on the long distance transport of ferrar magmas the distribution and geochemical relationships of the early jurassic ferrar large igneous province lip are examined and it is concluded that they support the lateral flow model for the emplacement of the province with a source along the strongly magmatic early jurassic antarctica africa rifted margin published data and new analyses from the pensacola range are used to show that the dominant magma type in the ferrar the mount fazio chemical type mfct occurs in the theron mountains shackleton range whichaway nunataks pensacola mountains all antarctica and south africa as well as well known outcrops in victoria land antarctica se australia and new zealand chemical compositions are shown to be somewhat varied but similar enough for them to be considered as representing closely related magmas examination of geochemical trends with distance from the interpreted magma source indicates that mg and mgo abundances decline with distance travelled and it is argued that this is consistent with the lateral flow model the scarab peak chemical type spct which occurs as sills in the theron mountains and whichaway nunataks and as lavas in victoria land is geochemically very homogeneous despite this mg mgo ti y and ti zr all fall with distance from the interpreted source consistent with fractional crystallization occurring during the lateral flow of the magmas flow took place in dykes or more likely sills no feeder dyke swarm has been identified the distances flowed at least 4100 km for mfct and 3700 km for spct are the longest interpreted lateral magma flows on earth

flow directions in dikes from anisotropy of magnetic susceptibility data the bootstrap way one of the first applications of anisotropy of magnetic susceptibility ams was an attempt to determine flow directions from mafic dikes khan 1962 since the seminal work of knight and walker 1988 defining the expected behavior of ams in response to magma flow there has been increasing interest in using ams for this purpose here we present a quantitative method for interpretation of ams data from dikes using a parametric bootstrap first dikes must be sampled with at least five and preferrably more samples from within 10 cm of the dike margin the distributions of the eigenvalues and eigenvectors of the ams tensor are delineated by calculating eigenparameters of many bootstrapped paradata sets we generate paradata sets by first selecting a sample at random then calculating a replacement set of data by drawing tensor elements from normal distributions with the mean and standard deviation of the entire site the bounds containing 95 of the eigenparameters of the bootstrapped data serve as confidence limits for the parameter of interest classification of dikes proceeds as follows sites whose maximum and intermediate eigenvalues could not be distinguished are deemed uninterpretable in addition sites with principal eigenvectors with angles 45 away from the dike margin inverse or with markedly different directions on either side of the dike scissored are excluded the remaining dikes are classified as having unique flow direction information if the principal eigenvectors from at least one side are distinct from the dike plane based on the distribution of the bootstrapped principal eigenvectors if neither side has principal eigenvectors distinct from the dike plane the dikes are classified as having lineation information only a study comprising 251 dikes from the troodos ophiolite has 151 sites with directional data 38 sites with lineations only 7 inverse sites 5 scissored sites and 55 sites not fitting into any other category the flow directions interpreted from the data were generally southerly toward a fossil transform zone

physical volcanology and geological relationships of the jurassic ferrar large igneous province antarctica abstract the ferrar large igneous province forms a linear belt for 3500 km along the transantarctic mountains and as a geochemical province extends into southeastern australasia the principal components of the ferrar are intrusive ferrar dolerite sills and dikes and dufek intrusion pyroclastic the prebble mawson and exposure hill formations effusive the kirkpatrick basalt in terms of the three dimensional architecture of the ferrar a range of facies can be recognized in each of the principal components the ferrar province was initiated with a major episode of phreatomagmatism leading to formation of tephra cones and associated deposits and near surface vent structures activity switched to predominantly quiet effusion of alternating thick flood basalt flows and thin pahoehoe lobes and flows intrusive bodies were emplaced early given the occurrence of dolerite clasts in tuff breccias but most sills were probably intruded after accumulation of extrusive rocks pre existing rift structures played a major role in controlling the transport and distribution of the ferrar magmas and the apparent centers of extrusive activity the associated paleohydrology controlled the eruption styles

carbon isotopic composition of hydrocarbons in ocean transported bitumens from the coastline of australia abstract bitumens stranding along the coastlines of the northern territory western australia south australia victoria and tasmania often have biomarker signatures which closely match those of oils of s e asian origin a suite of these bitumens was studied to determine the isotopic signatures of their alkanes and to compare them to similar oils from the central sumatra basin saturated hydrocarbons were separated into a fraction containing n alkanes and isoalkanes and one containing the multibranched cyclic components using adduction into silicalite gas chromatography isotope ratio mass spectrometry gc irms of the n alkanes revealed 13 c signatures covering a wide range of values from 25 5 to 29 pdb but generally falling between those of the botryococcane containing minas and duri oils from the central sumatra basin n alkanes of the minas oil are 3 4 lighter than their duri counterparts the isotopic compositions of pristane and phytane cover a similar range 13 c 24 to 27 botryococcane is consistently heavy with 13 c values in the range 11 to 14 one bitumen sample with no botryococcane but abundant bicadinanes showed n alkane 13 c values in the range 28 to 29 at the light extreme for waxy bitumens in our sample suite sample to sample differences in carbon isotopic signatures of n alkanes are attributed mainly to variations in primary source with weathering and biodegradation as minor causes instances of low precision for replicate analyses 2 are caused by the relative abundance of co eluting isoalkanes overall the isotopic patterns of waxy bitumens from the australian coastline provide independent confirmation of their similarity to central sumatran lacustrine oils on the other hand asphaltic bitumens from the southern australian coastline are isotopically light with n alkane 13 c values in the range 31 5 to 33 this distinctive feature may assist identification of their source

cracking the lid sill fed dikes are the likely feeders of flood basalt eruptions although subparallel swarms of dikes are thought to be the primary feeders to voluminous volcanic eruptions increasing recognition of volumetrically significant sill complexes suggests that they too play an important role in magma ascent through the shallow crust however the extent to which sills and interconnected sill fed dikes actually transport magma to the earth s surface in many large igneous provinces lip is presently unclear by analyzing field relationships and dimensions of intrusions of the ferrar lip in south victoria land antarctica we show that sill fed dikes were the likely feeders for voluminous flood basalt eruptions these intrusions are small but numerous with cumulative dimensions equivalent to a feeder network 308 000 km long and 1 8 m wide due to the tremendous aerial extent of this intrusive network each individual dike feeder segment would only be required to actively feed magma for 2 to 3 days on average to erupt the 70 000 km3 of flood lavas represented by the kirkpatrick basalts the ferrar intrusions form a broadly distributed array of small moderately dipping dikes 2 km long 1 8 m wide 56 mean dip exhibiting almost any orientation this sill fed dike network contrasts with dike swarms conventionally depicted to feed flood basalt provinces and has the appearance of a variably cracked lid atop a sill complex the cracked lid model may apply to a range of shallow feeder systems 4 km depth intruding sedimentary basins where the effects of far field tectonic stresses are negligible and sill intrusions exert the dominant control on dike orientations we conclude that sill inflation and resulting deformation of surrounding host rock plays a critical role in the ascent of magma in shallow volcanic systems that span the full spectrum of eruptive volumes

mapping real time growth of experimental laccoliths the effect of solidification on the mechanics of magmatic intrusion abstract the dynamics of solidification front growth along the margins of magmas have been widely found to be fundamental in controlling magma transport and emplacement in this vein the role of solidification fronts in determining the basic growth mechanics of laccoliths are investigated here in a series of scaled experiments using two contrasting magma analogs water and molten wax that are injected into a visco elastic gelatin based crustal analog in non solidifying water style experiments intrusion is a relatively simple process in contrast wax magma emplacement displays a vast palette of compelling behaviors propagation can slow stop and reactivate and the directionality of lateral growth becomes much more variable small flow deviations in water based intrusions are likely the product of flow instabilities the result of injecting a viscous fluid along an interface similar to hele shaw cell experiments however the much more complex emplacement style of the wax experiments is attributed to solidification at the leading edge of the crack the overall effects of solidification during emplacement can be described by a non dimensional parameter measuring the relative competition between the rates of crack propagation and solidification at the crack leading edge in this context laccolith growth mechanics can be separated into three distinctive characteristic stages namely i a thin pancake style sill initially emanating radially from a central feeder zone ii as solidification stalls magma propagation at the leading edges enhanced thickening begins forming a true low aspect ratio laccolith and iii as stresses accumulate tears and disruptions readily occur in the solidified margin causing fresh breakouts thus reactivating lateral growth into new lobes the competitive combination of these latter stages often leads to a characteristic pulsatile growth the unexpected richness of these results promises to add fundamentally to the basic understanding of laccolith growth mechanisms and also adds key observations to growth processes to be sought in field studies that have been hitherto suspected but rarely observed despite seemingly simple shapes the growth history of laccolithic intrusions is likely quite complex

