emplacement and inflation of the al halaq al kabir lava flow field central part of the al haruj volcanic province central libya abstract numerous of lava rise plateaus and tumuli developed in the medial and distal portions of the al halaq al kabir lava flow field during the last holocene eruption in the central part of the al haruj volcanic province ahvp these inflation structures provide important data on the lava emplacement mechanism in this part of the al haruj region where the widespread occurrence of tumuli and lava rise plateaus are good indicators of the mode of emplacement we report the results of detailed measurements of the maximum and minimum diameters in plan view of 551 lava rise plateaus and 289 tumuli from the distal part of the al halaq al kabir lava field using arcgis and field observations tumuli and lava rise plateaus may be divided into subpopulations according to abrupt changes in the scaling exponents on log log plots of their frequency versus diameter using the estimated stiffness young s modulus of the basaltic rocks in the study area of 10 34 gpa numerical and analytical results show that theoretical maximum tensile stresses in the inflated upper solidified crustal layers of the developing tumuli and lava rises at tens of mega pascals mpa this theoretical stress is orders of magnitude higher than typical in situ tensile strengths of rocks 0 5 9 mpa and thus high enough to rupture the crustal layers of the lava rises and tumuli the high tensile stresses are generated during crustal doming driven by a magmatic overpressure of only about 1 mpa our results partly explain the abundance of tension fractures at the surface of the al halaq al kabir lava flow field tumuli observed in the area are remarkably similar in morphology and aspect height width ratios to the flow lobe tumuli in holocene lava flow fields in iceland suggesting an analogous mechanics of formation there appears to be a coincidence between the age of an initial volcanism in the ahvp 7 9 5 3 ma and a local fauna and flora disappearance in the as sahabi area ne sirt basin during messinian zanclean time 7 5 to 5 ma we speculate that the volcanism may have had a local negative environmental impact and contributed to the reported decline in the fauna and flora in the area

segmented lateral dyke growth in a rifting event at barðarbunga volcanic system iceland crust at many divergent plate boundaries forms primarily by the injection of vertical sheet like dykes some tens of kilometres long1 previous models of rifting events indicate either lateral dyke growth away from a feeding source with propagation rates decreasing as the dyke lengthens2 3 4 or magma flowing vertically into dykes from an underlying source5 6 with the role of topography on the evolution of lateral dykes not clear here we show how a recent segmented dyke intrusion in the bar arbunga volcanic system grew laterally for more than 45 kilometres at a variable rate with topography influencing the direction of propagation barriers at the ends of each segment were overcome by the build up of pressure in the dyke end then a new segment formed and dyke lengthening temporarily peaked the dyke evolution which occurred primarily over 14 days was revealed by propagating seismicity ground deformation mapped by global positioning system gps interferometric analysis of satellite radar images insar and graben formation the strike of the dyke segments varies from an initially radial direction away from the bar arbunga caldera towards alignment with that expected from regional stress at the distal end a model minimizing the combined strain and gravitational potential energy explains the propagation path dyke opening and seismicity focused at the most distal segment at any given time and were simultaneous with magma source deflation and slow collapse at the bar arbunga caldera accompanied by a series of magnitude m 5 earthquakes dyke growth was slowed down by an effusive fissure eruption near the end of the dyke lateral dyke growth with segment barrier breaking by pressure build up in the dyke distal end explains how focused upwelling of magma under central volcanoes is effectively redistributed over long distances to create new upper crust at divergent plate boundaries

the volume of lava erupted during the 2014 to 2015 eruption at holuhraun iceland a comparison between satellite and ground based measurements

formation of lava tubes and extensive flow field during the 1991 1993 eruption of mount etna detailed mapping during the 1991 1993 eruption of mount etna has shown that there is a relationship between tumuli ephemeral vents lava tubes and their parent lava flows during this eruption many tubes formed in stationary inflated a a lava flows ephemeral vents at the fronts of these stationary flows and above lava tubes fed secondary lava flows many of which subsequently developed new tubes the resulting complex network of tubes ephemeral vents and secondary flows was responsible for most of the widening thickening and lengthening of the 1991 1993 etna lava flow field the supply of relatively uncooled lava via tubes to distal parts of this flow field allowed lava to flow 3 km farther from the vent than the longest channel fed lava flow our observations suggest that lava tubes play a more important role in the formation of extensive a a flow fields on etna than has previously been recognized

tremor rich shallow dyke formation followed by silent magma flow at barðarbunga in iceland magma movement is thought to trigger volcanic tremor however analysis of seismic data suggests that tremor prior to the bar arbunga eruption in iceland instead marked the crust cracking open whereas subsequent magma flow was seismically silent

modelling satellite derived magma discharge to explain caldera collapse many effusive eruptions are characterized by effusion rates that decay exponentially with time a trend which is generally ascribed to elastic relaxation of a deep magma chamber thermal emissions detected by satellite during the a d 2014 2015 bar arbunga holuhraun eruption iceland indicate that the volume of the erupted magma and effusion rates followed an overall exponential trend that fits the observed major subsidence of the bar arbunga caldera floor this trend continued until a critical flow rate was reached hence the subsidence slowed down and the eruption rapidly ceased reflecting the ultimate closure of the magma path we present a model of inelastic magma withdrawal that very closely reproduces all the observed phenomena and provides new insights into the caldera collapses and the driving pressure of other effusive eruptions

toothpaste lava characteristics and origin of a lava structural type transitional between pahoehoe and aa toothpaste lava an important basalt structural type which illustrates the transition from pahoehoe to aa is particularly well displayed on the 1960 kapoho lava of kilauea volcano its transitional features stem from a viscosity higher than that of pahoehoe and a rate of flow slower than that of aa viscosity can be quantified by the limited settling of olivine phenocrysts and rate of flow by field observations related to the low angle slope on which the lava flowed much can be learned about the viscosity rheologic condition and flow velocity of lavas long after solidification by analyses of their structural characteristics and it is possible to make at least a semiquantitative assessment of the numerical values of these parameters

the dynamics of a long lasting effusive eruption modulated by earth tides abstract deciphering eruptive dynamics in near real time is essential when dealing with hazard assessment and population evacuation recognition of specific patterns in time series measured during volcanic activity may help decipher distinctive behavior at active volcanoes providing insights into the underlying driving mechanisms multi parameter data sets usually agree on the overall trend characterizing the temporal evolution of an eruption providing insights into the first order eruptive dynamics however second order variations detected in different data sets remain often poorly understood the 2014 2015 holuhraun eruption iceland offers an excellent opportunity to investigate the dynamics of a long lasting effusive eruption we analyze the seismic tremor and the volcanic radiated power emitted by the lava field during the 6 months of the eruption using singular spectrum analysis ssa in both geophysical time series we identify periods from 5 to 32 days coinciding with periods of earth tides here we show that 50 of both signals are composed of tidal periods suggesting that magma movements follow frequencies imposed by lunisolar forces within the crust and at earth s surface

intense seismicity during the 2014 2015 barðarbunga holuhraun rifting event iceland reveals the nature of dike induced earthquakes and caldera collapse mechanisms

assimilation and crystallization in basic magma chambers trace element and nd isotopic variations in the kerns sill nipissing diabase province ontario an investigation has been made of the trace element and nd isotopic effects of assimilation at the roof of the proterozoic kerns sill in the 2 2 ga nipissing diabase province in ontario the ratios

the roza member columbia river basalt group a gigantic pahoehoe lava flow field formed by endogenous processes we present studies on the physical volcanology of the 15 ma roza member of the wanapum formation in the columbia river basalt group the roza member represents a compound pahoehoe flood basalt lava flow field with an area of 40 300 km 2 and a volume of 1300 km 3 it consists of 4 major lava flows each composed of numerous decimeter to kilometer long pahoehoe lobes roza lavas feature a wide range of pahoehoe surface structures such as lava rise plateaus tumuli and surface breakouts and we illustrate that the lava morphology is inconsistent with previous proposals of rapid emplacement for these lavas an integral component of the roza flow field is the sheet lobe with internal structures identical to those of inflated pahoehoe sheet lobes from hawaii and iceland both at the same scale and at much larger scales we identify a three part division of the sheet lobes into basal crust lava core and lava crust which are interpreted as the equivalent to the bottom crust the liquid lava core and the surface crust of an active inflating pahoehoe lobe the upper lava crust grows continuously during lava emplacement and its growth rate can be approximated by conductive cooling this relationship is used to calculate the emplacement time for individual roza sheet lobes and to derive a first order estimate on the duration of the roza eruption the results indicate that the emplacement of individual roza lobes lasted for months to years and that the lava flow field was constructed over a period of at least 14 years we propose that the roza flows achieved great areal dimensions and thicknesses by inflation and endogenous growth as the lava flowed from vent to flow front it traveled under an insulating crust which maintained cooling rates of 0 1 c km and allowed for efficient transport of lava over distances up to 300 km

the significance of slab crusted lava flows for understanding controls on flow emplacement at mount etna sicily slab crusted flows on mount etna sicily are defined here as those whose crust has ridden on the flow core without significant disruption or deformation and have a high length to width ratio they typically erupt from ephemeral boccas as late stage products on dominantly aa flow fields such as that of the 1983 eruption on mount etna slab crusted flows tend to inflate mainly as they approach and after they reach the maximum length of slab crust formation the flow interior acting as a preferential pathway for injecting lava under a stable crust coalescence of vesicles under successive crusts causes separation between core and crust giving a new cooling surface within the flow on which ropy surfaces and occasionally aa textures of limited areal extent may develop slab crusted flows tend to form at ephemeral boccas together with other surface textural types including toes ropy pahoehoe sheets and aa flows this suggests that on etna slab crusted flows form from lava of the same rheological properties as both aa and pahoehoe textured flows they do not represent a transition between aa and pahoehoe as argued for toothpaste flows in hawaii we conclude that slab crusted flows on etna owe their morphology to a relatively high critical ratio of effusion rate to advance rate related to vent cross sectional area and the slope over which the flow forms

secular variation of northern hemisphere 50 kpa geopotential height abstract there is accumulating evidence in the literature that different short period climate regimes subclimates may have characterized the northern hemisphere during the past 40 years we therefore investigate the 40 yr record of 50 kpa height 1946 85 and analyze the time series of zonal anomalies stratified by season we find that there appears to be two contiguous regimes with a rather abrupt transition during the early 1960s which had significantly different means trends and degrees of variability the results are compared with those from recent investigations of northern hemisphere surface and or tropospheric temperature variation the possibility of a climatic jump during the early 1960s is discussed our results raise the question of an appropriate period to use for determining normals whether for standard level surfaces or more generally for calculating the statistics of the general circulation both in the horizontal and vertical

