cirque to within the last six centuries no evidence for earlier glaciation is recognized in the core records indicating that the threshold for glaciation in the cirque was not reached during prior neoglacial advances local climate events favouring glacier expan sion were either of greater magnitude or of longer duration during the little ice age than at any other time during the holocene

an improved technique for the reconstruction of former glacier mass balance and dynamics abstract the recognition of past glacier extent and dynamics is a fundamental aspect of investigations of the climatic sensitivity of glaciers especially when examining short lived climate events such as the younger dryas or little ice age existing approaches to the reconstruction of glacier form and dynamics depend on speculative reasoning of key glacier dynamic parameters including the role of basal slip and subglacial deformation in glacier mass transfer this study reviews approaches to glacier reconstruction derivation of former glacier equilibrium line altitudes ela s and estimation of mass balance and dynamics concluding that most reconstructions of glacier mass balance are compromised by a lack of glaciological considerations an alternative approach to glacier reconstruction is presented demonstrated and discussed by which an empirical relationship between ablation gradient and mass loss at the ela is used to derive mass balance mass flux through the ela and average balance velocity at the ela this glaciological approach is applied to four reconstructed glaciers to test previous interpretations that each reflects younger dryas glaciation in the uk the study concludes that this approach provides a more robust technique for reconstructing former glacier dynamics and may be applied to test geomorphological interpretations of former mountain glaciation

time span of plutonism fabric development and cooling in a neoproterozoic magmatic arc segment u pb age constraints from syn tectonic plutons sark channel islands uk abstract new u pb zircon and titanite dates from syn tectonic plutons on the british channel island of sark constrain the time span of plutonism fabric development and cooling in this part of the neoproterozoic cadomian magmatic arc the tintageu leucogneiss is a mylonitic unit that was dated previously at 615 6 4 2 2 3 ma the port du moulin quartz diorite which intruded the tintageu unit contains a high strain solid state deformation fabric that is less intense than but parallel to fabrics in the leucogneiss and yields a u pb zircon date of 613 5 2 3 1 5 ma the little sark quartz diorite also displays solid state deformation fabrics in addition to relict magmatic textures and yields a u pb zircon date of 611 4 2 1 1 3 ma the north sark granodiorite is largely penetratively undeformed exhibits mainly magmatic fabrics and textures and has a u pb zircon date of 608 7 1 1 1 0 ma two fractions of titanite from each intrusion are essentially concordant and are identical within error with mean dates of 606 5 0 4 ma port du moulin quartz diorite 606 2 0 6 ma little sark quartz diorite 606 4 0 6 ma north sark granodiorite the new u pb data in combination with previous u pb and 40 ar 39 ar data and previous field studies confirm the syn tectonic nature of the sark plutons and quantify the time span ca 7 m y required for intrusion and sufficient crystallization of each body to record incremental strain during waning deformation titanite u pb and hornblende 40 ar 39 ar dates mark final cooling about 2 m y after intrusion of the last pluton

s c mylonites two types of foliations are commonly developed in mylonites and mylonitic rocks a s surfaces related to the accumulation of finite strain and b c surfaces related to displacement discontinuities or zones of relatively high shear strain there are two types of s c mylonites type i s c mylonites described by berthe et al typically occur in deformed granitoids they involve narrow zones of intense shear strain which cut across mylonitic foliation type ii s c mylonites described here have widespread occurrence in quartz mica rocks involved in zones of intense non coaxial laminar flow the c surfaces are defined by trails of mica fish formed as the result of microscopic displacement discontinuities or zones of very high shear strain the s surfaces are defined by oblique foliations in the adjacent quartz aggregates formed as the result of dynamic recrystallization which periodically resets the finite strain clock these oblique foliations are characterized by grain elongations alignments of segments of the grain boundary enveloping surfaces and by trails of grains with similar c axis orientations examples of this aspect of foliation development in mylonitic rocks are so widespread that we suggest the creation of a broad class of s c tectonites and a deviation from the general tradition of purely geometric analysis of foliation and time relationships kinematic indicators such as those discussed here allow the recognition of kilometre scale zones of intense non coaxial laminar flow in crustal rocks and unambiguous determination of the sense of shear

oriented growth of sillimanite in andalusite placitas juan tabo area new mexico u s a in metapelitic schists near the sandia granite in the placitas juan tabo area new mexico nucleation sites for sillimanite are very variable but growth of sillimanite in andalusite is common either as bundles of fibrous fibrolitic sillimanite crystals or as coarser grained parallel prisms or dendritic crystals of sillimanite optical relationships indicate a coaxial relationship between the andalusite and the sillimanite but with a and b axes interchanged stacking faults formed by dissociated screw dislocations in the andalusite may have provided nucleation sites for sillimanite some large sillimanite grains appear to have formed by coarsening of fibrous sillimanite but others show no evidence of such coarsening some fibrous sillimanite occurs in folia in zones of inferred noncoaxial strain accumulation some occurs in radiating or crystallographically controlled aggregates in low strain zones between sillimanite folia these aggregates do not necessarily indicate postdeformation growth exce