magma flow directions in dikes of the koolau complex oahu determined from magnetic fabric studies we compared the magnetic fabric with the macroscopic surface lineation direction previously assumed to be parallel with magma flow direction for 35 dikes of the koolau complex oahu anisotropy of magnetic susceptibility ams was determined for 530 samples from 59 dikes including a sill and a pluglike intrusive body and two filled lava tubes and statistically significant ams clusters were found in all but five dikes for the 35 lineated dikes the mean maximum ams direction 1 coincides with the macroscopic lineations to within 25 in 18 and to within 15 in eight the ams ellipsoid shape in about half of the samples is prolate cigar shaped and in about half is oblate pancake shaped we interpret the ams to be determined by shape anisotropy of ferromagnetic grains the mean total anisotropy is 2 2 and total anisotropy h ranges from 0 24 to as high as 14 12 the principal ams axes for samples from a dike are tightly grouped on equal area plots and for most of the dikes the minimum ams axes plot near to the pole of the dike our ams measurements enable us to infer absolute magma flow directions for half the dikes studied the maximum ams axes of samples from one side of the dike form a tight cluster on an equal area plot and those from the other side of the dike form another tight cluster the two clusters are close together separated by 10 30 for narrow dikes 100 cm wide and are farther apart 30 60 for wide dikes and are symmetrically disposed on either side of the plane of the dike we infer that these paired clusters are caused by imbrication of nonequant ferromagnetic crystals against each margin of the dike during deposition in a velocity gradient and hence indicate the flow azimuth i e the absolute magma flow direction nearly half of the dikes measured 25 gave paired ams plots in 12 the magma flowed up at low oblique angles 5 30 from the horizontal in five it flowed down at 5 20 in four it flowed horizontally 5 in three it flowed up at a steep angle 50 75 and in one it flowed down at a steep angle the magma flow in general was rarely vertical or horizontal

magma flow directions of shallow dykes from the east greenland volcanic margin inferred from magnetic fabric studies abstract the role played by plume generated crustal magmatic complexes in the segmentation of volcanic margins is highlighted by a preliminary study of magma flow directions in shallow intrusives from the east greenland volcanic margin we investigate the magmatic texture using anisotropy of magnetic susceptibility for eight dykes of tholeitic affinity belonging to a dyke swarm associated with the tertiary opening of the north atlantic ocean the thickness of the sampled dykes ranges from 3 to 37 m the dykes are of doleritic texture and contain up to 12 of opaque minerals and 35 of plagioclase laths dykes showing a magnetic foliation plane within the dyke plane i e a magnetic fabric usually attributed to magmatic processes represent 40 of the samples from the studied swarm these dykes have a low degree of anisotropy and their ellipsoid of magnetic susceptibility is strongly oblate inverse magnetic fabrics where the maximum principal susceptibility axis lies near the pole to the dyke account for 60 of the data we interpret these inverse fabrics either as alteration minerals with highly prolate ellipsoids of magnetic susceptibility or primary titanomagnetites with oblate ellipsoid of low anisotropy the flow direction is inferred for normal fabric dykes using the mirror imbrication of magnetic lineation analysis of thin sections shows a good agreement between magnetic fabric directions and phenocryst preferred orientations the inferred flow directions are predominantly horizontal throwing a new light on volcanic margin development

the 1996 subaqueous eruption at academii nauk volcano kamchatka and its effects on karymsky lake a subaqueous eruption in karymsky lake in the academii nauk caldera dramatically changed its water column structure water chemistry and biological system in less than 24 h sending major floodwaves down the discharging river and eruption plumes with ash and gases high into the atmosphere prior to the eruption the lake had a ph of about 7 was dominated by bicarbonate and well stocked with fish but turned in early 1996 into a stratified initially steaming waterbody dominated by sulfate with high na and k levels and devoid of fish blockage of the outlet led to rising waterlevels followed by dam breakage and catastrophic water discharge the total energy input during the eruption is estimated at about 1016 j the stable isotope composition of the lake water remained dominated by the meteoric meltwaters after the eruption

isotopic biogeochemistry of the oxford clay formation jurassic uk a total of 165 samples was obtained from the oxford clay formation at seven different sites nearly all were from the peterborough member lower oxford clay but seven were from the stewartby and weymouth members middle and upper oxford clay respectively five samples from the underlying kellaways formation were also examined stratigraphic relationships were estimated on the basis of ammonite subzones and results from all locations can be placed along a single stratigraphic scale the following were determined for all samples abundance and isotopic composition of organic carbon abundances of carbonate carbon and total sulphur and the rock eval pyrolysis parameters hydrogen index oxygen index and t max for a subset of eight samples selected to be representative of geochemical and apparent palaeoenvironmental variations soluble organic compounds were extracted and the isotopic composition of pristane phytane and long chain n alkanes determined by isotope ratio monitoring gas chromatograph mass spectrometry concentrations of organic carbon in samples from the peterborough member ranged from 0 5 to 16 6 and values of total organic carbon toc ranged from 27 7 to 23 1 v pdb shales dominated by epifaunal bivalve assemblages have high concentrations of toc and values of h index approaching 800 indicating preservation of hydrogen rich organic material conversely shell beds and calcareous and silty clay beds have lower abundances of toc and values of h index dropping below 100 indicating extensive oxidation of the organic matter isotopic composition of pristane and phytane in the peterborough and stewartby members average 31 7 those in the weymouth member average 29 8 values of for long chain n alkanes average 28 together these results indicate values for primary inputs as follows terrestrial vascular plants 23 5 peterborough member algae 28 2 stewartby member algae 29 1 weymouth member algae 26 6 comparison of primary values to those of toc indicates that in some cases secondary processes enriched toc relative to primary inputs by as much as 4 palaeontological evidence in these same beds indicates development of extensive food webs and supports attribution of this isotopic enrichment to heterotrophic reworking

satellite thermal observations of the bezymianny lava dome 1993 2008 precursory activity large explosions and dome growth 1 fifteen years worth of advanced very high resolution radiometer avhrr data is presented and used to quantitatively assess processes occurring at bezymianny this andesitic volcano is one of kamchatka s most dangerous volcanoes with 16 eruptions in the last decade that have dispersed ash into north pacific air routes all known episodes of increased activity for which data were available were detected in band 3 3 53 3 93 m avhrr thermal data twenty three peaks can be seen in the data nineteen peaks correspond to known explosions while the remaining three peaks correspond to known phases of dome growth that were not believed to have been accompanied by explosive activity start and end dates of extrusive phases defined by the thermal data are presented repose times between phases of extrusion vary from four months to just over two and half years with an average of just less than a year using rank order statistics a maximum time interval between consecutive explosions of 1288 170 days is determined this could serve as a cut off time for declaring the current dome growth activity over the calculated cumulative erupted volume 0 28 km3 and time averaged extrusion rate 0 6 m3 s 1 from 1993 to 2008 corresponds to values found at bezymianny from 1956 to 1976 showing that the satellite based methodology provides a good way of quantitatively assessing dome growth three different types of precursors to explosive behavior have been identified at bezymianny 1 values that cluster around the mode of the data set prior to explosion potentially due to endogenous dome growth 2 upward trends that commence 15 20 days prior to explosion and reach sensor saturation levels are due to significant extrusion and 3 a gradual upward trend that starts 5 days prior to explosion probably due to ramping up of extrusion this work shows that retrospectively analyzing and modeling of a volcano s thermal signal provides increased insight into its characteristic behavior the methods used in this paper can be used at other dome building volcanoes around the world the insights presented here can be used to improve monitoring capabilities to aid in providing early warnings to large explosions at bezymianny

