co 2 degassing in the hartousov mofette area western eger rift imaged by co 2 mapping and geoelectrical and gravity surveys strong subcontinental mantle dominated co2 degassing occurs in the hartousov and bublak mofette fields in the western eger rift the combination of co2 gas flux and soil gas measurements as well as gravity and geoelectric surveys provides insight into the surface and subsurface of this unique mofette area co2 soil gas and gas flux measurements reveal that large amounts of carbon dioxide are released via channels with diameters below 1 m carbon dioxide emissions of several tens and up to more than 100 kg day 1 are ejected via these small seeps measurements with small spacings are necessary to account for the point like focused gas discharge in the lesser degassing surrounding we estimate that between 23 and 97 tons of co2 are released over an area of about 350 000 m2 each day in the hartousov mofette field the application of widely used geostatistical tools leads to estimations of the co2 discharge with very high standard deviations due to the strong positive skewness of the data distribution geophysical investigations via electrical resistivity tomography and gravity measurements were carried out over areas of strong seepage and reveal distinct anomalies in the subsurface below mofettes indicating rock and sediment alterations and or sediment transport by pressurised ascending co2 and water mobilised by it this study reveals that the gas emanations only occur west of a morphological step which is related to a n s oriented fault zone the pocatky plesna fault zone the results of co2 mapping and the geophysical studies can track the course of this fault zone in this area our results fit into a tectonic model in which the mofette fields are in the centres of two independent pull apart basin like structures we hypothesise that the sinistral strike slip movement of the pocatky plesna fault zone leads to a pull apart basin like opening at which the strong mantle derived co2 degassing occurs nowadays since the hartousov and bublak mofette fields only illustrate examples along the n s striking pocatky plesna fault zone its role and other n s striking faults roles of the regensburg leipzig rostock zone for upper mantle degassing might have been underestimated previously

on spatial and temporal separation of geomagnetic anomalies at the southern tip of the indian peninsula abstract in this communication the applicability of differential geomagnetic deep sounding at the southern tip of the indian peninsula has been investigated by analysing the nature of anomalies at annamalainagar ann and trivandrum trd hyderabad hyb has been chosen as a reference station for this purpose the results indicate that despite a strong current channelling in this region the anomalies do not permit separation into the spatial and temporal components which is possible in other areas with strong current channelling like the pyrenees and the rhine graben this non relationship between h a and z a at ann and trd has been attributed to contributions from both coast effect local induction and channelling regional effect being simultaneously present in the area during the day the geometry of the source field produces further differences

discovery of the first quaternary maar in the bohemian massif central europe based on combined geophysical and geological surveys abstract based on results of previous investigations of tephra tuff volcaniclastic deposits and a geophysical survey in the surroundings of the elezna h rka quaternary volcano west bohemia we performed detailed geophysical surveys using gravimetry magnetometry and electrical conductivity techniques striking anomalies were revealed in a morphological depression near m tina west bohemia as a strong evidence of the assumed maar diatreme structure the sharp isometric gravity low of 2 30 mgal as well as the corresponding positive magnetic anomaly of 200 nt with a negative rim on its northern side indicate a steeply dipping geological body of low density and containing magnetic rocks minerals magnetic survey also showed pronounced local anomalies outside the depression that can reflect relicts of the tephra rim of the maar this geophysical evidence was then proven by an exploratory drilling near the centre of the gravity anomaly macroscopic on site evaluation of the core and more detailed sedimentological petrochemical palynological and microbiological laboratory analyses further confirmed the existence of a maar structure filled by 84 m of lake sediments reflecting a succession of several warm and cold climatic periods results of palynological analyses confirm the presence of a continuous palaeoclimate archive with at least three successive warmer periods of most probably interstadial character from the upper quaternary saalian complex therefore the recovered sediment sequence holds strong potential for in depth paleoclimate reconstruction and deep biosphere studies at the bottom of the m tina 1 my 1 borehole 84 85 5 m country rock debris was found containing also volcanic bombs and lapilli the discovered volcanic structure is considered to be the first known quaternary maar diatreme volcano on the territory of the bohemian massif because of hidden active magmatic processes in combination with earthquake swarm seismicity ca 20 30 km north of the m tina maar reconstruction of the palaeovolcanological evolution is important for evaluation of hazard potential of the ne and e part of the cheb basin

monitoring of helium and carbon isotopes in the western eger rift area czech republic relationships with the 2014 seismic activity and indications for recent 2000 2016 magmatic unrest abstract we report new data of the regional distribution pattern of total gas compositions as well as he and co2 isotopic compositions from 25 gas exhalations in the western eger rift and its surroundings additionally the first time series data from gas exhalations in a clay pit within the cheb basin cb are given at 21 degassing locations the first data were obtained 20 years ago from 7 locations within the degassing center cb and from 3 degassing sites belonging to the marianske lazn ml degassing center neon and argon isotope compositions were determined also co2 is the major component at all degassing sites the 13c values display a small range 1 7 to 5 1 and the 3he 4he ratios vary from 1 9 to 5 9 ra the highest 3he 4he ratios are found at locations along the pocatky plesna fault zone followed by the degassing site in the clay pit on the nova ves fault and the locations on the ml fault at the edge of the cb although gas flow and co2 concentrations in all degassing centers are very high the fractions of mantle derived helium are different with presently up to 94 in relation to the sclm 3he 4he of 6 32 ra in the cb up to 73 in the ml and up to 35 in the karlovy vary degassing center at the locations in the eastern part of the cb a clear progressive increase of the 3he 4he ratio has been observed since the first sampling campaigns there in 1993 and 1994 whereas at the other degassing sites the helium isotope ratio remained essentially the same the progressive increase of the 3he 4he ratio in the eastern part of the cb together with further short time increases up to 6 3 ra at one location bublak before both the 2000 and 2008 earthquake swarms indicate an ongoing magmatic process beneath this area which seems to be associated with the occurrence of seismicity the cb is located close to the nov kostel focal zone where since the beginning of our investigations four strong periods of seismicity with magnitudes 3 occurred the latest gas data confirm our earlier findings time series studies showed that in relation with seismic events decreased 3he 4he ratios were repeatedly observed due to admixed seismically released crustal helium presently the eastern part of the cb is the most active non volcanic region in the european cenozoic rift system with gas signatures similar to those found in free mantle derived gases from the east african rift system