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

on granitoid emplacement and related structures a review granitoid magmas are emplaced at the upper crust under a complex interaction of gravitational processes and horizontal tectonics natural intrusive bodies show a wide variety of structural patterns that must be strongly related with their dynamic history of ascent and emplacement comparisons of natural structural patterns with experimental and numerical models are necessary to interpret in a coherent fashion the emplacement mechanism involved from natural experimental numerical and theoretical considerations one can reach important conclusions on the problem of ascent and final emplacement of granitoid magmas in the earth s crust the present paper reviews the principal emplacement mechanisms referred to in the literature that is doming diapirism ballooning stoping cauldron subsidence and dike propagation dike propagation is the most effektive process in magma transport from deep zones in the crust and upper mantle extensional fractures for dike propagation and magma ascent can be developed at depth in the crust according to the modern dike propagation theory in orogenic domains magmas reach the upper crust through narrow channels or dikes and are accumulated in a final reservoir in the form of a discordant supracrustal pluton or a ballooning pluton if during emplacement any regional deformation acts simultaneously

modern glacier characteristics as a basis for inferring former climates with particular reference to the loch lomond stadial abstract studies of the mass balance of modern glaciers have indicated that the equilibrium line altitude ela is the most critical parameter in the link between glaciers and climate average accumulation on a glacier includes components derived from direct precipitation on the glacier surface as well as wind drifting and avalanching of snow and approximates closely to accumulation at the equilibrium line ablation is most usefully predicted by mean summer temperature and there is a close non linear relationship between accumulation and mean summer temperature at the equilibrium line following discussion of methods of reconstructing former glaciers and calculating their equilibrium line altitudes the application of the above relationships to the loch lomond readvance glaciers of highland britain is considered and an outline of the precipitation pattern and the mean summer temperature of the loch lomond stadial is given

quartz fabric transition in a cooling syntectonic granite hermitage massif france abstract the hermitage granite situated in the northwest massif central france is a syntectonic hercynian leucogranite emplaced along an active transcurrent shear zone during emplacement and cooling the progressive deformation is marked by the development of a primary homogeneous foliation gradually affected by ductile shear bands c s mylonites increase in strain heterogeneity during cooling corresponds to a change of dominant deformation mechanism of the quartz phase from grain growth and migration recrystallization to intracrystalline a slip and rotation recrystallization migration recrystallization is characterized by preferred orientations of c axes close to the principal extension direction we discuss relevant deformation mechanisms and rheological implications for syntectonic plutons in particular we argue that the transitions between homogeneous and heterogeneous accumulation of strain cannot generally be correlated with transition between magmatic and solid state flow

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

the mortagne granite pluton france emplaced by pull apart along a shear zone structural and gravimetric arguments and regional implication the emplacement mechanism and kinematics and the 3 d geometry of the variscan granite pluton of mortagne are interpreted using systematic measurements of the granite structure allied with micro structural observations from a detailed gravimetric study it is proposed that magma infilled a pull apart structure which formed along a jog of a northwest southeast trending sinistral zone of shear a second episode of shearing under a dextral regime and independent of emplacement was responsible for perigranitic tectonites these successive transcurrent opposite movements already documented for variscan times in western france are discussed concerning the age of the mortagne pluton 313 15 m y

contrasting deformation of s and i type granitoids in the lachlan fold belt eastern australia abstract several examples of contrasting deformation under greenschist facies conditions of closely associated silurian devonian s type peraluminous and i type mainly metaluminous granitoid plutons of very similar age occur in the lachlan fold belt of eastern new south wales australia they occur in and or near the wologorong batholith the wyangala batholith and the kosciusko batholith the s type granitoids generally are strongly foliated and locally mylonitic whereas most of the i type granitoids typically show alteration to hydrous minerals chlorite epidote and actinolite but are unfoliated or only locally weakly foliated commonly fractured and have spaced ductile shear zones the more obvious and penetrative deformation in the s type granitoids probably is due mainly to their larger contents of relatively weak and or ductile minerals especially quartz and biotite and to the common occurrence of quartz in relatively large patches these features providing more continuous strained volumes and enabling quartz and mica rich folia to develop between resistant grains of feldspar in most of the i type granitoids the smaller amounts of quartz and biotite together with the common occurrence of quartz in smaller more scattered patches produce more localized strained volumes and may give rise to local stress concentrations that lead to fracturing the latter provides access to fluids responsible for hydrothermal alteration however some i type granitoids have high enough proportions of less ductile minerals to develop foliations although typically this occurs only adjacent to major faults some variation in the deformation of s types also is to be expected thus the main factor controlling the development of foliations appears to be the ratio of strong to weak or brittle to ductile minerals rather than the s i subdivision with which it generally correlates although other possible factors need further investigation such contrasting styles of deformation could lead to the erroneous interpretation that the massive i types are post deformation plutons and that the s types which commonly are slightly older are foliated by syn emplacement deformation whereas in fact both are pre deformation granitoids