magnetic versus crystallographic fabrics in a basaltic lava flow combined anisotropy of magnetic susceptibility ams and crystallographic studies were performed within a quaternary lava flow for which we have a thorough knowledge of the flow direction microscope examinations microprobe analyses and studies of rock magnetic properties show that ams is carried by homogeneous multidomain ti rich titanomagnetite xc0 6 this mineral forming either subhedral isolate individuals or grouped in various elongated aggregates represents a late crystallized interstitial phase ams determined from samples collected in the lower the middle and the upper part of the flow is characterized by a well defined magnetic foliation whereas magnetic lineation is generally poorly grouped and therefore meaningless the foliation plane of the lower and upper part of the flow show an obliquity which is interpreted as an opposite imbrication indicating a westward flow in agreements with the known flow direction in the lower part of the lava flow the tight correlation between ams and plagioclase lattice preferred orientation suggests that a silicate framework control the titanomagnetite crystallization and thus the orientation of the ams ellipsoid d 2005 elsevier b v all rights reserved

geological evolution of the coombs allan hills area ferrar large igneous province antarctica debris avalanches mafic pyroclastic density currents phreatocauldrons the jurassic ferrar large igneous province of antarctica comprises igneous intrusions flood lavas and mafic volcaniclastic deposits now lithified the latter rocks are particularly diverse and well exposed in the coombs allan hills area of south victoria land where they are assigned to the mawson formation in this paper we use these rocks in conjunction with the pre ferrar sedimentary rocks beacon supergroup and the lavas themselves kirkpatrick basalt to reconstruct the geomorphological and geological evolution of the landscape in the early jurassic the surface of the region was an alluvial plain with perhaps 1 km of mostly continental siliciclastic sediments underlying it after the fall of silicic ash from an unknown but probably distal source mafic magmatism of the ferrar province began the oldest record of this event at allan hills is a 180 m thick debris avalanche deposit member m of the mawson formation which contains globular domains of mafic igneous rock these domains are inferred to represent dismembered ferrar intrusions emplaced in the source area of the debris avalanche shallow emplacement of ferrar magmas caused a slope failure that mobilized the uppermost beacon supergroup and the silicic ash deposits into a pre existing valley or basin the period which followed mawson time was the main stage for explosive eruptions in the ferrar province and several cubic kilometres of both new magma and sedimentary rock were fragmented over many years phreatomagmatic explosions were the dominant fragmentation mechanism with magma water interaction taking place in both sedimentary aquifers and existing vents filled by volcaniclastic debris at coombs hills a vent complex or phreatocauldron was formed by coalescence of diatreme like structures at allan hills member m of the mawson formation consists mostly of thick coarse grained poorly sorted layers inferred to represent the lithified deposits of pyroclastic density currents meanwhile at carapace nunatak mafic clasts were mixed with detrital material to form the carapace sandstone in alluvial and eventually lacustrine environments eruptions then became largely effusive producing hundreds of metres of flood lavas that covered the landscape kirkpatrick time in places lava flowed into ephemeral lakes to form pillow palagonite breccias base of sequence carapace nunatak or pillow lavas top of sequence coombs hills several generations of ferrrar intrusions were emplaced during the course of these events at least three can be distinguished based on field relations new geochemical data indicates that for the ferrar province magma involved in the explosive eruptions had the same major element composition as that which produced shallow intrusions and lavas we also note the possibility that flood lavas were fed by plugs cross cutting the mawson formation at coombs hills rather than by major dikes extending to the surface finally we infer that eruption plumes were limited to the troposphere and that direct environmental impacts were thus likely restricted to the southern hemisphere

thermal and mechanical aspects of magma emplacement in giant dike swarms we consider the thermal history and dynamics of magma emplacement in giant feeder dikes associated with continental flood basalts for driving pressure gradients inferred for giant dike swarms thicknesses of 10 m would enable dikes to transport magma laterally over the distances observed in the field up to thousands of kilometers without suffering thermal lock up using time dependent numerical solutions for the thermal evolution of a dike channel under laminar and turbulent flow conditions in the presence of phase transitions we investigate the possibility that the observed dike thicknesses of the order of 100 m result from thermal erosion of the country rocks during dike emplacement this implies that the observed range of dike widths in giant dike swarms may reflect variations in the source volume and not the excess magma pressure it is found that the total volume of intruded magma required to produce an order of magnitude increase in dike width via wall rock melting broadly agrees with the estimated volumes of individual flows in continental flood basalts the presence of chilled margins and apparently low crustal contamination characteristics of some giant dikes may be consistent with turbulent magma flow and extensive melt back during dike emplacement in this case measurements of the anisotropy of magnetic susceptibility most likely indicate magma flow directions during the final stages of dike intrusion shear stresses generated at the dike wall when the dike starts to freeze strongly decrease with increasing dike width which implies that thicker dikes may have less tendency to produce consistent fabric alignment our results suggest that if the dike was propagating downslope off a plume related topographic swell the mechanism responsible for flow termination could possibly have been related to underpressurization and collapse implosion of the shallow magma plumbing system feeding the intrusion radial dikes that erupted at the periphery of the topographic uplift might have increased rather than decreased extensional stresses in the crust within the topographic uplift upon their solidification

anisotropy of magnetic susceptibility studies in tertiary ridge parallel dykes iceland tertiary margin normal aishihik dykes yukon and proterozoic kenora kabetogama composite dykes minnesota and ontario abstract mafic dykes of different ages were collected from three different tectonic settings and analyzed using anisotropy of magnetic susceptibility ams as a proxy for magmatic flow during intrusion in iceland ridge parallel basaltic dykes were sampled on each side of the active tectonic boundary the dykes are k max orientation indicating vertical emplacement the eocene aishihik dyke swarm intrudes the yukon tanana terrane in the yukon province canada over an area 200 by 60 km these dykes were intruded normal to the accretionary margin are porphyritic andesites and have an intermediate geochemical signature based on major and trace element analyses ten dykes were sampled and 111 cores analyzed using ams and the dykes preserve a vertical k max orientation indicating intrusion was vertical through 30 km of continental crust the 2 06 ga kenora kabetogama dykes in northern minnesota and western ontario crosscut a variety of archean terranes thickness 50 km in a radiating pattern the unmetamorphosed basaltic dykes are 1 120 m wide 10 110 km in length are vertical in orientation and can be grouped as either being single intrusion or multiple intrusion composite dykes ams data preserve a vertical k max orientation for the southerly locations 2 dykes n 53 and horizontal k max for the remainder to the northwest 15 dykes n 194 maximum magnetic susceptibility axes 4 dykes n 92 for composite dykes are scattered and yield inconsistent flow directions with regard to the dyke margin almost all of our results are normal in that the magnetic foliation the plane containing k max and k int normal to k min is parallel to the dyke planes which gives us confidence that the magnetic lineations i e k max orientations are parallel to magmatic flow

magma budgets and steady state activity of vulcano and stromboli we present three models for magma budget during steady state volcanic activity by which non erupted magma is emplaced as dykes or cumulates or crystallises in place using gas and thermal data we apply our models at vulcano to calculate degassing cooling and crystallisation of magma at a rate of 40 375 kg s 1 within a magma body with an upper surface at a 2 km depth at stromboli we calculate a steady magma supply of 300 1300 kg s 1 to shallow 1 km depths

