phanerozoic evolution of the basins of northern egypt and adjacent areas the results of integrating geological well data and geophysical information from the subsurface of northern egypt are presented in terms of basin dynamics recent biostratigraphic data from wells and scarce outcrops are shown to be critical to an understanding of syndepositional tectonics six tectonostratigraphic phases of basin evolution are recognized to span the phanerozoic these phases initially record the development of intracratonic subsidence controlled by deep crustal strike slip tectonics as nubian continental and tethyan marine influences competed across the northern margin of gondwanaland evidence is also presented for the formation of the present day continental margin to northern egypt after a phase of crustal stretching oceanic rifting focused on the western margin of the arabian platform propagating progressively westwards during the early mid jurassic thereafter the effects of passive subsidence on the continental margin were disturbed by discrete phases of intracratonic strike slip associated syrian arc folding and the formation of deep basins in the opening red sea and gulf of suez three structural fabrics persisted throughout phanerozoic basin evolution the result of repeated extensional reactivation and inheritance from pan african basement

the los alamos sferic array a research tool for lightning investigations 1 since 1998 the los alamos sferic array lasa has recorded electric field change signals from lightning in support of radio frequency rf and optical observations by the fast on orbit recording of transient events forte satellite by sferic a colloquial abbreviation for atmospheric we refer to a remote measurement of the transient electric field produced by a lightning flash lasa consisted of five stations in new mexico in 1998 and was expanded to 11 stations in new mexico texas florida and nebraska in 1999 during the 2 years of operation described in this paper the remote stations acquired triggered 8 or 16 ms duration 12 bit waveforms and gps based sferic time tags 24 hours per day year round source locations were determined daily using differential time of arrival techniques and the waveforms from all geolocated events were transferred to los alamos national laboratory lanl where they have been archived for further analysis including event classification and characterization we evaluated lasa location accuracy by comparing temporally coincident occurring within 100 s lasa and national lightning detection network nldn event locations approximately one half of the locations agreed to within 2 km with better agreement for events that occurred within the confines of lasa subarrays in new mexico and florida of the 900 000 events located by the sferic array in 1998 and 1999 nearly 13 000 produced distinctive narrow bipolar field change pulses resembling those previously identified as intracloud discharges

mapping lightning in the sky with a mini array mini arrays are commonly used for infrasonic and seismic studies here we report for the first time the detection and mapping of distant lightning discharges in the sky with a mini array the array has a baseline to wavelength ratio 4 2 10 2 to record very low frequency electromagnetic waves from 2 to 18 khz it is found that the mini array detects 69 lightning pulses per second from cloud to ground and in cloud discharges even though the parent thunderstorms are 900 1100 km away and a rigorous selection criterion based on the quality of the wavefront across the array is used in particular lightning pulses that exhibit a clockwise phase progression are found at larger elevation angles in the sky as the result of a birefringent subionospheric wave propagation attributed to ordinary and extraordinary waves these results imply that long range lightning detection networks might benefit from an exploration of the wave propagation conditions with mini arrays

physical properties of partly melted tholeiitic basalt melting experiments on centimetre scale blocks of tholeiitic holyoke basalt from the mesozoic hartford basin of connecticut reveal that when this basalt is only 30 crystallized a relatively strong network of crystals exists cubes of the basalt melted to this degree retain their shape as the interstitial liquid drains easily from the crystal network the intrinsic permeability of a sample containing 34 crystals was determined to be 3 10 10 m2 which is similar to that of coarse gravel serial sections through partly melted samples reveal that the network owes its strength to monomineralic strings of plagioclase and pyroxene crystals although these strings are clearly evident once the rock has been partly melted they are difficult to see in thin sections of the initial basalt but they are present the compressive strength of the mush increases dramatically from 336 to 4333 pa as the percentage of crystals increases from 33 to 37 this rapid strengthening is believed to explain why sheets of segregation liquid in tholeiitic flood basalts have compositions that correspond to no more than 35 fractional crystallization of the host basalt these sheets are proposed to form through compaction of the crystal mush in the lower part of thick flows the compaction occurring only while the mush remains weak that is while it has 35 crystals

accuracy of the lightning mapping array 1 the location accuracy of the new mexico tech lightning mapping array lma has been investigated experimentally using sounding balloon measurements airplane tracks and observations of distant storms we have also developed simple geometric models for estimating the location uncertainty of sources both over and outside the network the model results are found to be a good estimator of the observed errors and also agree with covariance estimates of the location uncertainties obtained from the least squares solution technique sources over the network are located with an uncertainty of 6 12 m rms in the horizontal and 20 30 m rms in the vertical this corresponds well with the uncertainties of the arrival time measurements determined from the distribution of chi square values to be 40 50 ns rms outside the network the location uncertainties increase with distance the geometric model shows that the range and altitude errors increase as the range squared r2 while the azimuthal error increases linearly with r for the 13 station 70 km diameter network deployed during steps the range and height errors of distant sources were comparable to each other while the azimuthal errors were much smaller the difference in the range and azimuth errors causes distant storms to be elongated radially in plan views of the observations the overall results are shown to agree well with hyperbolic formulations of time of arrival measurements e g proctor 1971 two appendices describe 1 the basic operation of the lma and the detailed manner in which its measurements are processed and 2 the effect of systematic errors on lightning observations the latter provides an alternative explanation for the systematic height errors found by boccippio et al 2001 in distant storm data from the lightning detection and ranging system at kennedy space center

geology of the snap lake kimberlite intrusion northwest territories canada field observations and their interpretation the cambrian 523 ma snap lake hypabyssal kimberlite intrusion northwest territories canada is a complex segmented diamond bearing ore body detailed geological investigations suggest that the kimberlite is a multi phase intrusion with at least four magmatic lithofacies in particular olivine rich ork and olivine poor opk varieties of hypabyssal kimberlite have been identified key observations are that the olivine rich lithofacies has a strong tendency to be located where the intrusion is thickest and that there is a good correlation between intrusion thickness olivine crystal size and crystal content heterogeneities in the lithofacies are attributed to variations in intrusion thickness and structural complexities the geometry and distribution of lithofacies points to magmatic co intrusion and flow segregation driven by fundamental rheological differences between the two phases we envisage that the low viscosity opk magma acted as a lubricant for the highly viscous ork magma the presence of such low viscosity crystal poor magmas may explain how crystal laden kimberlite magmas 60 vol are able to reach the surface during kimberlite eruptions we also document the absence of crystal settling and the development of an unusual subvertical fabric of elongate olivine crystals which are explained by rapid degassing induced quench crystallization of the magmas during and after intrusion supplementary material additional figures are available at http www geolsoc org uk sup18503

tectonic development of the eastern mediterranean region an introduction the eastern mediterranean is one of the key regions for the understanding of fundamental tectonic processes including continental rifting passive margins ophiolites subduction accretion collision and post collisional exhumation it is also ideal for under standing the interaction of tectonic sedimentary igneous and metamorphic processes through time that eventually lead to the development of an orogenic belt below we will outline some milestones in the development of tectonic related research in the eastern mediterranean region we will mention how studies of the eastern mediterranean contrib ute to our understanding of fundamental tectonic processes and indicate how papers in this volume contribute to this aim current and emerging research themes will be highlighted we will also outline the main alternative tectonic reconstructions of the region see fig 1 and mention which of these the different contributors favour tethyan nomenclature remains controversial and we will suggest an appropriate informal terminology for the various oceanic basins that existed an entr6e to some of the key literature sources is also provided citations here are mainly to edited volumes which provide access to this large subject area many of the papers in this book integrate and synthesize large amounts of geological information for extended periods of geological time the papers are ordered in a general time sequence with a view to linking those that consider comparable tectonic setting and pro cesses the locations of the areas are shown in figures 2 and 3 figure 2 also shows the main sutures and figure 3 illustrates the main neotectonic elements of the region

quantitative measures of textural anisotropy resulting from magmatic compaction illustrated by a sample from the palisades sill new jersey abstract early in the crystallization of many tholeiitic basaltic magmas plagioclase crystals cluster together into a 3 d cellular network which forms a passive marker capable of recording the deformation that accompanies compaction of crystal mush although irregular in detail the overall network is initially isotropic and only becomes anisotropic as a result of compaction we have developed four independent methods to quantify the 3 d textural anisotropy of a basalt sample using at least three non parallel thin sections three of the methods are based on the geometrical properties of digitized maps of the feldspar chain networks one approach focuses on the angular variation of the mean intercept along parallel traverses through the network another examines the orientation and size distribution of individual links and the third considers the average shape of interstitial regions outlined by the plagioclase network the fourth technique approximates the textural anisotropy by the variogram anisotropy of a scanned thin section image we illustrate the methods using five oriented non parallel thin sections from a sample of diabase 146 m above the base of the 300 m thick palisades sill of new jersey compaction of crystal mush in this sill has previously been postulated on the basis of chemical evidence the 3 d feldspar network anisotropy based on the first three approaches suggests nearly uniaxial compaction on the order of 8 6 in a direction within 3 of the intersection of the columnar joints at the sample site a rigorous statistical test based on the statistics of elliptically contoured non normal multivariate distributions documents that the link vector distribution in vertical sections are statistically anisotropic at a 95 confidence level and that the overall compaction is 7 9 2 6 the orientation and magnitude of the 3 d textural anisotropy determined by the image variogram of the non opaque minerals is almost identical to the mean feldspar network anisotropy 8 5 compaction in a direction 10 from the columnar joint intersections the major silicate textural and feldspar network anisotropy axes both plunge almost directly down dip of the sill on the other hand the major axis of the variogram anisotropy of the opaque minerals is approximately parallel to the strike of the sill and to the major axis of the anisotropic magnetic susceptibility the anisotropy of the silicate mineral fabric may reflect down dip flow of a deformable melt rich crystal mush whereas the ams and opaque textural anisotropy reflects the influence of gravitational stresses during the growth of magnetite in the final stages of melt crystallization evidently the palisades sill was not originally horizontal but was intruded in an orientation close to its present attitude