late pleistocene glacial equilibrium line altitudes in the colorado front range a comparison of methods abstract six methods for approximating late pleistocene pinedale equilibrium line altitudes elas are compared for rapidity of data collection and error rmse from first order trend surfaces using the colorado front range trend surfaces computed from rapidly applied techniques such as glaciation threshold median altitude of small reconstructed glaciers and altitude of lowest cirque floors have relatively high rmses 97 186 m because they are subjectively derived and are based on small glaciers sensitive to microclimatic variability surfaces computed for accumulation area ratios aars and toe to headwall altitude ratios thars of large reconstructed glaciers show that an aar of 0 65 and a thar of 0 40 have the lowest rmses about 80 m and provide the same mean ela estimate about 3160 m as that of the more subjectively derived maximum altitudes of pinedale lateral moraines rmse 149 m second order trend surfaces demonstrate low elas in the latitudinal center of the front range perhaps due to higher winter accumulation there the mountains do not presently reach the ela for large glaciers and small front range cirque glaciers are not comparable to small glaciers existing during pinedale time therefore pleistocene ela depression and consequent temperature depression cannot reliably be ascertained from the calculated ela surfaces

nature and timing of deformation in the foothills terrane central sierra nevada california its bearing on orogenesis detailed mapping and structural analysis combined with new age dates using u pb and 40 ar 39 ar techniques have allowed us to constrain the timing of pre ductile and ductile deformation in the foothills terrane of the central sierra nevada by using strain and other data it can be shown that rigid rotation of beds folding faulting predated the onset of ductile deformation and probably occurred between 160 and 151 ma ductile structures consisting of continuous and secondary cleavages and associated folds and lineations started forming ca 151 ma in the bear mountains fault zone and then ca 145 ma began moving away from the fault zone forming diachronously over an 30 m y period the last documented ductile structure formed ca 123 ma although some secondary structures may be younger metamorphism of these rocks is generally upper greenschist facies although higher grade belts one bearing staurolite andalusite and sillimanite are present strain was preferentially partitioned into one of these belts of higher metamorphic grade and sporadically elsewhere the structural history here is much more complex and at least one and locally two complete transpositions of the original cleavage have occurred in these zones of complex deformation it is in most cases possible only to identify a composite foliation consisting of new continuous cleavage and relicts of earlier phases all lying mutually parallel timing constraints indicate that the pre ductile structures may correspond to a very late stage of the nevadan orogeny that is 155 3 ma but the ductile structures postdate that orogeny as defined by as much as about 25 30 m y models which relate the ductile structures in the central foothills terrane to nevadan plate tectonic events are untenable in addition recent work indicates that late cretaceous ductile deformation in the central and southern sierra nevada may be relatively widespread indicating that tectonic models for the sierra nevada need to be reassessed

isotopic and structural responses of granite to successive deformation and metamorphism within the sybella granite west of mount isa in northern australia differential response of u pb and rb sr isotopic systems to deformation metamorphism enables ages of emplacement and three discrete deformation metamorphic events to be determined based on zircon u pb systems two of the plutons were emplaced at 1671 pm 8 ma and 1668 pm 26 21 ma and the third at 1610 pm 10 ma a separate microgranite body gives aberrantly old u pb ages of up to 1780 ma due to partial inheritance of older zircon the three discrete deformation metamorphic events d 1 d 2 and d 3 occurred at 1610 pm 13 ma 1544 pm 12 ma and 1510 pm 13 ma respectively based on whole rock rb sr isotopic systems the youngest body was emplaced syntectonically and has possible significance to the origin of the mount isa ag pb zn orebodies homogenization of rb and sr isotopes via extensive syntectonic fluid migration associated with deformation partitioning and resultant solution transfer appears to have been

grain size reduction and foliation development in a deformed granitoid batholith abstract the predominantly peraluminous wologorong batholith in eastern new south wales australia has undergone heterogeneous deformation it always has at least one gneissic foliation but in strongly deformed zones it has two foliations one of these is a gneissic foliation s 1 consisting of relatively discontinuous fine grained micaceous and feldspathic folia anastomosing between feldspar relics and elongate aggregates of recrystallized quartz the other foliation s 2 is more continuous than s 1 and the folia are fine grained and commonly laminated as in mylonites the two foliations could have formed siimultaneously or sequentially during a single deformation s 2 formed oblique up to 30 to s 1 in order to accommodate an imposed shear component of the strain in strongly deformed parts of the batholith s 2 folia appear to have initiated on suitably oriented parts of anastomosing s 1 folia continued deformation locally reduced the angle between s 1 and s 2 and resulted in the development of mylonite zones grain size reduction by recrystallization and or neocrystallization occurred in all minerals during the deformation but quartz appears to have attained a steady state grain size of around 0 15 mm which was not reduced during more intense deformation deformation mechanisms are difficult to determine but microfracturing associated with offsetting and microboudinage intragranular slip and solution transfer of material may have operated in the earlier stages of deformation and grain boundary sliding and or solution transfer of material may have dominated the later stages the material transfer may have been associated with chemical and mineralogical changes that accompanied neocrystallization

late holocene glacier fluctuations in bevringsdalen jostedalsbreen region western norway ca 3200 1400 bp lithostratigraphy and radiocarbon dates from a 1 3 m deep gully section in bevringsdalen sw of jostedalsbreen in western norway with alternating minerogenic glacial and peat non glacial layers demonstrate that glaciers upvalley from the site were present during the following intervals 2595 85 bp 840 700 cal bc to 2360 80 bp 525 385 cal bc between 2250 65 bp 395 225 cal bc and 2150 80 bp 360 105 cal bc between 1740 75 bp cal ad 205 385 and 1730 75 bp cal ad 210 395 and subsequent to 1430 45 bp cal ad 595 645 detailed altitudinal fluctuations of the glaciation threshold equilibrium line relative to the present have been reconstructed for the time interval between 1430 45 bp cal ad 595 645 and 3180 90 bp 1540 1395 cal bc

