what is diatomite different types of biogenic remains ranging from siliceous algae to carbonate precipitates accumulate in the sediments of lakes and other aquatic ecosystems unicellular algae called diatoms which form a siliceous test or frustule are an ecologically and biogeochemically important group of organisms in aquatic environments and are often preserved in lake or marine sediments when diatoms accumulate in large numbers in sediments the fossilized remains can form diatomite in sedimentological literature diatomite is defined as a friable light coloured sedimentary rock with a diatom content of at least 50 however in the quaternary science literature diatomite is commonly used as a description of a sediment type that contains a large quantity of diatom frustules without a precise description of diatom abundance here we pose the question what is diatomite what quantity of diatoms define a sediment as diatomite is it an uncompacted sediment or a compacted sediment we provide a short overview of prior practices and suggest that sediment with more than 50 of sediment weight comprised of diatom sio2 and having high 70 porosity is diatomaceous ooze if unconsolidated and diatomite if consolidated greater burial depth and higher temperatures result in porosity loss and recrystallization into porcelanite chert and pure quartz less

sector trilling in cordierite and equilibrium overstepping in metamorphism the origin of sector trilling in cordierite is due to the hexagonal orthorhombic al si ordering transformation which under non equilibrium conditions proceeds via a short range ordered modulated structure the growth of these distortion waves associated with progressive ordering produces a strain field which is minimized by a cyclic distribution of symmetrically equivalent modulations sector and complexly trilled cordierites in metamorphic rocks grew as the hexagonal polymorph with a considerable degree of al si disorder the enthalpy and entropy of disorder are evaluated from recent experimental work the implication is that in metamorphic rocks substantial overstepping of stable equilibrium phase boundaries is required to nucleate hexagonal cordierite moreover its composition coexisting with other phases will also be significantly different from that of the stable ordered form

sub volcanic crystallization at stromboli aeolian islands southern italy preceding the sciara del fuoco sector collapse evidence from monzonite lithic suite we describe texture mineralogy and whole rock composition of cognate monzonite sub volcanic clasts within debris flow deposits related to the 5000 years catastrophic phreatomagmatic eruption probably linked to the sciara del fuoco sector collapse the debris flows are at the top of accretionary lapilli rich ash deposits overlying potassic ks shoshonites lavas of the neostromboli period the monzonites are inferred to be crystallized in situ at low p at the side walls and or roof margins of a shallow magma chamber and to be cogenetic with the ks neostromboli extrusives they can be considered ideal orthocumulates since they approximately retain a bulk liquid composition and possibly represent slowly cooled equivalents of their ks shoshonite host rock the closure temperature of final solidification of the monzonite lithic suite was estimated through ternary feldspar geothermobarometry plagioclase k feldspar and k feldspar biotite equilibria and is in the range of 750 790 c with a maximum logfo2 around 15 1 15 3 the estimated pressure of crystallization is 0 5 kbar potassic lavas and dikes previously emplaced during the neostromboli period also resemble the monzonites in both major trace elements and mineral chemistry the cogenetic relationship between ks neostromboli extrusives and the monzonite host rock magma from which the sub volcanic clasts were derived is clear evidence that a shallow magma chamber existed between the caldera collapse of the vancori period and the sciara del fuoco sector collapse i e between 13 000 and 5000 years the monzonite clasts were derived from crystallization at very shallow depth ca 1 km and strongly support the hypothesis of violent decompression of the shallow magmatic plumbing system during the sciara del fuoco sector collapse climax of the regressive landslide event with maximum disruption of the chamber walls took place during emplacement of the debris flows i e during the late stage of the neostromboli phreatomagmatic eruption

eoarchean paleoproterozoic zircon inheritance in japanese permo triassic granites unazuki area hida metamorphic complex unearthing more old crust and identifying source terrranes abstract u pb zircon geochronology of two permo triassic granites samples ot 52 and ot 272 with ages of 229 8 ma and 256 2 ma respectively in the unazuki area hida metamorphic belt southwest japan revealed the presence of eoarchean to paleoproterozoic inheritance inheritance is consistent with both samples showing low zircon saturation temperatures for their bulk compositions in ot 52 dark in cl low th u zircon domains have a mean 207pb 206pb age of 1940 17 ma which is consistent with an age of 1937 6 ma for anatexis in the precambrian busan gneiss complex in korea eoarchaean inherited zircons with 207pb 206pb ages from ca 3750 to 3550 ma are common in ot 272 but are few in ot 52 suggesting a source from rocks with affinities to those in the anshan area in the northeast china part of the north china craton on the other hand a hida metamorphic belt metasedimentary gneiss into which the granites were intruded contains ca 1840 1130 580 360 285 and 250 ma zircons sano et al 2000 these ages suggest that the unazuki mesozoic granites did not originate from proximal hida metamorphic complex rocks but instead from unrelated rocks obscured at depth the predominance of eoarchean to paleoproterozoic age components and the marked lack of 900 700 ma components suggest that the source was the extended fringe of the north china craton rather than from yangtze craton crust the mesozoic evolution of japan and its linkages to northeast asia are discussed in the context of these results

the role of hydrothermal processes in concentrating high field strength elements in the strange lake peralkaline complex northeastern canada abstract the middle proterozoic peralkaline pluton at strange lake quebec labrador comprises hypersolvus to subsolvus phases which are unusually enriched in zr y rees nb be and f as exotic alkali and alkaline earth silicate minerals the highest concentrations of these elements are in subsolvus granite which underwent intense low temperature 200 c hydrothermal alteration involving hematization and the replacement of alkali high field strength element hfse minerals by calcic equivalents this alteration is interpreted to have been caused by meteoric or formational waters high temperature 350 c alteration attributed to orthomagmatic fluids is evident in other parts of the subsolvus granite by the replacement of arfvedsonite by aegirine comparisons of the chemical compositions of fresh and altered rocks indicate that rocks subjected to high temperature alteration were chemically unaffected except for depletion in zr y and hrees these elements were appreciably enriched in rocks that underwent low temperature alteration other elements affected by low temperature alteration include ca and mg which were added and na which was removed available data on hfse speciation in aqueous fluids and the chemistry of the pluton suggest that the hfses were transported as fluoride complexes if this was the case the low temperature fluid could not have been responsible for hfse transport because the high concentration of ca and low solubility of fluorite would have buffered f activity to levels too low to permit significant complexation we propose that hfse mineralization and accompanying alteration were the result of mixing in the apical parts of the pluton of a f rich essentially ca free orthomagmatic fluid containing significant concentrations of hfses with an externally derived meteoric dominated fluid enriched in ca as a result of interaction with calc silicate gneisses and gabbros according to this interpretation the latter fluid was responsible for the exchange of ca for alkalis mainly na in hfse rich minerals and by sharply reducing f activity in the mixed fluid through fluorite precipitation and or increasing ph destabilised the hfse fluoride complexes causing deposition of hfse bearing minerals an important implication of this study is that major hfse enrichment may be restricted to those rare cases where f rich ca free metal leaching environments and ca rich depositional environments are juxtaposed

dendritic cordierite in argillaceous hornfels from the toki area gifu prefecture central japan dendritic cordierite occurs in argillaceous hornfels from the toki area gifu prefecture japan the cordierite crystal consists of c arms elongated parallel to the c axes and a arms perpendicular to the c axis the latter arms could be divided into six kinds of untwinned a arms with different growth directions elongated parallel to the respective a axis and twinned a arms elongated parallel to the 110 twin plane a arms branch out from c arms or other a arms with different growth directions and c arms sometimes branch out from a arms leading to a tree like structure each of the c arms contains three kinds of domains related by a three fold axis about the c axis these domains are irregularly distributed without any relation to the shape of the c arm and the domain boundaries are of zigzag shape this domain arrangement suggests that c arms grew as hexagonal cordierite and were later transformed into orthorhombic cordierite the fact that each untwinned a arm has a fixed growth direction to its orientation suggests that the a arms grew as an orthorhombic cordierite from the growth directions of c and a arms orthorhombic and hexagonal phases are considered to grow preferentially along the c and a axes respectively the branching of a new arm is explained by nucleation on an old arm with a different preferred growth direction the preferential growth is discussed in terms of a significant chemical potential gradient of the cordierite component this has been preserved in the mineral zoning observed in the matrix around the cordierite porphyroblast

triassic paragonite and garnet bearing epidote amphibolite from the hida mountains japan paragonite and garnet bearing high grade epidote amphibolite pgea in the ise area of the hida mountains japan is characterized by the high pressure hp epidote amphibolite facies parageneses m1 garnet hornblende clinozoisite paragonite quartz rutile paragonite and garnet of the peak m1 stage are locally replaced by retrograde albite oligoclase and chlorite m2 respectively phase equilibria constrain peak metamorphic conditions of p 1 1 1 4 gpa and t 530 570 c and a decompressional p t path for this rock mineral parageneses of prograde epidote amphibolite facies are comparable to some hp rocks from the hongan region of western dabie but differ from other hp mafic schists with cooling ages of c 330 ma in the hida mountains new paragonite k ar dating for the pgeayields a triassic cooling event at 210 ma that is coeval with regional cooling and exhumation of the sulu dabie qinling sdq belt both petrological and geochronological data of the triassic hp epidote amphibolite in hida mountains support our earlier hypothesis that the sdq belt extends across the korean peninsula to sw japan

pyrometamorphic processes at the magma hydrothermal system interface of active volcanoes evidence from buchite ejecta of stromboli aeolian islands italy pyrometamorphic ejecta erupted during recent paroxysmal explosions and hydrothermally altered volcanic and subvolcanic rocks from stromboli volcano aeolian islands italy were studied by combined polarizing microscopy electron microprobe scanning electron microscope x ray diffraction transmission electron microscope and whole rock inductively coupled plasma optical emission spectrometry mass spectrometry analysis the pyrometamorphic ejecta are compositionally heterogeneous at the macroand micro scale and are classified as buchites that is glass coupled with a high temperature low pressure modal mineralogy three distinct facies i e cordierite plagioclase mullite plagioclase palisade and tridymite clinopyroxene are recognized among the buchites whose bulk rock chemistry is compatible with aluminousto silica rich protoliths abundant mineral growth e g plagioclase palisades and clinopyroxene coronae occurs at the contact between the ejecta and the crystal rich host shoshonitic basalt which typically coats the pyrometamorphic blocks mineral constraints pseudoporphyritic microstructures plagioclase relict phenocrysts and major and trace element compositions strongly support the origin of the buchite ejecta as hydrothermally altered rocks from thevancori edifice a period of activity spanning 410 kyr which underwent high temperature low pressure contact metamorphism in the uppermost magmatic system of an active island arc volcano such as stromboli volcanic and subvolcanic rocks usually undergo alteration processes induced by acid sulphate hydrothermal systems the circulation of acidic fluids results in leaching of the stromboli rocks in the upper part of the volcano edifice and depending on the ph temperature and exposure time to the hydrothermal fluids production of different alteration facies the hydrothermally altered stromboli rocks show facies consistent with argillic to silicic alteration containing abundant hydrous sulphate and hydroxy sulphate minerals such as the alunite group minerals hexahydrite millosevichite pickeringite and kieserite the hydrothermally altered wall rocks heated by contact with the basaltic magma of the feeder dyke system of stromboli can easily undergo pyrometamorphic processes inducing partial melting and subsolidus crystallization of the volcanic protoliths this results in the development of buchite rocks at the magma hydrothermal system interface

