the composition and role of the fluid in migmatites a fluid inclusion study of the front range rocks monophase negative crystal shaped co2 inclusions occurring isolated in small clusters or in well healed intragranular fractures are common in the leucosome quartz of the 1700m y old migmatites from the east central colorado front range they are however quite rare in the mafic selvage and paleosome host rock quartz the mode of occurrence suggests that these are the earliest inclusions to form in addition to the difference in abundance of the inclusions there is a difference in co2 density distribution between migmatitic zones the temperatures of homogenization for the leucosome inclusions range and l c from 67 c to 20 c with two maxima at 21 c while those for the paleosome and selvage inclusions are 37 c to 20 c with a single maximum at 5 c these differences between the migmatitic zones which occur on the scale of a few centimeters suggest that the formation of these inclusions was related to the migmatization process the densities corresponding to the th maxima are appropriate for the p t conditions for migmatization estimated from the mineral geobarometer geothermometer these inclusions must contain nearly pure co2 as their final melting temperatures 56 5 to 57 2 c are very close to that of the triple point of co2 their composition also was confirmed by raman spectroscopic analyses

new insights into source and dispersal of mediterranean s1 tephra an early holocene marker horizon erupted at mt erciyes turkey abstract deposition of early holocene eastern mediterranean s1 tephra and a black sea cryptotephra coincides with cultural transitions in the fertile crescent termed the neolithic revolution as well as sapropel formation during climate variability of the african humid period classifying them as paramount regional marker horizons for archaeology as well as paleoclimatology their correlations with specific eruptions of the mt erciyes stratovolcanic complex central anatolia remained inconclusive though here we use zircon double dating by u th he and u th disequilibrium methods major and trace element tephra glass geochemistry and probabilistic modeling of tephra dispersal in an attempt to characterize all major late quaternary proximal tephras of mt erciyes and to correlate them with distal deposits furthermore we discuss contrasting proximal and distal tephra dispersal three nearly coeval rhyolitic satellite domes dikkartin perikartin and karagullu erupted at mt erciyes in the early holocene and their dome extrusions were all preceded by explosive phases producing pyroclastic material that formed tephra fall and pyroclastic flow deposits the new eruption age of 9 03 0 55 ka 1 uncertainty here and elsewhere for proximal dikkartin pumice is consistent with 14c based s1 tephra chronologies in distal locations averaging 8 92 0 03 cal ka bp perikartin pyroclastic flow deposits predate s1 tephra by ca 0 8 ka according to a pair of published 14c ages and stratigraphically overlie karagullu fall out here dated to 8 2 1 8 ka previously undated proximal tephras of mt erciyes erupted in the late 85 2 4 9 ka and middle pleistocene 154 5 5 3 ka s1 tephra glass is chemically similar to that of dikkartin fall out but also indistinguishable from that of perikartin fall out karagullu pumice is characterized by a distinct glass chemical composition which correlates with that of unnamed cryptotephra reported for the southeastern black sea instead where these results call for a re evaluation of existing age models maximum lithic clast size isopleths for proximal dikkartin fall out indicate eastward dispersal of a 20 5 km high eruption plume by stratospheric winds in agreement with results of probabilistic tephra dispersal modeling this azimuth contrasts with the known distribution of s1 tephra at distal locations that are all south of mt erciyes significant tephra occurrences at up to 1300 km distance and orthogonal to prevalent stratospheric wind directions either result from very atypical wind conditions probability 10 or are caused by tephra transport by prevailing low altitude winds two scenarios are proposed for low altitude transport eolian reworking of primary fall out more likely from the more widespread dikkartin deposits or co ignimbrite ash cloud dispersal more likely from the perikartin eruption which predominantly produced pyroclastic flows because s1 tephra is chemically indistinguishable from both dikkartin and perikartin by major and trace element glass compositions its exact source and dispersal mechanism remain ambiguous although existing 14c ages for perikartin predating those for s1 tephra favor dikkartin as its source

quaternary counterclockwise rotation of south kyushu southwest japan paleomagnetic data from latest miocene to pliocene sedimentary rocks in southeast kyushu as well as those previously reported from middle to late miocene formations show that a large part of south kyushu has been rotated 30 counterclockwise with respect to north kyushu and eurasia during the past 2 m y this rotation started synchronously with rifting of the continental crust beneath south kyushu and the northern okinawa trough which commenced around the pliocene pleistocene boundary and continues to the present the coincidence of rotation and extension implies that arc rotation can take place during rifting of continental crust

reverse age relations of talc and tremolite deduced from reaction textures in metamorphosed siliceous dolomites of the southern damara orogen namibia the regional metamorphosed siliceous dolomites of the southern damara orogen namibia show a distinct talc bearing zone on the lower metamorphic grade side and a distinct tremolite bearing zone on the higher metamorphic grade side separated by the occurrence of the fivemineral assemblage i tremolite talc calcite dolomite quartz

quantifying uncertainties in marine volcanic ash layer records from ocean drilling cores abstract ocean drilling provides a global record of deposits throughout the oceans an international collaborative ocean research programme was established in 1966 and the international ocean discovery program iodp is the most recent manifestation of this during each expedition a large amount of data are generated and collected by the shipboard science team it could be suggested that due to the different staff and objectives during each expedition there would be significant variations in the consistency of data recorded in the shipboard visual core descriptions vcds use of shipboard vcd data in a global study of volcanism through time required the ground truthing of vcd data to assess the consistency of ash layer reporting and to identify the amount of under over recording of volcanic ash layers in cores approximately 1400 ash layers in dsdp odp iodp and jamstec cores were examined and it was found that on average 70 75 of recorded volcanic ash layers were present as described an average of 17 20 were over recorded and 10 15 were under recorded a number of factors could contribute to this variability such as vcd format lack of time for shipboard sampling of every ash layer significant ash layer colour changes since time of coring or differences in vcd recording and volcanic ash layer identification and description schemes between expeditions these findings are important and will allow greater confidence in further studies based on data compiled from shipboard vcds

new insights into deformation and fluid flow processes in the nankai trough accretionary prism results of ocean drilling program leg 190 moore g f taira a klaus a becker l boeckel b cragg b a dean a fergusson c l henry p hirano s hisamitsu t et al 2001 new insights into deformation and fluid flow processes in the nankai trough accretionary prism results of ocean drilling program leg 190 geochemistry geophysics geosystems 2 article no 2001gc000166

halogen bearing minerals in syenites and high grade marbles of dronning maud land antarctica monitors of fluid compositional changes during late magmatic fluid rock interaction processes meta sedimentary rocks including marbles and calcsilicates in central dronning maud land cdml in east antarctica experienced a pan african granulite facies metamorphism with peak metamorphic conditions around 830 20 c at 6 8 0 5 kbar which was accompanied by the post kinematic intrusion of huge amounts of syenitic charnockitic magmas at 4 5 0 7 kbar the marbles and calcsilicates may represent meta evaporites as indicated by the occurrence of metamorphic gypsum anhydrite and cl rich scapolite that formed in the presence of saline fluids with x nacl in the range 0 15 0 27 the marbles and calcsilicates bear biotite tremolite and or hornblende and humite group minerals clinohumite chondrodite and humite which are inferred to have crystallized at about 650 c and 4 5 kbar the syenitic intrusives contain late magmatic biotite and amphibole formed between 750 and 800 c as well as relictic magmatic fayalite orthopyroxene and clinopyroxene two syenite and two calcsilicate samples contain fluorite corona textures in the marbles and calcsilicates suggest very low fluid rock ratios during the formation of the retrograde 650 c assemblages biotite in all but two syenite samples crystallized at log f h 2 o f hf ratios of 2 9 0 4 while in the calcsilicates both biotite and humite group minerals indicate generally higher log f h 2 o f hf values of up to 5 2 a few samples though overlap with the syenite values log f h 2 o f hcl derived from biotite covers the range 0 5 2 6 in all rock types within a single sample the calculated values for both parameters vary typically by 0 1 to 0 8 log units water and halogen acid fugacities calculated from biotite olivine orthopyroxene feldspar quartz equilibria and the above fugacity ratios are 1510 2790 bars for h2o 1 3 5 3 bars for hf and 7 600 bars for hcl the results are interpreted to reflect the reaction of relatively homogeneous magmatic fluids in terms of log f h 2 o f hf derived from the late magmatic stages of the syenites with both earlier crystallized still hotter parts of the syenites and with adjacent country rocks during down temperature fluid flow fluorine is successively removed from the fluid and incorporated into f bearing minerals close to the syenite into metamorphic fluorite in the course of this process log f h 2 o f hf increases significantly chlorine preferably partitions into the fluid and hence log f h 2 o f hcl does not change markedly during fluid rock interaction

constraints on the timing of explosive volcanism at aso and aira calderas japan between 50 and 30 ka new insights from the lake suigetsu sedimentary record sg14 core

identification of the source caldera for a pliocene ash flow tuff in northeast japan based on apatite trace element compositions and zircon u pb ages abstract in tephrochronology trace element compositions of apatite phenocrysts are useful because they change in response to various magmatic conditions as apatite crystallizes moreover because apatite tolerates burial diagenesis and welding processes without chemical changes its trace element compositions are a powerful tool for correlating pre quaternary tephra however this method is not extensively applied the hirosegawa tuff composed of a pair of pliocene ash fall and ash flow tuffs is a distinctive marker tephra that is used in geological mapping and for correlating sedimentary rocks in the eastern part of central ne japan however the source volcano of the hirosegawa tuff has not been identified because many calderas coexisted in ne japan during the pliocene analysis of the trace element compositions of apatite major element compositions of ilmenite and u pb zircon ages demonstrate that depending on the area the previously mapped hirosegawa tuff comprises different volcanic ejecta furthermore this study identified that the source volcano of the hirosegawa tuff in the type section was the shiroishi caldera located 50 km south of sendai city