shape and microstructure of microgranitoid enclaves indicators of magma mingling and flow abstract at tarandore point 328 km south of sydney new south wales australia two tonalite phases are in contact with a gabbroic diorite all belonging to the moruya batholith lobate to crenulate contacts pillowing of the more mafic phase in the more felsic phase net veining of the more mafic phase by the more felsic local chilling of the more mafic phase against the more felsic and an abundance of rounded to elongate microgranitoid enclaves all suggest mingling of magmas at the site of emplacement therefore all phases were emplaced before the others solidified and an order of intrusion cannot be determined the variety of microgranitoid enclaves suggests that repeated magma mingling has occurred linear geochemical trends indicate either magma mixing or restite unmixing as a prime cause of variation in the members of the moruya suite of granitoids direct evidence of mixing is not present but evidence that the magmas were substantially liquid at the time of emplacement sugests that mixing is possible restite unmixing is unlikely to be the prime process because near minimum melts which would occur in all granitoid phases according to that model should mix easily rather than mingling in fact mingling has occurred between tonalite phases of very similar composition which would not be expected if the liquid parts of enclaves were minimum melts available experimental and theoretical data on mixing in both magma chambers and conduits cannot be applied directly to the occurrence at tarandore point owing to inadequately constrained parameters but mixing generally should be favoured by higher temperatures which is consistent with our inference that relatively high proportions of melt were present in the granitoid phases at the time of emplacement conduit mixing may be reflected in a local zone of strong to extreme elongation of enclaves in which the distortion has been accomplished by magmatic flow without solid state deformation as evidenced by strong dimensional preferred orientations coupled with a lack of microstructural evidence of intragranular plastic strain this suggests that elongate enclaves should not be used as indicators of solid state deformation or as tectonic strain markers without microstructural evidence that suitably strong intracrystalline plastic deformation has taken place

on curved laminae graded layers convection currents and dynamic crystal sorting in the ploumanac h brittany subalkaline granite curved layered objects in a subalkaline potassic intrusive granite are analyzed biotite laminae and cyclic reverse size and modal layers are encountered in an annular zone both cyclic and intermittent layers are observed in rhythmic arrangement truncation the bifurcation curvature of layers with ladle shape represents the action of magmatic currents as would convection cells or fluid dynamic fingers emphasis is put on the bagnold effect related to such currents which would explain the reverse size grading of layers this kind of size sorting hydrodynamic occurs in highly viscous granitic magma simple convection seems more likely than diffusive convection

emplacement of the zoned zaer pluton morocco the emplacement history of the zaer pluton was studied using structural data and field relationships the pluton is one of the hercynian granitoid bodies that crops out in the central paleozoic massif of morocco the principal granitoid rocks are relatively mafic at the margins of the pluton and change inward with or without discontinuities to a more felsic facies thus defining a concentrically zoned structure the emplacement of the pluton was by forceful intrusion of the magma the elements of granite tectonics observed in the enclosing metasedimentary rocks include deflection of regional trend around the pluton and abundant faulting with a predominantly radial pattern with respect to the granite contact the emplacement of the pluton is conceived as a polyphase diapiric process that in part obliterated the gradation from biotite granodiorite to two mica monzogranite the margins of the plutonic body solidified first and were subjected to deformation during diapiric rise and expansion resulting in a preferred orientation of mineral grains in the granitic rocks

equilibrium line altitudes and paleoenvironment in the merchants bay area baffin island n w t canada the fiordlands south of merchants bay contain an extensive well preserved moraine record of a late foxe advance of local valley glaciers this has allowed accurate reconstruction of former glacier margins and computation of former equilibrium line altitudes elas by a variety of methods statistical comparison of three methods maximum lateral moraine elevation median elevation and accumulation area ratio aar shows that different techniques can give different results for the same glaciers lateral moraines gave estimates that were too low probably due to post glacial erosion or to non deposition median elevations and the aar method produced statistically similar results but only for glaciers of simple geometry the median elevation method fails to take into account variations in valley morphology and glaciological parameters and so is not reliable in all situations the aar method is supported by empirical evidence and is the best of the three methods for estimating former elas analysis of trend surfaces of present and late foxe elas shows changes in elevation and orientation through time due to changing environmental factors present elas are strongly influenced by local factors southerly storm tracks and warm maritime conditions paleo elas do not show this influence suggesting that davis strait may have been ice covered during the late foxe stade and that storm tracks were from the north