experimental folding and fabric development in multilayered ice abstract deformation of multilayered crystalline ice in plane strain at 1 c and under a constant load has produced folds varying strain distributions and a variety of microfabrics three different specimen configurations were used to produce the folds 1 1 layers of polycrystalline ice separated by thin plastic films and unconstrained in the extension direction these formed large symmetric sinusoidal folds where layer parallel shear contributed to the fold shape 2 2 bonded plastic coated layers of polycrystalline ice constrained in the extension direction these developed symmetric disharmonie folds of one wavelength layer boundaries remained attached except in fold hinges and there was no evidence for layer boundary slip 3 3 multilayered fibrous ice unconstrained in the extension direction these produced gentle half wavelength buckles finite strain distributions were different in each experiment and varied between layers of different grain size the greatest strains were observed in the fine grained layers principal elongations fan about the axial surface of folds where layers have undergone buckling late in their deformation history under co axial deformation conditions the axes of the strain ellipses parallel the axes of bulk strain except in the constrained regions progressive deformation involving intracrystalline slip recrystallization and recovery processes serve to continuously modify the crystallographic fabric variation in the patterns of c axis preferred orientation correlate with strain variations and differences in deformation path the presence of a strong initial c axis orientation and grain shape distribution can also govern the strength of the final pattern of preferred orientation

paragenetic trends of oxide minerals in carbonate rich kimberlites with new analyses from the benfontein sill south africa the relationship among kimberlites carbonate rich bodies associated with them and the carbonatites associated with alkalis rock complexes are reviewed particular attention is paid to the parageneses of oxide minerals in six carbonate kimberlites peuyuk tunraq wesselton liqhobong de beers and benfontein new analyses of spinel limonite and perovskite from the lower benfontein sill are consistent with previous reports and can be divided into 1 early macrocrysts and cores of grains and 2 late rims and groundmass grains the evolution of a carbonate rich residuum with progressive crystallization appears to be typical of carbonate rich kimberlite magmas and is texturally related to the two stages of oxide precipitation in these carbonate kimberlites thus early mg ilmenite and cr rich spinel are separated by reaction textures and carbonate from later mg al titanomagnetite perovskite and accessory utile and apatite the spinels span a large range in composition from mg al chromite to mg al titanomagnetite with an intermediate gap this simplified paragenetic scheme and in particular the spinel trend is repeated in the five other carbonate kimberlites reviewed it may be representative of the hypabyssal kimberlites in general and others where fluidization processes did not completely disrupt the crystallization sequence

induction models of southern india and the effect of off shore geology abstract simple numerical tests based on thin sheet modelling are used to define the conductors most probably responsible for current channelling in the region including southern india a combination of crustal conductors located in the indo ceylon graben and underneath the comorin ridge best reproduces the observations at periods of 50 100 min in so far as channelling is concerned daytime variations do not help to define the location of conductors any better than night time data and may thus be ignored

curie temperatures of synthetic titanomagnetites in the fe ti o system effects of composition crystal chemistry and thermomagnetic methods 1 the present study is aimed at improving the calibration of the compositional dependence of the curie temperature tc of titanomagnetite tmt on the basis of temperature dependent magnetic susceptibility c t curves measured on synthetic tmts in the fe ti o system in order to assess the possible influence of high temperature cation vacancies onto the tc values we have synthesized two types of assemblages in subsolidus conditions at 1 bar 1100c and 1300c under controlled oxygen fugacity conditions tmts synthesized in equilibrium with ilmenite hematitess ilmss are expected to have the highest vacancy concentrations those in equilibrium with wustite wus the lowest the composition and homogeneity of the synthetic tmts were carefully checked with a scanning electron microscope sem and an electron microprobe emp tc was determined from c t curves using a kappabridge and for comparison from ms t curves measured with a variable field translation balance our data set shows systematically higher tc values for tmt coexisting with ilmss than for tmt coexisting with wus most c t curves are nonreversible whereby the largest dtc 40 k concern tmt ilmss o f intermediate compositions synthesized at 1300c nonreversibility is interpreted as reflecting cation reordering in tmt during the high temperature c t measurements tc values obtained from ms t curves are higher than those obtained from the c t curves whereby the difference regularly increases up to 40 k with increasing ti content up to xusp 0 6 our new calibration curves are suitable to retrieve tmt compositions in basalts that were rapidly cooled and not oxidized by deuteric or hydrothermal fluids citation lattard d r engelmann a kontny and u sauerzapf 2006 curie temperatures of synthetic titanomagnetites in the fe ti o system effects of composition crystal chemistry and thermomagnetic methods j geophys res 111 b12s28

crystal growth in cataclasites diagnostic microstructures and implications abstract microstructures in cataclasites from low and high angle fault zones in granitic basement rocks of the scandinavian caledonides indicate the operation of several processes intensive formation of microcracks filled with fine grained mineral fragments indicates brittle deformation the formation of quartz crystals with euhedral terminations suggests crystal growth occurrence of undulose extinction deformation lamellae and grain boundary recrystallization in other quartz grains illustrates plastic deformation crystal growth causes micro cracks to heal and thereby changes the behaviour of rocks undergoing brittle deformation the crystallization products vary in size from c 10 m to c 5 mm narrow banding parallel to rhomb and prism planes is indicative of crystal growth the growth bands show slightly different crystallographic misorientation in some cases the boundaries of these bands could be identified as dislocation arrays decorated by bubbles the occurrence of fibrous chalcedony aggregates and transitions from extremely fine grained quartz to large grains with euhedral terminations suggests the presence of colloidal silica bearing fluids during growth the crystallization process leads to the formation of vein like structures after crystallization plastic deformation may take place followed by brittle deformation and new crystal growth it is concluded that during the formation of the cataclasites a cyclic operation of brittle failure crystal growth followed by plastic deformation took place and this cycle was repeated several times

seismically triggered anomalies in the isotope signatures of mantle derived gases detected at degassing sites along two neighboring faults in nw bohemia central europe the vogtland and nw bohemia region is known for its earthquake swarms the most intensive swarm since 1985 86 occurred in october 2008 to find further indications for the interaction of ascending mantle derived fluids and the occurrence of earthquake swarms detailed fortnightly studies of gas compositions co2 n2 ar he h2 and ch4 and isotope ratios 13c 15n and 3he 4he were carried out between october 2008 and april 2011 at four locations close to the nov kostel focal zone and at the wettinquelle spring bad brambach from the start of the 2008 earthquake swarm seismically induced isotope geochemical anomalies were recorded at locations along the pocatky plesna fault zone ppz and were for the first time also found at degassing locations on the marianske lazn fault zone mlf variations were observed in both the temporal and spatial distributions of the anomalies as well in anomaly strengths probably due to the positions of these fault zones relative to the focal zone and to differences in fluid migration pathways prior to both the 2000 and 2008 swarms 3he 4he ratios 6 ra were recorded at the bublak mofette these anomalous pre seismic 3he 4he ratios suggest that both the 2000 and 2008 swarms may have been associated with the supply of fresh magma from a less degassed reservoir in the lithospheric mantle the temporal 13cco2 pattern from detailed studies at bublak between 2005 and 2011 indicates progressive magma degassing as well as seismically induced variations in the 13c providing additional support to the interpretation derived from the 3he 4he ratios