degassing explosions at karymsky volcano kamchatka during the summer of 1997 karymsky vol cano produced summit explosions about six times each hour typical explosive episodes lasted between 30 seconds and three minutes produced gas and ash columns several hun dred meters high and ejected some incandescent material to better understand the physical source mechanisms re sponsible we recorded hundreds of explosions with a three component broad band seismometer and microphone lo cated 1650 meters from the active vent nearly every explo sion is recorded as an emergent yet identical seismic wavelet which is followed 4 15 s later by an impulsive acoustic ar rival we interpret the signals as a near surface gas volume burst which fractures the vent plug lowers the lithostatic pressure within the magma column and often induces fur ther degassing when degassing continues it is generally manifested as either a series of regular one second chug ging 1 explosions steady higher frequency jetting or a hy brid combination we believe that the seismic signature for chugs short duration harmonic tremor with integer over tones is the result of repeated gas volume bursts at the vent in contrast seismograms for jetting are non harmonic and contain higher frequencies we believe that the competing degassing behaviors are influenced by the gas flux as well as the plug conduit characteristics we propose that a plug exists due to a viscosity gradient caused by volatile depletion in the upper conduit

sampling strategies and the anisotropy of magnetic susceptibility of dykes abstract most studies of the anisotropy of magnetic susceptibility ams of dykes have assumed that susceptibility axes should define a unique orientation relative to the dyke walls and magma flow direction theoretical considerations however predict systematic variations of ams as a function of the amount of shear experienced by the flowing magma although this feature of ams might seem undesirable at first sight based in a theoretical model it has been suggested that actually we can take advantage of such variation in the orientation of the ams axes to infer magma flow directions more confidently than until now if proper attention is given to the scheme followed during sample collection in this work we report the results of a pilot study made to test those theoretical predictions we resampled two dykes from the ko olau dyke complex in o ahu and for which magma flow direction was previously inferred albeit with some uncertainty the resampling was made following the guidelines suggested by the theoretical work as closely as possible i e collecting more than one profile parallel to the dyke walls and across the dyke the results of our measurements provide the first empirical evidence supporting the occurrence of a cyclic fabric acquisition during the emplacement of at least some dykes the procedure described in this paper therefore constitutes a self contained approach that can be followed to test in a case by case basis the occurrence of such fabric behavior this in turn should provide enough elements to increase the reliability of the interpretation in the obtained results

geochemical and climate modeling evidence for holocene aridification in hawaii dynamic response to a weakening equatorial cold tongue abstract a 13 5 m sequence of holocene limnic sediments from a sinkhole on oahu hawaii provides a valuable paleoclimatic record for the central subtropical pacific 13 c analysis of plant leaf waxes n alkanes n c 27 n c 29 n c 31 and n c 33 is used to infer vegetative changes average 13 c values of the suite of n alkanes increase from approximately 31 0 5 at 10 ca kyr bp calibrated thousand years before present to about 27 0 5 by 6 ca kyr bp and then remain roughly constant until the polynesian arrival about 1 15 ca kyr bp the increase in 13 c values of n alkanes is interpreted to indicate a shift in the local vegetation from c 3 to c 4 dominated flora based on mass balance calculations the observed increase in the 13 c values translates to at least a doubling of the relative abundance of c 4 plants we argue that the expansion of c 4 plants was a response to decreased overall water availability aridification due to reduced wintertime precipitation model simulations of an orbitally induced increase in insolation along the equator during the holocene provide evidence for a wintertime drying trend in the eastern subtropical north pacific this trend is associated with boreal fall to winter warming of the cold tongue in the eastern equatorial pacific eep these model results provide a conceptual framework to explain a dynamic link between the reconstructed holocene drying trend in hawaii and orbitally forced climate change in the eep that is analogous to the modern el nino southern oscillation teleconnection

an isotopic study of biogeochemical relationships between carbonates and organic carbon in the greenhorn formation carbon isotopic compositions of total carbonate inoceramid carbonate micritic carbonate secondary cements total organic carbon and geoporphyrins have been measured in 76 different beds within a 17 m interval of a core through the greenhorn formation an interbedded limestone and calcareous shale unit of cretaceous age cenomanian turonian from the western interior seaway of north america results are considered in terms of variations in the processes of primary production which led to the biosynthesis of the molecular precursors of the geoporphyrins and in secondary processes those mediating the transformation of primary organic material into sedimentary total organic carbon it is shown that the porphyrin isotopic record reflects primary isotopic variations more closely than the toc isotopic record and that in these sediments toc is enriched in 13c relative to its primary precursor by 0 6 to 2 8 this enrichment is attributed to isotope effects within the consumer foodweb and is associated with respiratory heterotrophy variations in this secondary enrichment are correlated with variations in the isotopic composition of marine carbonate this correlation is attributed to effects of environmental changes on the marine foodweb these may have included increased atmospheric oxygen associated with the cenomanian turonian oceanic anoxic event the isotopic fractionation associated with fixation of carbon by primary producers is observed to have varied by 1 5 during the interval of deposition it is suggested that this change is due to a variation in the makeup of the community of primary producers and or to a decrease in the atmospheric abundance of co2 during the oceanic anoxic event

numerical modelling of the growth dynamics of a simple silicic lava dome 1 two dimensional axisymmetrical computational models have been developed using finite element techniques to represent the rheological stiffening due to degassing induced crystallisation and the effects of a brittle carapace within a simple lava dome the dome is modelled numerically considering the effects of temperature pressure and rate of extrusion using these state variables the bulk viscosity is derived from empirical equations and the bulk rheology approximated using a solidification viscosity dividing the dome into solid dominated and fluid dominated domains elastoplastic equations for the solid component and fluid mechanical equations for the fluid domain are solved simultaneously allowing continuous stress across the fluid solid interface to ensure the two components move in unison we apply this model a hookean solid carapace model and a purely fluid lava dome model to the case of the october 1980 lava dome at mount st helens the results show that dynamic growth models involving a solid carapace are required to simulate this lava dome

seismological study of the kliuchevskoi flank eruption of 1983 kamchatka abstract a flank eruption called the predskazanny eruption occurred at an altitude of 2875 m on the east flank of the kliuchevskoi volcano from march 8 to june 27 1983 the eruption was largely effusive with a constant chemical composition of the lavas calc alkaline aluminium basalts their volume is estimated at 0 11 km 3 the seismic precursors of the predskazanny eruption was concentrated beneath the new eruption center first at depths of between 10 and 15 km earthquake of february 28 k s 8 3 m 3 5 and then at depths between 5 km b s l and 3 km a s l earthquake swarm of march 1 7 volcanic tremor during the earthquake swarm of march 1 7 was absent with the approach of an eruption the depth of earthquake foci in the swarm decreased an analysis of the seismicity implies that the magma was apparently ascending in the newly formed channel from a depth of at least 5 km the feeding area of the predskazanny eruption was apparently connected with the major magma channel of kliuchevskoi at depths between 5 and 10 km but not deeper than 15 km

satellite thermal infrared data of shiveluch kliuchevskoi and karymsky 1993 2008 effusion explosions and the potential to forecast ash plumes this paper presents an analysis of advanced very high resolution radiometer avhrr thermal data from shiveluch kliuchevskoi and karymsky kamchatka russia from 1993 to 2008 these different volcanoes show contrasting and variable patterns in their thermal data and lack reliable precursory thermal trends prior to large explosions pixel integrated temperatures pirt at shiveluch were above background during three phases 1 1993 1995 2 2001 2005 and 3 2006 time of writing each of which was associated with growth of an andesitic dome punctuated by explosions the coarse spatial resolution of the avhrr may have prevented observation of precursory thermal patterns at this volcano kliuchevskoi showed five phases these show a rapid days or gradual weeks to months increase in temperature followed by rapid drop offs suggesting these basaltic eruptions start explosively followed by lava effusion or vice versa fast magma ascent rates probably prevent the generation of thermal precursors at karymsky elevated pirt values cluster into seven phases showing three trends 1 persistently high pirt 2 a gradual increase and decrease and 3 gradual increase followed by steep drop offs these trends are due to the extrusion of viscous andesitic dacitic lava not to strombolian vulcanian activity and show no consistent pattern prior to large explosions pirt values at karymsky lake reflect the dyke intrusion that started the 1996 eruptive cycle at karymsky the values obtained here provide a baseline against which to monitor these volcanoes and karymsky lake in the future