a gps based three dimensional lightning mapping system initial observations in central new mexico a gps based system has been developed that accurately locates the sources of vhf radiation from lightning discharges in three spatial dimensions and time the observations are found to reflect the basic charge structure of electrified storms observations have also been obtained of a distinct type of energetic discharge referred to as positive bipolar breakdown recently identified as the source of trans ionospheric pulse pairs tipps observed by satellites from space the bipolar breakdown has been confirmed to occur between the main negative and upper positive charge regions of a storm and found to be the initial event of otherwise normal intracloud discharges the latter is contrary to previous findings that the breakdown appeared to be temporally isolated from other lightning in a storm peak vhf radiation from the energetic discharges is observed to be typically 30 db stronger than that from other lightning processes and to correspond to source power in excess of 100 kw over a 6 mhz bandwidth centered at 63 mhz

stratigraphic evidence for shear in structural development of the triassic levant margin new borehole data on the epicontinental to deep marine transition in israel abstract triassic tectonic movements that include shear along a significant portion of the levant margin are evidenced from microfacies analysis of material recovered from the asher atlit 1 ga ash 2 meged 2 devora 2 and ramalla 1 onshore boreholes seismic studies showed that structural lineaments attributed to early mesozoic extension underlie coastal and central israel trending ne sw beneath southern israel and sub parallel to the then extensional palmyride basin of syria a more curved trend approximately nnw sse lies to the north beneath central israel coast parallel sedimentary domains formed above these lineaments which constitute the newly formed passive margin of the levant coast in the triassic the sedimentary history of these domains indicates that some were linked to each other and others disconnected the relative vertical movement between one domain and another is explained by activation of transpressional and trans tensional shear movements on the underlying curved faults these subordinate vertical movements also created the discontinuous barriers and small subsiding basins that separate the epicontinental sedimentary domain from the open tethys causing partial restriction necessary for the intermittent development of thick evaporites in the internal domains alternating with a regionally suppressed carbonate system this zone is here named the onshore levant margin shear zone olmsz shear was invoked theoretically in a number of models for the tectonic evolution of the eastern mediterranean as part of a neotethyan opening system this paper provides rock based evidence for such shear applicable to 20 of the eastern levant margin in the triassic

post emplacement melt flow induced by thermal stresses implications for differentiation in sills abstract we present the first steps of a new explanation model for differentiation in sills using a combination of geochemical data and field observations numerical modeling and dimensional analysis geochemical data from a saucer shaped dolerite sill intruded into the karoo basin south africa reveal a differentiation process which causes d shaped profiles the geometry name is based on the variation in whole rock mg number mg mg mg fe from floor to roof in a sill the d shaped geochemical profiles represent sheet intrusions with the most primitive composition i e high mg in its center and progressively more evolved composition i e low mg towards the upper and lower margins the differentiation is reversed compared to the normal differentiation produced by fractional crystallization c shaped profiles c shaped profiles are believed to be formed by segregation of crystals from the magma we propose that the opposite the d shaped profile may result from melt segregation from the crystal mush this is achieved by porous melt flow through a consolidated crystal network after the main phase of emplacement and before complete solidification we show that a significant flow is feasible under natural occurring conditions an underpressure of magnitude 108 pa develops at the cooling margins due to volume reduction of the crystallizing porous melt the resulting pressure gradient is the driving force for the melt flow towards cooling margins considered in this work as a result the margins will be enriched in the incompatible elements associated with the melt phase while the center will be depleted we show that the amount of flow is primarily a function of viscosity of the melt and permeability of the crystal network which in turn is a transient phenomenon dependent on a number of parameters diagrams have been constructed to evaluate the feasibility of substantial melt extraction in terms of these poorly constrained parameters data from the golden valley sill and many other natural occurrences of d and i shaped geochemical profiles show a reasonable agreement with our predictions of melt flow potential and are thus well explained by the presented model we conclude that in order to fully understand differentiation processes occurring in sheet intrusions we need to account for post emplacement segregation of melt from crystals and not only segregation of crystals from melt

crystal mush compaction in the cohassett flood basalt flow hanford washington abstract the 40 m thick central part of the cohassett flow which was probably emplaced by inflation of an earlier more ti rich flow exhibits textural evidence of crystal mush compaction during solidification although most of the crystallization started in the roof zone as water circulated through fractures in the crust plumes of dense crystal mush must have dripped from the roof to the floor of the sheet thus displacing upward the colonnade entablature boundary the mush initially consisted of loosely stacked plagioclase crystals and liquid surrounding rapidly grown pyroxene oikocrysts containing radial chadacrysts of plagioclase upon compaction in the floor zone the liquid between the loosely stacked plagioclase crystals was expelled as the crystals packed tightly together to form sub parallel grains wrapped around the pyroxene oikocrysts which recrystallized into granular aggregates of augite and pigeonite stacks of sinking plagioclase crystals and rising liquid accumulated on the upper and lower sides respectively of horizontal plagioclase phenocrysts this asymmetric texture clearly indicates the relative motion of solids and liquid the degree of compaction as determined from variations in the amount of interstitial liquid and quantitative measures of textural anisotropy accounts for the chemical variation through the central part of the flow with compatible elements being concentrated in the lower part of the flow and incompatible elements concentrated in the upper part modeling of the compaction process using the iridium melt infiltration and reaction program of boudreau a 2003 iridium a program to model reaction of silicate liquid infiltrating a porous solid assemblage computers and geosciences 29 423 429 shows that the observed chemical and compaction dilation profiles are to be expected in a 40 m thick sheet of basaltic magma solidifying on the earth s surface compaction of crystal mush should be even more likely in slowly cooled intrusive bodies

the formation of plagioclase chains during convective transfer in basaltic magma the basaltic rock in the lower part of the thick holyoke lava flow in connecticut and massachusetts has been shown to have a remarkable texture with crystals of feldspar linked together in a continuous three dimensional network of chains1 heating experiments have revealed that this network persists to temperatures where the rock is 75 liquid2 and therefore the network was interpreted to have formed at an early stage of crystallization and to have played an important role in the compaction of crystal mush in the lower part of the flow3 4 despite the texture s importance to our understanding of how such basalt flows form the origin of the texture has remained uncertain1 2 3 here we show that although the network is present in the lower third of the flow it was actually formed in the upper solidification front and was transported down in plumes of dense crystal mush convection of this type has been postulated for intrusive magma chambers but corroborative field evidence has been equivocal especially in lava lakes and flows preservation of the roof generated texture in the lower part of a thick flood basalt flow therefore constitutes important evidence for the role of convection in the solidification and differentiation of a simple magma sheet

the role of crystal frameworks in the preservation of enclaves during magma mixing abstract the dacitic lava flows of nea kameni santorini greece contain a variety of partially crystalline mafic enclaves each enclave type is derived from the break up of a layer of replenishing magma emplaced in the dacite chamber prior to eruption crystallisation induced vesiculation of this layer driven by the temperature contrast between the two magmas was sufficient to drive upwelling and overturn of the layer resulting in the formation of mafic enclaves within the host the replenishing magmas are preserved as enclaves due to the presence of a plagioclase crystal framework spatial distribution pattern sdp analysis and melting experiments demonstrate that the plagioclase crystallinity and crystal aspect ratios observed in the kameni enclaves are sufficient to form a touching framework of crystals observations on the coherence of the framework during exsolution of volatiles and enclave transport suggest that the morphology of the dominant framework forming phase places a significant control on the strength and viscosity of the crystal framework which in turn determines the extent to which the replenishing magmas will fragment and mix with the dacite host frameworks composed of high aspect ratio crystals are weak and respond to rapid vesicle expansion in a brittle manner the replenishing magma then disaggregates to become a source of crystals dispersed throughout the host magma in contrast low aspect ratio crystals form strong crystal frameworks that are more resistant to rapid vesicle expansion resulting in preservation of the replenishing magma as vesicular enclaves

on bimodal differentiation by solidification front instability in basaltic magmas part 1 basic mechanics extensive coarse grained silicic lenses are common in the upper portions of large diabase sills lava lakes and gabbroic intrusions these lenses which often contain up to 10 wt more silica than their host rocks record a clear process of bimodal differentiation that may play a fundamental role in generating significant quantities of silicic magma in predominantly basaltic systems the spatial compositional textural and contact relations suggest that these silicic segregations form by infilling of tears formed during gravitational instability of the upper solidification front this process is investigated in some detail by exploring the thermal and mechanical conditions leading to internal failure of the front and segregation formation as the upper solidification front grows inward and thickens the local strength of the developing crystalline network must increase upward through the front sufficiently fast to offset the increasing weight of the front itself this necessary local variation in strength dictates how crystallinity must vary to prevent failure but the actual variation in crystallinity is determined by phase equilibria which in general varies in a fashion that is noncovariant with that required for mechanical stability it is this mismatch that apparently leads to failure and formation of silicic segregations the rate of filling of the tears by porous flow of interstitial melt from below regulates the rate of tear opening and the overall size of the tears is regulated by the local rate of advance of the solidification front segregations therefore thicken downward as the growth of the front slows and then die out altogether with approach of the lower solidification front this process irreversibly introduces siliceous noise into basaltic systems the silicic signal can be enhanced through subsequent reprocessing of the host rock to form volumetrically important masses of silicic magma this process may be fundamental to achieving the strong compositional diversity of the igneous rocks to yielding continental masses and to the differentiation of earth itself