geology and tectonics of japanese islands a review the key to understanding the geology of asia abstract the age of the major geological units in japan ranges from cambrian to quaternary precambrian basement is however expected as the provenance of by detrital clasts of conglomerate detrital zircons of metamorphic and sedimentary rocks and as metamorphic rocks intruded by 500 ma granites although rocks of paleozoic age are not widely distributed rocks and formations of late mesozoic to cenozoic can be found easily throughout japan rocks of jurassic age occur mainly in the jurassic accretionary complexes which comprise the backbone of the japanese archipelago the western part of japan is composed mainly of cretaceous to paleogene felsic volcanic and plutonic rocks and accretionary complexes the eastern part of the country is covered extensively by neogene sedimentary and volcanic rocks during the quaternary volcanoes erupted in various parts of japan and alluvial plains were formed along the coastlines of the japanese islands these geological units are divided by age and origin i e paleozoic continental margin paleozoic island arc paleozoic accretionary complexes mesozoic to paleogene accretionary complexes and cenozoic island arcs these are further subdivided into the following tectonic units e g hida oki unazuki hida gaien higo hitachi kurosegawa south kitakami nagato renge nedamo akiyoshi ultra tamba suo maizuru mino tamba chichibu chizu ryoke sanbagawa and shimanto belts the geological history of japan commenced with the breakup of the rodinia super continent at about 750 ma at about 500 ma the paleo pacific oceanic plate began to be subducted beneath the continental margin of the south china block since then proto japan has been located on the convergent margin of east asia for about 500 ma in this tectonic setting the most significant tectonic events recorded in the geology of japan are subduction accretion paired metamorphism arc volcanism back arc spreading and arc arc collision the major accretionary complexes in the japanese islands are of permian jurassic and cretaceous paleogene age these accretionary complexes became altered locally to low temperature and high pressure metamorphic or high temperature and low pressure metamorphic rocks medium pressure metamorphic rocks are limited to the unazuki and higo belts major plutonism occurred in paleozoic mesozoic and cenozoic time early paleozoic cambrian igneous activity is recorded as granites in the south kitakami belt late paleozoic igneous activity is recognized in the hida belt during cretaceous to paleogene time extensive igneous activity occurred in japan the youngest granite in japan is the takidani granite intruded at about 1 2 ma during cenozoic time the most important geologic events are back arc opening and arc arc collision the major back arc basins are the sea of japan and the shikoku and chishima basins arc arc collision occurred between the honshu and izu bonin arcs and the honshu and chishima arcs

origin of sector trilling in cordierite in daimonji hornfels kyoto japan sector trilling of cordierite in hornfels in the inner part of a contact aureole at daimonji japan is a new type which consists not only of six 100 sectors a sectors forming trilling but also of 001 sectors c sectors and high index sectors h sectors complex twins within and among these sectors were studied from a viewpoint of a pseudo twin the complex texture originated from both growth and transformation processes the c sector consists of three groups of domains which are related by a pseudo twin this intrasector pseudo twin indicates that the initial phase of the c sector was hexagonal cordierite indialite which later transformed to orthorhombic the a sector is related to adjacent sectors by a rotation of 120 around the c axis resulting in an intersector pseudo twin the a sector is interpreted to have formed by overgrowth of orthorhombic cordierite on prism faces of indialite the h sector with the dendritic texture is also interpreted to have grown as orthorhombic cordierite in hornfels in the middle part of the aureole cordierites with sector trilling often coexist with single crystals of cordierite and the sector trilling has no c and h sectors this trilling type suggests that nucleation of indialite was subsequently followed by growth of orthorhombic cordierite in its stable field

thermal structure of the venus atmosphere in the middle cloud layer thermal structure measurements obtained by the two vega balloons show the venus middle cloud layer to be generally adiabatic temperatures measured by the two balloons at locations roughly symmetric about the equator differed by about 6 5 kelvins at a given pressure the vega 2 temperatures were about 2 5 kelvins cooler and those of vega 1 about 4 kelvins warmer than temperatures measured by the pioneer venus large probe at these levels data taken by the vega 2 lander as it passed through the middle cloud agreed with those of the vega 2 balloon study of individual frames of the balloon data suggests the presence of multiple discrete air masses that are internally adiabatic but lie on slightly different adiabats these adiabats for a given balloon can differ in temperature by as much as 1 kelvin at a given pressure

indialite from unazuki pelitic schist japan and its transition texture to cordierite indialite hexagonal cordierite has been found in a cordierite vein of polymetamorphosed pelitic rock a member of the unazuki schists in hida terrane central japan most of the indialite grains show intergrowth textures with cordierite of orthorhombic symmetry this is the second identification of indialite since the first one from a fused sediment in india

fe rich cordierites from acid volcanic rocks an optical and x ray single crystal structure study low cordierites from volcanic rocks of tuscany italy lipari italy and of the cerberean cauldron australia were investigated both single crystal structure refinements and optical data indicate that the italian samples contain only low concentrations of volatiles 0 4 and provide additional information about the crystal structure of fe rich cordierites with increasing fe mg substitution the mean t11 al o distance decreases slightly which is probably not caused by substitution of smaller cations on t11 but by angular distortion of the tetrahedron

experimental studies on the mobility of lanthanides accompanying alteration of andesite by acidic hot spring water abstract the mobility of lanthanides lns accompanying interactions of powdered andesitic rocks with acidic hot spring water and acidic hot spring water vapor steam was studied in the experiments set up in the field at the early stage of rock alteration light lns were slightly easier to be leached out by acidic hot spring waters from andesitic rocks than heavy lns this result qualitatively agreed with the result obtained in the previous experiments carried out in the laboratory it was also found that the ln abundance patterns ln patterns obtained by normalization with ln contents of the original rock showed slightly positive eu anomalies at the early stage of rock alteration and turned to show negative eu anomalies and the extent of negative anomaly monotonously increased as rock alteration proceeded this trend in the direction of eu anomaly was correlated to the degrees of decompositions of major rock forming minerals and interstitial materials in the rock at the earliest stage of rock alteration in acidic environments the interstitial materials with relatively low eu contents were decomposed which resulted in the positive eu anomaly in the following stage feldspar that had a relatively high eu content was decomposed which led to the negative eu anomaly

40ar 39ar mineral ages from the oki metamorphic complex oki dogo southwest japan implications for regional correlations abstract the oki metamorphic complex exposed in the oki dogo islands consists predominantly of psammitic and pelitic gneisses with subordinate amphibolite and rare calcareous gneiss the oki gneisses were regionally metamorphosed to general amphibolite facies conditions with local development of granulite facies assemblages peak metamorphic conditions of c 800 c have been suggested hornblende concentrates from amphibolites collected within the oki metamorphic complex record 40 ar 39 ar isotope correlation ages of 199 192 ma these are interpreted to date the post metamorphic cooling through temperatures required for intracrystalline retention of argon c 500 c muscovite concentrates record 40 ar 39 ar plateau ages of 167 168 ma these are interpreted to date post metamorphic cooling through appropriate closure temperature of muscovite c 400 375 c combined with the previously reported geochronological data the oki metamorphic complex appears to have experienced peak metamorphic conditions at c 250 ma subsequently it cooled and was exhumed at the earth s surface at c 90 ma with cooling rate of c 5 c ma the oki metamorphic complex records a similar prograde metamorphic event as the hida metamorphic complex exposed in central japan the cooling and exhumation rates of the hida metamorphic complex were significantly more rapid compared with the oki metamorphic complex and they were exhumed with extensively intruded jurassic granites funatsu granites

timing of mylonitization in the funatsu shear zone within hida belt of southwest japan implications for correlation with the shear zones around the ogcheon belt in the korean peninsula abstract the funatsu shear zone is an early mesozoic dextral ductile shear zone located in the hida belt of southwest japan consisting mainly of granite mylonites the jurassic funatsu granites intrude the hida metamorphic rocks and the granite mylonites the shrimp u pb zircon ages of granite mylonites in the funatsu shear zone around the tateyama area are 250 2 2 ma and 240 2 ma shrimp u pb zircon age of the okumayama granodiorite which is a member of the funatsu granites and which intrudes the granite mylonite is 191 3 ma we interpret that the timing of mylonitization in the funatsu shear zone to be after 240 ma and prior to 191 ma triassic to early jurassic and possibly around 215 211 ma late triassic corresponding to the k ar ages of hornblende in basic inclusions of the granite mylonite in the korean peninsula dextral ductile shear movement occurred in the cheongsan shear zone of south central ogcheon belt during middle to late triassic time accompanied by the intrusion of jurassic daebo granites which are correlated to the funatsu granites the similarities in geology deformation characteristics timing of mylonitization and paleogeographic location suggest that the funatsu shear zone can be correlated to the cheongsan shear zone

geochemistry of holocene cryptotephras from the north iceland shelf md99 2269 intercalibration with radiocarbon and palaeomagnetic chronostratigraphies tephra grain counting morphology and geochemistry in the 150 1000 m size fraction were used to identify 22 individual tephra horizons and one visible tephra layer saksunarvatn from postglacial sediment of the north iceland shelf core md99 2269 66 37 53 n 20 51 16 w water depth 365 m length 2533 cm from the reykjafjardarall basin is constrained at the base by the vedde tephra c 12 000 cal yr bp geochemical analyses and stratigraphical position of the 22 tephra horizons were used to identify the following cryptotephras kol 1372 ad 1372 hekla 1104 ad 1104 snaefellsnes 1 c 1790 cal yr bp hekla 3 c 2970 cal yr bp hekla 4 c 4230 cal yr bp tv 5 c 6860 cal yr bp and suduroy c 8070 cal yr bp a tephra of the same geochemistry as kol 1372 was found near the base of the core and is here named kol3 2269 11 000 cal yr bp eleven additional cryptotephras were geochemically typed to their respective icelandic volcanic centres of origin and their ages constrained four teph