the stable isotope signature of kilometre scale fracturedominated metamorphic fluid pathways mary kathleen australia abstract large calcite veins and pods in the proterozoic corella formation of the mount isa inlier provide evidence for kilometre scale fluid transport during amphibolite facies metamorphism these 10 to 100 m scale podiform veins and their surrounding alteration zones have similar oxygen and carbon isotopic ratios throughout the 200 10 km mary kathleen fold belt despite the isotopic heterogeneity of the surrounding wallrocks the fluids that formed the pods and veins were not in isotopic equilibrium with the immediately adjacent rocks the pods have 13ccalcite values of 2 to 7 and 18ocalcite values of 10 5 to 12 5 away from the pods metadolerite wallrocks have 18owhole rock values of 3 5 to 7 and unaltered banded calc silicate and marble wallrocks have 13ccalcite of 1 6 to 0 6 and 18ocalcite of 18 to 21 in the alteration zones adjacent to the pods the 18o values of both metadolerite and calc silicate rocks approach those of the pods large calcite pods hosted entirely in calc silicates show little difference in isotopic composition from pods hosted entirely in metadolerite thus 100 to 500 m scale isotopic exchange with the surrounding metadolerites and calc silicates does not explain the observation that the 18o values of the pods are intermediate between these two rock types pods hosted in felsic metavolcanics and metasiltstones are also isotopically indistinguishable from those hosted in the dominant metadolerites and calc silicates these data suggest the veins are the product of infiltration of isotopically homogeneous fluids that were not derived from within the corella formation at the presently exposed crustal level although some of the spread in the data may be due to a relatively small contribution from devolatilization reactions in the calc silicates or thermal fluctuations attending deformation and metamorphism the overall l shaped trend of the data on plots of 13c vs 18o is most consistent with mixing of large volumes of externally derived fluids with small volumes of locally derived fluid produced by devolatilization of calc silicate rocks localization of the vein systems in dilatant sites around metadolerite calc silicate boundaries indicates a strong structural control on fluid flow and the stable isotope data suggest fluid migration must have occurred at scales greater than at least 1 km the ultimate source for the external fluid is uncertain but is probably fluid released from crystallizing melts derived from the lower crust or upper mantle intrusion of magmas below the exposed crustal level would also explain the high geothermal gradient calculated for the regional metamorphism

dynamics of giant volcanic ash clouds from supervolcanic eruptions 1 the largest explosive volcanic eruptions that have occurred on earth generated giant ash clouds from rising plumes that spread in the stratosphere around a height of neutral buoyancy with estimated supply rates that are in the range 1011 to 1013 m3 s these giant ash clouds are controlled by a balance between gravity and coriolis forces forming spinning bodies of nearly fixed proportions after a few hours and are initially insensitive to stratospheric winds in contrast volcanic plumes from eruptions with small to intermediate magnitude spread as inertial intrusions under the influence of stratospheric winds with the earth s rotation being unimportant in the largest eruptions the giant spinning ash clouds typically develop diameters greater than 600 km and up to 6000 km in the most powerful super eruptions thus explaining why areas of continental size can be covered with volcanic ash the radial expansion and spinning velocities are calculated at tens of metres per second and increase with eruption intensity higher spreading velocities carry larger ash grain sizes to a given radius so that grain size at a given distance from the source increases with eruption intensity consistent with geological observations

rapid rotation of southwest japan palaeomagnetism and k ar ages of miocene volcanic rocks of southwest japan summary miocene volcanic rocks have been sampled from the san in district in the central part of southwest japan reliable palaeomagnetic direction and k ar dating data have been obtained from 28 localities a clockwise deflection in declination d 38 5 is observed in the kawai formation having an age of 16 1 1 4 ma whereas a northerly declination is observed in formations younger than 14 2 0 6 ma these data indicate that southwest japan had ceased rotational motion by about 14 ma when compared with the amount of rotation estimated from cretaceous palaeomagnetic data it is apparent that more than 80 per cent of the overall clockwise rotation occurred between about 16 and 14 ma we conclude that the angular velocity of southwest japan about a rotation pole at 129 e 34 n reached 20 myr 1 at about 15 ma the corresponding rate of linear motion of the eastern part of southwest japan was 21 cm yr 1

towards a climate event stratigraphy for new zealand over the past 30 000 years nz intimate project it is widely recognised that the acquisition of high resolution palaeoclimate records from southern mid latitude sites is essential for establishing a coherent picture of inter hemispheric climate change and for better understanding of the role of antarctic climate dynamics in the global climate system new zealand is considered to be a sensitive monitor of climate change because it is one of a few sizeable landmasses in the southern hemisphere westerly circulation zone a critical transition zone between subtropical and antarctic influences new zealand has mountainous axial ranges that amplify the climate signals and consequently the environmental gradients are highly sensitive to subtle changes in atmospheric and oceanic conditions since 1995 intimate has through a series of international workshops sought ways to improve procedures for establishing the precise ages of climate events and to correlate them with high precision for the last 30 000 calendar years the nz intimate project commenced in late 2003 and has involved virtually the entire new zealand palaeoclimate community its aim is to develop an event stratigraphy for the new zealand region over the past 30 000 years and to reconcile these events against the established climatostratigraphy of the last glacial cycle which has largely been developed from northern hemisphere records e g last glacial maximum lgm termination i younger dryas an initial outcome of nz intimate has been the identification of a series of well dated high resolution onshore and offshore proxy records from a variety of latitudes and elevations on a common calendar timescale from 30 000 cal yr bp to the present day high resolution records for the last glacial coldest period lgcp including the lgm sensu stricto and last glacial interglacial transition lgit from auckland maars kaipo and otamangakau wetlands on eastern and central north island marine core md97 2121 east of southern north island speleothems on northwest south island okarito wetland on southwestern south island are presented discontinuous fragmentary records comprising compilations of glacial sequences fluvial sequences loess accumulation and aeolian quartz accumulation in an andesitic terrain are described comparisons with ice core records from antarctica epica dome c and greenland gisp2 are discussed a major advantage immediately evident from these records apart from the speleothem record is that they are linked precisely by one or more tephra layers based on these new zealand terrestrial and marine records a reasonably coherent regionally applicable sequence of climatically linked stratigraphic events over the past 30 000 cal yr is emerging three major climate events are recognised 1 lgcp beginning at ca 28 000 cal yr bp ending at termination i ca 18 000 cal yr bp and including a warmer and more variable phase between ca 27 000 and 21 000 cal yr bp 2 lgit between ca 18 000 and 11 600 cal yr bp including a lateglacial warm period from ca 14 800 to 13 500 cal yr bp and a lateglacial climate reversal between ca 13 500 and 11 600 cal yr bp and 3 holocene interglacial conditions with two phases of greatest warmth between ca 11 600 and 10 800 cal yr bp and from ca 6 800 to 6 500 cal yr bp some key boundaries coincide with volcanic tephras copyright 2007 john wiley sons ltd

fluid record of rock exhumation across the brittle ductile transition during formation of a metamorphic core complex naxos island cyclades greece fluid inclusions trapped in quartz veins hosted by a leucogneiss from the southern part of the naxos metamorphic core complex attic cycladic massif greece were studied to determine the evolution of the fluid record of metamorphic rocks during their exhumation across the ductile brittle transition three sets of quartz veins v m2 v bd v b are distinguished the v m2 and v bd are totally or respectively partially transposed into the foliation of the leucogneiss they formed by hydrofracturing alternating with ductile deformation accommodated by crystal plastic deformation the v b is discordant to the foliation and formed by fracturing during exhumation without subsequent ductile transposition fluids trapped during crystalplastic deformation comprise two very distinct fluid types namely a co2 rich fluid and a high salinity brine that are interpreted to represent immiscible fluids generated from metamorphic reactions and the crystallization of magmas respectively they were initially trapped at approximate to 625 degrees c and 400mpa and then remobilized during subsequent ductile deformation resulting in various degrees of mixing of the two end members with later trapping conditions of approximate to 350 degrees c and 140mpa in contrast brittle microcracks contain aqueous fluids trapped at 250 degrees c and 80mpa all veins display a similar 13c pointing to carbon that was trapped at depth and then preserved in the fluid inclusions throughout the exhumation history in contrast the d signature is marked by a drastic difference between i v m2 and v bd veins that are dominated by carbonic aqueous carbonic and high salinity fluids of metamorphic and magmatic origin characterized by d between 56 parts per thousand and 66 parts per thousand and ii v b veins that are dominated by aqueous fluids of meteoric origin characterized by d between 40 parts per thousand and 46 parts per thousand the retrograde pt pathway implies that the brittle ductile transition separates two structurally chemically and thermally distinct fluid reservoirs namely i the ductile crust into which fluids originating from crystallizing magmas and fluids in equilibrium with metamorphic rocks circulate through a geothermal gradient of 30 degrees c km1 at lithostatic pressure and ii the brittle upper crust through which meteoric fluids percolate through a high geothermal gradient of 55 degrees c km1 at hydrostatic pressure

tephrochronology of the kamchatka kurile and aleutian arcs evidence for volcanic episodicity abstract volcanic ash layers in north pacific deep sea sediment provide a record of episodic explosive volcanism in the kamchatka kurile and aleutian arcs over the past five million years we counted 450 ash layers determined layer thickness and cumulative ash thickness to quantify the flux of ash with time we use this record to investigate the eruptive history of these arcs test the reliability of the marine ash record and inquire into the regional episodicity of north pacific explosive volcanic history episodes of explosive volcanism occurred at approximately 0 2 0 5 0 7 0 9 1 5 1 7 and 2 5 2 65 ma in the kamchatka arc and 0 15 0 4 1 7 1 8 2 55 2 65 and at 3 0 3 1 ma in the eastern aleutian arc these generally coeval eruptive episodes suggest that the pulses in explosive volcanism in the north pacific enumerated here and recognized by others are regionally episodic over a wide portion of the pacific rim and not just a response to local volcanogenic processes

grain boundary migration of water and carbon dioxide during uplift of garnet zone alpine schist new zealand deformed quartz veins in garnet zone schist adjacent to the active alpine fault new zealand have fluid inclusions trapped along quartz grain boundaries textures suggest that the inclusions formed in their present shapes during annealing of the deformed veins many of the inclusions are empty but some contain carbon dioxide with densities that range from 0 16 to 0 80 g cm 3 no water nitrogen or methane was detected the inclusions are considerably more co2 rich than either the primary metamorphic fluid 5 co2 or fluids trapped in fracture related situations in the same or related rocks 50 co2 enrichment of co2 is inferred to have resulted from selective migration wicking of saline water from the inclusions along water wet grain boundaries after cooling induced immiscibility of a water co2 mixture inclusion volumes changed after loss of water non wetting co2 remained trapped in the inclusions until further percolation progressively removed co2 in solution this mechanism of fluid migration dominated in ductile quartz rich rocks near but below the brittle ductile transition at deeper levels hydraulic fracturing is also an important mechanism for fluid migration whereas at shallower levels advection through open fractures dominates the fluid flow regime

vapour loss boiling as a mechanism for fluid evolution in metamorphic rocks the calculation of fluid evolution paths during reaction progress is considered for multicomponent systems and the results applied to the ternary system co2 h2o nacl fluid evolution paths are considered for systems in which a co2 rich phase of lesser density vapour is preferentially removed from the system leaving behind a saline aqueous phase liquid such boiling leads to enrichment of the residual aqueous phase in dissolved components and for certain reaction stoichiometries to eventual saturation of the fluids in salt components distinctive textures particularly radiating growths of prismatic minerals such as tremolite or diopside are associated with saline fluid inclusions and solid syngenetic salt inclusions at a number of field localities the most thoroughly studied of these localities is campolungo switzerland where metasomatic rocks have developed in association with fractures and veins at 500 c and 2 000 bars of pressure the petrography of these rocks suggests that fluid phase separation into liquid and vapour has been an important process during metasomatism fracture systems with fluids at pressure less than lithostatic may facilitate the loss of the less dense vapour phase to conditions of the amphibolite facies