electrical structure in thunderstorm convective regions 3 synthesis in this paper results from nearly 50 electric field soundings through convective regions of mesoscale convective systems mcss isolated supercells and isolated new mexican mountain storms are compared and synthesized these three types of thunderstorm convection are found to have a common basic electrical structure within convective updrafts the basic charge structure has four charge regions alternating in polarity and the lowest is positive outside updrafts of convection there are typically at least six charge regions alternating in polarity and the lowest is again positive among the three storm types there are differences in the heights and temperatures at which the basic four charge regions are found in updrafts the height temperature of the center of the main negative charge region averages 6 93 km 16 c in mcs convective region updrafts 9 12 km 22 c in supercell updrafts and 6 05 km 7 c in new mexican mountain storm updrafts in updraft soundings through all three storm types the center height of the main negative charge region increases with increasing average balloon ascent rate and updraft speed at a rate of about 0 3 km per 1 m s 1 with a correlation coefficient of 0 94 a schematic illustrates the basic four and six charge structure for thunderstorm convective regions and it is offered as an improved model for thunderstorm charge structure

consequences of crystal shape and fabric on anisotropic permeability in magmatic mush crystals that form an interconnected porous network can become preferentially oriented both prior to and during compaction of magmatic mush this introduces anisotropy in the melt pore space that can reduce permeability in the direction of compaction and in turn decrease melt flux and compaction rate using a number of grain scale numerical models the consequences of end member magmatic fabrics on the directional dependence of permeability are tested over a range in melt fraction from 22 to 77 as the crystal aspect ratio i e ratio of long to short axis length increases from 2 to 10 isotropic permeability decreases by a factor of 2 and 5 for randomly oriented prolate and oblate shaped crystals respectively at a melt fraction of 22 with a flattening fabric permeability is reduced in the compaction direction no more than approximately a factor of 2 relative to the isotropic permeability at the same melt fraction and crystal shape for both oblate and triaxial prisms however permeability is enhanced in directions orthogonal to the compaction direction for example permeability is enhanced up to a factor of 11 relative to the isotropic permeability at a melt fraction of 22 for oblate prisms with a ratio of the long to short axis length of 10 anisotropy in permeability increases as the melt fraction decreases and the crystal aspect ratio increases ratios of the principal permeabilities are sufficiently large based on the realistic crystal shapes tested here to warrant including anisotropic permeability into macroscale melt segregation models including those for compaction

electric fields preceding cloud to ground lightning flashes we analyzed in detail the electric field variations preceding the first return strokes of 80 cloud to ground lightning flashes in nine different storms observed at the nasa kennedy space center during the summers of 1976 and 1977 the electric field variations are best characterized as having two sections preliminary variations and stepped leader the stepped leader electric field change begins during a transition period of a few milliseconds duration marked by characteristic bipolar pulses the durations of stepped leaders lie most frequently in the range 6 20 milliseconds we infer from our measurements and critical review of the previous literature that there is only one type of stepped leader not the two types and often referred to in the literature

radio interferometric observations of cloud to ground lightning phenomena in florida radio frequency observations of cloud to ground lightning in florida have been analyzed to document a number of features of the lightning the observations have been made using an interferometer system which determined the direction to the lightning radiation as a function of time during close lightning discharges observations are presented for about 50 radiating events during five multiple stroke normal polarity flashes to ground the results confirm and extend results of a similar study of new mexico lightning by rhodes et al 1994 dart leaders in cloud k events and attempted leaders are found to be the same phenomena namely a negative polarity streamer that propagates horizontally and or vertically to ground at estimated speeds of about 10 7 ms 1 down to 10 6 ms 1 the step or impulsive fast electric field change produced by some k events is found to be caused by positive breakdown back at the starting point of the negative streamer after the streamer has progressed over some or all of its distance this breakdown appears to initiate a forward stroke along the streamer channel which can renew the breakdown at the front end of the channel k breakdown which happens to occur during a continuing current discharge to ground produces an m event channel brightening when it connects with the conducting channel to ground the step fast field change of the m events is found to be produced at the time of connection inside the cloud no fast field change is detected when this breakdown reaches ground that would be associated with a return stroke m events can also be initiated by fast 10 7 ms 1 positive streamers which often propagate away from the leader source region within a few milliseconds of the arrival of a return stroke back in the source region these streamers often generate an even faster negative recoil event back along their extent which propagates down the channel to ground as the m event in all cases the current increase or channel brightening produced by k and m events is predicted to occur in a forward direction that is toward or down the channel to ground in the same direction as the initiating negative streamer positive breakdown is detected only immediately following return strokes or during some k streamers in both cases the electric stresses are expected to be very large suggesting that positive breakdown which produces a conducting channel is difficult to initiate results for one flash suggest that negative charge was left at low altitude by the initial stroke to ground this forced the subsequent leaders to develop a new path to ground first as series of attempted leaders and then as a dart stepped leader

the skaergaard layered series part iii non dynamic layering layering in the skaergaard intrusion has been divided into two introduction general types one produced by magmatic flow and another by recent studies of the structural and textural features of processes resulting from variations of rates of nucleation and crysthe skaergaard intrusion mcbirney nicolas 1997 tallization and in the case of the layered series by compactionhave distinguished two broad types of layering one related processes modal variations caused by shifts of cotectic produced by the dynamic effects of magmatic flow and proportions produce thick layers which in the layered and upper another by processes that operate in situ such as varied border series are diffuse and normally lack strong foliation and nucleation and growth of crystals recrystallization or by lineation in the marginal border series the layers are thinner and compaction related mechanisms we refer to layering sharper possibly because the rate of accumulation was slower formed by these latter processes as non dynamic to oscillatory nucleation may have played a role in producing fineemphasize that it is not the result of fluid dynamic scale cyclic layers but it was less important than solution and processes although most layering combines elements of reprecipitation during slow cooling and ostwald ripening evidence more than one process the contribution of each mechfor compaction is found in deformed plagioclase laths and a relative anism can usually be recognized from its distinctive form deficiency of incompatible elements in rocks formed on the floor and setting layering related to compaction becomes sharper with increasing the distinguishing features of dynamic magmatic layheight in the layered series until it suddenly disappears above the ering have been described in part ii of this series mcbirtrough horizon near the base of upper zone b mechanical sorting ney nicolas 1997 they are best seen near the steep during compaction may have produced crude layering but if it did margins of the layered series in what wager brown the evidence has long since been destroyed by the superimposed effects 1968 referred to as the cross bedded zone where the of solution and reprecipitation when interstitial liquid rose through layering is disrupted by slumping and channeling and the overlying crystals and re equilibrated with them numerical the rocks have a marked foliation and lineation simulations illustrate how small differences of surface energy caused layering not associated with magmatic flow takes a by variations of grain size textural dependence of solubility and variety of forms but we can distinguish two general pressure solution can cause segregation of minerals into layers during end members each of which has a distinct origin and solution and reprecipitation characteristics the first results from varied rates of

magmatic processes under mid ocean ridges a detailed mineralogic study of lavas from east pacific rise 9 30 n 10 30 n and 11 20 n 1 detailed petrologic study has been made for lavas from the northern east pacific rise epr 9 30 n 11 20 n and 10 30 n 9 30 n and 11 20 n have robust magma supply and a shallow melt lens while 10 30 n has nonrobust magma supply and no shallow melt lens lavas from all three localities are sparsely phyric and glassy containing plagioclase olivine pyroxene typically the lavas contain several to many up to seven distinct chemical groups of plagioclase that are not always distinct texturally the lavas may also contain up to three chemically distinct groups of olivine and two groups of pyroxene the lavas contain both individual crystals and groups comprising reticulate and dendritic clots that we interpret to represent bits of crystal networks forming in mushy zones of an axial magma chamber 21 of the 23 samples studied in detail have diverse crystal compositions and require mixing which most likely occurs when mostly liquid magma passes through mushy zones we find no significant systematic differences between robust and nonrobust segments in terms of their crystal content proportion of texturally distinct xenocrysts crystal size aspect ratio roundness modal abundance magma residence time number of diverse mineral chemical groups and characteristics of mixing like the total range of composition of disequilibrium minerals present and the magnitude of the chemical gaps between disequilibrium and equilibrium compositions this unexpected and remarkable similarity suggests that the presence or absence of a seismically imaged shallow melt lens has essentially no effect on the mineralogy of erupted lavas we conclude that the fundamentally important magmatic process under mid ocean ridges from slow to fast is the formation of crystal networks and their subsequent compaction the seismically detected shallow melt lenses likely contain highly evolved magma formed by expelled interstitial melt during crystal network compaction and play very little role in crustal accretion our conclusion implies that the thick 3 km low velocity zone near the base of the crust produces the thin 30 m shallow melt lenses not the other way around