origin of high silica liquids at stromboli volcano aeolian islands italy inferred from crustal xenoliths high silica igneous xenoliths granophyre and obsidian fragments with sio2 ca 75 wt and high silica glass sio2 between ca 64 and 75 wt within glass bearing tonalitic and dioritic xenoliths have been discovered at stromboli they are well beyond the silica range of the volcanic rocks erupted during the subaerial activity of the volcano the granophyre and the obsidian fragments occur within the petrazza pyroclastics high k andesite pumiceous scoriae of the paleostromboli i period 61 ka whereas the glass bearing tonalites and diorites are hosted in the omo basaltic andesite lava flows of the paleostromboli ii period 64 55 ka the obsidian represents an extremely evolved liquid derived from low pressure fractional crystallization of high k calc alkaline magmas of stromboli coupled with minor assimilation of upper crust or terrigenous sediments the other studied high silica products have an anatectic origin the granophyre composition is compatible with a genesis by low degree melting of leucotonalites similar to some calabrian arc lithotypes partial melting of crustal rocks from the stromboli basement is also demonstrated by interstitial glass in the tonalite and diorite xenoliths textural evidence and the presence of variable glass compositions suggest that in these plutonic xenoliths the melt chemistry was controlled by dehydration melting of biotite and non modal melting of local mineralogy high degree undercooling of granophyre melt and of the partially melted xenoliths is consistent with rapid rise of the host magmas leading to eruption whether partial melting was initiated during stoping and transport of xenoliths within the rising magma or in situ during magma storage within the crust has not been unequivocally established

subdivision of the hida metamorphic complex central japan and its bearing on the geology of the far east in pre sea of japan time abstract petrological and structural characteristics of the regional metamorphic rocks in south west japan and in the korean peninsula make it possible to speculate on the geological correlation between japan and the asian continent prior to the opening of the sea of japan a typical marginal sea the hida metamorphic complex situated on the sea of japan side of southwest japan is subdivided into two distinct geological units the hida gneisses and the unazuki schists the hida gneisses are polymetamorphosed precambrian rocks while the unazuki schists occurring on its eastern and southern sides are low to medium grade metamorphic rocks originating from upper paleozoic deposits sedimentary facies and other geological features suggest that the hida gneisses were the basemen of the unazuki schists consequently the geotectonic framework of southwest japan is revised from north to south as follows hida gneiss region precambrian massif unazuki zone late permian intermed p t metamorphic belt circum hida tectonic zone mid to late paleozoic melange zone mino tanba terrain late paleozoic to mesozoic geosynclinal region and so on the unazuki zone is similar to the okcheon zone in the korean peninsula in respect of age lithology and biofacies of sedimentary rocks as well as the age and type of regional metamorphism furthermore the hida gneisses and the gyeonggi polymetamorphosed precambrian gneisses in the korean peninsula are similar in the apparent baric type of metamorphism radiometric ages and the relationship with the overlying metamorphosed formations the similarity of the geotectonic frameworks of southwest japan and the korean peninsula suggests that the unazuki zone and the okcheon zone once formed a continuous geotectonic unit thus we have a new geological coordinate in reconstructing the paleogeography prior to the opening of the sea of japan

a new high resolution holocene tephra stratigraphy in eastern iceland improving the icelandic and north atlantic tephrochronology a new and improved holocene tephra stratigraphy and tephrochronological framework for eastern and northern iceland is presented investigations of a sediment sequence from lake logurinn have revealed a comprehensive tephra record spanning the last 10 200 years a total of 157 tephra layers have been identified whereof 149 tephra layers have been correlated to its source volcanic system using geochemistry stratigraphy and age fifteen layers have chemical composition of two affinities that possibly represent two very closely spaced eruptions thus these 157 tephra layers are believed to represent 172 explosive eruptions nineteen tephra marker layers have been identified in the lake logurinn record g1922 a1875 v1477 v1410 h1636 k1625 o1362 g1354 k1262 v874 hrafnkatla sn 1 grakolla hy h3 h4 ho ll1755 and reitsvik 8 tephra markers new potential tephra markers are the silicic askja l 9400 cal bp the low titanium basalt layers ll 1774 10 150 cal bp and ll 1755 9990 cal bp assigned to veidivotn bardarbunga and the tephra layers ll 1527 8 7850 cal bp ll 911 2 2370 cal bp ll 908 4 2350 cal bp ll 781 9 1930 cal bp ll 644 4 1480 cal bp not yet correlated to a source volcanic system a silicic tephra marker layer reitsvik 8 correlated to the fosen tephra in norway has been identified in lake logurinn the lake logurinn tephra record has been connected and integrated with the icelandic terrestrial tephrochronology and stratigraphy through 102 tephra layers the marine tephra stratigraphy through 39 layers and overseas through 9 tephra layers this record is the first high resolution tephra stratigraphical and chronological framework for the holocene in eastern iceland as well as the most detailed and continuous record and has considerable potential to serve as a key section or a stratotype for the holocene in eastern iceland and the north atlantic

fluid circulation at stromboli volcano aeolian islands italy from self potential and co2 surveys this work addresses the study of fluid circulation of the stromboli island using a dense coverage of self potential sp and soil co2 data a marked difference exists between the northern flank and the other flanks of the island the northern flank exhibits 1 a typical negative sp altitude gradient not observed on the other flanks and 2 higher levels of co2 the general sp pattern suggests that the northern flank is composed of porous layers through which vadose water flows down to a basal water table in contrast to the other flanks where impermeable layers impede the vertical flow of vadose water in the sciara del fuoco and rina grande le schicciole landslide complexes breccias of shallow gliding planes may constitute such impermeable layers whereas elsewhere poorly permeable fine grained pyroclastites or altered lava flows may be present this general model of the flanks also explains the main co2 patterns concentration of co2 at the surface is high on the porous north flank and lower on the other flanks where impermeable layers can block the upward co2 flux the active upper part of the island is underlain by a well defined hydrothermal system bounded by short wavelength negative sp anomalies and high peaks of co2 these boundaries coincide with faults limiting ancient collapses of calderas craters and flank landslides the hydrothermal system is not homogeneous but composed of three main subsystems and of a fourth minor one and is not centered on the active craters the latter are located near its border this divergence between the location of the active craters and the extent of the hydrothermal system suggests that the internal heat sources may not be limited to sources below the active craters if the heat source strictly corresponds to intrusions at depth around the active conduits the geometry of the hydrothermal subsystems must be strongly controlled by heterogeneities within the edifice such as craters caldera walls or gliding planes of flank collapse as suggested by the correspondence between sp co2 anomalies and structural limits the inner zone of the hydrothermal subsystems is characterized by positive sp anomalies indicating upward movements of fluids and by very low values of co2 emanation this pattern suggests that the hydrothermal zone becomes self sealed at depth thus creating a barrier to the co2 flux in this hypothesis the observed hydrothermal system is a shallow one and it involves mostly convection of infiltrated meteoric water above the sealed zone finally on the base of co2 degassing measurements we present evidence for the presence of two regional faults oriented n41 and n64 and decoupled from the volcanic structures

high temperature rapid pyrometamorphism induced by a charcoal pit burning the case of ricetto central italy bulk chemistry and mineralogy of the peculiar rock of ricetto carseolani mts central apennines italy was studied to resolve its controversial origin igneous dyke or anthropic product this hybrid rock consists of a colorless felsic component made up of glass plus quartz and a brown femic component made up of fans and spherulites of diopside calcic plagioclase wollastonite and melilite textural relationships indicate very rapid cooling and immiscibility phenomena the bulk chemistry of the rock is the same as that of the surrounding siliciclastic sandstone the 14c analysis of a coal fragment from bottom of the body yields the conventional age of 227 50 years the ricetto occurrence is an example of pyrometamorphism of a siliceous limestone induced by a charcoal pit burning the small size of the heat source at ricetto caused an intense but short lived melting of the country rock prograde metamorphism caused a temperature increase up to 1 000 1 100 c when melilite crystallization conditions were reached at appreciable p co2 and high f o2 melting occurred in a close system represented by the simplified equation 3cal 16 5qtz ms bt mel melt 2h2o 3co2 0 5o2 diopside calcic plagioclase wollastonite formed by melilite breakdown during rapid cooling through the reaction 6mel 6qtz 0 5o2 3di 2an 7wo liquid immiscibility caused the separation between the felsic melt component and the femic melilite bearing component immiscibility was characterized by different fractionation of alumina and alkalies between these two phases differences in bulk glass and mineral chemistry between the ricetto and other melilite bearing pyrometamorphic rocks can be attributed mainly to different protoliths

zincian staurolite in the dry river south volcanic hosted massive sulfide deposit northern queensland australia an assessment of its usefulness in exploration abstract staurolite from the dry river south volcanic hosted massive sulfide deposit in northern queensland australia is enriched in zno 2 5 6 8 only within the massive sulfide lens or in highly pyritic biotite chlorite schist just below the massive sulfide lens in the footwall alteration zone staurolite zno levels vary between 0 4 and 1 3 whereas in hanging wall metagraywackes and metapelites the zno content is mainly below 1 0 as staurolite from metapelitec rocks contains up to 7 9 zno high zno levels in staurolite do not necessarily indicate a relationship to zn rich massive sulfide staurolite grains from the dry river south amd other massive sulfide lenses have low tio2 concentrations mainly 0 4 the low concentration of tio2 in staurolite from the massive sulfide lens results from the low initial ti concentration in exhalative ores high zno and low tio2 values are indicative of staurolite associated with zn rich massive sulfide zincian staurolite is a potential exploration indicator at both prospect and reconnaissance scales at the prospect scale zinc levels have potential in distinguishing true from false gossans distinguishing low grade portions of massive sulfide lenses from barren massive pyrite bodies and characterizing alteration zones at the reconnaissance scale staurolite can be collected in the heavy mineral fraction of stream sediments and multiple grains can be analyzed rapidly using modern electron microprobes