dyke sill relationships in karoo dolerites as indicators of propagation and emplacement processes of mafic magmas in the shallow crust abstract this paper describes the spatial and temporal relationships between karoo age ca 180 ma dolerite dykes and a regional scale saucer sill complex from the secunda coal mine complex in the northeastern parts of the karoo basin of south africa unlike parallel dyke swarms of regional extensional settings mafic dykes commonly show curved geometries and highly variable orientations short strike extents and complex cross cutting and intersecting relationships importantly the dyke networks originate from the upper contacts of the first order dolerite sill saucer structure and are not the feeders of the saucer complex cross cutting relationships indicate the largely contemporaneous formation of dykes and the inner sill and inclined sheets of the underlying saucer systematic dykes form a distinct boxwork type pattern of two high angle interconnected dyke sets the formation and orientation of this dyke set is interpreted to be related to the stretching of roof strata above elongated magma lobes that facilitated the propagation of the inner sill similar to the cracked lid model described for large saucer complexes in antarctica dyke patterns generally reflect the saucer emplacement process and the associated deformation of wall rocks rather than far field regional stresses

rock texture and magnetic lineation in dykes a simple analytical model abstract we develop two simple models for simulating the combination of magnetic sub fabrics related to magma flow in dykes the basic assumptions are i the petrofabric is representative of the flow fabric and ii the petrofabric is composed of s c type structures related to flow the first model consists of summing the magnetic tensors of two identical sub fabrics differing solely by their relative rotation this model accounts for the possible change of the macroscopic magnetic lineation from a flow related fabric to a lineation situated at the geometric intersection between the two sub fabrics such a result is obtained in the case of oblate to highly oblate sub fabric ellipsoids the second model integrates the effect of very oblate grains of variable orientations into calculating the shape controlled magnetic tensor of each sub fabric and emphasizes the possible under estimation of fabric superposition due to microscopic disordering the magma fluxes along the east greenland volcanic margin are illustrated by the flow pattern within the major dyke swarm the magmatic flow vectors inferred from the imbrication of magnetic foliation at the dyke margins are primarily horizontal the classic use of magnetic lineation can lead to contradictory results giving flow vectors perpendicular to the flow directions the magnetic lineation is situated close to the zone axis of magnetic foliation planes over a wide range of scales throughout the dyke swarm suggesting that the contradiction may arise from the association of several textural domains at the sample scale forward modelling of macroscopic magnetic fabrics using the first model yields good agreement with the measured magnetic fabric of the east greenland dykes our results which are applicable to strained sedimentary rocks highlight the possible misuse of the magnetic lineation due to combination of magnetic textures the exchange between a microscopic lineation i e mineralogical lineation and a macroscopic lineation i e intersection lineation is particularly expected for dykes that generally bear oblate magnetic textures

photosynthetic fractionation of 13c and concentrations of dissolved co2 in the central equatorial pacific during the last 255 000 years carbon isotopically based estimates of co2 levels have been generated from a record of the photosynthetic fractionation of 13c is equivalent to epsilon p in a central equatorial pacific sediment core that spans the last approximately 255 ka contents of 13c in phytoplanktonic biomass were determined by analysis of c37 alkadienones these compounds are exclusive products of prymnesiophyte algae which at present grow most abundantly at depths of 70 90 m in the central equatorial pacific a record of the isotopic composition of dissolved co2 was constructed from isotopic analyses of the planktonic foraminifera neogloboquadrina dutertrei which calcifies at 70 90 m in the same region values of epsilon p derived by comparison of the organic and inorganic delta values were transformed to yield concentrations of dissolved co2 is equivalent to c e based on a new site specific calibration of the relationship between epsilon p and c e the calibration was based on reassessment of existing epsilon p versus c e data which support a physiologically based model in which epsilon p is inversely related to c e values of pco2 the partial pressure of co2 that would be in equilibrium with the estimated concentrations of dissolved co2 were calculated using henry s law and the temperature determined from the alkenone unsaturation index u k 37 uncertainties in these values arise mainly from uncertainties about the appropriateness particularly over time of the site specific relationship between epsilon p and 1 c e these are discussed in detail and it is concluded that the observed record of epsilon p most probably reflects significant variations in delta pco2 the ocean atmosphere disequilibrium which appears to have ranged from approximately 110 microatmospheres during glacial intervals ocean atmosphere to approximately 60 microatmospheres during interglacials fluxes of co2 to the atmosphere would thus have been significantly larger during glacial intervals if this were characteristic of large areas of the equatorial pacific then greater glacial sinks for the equatorially evaded co2 must have existed elsewhere statistical analysis of air sea pco2 differences and other parameters revealed significant p 0 01 inverse correlations of delta pco2 with sea surface temperature and with the mass accumulation rate of opal the former suggests response to the strength of upwelling the latter may indicate either drawdown of co2 by siliceous phytoplankton or variation of co2 si oh 4 ratios in upwelling waters

grain size dependence of the rock magnetic properties for a natural maghemite the natural maghemite from the robe river mining district australia is shown to be thermally very stable the maghemite hematite inversion occurs at 650 c for sized fractions 250 m to 5 m enabling determination of t c for maghemite at 610 c the maghemite is intimately intergrown with hematite and j s of the maghemite corrected for the hematite content is 64 am 2 kg j rs h cr and h c range between 7 46 10 18 am 2 kg 16 90 23 30 mt and 6 38 9 00 mt respectively indicating psd maghemite with grain sizes between 1 and 20 m the grain size dependence of the rock magnetic parameters of the maghemite is less prominent than those of magnetite of nominally the same size it is suggested that the lt behavior of arm can be diagnostic of the presence of maghemite upon cooling to 196 c it shows no change upon rewarming a gradual decrease in intensity occurs starting at 120 c

asymmetrical to symmetrical magnetic fabric of dikes paleo flow orientations and paleo stresses recorded on feeder bodies from the motru dike swarm romania the fabric in a dike is representative of the magmatic flow considered as newtonian the anisotropy of magnetic susceptibility of the rocks gives a good representation of the shape preferred orientation which in turn is a marker of the magmatic flow generally a symmetrical pattern of the fabric across the dike is in agreement with a flow of magma within a channel the flow direction is then reliable with this imbrication an asymmetrical fabric is dependent on the flow and displacement of the wall we present the case of both symmetrical and asymmetrical dike fabrics recording different emplacements from a pan african calc alkaline dike swarm of basaltic andesitic dacitic rhyolitic composition of the alpine danubian window from south carpathians romania two populations of dikes have been described thick 1 30 m n s trending dikes and thin 1 m e w dikes the first display asymmetrical fabric and record the regional sinistral movement of the walls in contrast the thin dikes are symmetrical and frequently display an arteritic morphology that limits the dike length with no cartographic extension we propose to relate the two types of dikes to the same regional stress field in a continuum of emplacement during a regional brittle event

temporal trends in lava dome extrusion at santiaguito 1922 2000 we present a means of extracting lava dome extrusion rates from data provided by the thematic mapper and enhanced thematic mapper plus instruments flown on the landsat satellites extrusion rates derived from the landsat data for santiaguito dome complex guatemala during november 1987 and january 2000 of 0 72 0 08 and 0 48 0 09 m3 s 1 compare favorably with ground based estimates of 0 63 0 28 and 0 48 0 17 m3 s 1 a satellite data derived set of 18 extrusion rate estimates between 1987 and 2000 along with ground based volume estimates prior to 1987 allow us to infer volumes of magma erupted since 1922 these data reveal cyclic extrusion at santiaguito each cycle begins with a 3 6 year long phase of high extrusion rate 0 5 2 1 m3 s 1 followed by a longer 3 11 years phase of low extrusion rate 0 2 m3 s 1 the 8th cycle began in 1996 and was still in its high extrusion rate phase during january 2000 with time however the durations of the low extrusion rate phases have increased peak extrusion and time averaged extrusion rates for each cycle have decreased and the difference between extrusion rates during the high and low extrusion rate phases of each cycle has decreased these trends may be the result of depressurization and exhaustion of the source in this case the current eruption may be expected to end around 2020 alternatively santiaguito may be entering a period of persistent activity maintained by a stable magma supply in this case we may expect extrusion to become less cyclic and to stabilize at 0 2 0 4 m3 s 1 however a 2 wt decrease in sio2 content of erupted products since 1970 appears to be consistent with chamber exhaustion as well as an increase in block lava flow lengths during 1970 2000