glacier fluctuations during the past 2000 years abstract a global compilation of glacier advances and retreats for the past two millennia grouped by 17 regions excluding antarctica highlights the nature of glacier fluctuations during the late holocene the dataset includes 275 time series of glacier fluctuations based on historical tree ring lake sediment radiocarbon and terrestrial cosmogenic nuclide data the most detailed and reliable series for individual glaciers and regional compilations are compared with summer temperature and when available winter precipitation reconstructions the most important parameters for glacier mass balance in many cases major glacier advances correlate with multi decadal periods of decreased summer temperature in a few cases such as in arctic alaska and western canada some glacier advances occurred during relatively warm wet times the timing and scale of glacier fluctuations over the past two millennia varies greatly from region to region however the number of glacier advances shows a clear pattern for the high mid and low latitudes and hence points to common forcing factors acting at the global scale globally during the first millennium ce glaciers were smaller than between the advances in 13th to early 20th centuries ce the precise extent of glacier retreat in the first millennium is not well defined however the most conservative estimates indicate that during the 1st and 2nd centuries in some regions glaciers were smaller than at the end of 20th early 21st centuries other periods of glacier retreat are identified regionally during the 5th and 8th centuries in the european alps in the 3rd 6th and 9th centuries in norway during the 10th 13th centuries in southern alaska and in the 18th century in spitsbergen however no single period of common global glacier retreat of centennial duration except for the past century has yet been identified in contrast the view that the little ice age was a period of global glacier expansion beginning in the 13th century or earlier and reaching a maximum in 17th 19th centuries is supported by our data the pattern of glacier variations in the past two millennia corresponds with cooling in reconstructed temperature records at the continental and hemispheric scales the number of glacier advances also broadly matches periods showing high volcanic activity and low solar irradiance over the past two millennia although the resolution of most glacier chronologies is not enough for robust statistical correlations glacier retreat in the past 100 150 years corresponds to the anthropogenic global temperature increase many questions concerning the relative strength of forcing factors that drove glacier variations in the past 2 ka still remain

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

reconstructing glacier retreat since the little ice age in se tibet by glacier mapping and equilibrium line altitude calculation abstract temperate glaciers in the eastern nyainqentanglha range southeastern tibet are highly sensitive to climate change and therefore of particular high interest for research on late holocene changes of the monsoonal climate in high asia however because of the remoteness of the area the scarcity of empirical data and the challenges to remote sensing work posed by cloud and snow cover knowledge about the glacier dynamics and changes in this region is still very limited in this study we applied a remote sensing approach in which 1964 glaciers were mapped from a landsat etm scene and subsequently parameterized by dem supported measurements geomorphological evidence i e trimlines and latero frontal moraines were used to obtain quantitative data on the glaciers morphological characteristics and the changes since the little ice age lia maximum glacier advance statistical analysis of glacier length change revealed an average retreat of 27 and a trend toward stronger retreat for smaller glaciers an evaluation of different methods to calculate equilibrium line altitudes elas indicates that an optimized toe to ridge altitude method tram is more suitable than other methods in settings with complex topography and a lack of mass balance measurements a large number of glacier measurements are crucial for high quality of tram results and special attention has to be paid to different glacier characteristics in order to determine the best fitting tram ratio value and to test the quality of the calculated elas a remote sensing approach was applied for each investigated glacier the altitudes of transient snowlines visible in the late summer landsat scene were measured from the dem and compared to tram results the interpolated ela results show a se nw gradient ranging from 4400 to 5600 m asl and an average ela rise of 136 m since the lia because of the high spatial resolution of measurements the ela distribution reveals topographic effects down to the catchment scale specifically orographic rainfall and leeward shielding the interpretation of these patterns reveals that the eastern nyainqentanglha range is influenced by both the indian ism and east asian summer monsoon easm however the easm does not reach the western part of the study area the results indicate that the monsoonal temperate glaciers high sensitivity to climate change is driven by two double forcings owing to the coincidence of accumulation and ablation phases

anisotropy of magnetic susceptibility and magmatic structures in the guerande granite massif france a multidisciplinary approach has been used in order to map out the syntectonic magmatic structures of the guerande leucogranite in southern brittany western france on one hand extensive field work and microscopic observations and on the other a detailed magnetofabric investigation have been carried out the former showed a magmatic flow plane trending generally to the ene wsw with a moderate dip to the north and a flow direction slightly dipping toward nne these observations suggest a blade shaped body which is not deeply rooted the magnetofabric as defined by the anisotropy of magnetic susceptibility is mainly related to hematite ilmenite grains with a mean rock susceptibility of about 3 10 6 g oe there is an excellent agreement between the magnetic lineation kmax and the magmatic flow direction the agreement between the magnetic foliation kmax kint plane and the magmatic flow plane is not as good the quantitative analyses of the anisotropy allows one to group the data into two domains the one with planolinear ellipsoids corresponding to the central part of the granitic body where flow was mainly achieved on the viscous state and the other in the flattening domain related to the northern border area which exhibits incipient orthogneissification that is some deformation on the solid state such a favorable comparison with the classical structural method is encouraging for using the anisotropy of magnetic susceptibility technique more routinely for structural mapping of granitic bodies provided that the microstructural state of the rock is already well known