the summit hydrothermal system of stromboli new insights from self potential temperature co2 and fumarolic fluid measurements with structural and monitoring implications accurate and precisely located self potential sp temperature t and co2 measurements were carried out in the summit area of stromboli along 72 straight profiles sp data were acquired every metre and t data every 2 5 m co2 concentrations were acquired with the same density as t but only along seven profiles the high density of data and the diversity of the measured parameters allows us to study structures and phenomena at a scale rarely investigated the shallow summit hydrothermal activity pizzo fossa area is indicated by large positive sp t and co2 anomalies these anomalies are focused on crater faults suggesting that the fracture zones are more permeable than surrounding rocks at stromboli the analysis of the distribution of these linear anomalies coupled with the examination of the geologic photographic and topographic data has led us to propose a new structural interpretation of the summit of stromboli this newly defined structural framework comprises 1 a large pizzo circular crater about 350 m in diameter 2 a complex of two concealed craters nested within the pizzo crater the large and the small fossa craters thought to have formed during the eruption of the pizzo pyroclastites unit the small fossa crater is filled with highly impermeable material that totally impedes the upward flow of hydrothermal fluids and 3 the present complex of active craters on the floor of the fossa short wavelength sp lows are organized in drainage like networks diverging from the main thermal anomalies and converging toward the topographic low in the fossa area inside the small fossa crater they are interpreted as the subsurface downhill flow of water condensed above the thermal anomalies we suspect that water accumulates below the small fossa crater as a perched water body representing a high threat of strong phreatic and phreatomagmatic paroxysms t and co2 anomalies are highly correlated the two types of anomalies have very similar shapes but the sensitivity of co2 measurements seems higher for lowest hydrothermal flux above t anomalies a pronounced high frequency sp signal is observed isotopic analyses of the fluids show similar compositions between the gases rising through the faults of the pizzo and large fossa craters this suggests a common origin for gases emerging along different structural paths within the summit of stromboli a site was found along the large fossa crater fault where high gas flux and low air contamination made gas monitoring possible near the active vents using the alkaline bottle sampling technique

a precisely dated lake level rise marked by diatomite formation in northeastern ireland the intercorrelation of palaeoclimate events from various studies is often hindered by a lack of precise chronological control tephra isochrons can overcome this problem by providing direct site linkages this paper outlines a study of holocene peat and diatomite deposits that accumulated within the floodplain of lough neagh northern ireland the icelandic hekla 4 tephra has been identified at the base of diatomite deposits at a number of sites and provides firm dating evidence for a widespread flooding event in the area at ca 2300 bc the evidence is consistent with other studies in ireland and elsewhere for increased wetness at this time the results demonstrate that the terrestrial deposits around lough neagh contain an important record of holocene lake level change dendrochronological evidence from the lough neagh area provides additional information about lake level fluctuations over the past two millennia copyright 2004 john wiley sons ltd

a refined garnet biotite fe mg exchange geothermometer and its application in amphibolites and granulites a new formulation of garnet biotite fe mg exchange thermometer has been developed through statistical regression of the reversed experimental data of ferry and spear input parameters include available thermo chemical data for quaternary fe mg ca mn garnet solid solution and for excess free energy terms associated with mixing of al and ti in octahedral sites in biotite solid solution the regression indicates that fe mg mixing in biotite approximates a symmetrical regular solution model showing positive deviation from ideality withw femg bi 1073 490 cal mol h r and s r for the garnet biotite exchange equilibrium were derived to be 4301 cal and 1 85 cal respectively the resultant thermometer gives consistent results for rocks with a much wider compositional range than can be accommodated by earlier formulations

river response to rapid holocene environmental change evidence and explanation in british catchments macklin m g jones a f lewin j 2010 river response to rapid holocene environmental change evidence and explanation in british catchments quaternary science reviews 29 13 14 1555 1576 sponsorship welsh assembly government and the higher education funding council for wales for funding this study through its support of the centre for catchment and coastal research at aberystwyth university

glass bearing crustal xenoliths buchites erupted during the recent activity of stromboli aeolian islands abstract three xenoliths erupted as ejecta during recent violent explosion of stromboli volcano aeolian islands were investigated in this paper they consist of high temperature mineral association cordierite hercynite spinels sillimanite plagioclase mullite corundum and abundant glass 10 70 vol and may be classified as buchites the peraluminous composition of the xenoliths their trace element distribution and ree patterns support their origin from granulite and amphibolite facies metapelites of the calabrian continental crust which is considered the crystalline basement beneath stromboli buchites have an isotopic composition comparable to that of stromboli extrusives and significantly different from that of the calabrian basement the glass is generally colourless and has a si al alkali rich composition except for one sample where a fe mg ca rich reddish brown glass also occurs these two kinds of glass show complicated textures where patches of reddish brown glass are often surrounded by plagioclase and or cordierite or forms streaks and swirls with the colourless glass cordierite plagioclase and oxides have different compositions according to their position in the xenoliths ca rich plagioclase an72 95 mg poor cordierite mg values 47 66 and al rich spinels are in the inner portions of the xenoliths and associated with colourless glass on the contrary close to the contact with the host lava or associated with coloured glass cordierite shows higher mg values ti fe bearing oxides occur and plagioclase is chemically similar to the basalt phenocrysts an66 71 the abundant and fresh glass and the idiomorphic shape of the high temperature minerals suggest that the xenoliths were hold in the basaltic magma before its extrusion for a significant time to allow their partial or nearly complete melting and subsequent nucleation and growth of new phases during this stage the interaction between the anatectic liquid and the basaltic magma affected the original isotopic composition of the xenoliths and in some cases produced glass and mineral phases cordierite plagioclase and oxides with different composition

pyrometamorphism and the contamination of basaltic magma at tieveragh co antrim a tertiary dolerite plug at tieveragh co antrim cuts old red sandstone tuffaceous sedimentary rocks glassy buchites have formed by disequilibrium partial melting induced by convective heat transfer from the basaltic magma variation in bulk rock chemistry has produced glasses coexisting with variable proportions of pyroxene cordierite ilmenite hematite magnetite mullite plagioclase and alkali feldspar mixing of the basaltic magma with acid melt illustrates how up to 10 contamination may occur without radically altering the course of crystallization mineral geothermometers indicate maximum temperatures at the contact around 1100 c falling to only 940 at 10 m

onset of the persistent activity at stromboli volcano italy stromboli known worldwide as the lighthouse of the mediterranean is commonly believed to have been in a state of persistent activity for the past 2000 2500 years however historical sources older than 1000 a d are not accurate enough to assess if the activity of the volcano was exactly the same as we see at present in order to attempt to identify the onset of the present eruptive regime and assess if it has been maintained with the same characteristics through time stratigraphic and radiometric studies of the recent tephra deposits were undertaken up to 4 m deep stratigraphic trenches dug at a height of approximately 500 m on the ne flank of the volcano exposed a conformable tephra pile containing charcoal fragments one of the most interesting finds was the discovery of a 7 cm thick weathered bed rich in organic matter thin palaeosol approximately 3 m below the surface the sequence underneath the palaeosol consists of decimetre thick lapilli fallout beds alternating with ash deposits bearing small charcoals with calibrated ages of between the fourth century b c and the first century a d the sequence above the palaeosol is charcoal free and consists of coarse ash deposits with discrete centimetre thick lapilli fallout beds composed of crystal poor golden pumice and subordinate crystal rich black scoriae similar to scoria pumice pairs emitted during the more energetic explosions of the present day activity the data collected indicate that between the third and seventh centuries a d after a period of quiescence the activity resumed with an eruptive style identical to the present one we conclude that the lighthouse of the mediterranean actually began its activity in a period much later than previously thought

tectonometamorphic evolution of the permo triassic songrim indosinian orogeny evidence from the late paleozoic pyeongan supergroup in the northeastern taebaeksan basin south korea the deformed and metamorphosed middle pennsylvanian to early triassic rocks of the pyeongan supergroup occurring in northeastern flank of the paleozoic taebaeksan basin east central south korea record the impact of the late permian triassic songrim indosinian collisional orogeny in the eastern eurasia margin analysis of meso and microstructures and their relationship with porphyroblast growth has revealed that these metasedimentary rocks were affected by four deformation events d1 d4 during the polyphase deformations successive foliations with alternately steep s1 and s3 and flat lying s2 and s4 orientations were produced with growth of chloritoid andalusite and kyanite porphyroblasts during d1 and d2 and growth of garnet staurolite and andalusite porphyroblasts during d3 and d4 shrimp u pb detrital zircon ages 330 310 ma from metapelites in the oldest unit of the pyeongan supergroup in the study area combined with the previous data on sandstone compositions indicate magmatic activity that was contemporaneous with the initial deposition of the pyeongan supergroup this also suggests that the pyeongan supergroup was deposited in an arc related foreland basin at an active continental margin during the late carboniferous and permian time two contractional deformation events d1 and d3 and two events related to gravitational flattening d2 and d4 along with barrovian type medium pressure regional metamorphism may have resulted from the late permian triassic songrim orogeny related to collision between the north and south china blocks and or collision between the eastern eurasia margin and the proto japan terrane

biogenic versus metamorphic origins of diverse microtubes in 2 7 gyr old volcanic ashes multi scale investigations abstract titanite bearing microtubes in metabasalts have been interpreted as evidence for early microbial life thriving in the oceanic crust up to 3 5 ga ago based on similarities with microtubular pitting occurring in modern volcanic glass an alternative abiogenic origin as ambient inclusions trails aits has been debated but textural evidence such as the absence of diagnostic terminal inclusions was used to discard this possibility here we describe a variety of microtubes occurring in pyroclastic tuff of the 2 72 ga tumbiana formation western australia some of which resemble titanite filled microtubes reported in metamorphosed archean pillow basalts to assess the origin of the tumbiana microtubes we investigated their structure and chemistry and their root zone down to the sub micrometer scale using a combination of raman microspectroscopy scanning electron microscopy sem focused ion beam fib milling and scanning transmission electron microscopy stem coupled with energy dispersive x ray spectrometry edxs we report four types of microtubes type 1 comprises calcite microtubes type 2 comprises aits showing terminal pyrite and trails with negative crystal shapes type 3 comprises titanite microtubes in chlorite displaying morphologies similar to those reported in 3 5 ga old archean lavas at the sub micrometer scale they display a dendritic structure depending on their localization type 3 microtubes have been divided in three main sub types i type 3a extends in pores filled by chloritized cement ii type 3b occurs in pyroclasts and iii type 3c overgrows and thus post dates type 2 aits type 4 comprises titanite microtubes confined to quartz and calcite rims types 3 and 4 microtubes are terminated by sub micrometric carbonaceous and or mineral inclusions altogether these features suggest that the tumbiana titanite microtubes have formed as dendritic aits associated with displacement of mineral and or organic inclusions in pyroclasts and in surrounding void filling cements during recrystallization they are therefore unlikely to represent relics of the activity of early microbial life rather abiotic features formed in the presence of organic matter during burial metamorphism in that sense they may represent some sort of indirect evidence for life