volcano tectonic interactions during rapid plate boundary evolution in the kyushu region sw japan evolution of the local plate tectonic and volcanic system relationship at kyushu island is defined by major changes in tectonics and volcanic style at ca 15 10 6 and 2 ma plate reconstructions presented here suggest that prior to 15 ma the pacific plate subduction dominated kyushu tectonics from 15 to 6 ma the evolving relative plate motions shifted the triple junction between the pacific plate philippine sea plate and southwest japan northwards so that the philippine sea plate was subducted beneath kyushu we suggest that a lack of subduction related volcanism from 10 to 6 ma is due to shallow subduction of the young shikoku basin lithosphere by 6 5 ma changes in the philippine sea plate motion led to more rapid nearly trench normal subduction of the eocene west philippine basin crust beneath kyushu this model is supported by an increase in arc like geochemistry of lavas since ca 6 5 ma subduction of fluid rich features such as the kyushu palau ridge introduced large volumes of fluids into the kyushu arc system leading to voluminous volcanism across kyushu focused particularly in areas where the ridge subduction occurs in tandem with local extensional tectonics key issues such as the timing of izu arc collision with central japan and the history of motion of the philippine sea plate are reassessed here resulting in a model that favors izu arc central japan collision at ca 8 6 ma rather than the more widely accepted date of ca 15 ma

particle size analyses of late quaternary allophane dominated andesitic deposits from new zealand abstract on the western north island new zealand a late quaternary sequence of allophane dominated cover bed andisol deposits have accumulated from intermittent accretion and rapid subsequent weathering of aerially transported detritus of dominantly andesitic provenance particle size analyses of andisol samples were attempted for textural classification and provenance studies the hydrometer and sedigraph techniques were unsuccessful due to difficulties arising from the flocculation of short range order clay and organic constituents sroco which prevented complete particle dispersion neither acidic hcl nor alkaline nh 4 oh or naoh solutions were effective in completely dispersing samples so an alternative chemical procedure was devised this alternative pretreatment involves the selective dissolution of andisol sroco constituents by 0 2 mol acid oxalate reagent ph 3 0 3 5 and has considerable potential in the determination of particle size soil textural classification and provenance of allophane dominated andesitic deposits

on the role of slab pull in the cenozoic motion of the pacific plate we analyze the role of slab pull acting on the pacific plate during its early tertiary change in motion slab pull forces are estimated by integrating the negative buoyancy of a 700 km long slab along a revised subduction boundary model adopting the muller et al 2008 seafloor age reconstructions our results indicate that torques predicted from a simple slab pull model match the pacific plate euler vectors during the tertiary fairly well the change of the pacific motion at similar to 50 40 ma appears to be driven by the onset of the izu bonin mariana system and soon afterwards by the tonga kermadec subduction zones

chronology of palaeoclimatic change at the end of the last glaciation analysis of sediments recorded in a piston core located east of southern north island new zealand gives a detailed record of climate change at the end of the last glacial accumulation rates1 of both detrital quartz and biological carbonate and biogenic silica components of the sediment are much higher during glacial than post glacial time and they all show a synchronous rapid decline at 14 700 yr bp we attribute this to a decline in intensity of the strong glacial westerly winds in the new zealand region as the polar winds contracted to their present latitudes2 6 the greatest rate of quartz accumulation occurs between 16 200 and 14 700 yr bp and is not matched by any change in carbonate or silica accumulation we believe this reflects accelerated fluvial transport of detritus out of the mountain ranges and consequently increased aeolian dust transport before the decline of the polar westerlies

the new worldwide collapse caldera database ccdb a tool for studying and understanding caldera processes collapse calderas are one of the most important volcanic structures not only because of their hazard implications but also because of their high geothermal energy potential and their association with mineral deposits of economic interest the objective of this work is to describe a new general worldwide collapse caldera database ccdb in order to provide a useful and accessible tool for studying and understanding caldera collapse processes the principal aim of the ccdb is to update the current field based knowledge on calderas merging together the existing databases and complementing them with new examples found in the bibliography and leaving it open for the incorporation of new data from future studies this database does not include all the calderas of the world but it tries to be representative enough to promote further studies and analyses we have performed a comprehensive compilation of published field studies of collapse calderas including more than 200 references and their information has been summarized in a database linked to a geographical information system gis application thus it is possible to visualize the selected calderas on a world map and to filter them according to different features recorded in the database e g age structure the information recorded in the ccdb can be grouped in seven main information classes caldera features properties of the caldera forming deposits magmatic system geodynamic setting pre caldera volcanism caldera forming eruption sequence and post caldera activity additionally we have added two extra classes the first records the references consulted for each caldera the second allows users to introduce comments on the caldera sample such as possible controversies concerning the caldera origin a further purpose of this work is to construct the ccdb web page in this web page where registered users can acquire the current database version as well as to propose corrections or updates and to exchange information with other registered members also involved in the study of caldera collapse processes additionally the ccdb includes a formulary that will facilitate the incorporation of new calderas into the database

mid latitude trans pacific reconstructions and comparisons of coupled glacial interglacial climate cycles based on soil stratigraphy of cover beds abstract south westland new zealand and southern chile are two narrow continental corridors effectively confined between the pacific ocean in the west and high mountain ranges in the east which impart significant influence over regional climate vegetation and soils in both these southern mid latitude regions evidence for extensive and repeated glaciations during cold phases of the quaternary is manifested by arrays of successively older glacial drift deposits with corresponding outwash plain remnants in south westland these variably aged glacial landforms are mantled by layered multisequal soils characterised by slow loess accretion and pedogenesis in an extreme leaching and weathering environment these cover bed successions have undergone repeated coupled phases of topdown and upbuilding soil formation that have been related to fluctuating cycles of interglacial warm and glacial cold climate during the quaternary in this study we recognise multisequal soils overlying glacial landforms in southern continental chile but unlike the spodic podzolic soil sequences of south westland these are of dominantly volcanigenic andic provenance and are very similar to multisequal soils of andic provenance that predominate in and adjacent to areas of rhyolitic to andesitic volcanism in north island new zealand here we develop a soil stratigraphic model to explain the observed occurrence of multisequal soils mantling dominantly glacial landforms of southern continental chile based on proxy data from southern chile we propose that persistent vegetation cover and high precipitation on the western side of the andes during colder than present episodes tended to suppress the widespread production of glacially derived loessial materials despite the pervasive occurrence of glacial and glacio fluvial deposits that have frequently inundated large tracts of this landscape during the quaternary given the lack of loess cover beds that have traditionally assisted in the relative dating of glacial episodes prior to the late quaternary surface exposure dating techniques could provide another chronological alternative to address this issue however there have been two main obstacles to successfully apply this dating technique in patagonia first minimum exposure ages may be obtained on moraines older than the last glacial cycle due to erosion although dating outwash plains is more robust second on the wet western side adjacent to the andes persistent vegetation cover during both glacial and post glacial times as well as widespread inundation by volcanic mass flows appear preventive we make a case that soil genesis within this region appears to be dominated by a constant flux of intermittently erupted andean sourced tephra which has continued to upbuild soils at the ground surface separated by intervals where topdown weathering processes are intensified as already demonstrated by new zealand studies multisequal soil successions have a clear implied connection to coupled glacial and interglacial climate cycles of the quaternary on this basis similar sequences in northwest patagonia provide a relatively untapped archive to enable quaternary glacial and environmental changes in this pervasively glaciated volcanic region to be constructed

tephra dispersal from myojinsho japan during its shallow submarine eruption of 1952 1953 a new and detailed bathymetric map of the myojinsho shallow submarine volcano provides a framework to interpret the physical volcanology of its 1952 1953 eruption especially how the silicic pyroclasts both primary and reworked enlarged the volcano and were dispersed into the surrounding marine environment myojinsho 420 km south of tokyo along the izu ogasawara arc was the site of approximately 1000 phreatomagmatic explosions during the 12 5 month eruption these explosions shattered growing dacite domes producing dense clasts that immediately sank into the sea minor amounts of pumice floated on the sea surface after some of these events the myojinsho cone has slopes of almost precisely 21 in the depth range 300 700 m we interpret this to be the result of angle of repose deposition of submarine pyroclastic gravity flows that traveled downslope in all directions many of these gravity flows resulted from explosions and associated dome collapse but others were likely triggered by the remobilization of debris temporarily deposited on the summit and steep upper slopes of the cone tephra was repeatedly carried into air in subaerial eruption columns and fell into the sea within 1 2 km of the volcano s summit entering water as deep as 400 m because the fall velocity of single particles decreased by a factor of 30 in passing from air into the sea we expect that the upper part of the water column was repeatedly choked with hyperconcentrations of fallout tephra gravitational instabilities within these tephra choked regions could have formed vertical density currents that descended at velocities greater than those of the individual particles they contained upon reaching the sea floor many of these currents probably continued to move downslope along myojinsho s submarine slopes fine tephra was elutriated from the rubbly summit of the volcano by upwelling plumes of heated seawater that persisted for the entire duration of the eruption ocean currents carried this tephra to distal areas where it presumably forms a pyroclastic component of deep sea sediment

relationship between tectonics volcanism sedimentation and basin development late cenozoic central part of northern honshu japan abstract a pronounced interplay between tectonics volcanism and sedimentation can be established in the volcanic arc region of the central part of northern honshu during the early miocene to quaternary interval four stages are recognized with the type of volcanism and sedimentation varying according to the tectonic stress regime 1 1 rifting stage 22 15 ma ns trending half grabens were formed under an extensional stress regime related to the rifting of the sea of japan basins were rapidly filled by intermediate to felsic volcanic products which are often associated with subaerial fluvial and lacustrine sediments 2 2 back arc basin opening stage 15 13 ma with more advanced stagess of rifting subsidence from crustal stretching resulted in marked marine incursion and an overall transgressive succession developed during this stage the back arc side of northern honshu subsided rapidly to middle bathyal environments at the same time associated with the opening of the sea of japan large volumes of regionally extensive mafic lavas and associated hyaloclastites were erupted within submarine grabens in contrast in the present backbone ranges felsic volcanism occurred within bathyal to shallow marine environments igneous rock types in this stage display a bimodal mafic felsic chemistry 3 3 transitional stage 13 2 4 ma a thermal subsidence substage 13 8 ma an intermediate stress regime developed which included phases of both weak extension and compression consequently grabens along the sea of japan ceased to form later lithospheric cooling eventually led to thermal subsidence of the back arc region and hemipelagic sediments mantled the previously active mafic volcanic apron volcanism at this time was mainly restricted to a narrow zone along the present backbone ranges where felsic to intermediate volcanic products accumulated within shallow marine environments b incipient compressional substage 8 2 4 ma hemipelagic sedimentation continued on the back arc side of northern honshu along the present backbone ranges the intermediate stress regime continued with formation of many large caldera structures associated with subaerial felsic volcanism 4 4 shortening deformation stage 2 4 ma present the change of the absolute direction of motion of the pacific plate at the early to middle pliocene changed the regional stress regime of the volcanic arc from intermediate to compression movement of back arc thrusts along the sea of japan coast began 2 3 ma and led to uplift of the volcanic arc continued compression in the volcanic arc produced narrow uplifted zones with associated basins bounded by reverse faults these basins were filled rapidly by terrestrial sediments containing upward coarsening sequences under this highly compressional tectonic stress regime volcanism became intermediate mafic in composition with large stratovolcanoes becoming prominent