compositional heterogeneity of the 3 4 km3 blue dragon flow craters of the moon volcanic field idaho abstract the blue dragon lava flow in southern idaho is one of the largest holocene basaltic flows in the contiguous u s multispectral remote sensing and field mapping of the flow have revealed its 280 km2 surface is divided into five large sub areas with different spectral reflectance and morphology that correspond with distinct periods of the eruption the flow grew outward from its source fissures primarily via a complex system of lava tubes and stratigraphic relations at the boundaries of the mapped sub areas provide temporal information about their order of emplacement this offers a unique opportunity to reconstruct chemical and mineralogical changes in the source magmas as the eruption progressed in this first comprehensive study of the compositional diversity of the blue dragon flow geochemical data from 28 rock samples show that over the course of the eruption the lavas became progressively more primitive and depleted in incompatible trace elements and pb isotopes show subtle increases these observations are best explained by eruption from a zoned magma source due to variable assimilation fractional crystallization afc with the initial eruption of more evolved and enriched magmas that may have been residual from the previous eruption followed by progressively higher proportions of a more primitive and depleted component from deeper in the system differences in lava surface color and morphology among the five mapped eruptive phases may indicate changes in eruptive temperature flow rate or both as the blue dragon eruption progressed the results support a growing body of evidence that systematic studies of geochemical variations in monogenetic and short duration lava flows can reveal the relative influence of processes that affect single batches of magma

pahoehoe and aa in hawaii volumetric flow rate controls the lava structure the historical records of kilauea and mauna loa volcanoes reveal that the rough surfaced variety of basalt lava called aa forms when lava flows at a high volumetric rate 5 10 m3 s and the smooth surfaced variety called pahoehoe forms at a low volumetric rate 5 10 m3 s this relationship is well illustrated by the 1983 1990 and 1969 1974 eruptions of kilauea and the recent eruptions of mauna loa it is also illustrated by the eruptions that produced the remarkable paired flows of mauna loa in which aa formed during an initial short period of high discharge rate associated with high fountaining and was followed by the eruption of pahoehoe over a sustained period at a low discharge rate with little or no fountaining the finest examples of paired lava flows are those of 1859 and 1880 1881 we attribute aa formation to rapid and concentrated flow in open channels there rapid heat loss causes an increase in viscosity to a threshold value that varies depending on the actual flow velocity at which when surface crust is torn by differential flow the underlying lava is unable to move sufficiently fast to heal the tear we attribute pahoehoe formation to the flowage of lava at a low volumetric rate commonly in tubes that minimize heat loss flow units of pahoehoe are small usually 1 m thick move slowly develop a chilled skin and become virtually static before the viscosity has risen to the threshold value we infer that the high discharge rate eruptions that generate aa flows result from the rapid emptying of major or subsidiary magma chambers rapid near surface vesiculation of gas rich magma leads to eruptions with high discharge rates high lava fountains and fast moving channelized flows we also infer that long periods of sustained flow at a low discharge rate which favor pahoehoe result from the development of a free and unimpeded pathway from the deep plumbing system of the volcano and the separation of gases from the magma before eruption achievement of this condition requires one or more episodes of rapid magma excursion through the rift zone to establish a stable magma pathway

shallow impact isotopic insights into crustal contributions to the sudbury impact melt sheet abstract the largest known terrestrial impact melt sheet occurs within the 1850 ma sudbury structure ontario in order to evaluate the relative contributions of different target lithologies to the melt sheet we have investigated the pb isotope compositions of feldspar separates from early formed quartz diorite magmas within offset dykes from around the impact structure the samples define a linear array on plots of age corrected 206 pb 204 pb versus 207 pb 204 pb samples from offset dykes hosted by the huronian supergroup south range have a range of 206 pb 204 pb 1850 from 15 424 to 17 255 and 207 pb 204 pb 1850 from 15 390 to 15 801 whilst those hosted by archean gneisses of the superior province north range cluster around 206 pb 204 pb 1850 14 8 and 206 pb 204 pb 1850 15 1 these values can be approximated by binary mixing between the two major groups of target lithologies a mix of 60 70 of superior province gneisses with 30 40 of huronian metasedimentary material closely matches the pb isotope compositions of north range offset dyke samples whereas in the south range the required huronian component is up to ca 80 these mixing proportions are consistent with sr nd and os isotope and trace element constraints a third minor component either locally exposed paleoproterozoic mafic rocks or the lower crust is also required however the isotopic trace element and ni cu platinum group element characteristics of the melt sheet can be accommodated without the involvement of an average lower crustal or meteoritic component a major contribution of huronian supracrustal material which had a pre impact thickness of up to 12 km is required to explain the chemical characteristics of the impact melts which also have a strong upper crustal affinity e g eu sm 0 22 rb sr 0 2 0 35 as such a shallower level of melting is apparent than that predicted by many previous impact models for the sudbury event this can be accommodated by considering approach trajectories for the impactor oblique to the earth s surface in addition the isotopic and trace element variability identified indicates that the melt sheet was heterogeneous at an early stage and may not have been completely homogenised during crater formation our findings have significant implications for the nature of the sudbury impact event the evolution of the melt sheet and the crustal sources of metals contained in sudbury s world class ni cu pge sulphide ores

the distal segment of etna s 2001 basaltic lava flow etna s 2001 basaltic lava flow provided a good example of the distal flow segment between the flow front and stable channel across which the flow evolves from channel contained to dispersed this zone was mapped with meter precision using lidar data collected during 2004 and 2005 these data supported by field mapping show that the flow front comprised eight lobes each 10 to 20 m high the flow front appears to have advanced not as a single unit but as a series of lobes moving forward one lobe at a time primary lobes were centered on the channel axis and marginal lobes were off axis the lobes advanced as breakouts of low yield strength lava from the flow core of the stalled flow front marginal lobes were abandoned and contributed to marginal levees flanking the transitional channel for etna s 2001 flow the transitional channel is 140 m wide 700 m long and fed a 240 m long zone of dispersed flow the change from stable to transitional channel occurred at a major reduction in slope above this the stable channel is 5 2 km long 55 to 105 m wide and bounded by 15 to 25 m high levees and the stable channel is located over a previous channel in a final stage of activity lava ponding at the break in slope that marks the terminus of the stable channel put pressure on the eastern levee causing it to fail liberated lava then fed a final break out to the east similar flow front features occur at other volcanoes indicating that similar processes are characteristic of dispersed flow zones

evolution of the sublayer of the sudbury igneous complex geochemical sm nd isotopic and petrologic evidence abstract the mineralized sublayer at the base of the sudbury igneous complex sic consists of two variants the noritic contact sublayer and radial and concentric quartz dioritic offset dykes both are characterized by the presence of significant quantities of ni cu pge sulphides and by a prominent population of recrystallized diabasic textured and melanocratic to ultramafic fragments the two variants of the sublayer contain compositionally distinct inclusion populations and inclusion bearing matrices contact sublayer and offset dykes hosted by north range granitoid footwall can be distinguished from those hosted by south range basaltic and metasedimentary footwall environments the compositional variation in sic rocks can be described in terms of contributions from exposed crustal rocks and differentiation of the resultant melt s the basaltic inclusion population is characterized by hornfels recrystallization of the plagioclase and is geochemically and isotopically identified with huronian basalts which comprise the south range footwall with ce yb n ratios of around 2 5 and e nd 1850 between 2 to 5 the melanocratic inclusions in the sublayer are typically coarse grained and undeformed with incompatible element contents and radiogenic isotopic compositions intermediate between those of the basaltic inclusions and those of the melt sheet which has ce yb n ratios of around 10 and e nd 1850 around 9 calculated crystallization models are consistent with derivation of the ultramafic inclusions by crystallization from a magma produced by mixing of molten basaltic footwall with basal melt sheet it is proposed that the sublayer appeared as the marginal facies of a meteorite impact melt sheet as a result of footwall melting following the impact this basal layer was progressively enriched in sulphides and mafic cumulates from above through differentiation during cooling offset dykes were emplaced and the magmas effectively removed from the system subsequently continued evolution of the marginal facies produced the more mafic inclusions in the contact sublayer no extracrustal e g mantle component is envisioned in this model to explain the silicate compositional distributions in the sic and mafic crustal rocks in the target zone are implicated as the metal source for the sic deposits

upper crustal basement involved folding in the east range of the sudbury basin ontario inferred from paleomagnetic data and spatial analysis of mafic dykes tilting of crystalline basement rocks associated with folding strain at uppermost crustal levels is difficult to recognize if basement rocks are devoid of traceable marker planes here we use the spatial variation in strike of paleoproterozoic mafic dyke segments complemented by compiled paleomagnetic data to identify tilting in archean basement rocks associated with kilometre scale folds of the eastern sudbury basin ontario spatial analysis of the strike of dyke segments is consistent with generation of the ne lobe and a newly identified anticline referred to as the west bay anticline in the layered sudbury igneous complex sic this anticline accounts better for the structural characteristics of the eastern sudbury basin than a previously proposed anticline with west plunging hinge line the west bay anticline is characterized by abrupt plan view thickness variations in the lower sic and curved faults displaying significant strike separations of sic contacts these structural characteristics are co

geochemistry of the siberian trap of the noril sk area ussr with implications for the relative contributions of crust and mantle to flood basalt magmatism the sequence investigated of the siberian trap at noril sk ussr consists of at least 45 flows that have been divided into six lava suites the lower three suites consist of alkalic to subalkalic basalts the ivakinsky suite overlain by nonporphyritic basalts the syverminsky suite and porphyritic and picritic basalts the gudchikhinsky suite the upper three suites are tholeiitic the uppermost 750 m of dominantly non porphyritic basalt belong to the mokulaevsky suite and are characterized by a nearly constant mg number 0 54 0 56 sio2 48 2 49 1 wt ce 12 18 ppm and ce yb 5 8 the underlying 1100 m of dominantly porphyritic basalt belong to the morongovsky and nadezhdinsky suites there is a continuous increase in sio2 48 1 55 2 wt ce 12 41 ppm and ce yb 5 18 from the top of the mokulaevsky to the base of the nadezhdinsky with little change in the mg number 0 53 0 59 mokulaevsky magmas have trace element signatures similar to slightly contaminated transitional type mid ocean ridge basalts the change in major and trace element geochemistry in the upper three suites is consistent with a decline in the degree of anatexis and assimilation of tonalitic upper crust by mokulaevsky magma the nadezhdinsky and underlaying lavas thicken within and thus appear to be related to an elongate basin centred on the noril sk talnakh mining camp the mokulaevsky and morongovsky lavas thicken to the east and appear to be related to a basin centred more than 100 km to the east of the noril sk region these magmas may have risen up out of a different conduit system