modification of garnet by fluid infiltration during regional metamorphism in garnet through sillimanite zone rocks dutchess county new york metapelitic rocks from a progressive metamorphic sequence in dutchess county new york record evidence for reaction between garnet and fluids associated with quartz plagioclase veins and for net transfer among garnet interiors mineral inclusions and fluid garnet fluid reaction resulted in modification of preexisting garnet textures compositions and growth zoning patterns the textural and compositional record of garnet fluid interaction varies with grade and with proximity of garnet to quartz veins garnet zone rocks do not contain evidence for extensive reaction with vein forming fluids in upper stauroliteand kyanite zone rocks garnet that is crosscut by quartz veins contains a fluid inclusion filled region near the garnet vein interface this region truncates growth zoning patterns and quartz inclusions fluid inclusions in garnet decrease in abundance away from quartz veins in some rocks lacking quartz veins fluid inclusions are concentrated in garnet interiors and in particular near fractures and are notably lacking around mineral inclusions in garnet inferences from textural and compositional features combined with thermobarometric results indicate that preexisting garnet grains were modified at t 525 550 c and 4 kbar by one or more reactions involving fluids the fluid pathways included foliationparallel channels in the rock as well as microcracks in mineral grains

the influence of deformation on the formation of axial planar leucosomes and the segregation of small melt bodies within the migmatitic napperby gneiss central australia in the napperby gneiss central australia a distinctive group of elongate leucosomes occurs along the axial planes of mesoscopic crenulations that have harmonic two dimensional kink band like geometries the leucosomes truncate a fabric defined by biotite quartz k feldspar plagioclase sillimanite and are chiefly composed of k feldspar and quartz with or without plagioclase they are characterized by accessory garnet or aggregates of intergrown ilmenite and magnetite produced during the melting reactions bi plag q sill g ksp melt and bi plag q ru ilm mt ksp melt the absence of garnet and intergrown ilmenitemagnetite aggregates in the gneiss surrounding the crenulation zones indicates that these melting reactions preferentially occurred in the deformation zones in spite of a homogeneous distribution of reactant phases in the gneiss this means that strain partitioning and partial melting are coupled processes in which the garnet and ilmenite magnetite producing melt reactions initially occurred in high strain zones where the melting reaction activation energy was first overstepped this was a consequence of an additional strain induced matrix free energy component on top of the temperature effect once reaction product nucleation had occurred the deformation zones became the sites for continued melting which was energetically favoured over nucleating garnet and ilmenite magnetite elsewhere the melt reactions producing garnet and ilmenite magnetite resulted in the formation of grain supported leucosomes with a higher melt component than the surrounding gneiss and the leucosomes were therefore relatively incompetent in a differential stress field diffusional processes will cause elongation of the leucosome in a plane normal to 1 parallel to the axial planes of folds if sufficient melting has occurred an interconnected leucosome network will result creating a potentially important buoyancy driven melt drainage system in the napperby gneiss interconnected leucosome bearing crenulation zones are mostly vertical which is an ideal orientation for buoyancy driven diffusive melt migration however melt segregations remained small due to a melt impermeable lithological boundary overlying the gneiss

integrated geophysical and geological methods to investigate the inner and outer structures of the quaternary mýtina maar w bohemia czech republic the m tina maar is the first known quaternary maar in the bohemian massif based on the results of mrlina et al j volcanol geother res 182 97 112 2009 a multiparametric geophysical electrical resistivity tomography gravimetry magnetometry seismics and geological petrochemical research study had been carried out the interpretation of the data has provided new information about the inner structure of the volcanic complex 1 specification of the depth of post volcanic sedimentary fill up to 100 m and 2 magnetic and resistivity signs of one or two hidden volcanic structures interpreted as intrusions or remains of a scoria cone the findings at the outer structure of the maar incorporate the 1 evidence of circular fracture zones outside the maar 2 detection and distribution of volcanic ejecta and tephra fall deposits at the surface and 3 indications from electrical resistivity tomography and gravity data in the area between the m tina maar and elezna h rka scoria cone interpreted as a palaeovalley filled by volcaniclastic rocks and aligned along the strike line nw se of the tachov fault zone these findings are valuable contributions to extend the knowledge about structure of maar volcanoes in general because of ongoing active magmatic processes in the north east part of the cheb basin ca 15 30 km north of the investigation area the m tina maar diatreme volcano and surroundings is a suitable key area for research directed to reconstruction of the palaeovolcanic evolution and assessment of possible future hazard potential in the bohemian massif

electron probe microanalysis study on processes of low temperature oxidation of titanomagnetite abstract partially oxidized titanomagnetite grains in various kinds of volcanic rocks were investigated by electron probe microanalyzer epma in order to clarify the process of oxidation at low temperature the following results were obtained by the present investigation 1 primary composition of titanomagnetite is homogeneous in individual grains although variation in composition among different grains is observed on each thin section 2 migration of fe cations during low temperature oxidation is clearly seen in all oxidized grains some other constituent cations are also bleached and consequently the relative content of the remaining cations becomes large 3 the detailed internal structures of titanomagnetite grains are observed as backscattered electron images bei with an electronprobe microanalyzer and it seems likely that the structures depend upon the degree of low temperature oxidation 4 the chemical and physical properties of oxidized titanomagnetites imply that low temperature oxidation is not a simple process but a complex one such an oxidation process is correlatable to both the mobility of cation and the oxidation condition such as a circulation of some active hydrothermal materials at low temperature

the origin of kinks in polycrystalline ice abstract in situ observations of events leading to development of kink hands kbs and kink band boundaries kbbs and changes in their morphology are recorded during the deformation of layered polycrystalline ice at temperatures above 10 c slip on 0001 preceeded kb initiation and two different mechanisms a shear mode and a buckling mode are proposed for the development of the observed kbs the shear mode occurs with axial compression parallel to 0001 and is restricted to a band of material with sharply defined kbbs involved with an effective macroscopic simple shear sub perpendicular to the slip plane during deformation these bands progressively reduce their width while maintaining a stable orientation secondary kbs and microfractures are propagated within the kb as a result of increasing shear deformation in the band these phenomena are attributed to a limiting of the shear deformation to a band and the necessity to accommodate the dilatation changes in the buckling mode kb initiation is preceeded by the formation of deformation bands and this type of kb can initiate from inherent heterogeneities within the grain aggregate microstructural sensitivity is put forward to explain the apparent instability of this type of kb which is often curved and capable of migrating through a crystalline lattice the buckling mode occurs in grains where 0001 is oblique to the compression direction