the effect of fluid salinity on infiltration driven contact metamorphism of carbonate rocks calculated phase equilibria involving minerals and h2o co2 nacl fluid lead to predictions of how infiltration of rock by h2o nacl fluids with xnacl in the range 0 0 3 0 58 wt nacl drives the reactions calcite quartz wollastonite co2 and dolomite periclase calcite co2 calculations focus on metamorphism in four aureoles that together are representative of the normal p t conditions and processes of infiltration driven contact metamorphic reactions the effect of salinity on the spatial extent of oxygen isotope alteration was also computed the time integrated input fluid flux q that displaces the mineral reaction front an increment of distance along the flow path always increases with increasing xnacl for input fluids with salinity up to approximately five times that of seawater xnacl 0 05 values of q required to explain the spatial extent of decarbonation reaction are no more than 1 1 1 5 times that computed assuming the input fluid was pure h2o for more saline fluids values of q may be up to 1 4 7 9 times that for pure h2o except for reaction in the presence of halite and vapor v infiltration of h2o nacl fluids expands the region of oxygen isotope alteration relative to the size of the region of mineral reaction the expansion is significant only for saline fluids with xnacl 0 1 immiscible fluid phase separation and differential loss of the liquid l or v phase from the mineral reaction site increases the amount of reactive fluid required to advance the mineral reaction front compared to conditions under which equilibration of minerals and fluid is attained with no loss of l or v decarbonation reactions driven by infiltration of fluids with even modest seawater like salinity can explain the occurrence of salt saturated fluid and solid halide inclusions in contact metamorphosed carbonate rocks

the preservation potential of ash layers in the deep sea the example of the 1991 pinatubo ash in the south china sea following the eruption of mount pinatubo on 15 june 1991 volcanic ash was transported westward to the south china sea in an atmospheric plume falling out and settling to the sea floor within days and forming an up to 10 cm thick layer on an area 400 000 km 2 immediately after deposition surviving deepburrowing animals re opened their connection to the sea floor to obtain water for respiration and or food take up later small sized meiofauna and then macrofauna re colonized the sea floor mixing newly deposited organic fluff with the underlying ash consequently ash deposits thinner than 1 mm have not often been observed as a continuous layer when cored six years after the eruption while ash about 2 mm thick is now patchily bioturbated in areas covered by ash thicker than 5 mm mixing by benthic animals is controlled mainly by the adaptation of the burrowing fauna to variations in grain size the rate of background sedimentation the availability of benthic food on and within the sediment and pore water oxygen levels with respect to these factors four provinces can be distinguished i along the philippines margin run off from land fuels primary production that in turn leads to a high benthic food content the benthic fauna is adapted to a variable grain size and rapid sedimentation therefore mixing is intense and the preservation potential of the ash layer is low ii in areas affected by deposition of hyperpycnites and turbidites i e in canyons in front of river mouths and in the manila trench the ash layer is preserved due to rapid burial iii the area to the west to about 116 e receives low amounts of benthic food benthic mixing is less intense and the preservation potential of the ash is high iv the central south china sea where the ash is thinner than 3 cm is affected by intense wind mixing and upwelling and the benthic food content is high thus the chance that the ash will be preserved as a sharp based layer is low consequently the style of ash preservation has palaeo environmental significance older buried and burrowed event layers provide further information to elucidate the fate of the 1991 pinatubo ash layer in general their appearance fits with observations in the recent

magmatic co 2 and saline melts from the sybille monzosyenite laramie anorthosite complex wyoming there are three populations of fluid inclusions in quartz from the sybille monzosyenite early co2 secondary co2 and rare secondary brines the oldest consist of low density co2 0 70 inclusions that appear to be co magmatic the densities of these inclusions are consistent with the inferred crystallization conditions of the sybille monzosyenite namely 3 kilobars and 950 1000 c the other types of inclusions are secondary they contain co2 0 50 and secondary brine inclusions that form trains radiating out from a decrepitated inclusion the sites of these decrepitated inclusions are now marked by irregularly shaped fluid inclusions and solid inclusions of salt and carbonate rather than fluid inclusions feldspar contain abundant solid inclusions these consist of magmatic minerals hedenbergite hornblende ilmenite apatite and graphite intimately associated with k na chlorides we interpret these relations as follows the sybille monzosyenite formed from a magma that contained immiscible droplets of a halide rich melt along with a co2 vapor phase the salt was trapped along with the other obvious magmatic minerals during growth of the feldspars co2 may have also been included in the feldspars but it probably leaked later during exsolution of the feldspars and was not preserved both the saline melt and the co2 vapor were trapped in the quartz the melt inclusions in the quartz later decrepitated perhaps due to progressive exsolution of fluids to produce the secondary h2o and co2 inclusions these observations indicate that the sybille monzosyenite which is a markedly anhydrous rock was actually vapor saturated rather than being h2o however the vapor was co2 rich and possibly related to an immiscible chloride rich melt

late quaternary tephra derived paleosols in central italy s carbonate apennine range stratigraphical and paleoclimatological implications abstract detailed stratigraphical pedological and geochronological 14c dating research was carried out on numerous sections located in the carbonate apennine range of central italy two paleosols late pleistocene pedomarker a and holocene pedomarker b in age were recognized as having developed from air fall pyroclastic material given their special properties and widespread distribution both soils represent valuable markers in the late quaternary stratigraphy of central italy information about the climatic conditions that have influenced their pedogenesis through time has been obtained pedomarker a formed under temperate wet conditions related to the last interstadial fluctuations of the pleniglacial its development ceased after ca 30 ka because of the onset of last glacial maximum dry cold conditions pedomarker b formed at the beginning of the holocene under udic and perudic soil moisture regimes its development ceased in some localities because of a change towards a drier climate after ca 4 5 ka petrographic and geochemical characteristics of the parent materials are discussed and correlations with the campanian ignimbrite pedomarker a and neapolitan yellow tuff pedomarker b both related to activity in the phlegrean fields are proposed

some aspects of fluid motion during metamorphism most of the mineralogical chemical and textural features that can be observed in metamorphic rocks are produced during devolatilization reactions fyfe et al 1978 thompson 1983 in many cases only the last such event is recorded between devolatilization pulses fluid rock interaction will be minimal and microstructural evidence of even the last event is often modified by recrystallization ridley thompson 1986 the mechanisms by which the fluids escape varies depending upon whether a connected porosity or fracture network is available and the magnitudes of temperature and fluid pressure gradients e g norton knight 1977 etheridge et al 1984 yardley 1986 these factors will change during the metamorphic process fluids released deeper in the metamorphic pile do not necessarily flow pervasively through the overlying rocks but rather appear to be focused into high permeability channelways through a variety of processes fyfe et al 1978 wood walther 1986 the patchiness of retrogressive alteration points also to the focused flow of fluid after a metamorphic peak and perhaps under different rheological conditions metamorphism in the absence of fluid results in incomplete mineral reactions and other disequilibrium features in metamorphic rocks thompson 1983 ridley dixon 1984 many papers have appeared in recent years dealing with aspects of fluid motion during metamorphism they have variously demonstrated the transient nature of fluid flow indicated some controls on different modes of fluid behaviour and suggested that mechanical responses will be different depending upon whether a rock is undergoing devolatilization or not attention is focused here on

asynchronous climate change between new zealand and the north atlantic during the last deglaciation climatic fluctuations recorded in antarctica and greenland during the last deglaciation 18 10 ka differ markedly in their timing it remains controversial whether local climate fluctuations recorded in southern mid latitudes relate primarily to northern or southern polar records we present multiproxy results from new zealand that show strong evidence for a minor cooling or slowdown in the rate of warming at the time of the north atlantic late glacial interstadial the younger dryas chronozone in new zealand was a period of resumed warming and increased westerly airflow differences between the hemispheres at this time were probably due to a reorganization of the thermohaline circulation system and associated changes in the meridional temperature gradient

relationship between outer forearc subsidence and plate boundary kinematics along the northeast japan convergent margin 1 tectonic erosion along convergent plate boundaries whereby removal of upper plate material along the subduction zone interface drives kilometer scale outer forearc subsidence has been purported to explain the evolution of nearly half the world s subduction margins including part of the history of northeast japan here we evaluate the role of plate boundary dynamics in driving forearc subsidence in northeastern japan a synthesis of newly updated analyses of outer forearc subsidence the timing and kinematics of upper plate deformation and the history of plate convergence along the japan trench demonstrate that the onset of rapid fore arc tectonic subsidence is contemporaneous with upper plate extension during the opening of the sea of japan and with an acceleration in convergence rate at the trench in plio quaternary time relative uplift of the outer forearc is contemporaneous with contraction across the arc and a decrease in plate convergence rate the coincidence of these changes across the forearc arc backarc system appears to require an explanation at the scale of the entire plate boundary similar observations along other western pacific margins suggest that correlations between forearc subsidence and major changes in plate kinematics are the rule rather than the exception we suggest that a significant component of forearc subsidence at the northeast japan margin is not the consequence of basal tectonic erosion but instead reflects dynamic changes in plate boundary geometry driven by temporal variations in plate kinematics if correct this model requires a reconsideration of the mass balance and crustal recycling of continental crust at nonaccretionary margins

a last interglacial pollen temperature reconstruction central north island new zealand abstract we present new pollen temperature reconstructions for the last interglacial from central north island new zealand using partial least squares regression pls and modern analogue technique applied with the new zealand pre deforestation calibration pollen dataset the pollen bearing organic sequence includes numerous millimetre to decimetre thick tephra mostly from the adjacent tongariro volcanic centre and is overlain by tephric cover beds including the c 25 4 ka cal bp kawakawa oruanui tephra fine resolution pollen and preliminary diatom analyses above and below prominent tephra layers showed that significant vegetation impact followed only the thickest ashfall event 22 cm thickness with vegetation recovery taking several hundred years apart from this changes in the longer term pollen record are likely to be related to climate oscillations that resemble the classic five fold subdivision of mis 5 the warmest interval ascribed to mis 5e was characterised by tall temperate rainforest and occurs at the base of the sequence with mean annual temperatures reaching around 1 1 c higher than present mean annual temperatures declined to 4 c below present during mis 5d and mis 5b and were within 1 2 c of present during mis 5c the pls temperature reconstructions are corroborated by estimates derived independently from elevational changes to vegetation communities corresponding to modern temperature controls inferred from the karioi pollen spectra temperatures reconstructed quantitatively by the modern analogue technique were up to 1 3 c higher for mis 5e mis 5d and mis 5b possibly reflecting weaker modern vegetation analogues for these intervals