multiple coincident eruptive seismic tremor sources during the 2014 2015 eruption at holuhraun iceland we analyze eruptive tremor during one of the largest effusive eruptions in historical times in iceland 2014 15 holuhraun eruption seismic array recordings are compared with effusion rates deduced from moderate resolution imaging spectroradiometer modis recordings and ground video monitoring data and lead to the identification of three coexisting eruptive tremor sources this contrasts other tremor studies that generally link eruptive tremor to only one source usually associated with the vent the three sources are i a source that is stable in back azimuth and shows bursts with ramp like decrease in amplitude at the beginning of the eruption we link it to a process below the open vents where the bursts correlate with the opening of new vents and temporary increases in the lava fountaining height ii a source moving by a few degrees per month while the tremor amplitude suddenly increases and decreases back azimuth and slowness correlate with the growing margins of the lava flow field whilst contact with a river led to fast increases of the tremor amplitude iii a source moving by up to 25 southwards in 4 days that cannot be related to any observed surface activity and might be linked to intrusions we therefore suggest that eruptive tremor amplitudes energies are used with caution when estimating eruptive volumes effusion rates or the eruption explosivity as multiple sources can coexist during the eruption phase our results suggest that arrays can monitor both the growth of a lava flow field and the activity in the vents

fracture movements and graben subsidence during the 2014 barðarbunga dike intrusion in iceland abstract a dike propagated 48 km from the bar arbunga central volcano into one of its fissure swarms in august and early september 2014 the dike intrusion was accompanied by caldera subsidence in the ice covered bar arbunga central volcano as well as a propagating earthquake swarm graben subsidence and fissure eruptions in the fissure swarm most of the dike was emplaced in the glacier covered part of the fissure swarm but a 10 km long section at the distal northern end of the dike is ice free new ground fractures were observed in the ice free part during the dike propagation and prior to the outbreak of a major lava producing eruption the fractures delineate two graben structures in direct continuation of each other here we show the extent and depth of the grabens and maps of fractures and eruptive fissures that were formed or reactivated north of the vatnajokull glacier during the dike intrusion the active graben subsidence was identified 3 days after seismicity reached the ice free area then fractures delineated a 700 1000 m wide and 5 km long graben visible from the northern edge of the vatnajokull glacier farther north a narrower 250 450 m wide graben was seen a short lived minor eruption occurred between these grabens on the 29th of august 2014 2 days after the grabens were identified the northern graben was extended southwards during or before the eruption and included the eruptive fissure on the 31st of august 2014 a much larger eruption began on the same eruptive fissure the fissure quickly obtained its maximum length of 2 km this eruption lasted 6 months a minor eruption lasting 2 days or less occurred on the southern graben on the 5th of september 2014 the first two eruptions took place on the same eruptive fissure that formed the pre existing holuhraun lava presumably in the 18th century measurements in january 2015 show that the southern graben was 3 5 5 5 m deep but the northern graben had been covered by lava from the depth and the opening of the graben we estimate that the dip of the boundary faults of the graben is 75 the narrow grabens observed before the eruptions indicated that magma was at shallow depth likely much less than 300 m 2 days before it opened to the surface such observations can serve as a tool to estimate likelihood of eruptions during dike intrusions

a new plumbing system framework for mantle plume related continental large igneous provinces and their mafic ultramafic intrusions abstract the magmatic components of continental large igneous provinces lips include flood basalts and their plumbing system of giant mafic dyke swarms radiating linear and the recently discovered circumferential type mafic sill provinces a lower crustal magmatic underplate mafic ultramafic m um intrusions associated silicic magmatism and associated carbonatites and kimberlites this paper proposes a new plumbing system framework for mantle plume related continental lips that incorporates all of these components and provides a context for addressing key thematic aspects such as tracking magma batches upstream and downstream and their geochemical evolution assessing the setting of m um intrusions and their economic potential interpreting deep magmatic component identified by geophysical signatures and estimating magnitudes of extrusive and intrusive components with climate change implications this plumbing system model and its associated implications needs to be tested against the rapidly improving lip record

remobilisation of the continental lithosphere by a mantle plume major trace element and sr nd and pb isotope evidence from picritic and tholeiitic lavas of the noril sk district siberian trap russia the late permian to early triassic siberian traps have been sampled by drill core core sg 9 and from surface exposure section 1f in the noril sk region of the siberian platform russia combined major trace element and nd sr and pb isotope data on selected samples through the siberia trap offer new chemostratigraphic criteria for the identification and characterisation of two fundamentally different magma types and 9 of the 11 formations of lava developed near noril sk a lower sequence of sub alkalic basalts tholeiites and picritic basalts upwards these are the ivakinsky syverminsky and gudchichinsky formations are overlain by an upper sequence of picritic basalts and tholeiites interbedded with tuffs upwards these are the khakanchansky tuklonsky nadezhdinsky morongovsky mokulaevsky and kharayelakhsky formations the gudchichinsky and tuklonsky formations contain both picritic and tholeiitic lavas the tuklonsky formation tholeiites and picrites have moderate gd yb 1 6 1 8 low tio2 0 45 0 95 wt a significant negative ta and nb anomaly nb la 0 42 0 57 and unradiogenic nd nd chur to 4 6 in contrast both the gudchichinsky formation tholeiites and picrites have high gd yb 2 3 3 1 and tio2 1 2 2 3 wt no significant nb or ta anomaly nb la 0 8 1 1 and radiogenic nd nd chur to 7 3 the low ti and nb la high la sm and unradiogenic nd isotope signatures of the picritic tuklonsky formation lavas and the tholeiitic lavas of the upper sequence are characteristic of magmas strongly influenced by material from the continental lithosphere whereas the high ti and nb la low la sm and radiogenic nd isotope signatures of the lower sequence are more comparable to deeper asthenospheric mantle plume generated lavas similar to oceanic island basalts the lavas overlying the tuklonsky formation have mg numbers of 0 63 to 0 68 and are more evolved than the tuklonsky mg number 0 62 and have more radiogenic nd chur tuklonsky 0 03 to 4 66 mokulaevsky 0 60 to 1 61 but have many of the incompatible trace element features of the tuklonsky sky type magma these lavas show a progressive upwards decline in sio2 55 49 wt la sm 4 6 2 0 and ur sr 67 to 13 which has previously been attributed to a decrease in the proportion of crustal material contributed to the magma this paper explores and alternative model where a component of the crustal contribution might be derived from within an ancient region of the mantle lithosphere as recycled sediment rather than from the overlying continental crust

climatology and variability of historical soviet snow depth data some new perspectives in snow indian monsoon teleconnections this study presents the monthly climatology and variability of the historical soviet snow depth data this data set was developed under the bilateral data exchange agreement between united states of america and the former union of soviet socialist republics the original data is for 284 stations for periods varying from 1881 upto 1985 the seasonal cycle of the mean snow depth has been presented both as spatial maps and as averages over key locations the deepest snow 80 cms day areas are found over siberia in particular over 80 100 e 55 70 n during march over the course of the annual cycle average snow depth over this region changes dramatically from about 10 cms in october to about 80 cms in march the variability is presented in the form of spatial maps of standard deviation to investigate the interaction of snow depth with indian monsoon rainfall imr lag and lead correlation coefficients are computed results reveal that the winter time snow depth over western eurasia surrounding moscow eastern eurasia in central siberia shows significant negative positive relationship with subsequent imr following the monsoon the signs of relationship reverse over both the regions this correlation structure is indicative of a midlatitude longwave pattern with an anomalous ridge trough over asia during the winter prior to a strong weak monsoon as the time progresses from winter to spring the coherent areas of significant relationship show southeastward propagation empirical orthogonal function analysis of the snow depth reveal that the first mode describes a dipole type structure with one centre around moscow and the other over central siberia depicting similar pattern as the spatial correlation structure the decadal scale imr variations seem to be more associated with the northern hemisphere midlatitude snow depth variations rather than with the tropical enso el nino southern oscillation variability

regional analysis of northern hemisphere 50 kpa geopotential heights from 1946 to 1985 abstract in knox et al the interannual variation of the northern hemisphere 50 kpa geopotential height field averaged between 30 and 80 n was investigated for the 40 year period from 1946 to 1985 we presented strong statistical evidence supporting the notion that a rather abrupt transition in the climate system took place during the early 1960s there was no attempt to compare the spatial distribution of the 50 kpa height difference between regime 1 1946 62 and regime 2 1963 85 as a sequel to the first paper we investigate the spatial characteristics of the transition height field we find that the difference in the 50 kpa height field between regime 1 and regime 2 is characterized by low frequency circulation modes of the pacific north american pna teleconnection pattern the north atlantic oscillation nao and an arctic oscillation there was an increase in the residual sense of the frequency and amplitude of the positive phase of the pna in regime 2 relative to regime 1 fourier analysi

morphology and mechanism of eruption of postglacial shield volcanoes in iceland postglacial icelandic shield volcanoes were formed in monogenetic eruptions mainly in the early holocene epoch shield volcanoes vary in their cone morphology and in the areal extent of the associated lava flows this paper presents the results of a study of 24 olivine tholeiite and 7 picrite basaltic shield volcanoes for the olivine tholeiitic shields the median slope is 2 7 the median height 60 m the median diameter 3 6 km the median aspect ratio height against diameter 0 019 and the median cone volume 0 2 km3 the picritic shield volcanoes are considerably steeper and smaller a shield volcano cone forms from successive lava lake overflows which are of shelly type pahoehoe a widespread apron surrounding the cone forms from tube fed p type pahoehoe the slopes of the cones have a a planar or slightly convex form b a concave form or c a convex concave form a successive stage of a shield volcano is determined on the basis of cone morphology and lava assemblages a shield producing eruption has alternating episodes of lava lake overflows and tube fed delivery to the distal parts of the flow field in the late stages of eruption the cone volume increases in response to the increased amount of rootless outpouring on the cone flanks normally only a small percentage of the total erupted volume of a shield volcano sometimes as little as 1 3 is in the shield volcano cone itself the main volume being in the apron of the shield

multiple ages of nipissing diabase intrusion paleomagnetic evidence from the englehart area ontario nipissing diabase sills and baked host sediments of the coleman member of the huronian supergroup east of englehart ontario are shown to have a characteristic remanent magnetization direction called n3 that is steeply up and to the west d 268 0 i 59 0 k 42 95 6 0 petrographic study indicates that fresh pyroxene gabbro carries the n3 component at most sill sites a baked contact test with the coleman member suggests that the magnetization is primary the n3 magnetization direction is unlike either the n1 or n2 magnetization direction reported for nipissing sills at other localities in the southern province three distinct ages of nipissing sill emplacement are proposed a single nipissing sill site in the sampling area carries the n1 direction a northeast trending diabase dyke crosscuts both the nipissing sills and coleman sediments it carries an n2 direction and has overprinted nearby intrusive and sedimentary rocks d 282 0 i 61 1 k 48 95 5 8 several n3 sill sites