oligocene initiation of the south tibetan detachment system constraints from syn tectonic leucogranites in the kampa dome northern himalaya abstract himalayan leucogranites provide a robust record of the thermal and tectonic processes that occurred during convergence of the eurasian and indian tectonic plates we present structural petrological mineralogical whole rock geochemical sr nd isotope and geochronological results for cenozoic leucogranites from the kampa dome northern himalaya the kampa leucogranites are typical syn tectonic granites and occur as a series of sills dikes and puddings in the kampa shear zone which is considered to be the exhumed portion of the south tibetan detachment system stds in the northern himalaya the kampa syn tectonic leucogranites provide information about the timing and nature of regional kinematics and record thermal conditions and the initiation of the stds whole rock geochemistry and sr nd isotope analyses show that the kampa leucogranites are characterized by the following 1 they are peraluminous and have high sio2 al2o3 and a cnk low tio2 mgo p2o5 and tfe2o3 and variable cao na2o k2o and total alkalis 2 they are enriched in large ion lithophile elements e g k and rb and depleted in high field strength elements e g zr and ti with negative eu anomalies and 3 they display variable initial 87sr 86sr compositions 0 7507580 826065 and their end i values range between 7 6 and 12 2 anatexis of graywackes and metapelites in the great himalayan crystalline series played an important role in the formation of the kampa leucogranites anatexis was controlled by fluid absent partial melting of muscovite mineralogical and petrological analyses show that zircons belong to an early crystallization phase whereas monazites are remnants of the final crystallization phase of the granitic melt zircon u pb dating reveals that anatexis in the deep himalayan crust occurred at ca 32 23 ma during the oligocene monazites yield homogeneous 208pb 232th ages of ca 23 5 ma and record rapid emplacement in the kampa shear zone these results indicate that movement on the stds was initiated during the early oligocene and became well developed during the late oligocene in the kampa region the oligocene was a unique period of counterbalance between continued plate convergence and intense extension in the himalayan orogen

field chemical and physical constraints on mafic felsic magma interaction in the lamarck granodiorite sierra nevada california evidence of magma interactions resulting in both hybridization and mingling are preserved in a diverse suite of gabbroic to intermediate rocks associated with the compositionally zoned hornblende biotite lamarck granodiorite of the eastern sierra nevada california ellipsoidal mafic enclaves were formed by quenching of small amounts of high alumina basaltic magma upon injection into and dispersal through granodiorite magma early in its crystallization synplutonic intrusions of hornblende gabbro through hybridized mafic granodiorite represent injection of mafic magma at a later stage of crystallization of the granodiorite as they crosscut regional trends in foliation and compositional zoning in the host pluton where compositional contrasts between intrusion and host granodiorite are large contacts are sharp and abundant enclaves derived from the mafic intrusion are present in the granodiorite where the host is relatively mafic or where the local scale proportion of mafic magma is large contacts are zones of extensive hybridization that contain both enclaves and hybrid schlieren uncontaminated mafic intrusions have high alumina basaltic compositions whereas hybridized intrusions have silica contents as high as 63 5 mafic intrusions locally contain coarse grained cumulus gabbro inclusions mafic schlieren in granodiorite far from mafic intrusions represent localized accumulations of hornblende fe ti oxides and biotite from the granodiorite intrusion of late mafic dikes mobilized and entrained granitic residue from the granodiorite and formed composite dikes of aplite and pillowed diorite whether interacting magmas mix or mingle is a function of the heat contents and mass fractions of the end members calculations that account for compositions heats of fusion heat capacities of liquids and crystals and a range of initial temperatures crystallinities crystal sizes and magma water contents indicate that in most circumstances the basalt end member quenches the resulting large viscosity contrast between the end members prevents hybridization homogenization is likely only if the compositional difference between host and injected mafic magma is less than 10 sio2 or if the mass fraction of mafic magma is greater than 0 5 resulting mixtures have the composition of tonalite or mafic granodiorite thus the more silicic rocks of the granodiorite pluton must represent differentiation products rather than direct hybrids of mafic or intermediate magma and felsic magma

paleoclimatic implications based on equilibrium line altitude depressions of reconstructed younger dryas and holocene cirque glaciers in inner nordfjord western norway abstract relative to a present cirque glacier in innner nordfjord western norway equilibrium line altitude ela depressions for reconstructed cirque glaciers formed during the younger dryas 11 000 10 000 yr b p the erdalen event 9100 200 yr b p and the little ice age mid 18th century are calculated by the use of accumulation area ratio aar and compared to the corresponding values for plateau glaciers the temperature precipitation ela tp ela as reflected by plateau glaciers gives considerably larger ela depressions than use of the temperature precipitation wind ela tpw ela for cirque glaciers ela depressions during the younger dryas erdalen event and the little ice age thus strongly indicate that cirque glaciers are much more sensitive to changes in winter precipitation than plateau glaciers the difference in ela depressions of contemporaneous plateau and cirque glaciers during the younger dryas erdalen event and the little ice age suggests that winter precipitation was reduced to 59 7 71 6 and 88 7 compared to present values taken into account the reduced winter precipitation the corresponding mean ablation season temperature depressions were probably 4 3 0 3 3 0 0 2 0 3 and 1 4 0 3 0 2 c respectively

the use of hypsometry to indicate long term stability and response of valley glaciers to changes in mass transfer a simple equation is derived relating the net mass balance and hypsometric curves of a steady state valley glacier it is used to examine how valley shape is linked to disparate extents and responses of glaciers subjected to similar climatic conditions examples are given which show that area based indices e g aar for estimating the equilibrium line altitude ela may be subject to a substantial built in variance because they implicitly rely upon similarity of glacier shape and regimen over a region if accurate topographic maps are available the equation may be used to infer the regimen of modern glaciers in the form of a dimensionless ratio of net mass balance gradients alternatively if similar information is available concerning regional glacier regimen disparate extents and responses may be collectively utilized to estimate values of ela or to infer climatic influence taking glacier hypsometry into account