crustal development of the hida belt japan evidence from nd sr isotopic and chemical characteristics of igneous and metamorphic rocks abstract chemical and sr nd isotopic investigations were performed on the igneous and metamorphic rocks in the hida belt central japan to clarify their ages and possible sources and to provide constraints on the crustal evolution of the eastern margin of the asian continent igneous rocks of three main stages in the hida belt represented by the late silurian amphibolites first stage the middle carboniferous mafic dikes second stage and the late triassic to early jurassic granite gabbro plutons third stage show alkaline to calc alkaline chemical affinity major and trace element characteristics show that the three stages of igneous rocks were emplaced in a continental margin or continental arc environment the mafic igneous rock suites have relatively high e nd 0 5 to 5 5 and low 87 sr 86 sr 0 7049 to 0 7061 values indicating their origin from upper mantle sources though the third stage granitoids contain recycled crustal components the hida gneisses of clastic origin show two groups of model ages t dm middle proterozoic 1 4 2 2 ga and late proterozoic to early paleozoic 0 55 0 74 ga consistent with geological geochemical and radiometric age data are that the sedimentation and basaltic volcanism occurred in early to middle paleozoic and the protoliths with middle proterozoic model ages are detritals from the proterozoic continental provenances a synthesis of available geological and geochemical data for the basement metamorphic and igneous rocks in eastern asia suggests two possibilities for the paleozoic to early mesozoic history of the hida belt 1 the hida belt was formed at the eastern margin of the north china block with later evolution as a suture zone between the north and south china blocks or 2 it evolved as a part of the east central asian orogenic belt ecaob to the north

pressure temperature trajectory of the sanbagawa metamorphism deduced from garnet zoning abstract most garnets in a small volume of the pelitic sanbagawa schists nucleated simultaneously grew and then ceased with their growth maintaining near equilibrium with coexisting minerals such as chlorite and biotite during the prograde metamorphism chemical trends of zoned garnets systematically shift from the pyrope poor to pyrope rich portions in a ternary mn fe mg system in order of ascending metamorphic grade a ternary mn fe mg model system suggests that the higher grade garnets started to grow at lower pressures and higher temperatures than the lower grade ones during prograde metamorphism it follows that high grade metamorphism took place at lower pressures in the garnet to oligoclase biotite zones of the sanbagawa metamorphic terrain in central shikoku

evidence of a partial melt zone beneath stromboli volcano italy from inversion of teleseismic receiver functions teleseismic body waves from broadband seismic stations are used to investigate the crustal and uppermost mantle structure of stromboli volcano through inversion of the receiver functions rfs first we computed rfs in the frequency domain using a multiple taper spectral correlation technique then the non linear neighbourhood algorithm was applied to estimate the seismic shear wave velocity of the crust and uppermost mantle and to define the main seismic velocity discontinuities the stability of the inversion solution was tested using a range of initial random seeds and model parameterizations a shallow moho present at depth of 14 8 km is evidence of a thinned crust beneath stromboli volcano however the most intriguing and innovative result is a low s velocity layer in the uppermost mantle below 32 km the low s velocity layer suggests a possible partial melt region associated with the volcanism as also recently supported by tomographic studies and petrological estimations

progressive sequence of reactions of the ryoke metamorphism in the yanai district southwest japan the formation of cordierite the compositions of biotite and muscovite were examined in terms of the paragenesis and the metamorphic grade in low to medium grade pelitic rocks of the ryoke metamorphism in the yanai district southwest japan the biotite and muscovite that coexist with k feldspar have a higher k component in an a kf diagram than those in rocks lacking k feldspar this fact reflects an increase in the k2o content in muscovite but in biotite it reflects an increase of not only the k2o content but also of the octahedral vacancy at higher metamorphic grade beyond the cordierite isograd where cordierite coexists with neither chlorite nor k feldspar the biotite shows an increase in illite k aliv xii 1 si 1 and tschermak components alvi aliv r 1 si 1 where xii and r denote the interlayer vacancy and fe mg mn respectively a reaction to define the cordierite isograd is proposed by treating this chemical change as being responsible for the first appearance of cordierite i e k al poor biotite phengitic muscovite k al rich biotite cordierite quartz water by treating this as a key reaction in medium grade metamorphism a set of reaction in a progressive metamorphism is established for the ryoke metamorphism a typical low pressure type metamorphism some textures in one of the high grade areas the k feldspar cordierite zone suggest that a further two prograde reactions have taken place i e andalusite biotite quartz cordierite k feldspar water and andalusite sillimanite quartz cordierite k feldspar water this implies that this zone probably has a p t path involving isobaric heating

the role of the grain boundary at chemical and isotopic fronts in marble during contact metamorphism carbon and oxygen isotopic profiles around a low pressure metasomatic wollastonite reaction front in a marble of the hida metamorphic terrain central japan display typical metamorphic fluid enhanced isotopic zonations isotopic profiles obtained from detailed microscale analyses perpendicular to the chemical reaction front in calcite marble show that diffusion enhanced isotopic exchange may control these profiles carbon and oxygen isotopic behaviour in grain boundaries is remarkably different oxygen isotopic troughs 18o depleted rims around the calcite grain boundaries are widely observed in this contact aureole demonstrating that diffusion of oxygen in calcite grain boundary dominates over lattice diffusion in calcite in contrast no difference is observed in carbon isotopic profiles obtained from grain cores and rims there is thus no specific role of the grain boundary for diffusion of carbonic species in the metamorphic fluid during transportation carbon chemical species such as co2 and co3 ions in metamorphic fluid migrate mainly through lattice diffusion the carbon and oxygen isotope profiles may be modelled by diffusion into a semi infinite medium empirically lattice diffusion of oxygen isotopes is almost six times faster than that of carbon isotopes and oxygen grain boundary diffusion is ten times faster than oxygen lattice diffusion oxygen isotopic results around the wollastonite vein indicate that migration of the metamorphic fluid into calcite marble was small and was parallel to the aquifer from the stability of wollastonite and the attainment of oxygen isotopic equilibrium we suggest that diffusion of oxygen occurred through an aqueous fluid phase the timescale of formation of the oxygen isotopic profile around the wollastonite vein is calculated to be about 0 76 106 years using the experimentally determined diffusion constant

dynamics of magma mixing and degassing recorded in plagioclase at stromboli aeolian archipelago italy crystal rich materials scoriae and lava flows emitted during the 1985 2000 activity of stromboli were taken into consideration for systematic study of bulk rock matrix glass chemistry and in particular for the study of chemical and textural zoning of plagioclase the most abundant mineral phase over the considered time period bulk rock composition remained fairly constant in both major sio2 49 2 50 9 wt and k2o 1 96 2 18 wt and trace elements the quite constant chemistry of matrix glasses also indicates that the degree of crystallization of magma was maintained at around 50 vol plagioclase ranges in composition between an62 and an88 and is characterized by alternating 10 100 m thick bytownitic and labradoritic concentric layers although the dominant and representative plagioclase of scoriae is an68 the labradoritic layers an62 70 show small scale 1 5 m oscillatory zoning are free of inclusions and appear to record episodes of slow crystal growth in equilibrium with a degassed liquid having the composition of the matrix glass in contrast the bytownitic layers an70 an88 are patchy zoned show sieve structure with abundant micrometric glass inclusions and voids and are attributed to rapid crystal growth

transient processes in stromboli s shallow basaltic system inferred from dolerite and magmatic breccia blocks erupted during the 5 april 2003 paroxysm we describe the mineralogy geochemistry and mesomicrostructure of fresh subvolcanic blocks erupted during the 5 april 2003 paroxysm of stromboli aeolian islands italy these blocks represent 50 vol of the total erupted ejecta and consist of fine to medium grained basaltic lithotypes ranging from relatively homogeneous dolerites to strongly or poorly welded magmatic breccias the breccia components are represented by angular fragments of dolerites entrapped in a matrix of vesiculated lava like to scoriae crystal rich cr basalt all of the studied blocks are cognates with the cr basalt of the normal strombolian activity or lavas and they are often coated by a few centimeter thick layer of crystal poor cp basaltic pumice erupted during the paroxysm we suggest that they result from the rapid increase of pressure and related subvolcanic rock failure that occurred shortly before the 5 april 2003 explosion when the uppermost portion of the edifice inflated and suffered brecciation as the result of the sudden rise of the gas rich cp basalt that triggered the eruption dolerites and magmatic matrix of the breccias show major and trace element compositions that match those of the cr basalts erupted during normal strombolian activity and effusive events at stromboli volcano dolerites consist of a phenocrysts normally found in the cr basalts and b late stage magmatic minerals such as sanidine an60 28 plagioclase fe mn rich olivines fo68 48 phlogopite apatite and opaque mineral pairs magnetite and ilmenite most of which are never found both in lava flows and scoriae erupted during the persistent explosive activity that characterizes typical strombolian behavior subvolcanic crystallization of the stromboli cr magma leading to slowly cooled equivalents of basalts could result from transient drainage of the magma from the summit craters to lower levels fingering and engulfing of the material that collapsed from the summit crater floor into the shallow basaltic system during the late evening of 28 december 2002 coupled with the short break in the summit persistent explosions between december 2002 and march 2003 permitted the cr magma pockets to solidify as dolerites which were confined to the uppermost portion of the system and thus not involved in the ongoing flank effusive activity crystal size distribution of the basaltic blocks and crystallization of the finer grained 0 1 mm mafic minerals of the dolerites over a time interval of 100 days closely agrees with the above interpretation vesicle filling miarolitic cavities locally found in some dolerites with minerals deposited as vapor phase crystallization is a result of continuous gas percolation through the rocks of the uppermost portion of the volcanic system poorly welded magmatic breccias formed during syn eruptive processes of 5 april 2003 when the paroxysm strongly shattered the shallow subvolcanic system and many dolerite fragments were entrapped in the cr magma in contrast the high degree of welding between the dolerite clasts and the cr basaltic matrix in the strongly welded magmatic breccias provides a snapshot of subvolcanic intrusions of the cr basalt into the dolerite when after a 2 month break in activity cr magmas started to rise again to the summit craters blocks similar to these subvolcanic ejecta of 5 april 2003 were also erupted during previous paroxysms e g 1930 suggesting that changes in the usual strombolian activity e g short breaks in the persistent mild explosions and or flank effusive activity lead to transient crystallization of dolerites in the shallow plumbing system

behavior of the rare earth elements and other trace elements during interactions between acidic hydrothermal solutions and silicic volcanic rocks southwestern japan abstract rare earth elements and other trace elements in some roseki deposits mostly pyrophyllite and sericite silicastones alunites and related rocks were determined in order to examine behavior of the trace elements in the acidic hydrothermal alteration of silicic volcanic rocks the analyzed concentrations were normalized to the probable unaltered original rock values inferred from the averaged data of some silicic volcanic rocks the trace element characteristics for those materials are as follows 1 most of the elements such as na fe ba and light ree were leached from the silicastones while heavy ree th hf and zr were retained in them 2 alunite samples have light ree enriched and heavy ree depleted features 3 the typical roseki deposits are characterized by middle ree depletions and have v shaped ree patterns on the normalized concentrations vs atomic number diagram such characteristic patterns of the roseki deposits can be explained by superimposition of the light ree enriched and heavy ree enriched materials such as alunite and silica it is important that trace element behaviors are highly selective and some elements e g yb lu hf and zr were strongly retained in the rocks even under strongly acidic hydrothermal processes