the lead isotope composition of ore minerals from precious metal bearing polymetallic vein systems in the cobalt embayment northern ontario metallogenetic implications the cobalt embayment is a large 60 000 km 2 irregular domain of paleoproterozoic 2 5 2 2 ga siliciclastic sedimentary rocks i e the huronian supergroup that unconformably overlies archean basement rocks of the abitibi greenstone belt the nipissing diabase regionally distributed complex of mafic sills and dikes intruded the huronian sedimentary rocks ca 2 2 ga the sedimentary rocks were subsequently affected by subgreenschist facies metamorphism and by a regionally distributed k and na metasomatic events at ca 1 7 ga related to the penokean orogeny although best known for the economically important ag co veins of the cobalt mining camp the cobalt embayment also hosts numerous other hydrothermal base and precious metal mineralized calcite quartz vein systems the lead isotope compositions of pyrite and chalcopyrite from nine widely separated polymetallic vein systems yield a pb pb errorchron age of 2236 180 ma n 24 in contrast the pb isotope compositions of late stage galena n 11 from six regionally distributed vein systems yield a pb pb secondary isochron age of ca 1675 ma these pb isotope data for the mineralized vein systems demonstrate the occurrence of at least two major episodes of hydrothermal fluid activity throughout the cobalt embayment ca 2220 ma and ca 1700 ma indicate that the emplacement of the nipissing diabase was the most likely driver of regional hydrothermal fluid circulation at ca 2200 ma and provide supporting evidence for the basin wide extent of the regional k and na metasomatic event at ca 1700 ma most likely related to the waning stages of the penokean orogeny

crustal contamination identified in keweenawan osler group tholeiites ontario a trace element perspective in the lake superior area voluminous middle proterozoic tholeiitic basalt with minor rhyolite and interflow sediments occupy the midcontinent rift and overlie archean and older proterozoic basement the 3000 m thick section of gently dipping 10 sse basalts on the black bay peninsula is divided into three suites based on the relationship between stratigraphy petrography and geochemical variations e g mg number a1 2 o 3 la sm and gd yb the lower suite consists of augite olivine porphyritic lavas with high mg number sio 2 tio 2 and gd yb but low la sm the overlying central suite flows are either aphyric or plagioclase porphyritic and have lower mg number sio 2 la sm and gd yb decline upward through the central suite the upper suite lavas are either aphyric or plagioclase porphyritic and element ratios plot on slightly different trends compared to the central suite the lower suite has a narrow compositional range the average of the four most primitive lavas is used

tandem x time series analysis reveals lava flow volume and effusion rates of the 2012 2013 tolbachik kamchatka fissure eruption assessing eruption volumes is one of the major challenges in volcano research but provides valuable insights into the dynamics of an eruption and the associated hazard one way to estimate this important parameter is the generation and differencing of digital elevation models dems acquired before during and after an eruption the satellite mission tandem x enables generation of time series of dems using synthetic aperture radar satellite imagery we use these data to study the 2012 2013 eruption of tolbachik in kamchatka we developed a processing scheme for generation of 18 dems from tandem x imagery that relies on the generation of a preeruption dem which is used to process the syneruption and posteruption data pairs differencing each dem with the preeruption dem enables mapping the lava flows and measuring lava flow volume over time and to estimate lava extrusion rates we find a final lava flow volume of 0 53 km3 covering an area of 36 km2 by the end of the eruption an uncertainty analysis is performed while analyzing the dem differences in areas where no topographic change is expected leading to an error of 0 01 km3 for the final lava flow volume the lava effusion was with 247 92 m3 s very high in the first days of the eruption and rapidly decayed toward its end while many basaltic eruptions follow an exponentially decaying flow model the extrusion rates at tolbachik are more compatible with a 1 t model this special characteristic might be useful to gain further insight into the eruption process at tolbachik

characterization of subaerial volcanic facies using acoustic image logs lithofacies and log facies of a lava flow deposit in the brazilian pre salt deepwater of santos basin abstract volcanic rock facies characterization in subsurface log data have always being challenging even though considerable types of well logs are acquired the results achieved on facies characterization with the conventional log suits are very limited conversely high resolution borehole image logs calibrated with side wall core samples can provide the necessary structural and textural information for facies definitions in this case study an integration of good quality acoustic image log data side wall core petrography and geochemical analyses provided a good understanding of volcanic facies and stratigraphic relationships additionally outcrop data from the analogous serra geral formation and other large igneous provinces were used for comparison in the studied well from santos basin brazil it was possible to identify several kinds of subaerial basaltic lava flow units such as compound pahoehoe sheet pahoehoe and rubbly pahoehoe lava flows vesicles amygdales vesicle cylinders sub horizontal vesicle sheets autobreccias and entablature are some of the structures described in this study as a result 2 image catalogues of subaerial volcanic rocks were produced characterizing facies and flow units along with a stratigraphic model of the history of this volcanism this is the first time that pahoehoe lava flow units could be characterized at an offshore brazilian basin the results achieved are important for the understanding of the cretaceous volcanism events in the pre salt layer and also provide support for the evaluation and geological modelling of the volcanic rocks in santos basin oil fields

pāhoehoe a ā and block lava an illustrated history of the nomenclature lava flows occur worldwide and throughout history various cultures and geologists have described flows based on their surface textures as a result surface morphology based nomenclature schemes have been proposed in most languages to aid in the classification and distinction of lava surface types one of the first to be published was likely the nine class italian language description based classification proposed by mario gemmellaro in 1858 by far the most commonly used terms to describe lava surfaces today are not descriptive but instead are merely words specifically the hawaiian words a rough brecciated basalt lava and p hoehoe smooth glassy basalt lava plus block lava thick brecciated lavas that are typically more silicic than basalt a and p hoehoe were introduced into the western geological vocabulary by american geologists working in hawai i during the 1800s they and other nineteenth century geologists proposed formal lava type classification schemes for scientific use and most of them used the hawaiian words in 1933 ruy finch added the third lava type block lava to the classification scheme with the tripartite system being formalized in 1953 by gordon macdonald more recently particularly since the 1980s and based largely on studies of lava flow interiors a number of sub types and transitional forms of all three major lava types have been defined this paper reviews the early history of the development of the p hoehoe a and block lava naming system and presents a new descriptive classification so as to break out the three parental lava types into their many morphological sub types

icecap and subglacial crustal deformation inferred from sar pixel tracking the 2014 dike intrusion episode in the barðarbunga volcanic system iceland

channel overflows of the pōhue bay flow mauna loa hawai i examples of the contrast between surface and interior lava a number of overflows from a large lava channel and tube system on the southwest rift zone of mauna loa were studied initial overflows were very low viscosity gas rich p hoehoe evidenced by flow unit aspect ratios and vesicle sizes and contents calculated volumetric flow rates in the channel range between 80 and 890 m3 s and those of the overflows between 35 and 110 m3 s after traveling tens to hundreds of meters the tops of these sheet like overflows were disrupted into a surface composed of clinker and p hoehoe fragments after these a overflows came to rest lava from the interiors was able to break out on to the surface as p hoehoe the surface structure of a lava flow records the interaction between the differential shear rate usually correlated with the volumetric flow rate and viscosity induced resistance to flow however the interior of a flow being better insulated may react differently or record a later set of emplacement conditions clefts of toothpaste lava occurring within fields of clinker on proximal type a flows also record different shear rates during different times of flow emplacement the interplay between viscosity and shear rate determines the final morphological lava type and although no specific portion of lava ever makes a transition from a back to p hoehoe parts of a flow can appear to do so

strain fabric evolution within and near deformed igneous sheets the sudbury igneous complex canada abstract deformation structures differing in style and orientation within a given terrane are often attributed to distinct tectono metamorphic events however mechanical heterogeneities may locally cause strain perturbations that can have a profound effect on the geometry of such structures here we document highly variable orientations of planar structures metre to kilometre scale folds and shortening directions inferred from brittle fault analysis within the synclinal and layered sudbury igneous complex sic and its huronian host rocks nw se shortening during palaeoproterozoic deformation led to the formation of planar structures in the host rocks that are parallel to the ne sw striking contact of the southern sic during deformation local contact parallel shortening became more important than regional nw se shortening and generated contact orthogonal planar mineral fabrics and folds local contact parallel shortening is attributed to the shape change of the southern sic from a convex outward to a concave inward curvi planar geometry contact parallel shortening accounts for the formation of a previously unidentified kilometre scale buckle fold in the sic and respective axial planar mineral fabrics in huronian host rocks this buckle fold shares similar structural characteristics with known higher order buckle folds of the eastern sic we suggest that non cylindrical buckling and associated mineral fabric development accommodated the shape change of the sic this resulted in mutually perpendicular fabric orientations which are compatible with overall nw se shortening the original shape of the sic seems to have had a profound influence particularly on the geometry of metamorphic foliations our structural analysis supports earlier structural studies advocating that highly discordant planar strain fabrics can be generated by local strain perturbations near igneous sheets under uniform regional shortening

cooling and crystallization of lava in open channels and the transition of pāhoehoe lava to a ā samples collected from a lava channel active at kilauea volcano during may 1997 are used to con strain rates of lava cooling and crystallization during early stages of flow lava erupted at near liquidus tem peratures f1150 7c cooled and crystallized rapidly in upper parts of the channel glass geothermometry indi cates cooling by 12 14 7c over the first 2 km of trans port at flow velocities of 1 2 m s this translates to cooling rates of 22 50 7c h cooling rates this high can be explained by radiative cooling of a well stirred flow consistent with observations of non steady flow in proximal regions of the channel crystallization of plag ioclase and pyroxene microlites occurred in response to cooling with crystallization rates of 20 50 per hour crystallization proceeded primarily by nucleation of new crystals and nucleation rates of f10 4 cm 3 s are similar to those measured in the 1984 open channel flow from mauna loa volcano there is no evidence for the large nucleation delays commonly assumed for plagioclase crystallization in basaltic melts possibly a reflection of enhanced nucleation due to stirring of the flow the transition of the flow surface morphology from pahoehoe to a aoccurred at a distance of 1 9 km from the vent at this point the flow was thermally stratified with an interior temperature of f1137 7c and crystallinity of f15 and a flow surface tempera ture of f1100 7c and crystallinity of f45 a afor mation initiated along channel margins where crust was continuously disrupted and involved tearing and clotting of the flow surface both observations suggest that the transition involved crossing of a rheological threshold we suggest this threshold to be the develop ment of a lava yield strength sufficient to prevent vis cous flow of lava at the channel margin we use this concept to propose that a aformation in open chan nels requires both sufficiently high strain rates for con tinued disruption of surface crusts and sufficient groundmass crystallinity to generate a yield strength equivalent to the imposed stress in hawai i where lava is typically microlite poor on eruption these combined requirements help to explain two common observations on a aformation a a aflow fields are generated when effusion rates are high thus promoting crustal disruption and b under most eruption conditions lava issues from the vent as pahoehoe and changes to a aonly after flowing some distance thus permitting sufficient crystallization