antitaxial crack seal vein microstructures and their relationship to displacement paths abstract the microstructures developed in an example of a syntectonic crack seal vein indicate that antitaxial fibres do not necessarily track the incremental opening history during crack seal vein growth this observation serves as a caution against the uncritical use of fibrous microstructures to make inferences about displacement histories during fibre formation it is demonstrated that crack seal processes can lead to the development of both irregular and laminated vein microstructures as well as fibrous microstructures the types of microstructures which develop in crack seal veins and the extent to which they reflect the opening paths of veins depend on a range of factors the most important of these include the nucleation and growth kinetics of phases precipitated from fluids in opening fractures and the location of sites of material accretion during successive crack seal increments

low temperature emplacement of phreatomagmatic pyroclastic flow deposits at the monogenetic mt gambier volcanic complex south australia and their relevance for understanding some deposits in diatremes the occurrence of pyroclastic flow deposits is not restricted to polygenetic and or felsic volcanic systems but can also occur at mafic monogenetic volcanic centres at the c 5 ka mt gambier volcanic complex australia two small volume pyroclastic flow deposits resulted from phreatomagmatic eruptive phases of the blue lake east and the valley lake maar craters the facies descriptions of the two massive poorly sorted lapilli tuff and tuff breccia deposits are given low grade carbonized wood fragments in the deposits mark low emplacement temperatures 180 270 c for these deposits with only c 12 23 of the total thermal energy of the original magma preserved at the time of deposition the blue lake east vent erupted by forming a short lived vertical eruption column which could not be sustained and collapsed the valley lake pyroclastic flow deposit has a highly asymmetric dispersal to the west indicating that this deposit was formed during an eruptive phase with a large westward directed lateral component such massive poorly sorted deposits outside the maar crater indicate that some similar deposits in diatremes may have originated from surface eruptions and not just from subsurface debris jets

the stress distribution related to the boudinage of a visco elastic material examples from a polar outlet glacier abstract quantitative stress measurements related to the development of mesoscale structures in rock are difficult if not impossible a method for determining the stress distribution and history during the development of mesoscale boudinage structures in ice is introduced here boudinage structures in fracture trace ice have been observed in the outlets glaciers of the framnes mountains east antarctica fracture traces are preserved when creasses fill with surface melt water which freezes to form coarse grained columnar ice a 4 0 km flow parallel traverse across the central ice stream of the framnes mountains is presented to illustrate the boudinage of fracture traces with a mean width of 0 30 m field based measurement of the geometric evolution of boudinage structures has been combined with surface flow rate measurements to quantitatively determine the strain rate at which the boudinage structures formed the strain rate measurements provide boundary constraints on several two dimensional finite difference models that have been used to analyse the stress distribution related to the formation of boudinage structures in a visco elastic solid the results reveal the development of pressure shadows during the boundinage of layered rocks and demonstrate the degree of refraction of stress across rheological boundaries which have important ramifications for the analysis of planar and linear fabrics in rocks

shear bands crenulations and differentiated layering in ice mica models abstract thin sheets of composite ice mica have been deformed in order to simulate the development of cleavages in quartz mica rocks a strong initial mica preferred orientation was variably oriented to the shortening direction deformation parallel to the foliation results in a crenulation type cleavage developing from shear bands initiated after a component of pure shear deformation oblique to the foliation produces a differentiated cleavage and involves a large component of shear strain subparallel to the original anisotropy the strain is accommodated by intra and intercrystalline processes that produce extensive grain elongation and rearrangement of the ductile matrix thereby forming ice vs mica rich regions on the other hand there is no drastic morphological change when a sample is shortened perpendicular to an original foliation that is where the micas lie in the plane of no shear strain instead the mica fabric is strengthened and the grains in the ductile matrix are flattened two models are presented for the initiation propagation and evolution of the observed crenulation versus differentiated cleavage types these depend on mica stacking and orientation relative to the transverse properties of the sample and also on the direction of anisotropy to the xy plane of the bulk strain ellipsoid the models invoke shear on planes of high shear strain and rotation of the shear bands and rigid mica grains into a direction approximately parallel to the bulk extension direction

rapid surficial oxidation of synthetic fe ti oxides at high temperature observations and consequences for magnetic measurements 1 synthetic polycrystalline samples of fe ti oxides titanomagnetite tmtss ilmenite hematitess ilmss pseudobrookitess psbss are very sensitive to changes in the redox conditions at high temperatures either during synthesis experiments or during thermomagnetic measurements for instance exposure to air for a few seconds at the end of a synthesis run at 1300 c of a tmtss ilmss sample produces surficial oxidation down to a depth of some 100 m this oxidation zone is well visible on backscattered electron images of polished sections through the sample pellet it is characterized by so called trellis oxyexsolution textures i e fine lamellae of ilmss within the tmtss crystals and lamellae of psbss within the ilmss crystals in this oxidation zone the newly grown ilmss lamellae and the surrounding tmtss are more fe rich than the original crystals the presence of trellis textures in the crystals of both coexisting phases tmtss and ilmss show that only short scaled elemental transport within the crystals was involved and that equilibrium was not attained even though the oxidation zone is very narrow the imprint of the new tmtsscompositions is well recognizable in temperature dependent magnetic susceptibility curves in temperature dependent saturation magnetization ms t curves however the contribution of more fe rich tmtss from the oxidation zone can be easily overseen however surficial oxidation of tmtss does occur during ms t measurements with a variable field translation balance apparently in relation with insufficient ar flowing around the sample further examples of rapid surficial oxidation of fe ti oxide samples are also discussed