petrology of aoso volcano northeast japan arc temporal variation of the magma feeding system and nature of low k amphibole andesite in the aoso osore volcanic zone the aoso volcano is a member of the newly defined volcanic front of northeast japan characterized by the occurrence of low k and hornblende andesites its activity can be divided into three stages the early caldera forming and late stages while petrographic and geochemical data show all products underwent magma mixing or co mingling sr and nd isotopic ratios indicate that all are consanguineous the end member magmas are basaltic and andesitic in the early stage but basaltic and dacitic in the late stage in the caldera forming stage hornblende free and hornblende rich andesites co mingled which triggered an explosive eruption leading to caldera formation hornblende occurs also in the dacite from the early part of the late stage these hornblende andesites and dacites are lower in magmatic temperature compared to hornblende free andesites the estimated basaltic end member is low k and high in magmatic temperature and can be derived by a high degree of partial melting of mantle under the volcanic front the estimated andesitic and dacitic end members cannot be derived from the basaltic end member magma through fractional crystallization but can be derived from partial re melting of the solidified low k basalt leaving amphibolitic and gabbroic residues respectively

progressive metamorphism of the unazuki pelitic schists in the hida terrane central japan four progressive mineral zones i chloritoid quartz ii staurolite chlorite muscovite iii kyanite biotite and iv sillimanite muscovite have been mapped in a well defined stratigraphic unit of ferruginous pelitic composition from north to south over a distance of about 15 km in the unazuki area hida terrane central japan textural and chemical evidence indicates that a given metamorphic mineral assemblage was formed from the mineral assemblage that precedes it in a spatial sequence of mineral zones

venus summary and review of science research activities 1983 87 in the past four years the first high resolution synoptic images of the surface of venus have been obtained and we have learned more about the nature of its surface and atmosphere the major accomplishments of the u s s r in venus exploration have been observed with great interest by u s investigators some of whom have begun joint research efforts with soviet scientists venera 15 and 16 radar imaging experiments and new data obtained at the arecibo observatory have provided answers to some important questions conjectured volcanic features have been resolved into unmistakable calderas or distinct lava flow morphologies the question of whether venus like the earth may have high erosion rates is answered and from the observed number of presumed impact craters it appears that resurfacing rates on venus are much smaller than on earth no evidence of water or wind activity has been seen

formation of rock coatings induced by the acid fumarole plume of the passively degassing volcano of la fossa vulcano island italy at la fossa volcano vulcano island and in the surrounding environment rock coatings rc develop owing to exposure of the ground surface to a volcanic acid plume this plume is produced by the passive degassing of la fossa active cone proximal and distal with respect to the high temperature fumarolic field rc have been identified which differ in mineralogy texture and chemical composition proximal rc are characterised by high silica content massive texture and strong leaching at the expense of the pyroclastic material distal rc are characterised by the presence of silica jarosite and minor goethite laminated texture and less developed evidence of leaching the rc are produced by direct interaction between the acid fumarolic aerosol and rocks and by reaction of dews and rains acidified by the absorption of acid gases so2 hcl hf of the fumarole plume with volcanic material proximal rc are produced at conditions of ph 2 distal rc form at ph 2 3 based on the presence of jarosite although the occurrence of goethite in some samples suggests higher values of ph the influence of the volcanic plume in the development of these rc is indicated also by the coincidence of the rc areal distribution with the distribution of the volcanic plume controlled by the local wind field this is furthermore supported by the presence in rc of chloride and or sulphur bearing compounds enriched in volatile elements and metals commonly carried by volcanic aerosols

aerial seismology using balloon based barometers seismology on venus has long eluded planetary scientists due to extreme temperature and pressure conditions on its surface which most electronics cannot withstand for mission durations required for ground based seismic studies we show that infrasonic low frequency pressure fluctuations generated as a result of ground motion produced by an artificial seismic source known as a seismic hammer and recorded using sensitive microbarometers deployed on a tethered balloon are able to replicate the frequency content of ground motion we also show that weak artificial seismic activity thus produced may be geolocated by using multiple airborne barometers the success of this technique paves the way for balloon based aero seismology leading to a potentially revolutionary method to perform seismic studies from a remote airborne station on the earth and solar system objects with substantial atmospheres such as venus and titan

mineralogy at the magma hydrothermal system interface in andesite volcanoes new zealand ejecta from phreatomagmatic eruptions of ruapehu and white island andesite volcanoes in new zealand provide insight into the mineralogical reactions that occur when magma invades a vent hosted hydrothermal system at the surface and in ejected blocks from shallow depths hydrothermal alteration mineralogies are dominated by silica polymorphs anhydrite natroalunite and pyrite blocks from greater depths are composed mainly of cristobalite anhydrite halite and magnetite where altered material was heated to magmatic temperatures thermal decomposition reactions produced mullite wollastonite and indialite some ejected breccias contain osumilite cordierite sanidine and hypersthene indicative of reactions occurring near the osumilite cordierite phase boundary at 800 c and water pressure 0 2 kbar hedenbergite wollastonite andradite and magnetite are found in rare skarn fragments possibly formed by metasomatism of silica poor sulfate rich hydrothermal deposits high temperature parageneses of these types have not been reported before in shallow acidic volcano hydrothermal systems however they may be typical of the magma hydrothermal contact zone at many andesite volcanoes

venus atmospheric structure and dynamics from the vega lander and balloons new results and pds archive abstract the longest lived in situ measurement platforms at venus have been the soviet vega balloons in 1985 and the only high quality pressure temperature profile in the lowest 10 km of the atmosphere is that from the vega 2 lander here we review the mission and the resultant literature and report the archival of numerical data from these investigations on the nasa planetary data system atmospheres node to facilitate their access to the community we additionally report some new results including the striking absence of a signature of the planetary boundary layer in the near surface potential temperature profile from the vega 2 lander in contrast to the well defined boundaries seen in a comparable profile at titan

volcanological and magmatological evolution of stromboli volcano aeolian islands the roles of fractional crystallization magma mixing crustal contamination and source heterogeneity the present paper reports the results of a detailed stratigraphical petrological and geochemical investigation on the island of stromboli aeolian arc southern tyrrhenian sea major and trace element data determined on a large quantity of samples from well established stratigraphic positions indicate that the magmatological evolution of the island through time was more complex than previously known the activity of the exposed part of stromboli which occurred over a time span of about 100 000 years started with the emission of high k calc alkaline hkca volcanics which were covered by calc alkaline ca shoshonitic sho high k calc alkaline hkca and potassic ks products the most recent activity consists of hkca lavas and the present day sho basaltic volcanics emitted by mildly explosive strombolian activity most of the products are lavas with minor amounts of pyroclastic rocks emplaced mainly during the early stages of activity the transition from the sho to the ks cycle was associated with the collapse of the upper part of the volcanic apparatus the transition from ks to the present day sho activity has been found to have occurred at the time of the sliding of the western portion of the volcano that generated the sciara del fuoco depression the rock series cropping out at stromboli show variable enrichment in potassium incompatible trace elements and radiogenic sr which increase from ca through hkca and sho up to ks rocks major trace element and sr isotopic data agree in indicating that the hkca and sho series evolved by crystal liquid fractionation starting from different parental liquids whereas crustal assimilation appears to have been the leading process during the evolution of ks volcanics mixing processes also played a role although they can be well documented only when they occurred between magmas with different isotopic and geochemical characteristics geochemical modelling based on trace element and isotopic data indicates that the mafic magmas of the different volcanic series may be generated by melting of an upper mantle heterogeneously enriched in incompatible elements and radiogenic sr by addition via subduction of different amounts of crustal material geochemical data however are also in agreement with the alternative hypothesis that the most mafic magmas of the different series have been generated by combined processes of fractional crystallization assimilation and mixing of a ca magma in a deep sited magma chamber the mafic magmas formed by these complex processes were successively emplaced in a shallow reservoir where they evolved by simple fractional crystallization hkca and sho series and by assimilation of crustal material ks the occurrence of changes in the geochemical signatures of the magmas at the time of the structural modification of the volcano is believed to favour the hypothesis that the variable composition observed in the volcanic rocks of stromboli is the result of processes occurring within the volcanic system

permo triassic collision subduction zone metamorphism and tectonic exhumation along the east asian continental margin abstractconvergent plate motion at 320 210 ma generated the tongbai dabie sulu east central china imjingang gyeonggi central korea renge suo southwestern japan sikhote alin orogen along the paleo pacific edge of cratonal asia this amalgamated belt reflects collision between the sino korean and yangtze cratons on the sw portion and accretion of outboard oceanic arcs sialic fragments against the ne margin subducted proterozoic paleozoic continental and oceanic crustal complexes underwent high and ultrahigh pressure metamorphism at low to moderate temperatures tectonic slices of sialic crust episodically disengaged from the downgoing plate and driven by buoyancy ascended rapidly to midcrustal levels from depths exceeding 90 200 km after continental collision in east central china plus or minus korea and from 30 50 km after arrival of far traveled oceanic terranes in sw japan and the russian far east on achieving neutral buoyancy and stalling out at 10 20 km depth later doming gravitation

ground based near infrared imaging observations of venus during the galileo encounter near infrared images of venus obtained from a global network of ground based observatories during january and february 1990 document the morphology and motions of the night side near infrared markings before during and after the galileo venus encounter a dark cloud extended halfway around the planet at low latitudes 40 and persisted throughout the observing program it had a rotation period of 5 5 0 15 days the remainder of this latitude band was characterized by small scale 400 to 1000 kilometers dark and bright markings with rotation periods of 7 4 1 days the different rotation periods for the large dark cloud and the smaller markings suggests that they are produced at different altitudes mid latitudes 40 to 60 were usually occupied by bright east west bands the highest observable latitudes 60 to 70 were always dark and featureless indicating greater cloud opacity maps of the water vapor distribution show no evidence for large horizontal gradients in the lower atmosphere of venus