the skaergaard trough layering sedimentation in a convecting magma chamber the upper parts of the floor cumulates of the skaergaard intrusion east greenland contain abundant features known as troughs the troughs are gently plunging synformal structures comprising stacks of crescentic modally graded layers with a sharply defined mafic base that grades upward into plagioclase rich material the origin of the troughs and layering is contentious attributed variously to deposition of mineral grains by magmatic currents descending from the nearby walls or to in situ development by localised recrystallisation during gravitationally driven compaction they are characterised by outcrop scale features such as mineral lineations parallel to the trough axis evidence of erosion and layer truncation associated with migration of the trough axis and disruption of layering by syn magmatic slumping a detailed microstructural study of the modal trough layers using electron backscatter diffraction together with geochemical mapping demonstrates that these rocks do not record evidence for deformation by either dislocation creep or dissolution reprecipitation instead the troughs are characterised by the alignment of euhedral plagioclase crystals with unmodified primary igneous compositional zoning we argue that the lineations and foliations are therefore a consequence of grain alignment during magmatic flow post accumulation amplification of the modal layering occurred as a result of differential migration of an unmixed immiscible interstitial liquid with upwards migration of the si rich conjugate into the plagioclase rich upper part of the layers whereas the fe rich immiscible conjugate remained in the mafic base both field and microstructure evidence support the origin of the troughs as the sites of repeated deposition from crystal rich currents descending from the nearby chamber walls

complex zoning between super calcic pigeonite and augite from the graveyard point sill oregon a record of the interplay between bulk and interstitial liquid fractionation the 150 m thick late miocene graveyard point sill gps is situated at the idaho oregon border near the southwestern edge of the western snake river plain it records from bottom to top continuous fractional crystallization of a tholeiitic parent magma lower chilled border feo feo mgo 0 59 ni 90 ppm towards granophyres late pods and dikes feo feo mgo 0 98 78 wt sio2 3 5 wt k2o 4 ppm ni showing a typical trend of fe and p enrichment fractionating minerals are olivine fo79 fo2 augite xfe 0 18 0 95 feldspars an80or1 an1or62 fe ti oxides ti rich magnetite and ilmenite apatite and in two samples super calcic pigeonite wo18 28 fs41 54 the granophyres may bear some quartz compositionally zoned minerals record a large interval of the fractionation process in every single sample but this interval changes with stratigraphic height in super calcic pigeonite bearing samples olivine is scarce or lacking and because super calcic pigeonite occurs as characteristic overgrowths on augite its formation is interpreted to be related to the schematic reaction augite olivine component in melt sio2 in melt pigeonite that defines the cotectic between augite and pigeonite in olivine saturated basaltic systems line measurements with the electron microprobe reveal that the transition from augite to super calcic pigeonite is continuous however some crystals show an abrupt reversal towards augite after super calcic pigeonite growth two processes compete with each other in the gps fractional crystallization of the bulk liquid the bulk melt separates from solids and interstitial liquids in the solidification front and fractional crystallization of interstitial melt in the solidification front itself interplay between those two processes is proposed to account for the observed variations in mineral chemistry and mineral textures

evidence for late devonian vertical movements and extensional deformation in northern africa and arabia integration in the geodynamics of the devonian world 1 the upper paleozoic geodynamic evolution is discussed at the scale of a wide part of gondwana from north africa to arabia with the aim of giving an integrated tectonic scenario for the study domain we revisit six key areas namely the anti atlas belt morocco the bechar basin west algeria the hassi r mel high central algeria the talemezane arch south tunisia the western desert egypt and finally the high zagros belt iran below the so called hercynian unconformity which is in reality a highly composite discontinuity surface and subsurface data display a well known arch and basin geometry with basement highs and intervening paleozoic basins we show that this major feature results mainly from a late devonian event and can no longer be interpreted as a far effect of the variscan orogeny this event is characterized by a more or less diffuse extensional deformation and accompanied either by subsidence in the western part of the system or by an important uplift of probable thermal origin followed by erosion and peneplanation by the end of the devonian the whole region suffered a general subsidence governed by the progressive cooling of the lithosphere such a primary configuration is preserved in arabia with typical sag geometry of the carboniferous and permian deposits but strongly disturbed elsewhere by the conjugated effects of the variscan orogeny during the carboniferous and or by subsequent uplifts linked to the central atlantic and neo tethys rifting episodes in conclusion we try to integrate this new understanding in the geodynamics of the late devonian which at world scale is characterized by the onset of the variscan orogeny on the one hand and by magmatism rifting and basement uplift on the other hand

low temperature thermochronology of francolite insights into timing of dead sea transform motion cambrian siliciclastic sequences along the dead sea transform dst margin in southern israel and southern jordan host both detrital fluorapatite d apatite and u rich authigenic carbonate fluorapatite francolite a apatite d apatite and underlying neoproterozoic basement apatite yield fission track ft data reflecting paleozoic mesozoic sedimentary cycles and epeirogenic events and dispersed u th sm he ahe ages a apatite which may partially or completely replace d apatite yields an early miocene ft age suggesting formation by fracturing hydrothermal fluid ascent and intra strata recrystallisation linked to early dst motion the dst separating the african and arabian plates records 105 km of sinistral strike slip displacement but became more transtensional post 5 ma helium diffusion measurements on a apatite are consistent with thermally activated volume diffusion indicating tc 52 56 10 c cooling rate 10 c myr a apatite ahe data record pliocene cooling 35 40 c during the transtensional phase of movement this suggests that timing of important milestones in dst motion can be discerned using a apatite low temperature thermochronology data alone

mineral scale sr isotope constraints on magma evolution and chamber dynamics in the rum layered intrusion scotland sr isotopic zoning within single plagioclase crystals from rocks from unit 9 of the rum layered intrusion is used to infer events during crystal growth in a magma undergoing contamination the 87sr 86sr diversity among minerals and between cores and rims of plagioclase crystals increases as the boundary between unit 9 and the overlying unit 10 peridotite is approached models of near solidus interaction of the cumulate with a fluid or melt or large scale textural re equilibration cannot easily account for the systematic differences in 87sr 86sr between small crystals and the rims of larger crystals

crustal scale rheological transitions during late orogenic collapse abstract orogeny involves crustal thickening followed by thermal relaxation and radiogenic heat production in the thickened crust culminating in crustal melting and magma intrusion which decrease the crustal viscosity by several orders of magnitude and cause late orogenic collapse collapse of the canadian cordillera is expressed in the early tertiary shuswap metamorphic core complex british columbia which displays a three layer crustal section separated by two fundamental rheological discontinuities 1 the brittle ductile transition across which high angle normal faults in the upper crust control basin formation merge into a low angle detachment zone where leucogranite laccoliths ponded and deformed progressively under submagmatic to low temperature conditions and 2 the metatexite diatexite transition across which the rocks lose their solid framework and behave like a viscous magma this transition has the potential to mechanically decouple the upper crust from the rest of the lithosphere during a late orogenic gravitational collapse

map of low frequency electromagnetic noise in the sky the earth s natural electromagnetic environment is disturbed by anthropogenic electromagnetic noise here we report the first results from an electromagnetic noise survey of the sky the locations of electromagnetic noise sources are mapped on the hemisphere above a distributed array of wideband receivers that operate in a small aperture configuration it is found that the noise sources can be localized at elevation angles up to 60 in the sky well above the horizon the sky also exhibits zones with little or no noise that are found toward the local zenith and the southwest of the array these results are obtained by a rigorous analysis of the residuals from the classic dispersion relation for electromagnetic waves using an array analysis of electric field measurements in the frequency range from 20 to 250 khz the observed locations of the noise sources enable detailed observations of ionospheric modification for example caused by particle precipitation and lightning discharges while the observed exclusion zones enable the detection of weak natural electromagnetic emissions for example from streamers in transient luminous events above thunderclouds

segregation processes in vesiculating crystallizing magmas vesiculation of crystallising magma can produce either a mobile vesicular magma or a rigid network of crystals containing vesicular liquid where partially crystallized rigid mush underlies less crystallized magma such as near the base of a lava flow or in the cumulus pile of a magma chamber evolved interstitial melt and or gas may escape into the main body of magma the consequences of this may include contamination of the overlying liquid with gas and interstitial melt or intrusion of diapirs of vesicular evolved liquids to form vertical vesicle cylinders and other segregation features found in many basaltic lava flows and sills analog experiments were used to investigate some of the phenomena that can arise during vesiculation within a crystal mush which was simulated by pumping air through a porous plate that formed the floor of a container filled with a viscous liquid floored with a layer of glass beads experiments used either a single liquid or two stably stratified liquids with a liquid interface either coincident with the top of the porous layer of beads or slightly above the porous layer for a range of liquid viscosities and air flow rates vesiculation rates individual bubbles emerged from the top of the porous layer of beads and carried a thin trail of interstitial liquid into the overlying liquid the number of bubble trains leaving the surface of the porous bed increased with decreasing liquid viscosity and flow rate and with increasing bead size and hence with increasing permeability analog vesicle cylinders composed of diapirs of bubbly interstitial liquid were produced only when a layer of buoyant bubbly liquid lay above the surface of the porous layer the relative size of the bubbles and constrictions within the porous layer are argued to control whether individual bubbles leading to bubble trains or vesicular liquid leading to vesicle cylinders leaves the porous layer and hence whether vesicle cylinders can form