cooling rates of pyroclastic deposits inferred from mineral magnetic investigations a case study from the pleistocene mýtina maar czech republic tephra layers of the m tina maar czech republic contain ferrimagnetic mg al rich titanomagnetite which is suggested to originate from a fractionated alkaline co 2 rich lithospheric mantle melt we investigated the magnetic mineralogy and curie temperature t c from tephra deposits of two drill cores 9 m depth t c calculated 208 14 c from chemical composition fe 2 0 8 mg 0 5 fe 3 1 1 al 0 3 ti 0 3 o 4 is in accordance with tc retrieved from cooling curves of temperature dependent magnetic susceptibility measurements 195 232 c however thermomagnetic curves are irreversible either with lower type i or higher type ii tc in the heating curve all curves show transition temperatures above ca 390 c indicating maghemitization we interpret the irreversibility of tc t c in terms of different degrees of cation ordering overprinted or masked by different degrees of maghemitization which is a low temperature phenomenon negative t c indicates that original deposited titanomagnetite has cooled faster and therefore has stored a lower degree of cation ordering compared to heating cooling rate of 11 c min in the kappabridge type ii with positive t c indicates higher degree of cation ordering and therefore slower cooling rate the central part of this deposit shows most severe maghemitization indicating rather wet emplacement we therefore suggest different eruption styles for deposition of type i pyroclastics with more phreatomagmatic and type ii pyroclastics with more phreato strombolian eruption styles our study is a new approach to discriminate different cooling histories in maar deposits using the curie temperature of titanomagnetite we suggest that this method has the potential to discriminate different emplacement modes resulting from different eruption styles

curie temperatures of titanomagnetite in ignimbrites effects of emplacement temperatures cooling rates exsolution and cation ordering pumices ashes and tuffs from mt st helens and from novarupta contain two principal forms of titanomagnetite homogeneous grains with curie temperatures in the range 350 500 c and oxyexsolved grains with similar bulk composition containing ilmenite lamellae and having curie temperatures above 500 c thermomagnetic analyses and isothermal annealing experiments in combination with stratigraphic settings and thermal models show that emplacement temperatures and cooling history may have affected the relative proportions of homogeneous and exsolved grains and have clearly had a strong influence on the curie temperature of the homogeneous phase the exsolved grains are most common where emplacement temperatures exceeded 600 c and in laboratory experiments heating to over 600 c in air causes the homogeneous titanomagnetites to oxyexsolve rapidly where emplacement temperatures were lower curie temperatures of the homogeneous grains are systematically related to overburden thickness and cooling timescales and thermomagnetic curves are generally irreversible with lower curie temperatures measured during cooling but little or no change is observed in room temperature susceptibility we interpret this irreversible behavior as reflecting variations in the degree of cation ordering in the titanomagnetites although we cannot conclusively rule out an alternative interpretation involving fine scale subsolvus unmixing short range ordering within the octahedral sites may play a key role in the observed phenomena changes in the curie temperature have important implications for the acquisition stabilization and retention of natural remanence and may in some cases enable quantification of the emplacement temperatures or cooling rates of volcanic units containing homogeneous titanomagnetites

reconnaissance study of an inferred quaternary maar structure in the western part of the bohemian massif near neualbenreuth ne bavaria germany after a comprehensive geophysical prospecting the quaternary m tina maar located on a line between the two quaternary scoria cones komorni h rka kammerbuhl and elezna h rka eisenbuhl could be revealed by a scientific drilling at the german czech border in 2007 further geophysical field investigations led to the discovery of another geological structure about 2 5 km ese of the small town neualbenreuth ne bavaria germany inferred to be also a maar structure being the fourth volcanic feature aligned along the nw se trending tachov fault zone it is only faintly indicated as a partial circular rim in the digital elevation model though not expressed by a clear magnetic anomaly geoelectric and refraction seismic tomography strongly indicates a bowl shaped depression filled with low resistivity and low velocity material correlating well with the well defined negative gravity anomaly of 2 5 mgal below ca 15 m thick debris layer successions of mostly laminated sediments were recovered in a 100 m long sediment core in 2015 sections of finely laminated layers likely varves rich in organic matter and tree pollen were recognized in the upper 22 30 m and lower 70 86 m part of the core respectively interpreted as interglacials whereas mostly minerogenic laminated deposits poor in organic matter and almost barren of tree pollen are interpreted as clastic glacial deposits according to a preliminary age model based on magnetostratigraphy palynology radiocarbon dating and cyclostratigraphy the recovered sediments span the time window from about 85 ka back to about 270 ka covering marine isotope stages 5 8 sedimentation rates are in the range of 10 cm ka 1 in interglacials and up to 100 cm ka 1 in glacial phases the stratigraphic record resembles the one from m tina maar with its eruption date being derived from a nearby tephra deposit at 288 17 ka thus supporting the age model of the inferred neualbenreuth maar

thermal interactions of the ad79 vesuvius pyroclastic density currents and their deposits at villa dei papiri herculaneum archaeological site italy abstract pyroclastic density currents pdcs can have devastating impacts on urban settlements due to their dynamic pressure and high temperatures our degree of understanding of the interplay between these hot currents and the affected infrastructures is thus fundamental not only to implement our strategies for risk reduction but also to better understand pdc dynamics we studied the temperature of emplacement of pdc deposits that destroyed and buried the villa dei papiri an aristocratic roman edifice located just outside the herculaneum city during the ad79 plinian eruption of mt vesuvius italy by using the thermal remanent magnetization of embedded lithic clasts the pdc deposits around and inside the villa show substantial internal thermal disequilibrium in areas affected by convective mixing with surface water or with collapsed walls temperatures average at around 270 c min 190 c max 300 c where the deposits show no evidence of mixing with external material the temperature is much higher averaging at 350 c min 300 c max 440 c numerical simulations and comparison with temperatures retrieved at the very same sites from the reflectance of charcoal fragments indicate that such thermal disequilibrium can be maintained inside the pdc deposit for time scales well over 24 hours i e the acquisition time of deposit temperatures for common proxies we reconstructed in detail the history of the progressive destruction and burial of villa dei papiri and infer that the rather homogeneous highest deposit temperatures average 350 c were carried by the ash sized fraction in thermal equilibrium with the fluid phase of the incoming pdcs these temperatures can be lowered on short time less than hours and length scales meters to tens of meters only where convective mixing with external materials or fluids occurs by contrast where the villa walls remained standing the thermal exchange was only conductive and very slow i e negligible at 50 cm distance from contact after 24 hours we then argue that the state of conservation of materials buried by pdc deposits largely depends on the style of the thermal interactions here we also suggest that pdc deposit temperatures are excellent proxies for the temperatures of basal parts of pdcs close to their depositional boundary layer this general conclusion stresses the importance of mapping of deposit temperatures for the understanding of thermal processes associated with pdc flow dynamics and during their interaction with the affected environment