multi proxy evidence for holocene lake level and salinity changes at an loch mor a coastal lake on the aran islands western ireland abstract curves for holocene lake levels and salinity changes are presented for an loch mor a small oligohaline lake on the aran islands off the west coast of ireland based on palaeoecological investigations of a 12 m long lake sediment core new insights are also provided into holocene sea level change in the galway bay region particular emphasis has been placed on the ostracod fauna both past and present salinity and lake level changes were reconstructed from the fossil ostracod assemblages based on the known tolerances of individual species and on the assemblages as a whole additional evidence was provided by other proxies including strontium isotope ratios derived from ostracod shells and other carbonates plant macrofossil and pollen analyses and sedimentological changes the early holocene pre boreal i e 11 5 10 ka was characterised by low lake levels and slightly elevated salinity values probably the result of high evapotranspiration and low precipitation rather than elevated sea levels early holocene plant and animal migration to the island does not seem to have been impeded but relative sea levels were not necessarily so low below 40 m a s l that landbridges were present to the mainland between ca 10 and 8 5 ka relatively high lake levels prevailed at 8 3 and 7 5 ka minor fluctuations lowering of the lake level occurred that are assumed to relate to early holocene abrupt events beginning at 7 05 ka lake levels declined sharply a general trend towards rising lake levels started at ca 6 4 ka and accelerated at ca 5 6 ka as runoff increased as a result of neolithic clearances at ca 4 8 ka lake levels began to rise once again probably in response to changes in rainfall and or evapotranspiration and runoff lower lake levels during the first half of the 1st millennium ad were probably a response to decreased runoff as a result of a drier climate coupled with regeneration of woody vegetation the sharpest rise in both lake levels and salinity began during the ninth century ad which is attributed to a rapid rise in relative sea level

defining the potential source region of volcanic ash in northwest europe during the mid to late holocene abstract far travelled volcanic ash fine grained tephra clouds pose economic and societal risks largely through their potential impact on the aviation industry a long view of ash clouds extending over northwest europe assembled from the study and geochemical characterisation of cryptotephra i e tephra invisible to the naked eye in sedimentary records can help inform the understanding of the frequency of such events and the nature of eruptions that generate them here we review the records of cryptotephra deposition in northwest europe during the mid to late holocene the last eight millennia to gain insights into the sources of volcanic ash reaching this region we consider almost 500 published and unpublished datasets for cryptotephras recorded in sedimentary sequences ranging from ireland to latvia and on the basis of their major element geochemical composition we identify 90 unique ash horizons and their likely provenance the majority 72 of the cryptotephras derive from icelandic eruptions but a large proportion 24 originates from other volcanic regions including alaska the cascades kamchatka mexico the azores and possibly the mediterranean although moderate magnitude eruptions in iceland may potentially disperse ash clouds over europe it appears that only large magnitude events in more distant regions have generally had this capacity and then only when suitable meteorological conditions prevailed nevertheless the cryptotephra records demonstrate that ash clouds from most volcanic regions capable of producing large explosive eruptions in the northern mid to high latitudes particularly those to the west of europe as well as in tropical north america have the potential to extend to northwest europe volcanic ash forecasts for this region need therefore to take into account possible risks posed not only by icelandic eruptions but also by any large magnitude eruptions in north america or the north pacific area

the evolution of the magmatic system of stromboli volcano during the vancori period 26 13 8 ky stratigraphic changes in bulk rock and mineral chemistry within a volcanic sequence can be used to understand the evolution of the magma storage system beneath the volcano in particular changing eruptive styles and major changes in magma chemistry can be linked to open or closed system behaviour changes in phenocryst mineral chemistry often expressed as core rim zonation patterns or the development of reaction rims combined with thermodynamic analysis of appropriate mineral equilibria can provide powerful insights into the timing of inputs of new more primitive magma the vancori period 26 13 8 ky of the eruptive activity of stromboli has a relatively simple stratigraphy comprising three sub periods lower middle and upper vancori each one beginning and ending with an explosive volcanic event marked by breccias electron microprobe analyses of phenocryst and groundmass minerals olivine clinopyroxene plagioclase fe ti oxides in representative samples from the lower middle and upper vancori phases of activity allow tracking of the evolution of the magma chamber system with time thermodynamic analysis of olivine clinopyroxene mineral equilibria is used to constrain changes in temperature within the magmatic system the main stratigraphic discontinuities within the vancori sequence are clearly reflected by changes in bulk rock and mineral chemistry and evidence of textural and thermodynamic disequilibrium calculated temperatures in the eruptive products on the basis of these data the lower and middle vancori periods of the eruptive history of stromboli appear to be characterised by an open magma chamber system repeatedly re filled with basaltic magma which was continuously being erupted at the end of the middle vancori period the system became closed corresponding to a period of dormancy of the volcano and fractional crystallisation dominated following a major flank collapse of the volcanic edifice the upper vancori eruptive products show the most extreme range in bulk rock chemistry as the chamber was progressively flushed with new basaltic magma d 2005 elsevier b v all rights reserved

abrupt climatic changes and an unstable transition into a late holocene thermal decline a multiproxy lacustrine record from southern sweden the transition from a middle holocene relatively warm and stable climate to a cooler and unstable late holocene climate is reconstructed using sediments from lake igelsjon south central sweden this multiproxy study illustrates local regional and global scale responses to climatic change by focusing on a previously identified abrupt hydrological shift to cooler and or wetter conditions around 4000 cal yr bp the results suggest that between ca 4600 and ca 3400 cal yr bp the environment around and within the lake responded in two major well defined steps the first between 4450 and 4350 cal yr bp and the second between 4000 and 3800 cal yr bp a series of rapid fluctuations of short duration were superimposed on the general cooling trend with the most severe aquatic response peaking at ca 3800 cal yr bp pollen percentage and influx values show forest composition and pollen productivity changes and a distinct decline in total and corylus pollen influx in the period of 4000 3500 cal yr bp stomatal based reconstruction of atmospheric co2 concentration produced a tenuous decrease with a minimum between 3650 and 3500 cal yr bp copyright 2005 john wiley sons ltd

low frequency and high frequency changes in temperature and effective humidity during the holocene in south central sweden implications for atmospheric and oceanic forcings of climate an integrated use of independent palaeoclimatological proxy techniques that reflect different components of the climate system provides a potential key for functional analysis of past climate changes here we report a 10 000 year quantitative record of annual mean temperature tann based on pollen climate transfer functions and pollen stratigraphical data from lake flarken south central sweden the pollen based temperature reconstruction is compared with a reconstruction of effective humidity as reflected by a 18o record obtained on stratigraphy of lacustrine carbonates from lake igelsjon c 10 km from lake flarken which gives evidence of pronounced changes in effective humidity the relatively low tann and high effective humidity as reflected by a low evaporation inflow ratio suggest a maritime early holocene climate 10 000 8 300 cal year bp seemingly incompatible with the highly seasonal solar insolation configuration we argue that the maritime climate was due to the stronger than present zonal flow enhanced by the high early holocene sea surface temperatures in the north atlantic the maritime climate mode was disrupted by the abrupt cold event at 8 200 cal year bp followed at 8 000 cal year bp by a stable holocene thermal maximum the latter was characterized by tann values about 2 5 c higher than at present and markedly dry conditions indicative of stable summer time anti cyclonic circulation possibly corresponding with modern blocking anticyclonic conditions the last 4 300 year period is characterized by an increasingly cold moist and unstable climate the results demonstrate the value of combining two independent palaeoclimatic proxies in enhancing the reliability generality and interpretability of the palaeoclimatic results further methodological refinements especially in resolving past seasonal climatic contrasts are needed to better understand the role of different forcing factors in driving millennial scale climate dynamics

origin of silicic magma and magma feeding system of the shirataka volcano ne japan abstract stratovolcanoes in ne japan produce mixed andesites dacites with a silicic end member the petrologic features of this end member remained uncertain and its origin has long been debated here we suggest how the silicic magma is generated and interpret the magma feeding system for one such stratovolcano the shirataka 0 9 0 7 ma the rocks of the shirataka are divided into six petrologic groups g1 6 mafic inclusions are observed in g1 g2 g5 and g6 silica poor inclusions have tschermakitic hornblende in the groundmass while the others are hornblende free the detailed petrologic study revealed that all products were formed by magma mixing mingling between mafic and silicic end members mafic end members 1150 c 47 52 wt sio2 have magnesian olivine magnesian clinopyroxene and an rich plagioclase phenocrysts whereas silicic end members 750 900 c 63 68 wt sio2 have an poor plagioclase low mg pyroxenes hornblende and quartz the phenocryst compositions an mg and temperature of silicic end members have changed among the groups over time the trends defined by such mafic and silicic end members of each group are systematically parallel except for g3 and g4 which have distinct specific bulk compositions suggesting that the two end members for each group have co genetic relationships the trace element model calculations indicate that each estimated silicic end member can be produced through partial remelting of the corresponding solidified mafic end member leaving a gabbroic residue the presence of groundmass hornblende in silica poor mafic inclusions suggests that volatile rich mafic magmas ascended settled and solidified as gabbroic bodies in the lower or middle crust silicic magmas were then produced by partial remelting of these bodies and ascended to the shallower part of the crust to form chambers leaving the gabbro finally wet mafic magmas newly supplied along the marginal part of the gabbroic bodies and injected into the chambers triggered the eruption and the mixing mingling took place during ascent to the surface two distinct silicic magmas were simultaneously formed by this mechanism and they mixed with corresponding mafic magmas in g3 and g4 giving rise to two discrete mixed magmas finally these magmas erupted contemporaneously mingling with each other and forming pyroclastic flows

investigation of air temperature on the nightside of venus derived from virtis h on board venus express abstract we present the spatial distribution of air temperature on venus night side as observed by the high spectral resolution channel of virtis visible and infrared thermal imaging spectrometer or virtis h on board the esa mission venus express the present work extends the investigation of the average thermal fields in the northern hemisphere of venus by including the virtis h data we show results in the pressure range of 100 4 mbar which corresponds to the altitude range of 65 80 km with these new retrievals we are able to compare the thermal structure of the venus mesosphere in both hemispheres the major thermal features reported in previous investigations i e the cold collar at about 65 70 s latitude 100 mbar pressure level and the asymmetry between the evening and morning sides are confirmed here by comparing the temperatures retrieved by the virtis spectrometer in the north and south we find that similarities exist between the two hemispheres solar thermal tides are clearly visible in the average temperature fields to interpret the thermal tide signals otherwise impossible without day site observations we apply model simulations using the venus global circulation model venus gcm lebonnois s hourdin f forget f eymet v fournier r 2010b international venus conference aussois 20 26 june 2010 of the laboratoire de meteorologie dynamique lmd we suggest that the signal detected at about 60 70 latitude and pressure of 100 mbar is a diurnal component while those located at equatorial latitudes are semi diurnal other tide related features are clearly identified in the upper levels of the atmosphere