magnetic anisotropy produced by magma flow theoretical model and experimental data from ferrar dolerite sills antarctica summary volcanic rocks forming sills dykes or lava flows may display a magnetic anisotropy derived from the viscous flow during their emplacement we model a sill as a steadystate flow of a bingham fluid driven by a pressure gradient in a horizontal conduit the magma velocity as a function of depth is calculated from the motion and constitutive equations vorticity and strain rate are determined for a reference system moving with the fluid the angular velocity and the orientation of an ellipsoidal magnetic grain immersed in the fluid are calculated as functions of time or strain magnetic susceptibility is then calculated for a large number of grains with a uniform distribution of initial orientations it is shown that the magnetic lineation oscillates in the vertical plane through the magma flow direction and that the magnetic foliation plane changes periodically from horizontal to vertical the results are compared with the magnetic fabric of ferrar dolerite sills victoria land east antarctica derived from low field susceptibility measurements

is this magnetic fabric normal a review and case studies in volcanic formations abstract when studying weakly anisotropic rocks non standard relationships between magnetic and expected petrofabric axes are sometimes observed in particular the so called inverse or intermediate fabrics a review of possible explanations for these effects is presented and leads to the conclusion that a majority of abnormal magnetic fabrics often encountered in magnetite rich volcanic rocks are due to abnormal preferred orientations or distributions of magnetite grains through case studies in dikes from skye island yemen and the iberian peninsula and magma and ash flows from the ethiopian traps and southern corsica the various possible origins of such fabrics are examined it is possible to retrieve reliable magma flow directions from these sites provided proper data selection is performed leading to non unique interpretations

recognition of paleobiochemicals by a combined molecular sulfur and isotope geochemical approach study of organic matter in immature sediments from a messinian evaporitic basin shows that consideration of structures modes of occurrence and carbon isotopic compositions of free and sulfur bound carbon skeletons allow identification of biochemical precursors detailed information concerning biotic communities present during deposition of sediments can be retrieved in this way moreover unprecedented biochemicals were recognized these extend the horizon of biomarker geochemistry

development of symmetrical and asymmetrical fabrics in sheet like igneous bodies the role of magma flow and wall rock displacements in theoretical and natural cases abstract two orientations of fabrics are recognised in vertical dykes a symmetric orientation associated with magma injected into non deforming wall rocks and an asymmetric orientation usually associated with external non coaxial shearing or magma injected into an active fault the notion of two fabric arrangements stems from two planes of symmetry the dyke symmetry plane dsp and the fabric symmetry plane fsp this paper uses conceptual models to simulate all possible orientations of magma flow indicators that might be produced within a vertical dyke emplaced under coeval internal and external stresses the effect of magmatic buoyancy related stresses are portrayed in terms of magma flow velocities mfv and the external non coaxial tectonic related stresses in terms of wall displacement velocities divided by two wmv 2 the tectonic setting is that of a sinistral transcurrent fault using these assumptions five cases are proposed mfv wdv 2 mfv wdv 2 mfv wdv 2 mfv

physical controls and depth of emplacement of igneous bodies a review the formation and growth of magma bodies are now recognised as involving the amalgamation of successive discrete pulses such as sills sills would thus represent the building blocks of larger plutons sensu lato mechanical and thermal considerations on the incremental development of these plutons raise the issue of the crustal levels at which magma can stall and accumulate as sills reviewing the mechanisms that could a priori explain sill formation it is shown that principal physical controls include rigidity contrast where sills form at the interface between soft strata overlaid by comparatively stiffer strata rheology anisotropy where sills form within the weakest ductile zones and rotation of deviatoric stress where sills form when the minimum compressive stress becomes vertical comparatively the concept of neutral buoyancy is unlikely to play a leading control in the emplacement of sills although it could assist their formation these different controls on sill formation however do not necessarily operate on the same length scale the length scale associated with the presence of interfaces separating upper stiffer layers from lower softer ones determines the depth at which rigiditycontrolled sills will form on another hand the emplacement depths for rheology controlled sills is likely to be determined by the distribution of the weakest ductile zones whereas the emplacement depth of stress controlled sills is determined by a balance between the horizontal maximum compressive stress which favours sill formation and the buoyancy of their feeder dykes which drives magma vertically ultimately the depth at which a sill forms depends on whether crustal anisotropy or stress rotation is the dominant control i e which of these processes operates at the smallest length scale using dimensional analysis it is shown that sill formation controlled by remote stress rotation would occur on length scales of hundreds of meters or greater this therefore suggests that crustal heterogeneities and their associated anisotropy are likely to play a larger role than remote stress rotation in controlling sill emplacement unless these heterogeneities are several hundred meters or more apart this also reinforces the role of local stress barriers owing to interactions between deviatoric stress and crustal heterogeneities in the formation of sills

determining magma flow in sills dykes and laccoliths and their implications for sill emplacement mechanisms three dimensional seismic data from the faeroe shetland basin provides detailed information on the relationships between sills dykes laccoliths and contemporaneous volcanic activity the data shows that sills are predominantly concave upwards being complete or partial versions of radially or bilaterally symmetrical forms that possess flat inner saucers connected to a flat outer rim by a steeply inclined sheet such morphologies are only partially modified by pre existing faults sills can be sourced from dykes or the steep climbing portions of deeper sills both sills and dykes can provide magma to overlying volcanic fissures and sills can be shown to feed shallow laccoliths magma flow patterns as revealed by opacity rendering suggest that sills propagate upwards and outwards away from the magma feeder as an individual sill can consist of several leaves emplaced at different stratigraphic levels and as a sill or dyke can provide magma to volcanic fissures other sills and laccoliths the data suggests that neutral buoyancy concepts may not provide a complete explanation for the mechanism and level of sill emplacement instead the data suggests that the presence of lithological contrasts particularly ductile horizons such as overpressured shales may permit sill formation at any level below the neutrally buoyant level

flow dynamics in mid jurassic dikes and sills of the ferrar large igneous province and implications for long distance magma transport abstract magma flow paths in sill fed dikes of the ferrar large igneous province lip contrast with those predicted by classic models of dike transport in lips and magmatic rift settings we examine anisotropy of magnetic susceptibility ams flow paths in dike networks at terra cotta mountain and mt gran which intruded at paleodepths of 2 5 and 1 5 km these intrusions up to 30 m thick exhibit irregular interconnected dike sill geometries and adjoin larger sills 200 300 m thick at different stratigraphic levels both shallowly dipping and sub vertical magma flow components are interpreted from ams measurements across individual intrusions and often match macroscopic flow indicators and variations in dike attitudes flow paths suggest that intrusive patterns and magma flow directions depended on varying stress concentrations and rotations during dike and sill propagation whereas a regional extensional tectonic control was negligible or absent unlike giant dike swarms in lips elsewhere e g 1270 ma mackenzie lip dikes of the ferrar lip show no regionally consistent vertical or lateral flow patterns suggesting these intrusion were not responsible for long distance transport in the province in the absence of regionally significant colinear dike swarms or observed intrusions at crustal depths 4 km we suggest that long distance magma transport occurred in sills within beacon supergroup sedimentary rocks this interpretation is consistent with existing geochemical data and thermal constraints which support lateral magma flow for 3 500 km across the gondwana supercontinent before freezing