determining paleo flow directions from groundmass fabrics in the lyttelton radial dykes new zealand abstract the poles to 010 of groundmass feldspar in radial dykes cutting the dissected miocene volcano lyttelton banks peninsula form generally oblique girdles about the paleo flow direction the obliquity is a response to velocity gradients of magma within the dykes and the sense of obliquity relative to each dyke wall provides a unique determination of the sense of flow the fabrics give support to the model of blanchard et al 1979 for the movement of rigid particles in flowing magmas this method of flow determination overcomes the problem inherent in most others which provide a flow line but no sense of movement along that line methods of sampling and examples of the feldspar fabrics are described together with the relationship of these fabrics to other dyke features such as secondary shears and stretched vesicles

a method for the determination of the initial shapes of deformed xenoliths in granitoids abstract measuring strain from deformed xenoliths is problematic due mainly to the large initial shape variations of these markers a method is described which allows mean initial shape to be determined for a number of xenolith populations by displaying their logarithmic ranges log rfmax log rfmax on a range diagram the diagram contains a check on validity and allows bad samples to be recognised xenolith data from a deformed granite in northwest ireland is analysed using the method

timing equilibrium line altitudes and climatic implications of two early holocene glacier readvances during the erdalen event at jostedalsbreen western norway following the younger dryas the e rst evidence of glacial activity in southern norway in response to climatic change occurred during the early holocene when terminal moraines from the erdalen event formed beyond the position of later little ice age moraines in front of present outlet glaciers on both sides of the jostedalsbreen ice cap sets of pre little ice age marginal moraines have been morphostratigraphicallycorre lated with the erdalen event the lithostratigraphyin a peat bog at hellemyrane in jostedalen western norway provides e rm evidence for a two phase erdalen event associated with two glacier readvances of nigardsbreen at the preboreal boreal transition radiocarbon dates from the peat bog give age estimates for the two phases the e rst erdalen event readvance took place between 10 100 and 10 050 cal bp while the second occurred close to 9700 cal bp the lowering of the equilibrium linealtitude ela during these readvances is estimated using the little ice age ratio lr approach to be about 230 m and 215 m respectively the e rst readvance is attributed to an increase in winter precipitation while the second readvance may have been primarily caused by a marked drop in summer temperature which reactivated already existing ice masses

cannibal creek granite post tectonic ballooning pluton or pre tectonic piercement diapir the cannibal creek granite in northern queensland australia previously has been interpreted to be a post tectonic pluton which underwent solid state deformation during in situ ballooning a reinterpretation of structures in and around the pluton indicates that this pluton is more appropriately viewed as a pierce ment diapir emplaced by magmatic flow significant deformation took place after pluton emplacement in fact the cannibal creek granite has some characteristics similar to pre tectonic granites examined elsewhere therefore it is somewhat misleading to view the granite as a post tectonic pluton

little ice age variations of outlet glaciers from the jostedalsbreen ice cap southern norway a regional lichenometric dating study of ice marginal moraine sequences and their climatic significance complex moraine ridge sequences in front of seven outlet glaciers of the jostedalsbreen ice cap austerdalsbreen bergsetbreen fabergstolsbreen lodalsbreen stegaholbreen tuftebreen bodalsbreen are dated using families of lichenometric dating curves established previously at an eighth outlet nigardsbreen applicability of the nigardsbreen curves at the regional level is tested using independent historical evidence moraines deposited during the present century are dated to an accuracy of 9 4 yr 16 0 and most of them are dated to an accuracy of 5 5 yr 9 4 results from the moraine sequences are combined to form a composite jostedalsbreen record median predicted dates for moraine ridges cluster around ad 1939 2 yr 1929 3 1908 3 1886 5 1875 2 1867 4 1855 3 1842 5 1822 5 1807 4 and 1785 5 at least four glaciers reached their little ice age maxima prior to ad 1780 two nigardsbreen and bodalsbreen at ca 1750 one fabergstolsbreen at ca 1705 stegaholbreen attained its maximum ca 1863 since the little ice age maximum and despite large differences in glacier size frontal variations of the various outlets have exhibited a high degree of synchroneity which suggests that the moraine sequences contain a sensitive record of high frequency climatic variations over the last ca 250 yr during the early twentieth century measured readvances of the order of 5 150 m over 1 10 yr led to moraine formation dendroclimatic evidence indicates that since the late eighteenth century moraine ridges formed about 5 yr after summer temperature minima and correlate with runs of cool summers temperature depression of 0 5 1 0 c below the ad 1700 1950 average almost simultaneous glacier advances appear to have been caused by reduced ablation this near immediate response to climatic variation by glacier tongues that descend to relative low altitudes is superimposed upon the longer term dynamic response of the ice cap to climate

convection and crystallization in the criffell dalbeattie pluton it is argued that the asymmetric dalbeattie granodiorite granite pluton developed as a result of convectional circulation in the magma chamber during the consolidation of the outer xenolith bearing granodiorite shell the shell was deformed by the intrusion of aplite veins the development of a penetrative foliation and the emplacement of dykes with chilled margins due to the intermittent uprise of the magma body which eventually consolidated as granite a porphyrite porphyry series of dykes provides information concerning the degree of crystallization of the magmas that existed in the pluton d the final stages of its emplacement and consolidation oscillatory zoning in plagioclases can be explained by constitutional supercooling or by changes occurring during convection the effects of crystal fractionation and diffusion within the pluton are discussed