investigation of an aggrading paleosol developed into andesitic ring plain deposits ruapehu volcano new zealand within a sequence of andesitic volcaniclastic deposits on the northeastern ring plain of ruapehu volcano is a ca 10 m thick sequence of weathered andesitic tephras weathering and paleosol development is most evident in 3 6 m of fine ash in this sequence the ages of these tephras are constrained between ca 23 70 ka by dated rhyolite tephras erupted from central north island volcanoes mineralogy of the fine ash deposits reveals their origin and the processes involved in their soil development the fine ash deposits are almost totally locally derived either as primary volcanic ash or fines reworked from the ring plain itself by aeolian processes aerosolic quartz input associated with regional loess deposition during the cool climatic episodes of mid 18o stage 3 and 18o stage 4 is very low having been diluted by rapid accumulation of andesitic tephras in these episodes the observed weathering features and secondary minerals within the ash sequence were derived from a complex combination of factors including climate change accretion rate and post depositional modification relatively strong weathering development in two parts of the ash sequence is correlated with two widespread soil development episodes during the last glacial observed throughout the southern north island the accretion rate of the soil surface at these times also affected the expression of climate related weathering formation of allophane with an a1 si ratio of 2 1 and ferrihydrite occurred near the soil surface as the ash was accreting the amount of allophane and ferrihydrite through the sequence appears to be inversely related to the accretion rate of the soil surface upon burial of the ash materials by a thick 20 m sequence of lahar and tephra deposits halloysite was later formed in the buried ash the leaching of silica from the thick overburden of volcaniclastics into the ash material as well as perched water is thought to have decreased the a1 si ratio in the soil solution and thus promoted the formation of halloysite from weathering andesitic glass

ocean overturning since the late cretaceous inferences from a new benthic foraminiferal isotope compilation 1 benthic foraminiferal oxygen isotopic d 18 o and carbon isotopic d 13 c trends constructed from compilations of data series from multiple ocean sites provide one of the primary means of reconstructing changes in the ocean interior these records are also widely used as a general climate indicator for comparison with local and more specific marine and terrestrial climate proxy records we present new benthic foraminiferal d 18 o and d 13 c compilations for individual ocean basins that provide a robust estimate of benthic foraminiferal stable isotopic variations to 80ma andtentatively to 110ma first order variations ininterbasinal isotopicgradients delineate transitions from interior ocean heterogeneity during the late cretaceous 65 ma to early paleogene 35 65 ma homogeneity and a return to heterogeneity in the late paleogene early neogene 35 0 ma we propose that these transitions reflect alterations in a first order characteristic of ocean circulation the ability of winds to make water in the deep ocean circulate we document the initiation of large interbasinal d 18 o gradients in the early oligocene and link the variations in interbasinal d 18 o gradients from the middle eocene to oligocene with the increasing influence of wind driven mixing due to the gradual tectonic opening of southern ocean passages and initiation and strengthening of the antarctic circumpolar current the role of wind driven upwelling possibly associated with a tethyan circumequatorial current in controlling late cretaceous interior ocean heterogeneity should be the subject of further research

thermal metamorphism and h 2 o co 2 nacl immiscibility at patapedia quebec evidence from fluid inclusions the methamorphic history of the patapedia thermal zone gaspe quebec is re evaluated in the light of results obtained from a study of fluid inclusions contained in quartz phenocrysts of felsic dyke rocks the thermal zone is characterised by calc silicate bodies that have outwardly telescoping prograde metamorphic isograds and display extensive retrograde metamorphism with associated copper mineralization three distinct fluid inclusion types are recognized a low to moderate salinity high density aqueous fluid type i a low density co2 fluid type ii and a high salinity high density aqueous fluid type iii fluid inclusion types i and ii predominate whereas type iii inclusions form 10 of the fluid inclusion population all three fluid types are interpreted to have been present during prograde metamorphism temperatures and pressures of metamorphism estimated from fluid inclusion microthermometry and isochore calculations are 450 500 c and 700 1000 bars respectively a model is proposed in which the metamorphism at patapedia was caused by heat transferred from a low to moderate salinity fluid of partly orthomagmatic origin type i inclusions during the early stages and particularly in the deeper parts of the system co2 produced by metamorphism was completely miscible in the aqueous hydrothermal fluid and locally resulted in high xco2 fluids on cooling and or migrating to higher levels these latter fluids exsolved high salinity aqueous fluids represented by the type iii inclusions most of the metamorphism however took place at temperature pressure conditions consistent with the immiscibility of co2 and the hydrothermal fluid and was consequently accompanied by the release of large volumes of co2 vapour which is represented by type ii inclusions the final stage of the history of the patapedia aureole was marked by retrograde metamorphism and copper mineralization of a calcite free calc silicate hornfels in the presence of a low xco2 fluid

enrichment of co2 in fluid inclusions in quartz by removal of h2o during crystal plastic deformation abstract ductile strain induced leakage of h 2 o from mixed co 2 h 2 o fluid inclusions in quartz is proposed as a mechanism for producing occurrences of pure co 2 fluid inclusions in metamorphic rocks the h 2 o needed for hydrolytic weakening of quartz under stress may be provided by the h 2 o in fluid inclusions with dislocation creep as dislocations nucleate on the walls of fluid inclusions or intersect them h 2 o can be transported with the dislocations from the inclusion to the grain boundaries the process should continue so long as there is stress on the host quartz and the inclusion contains h 2 o the h 2 o taken to the grain boundaries would due to its wetting properties be wicked out along the grain boundaries if the h 2 o is totally removed from an inclusion by a flux of dislocations through the quartz during the crystal plastic flow then a residual inclusion bearing components other than water should remain a mixed co 2 h 2 o inclusion would as a consequence of the process become a pure co 2 fluid inclusion during dynamic recrystallization the co 2 would collect at grain boundary triple junctions and following grain boundary migration would become incorporated into the recrystallized quartz as fluid inclusions this mechanism of generating pure co 2 inclusions could result in co 2 fluid inclusions having densities appropriate for the pressure temperature conditions during deformation using estimates of temperature of deformation the total confining pressure during deformation could be determined from the density of the co 2 fluid in these inclusions

mineral fluid equilibria in the system cao mgo sio2 h2o co2 nacl and the record of reactive fluid flow in contact metamorphic aureoles phase equilibria in the system cao mgo sio2 co2 h2o nacl are calculated to illustrate phase relations in metacarbonates over a wide range of p t x h2o co2 nacl conditions calculations are performed using the equation of state of duan et al geochim cosmochim acta 59 2869 2882 1995 for h2o co2 nacl fluids and the internally consistent data set of gottschalk eur j mineral 9 175 223 1997 for thermodynamic properties of solids results are presented in isothermal isobarical plots showing stable mineral assemblages as a function of fluid composition it is shown that in contact metamorphic p t regimes the presence of very small concentrations of nacl in the fluid causes almost all decarbonation reactions to proceed within the two fluid solvus of the h2o co2 nacl system

the role of egmont sourced tephra in evaluating the paleoclimatic correspondence between the bio and soil stratigraphic records of central taranaki new zealand abstract on the lower eastern flanks of egmont volcano western north island new zealand several egmont sourced tephras have been correlated to a radiocarbon dated peat site that provides a late last glacial to early post glacial record of vegetation and climate change in central taranaki the pollen spectra at this site indicates a mosaic of grassland shrubland and prumnopitys taxifolia dominant forest at ca 13 100 bp and suggests a climate cooler and drier than at present the ominance of tall podocarp forest by ca 12 900 bp suggests that climatic amelioration was rapid towards the end of the last glacial period initially this forest was dominated by prumnopitys taxifolia but at ca 11 000 bp was succeeded by dacrydium cupressinum indicating a steady shift to warmer and moister climate tephra interbedded with peat allows precise chrono correlation into the andisol forming environment the rapidity of climatic amelioration identified from variations in andisol morphology and mineralogy concurs with that indicated from pollen changes in the peat

miocene to holocene marine tephrostratigraphy offshore northern central america and southern mexico pulsed activity of known volcanic complexes we studied the tephra inventory of fourteen deep sea drill sites of three dsdp and odp legs drilled offshore guatemala and el salvador legs 67 84 138 and one leg offshore mexico leg 66 marine tephra layers reach back from the miocene to the holocene we identified 223 primary ash beds and correlated these between the drill sites with regions along the volcanic arcs and to specific eruptions known from land in total 24 correlations were established between marine tephra layers and to well known quaternary eruptions from el salvador and guatemala additional 25 tephra layers were correlated between marine sites another 108 single ash layers have been assigned to source areas on land resulting in a total of 157 single eruptive events tephra layer correlations to independently dated terrestrial deposits provide new time markers and help to improve or confirm age models of the respective drill sites applying the respective sedimentation rates derived from the age models we calculated ages for all marine ash beds hence we also obtained new age estimates for eight known but so far undated large terrestrial eruptions furthermore this enables us to study the temporal evolution of explosive eruptions along the arc and we discovered five pulses of increased activity 1 a pulse during the quaternary 2 a pliocene pulse between 6 and 3 ma 3 a late miocene pulse between 10 and 7 ma 4 a middle miocene pulse between 17 11 ma and 5 an early miocene pulse 21 ma

the relationship between late cenozoic tectonic events and stress field and basin development in northeast japan the regional tectonic stress field basin development and crustal deformation of the ne japan arc in the interval between 32 ma to the quaternary can be synthesized based on dike vein and fault orientation data as well as on the compilation of the regional geology an extensional stress field became prevalent from 32 ma and major normal faulting started at 25 20 ma which resulted from back arc rifting normal faulting trending nearly parallel to the arc propagated from the present japan sea coast to the forearc side following the trenchward migration of the main volcanic field from 20 to 15 ma normal faults with an oblique trend to the arc developed due to the counterclockwise rotation of ne japan the rapid clockwise rotation of sw japan since 16 ma produced a nw se directed transtensional stress regime in the ne japan arc due to crustal stretching associated with this pull apart movement the back arc side of the ne japan arc subsided rapidly to middle bathyal environments after the termination of the opening of the japan sea at about 14 ma a neutral stress regime prevailed which included phases of both weak extension and compression lithospheric cooling eventually led to thermal subsidence of the back arc region and igneous underplating caused uplift of the axial zone of the volcanic arc the increase in velocity of the westward motion of the pacific plate at around 4 ma produced strong compression across the arc reactivating most of the miocene normal faults and uplifting the volcanic arc the greatest crustal shortening occurred in areas that were stretched the most in the miocene within the volcanic arc which implies tectonic inversion