lava water interaction and hydrothermal activity within the 2014 2015 holuhraun lava flow field iceland abstract lava that erupted during the 2014 2015 holuhraun eruption in iceland flowed into a proglacial river system resulting in aqueous cooling of the lava and an ephemeral hydrothermal system we carried out a monitoring study of this system from 2015 to 2018 to document the cooling of the lava over this time using thermocouple measurements and data logging sensors the heat loss rate from advection through this hydrothermal system in august 2015 was 5 5 108 w since eruption aqueous cooling likely accounted for 1 of the total heat loss from the lava this estimate excludes steam losses from fumaroles as well as any groundwater that was not released to the surface and thus is a lower bound near the terminus of the flow advection of heat by flowing water may have locally accounted for tens of percent of the total cooling of that part of the flow our data quantify the importance of water cooling for this lava flow and can be compared with models to better understand lava water interactions more generally we also provide detailed methods for simple low cost monitoring of similar instances in the future

an aeolian grainflow model for martian recurring slope lineae abstract recurring slope lineae rsl on mars have been enigmatic since their discovery their behavior resembles a seeping liquid but sources of water remain puzzling this work demonstrates that the properties of rsl are consistent with observed behaviors of martian and terrestrial aeolian processes specifically rsl are well explained as flows of sand that remove a thin coating of dust observed rsl properties are supportive of or consistent with this model which requires no liquid water or other exotic processes but rather indicates seasonal aeolian behavior these settings and behaviors resemble features observed by rovers and also explain the occurrence of many slope lineae on mars that do not meet the strict definition of rsl this indicates that rsl can be explained simply as aeolian features other processes may add complexities just as they could modify the behavior of any sand dune

assessment of the relative accuracy of hemispheric scale snow cover maps there are several hemispheric scale satellite derived snow cover maps available but none has been fully validated for the period october 23 december 25 2000 we compare snow maps of north america derived from the moderate resolution imaging spectroradiometer modis and the national oceanic and atmospheric administration noaa national operational hydrologic remote sensing center nohrsc which both rely on satellite data from the visible and near infrared parts of the spectrum we also compare modis and defense meteorological satellite program dmsp special sensor microwave imager ssm i passive microwave snow maps the maps derived from visible and near infrared data are more accurate for mapping snow cover than are the passive microwave derived maps however discrepancies exist as to the location and extent of the snow cover among those maps the large approx 30 km footprint of the ssm i data and the difficulty in distinguishing wet and shallow snow from wet or snow free ground reveal differences up to 5 32 million sq km in the amount of snow mapped using modis versus ssm i data algorithms that utilize both visible and passive microwave data which would take advantage of the all weather mapping ability of the passive microwave data will be refined following the launch of the advanced microwave scanning radiometer amsr in the fall of 2001

geology and geochemistry of intrusions and flood basalts of the noril sk region ussr with implications for the origin of the ni cu ores geochemical studies indicate that five principal magma types characterize the 3 8 km vertical thickness of flood basalt of the noril9sk region from base to top these are 1 a fractionated type with alkalic affiliations ivakinsky and syverminsky 2 an ni rich suite including picritic basalt gudchichinsky 3 a primitive but ni depleted suite with fiat rare earth element ree profiles and also including picritic basalts tuklonsky 4 a light ree enriched crustally contaminated suite lower nadezhdinsky nd 1 above 4 there is a transitional suite upper nadezhdinsky nd 2 and morongovsky mr 1 and mr 2 which is overlain by the fifth type a second primitive suite without picrites mokulaevsky similar but not identical in its chemistry to the tuklonsky type this is followed by tuffs and basalts of the kharayelakhsky kumginsky and samoyedsky suites which are largely composed of similar uncontaminated tholeiitic magma the latter three suites have not been studied by us intrusions of the region fall into five main groups 1 alkalic intrusions 2 ti rich dolerite dikes 3 dolerite sills and dikes 4 differentiated bodies not related to ore junctions and 5 differentiated bodies related to ore junctions the ni cu ores are associated with ni and cr rich type 5 olivine rich intrusions with flat ree profiles that are geochemicaly similar to the mokulaevsky magma light ree enriched ni and cr poor olivine rich type 5 intrusions with uneconomic mineralization occur closely associated with the strongly mineralized variants and resemble geochemically the basalts transitional between the lower nadezhdinsky and upper morongovsky they are cut by the strongly mineralized bodies indicating that the latter are of late morongovsky to mokulaevsky age the mineralized intrusions are associated with about 1 5 to 1 10 of their mass in sulfides this is a factor of 25 to 50 more than could have been carried in solution and deposited by in situ liquation from the magma of these intrusions the platinum group element pge concentrations in the ores require that the sulfides giving rise to them equilibrated with 15 to 200 times more magma than is represented by the intrusions much of the ore is very massive and crosscuts the host intrusions the sequence of igneous activity and mineralization in the immediate vicinity of noril9sk and talnakh from the base of the nadezhdinsky upward is thus interpreted to be 1 extrusion of highly crustally contaminated ni and cu poor basalt 2 extrusion of a series of basalt flows each progressively less contaminated and less ni and cu depleted than the preceding one accompanied by intrusion of contaminated ni depleted magma with weak mineralization 3 extrusion of uncontaminated ni and cu rich basalt accompanied by intrusion of uncontaminated ni rich magma with strong mineralization followed very closely by introduction of associated massive ore and 4 continued extrusion of ni and cu rich basalt it is proposed that crustal contamination of the original ni and cu rich magma occurred at the top of a vertically extensive fault controlled magma chamber and caused segregation of immiscible sulfides with a low r factor these depleted this magma in chalcophile elements and settled deeper in the chamber as they settled they reacted with less contaminated magma scavenging additional chalcophile elements they finally came to rest near the base of the chamber to form a zone of sulfide and thus chalcophile element enriched magma eruption and in some instances intrusion of progressively stratigraphically lower less contaminated and thus less depleted layers in the chamber gave rise to the observed sequence of basalts and intrusions the answer to the strong enrichment in ni cu and pge associated with the ore bearing intrusions is that these metals came from the magma that is now represented by the depleted basalts

a u pb age for mineralized nipissing diabase gowganda ontario concordant baddeleyite and rutile analyses from mineralized nipissing diabase at gowganda s castle mine yield a u pb age of baddeleyite is a primary phase of the diabase therefore the age dates the magmatic emplacement the genesis of rutile is less certain rutile could have formed during an episode of alteration veining and ag mineralization in which case the u pb age would also date the secondary event and demonstrate that ag mineralization was related to the nipissing magmatism however a primary magmatic origin of the rutile cannot be completely excluded for now thus the u pb age may not constrain the time of ag mineralization further research is needed to clarify this point

platinum group element mineralization in a hydrothermal cu ni sulfide occurrence rathbun lake northeastern ontario pt pd and au are concentrated in a hydrothermal cu ni sulfide occurrence near rathbun lake northeastern ontario the mineralization is associated with a sheared zone of the wanapitei intrusion where hydrothermal fluids have altered relatively pristine gabbronorite to chlorite sericite quartz epidote and biotite chalcopyrite and pyrite the principal sulfide minerals occur as massive and disseminated mineralization bismuthian merenskyite and to a lesser extent kotulskite michenerite and temagamite are the pd bearing minerals whereas pt occurs primarily in sperrylite 64 percent of the pd mineral grains are associated with altered silicates rather than sulfides although grains within sulfides may have been exsolved the size and number associated with silicates suggest many were precipitated independently grab samples average 9 percent cu 0 2 percent ni 20 829 ppb pd 9 736 ppb pt and 3 053 ppb au values for the other platinum group elements are near background levels no correlation is evident between cu and the platinum group elements or au the ratio of pt pd os ir ru is much larger than for tholeiitic hosted deposits of magmatic origin and probably reflects the relative solubilities of the platinum group elements

differentiation and emplacement of the worthington offset dike of the sudbury impact structure ontario the offset dikes of the 1 85 ga sudbury igneous complex sic constitute a key topic in understanding the chemical evolution of the impact melt its mineralization and the interplay between melt migration and impact induced deformation the origin of the melt rocks in offset dikes as well as mode and timing of their emplacement are still a matter of debate like many other offset dikes the worthington is composed of an early emplaced texturally rather homogeneous quartz diorite qd phase at the dike margin and an inclusion and sulfide rich quartz diorite iqd phase emplaced later and mostly in the centre of the dike the chemical heterogeneity within and between qd and iqd is mainly attributed to variable assimilation of host rocks at the base of the sic prior to emplacement of the melt into the dike petrological data suggest that the parental magma of the worthington dike mainly developed during the pre liquidus temperature interval of the thermal evolution of the impact melt sheet 1200 c based on thermal models of the cooling history of the sic the two stage emplacement of the worthington dike occurred likely thousands to about ten thousand years after impact structural analysis indicates that an alignment of minerals and host rock fragments within the worthington dike was caused by ductile deformation under greenschist facies metamorphic conditions rather than flow during melt emplacement it is concluded that the worthington offset dike resulted from crater floor fracturing possibly driven by late stage isostatic readjustment of crust underlying the impact structure

the millennium eruption of hekla in february 2000 the 18th historic eruption of hekla started on 26 february 2000 it was a short lived but intense event emitting basaltic andesitic 55 5 wt sio2 pyroclastic fragments and lava during the course of the eruption monitoring was done by both instruments and direct observations together providing unique insight into the current activity of hekla during the 12 day eruption a total of 0 189 km3 dre of magma was emitted the eruptive fissure split into five segments the segments at the highest altitude were active during the first hours while the segments at lower altitude continued throughout the eruption the eruption started in a highly explosive manner giving rise to a subplinian eruptive column and consequent basaltic pyroclastic flows fed by column collapses after the explosive phase reached its maximum the eruption went through three more phases namely fire fountaining strombolian bursts and lava effusion in this paper we describe the course of events of the eruption of hekla and the origin of its magma and then show that the discharge rate can be linked to different style of eruptive activity which are controlled by fissure geometry we also show that the eruption phases observed at hekla can be linked with inferred magma chamber overpressure prior to the eruption