linking the ukinrek 1977 maar eruption observations to the tephra deposits new insights into maar depositional processes abstract the ukinrek maars erupted 30 march to 9 april 1977 forming two maars a line of small pit craters and a tephra blanket extending to 2 km from the vents we combine photographic and written observations with stratigraphic analysis to reconstruct the eruption the eruption began with very low a few meters high fountaining from small craters above an inferred east west trending dike creating local scoria spatter agglomerate ramparts with a sandy matrix the eruption very quickly in minutes to hours centered on the west maar the west maar eruption lasted 1 2 days starting and ending with phreatomagmatic explosions with weak phreato strombolian activity in between initial explosions formed a 30 m wide crater enlarged by crater wall collapse and columns as high as 6500 m phreato strombolian activity produced 72 of the erupted volume including a small spatter cone and a scoria blanket around the vent a final explosion series emplaced a lithic rich breccia as ballistic blocks possibly as the northern half of the final crater collapsed into the southern vent area the east maar formed over the last nine days of the eruption and represents 93 of the total volume 4 6 106 m3 of the ukinrek eruption initial explosions were probably shallower than 10 20 m but most of the eruption occurred from explosions at 50 60 m below the pre eruptive surface with evidence of explosions to 90 m depth only at the very end of the eruption the east maar eruption mostly produced columns of lapilli ash and steam and the deposits are mostly fallout winds blew fallout mostly to the north for the first 5 6 days and to the south for the last three days of the eruption wind directed pyroclastic density currents collapsed from the column producing fines rich layers within the coarser fallout sporadic explosions produced weak density currents in the first few days and lithic and juvenile block rich breccias in the last few days of the eruption we interpret that collapse of the crater walls made a slurry that in part provided the water for phreatomagmatic interaction explosions came from depths

co2 discharge in an active non volcanic continental rift area czech republic characterisation δ13c 3he 4he and quantification of diffuse and vent co2 emissions abstract in the western eger rift er area along the pocatky plesna fault zone ppz co 2 degassing occurs predominantly within two mofette fields bublak and hartousov we studied 27 wet mofettes belonging to these mofette fields for gas emission rates repeatedly between 2007 and 2009 and selected mofettes for gas composition and isotope ratios 13 c 3 he 4 he detailed ground mapping along the ppz provided further two separated diffuse degassing structures dds within the mofette fields hartousov and bublak the dds hartousov was studied in detail by measurements of 682 co 2 soil gas concentrations 762 co 2 soil gas fluxes max 10 grid spacing and partly by analyses of isotope ratios 13 c 12 c 3 he 4 he of soil gas at the dds hartousov the total co 2 soil flux yielded 1 559 t m 2 d 1 in spring 2009 and the co 2 emission rate at the wet mofettes of hartousov mofette field yielded 0 62 t d 1 the total co 2 discharge of the 27 wet mofettes was 3 75 t d 1 at sites with high co 2 soil flux the portion of mantle derived helium is in the same range as the releasing at wet mofettes both cover the signature of the subcontinental mantle also the 13 c values analysed in the gas releasing from wet mofettes and those analysed in soil gas are nearly the same taking in account a biogenic soil co 2 flux of 25 g m 2 d 1 as background the mantle derived co 2 flux yielded approximately 1566 t m 2 d 1 as a result of the co 2 flux mapping of the dds hartousov it could be proved that 97 4 of the released soil co 2 1 518 t m 2 d 1 stems from sites with co 2 fluxes higher than 500 g m 2 d 1 pointing to dominantly fault related co 2 release at the central mofette bublak b2 the gas emission rate was determined for the first time in 1993 measurements repeated between 2007 and 2009 showed a clear increase in the gas emission rate of more than 40 correlating well with the increase of the 3 he 4 he ratios from 5 ra to approximately 6 ra between 1993 and 2008 at this location brauer et al 2009 the bublak mofette field is characterised by the highest co 2 emission rate along the ppz and in combination with the helium isotope signature of the european subcontinental mantle this area was identified as a deep reaching fluid injection zone

monogenetic volcanism personal views and discussion monogenetic volcanism produces small volume volcanoes with a wide range of eruptive styles lithological features and geomorphic architectures they are classified as spatter cones scoria or cinder cones tuff rings maars maar diatremes and tuff cones based on the magma water ratio dominant eruption styles and their typical surface morphotypes the common interplay between internal such as the physical chemical characteristics of magma and external parameters such as groundwater flow substrate characteristics or topography plays an important role in creating small volume volcanoes with diverse architectures which can give the impression of complexity and of similarities to large volume polygenetic volcanoes in spite of this volcanic facies complexity we defend the term monogenetic volcano and highlight the term s value especially to express volcano morphotypes this study defines a monogenetic volcano a volcanic edifice with a small cumulative volume typically 1 km3 that has been built up by one continuous or many discontinuous small eruptions fed from one or multiple magma batches this definition provides a reasonable explanation of the recently recognized chemical diversities of this type of volcanism

distribution of partial melt in a felsic system the importance of surface energy the texture distribution and infiltration tendency of a quartz albite melt in equilibrium with a synthetic texturally equilibrated quartzite was examined in a series of distribution and infiltration experiments at 1 250 c and 8 kbar hydrostatic pressure wetting angle measurements from melt distribution experiments show a dihedral angle of 60 degrees implying a quartz quartz interfacial energy approximately 1 7 times the quartz melt value because of this specific relationship between interfacial energies the system can achieve its lowest surface free energy state with the melt either in pools or along grain edge intersections possibly forming some interconnected channels stability of melt in pockets and along grain edge intersections was observed in a fourteen day dispersed melt experiment yet melt pools failed to disperse into the quartzite during infiltration experiments comparison of the observed dihedral angle with previously measured surface energy values for the melt and quartz shows excellent agreement and also demonstrates that an aggregate of randomly orientated anisotropic grains acts approximately isotropically

equilibrium dihedral angles in the system h2o co2 nacl calcite and implications for fluid flow during metamorphism fluid calcite calcite dihedral angles have been measured for fluids in the system h2o co2 nacl between 1 and 2 kbar and 550 750 c it is found that the calcite calcite h2o dihedral angle decreases steadily with addition of nacl from a value of about 80 pure water to 44 60 wt nacl the co2 h2o system displays a well defined minimum at x co 2 0 5 with a dihedral angle of 50 in contrast to those of pure co2 and h2o which are 90 and 80 respectively experiments containing fluids which are immiscible at run conditions showed a bimodal distribution of dihedral angles in the co2 h2o nacl system which can be approximately correlated with the compositions of the two fluid phases such bimodality was only observed for immiscible fluids in the h2o nacl system if the quench rate exceeded about 200 c per min this is probably due to the extremely rapid establishment of the single phase dihedral angle on quenching the fluid phase topology in devolatilising marbles will only be a connected network for very saline brines and fluids with x co 2 close to 0 5 fluids trapped in fluid inclusions in calcite grains in marbles may be predominantly h2o rich or co2 rich and of low salinity all other fluid compositions in the h2o co2 nacl calcite system will occupy isolated pores the largest of which will grow at the expense of the smallest escape of fluid produced during devolatilisation reactions under such conditions will occur by fluid overpressuring and hydrofracture in contrast previous experimental studies of quartz fluid dihedral angles between 950 and 1100 c watson and brenan 1987 predict that quartz dominated lithologies will permit pervasive flow of h2o nacl fluids but not of h2o co2 fluids documented geological examples of differences in permeability and fluid flow mechanism between metamorphic argillites psammites and limestones which support the results of the experimental studies are discussed