the compositional limits of fluid immiscibility in the system h2onaclco2 as determined with the use of synthetic fluid inclusions in conjunction with mass spectrometry abstract the compositional limits of fluid immiscibility in the system nacl h2o co2 were investigated from 500 to 700 c at pressures of 1 2 and 3 kbar synthetic fluid inclusions formed in quartz prisms were equilibrated with high temperature high pressure fluids in hydrothermal pressure vessels the inclusions were analyzed optically by mass spectrometry and by microthermometry the fields of immiscibility were defined as a function of temperature and pressure mass spectrometry was used to validate the existence of the immiscible fluids and to determine the co 2 h 2 o ratios of the two coexisting phases microthermometry i e the measurement of the melting temperature of solid sodium chloride was used in conjunction with the results of the mass spectrometry measurements to define the tie lines within the two phase fields isochores and the location of a portion of the isopleth were determined for composition nacl8 9 h2o76 1 co215 0

climate of the last glaciation in new zealand based on aerosolic quartz influx in an andesitic terrain abstract on western north island new zealand a record of climatic change during the last glaciation is preserved in a terrestrial coverbed sequence of dominantly andesitic provenance here a succession of five loess like andisol units postdates the global high sea level stand of oxygen isotope substage 5e

increased rates of large magnitude explosive eruptions in japan in the late neogene and quaternary tephra layers in marine sediment cores from scientific ocean drilling largely record high magnitude silicic explosive eruptions in the japan arc for up to the last 20 million years analysis of the thickness variation with distance of 180 tephra layers from a global data set suggests that the majority of the visible tephra layers used in this study are the products of caldera forming eruptions with magnitude m 6 considering their distances at the respective drilling sites to their likely volcanic sources frequency of visible tephra layers in cores indicates a marked increase in rates of large magnitude explosive eruptions at 8 ma 6 4 ma and further increase after 2 ma these changes are attributed to major changes in tectonic plate interactions lower rates of large magnitude explosive volcanism in the miocene are related to a strike slip dominated boundary and temporary cessation or deceleration of subduction between the philippine sea plate and southwest japan combined with the possibility that much of the arc in northern japan was submerged beneath sea level partly due to previous tectonic extension of northern honshu related to formation of the sea of japan changes in plate motions and subduction dynamics during the 8 ma to present period led to 1 increased arc normal subduction in southwest japan and resumption of arc volcanism and 2 shift from extension to compression of the upper plate in northeast japan leading to uplift crustal thickening and favorable conditions for accumulation of the large volumes of silicic magma needed for explosive caldera forming eruptions

low temperature diagenetic metamorphic and magmatic contributions of external co2 gas to a shallow ground water system abstract a small 2 low temperature 2 gas overpressured gently dipping paleozoic carbonate aquifer rests on precambrian granite in a narrow canyon along the eastern edge of the rocky mountain front range colorado the carbonate aquifer is bounded on three sides by granite and in the down dip direction by the front range fault the fault in a major continental intraplate zone of weakness along which magmatic fluids and gases could migrate to the surface and near surface from great depths the fault has also overthrusted slices of carbonate and clastic rocks several kilometres below the granitic basement stable isotopic 2 h and 18 o and discharge temperature data suggests that carbonate aquifer ground waters are of meteoric origin and have not circulated to depths greater than the base of the carbonate aquifer 650 m elevated co 2 and the 13 c of hco 3 in the carbonate aquifer suggest an external crustal source of co 2 gas 3 he 4 he o 2 n 2 and ar n 2 gas ratios indicate gas contributions from both magmatic and atmospheric sources atmosphere contributions account for about 25 of the exsolving gas whereas magmatic co 2 accounts for 7 to 14 possible external co 2 sources which are consistent with the mean hco 3 13 c 2 4 pdb are clay carbonate mineral diagenesis or low temperature metamorphism of siliceous carbonate rocks that have been overthrust by 3 to 6 km of granite diagenetic or metamorphic co 2 mixed with some magmatic gas appears to have migrated from the source rock area upward along the ute pass thrust fault until it encountered the shallow carbonate aquifer ground water system where it was further diluted with atmospheric gas

melting of albite and dehydration of brucite in h 2 o nacl fluids to 9 kbars and 700 900 c implications for partial melting and water activities during high pressure metamorphism the melting reaction albite solid h2o fluid albite h2o melt has been determined in the presence of h2o nacl fluids at 5 and 9 2 kbar and results compared with those obtained in presence of h2o co2 fluids to a good approximation albite melts congruently at 9 kbar indicating that the melting temperature at constant pressure is principally determined by water activity at 5 kbar the temperature t mole fraction x h2o melting relations in the two systems are almost coincident by contrast h2o nacl mixing at 9 kbar is quite non ideal albite melts 70 c higher in h2o nacl brines than in h2o co2 fluids for x h2o 0 8 and 100 c higher for x h2o 0 5 the melting temperature of albite in h2o nacl fluids of x h2o 0 8 is 100 c higher than in pure water the p t curves for albite melting at constant h2o nacl show a temperature minimum at about 5 kbar water activities in h2o nacl fluids calculated from these results from new experimental data on the dehydration of brucite in presence of h2o nacl fluid at 9 kbar and from previously published experimental data indicate a large decrease with increasing fluid pressure at pressures up to 10 kbar aqueous brines with dissolved chloride salt contents comparable to those of real crustal fluids provide a mechanism for reducing water activities buffering and limiting crustal melting and generating anhydrous mineral assemblages during deep crustal metamorphism in the granulite facies and in subduction related metamorphism low water activity in high pressure temperature metamorphic mineral assemblages is not necessarily a criterion of fluid absence or melting but may be due to the presence of low a h2o brines

fluid heterogeneities and hornblende stability in interlayered graphitic and nongraphitic schists tauern window eastern alps the assemblage hornblende white mica occurs in graphite free schists at two localities in the southwest corner of the tauern window eastern alps in interbedded graphitic layers 1 mm to 1 m thick however hornblende is typically replaced by pseudomorphs of biotite plagioclase epidote chlorite staurolite in the presence of white mica garnets adjacent to these pseudomorphs have pronounced growth discontinuities near their rims in contrast to the continuously zoned garnets in nongraphitic layers these observations imply that reactions of the type hbl white mica gar bio plag epid chl staur h2o occurred in the graphitic samples but that hbl white mica remained stable in graphite free layers calculation of the equilibrium constants for solid phases in five dehydration equilibria at locality 1 indicates thata h2o in the nongraphitic layers was 6 to 11 times greater thana h2o in the graphitic layers similar calculations involving six dehydration equilibria at locality 2 show no difference ina h2o between layers at the conditions of final equilibration initial differences in fluid composition maintained between the graphitic and nongraphitic layers caused the hbl white mica reaction to occur at differentp t conditions in different horizons of the schists these data indicate that systematic differences in fluid composition were generated during metamorphism of the interlayered graphitic and non graphitic schists but were subsequently homogenized at locality 2 the heterogeneities could initially have been produced while the rocks were in thep t field of co2 h2o immiscibility development of a penetrative layer parallel shear foliation at this time would have prevented subsequent mixing of the fluids across layers after temperatures exceeded the consolute temperature in the co2 h2o system late stage homogenization of fluids at locality 2 is thought to reflect loss of the buffer capacity of the mineral assemblage in response to total consumption of hornblende

the santa rita gold deposit in the proterozoic paranoa group goias brazil an example of fluid mixing during ore deposition abstract the santa rita gold deposit central goias brazil is hosted by middle to upper proterozoic carbonate pelite sequences of the paranoa group that have been metamorphosed in the greenschist facies the ore is contained in pyrite bearing quartz carbonate veins the mineralization is structurally controlled by wnw ese high angle faults and fractures resulting from the reactivation of older ne sw lineaments pyrite is the sole sulphide and it shows growth zones enriched in co ni and as up to 4 wt hydrothermal alteration zones are enriched in co ni and as and are characterized by diffuse albitization carbonatization silicification and pyritization a fluid inclusion study on quartz from pyrite bearing quartz carbonate veins led to the identification of two fluids 1 a highly saline co 2 n 2 rich aqueous fluid with halite and sylvite daughter minerals and 2 a co 2 n 2 rich aqueous fluid with moderate salinity the two fluid types occur in the same quartz domain and display great variation in the degree of filling and notable dispersion of the microthermometric data on heating all the inclusions decrepitate between 200 and 300 c raman spectrometry detected high concentrations of n 2 in the gas phase with a co 2 n 2 molar ratio between 1 and 19 and a small proportion of ch 4 up to 2 mole the simultaneous entrapment of compositionally variable fluids in the system h 2 o co 2 n 2 nacl kcl allow us to propose a mechanism of heterogeneous trapping the entrapment may result from the mixing of a high salinity fluid h 2 o nacl kcl system with a carbonic fluid h 2 o co 2 n 2 system produced by the devolatilization process of carbonate and phyllitic host rocks considering the absence of spatially and temporally related igneous activity and the low p t regional metamorphism in the paranoa group the brines are inferred to result from leaching of evaporites occurring in the lower part of the paranoa lithostratigraphic column gold was probably initially transported as an aucl 2 complex t 300 c low ph moderate o 2 pyrite field stability as temperature decreased below 290 c the switch over process would lead to the predominance of au hs 2 in the fluid pyrite precipitated in this temperature interval the oscillatory zoning of the as co ni bearing pyrites indicates episodic fluctuation of the fluid composition such changes in fluid composition are favoured by a mechanism of fluid mixing by intermittent supplies in the hydrothermal system the proposed mechanism of heterogeneous trapping of two separate fluids in the system h 2 o co 2 n 2 nacl kcl and the resulting changes in the physicochemical conditions caused by the fluid mixing appears as a conspicuous process for the santa rita hydrothermal fluid evolution a model based on the existence of a proterozoic geothermal system involving the regional thermal gradient is proposed