the contribution of fluid geochemistry to the volcano monitoring of stromboli abstract the persistent open vent mild explosive activity of stromboli volcano is episodically interrupted by more violent and dangerous explosive events major explosions and paroxysms according to the nature of erupted products paroxysms can be related either to the explosion of overpressured gas pockets located in the proximity of the magma column or to the sudden uprise of hot gas rich magma from a deep part of the plumbing system in both cases these more energetic explosive events should be preceded by an escape or a preferential uprise of the highly mobile volatiles which in turn should produce gas leakage anomalies at the surface in sites of high vertical permeability such as deep reaching faults in order to identify such gas leaking sites a systematic co2 soil flux survey has been carried out on the island using an accumulation chamber four hundred sixty one points have been measured with a high density in the summit crater area where high flux values have been found 10 3 10 2 cm s anomalous points are concentrated along the main ne sw axial feeding system of the volcano co2 soil flux decreases from the crater zone to the base of the volcanic cone where however an interesting gas leakage anomaly occurs pizzillo mofette in the pizzillo area thermal water wells also occur whose chemistry indicates an origin by sea water heated by hot gas soil gases have been sampled in the sites with the highest co2 flux in the crater area and at the base of the cone chemical and isotopic analyses indicate the presence of a deep gas component especially in the crater zone samples high co2 appreciable contents of he and h2 3he 4he values up to 3 55 13c of co2 2 the sc5 low flux fumarole on the crater rim has shown during six years a remarkable persistence of temperature 93 95 c with only minor fluctuations of chemistry appearance of anomalous peaks of h2 in correspondence with strombolian explosions was observed during a 2 h 30 min experiment of continuous recording of hydrogen content of the fumarole together with previous data on h2o co2 and he this experiment confirms that strombolian blasts produce rapid fluctuations in the fumarolic gas composition in the light of this study sc5 fumarole and pizzillo mofette look promising sites for the testing of a continuous geochemical monitoring system of stromboli volcano

implications of the vega balloon results for venus atmospheric dynamics both vega balloons encountered vertical winds with typical velocities of 1 to 2 meters per second these values are consistent with those estimated from mixing length theory of thermal convection however small scale temperature fluctuations for each balloon were sometimes larger than predicted the approximate 6 5 kelvin difference in temperature consistently seen between vega 1 and vega 2 is probably due to synoptic or planetary scale nonaxisymmetric disturbances that propagate westward with respect to the planet there is also evidence from doppler data for the existence of solar fixed nonaxisymmetric motions that may be thermal tides surface topography may influence atmospheric motions experienced by the vega 2 balloon

armalcolite bearing fe ti oxide assemblages in graphite equilibrated salic volcanic rocks with native iron from disko central west greenland native iron bearing strongly sediment contaminated andesitic to dacitic lavas from the malig t formation on disko contain an early phenocryst assemblage of plagioclase low ca pyroxene s and ilmenite the phenocrystic ilmenite has reacted to form complex fe ti oxide metal sulphide aggregates which contain one or more of the oxides ilmenite armalcolite and rutile the armalcolite is very similar to the lunar type 1 armalcolite of haggerty 1973 and approximate compositionally the ternary system feti2o5 mgti2o5 ti3o5 92 to 97 mol when evidence from several salic rocks is combined the fe ti oxide metal sulphide aggregates display reactions which may represent one isobaric invariant assemblage ilmenite armalcolite rutile iron and the 3 boundary univariant reactions in the system fe ti o the compositional and textural features of ferro magnesian silicates oxides and metals show that most rocks were affected by a rapidly declining fo2 during magma ascent and cooling as displayed in the fe ti oxide metal sulphide aggregates by the cross cutting of one or several t fo2 buffer curves in the system fe ti o prominent sulphidation reactions are observed in the oxide aggregates and are always of the type where feo in oxide is replaced by fes while the liberated oxygen is consumed in a reduction process carbon bound as graphite or cohenite occurs throughout the rocks and is mostly enclosed in phenocrysts and xenocrysts when the salic magmas ascended from pre eruption reservoirs at 1 to 1 5 kb the reduction was largely controlled by strongly pressure dependent carbon oxygen equilibria resulting in rapidly declining t fo2 paths recorded by the oxide assemblages in the simplified c o gas system carbon barometry sato 1979 applied to the selected rocks would indicate final equilibrium pressures of between 10 and 100 bars the scarcity of preserved graphite in the lavas would suggest that the carbon controlled reductions were terminated when available carbon was exhausted during the magma ascent and solidification

electron backscatter diffraction ebsd analyses of phyllosilicates in petrographic thin sections applications of electron backscatter diffraction ebsd to obtain crystallographic information of minerals in petrographic thin sections in mineralogy and petrology are increasing however platy phyllosilicates that mostly appear with their silicate layers terminated by the surface in the thin sections generally do not show sharp ebsd patterns in spite of gentle mechanical polishing tem examination indicated that this is due to crystal bending of phyllosilicates from the surface to a few micrometers in depth caused by the polishing process ion beam etching commonly used to prepare tem specimens was found to be applicable to remove the surface region with crystal bending as a result clear and sharp ebsd patterns were acquired from the phyllosilicates micas chlorite etc in petrographic thin sections by which their crystal orientations and polytypes were unambiguously determined

a new concept on tectonic correlation between korea china and japan histories from the late proterozoic to cretaceous abstract the dabie sulu collision belt in china extends to the hongseong odesan belt in korea while the okcheon metamorphic belt in korea is considered as an extension of the nanhua rift within the south china block the hongseong odesan belt divides korea s gyeonggi massif into northern and southern portions the southern gyeonggi massif and the yeongnam massif are correlated with china s yangtze and cathaysia blocks respectively while the northern gyeonggi massif is part of the southern margin of the north china block the southern and northern gyeonggi massifs rifted from the rodinia supercontinent during the neoproterozoic to form the borders of the south china and north china blocks respectively subduction commenced along the southern and eastern borders of the north china block in the ordovician and continued until a triassic collision between the north china and south china blocks while subduction was occurring on the margin of the north china block high p t metamorphic belts and accretionary complexes developed along the inner zone of southwest japan from the ordovician to the permian during the subduction the hida belt in japan grew as a continental margin or continental arc collision between the north and south china blocks began in korea during the permian 290 260 ma and propagated westwards until the late triassic 230 210 ma creating the sinistral tanlu fault in china and the dextral fault in the hida and hida marginal belt in japan phanerozoic subduction and collision along the southern and western borders of the north china block led to formation of the qinling dabie sulu hongseong hida yanji belt

mg cordierite si al ordering optical properties and distortion flux grown crystals of mg cordierite mg1 93 al3 95 si5 07 o18 synthesized by lee and pentecost 1976 appear biaxial 2vx 10 25 under the polarizing microscope whereas their distortion index 0 between crossed polars 001 sections display lamellar and cyclic twinning on 110 and less frequently 310 as duration of annealing at 1 300 c increased 2vx increased simultaneously undulatory extinction and intragrain variations in 2vx increased slightly up to 4 h annealing then steadily decreased for this mg cordierite which lacks significant channel h2o or co2 2vx and reach maxima of 88 589 nm and 0 25 after 42 h of annealing but other sectors still display lesser values for 2vx presumably to the extent 2vx is less than 88 these sectors represent intergrown submicros copically twinned orthorhombic domains and thus possess shortrange but not long range order annealing at 1 300 c likely increased long range order by promoting growth of larger domains at the expense of smaller ones ultimately two differently oriented domains growing toward each other by annexation and re orientation of smaller domains meet in a twin boundary that with time tends to become straight

chlorine rich pyrometamorphic magma at white island volcano new zealand abstract the 25 january 1987 phreatomagmatic eruption of congress vent on white island volcano ejected paralava bombs derived from pockets of pyrometamorphic magma the current white island magmas are calc alkaline basaltic andesite andesite but the paralavas are mostly highly peralkaline with molar na 2 o k 2 o al 2 o 3 ratios from 1 to 22 recorded in matrix glasses the glass compositions are highly variable though quench crystals of tridymite wollastonite and green clinopyroxene are ubiquitous while albite occurs only in the least peralkaline samples all have high alkali contents na 2 o k 2 o 10 and chlorine mostly 1 and up to 1 7 the paralava glasses represent the most cl rich volcanic melts yet discovered they display a strong positive correlation between cl and total fe but a negative correlation between cl and normative alkali feldspar content it is likely that the fe content of melts was the dominant control over cl solubility not their alumina alkali systematics possible parent rocks for the pyrometamorphic magmas include halite cemented crater lake sediments and acid sulfate hydrothermally altered vent breccias and tuffs as found in the eruption deposits together with the paralava bombs fusion probably occurred at temperatures between 830 and 1000 c and at a pressure below 5 mpa in a regime where silicate melts were buffered by immiscible nacl saturated aqueous vapor and hydrosaline melt the conditions required to form the paralava bombs appear to be uncommon but it is likely that similar pyrometamorphic melts could be generated at many volcanoes where shallow magma penetrates a hydrothermal system

complex interaction of aluminous metasedimentary xenoliths and siliceous magma an example from mt amiata central italy aluminous silica deficient metasedimentary xenoliths in siliceous lavas of mt amiata have preserved composite zoning patterns indicative for complex processes of magma rock interaction petrographic observations and small scale mineralogical and chemical differences between up to five distinct zones including the core and envelope of lava provide evidence that quartz poor muscovite biotite schists are considered to be the most likely parent rocks and it is believed that release of volatiles from decomposing micas played a significant role in the high temperature metamorphic evolution of the xenoliths and their interaction with the magma the conditions favourable for assimilation were enhanced by injection of mafic magma into the magma chamber although this concurrent operation of magma mixing precludes a quantitative estimate of contamination from the wall rocks which was probably of minor importance the present example indicates that dry acid magma may potentially become more mafic by interaction with partially melted hydrous rocks

vega balloon dynamics and vertical winds in the venus middle cloud region the vega balloons provided a long term record of vertical wind fluctuations in a planetary atmosphere other than earth s the vertical winds were calculated from the observed displacement of the balloon relative to its equilibrium float altitude the winds were intermittent a large burst lasted several hours and the peak velocity was 3 meters per second

mafic and ultramafic xenoliths in san bartolo lava field new insights on the ascent and storage of stromboli magmas mafic and ultramafic xenoliths are well represented within a large basaltic lava field of stromboli these basalts known as san bartolo lavas show a high k calc alkaline hkca affinity and were erupted 5 ka bp xenoliths consist of olivin gabbro gabbronorite anorthosite dunite wehrlite and clinopyroxenite thermobarometric estimates for the crystallization of gabbroic materials show minima equilibration pressures of 0 17 0 24 gpa at temperatures ranging from 940 to 1 030 c these materials interacted with hydrous ascending hkca basaltic magmas with temperatures of 1 050 1 100 c at pressures of about 0 2 0 4 gpa these pressure regimes are nearly identical to those found for the crystallization of phenocrystic phases within hkca basaltic lavas gabbroic inclusions are regarded as cumulates and represent crystallized portions of earlier hkca strombolian basalts