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

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

late ordovician glaciation under high atmospheric co2 a coupled model analysis the analysis of the geologic record has revealed a question concerning how the late ordovician glaciation could have occurred simultaneously with high co2 levels 10 18x sensitivity studies using a coupled atmosphere ocean sea ice model show that it is possible to maintain a permanent snow cover which corresponds to 60 of all the glacial deposits found on gondwana under 10x co2 levels warm fall cool spring orbital parameters a 4 5 reduction in solar luminosity a length of day of 21 5 hours and an enhanced snow sea ice albedo of 0 3 a cold summer orbit experiment with 10x co2 and a reduced snow sea ice albedo of 0 1 also sustains a permanent albeit less extensive snow cover the geographic configuration of the late ordovician results in an up to 42 increase in the global ocean poleward heat transport in the southern hemisphere relative to present day and a significant asymmetry relative to the equator

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

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

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

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

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

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

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

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

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

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

petrogenetic implications of neodymium isotope data from the kohistan batholith north pakistan neodymium data are presented for five granitoid trondhjemite granite and leucogranite plutonic units from the kohistan batholith aged 102 ma to 29 ma these have present day l43 nd 144 nd ratios of between 0 512980 and 0 512734 calculated initial 143 nd 144 nd ratios of between 0 512861 and 0 512705 and nd values of between 6 91 and 2 04 there is a decrease in nd with time which is inversely correlative with a similar increase in sr three plutonic units matum das gilgit and shirot formed from a source enriched in sm and depleted in rb or radiogenic sr relative to bulk earth whilst a fourth unit the indus confluence acid sheets is only slightly enriched in radiogenic sr these four units define a temporal trend from the least evolved matum das pluton to the most evolved indus confluence acid sheets this trend was produced as a result of subducting oceanic sediment or seawater altered oceanic crust which melted or dehydrated and increasingly modified the isotopic composition of an original mantle protolith situated above the subducting plate the data preclude any significant input to the magmatism from ancient crust new data presented here together with other published data indicate an immature metavolcanic crustal source for the matum das pluton and a plutonic basement crustal source for the indus confluence acid sheets these crustally derived units retain a mantle isotopic signature indicating that the geochemical signature of kohistan evolved by remobilization of recently formed arc crust in addition to new inputs of mantle derived magma a fifth plutonic unit the parri acid sheets shows a clear compositional break from the other units being significantly enriched in radiogenic sr and nd with respect to bulk earth the source to the parri acid sheets is interpreted as metasedimentary rocks with a high rb sr ratio and a crustal residence time of c 70 ma

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

late ordovician to earliest silurian graptolite and brachiopod biozonation from the yangtze region south china with a global correlation late ordovician to earliest silurian is an important geological period marked by large geological and biological events however the strata and fossils of this interval are not complete in many parts of the world based on studies of 43 sites in south china in particular the continuous sections on the yangtze platform we recognize a complete succession including seven graptolite zones and two shelly faunas in ascending order the graptolite zones are the dicellograptus complanatus dicellograptus complexus paraorthograptus pacificus including lower subzone tangyagraptus typicus subzone and diceratograptus mirus subzone normalograptus extraordinarius normalograptus ojsuensis normalograptus persculptus akidograptus ascensus and parakidograptus acuminatus zones the shelly faunas are the foliomena nankinolithus and hirnantia faunas which may be correlated with d complanatus zone and n extraordinarius n ojsuensis to part of n persculptus zones respectively the biozonation through this interval from the yangtze region can be correlated with that of other parts of the world such as dob s linn in scotland spain and portugal thuringia saxonia bavaria bohemia poland kazakhstan kolyma malaya peninsula yukon canadian arctic islands nevada argentina niger and victoria australia the hirnantian substage which has been proposed by us recently includes the n extraordinarius n ojsuensis zone hirnantia fauna and n persculptus zone the base of the hirnantian substage is marked by the first appearance data fads of n extraordinarius and n ojsuensis which have been determined to be synchronous on a global scale

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