fluid immiscibility in metamorphic rocks evidence of fluid immiscibility in metamorphic rocks comes in the best of all worlds from fluid inclusion observations in fact fluid immiscibility should be anticipated over the full range of metamorphic conditions provided that appropriate bulk fluid compositions are present in a review paper entitled metamorphic fluids the evidence from fluid inclusions crawford and hollister 1986 summarized the role of fluid immiscibility in metamorphism was only recognized after serious study of fluid inclusions in metamorphic rocks was underway in the late 1970s and has yet to attract the attention of more than a handful of petrologists studying metamorphic rocks since then tremendous progress has been made a huge amount of fluid inclusion studies have convincingly shown that immiscible fluids can be present in rocks of all bulk compositions and at all p t conditions thermodynamic databases of minerals solid solutions and fluid mixtures along with the development of gibbs free energy minimization programs now allow for detailed prediction of the evolution of phase assemblages and mineral compositions in p t space significant progress has also been made in understanding reaction kinetics diffusional and convective mass transport and the interpretation of fluid rock interaction during metamorphism given the vast fluid inclusion evidence of immiscibility it would appear however that phase petrology and mass transport in any specific rock where fluids are involved are not correctly interpreted if possible or proven immiscibility is not considered relatively few studies directly link mineral reactions with immiscible fluids therefore this review aims at working out the effects of fluid immiscibility on the progress of metamorphic reactions and fluid transport over a wide range of conditions questions arise directly from the fluid inclusion record in metamorphic rocks this chapter however is organized the other way round at first it summarizes phase relations of fluid systems pertinent to

lateglacial landscape and vegetation change and the younger dryas climatic oscillation in new zealand abstract lateglacial sequences in new zealand show progressive afforestation and landscape stabilization reflecting a warming climate between 14 500 bp and 11 500 bp afforestation and landscape stability was achieved throughout most of the north island and the northwest sector of the south island in the south island scrub and tree ferns were replacing previous grasslands in the east by 11 000 bp and broadleaved forest was spreading in the west no significant reversals of these trends occurred and afforestation was complete by 9500 bp glaciers of the high central part of the southern alps made a series of advances between 14 000 and 9000 bp most of these advances are poorly dated but two moraines are of younger dryas age glacial advances in the face of the general lateglacial warming trend may have been driven by stronger westerly winds increasing snowfall on high altitude neves and by reduced ablation as a consequence of moist cloudy low insolation summers the cause of the northern hemisphere younger dryas cooling is still uncertain and expected southern hemisphere responses may differ according to the mechanism proposed for the cooling poor chronological resolution and apparent conflict between the various types of evidence for climatic change make detection of an unambiguous younger dryas in new zealand problematical

isotopic characteristics of neogene quaternary tephra from iodp site u1438 a record of explosive volcanic activity in the kyushu ryukyu arc a m acknowledges support from the swiss national science foundation grant 200020 135511 to othmar muntener and grant p2lap2 171819 to a m and swiss iodp this work was also supported by grants to g m y and m b from nsf oce 1537135 and iodp

origin and motion history of the philippine sea plate abstract the philippine sea plate is the one major plate whose tertiary motion is poorly constrained and whose origin is problematical its southern boundary is the sorong fault system which is part of a major left lateral fault system at the northern margin of the australian plate the southern part of the plate in eastern indonesia has been neglected in most syntheses but includes some of the oldest rocks within the plate which are separated from remnant arcs of the daito ridge province of the northern philippine sea by the west philippine central basin the east indonesian islands of the halmahera waigeo region contain a good mesozoic and tertiary stratigraphic record indicating a long arc history for the southern part of the plate new palaeomagnetic data from these islands define two sub areas an area forming part of the philippine sea plate north of the sorong fault and an area within the sorong fault system the area north of the fault records a long term clockwise rotation history whereas that within the fault zone records local rotations interpreted as due to deformation at the plate edge rocks of philippine sea plate origin within both areas record similar latitudinal shifts the rotation of the area north of the sorong fault is considered to represent the motion of the southern part of the philippine sea plate the new data indicate large tertiary clockwise rotations similar to earlier suggestions for other parts of the plate but record a discontinuous and more complex motion history than previously suggested for the southern part of the plate there was 40 rotation with northward translation between 0 and 25 ma no significant rotation between 25 and 40 ma and there was 50 rotation with southward translation between 40 and 50 ma we show that the new palaeomagnetic data form part of a single set with earlier palaeomagnetic data from elsewhere in the plate the translation history of the southern part of the plate in eastern indonesia can be reconciled with northward motions recorded elsewhere and can be used to determine rotation poles for the plate 15 n 160 e for the interval 5 25 ma and 10 n 150 e for the interval 40 50 ma reconstructions based on these poles predict that at 45 ma the palau kyushu ridge had a wnw ese orientation which is very different from that postulated by many models used to explain the widespread boninite volcanism in the izu bonin marians forearc at this time the long arc history of the southern part of the plate and the reconstructions based on the rotation poles calculated from the palaeomagnetic data favour an origin for the west philippine basin by spreading in a backarc basin

depositional architecture provenance and tectonic eustatic modulation of miocene submarine fans in the shikoku basin results from nankai trough seismogenic zone experiment seismostratigraphy coring and logging while drilling during integrated ocean drilling program expeditions 319 322 and 333 sites c0011 c0012 show three miocene submarine fans in the ne shikoku basin with broadly coeval deposits at ocean drilling program site 1177 and deep sea drilling project site 297 nw shikoku basin the sediment dispersal patterns have major implications for paleogeographies at that time the oldest finer grained kyushu fan has sheet like geometry quartz rich flows were fed mostly from an ancestral landmass in the east china sea during prolonged hemipelagic mud deposition at c0011 c0012 similar to 12 2 to 9 1 ma sand supply continued at sites 1177 and 297 sand delivery to much of the shikoku basin halted during a phase of sinistral strike slip to oblique plate motion after which the daiichi zenisu fan similar to 9 1 to 8 0 ma was fed by submarine channels the youngest fan daini zenisu similar to 8 0 to 7 6 ma has sheet like geometry with thick bedded coarse grained pumiceous sandstones the pumice fragments were fed from a mixed provenance that included the collision zone of the izu bonin and honshu arcs the shift from channelized to sheet like flows was favored by renewal of relatively rapid northward subduction which accentuated the trench as a bathymetric depression increased sand supply appears to correlate with long term eustatic lowstands of sea level the stratigraphic position and 3 d geometry of the sandbodies have important implications for subduction related processes including the potential for focused fluid flow and fluid overpressures above and below the plate boundary fault in sheet like sands pathways for fluid flow have greater horizontal permeability compared with those in channel sands

a revised kinematic model for the relative motion between pacific oceanic plates and north america since the late cretaceous 1 the convergence between the pacific farallon and kula oceanic plates and the north american plate has provided a driving force for tectonic processes that have shaped the western margin of north america yet reconstructions of plate motion in the pacific basin have traditionally relied on the assumption of fixed hot spots in the last decade substantial cretaceous to paleogene motion between the pacific and atlantic hot spots has been recognized providing motivation to reevaluate the history of relative motion between pacific oceanic plates and north america by means of plate circuit reconstructions this paper presents new kinematic models based on two alternative plate circuits linking the pacific plate to north america since late cretaceous time when compared to models relying on fixity of pacific and indo atlantic hot spots our reconstructions suggest that the pacific kula and pacific farallon ridges were 600 1000 km closer to the western margin of north america and hence that the farallon and kula plates were smaller in late cretaceous to middle eocene time these findings cast significant doubt on the viability of a configuration of the farallon kula ridge that juxtaposes the kula plate with the southern part of the paleo north american margin during this time interval the results of our new reconstructions also suggest more oblique convergence between the farallon or kula plate and north america from the late cretaceous to the middle eocene related to the combination of dominantly northwest motion of the pacific plate and steady southwest motion of north america this provides an efficient mechanism for the coast parallel translation of some accreted terranes of north america it may also explain the structure of geological units in western north america such as the central belt of the franciscan complex which show a dominant coast parallel fabric formed during an interval coeval with the episode of oblique convergence

an 18 000 year long eruptive record from volcan chaiten northwestern patagonia paleoenvironmental and hazard assessment implications abstract the 2008 eruption of volcan chaiten vcha in northwestern patagonia was the first explosive rhyolitic eruption to have occurred within a century and provided an unprecedented scientific opportunity to examine all facets of the eruption ranging from magma rheology ascent rates to ash fall effects on biota and infrastructure up to very recently it was thought that the latest eruption prior to the 2008 event occurred c 9750 cal a bp although a number of researchers have recognised additional eruptive products but their stratigraphy age and geochemical attributes have not been systematically described and or recorded in this study we provide a detailed examination of andic cover beds and tephra bearing lake sequences located both proximally and distally to vcha which record a series of hitherto unknown rhyolitic eruptive products and place all previous observations firmly within a coherent stratigraphic framework through major and trace element glass shard geochemistry we are able to confidently verify eruptive source a total of 20 discrete tephra beds are recognised with at least 10 having widespread areal distributions and or depositional imprints broadly comparable to or greater than the 2008 tephra event this record indicates that vcha has been continuously but intermittently active as far back as the end of the last glacial maximum c 18 000 cal a bp with two dominant genetically related magma types and an intermediary mixed type before this the eruptive record has been largely obscured and or erased by widespread andean piedmont glaciation however based on the tempo of vcha activity over the last c 18 000 years older vcha eruptives can be anticipated to occur as well as future hazardous explosive events the new eruptive inventory will ultimately be useful for correlating equivalent aged sequences and refining long term eruptive tempo as well as corresponding temporal changes in magmatic evolution

construction of volcanic records from marine sediment cores a review and case study montserrat west indies detailed knowledge of the past history of an active volcano is crucial for the prediction of the timing frequency and style of future eruptions and for the identification of potentially at risk areas subaerial volcanic stratigraphies are often incomplete due to a lack of exposure or burial and erosion from subsequent eruptions however many volcanic eruptions produce widely dispersed explosive products that are frequently deposited as tephra layers in the sea cores of marine sediment therefore have the potential to provide more complete volcanic stratigraphies at least for explosive eruptions nevertheless problems such as bioturbation and dispersal by currents affect the preservation and subsequent detection of marine tephra deposits consequently cryptotephras in which tephra grains are not sufficiently concentrated to form layers that are visible to the naked eye may be the only record of many explosive eruptions additionally thin reworked deposits of volcanic clasts transported by floods and landslides or during pyroclastic density currents may be incorrectly interpreted as tephra fallout layers leading to the construction of inaccurate records of volcanism this work uses samples from the volcanic island of montserrat as a case study to test different techniques for generating volcanic eruption records from marine sediment cores with a particular relevance to cores sampled in relatively proximal settings i e tens of kilometres from the volcanic source where volcaniclastic material may form a pervasive component of the sedimentary sequence visible volcaniclastic deposits identified by sedimentological logging were used to test the effectiveness of potential alternative volcaniclastic deposit detection techniques including point counting of grain types component analysis glass or mineral chemistry colour spectrophotometry grain size measurements xrf core scanning magnetic susceptibility and x radiography this study demonstrates that a set of time efficient non destructive and high spatial resolution analyses e g xrf core scanning and magnetic susceptibility can be used effectively to detect potential cryptotephra horizons in marine sediment cores once these horizons have been sampled microscope image analysis of volcaniclastic grains can be used successfully to discriminate between tephra fallout deposits and other volcaniclastic deposits by using specific criteria related to clast morphology and sorting standard practice should be employed when analysing marine sediment cores to accurately identify both visible tephra and cryptotephra deposits and to distinguish fallout deposits from other volcaniclastic deposits