the rheology of two phase magmas a review and analysis abstract we consider the current state of our understanding of the rheology of two phase magmas that is suspensions of either bubbles or crystals in a viscous silicate melt the discussion is restricted to strain rates at which the suspending melt can be considered newtonian we start by considering the range of textures found in magmas and the bubble deformation and particle motions caused by shearing we then review proposed models for suspensions focussing on those functions of the form r f or f that have been most widely used to describe magmatic systems r is the relative apparent viscosity of the suspension is the volume fraction of the suspended phase is the driving stress and is the strain rate both theoretical and empirical methods are presented and then compared against the available analogue i e non magmatic and magmatic data the paper contains new data and significant re analysis of previously published data we present a new semi empirical constitutive model for bubble bearing magmas that is valid for steady and unsteady flow and large strains and strain rates this equation utilises a new parameter the capillarity cx that encapsulates the combined effect of shearing and unsteadiness on bubble suspensions we also present a new scheme for dealing with polydispersivity of bubble suspensions new data on the rheology of particle suspensions undergoing forced oscillations are presented these data show that the cox merz rule only holds for dilute particle suspensions 0 25 a re analysis of all available experimental data that relate rheology to particle aspect ratio provides distinct curves of maximum packing as a function of aspect ratio for smooth and rough particles with magmatic data lying on the curve appropriate for rough particles we analyse several rheological datasets of crystal bearing basaltic magmas and find that they are in good agreement with the constitutive equations derived from analogue data by contrast the same equations do not agree well with data for high viscosity haplogranitic melts this may be an effect of fracturing or viscous dissipation within these samples the paper concludes with a practical rheological recipes section giving a step by step method for calculating a constitutive equation for a two phase magmatic suspension and assessing its likely accuracy

plagioclase chain networks in slowly cooled basaltic magma plagioclase crystals in the slowly cooled interior of the thick holyoke flood basalt flow of connecticut linked to form monomineralic chains at an early crystallization stage partial melting experiments reveal that when the quartz tholeiite was only 25 crystallized the chains had already linked to form a continuous 3 d network at such an early stage of crystallization the network was weak highly permeable and easily deformed consequently the mush of plagioclase chains and interstitial pyroxene crystals underwent compaction in the lower third of the flow with the expelled liquid rising to the center of the flow where it crystallized to form coarse grained sheets of fractionated basalt plagioclase chains are most easily seen in the basalt after it has been partly melted and the late crystallizing minerals converted to glass the chains are several crystals wide the crystals which are approximately 0 5 mm long are attached together randomly normal zoning patterns indicate crystals had a brief period of growth before linking together the chains branch every few millimeters to form the 3 d network which was mapped using serial polished sections and x ray ct scans the chain frequency measured along vertical and horizontal traverses decreases toward the center of the flow in the compaction zone the frequency in the vertical direction is greater than in the horizontal making the reasonable assumption that these frequencies were initially the same the difference is used to calculate the degree of compaction the resulting pattern through the flow matches almost exactly the pattern indicated by variations in the incompatible elements plagioclase chains are also found in some coarser grained plutonic rocks if they are common their fabric may provide a new direct means of measuring the degree of compaction in crystal mushes

statistics and characteristics of cloud to ground lightning with multiple ground contacts 1 during the summer of 1997 386 cloud to ground cg lightning flashes were recorded on videotape near tucson arizona within this sample 136 flashes 35 struck the ground in two or more places that were separated by tens of meters or more within this subset of 136 which we term multiple channel flashes mcfs 88 exhibited two or more separate and distinct channels between the cloud base and the ground a type that we term a new channel flash ncf 37 forked or produced channels that struck the ground in two or more places and shared a common channel at higher altitudes a type that we term an altered channel flash acf and 11 exhibited both types of behavior the ratio of ncfs to acfs in arizona was 99 48 or 2 1 a value that is consistent with measurements in florida after allowing for differences in the cloud base heights altogether the 386 cg flashes produced 558 different strike points therefore the average number of strike points per cg flash was 1 45 67 of the new strike points were produced by the second stroke in the flash and 72 of the changes in channel geometry occurred after there had been just one stroke in the previous channel ten of the 48 acfs 21 developed along a visible branch of the previous channel and seven of the 136 mcfs 5 contained strokes that reilluminated the first channel after a second channel had formed the presence of a long continuing luminosity during the initial three or more consecutive video frames appeared to lower the probability of forming either a new or altered channel on the second stroke from 47 to 33 but the statistics are limited and our ability to identify individual strokes is biased by poor time resolution

dynamics of the development of the isle au haut gabbro diorite layered complex quantitative implications for mafic silicic magma interactions the isle au haut igneous complex provides a unique opportunity to examine in detail the in situ physical and chemical interactions between contemporaneously emplaced mafic and silicic magmas the complex contains a 600 m thick sequence of 11 alternating layers of gabbro and diorite typically 15 40 m thick purely on the basis of density contrasts 2 65 g cm 3 gabbro vs 2 55 g cm 3 diorite the entire system should have undergone wholesale instability and mixing it is instead arrested in a grossly unstable state of interaction while molten chilled margins along the lower contacts of the gabbros and structural integrity of the diorite layers indicate that near liquidus gabbroic magma invaded partly crystalline cooler diorite mineral assemblages chemical analyses and phase equilibria calculations indicate initial temperatures during emplacement of 11808c gabbro and 10008c diorite conductive thermal models yield solidification timescales of 15 60 years for single gabbro layers and about a thousand years for the entire complex there is ample evidence for two phases of small scale interfacial rayleigh taylor type instabilities of dioritic melt into the gabbros phase i occurred immediately upon gabbro emplacement whereas evenly spaced slender more silicic pipes represent a much later stage phase ii pipe geometry and spacing estimated viscosities of the gabbroic magma and silicic melt and the sudden increase in silica near the upper contact of the diorite all indicate a thin 18 53 cm buoyant layer at the upper contact of the diorite as the source of the pipes compaction of the diorite produced this layer over a period of about 10 years simultaneous solidification along the lower contact of the overlying gabbro thickening inwards increased viscosity enough to arrest pipe ascent after a few meters crystal size distribution analyses of the gabbro layers yield crystal growth rates go1 4 2 4 10 10 cm s and nucleation rates jo1 410 10 6 cm 3 s indicative of conductive cooling coupled with some sluggish convective stirring owing to collapse of the roof ward gabbro solidification fronts were the complex larger with a much longer solidification time all this evidence would have been lost thus suggesting that in larger systems similar processes may commonly take place leaving little direct evidence of their operation apart from the ultimate final petrological product

petrologic evolution of a nipigon diabase sill ontario canada insights from compositional and textural profiles petrographic and geochemical profiles collected through a 250 m thick nipigon diabase sill near black sturgeon lake ontario constrain the complex emplacement and differentiation processes that controlled the magmatic evolution of these rocks several nested reinjections of phenocryst bearing magma compactiondriven redistribution of mildly evolved interstitial liquids in the central portion of the sill and segregation of highly evolved interstitial liquids into micropegmatitic veins near the upper contact these processes impact not only the silicate mineralogy of the rocks but also distribution of sulfide phases both petrographic and geochemical data demonstrate that the sill was gradually inflated via several discrete injections of olivine bearing magma plagioclase crystal size trends exhibit several reversals that are correlated with increases in olivine abundance and bulk rock mgo content these textural and compositional reversals are attributed to reinjections of olivine bearing magma into partially solidified magma from earlier injections mixing between evolved resident magma and reinjections of less evolved magma is commonly proposed as a mechanism for triggering sulfide mineralization in this sill which contains no significant mineralization localized minor enrichments and depletions in copper content are associated with the margins of a well constrained reinjection horizon chemical differentiation of the magma was controlled by three distinct processes flow differentiation crystal mush compaction and solidification front instability although the mineralogy of the sill is dominated by plagioclase and clinopyroxene major oxide compositional variations are largely controlled by the mechanical concentration of olivine via flow differentiation or phenocryst redistribution within the individual reinjection pulses this redistribution of phenocryst phases is the primary factor controlling the major element composition of the rocks in most of the sill in the central portion of the sill the abundances of incompatible trace elements are influenced by the compaction of partially crystalline mush and the expulsion of incompatible rich interstitial liquid this is recognized by a negative correlation between the alignment of plagioclase crystals and concentrations of incompatible trace elements such as zr finally there is a 2 5 m thick silicic segregation approximately 32 m below the upper contact whose composition is consistent with residual liquid after 65 to 85 fractional crystallization of magma with a composition equivalent to that of the marginal rocks similar veins and patches are common throughout the upper 50 m of the sill indicating that this segregation process was common and widespread during the cooling and crystallization of the sill the complexity of intrusion and differentiation in this sill despite its generally unremarkable texture and composition suggests that many diabase sills may have experienced a range of processes that have previously been recognized to impact the petrologic evolution of larger igneous systems and that these processes can be identified in minor intrusions such as sills and dikes using simple and robust analytical techniques