root zone processes in the phreatomagmatic pipe emplacement model and consequences for the evolution of maar diatreme volcanoes abstract the understanding of processes within the root zone of maar diatreme volcanoes is important for the interpretation of the geology volcanology and even hazard assessment of these volcanoes in the phreatomagmatic model of pipe formation the irregularly shaped root zone is the site of the phreatomagmatic explosions and thus functions as the engine for pipe formation in this model the root zone grows over a period of time in a series of many single thermohydraulic i e phreatomagmatic explosions the explosions initially occur close to the surface and with ongoing explosive activity penetrate towards deeper levels the ejection of country rock clasts from the root zone results in a mass deficiency in the root zone that causes the overlying tephra and the adjacent country rocks to subside passively in a sinkhole like fashion into the root zone many phreatomagmatic eruptions consequently result in the formation of a cone shaped diatreme thus with ongoing eruptions the cone shaped diatreme has to grow systematically both in depth and diameter during its growth processes in the lower diatreme levels successively destroy the upper levels of the evolving root zone at the surface the maar crater in turn reacts to the underlying subsidence processes and also grows both in depth and diameter thermohydraulic explosions which fragment both magma and the surrounding country rocks mostly occur within the bottom part of the root zone violent explosions in small pipes may clear the overlying diatreme for a short period of time before tephra fall and collapse of the walls of the new crater refill the small initial diatreme in larger pipes via expansion of the mixture of highly pressurized water vapor juvenile gas phases and explosively produced tephra the confined and expanding eruption cloud has to pierce through the diatreme fill in a feeder conduit in order to erupt diatreme clearing events in large pipes are difficult or impossible to maintain since the explosive force in the root zone is only in exceptional instances strong enough to lift or entrain the entire diatreme tephra knowledge of the genetic relationships between root zones and diatremes is critical to understand pipe growth processes the combination of such processes can lead to substantial variation in volcanic behavior and thus produce fundamentally different volcano and rock types it is the purpose of this paper to outline important features of root zones and suggest their significance for the genesis and evolution of maar diatreme and related volcanoes

a three dimensional numerical study of induction in southern india by an electrojet source abstract the induction effect on geomagnetic variations due to the daytime electrojet in the region of the indian peninsula and sri lanka has been investigated numerically with the aid of a thin sheet algorithm the electrojet is represented by a gaussian current distribution over a band of about 600 km width with its maximum intensity close to the dip equator and a height of 110 km an inducing source comprising an equatorial electrojet superimposed on the uniform planetary field is also considered the results are presented in the form of contour plots and the differences between the magnetic field components associated with electrojet and uniform sources are highlighted it is observed that the non uniformity of the source in daytime events has a profound effect on the induced currents in the region the dual effect of reduced current intensity and opposing external and internal parts results in smaller vertical magnetic field variations over the southern peninsula especially close to the periphery of the electrojet it is confirmed that for a pure electrojet source the vertical field vanishes completely in the region of the permanent geomagnetic station at annamalainagar thereby lending credence to a recently proposed method of separating a daytime magnetic event into its ionospheric and magnetospheric parts an examination of field ratios shows that the magnetotelluric impedance is less dependent on the source effect over the whole region than other parameters finally it is shown that in the presence of a combined electrojet and uniform source field the observed equatorial enhancement is not proportional to the strength of the electrojet alone but is also critically dependent on the intensity of the uniform part of the field

kinematics of crystal growth in syntectonic fibrous veins abstract detailed observations of a set of fibrous antitaxial calcite veins in a slate reveal that some of the calcite fibres do not connect material markers on both sides of the vein and can therefore not have tracked the full opening trajectory during vein growth this calls for a better understanding of the mechanisms of fibre formation and reliable criteria to test the tracking hypothesis based on surface roughness characteristics of the vein wall we develop a simple model for shape growth of crystals in a crack seal environment which can account for both tracking and non tracking behaviours and propose a set of tracking criteria for antitaxial veins finally we discuss ways by which the model can be tested against natural examples

forced transport of thermal energy in magmatic and phreatomagmatic large volume ignimbrites paleomagnetic evidence from the colli albani volcano italy abstract few studies have detailed the thermal architecture of large volume pyroclastic density current deposits although such work has a clear importance for understanding the dynamics of eruptions of this magnitude here we examine the temperature of emplacement of large volume caldera forming ignimbrites related to magmatic and phreatomagmatic eruptions at the colli albani volcano italy by using thermal remanent magnetization analysis on both lithic and juvenile clasts results show that all the magmatic ignimbrites were deposited at high temperature between the maximum blocking temperature of the magnetic carrier 600 630 c and the glass transition temperature about 710 c temperature estimations for the phreatomagmatic ignimbrite range between 200 and 400 c with most of the clasts emplaced between 200 and 320 c because all the investigated ignimbrites magmatic and phreatomagmatic share similar magma composition volume and mobility we attribute the temperature difference to magma water interaction highlighting its pronounced impact on thermal dissipation even in large volume eruptions the homogeneity of the deposit temperature of each ignimbrite across its areal extent which is maintained across topographic barriers suggests that these systems are thermodynamically isolated from the external environment for several tens of kilometers based on these findings we propose that these large volume ignimbrites are dominated by the mass flux which forces the lateral transport of mass momentum and thermal energy for distances up to tens of kilometers away from the vent we conclude that spatial variation of the emplacement temperature can be used as a proxy for determining the degree of forced convection flow