source and differentiation of deccan trap lavas implications of geochemical and mineral chemical variations the basalt stratigraphy of the deccan trap between mahabaleshwar ghat and belgaum over steps the basement from north to south sr isotope and zr nb ratios and sr rb and ba concentrations correlate portions of the post poladpur stratigraphy over 250 km along the western ghats thereby confirming a southerly component of dip of 0 06 at the southwestern margin the stratigraphy extends upwards from the compositionally uniform ambenali formation cox hawkesworth 1984 into a sequence of grossly heterogeneous flow units which have been allocated to the mahabaleshwar and panhala formations lightfoot hawkesworth 1988 the mahabaleshwar formation is represented only by a sequence of highly fractionated flows termed the kolhapur unit with similar 87sr 86sr0 to the mahabaleshwar 0 7045 but with sr 2 25 succeeding the kolhapur unit are a series of flows with high 87sr 86sr0 0 7045 0 705 zr nb 13 and low sr 230 but trace element concentrations similar to the mahabaleshwar formation these have been allocated to the desur unit of the panhala geochemical variations in flows overlying the ambenali define two distinct trends one is attributed to gabbro fractionation and the other to variations in the compositions of the parental magmas and arguably their source regions there is little evidence for significant crustal contamination in these flows and the degree of fractionation and the composition of the phase extract are shown to vary along strike within the mahabaleshwar formation the high tio2 content of kolhapur unit flows is shown to be the result of shallow level gabbro fractionation rather than the presence of a primitive high ti magma mahabaleshwar formation basalts exhibit a broad negative correlation between the degree of fractionation and sr isotopic composition the endmember with lower 87sr 86sr0 has different zr y from the ambenali basalts and would appear to have been generated by lower degrees of melting of a similar source the other endmember has more radiogenic sr lower zr nb similar zr y but higher mg number the simplest interpretation is that these magmas were more primitive and hence hotter and more able to interact with the lithosphere en route to the surface and that they then mixed to produce the mahabaleshwar array the panhala formation basalts plot on the sr nd array defined by the mahabaleshwar formation and the desur unit basalts plot on an extension of this array this suggests that the source characteristics are also lithospheric the absolute elemental abundances may then be a function of melting and fractionation we are impressed by the apparent switch from crustal lithospheric contributions to mantle lithospheric contributions through the stratigraphy and suggest that this together with the more protracted fractionation of the magma reflects a change in the availability of the lithospheric components accompanying the southerly migration of the volcanic edifice

the importance of pahoehoe abstract pahoehoe lava flows are common in every basaltic province and their submarine variants pillow lavas and sheet flows cover the bulk of the earth pahoehoe flows are emplaced by inflation the injection of molten lava underneath a solidified crust only in the past few years has an understanding of the inflation process and the ability to recognize ancient inflated lava flows been achieved all large terrestrial basaltic flow fields studied to date including flood basalts were emplaced as thermally efficient inflated compound pahoehoe sheet flows this leads us to propose that this is the standard way of emplacing large lavas the swell hypothesis the atmospheric impact of such flood basalt eruptions could have been protracted and severe providing a plausible link between flood basalt eruptions and mass extinctions

the historic events at kilauea volcano in 2018 summit collapse rift zone eruption and mw 6 9 earthquake preface to the special issue

emplacement and inflation of pahoehoe sheet flows observations and measurements of active lava flows on kilauea volcano hawaii inflated pahoehoe sheet flows have a distinctive horizontal upper surface which can be several hundred meters across and are bounded by steep monoclinal uplifts the inflated sheet flows we studied ranged from 1 to 5 m in thickness but initially propagated as thin sheets of fluid pahoehoe lava generally 20 30 cm thick individual lobes originated at outbreaks from the inflated front of a prior sheet flow lobe and initially moved rapidly away from their source velocities slowed greatly within hours due to radial spreading and to depletion of lava stored within the source flow as the outward flow velocity decreases cooling promotes rapid crustal growth at first the crust behaves plastically as pahoehoe toes form after the crust attains a thickness of 2 5 cm it behaves more rigidly and develops enough strength to retain incoming lava thus increasing the hydrostatic head at the flow front the increased hydrostatic pressure is distributed evenly through the liquid lava core of the flow resulting in uniform uplift of the entire sheet flow lobe initial uplift rates are rapid flows thicken to 1 m in 1 2 hours but rates decline sharply as crustal thickness increases and as outbreaks occur from the margins of the inflating lobe one flow reached a final thickness of nearly 4 m after 350 hr inflation data define power law curves whereas crustal cooling follows square root of time relationships the combination of data can be used to construct simple models of inflated sheet flows as the flow advances preferred pathways develop in the older portions of the liquid cored flow these pathways can evolve into lavatube systems within a few weeks formation of lava tubes results in highly efficient delivery of lava at velocities of several kilometers per hour to a flow front that may be moving 1 2 orders of magnitude slower if advance of the sheet flow is terminated the tube remains filled with lava that crystallizes in situ rather than draining to form the cave like lava tubes commonly associated with pahoehoe flows inflated sheet flows from kilauea and mauna loa are morphologically similar to some thick icelandic and submarine sheet flows suggesting a similar mechanism of emplacement the planar sheet like geometry of flood basalt flows may also result from inflation of sequentially emplaced flow lobes rather than nearly instantaneous emplacement as literal floods of lava

formation of segregation structures in hafnarhraun pāhoehoe lobe sw iceland a window into crystal melt separation in basaltic magma to gain insights into crystal melt separation processes during basalt differentiation we have studied an 8 m thick p hoehoe lava lobe from the hafnarhraun lava flow field in sw iceland the lobe has abundant melt segregations porous cylindrical and sheet like structures generally interpreted as separated residual melts of a lava lobe we divide these melt segregations into three types based on morphology and composition vesicle cylinders vc type 1 horizontal vesicle sheets hvs1 and type 2 horizontal vesicle sheets hvs2 remarkably the studied vc are not simple residual melts generated by fractional crystallization but their composition points to removal of plagioclase from the parental lava hvs1 resemble vc but have fractionated more olivine ol plagioclase plg augite and have lost most if not all of their olivine phenocrysts hvs2 are fe rich and evolved corresponding to residual melts after 50 60 fractional crystallization of the lobe we suggest that the hafnarhraun vc formed in a two stage process firstly vc forming residual melt and vapor detached as rising diapirs from ol plg melt vapor mush near the lava base and later these vc diapirs accumulated ol phenocrysts and minor plg microphenocrysts in the lava core hvs1 represent accumulations of vc to the viscous base of the solidifying upper crust of the lobe and hvs2 formed as evolved vapor saturated residual melts seeped into voids within the upper crust such vapor aided differentiation here documented for the hafnarhraun lava may also apply to shallow crustal magma storage zones contributing to the formation of evolved basalts

proximal lava drainage controls on basaltic fissure eruption dynamics hawaiian basaltic eruptions commonly initiate as a fissure producing fountains spattering and clastogenic lava flows most fissures rapidly localize to form a small number of eruptive vents the location of which may influence the subsequent distribution of lava flows and associated hazards we present results from a detailed field investigation of the proximal deposits of episode 1 of the 1969 fissure eruption of mauna ulu k lauea hawai i exceptional preservation of the deposits allows us to reconstruct vent proximal lava drainage patterns and to assess the role that drainage played in constraining vent localization through detailed field mapping including measurements of the height and internal depth of lava tree moulds we reconstruct high resolution topographic maps of the pre eruption ground surface the lava high stand surface and the post eruption ground surface we calculate the difference in elevation between pairs of maps to estimate the lava inundation depth and lava drainage depth over the field area and along different segments of fissure aerial photographs collected during episode 1 of the eruption allow us to locate those parts of the fissure that are no longer exposed at the surface by comparing with the inundation and drainage maps we find that fissure segments that were inundated with lava to greater depths typically 1 6 m during the eruption later became foci of lava drainage back into the fissure internal drain back we infer that in these areas lava ponding over the fissure suppressed discharge of magma thereby favouring drain back and stagnation by contrast segments with relatively shallow inundation typically less than 1 m such as where the fissure intersects pre eruptive topographic highs or where flow away from the vent outflow was efficient are often associated with sub circular vent geometries in the post eruption ground surface we infer that these parts of the fissure became localization points for ongoing magma ascent and discharge we conclude that lava inundation and drainage processes in basaltic fissure eruptions can play an important role in controlling their localization and longevity

lava field evolution and emplacement dynamics of the 2014 2015 basaltic fissure eruption at holuhraun iceland abstract the 6 month long eruption at holuhraun august 2014 february 2015 in the bar arbunga vei ivotn volcanic system was the largest effusive eruption in iceland since the 1783 1784 ce laki eruption the lava flow field covered 84 km2 and has an estimated bulk i e including vesicles volume of 1 44 km3 the eruption had an average discharge rate of 90 m3 s making it the longest effusive eruption in modern times to sustain such high average flux the first phase of the eruption august 31 2014 to mid october 2014 had a discharge rate of 350 to 100 m3 s and was typified by lava transport via open channels and the formation of four lava flows no 1 4 which were emplaced side by side the eruption began on a 1 8 km long fissure feeding partly incandescent sheets of slabby p hoehoe up to 500 m wide by the following day the lava transport got confined to open channels and the dominant lava morphology changed to rubbly p hoehoe and a the latter became the dominating morphology of lava flows no 1 8 the second phase of the eruption mid october to end november had a discharge of 100 50 m3 s during this time the lava transport system changed via the formation of a 19 km2 of the flow field the primary lava morphology from this phase was spiny p hoehoe which superimposed on the a lava flows no 1 3 and extended the entire length of the flow field i e 17 km this made the 2014 2015 holuhraun a paired flow field where both lava morphologies had similar length we suggest that the similar length is a consequence of the p hoehoe is fed from the tube system utilizing the existing a lava channels and thereby are controlled by the initial length of the a flows

lava tubes on earth moon and mars a review on their size and morphology revealed by comparative planetology abstract sinuous collapse chains and skylights in lunar and martian volcanic regions have often been interpreted as collapsed lava tubes also known as pyroducts this hypothesis has fostered a forty years debate among planetary geologists trying to define if analogue volcano speleogenetic processes acting on earth could have created similar subsurface linear voids in extra terrestrial volcanoes on earth lava tubes are well known thanks to speleological exploration and mapping in several shield volcanoes with examples showing different genetic processes inflation and overcrusting and morphometric characters on the moon subsurface cavities have been inferred from several skylights in maria smooth plains and corroborated using gravimetry and radar sounder while on mars several deep skylights have been identified on lava flows with striking similarities with terrestrial cases nonetheless the literature on this topic is scattered and often presents inaccuracies in terminology and interpretation a clear understanding of the potential morphologies and dimensions of martian and lunar lava tubes remains elusive although it is still impossible to gather direct information on the interior of martian and lunar lava tube candidates scientists have the possibility to investigate their surface expression through the analysis of collapses and skylight morphology morphometry and their arrangement and compare these findings with terrestrial analogues in this review the state of the art on terrestrial lava tubes is outlined in order to perform a morphological and morphometric comparison with lava tube candidate collapse chains on mars and the moon by comparing literature and speleological data from terrestrial analogues and measuring lunar and martian collapse chains on satellite images and digital terrain models dtms this review sheds light on tube size depth from surface eccentricity and several other morphometric parameters among the three different planetary bodies the dataset here presented indicates that martian and lunar tubes are 1 to 3 orders of magnitude more voluminous than on earth and suggests that the same processes of inflation and overcrusting were active on mars while deep inflation and thermal entrenchment was the predominant mechanism of emplacement on the moon even with these outstanding dimensions with total volumes exceeding 1 billion of m3 lunar tubes remain well within the roof stability threshold the analysis shows that aside of collapses triggered by impacts tectonics most of the lunar tubes could be intact making the moon an extraordinary target for subsurface exploration and potential settlement in the wide protected and stable environments of lava tubes