lower silurian hot shales in north africa and arabia regional distribution and depositional model abstract lowermost silurian organic rich hot shales are the origin of 80 90 of palaeozoic sourced hydrocarbons in north africa and also played a major role in petroleum generation on the arabian peninsula in most cases the shales were deposited directly above upper ordovician peri glacial sandstones during the initial early silurian transgression that was a result of the melting of the late ordovician icecap deposition of the main organic rich shale unit in the north african arabian region was restricted to the earliest silurian rhuddanian stage acuminatus atavus and probably early cyphus graptolite biozones during this short period 1 2 m y a favourable combination of factors existed which led to the development of exceptionally strong oxygen deficiency in the area in most countries of the study area the post rhuddanian silurian shales are organically lean and have not contributed to petroleum generation the distribution and thickness of the basal silurian hot shales have been mapped in detail for the whole north african region using logs from some 300 exploration wells in libya tunisia algeria and morocco in addition all relevant accessible published and unpublished surface and subsurface data of the lower silurian shales in north africa and arabia have been reviewed including sedimentological biostratigraphic and organic geochemical data the lowermost silurian hot shales of northern gondwana are laterally discontinuous and their distribution and thickness were controlled by the early silurian palaeorelief which was shaped mainly by glacial processes of the late ordovician ice age and by pan african and infracambrian compressional and extensional tectonism the thickest and areally most extensive basal silurian organic rich shales in north africa occur in algeria tunisia and western libya while on the arabian peninsula they are most prolific in saudi arabia oman jordan and iraq the hot shales were not deposited in egypt which was a large palaeohigh at that time the depositional model presented may help in better understanding the source potential of the basal silurian shales in less explored regions of north africa and arabia including morocco northern niger and the kufra basin in southeast libya

anorthosite formation by plagioclase flotation in ferrobasalt and implications for the lunar crust abstract the sept iles layered intrusion quebec canada is dominated by a basal layered series made up of troctolites and gabbros and by anorthosites occurring 1 at the roof of the magma chamber 100 500 m thick and 2 as cm to m size blocks in gabbros of the layered series anorthosite rocks are made up of plagioclase with minor clinopyroxene olivine and fe ti oxide minerals plagioclase displays a very restricted range of compositions for major elements an 68 an 60 trace elements sr 1023 1071 ppm ba 132 172 ppm and sr isotopic ratios 87 sr 86 sr i 0 70356 0 70379 this compositional range is identical to that observed in troctolites the most primitive cumulates of the layered series whereas plagioclase in layered gabbros is more evolved an 60 an 38 the origin of sept iles anorthosites has been investigated by calculating the density of plagioclase and that of the evolving melts the density of the feo rich tholeiitic basalt parent magma first increased from 2 70 to 2 75 g cm 3 during early fractionation of troctolites and then decreased continuously to 2 16 g cm 3 with fractionation of fe ti oxide bearing gabbros plagioclase an 69 an 60 was initially positively buoyant and partly accumulated at the top of the magma chamber to form the roof anorthosite with further differentiation plagioclase 60 became negatively buoyant and anorthosite stopped forming blocks of anorthosite autoliths even fell downward to the basal cumulate pile the presence of positively buoyant plagioclase in basal troctolites is explained by the low efficiency of plagioclase flotation due to crystallization at the floor and or minor plagioclase nucleation within the main magma body dense mafic minerals of the roof anorthosite are shown to have crystallized from the interstitial liquid the processes related to floating and sinking of plagioclase in a large and shallow layered intrusion serve as a proxy to refine the crystallization model of the lunar magma ocean and explain the vertically stratified structure of the lunar crust with gabbro noritic rocks at the base and anorthositic rocks at the top we propose that the lunar crust mainly crystallized bottom up this basal crystallization formed a mafic lower crust that might have a geochemical signature similar to the magnesian suite without kreep contamination while flotation of some plagioclase grains produced ferroan anorthosites in the upper crust

textural evidence for dilatant shear thickening rheology of magma at high crystal concentrations investigation of the rheology of magmas at high crystal concentrations by experimental means has proved problematic an alternative approach is to study textures of igneous rocks that not only preserve evidence of the kinematics of magma flow such as flow direction but can also preserve evidence of rheology flow textures in multiply intruded trachyte dykes on fraser island eastern australia record evidence of dilatant flow during solidification this conclusion is reached by interpretation of microscopic ductile shear zones that disrupt the groundmass of aligned feldspar laths detailed three dimensional investigation demonstrates that the dihedral angle between conjugate micro shear zones is approximately 65 this conjugate angle is equivalent to that observed in dilatant granular materials such as sand dilatant behaviour is synonymous with shear thickening rheology indicating that the magma flow is time dependent and resists high flow rates some of the dykes contain autobrecciation fragments that may represent localities where the ductile flow rate threshold was exceeded newtonian or pseudoplastic shear thinning rheology of crystal poor magmas must progressively give way to shear thickening rheology during cooling and increasing crystal concentration

quantitative modeling of granitic melt generation and segregation in the continental crust 1 we present a new quantitative model of granitic in a broad sense melt generation and segregation within the continental crust we assume that melt generation is caused by the intrusion of hot mantle derived basalt and that segregation occurs by buoyancy driven flow along grain edges coupled with compaction of the partially molten source rock we solve numerically the coupled equations governing heating melting and melt migration in the source rock and cooling and crystallization in the underlying heat source our results demonstrate that the spatial distribution and composition of the melt depends upon the relative upward transport rates of heat and melt if melt transport occurs more quickly than heat transport then melt accumulates near the top of the source region until the rock matrix disaggregates and a mobile magma forms as the melt migrates upward its composition changes to resemble a smaller degree of melting of the source rock because it thermodynamically equilibrates with rock at progressively lower temperatures we demonstrate that this process of buoyancy driven compaction coupled with local thermodynamic equilibration can yield large volumes of mobile granitic magma from basaltic and meta basaltic amphibolitic protoliths over timescales ranging from 4000 years to 10 myr the thickness of basaltic magma required as a heat source ranges from 40 m to 3 km which requires that the magma is emplaced over time as a series of sills concurrent with melt segregation these findings differ from those of previous studies which have suggested that compaction operates too slowly to yield large volumes of segregated granitic melt

the plagioclase magma density paradox re examined and the crystallization of proterozoic anorthosites intermediate composition plagioclase an40 60 is typically less dense than the relatively evolved basaltic magmas from which it crystallizes and the crystallization of plagioclase produces a dens residual liquid thus plagioclase should have a tendency to float in these magmatic systems there is however little direct evidence for plagioclase flotation cumulates either in layered intrusions or in proterozoic anorthosite complexes the layered series of the poe mountain anorthosite southeast wyoming contains numerous anorthosite leucogabbro blocks that constrain density relations during differentiation all blocks are more mafic than their hosting anorthositic cumulates their plagioclase compositions are more calcic and each block is in strong sr isotopic disequilibrium with its host cumulate associated structures disrupted and deformed layering indicate that 1 a floor was present during crystallization and that plagioclase was accumulating and or crystallizing on the floor 2 compositional layering and plagioclase lamination formed directly at the magma crystal pile interface and 3 the upper portions of the crystal pile contained significant amounts of interstitial melt liquid densities are calculated for proposed high al olivine gabbroic parental magmas and fe enriched ferrodioritic and monzodioritic residual magmas of the anorthosites taking into account pressure oxygen fugacity p2o5 estimated volatile contents and variable temperatures of crystallization for all reasonable conditions calculated block densities are greater than those of the associated melt the liquid densities however are greater than those for an40 60 plagioclase which cannot have settled to the floor plagioclase must either have been carried to the floor in relatively dense packets of cooled liquid plus crystals or have crystallized in situ a sloping floor possibly produced by diapiric ascent of relatively light plagioclase rich cumulates is required to allow for draining and removal of the dense interstitial liquid produced in the crystal pile and may be a characteristic feature during the crystallization of many proterozoic anorthosites and layered intrusions

permeability and melt flow in simulated and natural partially molten basaltic magmas abstract a lattice boltzmann method is used to calculate grain scale low reynolds number single phase interstitial porous melt flow in two independent igneous microstructures 1 a microstructure simulated using a stochastic algorithm for progressive crystallization and 2 a natural microstructure obtained through x ray computed tomography ct of a partially melted basalt in both cases the error in the calculated flow field due to finite discretization and domain size has been estimated or demonstrated to be insignificant visually the porous melt flow tends to localize into high flux channels especially with increasing crystallinity and this impression is quantitatively confirmed by increasing skewness of the velocity distribution in the direction parallel to the imposed pressure gradient driving the flow a change from uniform to localized melt flow in naturally occurring situations may have a profound effect on the distribution of trace elements and if the melt is reactive the chemical and structural evolution of the igneous microstructure through localized phase change permeabilities of both microstructures are determined from the calculated steady flow field the permeabilities are then fitted to two different correlation models which are based on the rumpf gupte and carman kozeny relations in these models we express permeability as functions of melt fraction and either the mean crystal length or specific surface area extrapolated permeability to higher melt fractions using both correlation models for the partially melted basalt is shown to be within a factor of four of experimentally determined permeability of a similar sample we determine permeability estimates in the relatively unexplored melt fraction range of 30 80 and find consistency with previous work for permeability estimates in the melt fraction range of 20 30