structural and geochemical interactions between magma and sedimentary host rock the hovedoya case oslo rift norway two end member conceptual models are used to describe deformation of the earth s crust induced by magma intrusion mode i fracturing assumes tensile or opening mode elastic deformation while mode ii fracturing assumes plastic shear mode deformation around a viscous indenter field observations of both mechanisms exist but it remains unclear which mechanism dominates in which conditions we describe intrusion geometries host rock deformation and geochemical magma host rock interactions around 53 exceptionally preserved tephrite basanite permian dike segments of 0 5 to 30 cm thickness these thin dikes that is dikelets intruded late ordovician carbonate rich sedimentary rocks on hovedoya island oslo rift norway dikelets emplaced in preexisting fractures dominantly created cavities ahead of their narrow tapering tips and are associated with bent host rock broken bridges and stepped segmented geometries other tips are blunt with dense brittle fracturing around them also cross sectional intrusion segment opening profiles deviate from parabola shaped profiles typical for elastic media the observations demonstrate that dominant opening mode host rock deformation can coexist with shear mode deformation locally alignment of most dikelet segments along the dominant host rock fracture directions highlights the control of local structural orientations on magma emplacement analysis of bulk major and trace element compositions in situ micro xrf sample analysis and carbon and oxygen stable isotope compositions suggests that thermochemical interactions between magma and the carbonate rich host rock produced a low viscosity mixture of magma pore water and gas we propose that such low viscosity hybrid fluid may assist in the intrusion of magma in sedimentary rocks by filling the cavity ahead of propagating sheet intrusion tips

preparative hplc with ultrastable y zeolite for compound specific carbon isotopic analyses preparative high pressure liquid chromatography on us y zeolite shape selective molecular sieve was studied for carbon isotopic fractionation effects we tested a standard mixture 17 21 h hopane 5 cholestane and complex natural hydrocarbon mixtures dominated by tetra and pentacyclic triterpenoids extracted from oxford clay shales we confirmed that steroids and hopanoids were separated on the basis of stereochemical configuration while isotopic analysis of eluents indicated that shape selective chromatography did not result in isotopic fractionation us y zeolite chromatography can be used to simplify hydrocarbon mixtures and prepare well resolved mixtures of molecular fossils for compound specific isotopic analyses csia

magnetic fabric and inferred flow direction of dikes conesheets and sill swarms isle of skye scotland abstract we have measured the ams of 16 dikes 35 conesheets and three sills associated with the cuillin hills magmatic center of the isle of skye in the inner hebrides of scotland and of nine dikes located in the regional dike swarm of skye sixty three intrusives totalling 734 samples were studied to determine the plumbing of the skye volcanic system low field susceptibility versus temperature k t identified three different mineral phases in the area namely ti rich magnetite pyrrhotite and titanomaghemite the petrofabrics of the 63 intrusives yielded coherent flow azimuths regardless of their time of emplacement three main types of magnetic fabric a c were found fabric type a plane kmax kint parallel to the dike plane represents the magma flow direction within the intrusives and is the dominant fabric 55 of all the intrusives within the cuillin hills magmatic center and its regional dike swarm the kmax inclinations show that 55 of the intrusives were fed by horizontal to sub horizontal ams inclination of the kmax axis is equal or less than 30 magma fluxes and the rest of them were fed by inclined to vertical fluxes horizontal magma flow means lateral magma injection inside fractures and becomes more probable as the source is located further away

emplacement process of ferrar dolerite sheets at allan hills south victoria land antarctica inferred from magnetic fabric summary we analyse 10 representative intrusions from two sets of inclined diabase ferrar dolerite sheets exposed at allan hills south victoria land antarctica using petrographic and rock magnetic methods to determine microfabrics and infer magma flow directions at least one diabase sample was collected at the margins of each intrusion magnetite and pyrrhotite contribute to magnetic fabrics of the samples thirty six magnetic fabric directions inferred from the mutual arrangement of either the magnetic lineation or the magnetic foliation plane and local macroscopic flow indicators e g horn shaped apophyses and kinks at the tips and margins of each intrusion reveal composite i e both lateral and vertical flow paths recorded along each intrusive segment petrographic textures and multiple flow directions inferred at sheet segment tips reveal that passive injection of magma via hydrofracturing produced the local shallow large igneous province plumbing as a sill dominated intrusive complex very close to or intersecting the palaeosurface this contrasts with classic arrays of either vertically or laterally injected blade like dykes

evidence from magnetic fabric for the flow pattern of magma in the mackenzie giant radiating dyke swarm continental flood basalts and their associated swarms of mafic dykes are thought to result from melting in mantle plumes1 3 but the processes by which the resulting magma makes its way from mantle to crust remain obscure here we use magnetic anisotropy measurements to reconstruct the pattern of magma flow in the proterozoic mackenzie dyke swarm our results indicate that magma was injected vertically within 500 km of the focal point of the dyke swarm and then travelled horizontally at all further distances out to at least 2 100 km the sharp transition from vertical to horizontal flow at between 500 and 600 km may correspond to the outer boundary of melt generation in the mantle plume believed to be responsible for the mackenzie igneous events

monogenetic volcanoes fed by interconnected dikes and sills in the hopi buttes volcanic field navajo nation usa although monogenetic volcanic fields pose hazards to major cities worldwide their shallow magma feeders 500 m depth are rarely exposed and therefore poorly understood here we investigate exposures of dikes and sills in the hopi buttes volcanic field arizona to shed light on the nature of its magma feeder system shallow exposures reveal a transition zone between intrusion and eruption within 350 m of the syn eruptive surface using a combination of field and satellite based observations we have identified three types of shallow magma systems 1 dike dominated 2 sill dominated and 3 interconnected dike sill networks analysis of vent alignments using the pyroclastic massifs and other eruptive centers e g maar diatremes shows a nw se trend parallel to that of dikes in the region we therefore infer that dikes fed many of the eruptions dikes are also observed in places transforming to transgressive ramping sills estimates of the observable volume of dikes maximum volume of 1 90 106 m3 and sills minimum volume of 8 47 105 m3 in this study reveal that sills at hopi buttes make up at least 30 of the shallow intruded volume 2 75 106 m3 total within 350 m of the paeosurface we have also identified saucer shaped sills which are not traditionally associated with monogenetic volcanic fields our study demonstrates that shallow feeders in monogenetic fields can form geometrically complex networks particularly those intruding poorly consolidated sedimentary rocks we conclude that the hopi buttes eruptions were primarily fed by nw se striking dikes however saucer shaped sills also played an important role in modulating eruptions by transporting magma toward and away from eruptive conduits sill development could have been accompanied by surface uplifts on the order of decimeters we infer that the characteristic feeder systems described here for the hopi buttes may underlie monogenetic fields elsewhere particularly where magma intersects shallow and often weak sedimentary rocks results from this study support growing evidence of the important role of shallow sills in active monogenetic fields

thirty years of satellite derived lava discharge rates at etna implications for steady volumetric output 1 we present a 30 year long data set of satellite derived time averaged lava discharge rates tadr for mount etna volcano sicily italy spanning 1980 2010 and comprising 1792 measurements during 23 eruptions we use this to classify eruptions on the basis of magnitude and intensity as well as the shape of the tadr time series which characterizes each effusive event we find that while 1983 1993 was characterized by less frequent but longer duration effusive eruptions at lower tadrs 2000 2010 was characterized by more frequent eruptions of shorter duration and higher tadrs however roughly the same lava volume was erupted during both of these 11 year long periods so that the volumetric output was linear over the entire 30 year period increasing at a rate of 0 8 m3 s 1 between 1980 and 2010 the cumulative volume record can be extended back in time using data available in the literature this allows us to assess etna s output history over 5 centuries and to place the current trend in historical context we find that output has been stable at this rate since 1971 at this time the output rate changed from a low discharge rate phase which had characterized the period 1759 to 1970 to a high discharge rate phase this new phase had the same output rate as the high discharge rate phase that characterized the period 1610 1669 the 1610 1669 phase ended with the most voluminous eruption of historic times