topographic control of equilibrium line altitude depression on reconstructed little ice age glaciers grovabreen western norway little ice age marginal moraines in the grovabreen area inner sunnfjord are mapped and described the modem and little ice age mid eighteenth century equilibrium line altitude ela of the plateau glacier grovabreen is calculated by the use of an accumulation area ratio aar of 0 6 giving a little ice age ela depression of 125 m aar ela depression of the little ice age glaciers is also calculated for northern and southern outlet glaciers different estimates are considered to be the result of topographic differences other methods such as the mean elevation of glaciers meg and the toe to headwall altitude ratio thar gave ela depressions of 260 m and 315 m respectively these differences due to topographic conditions indicate that only glaciers with a uniform slope should be used to calculate the regional ela of former glaciers

metamorphic plumbing system in proterozoic calc silicates queensland australia a calc silicate rich terrain in northwest queensland exhibits spectacular examples of heterogeneous fluid rock interaction attending regional amphibolite facies metamorphism and deformation large areas of pristine calc silicate rocks show evidence for internal buffering of fluid composition and low fluid rock ratios f r as inferred from 18 o and 13 c signatures typical of metamorphosed marine carbonates the progress of calc silicate reactions and scapolite compositional variations between layers in contrast high variance assemblages are developed in pretectonic intrusive rocks as well as in metasomatic zones in calc silicates around their margins scapolitized metadolerites albitized calc silicates and large calcite pods and veins with 18 o and 13 c depleted values are typical of these regions and indicate localized throughput of predominantly externally derived fluid at high f r accompanying the metamorphic peak major competency contrasts between meta intrusive and calc silicate rock types influenced stress and strain patterns around the igneous bodies which in turn controlled fracture permeability and the focusing of the metamorphic fluid the relatively brittle behavior of the meta intrusive rocks favored the development of small scale fracture permeability and consequent pervasive alteration of these bodies calcite vein systems and intensely albitized calc silicate breccias are localized in shear zones and dilatant areas around the meta intrusions either where shear stresses were high or where all stresses were low resulting in shear and tensile failure respectively thus permeability enhancement and the development of major fluid pathways during regional metamorphism of the terrain are systematically related to variations in the stress field accompanying deformation similar factors may strongly influence the channeling of fluids during metamorphism of other terrains

pseudotachylyte and the development of ultramylonite bands in the saint barthelemy massif french pyrenees abstract in mylonitic gneisses of the saint barthelemy massif in the french pyrenees evidence was found that ultramylonite bands developed by ductile deformation of pseudotachylyte in the gneiss a mylonitic shape fabric was produced by a continuous structural event during retrogression from amphibolite to upper greenschist facies decrease in temperature caused gradual hardening in the gneiss which led to the development of pseudotachylyte bands by intermittent seismic slip these acted as weak zones in which ductile deformation was concentrated a microstructure typical of ultramylonite was produced in these deformed pseudotachylyte bands

high temperature crustal scale shear zone at the western margin of the eastern ghats granulite belt india implications for rapid exhumation abstract a mylonitic shear zone occurs along the western margin of the eastern ghats granulite belt india in the northern sector it separates metapelitic and mafic granulites from the granite gneisses of the bastar craton while in the southern sector it separates charnockitic gneisses and mafic granulites from the granite gneisses of the bastar craton this boundary shear zone is characterized by a mylonitic foliation and a stretching lineation microstructures characterize high grade conditions and quartz c axis patterns show strong point maxima close to the long axes of the strain ellipsoids indicating dominant prism c slip in quartz commonly interpreted in terms of ductile deformation at high temperatures quartz c axis patterns in the recrystallized and unrecrystallized domains also imply grain boundary migration as the principal mechanism of dynamic recrystallization at high temperature conditions a rapid exhumation during shearing in this marginal part of the convergent eastern ghats orogen is indicated by decompression reaction textures and retrograde hydration reactions presumably due to hydrous fluid ingress in the shear zone rocks

holocene glacier variations of blaisen hardangerjokulen central southern norway abstract a 1 m deep gully section 460 m beyond the maximum little ice age marginal moraines of blaisen hardangerjokulen central southern norway revealed alternations of minerogenic and organic sediments the geographical geological settings of the dated section provides a unique on off signal of holocene glacier fluctuations of blaisen lithostratigraphy sediment characteristics and radiocarbon dates from the study section indicate one period of glacier re advance between the late preboreal deglaciation of the inland ice sheet and 8660 100 yr b p a grey sand layer 56 57 cm below the surface is interpreted to be of fluvial colluvial origin and is radiocarbon dated to about 7700 yr b p at 48 cm below the surface a bluish grey sand silt layer is radiocarbon dated to 7590 12 yr b p 6560 6240 b c and interpreted to be glaciofluvial origin a minor glacier oscillation postdates 1130 70 yr b p 810 990 a d the medieval little ice age glacier advance of blaisen beyond its modern extent occurred after 1040 60 yr b p 960 1030 a d calculations of the modern and little ice age equilibrium line altitudes elas on hardangerjokulen suggest an ela depression of ca 130 m during the little ice age maximum