nature of a flood basalt magma reservoir based on the compositional variation in a single flood basalt flow and its feeder dike in the mesozoic hartford basin connecticut the erosional remains of the mesozoic holyoke basalt in the hartford pomperaug and deerfield basins of connecticut and massachusetts indicate an original flow volume of 1200 km3 its feeder dike which is about 50 m wide and 160 km long can be traced down through 2 km of mesozoic sediments and as a result of faulting associated with basin formation through an additional 6 km of paleozoic metamorphic rocks chemical profiles through the distal and proximal parts of the flow and through the dike at depths of 2 4 and 8 km provide sequential samples of the magma that rose during this one eruptive event the flow and dike have restricted compositions that indicate saturation with olivine augite and plagioclase at depth the flow consisted largely of a liquid at the pigeonite reaction point dike compositions can be modeled as mixtures of this liquid with up to 24 crystals of plagioclase augite and olivine the dike compositions indicate equilibration with these minerals at 3 8 kbar this pressure corresponds to a depth of 12 2 km which is believed to have been the depth of the brittle ductile transition in the crust at the time this transition appears to be the only reasonable barrier that could have caused ponding of the magma at the mid crustal level the holyoke liquid is interpreted to have segregated from a compacting crystal mush following 30 crystallization of the magma in this mid crustal reservoir eruption of the basalt exhausted the supply of segregated liquid and when the remaining crystal mush began to rise in the dike the average density of the magma column increased until it matched the average density of the intruded crust and the eruption ended by analogy with the differentiation that took place in the solidifying holyoke flow on the surface the mid crustal magma reservoir is estimated to have had a volume of at least 12 000 km3 the magma in this chamber must have come from a still deeper chamber because it was too fractionated to have come directly from a mantle source

pyroclast loss or retention during explosive volcanism on asteroids influence of asteroid size and gas content of melt we review the conditions under which explosive volcanism took place on early forming differentiated asteroids the pressure dependent solubility of typical asteroid volatiles in melts implies that the gas driving explosive volcanism on asteroids less than approximately 100 km in diameter was probably present mainly as a free phase capable of accumulating into large gas bodies and thus causing slug flow in melts approaching the surface in contrast in asteroids larger than approximately 100 km the gas was probably present largely as a dispersion of small bubbles we show that these gas distributions have implications for the size distribution of the pyroclastic droplets produced in explosive eruptions at the surface all pyroclastic melt droplets are accelerated by the expanding gases but their speeds lag the gas speed by a finite amount that is a function of the droplet size and density and the asteroid size and hence acceleration due to gravity we compute pyroclast speeds and by comparing them with escape velocities we identify the critical pyroclast diameter on a given size asteroid that distinguishes droplets lost to space from droplets that return to the surface identification of asteroidal pyroclasts and measurements of their sizes could throw light on the amounts of gas driving eruptions

vhf radio pictures of lightning flashes to ground we present information obtained from vhf radio pictures of 47 lightning flashes that struck ground 1430 m above mean sea level msl to the north of johannesburg over a period of 16 years radio pictures were obtained using a hyperbolic method i e by taking differences between times at which radio noise from lightning arrived at five widely spaced stations these data were supplemented by recordings of electric field change we found that stepped leaders and intracloud streamers emitted pulses and progressed at speeds that averaged 1 6 105 ms 1 stepped leaders ranged in length from 3 to 13 km bil breakdown intermediate leader waveforms of electric field change were caused by stepped leaders whose branched channels followed complicated paths the electric field changes they recorded in an effective bandwidth of 3 5 khz could be reproduced faithfully by calculations based on an assumption that the radio sources became charged at the expense of a region near the origin of each leader some return strokes radiated trains of noise called q noise whose sources extended at speeds near 108 ms 1 sources of this q noise retraced leader channels before extending them at these high speeds interstroke processes radiated q noise whose sources extended at speeds that averaged 8 7 107 ms 1 most q sources 98 were directed vertically but they pervaded regions that retrogressed at speeds that averaged 2 2 104 ms 1 in directions away from the starting points of the flashes this retrogression was directed horizontally but the vertical q streamers caused j changes to have positive or negative slopes according to the relative positions of q sources and the reversal cone sixty percent of our sample of ground flashes were endowed with portions that were cloud flashes or were themselves minor components of cloud flashes a more detailed summary appears at the end of the paper

the yield strength of subliquidus basalts experimental results yield strength is an important property of particle fluid suspensions in basaltic lavas that crystallize during flow emplacement the onset of yield strength may result in threshold transitions in flow behavior and flow surface morphology however yield strength crystallinity relations are poorly known particularly in geologic suspensions where difficulties of experimental and field measurements have limited data acquisition in the subliquidus temperature range here we describe two complementary experimental approaches designed to examine the effect of particle shape on the low shear yield strength of subliquidus basalts the first involves melting cubes of holocrystalline basalt samples with different initial textures to determine the temperature crystallinity at which these samples lose their cubic form these experiments provide information on the minimum crystal volume fractions 0 20 0 35 required to maintain the structual integrity of the cube the second set of experiments uses suspensions of corn syrup and neutrally buoyant particles to isolate the effect of particle shape on yield strength development from these experiments we conclude that the shape is important in determining the volume fraction range over which suspensions exhibit a finite yield strength as anisotropic particles may orient during flow the effect of particle shape will be controlled by the orientation distribution of the constituent particles we find that the so called excluded volume can be used to relate results of experiments on anisotropic particles to those of suspensions of spherical particles recent measurements of yield strength onset in basaltic melts at crystal volume fractions near 0 25 are consistent with our observations that crystal frameworks develop at low to moderate crystal volume fractions when crystals are anisotropic e g plagioclase we further suggest that conditions leading to yield strength onset at low crystallinities include rapid cooling increased crystal anisotropy heterogeneous nucleation which promotes extensive crystal clustering and large cluster anisotropy and static conditions random crystal orientations

characterization and applications of vlf lf source locations from lightning using the huntsville alabama marx meter array 1 arrays that detect and locate the four dimensional spacetime positions of radiation sources from lightning have largely utilized sensors sensitive to the very high frequency vhf regime with 15 km baselines or very low frequency low frequency vlf lf regime with 100 km baselines this paper details initial results from the newly developed huntsville alabama marx meter array hamma consisting of marx meters electric field change meters sensitive to a frequency band 1 hz to 400 khz the arrival time of hamma waveforms due to radiation sources from lightning are used to determine the spacetime position of these sources the locations are compared with two well documented and operational arrays the national lightning detection network nldn and the north alabama lightning mapping array nalma the standard deviation of the difference between hamma and nldn locations of return strokes is 305 and 266 m in x and y respectively while the standard deviation of the difference between hamma and nalma sources is 237 226 and 688 m in x y and z respectively we further show that nldn intracloud locations differ in horizontal distance from the corresponding hamma locations by a median value of 479 m in addition we use hamma source locations to map several lightning flashes in the vlf lf and show hamma sources largely map out the same electrical extent as vhf sources and provide unique insights to the properties of the discharges occurring finally we show that vlf lf sources can determine the leader polarity in several example flashes but not necessarily whether a flash comes to ground copyright 2013 american geophysical union all rights reserved

a low frequency near field interferometric toa 3 d lightning mapping array we report on the development of an easily deployable lf near field interferometric time of arrival toa 3 d lightning mapping array applied to imaging of entire lightning flashes an interferometric cross correlation technique is applied in our system to compute windowed two sensor time differences with submicrosecond time resolution before toa is used for source location compared to previously reported lf lightning location systems our system captures many more lf sources this is due mainly to the improved mapping of continuous lightning processes by using this type of hybrid interferometry toa processing method we show with five station measurements that the array detects and maps different lightning processes such as stepped and dart leaders during both in cloud and cloud to ground flashes lightning images mapped by our lf system are remarkably similar to those created by vhf mapping systems which may suggest some special links between lf and vhf emission during lightning processes

effects of internal rheology and surface cooling on the emplacement of lava flows 1 the emplacement dynamics of lava flows is modeled using a combination of laboratory experiments and theoretical scaling analyses for the case where a fixed volume of lava is rapidly released and spreads as a horizontal two dimensional flow we focus on the processes that determine the final runout length of the lava including the growth of a crust due to surface cooling and the presence of an internal yield strength we show that solidifying flows with no internal yield strength first spread in slumping and viscous flow regimes before a final regime where the yield strength of the growing crust stops the flow we then demonstrate that solidifying flows with an internal yield strength can be stopped by either the internal yield strength or the growing crust we also find that the yield strength of the solidified crust systematically increases with increasing internal yield strength we illustrate our results by predicting the flow regimes of two typical lavas a hawaiian lava with no interior yield strength and a mount etna lava with an interior yield strength in particular we find that the crust strength stops small volume breakouts of the mount etna lava while large volume breakouts are stopped by the interior yield strength

physical properties of volcanic lightning constraints from magnetotelluric and video observations at sakurajima volcano japan abstract the lightning generated by explosive volcanic eruptions is of interest not only as a promising technique for monitoring volcanic activity but also for its broader implications and possible role in the origin of life on earth and its impact on the atmosphere and biosphere of the planet however at present the genetic mechanisms and physical properties of volcanic lightning remain poorly understood as compared to our understanding of thundercloud lightning here we present joint magnetotelluric mt data and video imagery that were used to investigate the physical properties of electrical discharges generated during explosive activity at sakurajima volcano japan and we compare these data with the characteristics of thundercloud lightning using two weeks of high sensitivity high sample rate mt data recorded in 2013 we detected weak electromagnetic signals radiated by volcanic lightning close to the crater by carefully inspecting all mt waveforms that synchronized with visible flashes and comparing with high speed 3000 frame s and normal speed 30 frame s videos we identified two types of discharges the first type consists of impulses type a and is interpreted as cloud to ground cg lightning the second type is characterized by weak electromagnetic variations with multiple peaks type b and is interpreted as intra cloud ic lightning in addition we observed a hybrid mt event wherein a continuous weak current accompanied type a discharge the observed features of volcanic lightning are similar to thunderstorm lightning and the physical characteristics show that volcanic lightning can be treated as a miniature version of thunderstorm lightning in many respects the overall duration length inter stroke interval peak current and charge transfer all exhibit values 1 2 orders of magnitude smaller than those of thunderstorm lightning thus suggesting a scaling relation between volcanic and thunderstorm lightning parameters that is independent of the type of charged particles on the other hand the polarities which are estimated by long time 3 4 yrs mt 32 samples s and video 30 frame s observations are different than those of normal thunderstorm lightning these observations are consistent with the notion that charge structures in volcanic ash plumes are highly disordered and are characterized by numerous small charged regions with high charge density