structure and origin by injection of lava under surface crust of tumuli lava rises lava rise pits and lava inflation clefts in hawaii tumuli are positive topographic features that are common on hawaiian pahoehoe lava flow fields particularly on shallow slopes and 75 measured examples are presented here to document the size range tumuli form by up tilting of crustal plates without any crustal shortening and are thus distinguished from pressure ridges which are up buckled by laterally directed pressure the axial or star like systems of deep clefts that characterize tumuli are defined here as lava inflation clefts their tips advanced into red hot lava and they widened as uplift proceeded and while the lava crust was thickening flat surfaced uplifts formed like tumuli by injection of lava under a surface crust were previously called pressure plateaus but lava rise is proposed instead the pits that abound among lava rises previously attributed to collapse or subsidence are generally formed because the lava around them rose and the name lava rise pit is proposed unique examples of tumuli and lava rises from which lava drained out under a surface crust 1 5 to 2 5 m thick are described from kilauea caldera these examples show that in tumuli and lava rises the crust floats on considerable bodies of fluid lava and is able to do so because of its higher vesicle content the fluid lava loses many of its gas bubbles during residence beneath the crust the bulk densities of samples from tumuli show a general downward increase the form of the density profile is consistent with the relationship that for any given crustal thickness the density of fluid lava closely matched the average density of that crust suggesting that the lava was stably density stratified it is inferred that stable stratification was regulated by out flows of the more vesicular lava fractions loss of bubbles through the lava inflation clefts and entry of injected lava at its level of neutral buoyancy below the uppermost meter the downward decrease in vesicularity closely conforms with that expected by compression of a uniform mass of gas per unit mass of lava

long period seismicity reveals magma pathways above a laterally propagating dyke during the 2014 15 barðarbunga rifting event iceland abstract the 2014 15 bar arbunga holuhraun rifting event comprised the best monitored dyke intrusion to date and the largest eruption in iceland in 230 years a huge variety of seismicity was produced including over 30 000 volcano tectonic earthquakes vts associated with the dyke propagation at 6 km depth below sea level and large magnitude earthquakes accompanying the collapse of bar arbunga caldera we here study the long period seismicity associated with the rifting event we systematically detect and locate both long period events lps and tremor during the dyke propagation phase and the first week of the eruption we identify clusters of highly similar repetitive lps which have a peak frequency of 1 hz and clear p and s phases followed by a long duration coda the source mechanisms are remarkably consistent between clusters and also fundamentally different to those of the vts we accurately locate lp clusters near each of three ice cauldrons depressions formed by basal melting that were observed on the surface of dyngjujokull glacier above the path of the dyke most events are in the vicinity of the northernmost cauldron at shallower depth than the vts associated with lateral dyke propagation at the two northerly cauldrons periods of shallow seismic tremor following the clusters of lps are also observed given that the lps occur at 4 km depth and in swarms during times of dyke stalling we infer that they result from excitation of magmatic fluid filled cavities and indicate magma ascent we suggest that the tremor is the climax of the vertical melt movement arising from either rapid repeated excitation of the same lp cavities or sub glacial eruption processes this long period seismicity therefore represents magma pathways between the depth of the dyke vt earthquakes and the surface notably we do not detect tremor associated with each cauldron despite melt reaching the base of the overlying ice cap a concern for hazard monitoring

strike slip faulting during the 2014 barðarbunga holuhraun dike intrusion central iceland over a 13 day period magma propagated laterally from the subglacial bar arbunga volcano in the northern rift zone iceland it created 30 000 earthquakes at 5 7 km depth along a 48 km path before erupting on 29 august 2014 the seismicity which tracked the dike propagation advanced in short bursts at 0 3 4 7 km h separated by pauses of up to 81 h during each surge forward seismicity behind the dike tip dropped moment tensor solutions from the leading edge show exclusively left lateral strike slip faulting subparallel to the advancing dike tip releasing accumulated strain deficit in the brittle layer of the rift zone behind the leading edge both left and right lateral strike slip earthquakes are observed the lack of non double couple earthquakes implies that the dike opening was aseismic

operational response and hazards assessment during the 2014 2015 volcanic crisis at barðarbunga volcano and associated eruption at holuhraun iceland abstract on august 16 2014 an intense seismic swarm started below the eastern part of bar arbunga caldera in the north western part of vatnajokull ice cap iceland marking the onset of a major rifting event the intense seismicity corroborated by a complicated deformation pattern migrated away from the bar arbunga caldera for 45 km until a small effusive eruption started in holuhraun outside of the ice cap on august 29 which lasted a few hours on august 31 a second more intense eruption started it lasted 180 days and is the largest effusive eruption in iceland since the laki event in 1783 1784 a lava field covered about 84 km2 in the middle of the highlands with a bulk volume of 1 44 km3 although the potential danger of ice melting and subsequent flooding coupled with tephra fallout was the main concern at the beginning of the crisis the main associated hazard turned out to be an abundant and constant release of volcanic gases that polluted the country threatening human health and the environment for several months very little or almost no ash was produced the impact of the holuhraun eruption outside of iceland was minor if compared with what happened in 2010 when eyjafjallajokull erupted however on three occasions the dense gas cloud released by the fissure eruption reached some european countries where unusually high so2 concentrations were measured at ground level managing and living with such a prolonged effusive event was a major effort for the icelandic scientific community and civil protection authorities and it significantly affected the local population in the northern and eastern parts of the country this paper retraces the main events that accompanied the volcanic crisis at bar arbunga and focuses on the scientific and operative response provided throughout its duration particular attention is given to the direct links between the observed phenomena monitoring effort hazard assessment and concrete actions taken by the authorities in charge of risk and mitigation assessment the different roles of the involved institutions are clarified and the wide and collaborative response on a national basis is explained a major finding of this post event analysis is that a strong internal collaboration between the scientific community and operative institutions is the basic element for proper crisis management iceland has established protocols that while imperfect ensured a well coordinated response to the holuhraun eruption and the preceding unrest and will continue to provide a prompt and effective response for future events important realizations including the need for a proper ground based alert level system have been raised and they will be a matter for further development

lava rise plateaus and inflation pits in the mccartys lava flow field new mexico an analog for pāhoehoe like lava flows on planetary surfaces

the geology and geochemistry of the waterfall gorge section of the insizwa complex with particular reference to the origin of the nickel sulfide deposits the jurassic aged mafic rocks from the waterfall gorge section of the insizwa layered complex transkei range in composition from olivine gabbro and picrite basal zone through a series of gabbros central zone to monzonites roof zone the compositional data for the mineral phases olivine plagioclase bronzite and augite show significant features in the basal gabbro the trend in compositional variation is the reverse of that seen in the central zone of the intrusion and olivines from the picrite unit are the most forsteritic in the intrusion but they are depleted in ni compared to olivines from the basal gabbro and central zone the data for olivines from the picrite unit at tabankulu exhibit a similar but more significant degree of depletion mineral compositional and whole rock geochemical data for the basal olivine gabbro suggest that olivine control is primarily responsible for the compositional variation in this unit at insizwa however to account for the upward increase in the forsterite content of the cumulus olivine at the base the intrusion of successively less fractionated batches of a low mgo magma is suggested we suggest that the depletion of the olivines in ni can be attributed to the equilibration of the parent magma with sulfide and we show that these data are consistent with experimental distribution coefficient data for ni between olivine and sulfide permitting broad constraints to be placed on the grade as well as the tonnage and location of the ore extrapolation of these conclusions to the tabankulu intrusion suggest that the highly ni depleted olivines of the picrite have equilibrated with a magma from which a particularly high proportion of sulfide has segregated geophysical data fail to detect a massive orebody at the base of the intrusion though several small bodies may exist it is suggested that saturation may have occurred at depth and only a small amount of sulfide has been transported to the surface in the picrite and concentrated in depressions at the base of the intrusion massive and disseminated magmatic ni sulfide mineralization is confined to the lower basal zone and shows a consistent fractionation into pyrrhotite pentlandite rich ore at the base and chalcopyrite rich ore at the top in both massive sheets and globular ore the cause of sulfur saturation cannot be attributed to the reduction of the solubility of sulfur in the magma by increasing the sio 2 concentration contamination despite the close association of the ore with granophyric segregations in the basal olivine gabbro indeed the major and trace element data argue strongly against wholesale assimilation of crust at any stage in the production of the basal gabbro

investigating the volcanic versus aqueous origin of the surficial deposits in eastern elysium planitia mars abstract the elysium volcanic province consists of numerous overlapping flow units and may include the youngest lava flows on mars however it is possible that these volcanic units have been modified or overprinted by aqueous processes understanding the timing of the igneous and aqueous events in this region is therefore essential for constraining the geological and environmental history of mars during the amazonian period we investigate the geologic evolution of eastern elysium planitia to determine the relationship between major units with the support of a geological map and chronological constraints from crater size frequency distributions we also evaluate the hypothesized origin of these units via volcanic fluvial and or fluvioglacial processes using a detailed facies mapping approach the study area includes the eastern cerberus fossae rahway valles and marte vallis the surficial deposits in rahway valles were formerly interpreted to be modified by fluvial and fluvioglacial processes however our facies map reveals that the surface of eastern elysium planitia includes nineteen morphologically distinct regions i e facies which are interpreted to be the products of flood lava volcanism including a p hoehoe and transitional lava flow types in contrast to previous studies which determined that rahway valles and marte vallis consist of two distinct geologic units with middle to late amazonian ages the results of this work show that the region was resurfaced by at least two volcanic flows with much younger ages of 20 0 ma and 8 8 ma furthermore by coupling results of our geologic and facies mapping with chronological constraints as well as subsurface information provided by shallow radar reflectors we show that there is an erosional unconformity located between the two youngest lava flow units in marte vallis we interpret that this unconformity was generated by a catastrophic aqueous flooding event that occurred only 8 8 20 0 ma ago this implies alternating episodes of volcanism and aqueous flooding that have continued into the geologically recent past on mars and may again occur within elysium planitia