evidence of two holocene phreatomagmatic eruptions at stromboli volcano aeolian islands from paleomagnetic data 1 we present detailed stratigraphic sedimentological and paleomagnetic analyses of holocene phreatomagmatic deposits at stromboli volcano aeolian islands italy the investigated deposits belong to the secche di lazzaro succession sdl and to the advanced operations center of the department of civil defense coa succession both lying on the neostromboli lavas ca 13 5 ka the two stratigraphic successions have similar stratigraphic position and show a phreatomagmatic origin likely related to catastrophic magma water interaction processes during sector collapse events however the thermal remanent magnetization data of the lava lithics indicate that deposits of the sdl succession were emplaced at very low temperatures less than 140 c whereas the basal part of the coa deposit was emplaced at temperatures between 300 340 c paleomagnetic results indicate that the two investigated deposits may be related to two distinct eruptive events occurred during the holocene recent phreatomagmatic activity at stromboli apparently has occurred more frequently than previously believed consequently we must reconsider the recurrence interval of this dangerous eruptive scenario for stromboli

modification of the magnetic mineralogy in basalts due to fluid rock interactions in a high temperature geothermal system krafla iceland summary active high temperature 150 c geothermal areas like the krafla caldera ne iceland often show distinct magnetic lows in aeromagnetic anomaly maps suggesting a destruction of magnetic minerals by hydrothermal activity the main alteration processes in such an environment are low temperature oxidation 350 c maghemitization and fluid rock interactions we investigated the rock magnetic properties natural remanent magnetization nrm magnetic susceptibility and their temperature and field variation and the mineralogy using x ray diffraction microscopic methods and electron microprobe analyses of two drill cores kh1 and kh3 from the rim of the krafla caldera the drill cores have distinctly lower nrm values average 3 a m 1 compared to younger surface basalts average 20 a m 1 along with a large variation in magnetic susceptibility 1 3 10 7 4 9 10 5 m3 kg 1 the secondary mineral assemblage sulphides sphene rutile and chlorite indicates an alteration within the chlorite smectite zone for both cores without depth zoning optical miscroscopy in combination with the bitter technique and backscatter electron microscopy along with the thermomagnetic analyses allow distinguishing two different magnetomineralogical groups of titanomaghemite 1 titanomaghemite with intermediate titanium concentration and probably high vacancy concentration and 2 titanomaghemite with low titanium concentration and low vacancy concentration the mineral assemblages textures and magnetic properties deduced from the mentioned magnetic measurements indicate two stage transformation mechanism 1 dissolution of titanium at low ph under oxidizing conditions the ulvospinel component of titanomagnetite and ilmenite forms rutile or sphene and fe2 migrates out of the spinel lattice forming titanomaghemite 2 formation of pyrite and dissolution of remaining titanomaghemite under reducing and acidic conditions the latter mechanism produces ghost textures all titanomaghemite is transformed and only their former grain shapes are preserved with only paramagnetic minerals left and ferrimagnetic minerals nearly dissolved this mechanism could explain the significant magnetization loss which is seen in many local magnetic anomaly lows within the oceanic crust and volcanic islands like iceland or hawaii the production of nanoporous textures in titanomaghemites is suggested as a mechanism for the enhancement of the magnetic susceptibility values related to the hydrothermal alteration of krafla

quantification of vesicle characteristics in some diatreme filling deposits and the explosivity levels of magma water interactions within diatremes abstract vesicles within juvenile fragments in mafic pyroclastic deposits contain important information about the state of the magma at the time of fragmentation there have been few vesicle studies of juvenile pyroclasts from mafic phreatomagmatic deposits however and none we can find from maar diatreme volcanoes in this paper we document the vesicularity and vesicle population characteristics of juvenile fragments sampled from non bedded lithified deposits of the coombs hills diatreme complex part of the ferrar large igneous province antarctica the diatreme filling pyroclastic deposits dominated by lapilli tuffs and tuff breccias contain typically abundant lithic clasts derived mostly from the enclosing sedimentary sequence and several types of juvenile clasts ranging from blocky to fluidal or raggy in the samples measured 77 80 of the juvenile pyroclasts ranging in size from 0 5 mm to fine lapilli is in the non vesicular to incipiently vesicular range fluidal or rag shaped juvenile clasts some circular vesicles and the lack of microlites all suggest that the coombs hills magma had a relatively low viscosity prior to fragmentation despite the basaltic andesite composition this low viscosity allowed parts of the magma to be fragmented in a non brittle fashion during phreatomagmatic explosions and to form fluidal clasts phreatomagmatic explosions in diatremes can therefore produce diverse types of juvenile clasts simultaneously and the proportions of each will depend on the explosivity of the magma water slurry interaction and other factors recycling of fragments is also thought to be an important factor in generating mixtures of different types of juvenile fragments in diatremes

migmatite structures in the central gneiss complex boca de quadra alaska migmatite structures in the coast plutonic metamorphic complex are well exposed in the inlet of boca de quadra southeast alaska two types of anatectic migmatites are present patch migmatites formed by in situ melting and subsequent crystallization of melt diktyonitic migmatites comprise a discontinuous veined network of leucocratic material in which leucosomes enclose boudins of host rock the margins of these boudins show the development of both melanosomes and shear band fabrics strain analysis of diktyonitic melanosomes indicates that these regions have undergone volume decreases of 20 27 this volume decrease is attributed to melt extraction into the adjacent fracture filling leucosomes thus diktyonitic migmatites formed by shear induced segregation of partial melt whereas in patch migmatites the lack of shear stresses inhibited melt segregation the variable structural style of anatectic migmatites in boca de quadra is not related to host rock composition but may be due to differences in the amount of differential stress during migmatization these in turn may be controlled by host rock strength and or diachroneity of migmatization and deformation determination of volume changes during migmatization using strain analysis is potentially capable of discriminating intrusive and anatectic migmatites and consequently of documenting melt segregation and subsequent migration across crustal levels

crystal growth during a single stage opening event and its implications for syntectonic veins abstract the crystallization of a fluid filled vein or cavity and interpretation of the microstructure in a deformed rock is an important problem for geologists dynamic crystallization experiments using ice and an aqueous solution have been used as an analogue system for single stage opening events and have shown that the presence or absence of a deviatoric stress is an important factor in the development of texture as a result of crystallization from a fluid the textures can vary from 1 coarse crystal aggregates involving static growth where there is no significant macroscopic deviatoric stress at the time of crystallization the free face growth model to 2 polycrystalline aggregates involving static growth which develop from a mixture of skeletal crystals and fluid in a stressed environment in the latter situation the crystals and fluid coexist until the macroscopic stress can be transmitted between impinging crystals and at this stage fast dynamic recrystallization and grain boundary migration occurs this recrystallization has been termed the contact growth model and the resulting metamorphic texture is compared with examples in natural quartz veins during a single stage vein opening uncomplicated by intragranular deformation either free face and or contact growth textures can develop from the fluid filled void depending upon the kinematic environment