continental margin evolution of the northern arabian platform in syria copyright aapg 1993 reprinted by permission of the aapg whose permission is required for further use see also http atlas geo cornell edu syria best 1993 html

quantifying the building blocks of igneous rocks are clustered crystal frameworks the foundation most phenocryst populations in volcanic rocks and those preserved in shallow level igneous intrusions are clustered variously referred to as clots clumps or glomerocrysts these clusters of crystals are the building blocks that accumulate to form the high porosity touching crystal frameworks from which igneous cumulates form examination of touching crystal frameworks in olivine komatiite cumulates and experimental charges and plagioclase dominant crystal populations holyoke flood basalt connecticut usa reveal complex high porosity clustered crystal arrangements olivine touching frameworks in komatiite flows are interpreted to form in hundreds of days plagioclase frameworks are calculated to have formed in less than 17 years for a crystal growth rate of 1 x 10 10 mm s to less than 3 years for a growth rate of 5 x 10 10 mm s based on crystal size distributions the origin of crystal clusters is likely to involve either or a combination of heterogeneous nucleation remobilization of cumulate mushes or crystals sticking together during settling and or flow the spatial distribution pattern of clustered crystal frameworks from both natural and experimental examples constrains fields on spatial packing diagrams that allow the identification of touching and non touching crystal populations and further improve our understanding of crystal packing arrangements and cluster size distributions

shear rate dependence of the pāhoehoe to a ā transition analog experiments hawaiian lava flows typically erupt as pahoehoe and transform to a aas they travel away from eruptive vents although the exact conditions that govern this transformation are not well constrained here we describe a set of laboratory experiments that use corn syrup and ellipsoidal rice grains as an analog to lava with crystals to examine the depen dence of the transition on shear rate and particle concentration at a particle volume fraction of 0 3 increasing the shear rate produces a sequence of deformation regimes defined by increasing amounts of shear localization the same regimes may be traversed at constant shear rate by varying the particle concentration at high shear rates the onset of nonlaminar deformation corresponds to the percolation threshold thus providing a link between suspension microstructure and deformation behavior together these results high light the combined importance of shear rate and crystallinity in determining the flow behavior of basaltic lava

on the cluster analysis of grains and crystals in rocks cluster analysis has the potential to quantify the size and characteristics of groups or clusters of grains and crystals within a rock texture we present two techniques 1 the complete linkage hierarchical cluster analysis clhca technique that we use to analyze grain center distributions and 2 the density linkage cluster analysis dlca technique that we use to analyze grain boundary distributions clhca applies a cluster algorithm to the distance matrix calculated from grain center coordinates this produces a hierarchical cluster distribution that is characteristic of the spatial pattern of the texture this cluster distribution is normalized to that of a random distribution of points to identify clustered and ordered patterns in the data the technique successfully identified 3 d cluster sizes from 2 d sections of a modal data set in the application to real rock textures the clhca of a komatiite cumulate identified a glomerocryst population with cluster sizes in the range of 0 3 2 5 mm and also a variation of cluster patterns up through the cumulate pile the clhca of a polymodal texture from a pyroxene scapolite sphene granulite indicated a clustered distribution for the sphene which was restricted in growth pattern by the pyroxene and scapolite in the texture dlca computes a single solution of clusters that conforms to the search criteria input into the algorithm dlca performed poorly when used to identify distributions of large randomly packed clusters of small spheres mainly identifying smaller cluster patterns within each large cluster application of dlca to the komatiite cumulate example indicated cluster lengths of 0 72 0 80 mm similar to the clhca results and an average aspect ratio of 1 52

comparison of ground based 3 dimensional lightning mapping observations with satellite based lis observations in oklahoma 3 dimensional lightning mapping observations obtained in central oklahoma by the new mexico tech lightning mapping array lma have been compared with optical observations of the discharges from space obtained by nasa s lightning imaging sensor lis excellent spatial and temporal correlations were obtained between the two sets of observations all lightning discharges seen by lis were mapped by the lma most of the detected optical events were associated with lightning channels that extended into the upper part of the storm cloud to ground discharges that were confined to mid and lower altitudes were less well detected than intracloud discharges and tended to be detected late in the discharge intracloud discharges were readily detected by lis as soon as they extended into the upper part of the storm and often extensively illuminated the cloud at the end or part way through the discharge the extensive illumination was impulsive in nature and was also seen at the end of some cloud to ground discharges

extent of chondrule melting evaluation of experimental textures nominal grain size and convolution index dynamic crystallization experiments on the ordinary chondrite queen alexandra range que 97008 document textural features that occur in partially melted chondrules with changes in the degree of partial melting and cooling rate we carried out a matrix of experiments at peak temperatures of 1250 1350 1370 and 1450 c and cooling rates of 1000 100 and 10 c h and quenched all experimentally produced textures closely resemble textures of porphyritic chondrules because peak temperatures were well below the liquidi for typical chondrule compositions the textural similarities support an incomplete melting origin for most porphyritic chondrules our experiments can be used to determine the extent of melting of natural chondrules by comparing textural relationships among the experimental results with those of natural chondrules we used our experiments along with x ray computerized tomography scans of a semarkona chondrule to evaluate two other methods that have been used previously to quantify the degree of melting nominal grain size and convolution index proper applications of these methods can result in valid assessments of a chondrule s degree of melting but only if accompanied by careful interpretation as chondrule textures are controlled by more than just the extent of melting such measurements of single aspects of chondrule textures might be coupled with qualitative analysis of other textural aspects to accurately determine degree of melting

multiple reinjections and crystal mush compaction in the beacon sill mcmurdo dry valleys antarctica the beacon sill a member of the jurassic ferrar group of the transantarctic mountains south victoria land is a 150 m thick tholeiitic diabase intrusion uniform on a field and macroscopic scale it displays chemical and textural variability indicative of a sustained and complex history of emplacement and differentiation emplacement of the sill consisted of at least two and probably four discrete massive injections of magma each averaging 35 m thick over a time span of 100 years the final injection event is marked by a 30 m thick interval of significantly finer grained rock at the sill center these fine grained textures can be successfully reproduced by combining the results of thermal and crystal growth models but only if the sill was a multiple intrusion with the exception of a minor reinjection event captured in the chilled margin of the sill earlier reinjection events are not evident texturally most probably because of textural overprinting during prolonged cooling after initial crystallization the dominant process involved in the postemplacement differentiation of the beacon sill was compactiondriven redistribution of interstitial liquid transfer of residual liquid from the compacting lower solidification front to the dilating upper solidification front resulted in characteristic chemical and mineralogical effects such as the depletion of the lower half of the sill and the enrichment of the upper half of the sill in incompatible elements e g tio2 zr and modal granophyre based on thermodynamic models most of the compaction occurred at a crystallinity of roughly 33 geochemical profiles are distinctly segmented suggesting that the sill was repeatedly split and reinjected with fresh magma near the center after compaction had redistributed the interstitial liquid within the partially solidified magma the recognition of evidence for reinjection and compaction in a macroscopically uniform relatively quickly cooled sill suggests that these processes may be common in the construction of sills and other mesoscale igneous intrusions in general

constrains on the origin and history of the eastern mediterranean basin abstract the basin formed along the northern passive margin of gondwanaland as a relict of the mesozoic neotethys in early mesozoic time though direct information from the basin itself is meagre the geology of its passive margins and the regional framework of the tethys evolution constrain the formation and history of the basin the eastern mediterranean and its passive margins are interpreted to have formed as a result of several faulting and continental breakup phases from early permian to middle jurassic times before pangaea s complete disintegration this led to the detachment of the eratosthenes and tauride blocks from the margins of the levant and herodotus basins respectively the latter merged in the northeast with the cyprus basin that extended along arabia s northern margin the main rifting probably occurred in the triassic leading to seafloor spreading in the herodotus and cyprus basins while along the levant margin important rifting also occurred in the jurassic during the initial rifting stages extension perpendicular to the levant margin was important but subsequently the tauride block drifted mainly northward the existence of the passive margins and slopes of the eastern mediterranean is documented at least from the end of the middle jurassic until then the basin was probably narrow 200 300 km but during the main phase of the africa laurasia separation it grew to twice its present width or more this scenario depends critically on the interpretation that the tauride block was originally located next to northeastern africa on the western side of the eratosthenes block plate convergence and consumption of the northern portion of the basin have taken place since mid cretaceous times but the active convergent boundary on its northern side formed only in the neogene by modification of earlier structures some intra plate deformation also took place especially in the neogene but it hardly changed the original configuration of the remaining portion of the basin