pliocene change in pacific plate motion the absolute motion of the pacific plate has been nearly constant during the past 15 myr but epp1 recognized that some change took place between 15 myr and the present and tentatively chose 1 myr for the time of the change cox and engebretson2 found a change in pacific absolute motion based on hotspot tracks and a change in pacific antarctic relative motion the pliocene deformation in california and the juan de fuca rotations led them to postulate a 5 myr age for the change the manner and timing of the change are explored more thoroughly here and we put the time for the change in motion of the pacific plate at between 5 and 3 2 myr basing the younger limit on the correlation of computed hotspot tracks with pacific and nazca hotspot traces the change may explain several observations on the neighbouring continental and oceanic plate boundaries including direct adjustments at the pacific spreading ridges a likely mechanism for the change is a large clockwise torque caused by acceleration of the sinking slab beneath the kurile trench where a fossil spreading ridge is inferred to have been subducted

testing global synchronism in peri pacific arc volcanism abstract episodicity of arc volcanism along the pacific rim is quantitatively analysed based on the record preserved by ash layers in deep sea sediments drilled by the deep sea drilling project and the ocean drilling program two major pulses of arc volcanism have been found one during middle miocene times 18 13 ma the other during pliocene quaternary times 5 0 ma these pulses are shown to relate to the tectonic stress regime of the arc lithosphere rather than to subduction rate these episodes of arc volcanism activity coincide with major tectonic events documented on circum pacific subduction zones as a consequence a global control of plate kinematics could influence both volcanic and tectonic evolution of pacific convergent margins

weathering sequence of soils from volcanic ash involving allophane and halloysite new zealand abstract the clay minerals in a series of soils from rhyolitic ash having the same stratigraphy but different leaching environments were estimated quantitatively by oxalate dissolution infrared spectroscopy differential thermal analysis electron microscopy and x ray diffraction three soils were studied in detail these were the kereone soil mean annual rainfall 1200 mm the ohaupo soil 1400 mm and the mairoa soil 2600 mm the kereone soil contained halloysite as the predominant clay mineral whereas the mairoa soil was mainly allophanic the ohaupo soil contained considerable amounts of both allophane and halloysite thus the allophane content of the soils increased as rainfall increased reflecting a sequence of increased l leaching the si concentration in soil solution decreased as rainfall increased also reflecting increasing leaching of the soils at mairoa si is rapidly removed and allophane al si 2 1 with monomeric silicate is formed whereas at kereone less leaching occurs si levels are higher and halloysite al si 1 1 with polymeric silicate is formed at intermediate sites either allophane or halloysite may form the often reported situation of younger allophanic beds overlying older 10 000 year halloysitic beds may not be due to allophane weathering to halloysite but may result from lower temperature and drier climate during the last glacial maximum between 10 000 and 26 000 years before present bp a new weathering scheme for volcanic ash in new zealand is presented

internal control of fluid compositions in amphibolite facies scapolitic calc silicates mary kathleen australia unaltered metasediments of the mary kathleen fold belt are composed predominantly of layered amphibolite facies scapolitic calc silicate rocks in which minimal infiltration of externally derived fluids occurred during regional metamorphism there were substantial differences in volatile activities between different layers in the layered sequences in particular a co2 a h 2 o inferred from reaction progress estimates and analysis of biotite clinopyroxene fluid phase relations a nacl a h 2 o inferred from scapolite compositions and a hcl a h 2 o inferred from biotite compositions in one outcrop in which a clinopyroxene producing reaction dominated differences in approximate x co 2of up to 0 25 occurred between several samples collected over 50 metres variations in a h 2 o a hcl of up to one order of magnitude are inferred at 1 to 50 m scales from biotite cl contents and variations in nacl contents of scapolite from 0 0 to up to 0 6 cl atoms in the cl co3 so4 site reflect a large variation of a nacl in the coexisting fluid at similar scales most calcsilicate layers internally buffered fluid compositions in the h2o co2 nacl hcl system local occurrences of nacl rich scapolite suggest that some layers may have been in equilibrium with halite during early prograde metamorphism at peak metamorphic temperatures disolution of halite was complete but layers containing high nacl scapolite continued to buffer fluid at high values of a nacl fluid immiscibility does not appear to have affected the progress of the devolatilization reactions although fluid was predominantly internally buffered moderate quantities of fluid were released by prograde mineral reactions in many layers up to 30 cm3 fluid per 100 cm3 rock numerous episodes of fluid escape were required probably via microfractures such that the released fluid did not obviously influence reaction progress in the layers through which it passed the anomaly of beautifully preserved internal buffering signatures and the requirement for produced fluid locally to pass across layers in a deforming rock sequence suggest that the escaping fluid did not leave any readily observable tracks this is explained by rapid rates of fracture propogation and fluid migration therein this internally buffered system contrasts strongly with adjacent calc silicate rocks that show evidence for infiltration of externally derived fluids at high fluid rock ratios and highlights the broad range of fluid behaviour that can be expected in deforming heterogeneous rock sequences

short paper accretion and uplift in the shimanto belt sw japan k ar cleavage dating and fission track cooling ages have been combined with existing stratigraphic data to constrain the evolution of the shimanto belt a cretaceous neogene accretionary complex cleavage ages record two major phases of accretion during the late cretaceous and late eocene early oligocene the minimum time periods between sedimentation and deformation are constrained to 9 5 9 and 0ma intervals within four tectonic units containing youngest sediments of maastrichtian late eocene late eocene and early oligocene ages respectively one phase of middle to late miocene uplift is indicated for the whole study area by the fission track cooling ages frontal underplating combined with out of sequence thrusting are suggested as mechanisms for this regional uplift the cretaceous neogene shimanto belt fig la forms the outermost onshore exposure of accreted material in sw japan the boundaries of constituent accreted units of the shimanto belt are defined by a detailed stratigraphy taira et al 1980taira et al 1988 providing an opportunity to test the application of cleavage dating and fission track studies to accretionary complex evolution the butsuzo tectonic line fig la juxtaposes the shimanto belt to the jurassic sanbosan belt in the north younger accreted material extends offshore to the south as far as the present day boundary of the eurasian plate the nankai trough fig la continued accretion seaward of the shimanto belt has back rotated older accreted units to their present day steeply dipping orientations the type section of the shimanto belt taira et al 1980 lies in the eastern hata peninsula fig 1b which contains the study

paleogeographic reconstruction and origin of the philippine sea abstract our reconstruction of the philippine sea suggests that it formed by two distinct episodes of back arc spreading each of which resulted from seaward retreat of the trench in the first episode the protoizu bonin trench retreated northward and the west philippine basin formed behind the northern half of the palau kyushu ridge in the second episode the izu mariana trench retreated eastward and the shikoku and parece vela basins formed behind it during the last 17 ma the philippine sea basin has been moving northwestward with respect to eurasia shifting the ttt triple junction off central japan westward by about 50 km the motion of the philippine sea with respect to eurasia at the triple junction changed from north northwestward to west northwestward 10 5 ma ago for the period before 17 ma ago we construct two models retreating trench model and anchored slab model the izu bonin trench migrated from south to northeast rotating in a clock wise sense since 48 ma ago in the retreating trench model in the anchored slab model the trench has been fixed with respect to eurasian margin since 43 ma ago we prefer the retreating trench model because the deformation of the plate boundary along the eastern margin of eurasia during 30 17 ma ago is much simpler for this model than for the anchored slab model furthermore rotations of the bonin mariana islands are consistent with those predicted from the retreating trench model the 48 ma ages of the northern part of the palau kyushu ridge and of chichi jima of the bonin islands indicate that there was subduction beneath the northern half of the ridge beginning at least 48 ma ago from this and the subparallelism in trend between the northern part of the palau kyushu ridge and the central basin ridge we propose that the major part of the west philippine basin formed by back arc spreading in a n s direction behind the northern part of the palau kyushu ridge the pacific plate was moving northward with respect to hot spots from 48 to 43 ma ago which implies that the pacific plate is not likely to have been subducting beneath the west philippine basin during this time we speculate that another plate existed south of the pacific plate and thai it was subducting beneath both tile west philippine basin and australia the annihilation of this plate might he a cause for the sudden change of the pacific plate motion at 43 ma ago

tectonics of an arc arc junction an example from kyushu island at the junction of the southwest japan arc and the ryukyu arc abstract three distinctive geologic events occurred synchronously during the last 6 m y on kyushu island lying at the junction of the southwest japan arc and the ryukyu arc these events included 1 dextral fault displacement along a 100 km section of the median tectonic line 2 formation of a rectangular volcano tectonic depression 70 km long and 40 km wide and 3 approximately 30 of counterclockwise crustal rotation we propose an integrated tectonic model that explains these three tectonic features in terms of subduction of the philippine sea plate which resumed at around 6 ma after a halt of more than 5 m y oblique subduction of the philippine sea plate beneath the southwest japan arc detached a fore arc sliver that was displaced along a dextral fault the median tectonic line north of the nankai trough a volcano tectonic depression the hohi volcanic zone was formed by the pull apart structure on the western margin of the median tectonic line by contrast normal subduction of the philippine sea plate under the ryukyu arc caused back arc spreading observed as crustal extension in the northern okinawa trough the crustal extension caused the counterclockwise rotation for the northernmost ryukyu arc including southern kyushu

coring disturbances in iodp piston cores with implications for offshore record of volcanic events and the missoula megafloods piston cores collected from iodp drilling platforms and its predecessors provide the best long term geological and climatic record of marine sediments worldwide coring disturbances affecting the original sediment texture have been recognized since the early days of coring and include deformation resulting from shear of sediment against the core barrel basal flow in due to partial stroke loss of stratigraphy fall in sediment loss through core catchers and structures formed during core recovery and on deck transport the most severe disturbances occur in non cohesive sandy facies which are particularly common in volcanogenic environments and submarine fans although all of these types of coring disturbances have been recognized previously our contribution is novel because it provides an easily accessible summary of methods for their identification this contribution gives two specific examples on the importance of these coring disturbances we show how suck in of sediments during coring artificially created very thick volcaniclastic sand layers in cores offshore montserrat and martinique lesser antilles we then analyze very thick structureless sand layers from the escanaba trough inferred to be a record of the missoula mega floods these sand layers tend to coincide with the base of core sections and their facies suggest coring disturbance by basal flow in destroying the original structure and texture of the beds we conclude by outlining and supporting iodp led initiatives to further reduce and identify coring disturbances and acknowledge their recent successes in drilling challenging sand rich settings such as during iodp expedition 340