experimental modelling of shallow magma emplacement application to saucer shaped intrusions abstract saucer shaped dolerite and sandstone intrusions are common in sedimentary basins world wide we have conducted a series of scaled experiments simulating the process of magma emplacement in sedimentary basins with particular attention on the formation of saucer shaped sills the model materials were 1 cohesive fine grained silica flour representing brittle crust and 2 molten low viscosity oil representing magma the experiments were performed in both homogeneous and layered models in all the experiments oil injection resulted in doming of the surface in the homogeneous models the injected oil formed cone sheets and sub vertical dykes cone sheets formed for shallow injection 1 3 cm and vertical dykes formed for deeper injection 4 5 cm in layered models the injected oil always formed saucer shaped intrusions our experimental results show that 1 sill intrusion results in the formation of a dome with melt erupting at the rim 2 layering controls the formation of sills and saucer shaped sills 3 saucer shaped sills are fed from the bottom and the fluid flows upward and outward and 4 the diameter of saucer shaped sills increase with increasing emplacement depth the systematic relation between domes and sills and the depth dependence of sill diameters show that saucer shaped intrusions result from the interaction between a growing flat lying shallow sill and doming of the free surface we conclude that saucer shaped intrusions represent fundamental geometries formed by shallow magma intrusion in stratified basins

an experimental investigation of sill formation and propagation in layered elastic media a series of experiments are described where dyed water a magma analogue was intruded into solid gelatine a crustal analogue to investigate the formation of sills we considered a layered gelatine system with contrasting adjacent layers by varying the density and rigidity of the gelatine we found that experimental sills form when the upper layer is more rigid than the lower layer with intrusion occurring in a plane directly below the interface experimental dykes were observed to propagate to the surface when the young s modulus ratio of upper to lower gelatine layers was less than one experimental dyke arrest occurred when the upper layer was more rigid and the interface was strong two varieties of experimental sill formed when the upper layer was more rigid than the lower layer and the interface was sufficiently weak the form of the intrusion depends on the balance of driving pressures and the young s modulus ratio of contrasting adjacent layers when the rigidity ratio is high and there is a large driving pressure the experimental feeder dyke completely converts to propagate as a sill however when the rigidity ratio and driving pressure are both close to one a dyke sill hybrid forms under these conditions the experimental sill formation is accompanied by contemporaneous dyke intrusion into the overlying more rigid layer during sill propagation deformation structures such as faults and en echelon fractures are formed into the lower layer experimental sill propagation dynamics are controlled by viscous dissipation along the length of the sill causing acceleration with increasing length our study suggests that rigidity contrasts may play a major role in the location of sills and development of igneous complexes in ancient cratonic areas the moho is a suitable site for the preferential formation of sills with higher rigidity continental crust overlying weaker mantle mantle plumes impacting ancient continents provide a situation in which large sills can form to fractionate prior to eruption of flood basalts the boundary between the upper and lower crust conrad discontinuity may provide a preferential focus for the emplacement of sheets of silicic magma at continental arcs where the lower crust is weakened by prolonged heating and possible hydration

magnetic fabrics study and inferred flow directions of lavas of the old pali road o ahu hawaii abstract a section 600 700 m deep in the koolau tholeiitic lava shield volcano consists of mostly thin pahoehoe and aa flows cut by occasional dikes and outward dipping gravity driven intrusive sheets a magnetic fabric study of 250 specimens from 18 sites shows a tight clustering of k1 axes for some of the lava flows and is thought to fairly reliably define the lava flow direction a systematic plunge of the k1 axes appears to define an imbrication and yields a flow azimuth the azimuth differs by 60 from that anticipated but is readily explained by a change in shape of the koolau volcano during growth the tightest clustering is in massive aa lava flows 5 m thick samples collected from near the flow base give the most consistent orientations compound pahoehoe lavas with many small flow units give the least tightly clustered anisotropy of magnetic susceptibility ams axes and in some flows the orientation is random the gravity driven sheet has an ams fabric indicating a down dip magma flow direction after the koolau volcano was deeply eroded a cinder cone and lava flows of nephelinite were formed in the rejuvenation stage of volcanism the nephelinite is normally magnetized and the ams fabric indicates a generally downslope flow

saucer shaped intrusions occurrences emplacement and implications abstract magmatic intrusions and fluidized injected sands represent the two main types of sheet intrusions in the earth s crust in this paper we show that both intrusion types often display a saucer like geometry as revealed by 3d seismic imaging and field observations saucer shaped intrusions are fairly common in sedimentary basins as for example offshore in the norwegian and north sea basins and onshore in the karoo basin of south africa the formation of the saucer geometry is controlled by the low viscosity of the injected fluid and by the interaction between a growing shallow hydraulic fracture and overburden deformations statistics gathered from observations and modelling show a linear relationship between the depth of emplacement and the size of the saucer shaped intrusions we anticipate future cross disciplinary studies aiming to discover other occurrences of saucer shaped intrusions and to identify the physical processes controlling the development of this fundamental geometry

anisotropy of magnetic susceptibility in the ponta grossa dyke swarm brazil and its relationship with magma flow direction abstract measurements of anisotropy of magnetic susceptibility ams in 95 mafic dykes mainly tholeiites 10 200 m in width from the mesozoic ponta grossa swarm southern brazil revealed two main types of magnetic fabric type i fabric plane k 1 k 2 parallel to the dyke plane represents magma flow within the dykes whereas type ii plane k 1 k 3 parallel to the dyke plane is compatible with a fabric pattern reflecting vertical compaction of the magma column fabric type i dominates 51 of the dykes within the swarm whereas type ii 38 of the dykes concentrates mainly in the western region where the dykes intrude sediments considering the dykes with type i fabrics it is concluded that 58 of the dykes were fed by horizontal or sub horizontal k 1 inclinations less than 30 magmatic flow and 42 were fed by inclined to vertical k 1 inclinations more than 30 magma flow the latter are more frequent in the southeastern part of the swarm suggesting a magma source close to this area although there may have been other sources in other regions where dykes with inclined flow and distinct chemical characteristics are also found

magma flow in the east greenland dyke swarm inferred from study of anisotropy of magnetic susceptibility magmatic growth of a volcanic margin summary volcanic passive margins vpms are characterized by large volumes of melt emplaced within the lithosphere during break up processes several data and a recently proposed conceptual model of volcanic margin development suggest that vpms are fed from localized crustal zones of magma storage underlying large polygenetic volcanoes localized above diapir like instabilities of the asthenosphere we investigated the magma flow pattern within the coastparallel dyke swarm of the east greenland vpm which is the only outcropping vpm over a distance of 125 km the 44 sampled dykes are representative of the successive families of intrusions igneous petrofabrics are constrained by the measurements of the anisotropy of magnetic susceptibility the magnetic fabrics are of medium to low anisotropy p 0 flow related fabrics are recorded in 75 per cent of the sampled dykes we infer the flow directions from the imbrication geometry of the magnetic foliation planes at the dyke margins and check the results by measuring the preferred orientation of plagioclase in thin sections cut in the magnetic principal planes due to probable fabric superposition the magnetic lineation represents the zone axis for the distribution of magnetic foliation plane we obtained 23 reliable flow directions that are predominantly horizontal and directed away from identified crustal reservoirs this flow pattern supports the proposed model of vpm growth and emphasizes the localized nature of the magma sources in the mantle the entire flood basalt sequence appears to have been fed by a restricted number of crustal reservoirs and associated dyke swarms

interconnected sills and inclined sheet intrusions control shallow magma transport in the ferrar large igneous province antarctica field observations and structural data from intrusive complexes at allan hills and terra cotta mountain south victoria land antarctica demonstrate that interconnected sills and inclined sheets transported magma through the shallow subsurface these sills and sheets represent the upper crustal top 4 km plumbing system of the 183 ma ferrar large igneous province the sheets are short in length