the madinah eruption saudi arabia magma mixing and simultaneous extrusion of three basaltic chemical types during a 52 day eruption in 1256 a d 0 5 km3 of alkali olivine basalt was extruded from a 2 25 km long fissure at the north end of the harrat rahat lava field saudi arabia the eruption produced 6 scoria cones and a lava flow 23 km long that approached the ancient and holy city of madinah to within 8 km three chemical types of basalt are defined by data point clusters on variation diagrams i e the low k high k and hybrid types all three erupted simultaneously their distribution is delineated in both scoria cones and lava flow units from detailed mapping and a petrochemical study of 135 samples six flow units defined by distinct flow fronts represent extrusive pulses the high k type erupted during all six pulses the low k type during the first three and the hybrid type during the first two

differentiation and source of the nipissing diabase intrusions ontario canada major and trace element data are presented for 2 2 ga proterozoic diabase sills from across the nipissing magmatic province of ontario in situ differentiation of the magma coupled with assimilation of huronian supergroup roof sediments is responsible for the variation in composition between quartz diabase and granophyric diabase seen within many of the differentiated intrusions uniform trace element and isotope ratio signatures such as la sm 2 8 3 7 and endchur 2 7 to 5 9 characterize chilled margins and undifferentiated quartz diabases these chemical signatures suggest the existence of a single magma source that was parental to intrusions throughout the magmatic province this magma has higher la sm and lower ti y than primitive mantle and is displaced towards the composition of shales most chilled diabases and quartz diabases have a similar mg 0 64 and 0 60 and ni content 98 and 127 ppm and it is argued that the magma differentiated at depth and was emplaced as a uniform low mg magma

holocene volcanic activity at grimsvotn bardarbunga and kverkfjoll subglacial centres beneath vatnajokull iceland assessment of potential future eruptive behaviour of volcanoes relies strongly on detailed knowledge of their activity in the past such as eruption frequency magnitude and repose time the eruption history of three partly subglacial volcanic systems grimsvotn bardarbunga and kverkfjoll was studied by analysing tephra from soil profiles around the vatnajokull ice cap which extend back to 7 6 ka well known regional holocene marker tephra e g h3 h4 h5 were utilized to correlate profiles stratigraphic positions and geochemical compositions were used for fine scale correlation of basaltic tephra around vatnajokull ice cap 345 tephra layers were identified of which 70 originated from grimsvotn bardarbunga or kverkfjoll the eruption frequency of each volcanic system was estimated grimsvotn has been the most active with an average of 7 eruptions 100 years range 4 14 during prehistoric time before 870 ad bardarbunga has been the second most active with 5 eruptions 100 years range 1 8 and kverkfjoll has remained essentially calm with 0 3 eruptions 100 years but showing periodic activity with repose times of 1000 years all three volcanic systems experienced lulls in activity from 5 ka to 2 ka referred to as the mid holocene low this reduced eruption frequency appears to have resulted from a decrease in magma generation and delivery from the mantle plume rather than from changes in ice load glacier thickness in prehistoric time there was a time lag of 1000 3000 years between a peak of activity at volcanoes directly above the mantle plume versus at volcanoes located in the non rifting part of the eastern volcanic zone closer to the periphery of the island this time space relationship suggests that a significant future increase in volcanism can be expected there following increased levels of volcanism above the plume

the rheological evolution of the 2014 2015 eruption at holuhraun central iceland in the period from august 29 2014 to february 27 2015 the largest basaltic eruption of the last 200 years in iceland occurred within the tectonic fissure swarm between the bar arbunga vei ivotn and the askja volcanic systems the eruption took place in the holuhraun lava field 45 km northeast of the bar arbunga volcano and 20 km south of the askja volcano it emplaced over 1 2 km3 dense rock equivalent dre of lava in an area of very low topographic relief in light of the minimal topographic forcing lava flow emplacement can be viewed as having been effectively controlled by the lava s temperature dependent rheology here we combine field and remote sensing data collected during the week of the 17th to 22nd of november 2014 to constrain the lava s flow path its velocity deformation rate and thermal evolution during emplacement we combine these with measurements of the pure liquid viscosity and the sub liquidus rheological evolution of the lava during crystallization sub liquidus experiments were performed at a range of constant cooling and shear rates to mimic the conditions experienced by the lava during emplacement these data can also be used to infer flow conditions of partly degassed magma within dike swarms during transport towards the surface the data show that the effective viscosity of the lava drastically increases until reaching a specific sub liquidus temperature the rheological cutoff temperature tcutoff this departure to high viscosity is a consequence of the onset of crystallization and is found to be primarily controlled by the imposed cooling rate our data indicate that shear rate exerts a second order effect on this rheological departure and tcutoff we discuss the experimental dataset in the context of the reconstructions of the natural emplacement conditions and describe the implications for the 2014 2015 lava flow field at holuhraun as well as lava flow modelling in general

pahoehoe and aa lavas a discussion and continuation of the model of peterson and tilling abstract the graphical method of peterson and tilling for representing the behaviour of a lava flow is considered in terms of simple rheological theory assuming that a lava may be approximately described as a bingham fluid this approach helps resolve an apparent anomaly in the original treatment of peterson and tilling with respect to the representation of the pahoehoe to aa transition it also suggests further methods for quantitatively defining the limits of the pahoehoe and aa fields and the transition threshold zone

age petrogenesis and tectonic setting of the thessalon volcanic rocks huronian supergroup canada abstract the 2 5 ga huronian supergroup volcanic rocks in northern ontario represent one of the better preserved paleoproterozoic continental flood basalt sequences on earth the youngest age of huronian supergroup volcanism is refined to 2452 5 6 2 ma based on new u pb zircon analyses of the copper cliff rhyolite recent mapping and geochemical analyses of thessalon formation volcanic rocks define a well developed chemostratigraphy a lower series consisting of four geochemically distinct mafic lava sequences and an upper basalt andesite volcanic series these two mafic volcanic series are separated by felsic volcanic rocks rhyolite and dacite the mafic lavas are low ti tholeiites dominated by basalt and andesite and are characterized by enriched light rare earth element profiles and high th contents up to 12 ppm most basalt andesite sequences show some internal geochemical variation reflecting a combination of fractional crystallization and in some cases limited crustal contamination but each sequence represents a discrete magma batch derived by different degrees of partial melting in the subcontinental lithospheric mantle all magma batches display prominent negative nb ta and ti anomalies on primitive mantle normalized multi element diagrams interpreted to reflect melting of a heterogeneous and previously metasomatized garnet lherzolite that acquired some chemical characteristics of a source typical of subduction zone magmatism at least three distinct mantle source compositions are required to explain the range in the observed lava compositions the most unusual of these reservoirs has a number of geochemical features akin to upper continental crust and is characterized by high th yb 10 and low zr nb 11 this reservoir is interpreted to be peridotite modified through metasomatism and entrapment of arc magmas during northward neoarchean subduction along the southern superior craton margin

the effect of inflation on the morphology derived rheological parameters of lava flows and its implications for interpreting remote sensing data a case study on the 2014 2015 eruption at holuhraun iceland abstract morphology derived lava flow rheology is a frequently used tool in volcanology and planetary science to determine rheological parameters and deduce the composition of lavas on terrestrial planets and their moons these calculations are usually based on physical equations incorporating 1 lava flow driving forces gravity slope and flow rate and 2 morphological data such as lava flow geometry flow width height or shape of the flow outline all available methods assume that no geometrical changes occur after emplacement and that the measured flow geometry reflects the lava s apparent viscosity and or yield strength during emplacement it is however well established from terrestrial examples that lava flows may inflate significantly after the cessation of flow advance this inflation affects in turn the width to height ratio upon which the rheological estimates are based and thus must result in uncertainties in the determination of flow rheology as the flow height is one of the key parameters in the morphology based deduction of flow properties previous studies have recognized this issue but to date no assessment of the magnitude of this error has been presented this is likely due to a lack of digital elevation models dems at sufficiently high spatial and temporal resolution the 2014 15 holuhraun eruption in central iceland represents one of the best monitored large volume 1 5 km3 lava flow fields 85 km2 to date an abundance of scientific field and remote sensing data were collected during its emplacement moreover inflation plays a key role in the emplacement dynamics of the late stage of the lava field here we use a time series of high resolution dems acquired by the tandem x satellite mission prior during and after the eruption to evaluate the error associated with the most common methods of deriving lava flow rheology from morphological parameters used in planetary science we can distinguish two dominant processes as sources of error in the determination of lava flow rheology from morphology 1 wholesale inflation of lava channels and 2 post halting inflation of individual lava toes these result in a 2 4 to 17 fold overestimation of apparent viscosity and a 0 7 to 2 4 fold overestimation of yield strength when applied in planetary sciences this overestimation in rheological parameters translates directly to an overestimation of the respective lavas silica content we conclude that although qualitatively informative morphological analysis is insufficient to discern lava rheology and composition instead in situ analysis together with high resolution remote sensing data is needed to properly constrain the compositions involved in planetary volcanism

volcanism and hydrothermalism on a hotspot influenced ridge comparing reykjanes peninsula and reykjanes ridge iceland abstract current estimates indicate that the number of high temperature vents one of the primary pathways for the heat extraction from the earth s mantle at least 1 per 100 km of axial length scales with spreading rate and should scale with crustal thickness but up to present shallow ridge axes underlain by thick crust show anomalously low incidences of high temperature activity here we compare the reykjanes ridge an abnormally shallow ridge with thick crust and only one high temperature vent known over 900 km axial length to the adjacent subaerial reykjanes peninsula rp which is characterized by high temperature geothermal sites confined to four volcanic systems transected by fissure swarms with young holocene volcanic activity multiple faults cracks and fissures and continuous seismic activity new high resolution bathymetry gridded at 60 m of the reykjanes ridge between 62 30 n and 63 30 n shows seven axial volcanic ridges avr that based on their morphology geometry and tectonic regime are analogues for the volcanic systems and fissure swarms on land we investigate in detail the volcano tectonic features of all mapped avrs and show that they do not fit with the previously suggested 4 stage evolution model for avr construction instead we suggest that avr morphology reflects the robust or weak melt supply to the system and two or more eruption mechanisms may co exist on one avr in contrast to 4 stage evolution model our interpretations indicate that unlike on the reykjanes peninsula faults on and around avrs do not cluster in orientation domains but all are subparallel to the overall strike of avrs orthogonal to spreading direction high abundance of seamounts shows that the region centered at 62 47 n and 25 04 w between avr 5 and 6 is volcanically robust while the highest fault density implies that avr 1 and southern part of avr 6 rather undergo period of melt starvation based on our observations and interpretations we expect all of the avrs on reykjanes ridge to be hydrothermally active but morphological and hydrographic settings of this ridge may cause hydrothermal plumes to be quickly dispersed and diluted due to exposure to strong bottom currents therefore combined ctd and autonomous vehicles surveys are probably the most efficient methods for hydrothermal exploration along the reykjanes ridge