magma storage and ascent at lipari island aeolian archipelago southern italy at 223 81 ka the role of crustal processes and tectonic influence fluid inclusion studies together with volcanological and petrochemical data allow reconstruction of the magma feeding system of basaltic andesitic to andesitic activity during the oldest and intermediate stages of development of lipari island 223 81 ka a major magma storage zone is active during the overall investigated time span at depths of 22 km close to the crust mantle moho transition at which mantle derived mafic magmas tend to accumulate due to neutral buoyancy conditions beneath central type volcanoes m mazzacaruso m s angelo m chirica costa d agosto a shallower magma reservoir is located within the upper crust at 5 5 3 5 km associated with a major lithological discontinuity for fissural type volcanoes timpone ospedale monterosa m chirica tectonic structures are suggested to influence further magma ascent and storage at mid crustal depths 14 km with no ponding at shallower levels partial crustal melting processes at the roofs of the deep magma reservoirs 17 km are invoked to explain the origin of cordierite bearing lavas beneath m s angelo and m chirica costa d agosto volcanoes which were active during the intermediate stages of development of lipari 105 81 ka the generation of felsic anatectic melts in the lower crust could have created density and rheologic barriers to impede the passage of mafic melts and promote their ponding with influence on the subsequent evolution of lipari volcano

a seismic study of lithospheric flexure in the vicinity of tenerife canary islands seismic data have been used to determine the crustal and upper mantle structure of tenerife canary islands a volcanic island of tertiary age located on 140 ma oceanic crust reflection data show that oceanic basement dips gently towards the island forming a flexural moat which is infilled by 2 3 km of well stratified material the moat is characterised by a major angular unconformity which we attribute to volcanic loading of pre existing oceanic crust and overlying sediments and the subsequent infilling of the flexure by material that was derived at least in part from the islands refraction data show that the flexed oceanic crust has a mean thickness of 6 41 0 42 km and upper and lower crustal velocities of 4 8 5 4 km s 1 and 6 7 7 3 km s 1 respectively the flexure which has been verified by gravity modelling can be explained by a model in which tenerife and adjacent islands have loaded a lithosphere with a long term 106 yr elastic thickness of approximately 20 km seismic and gravity data suggest that up to 1 5 105 km3 of magmatic material has been added to the surface of the flexed oceanic crust which assuming an age of 6 16 ma for the shield building stage on tenerife implies a magma generation rate of about 0 006 to 0 02 km3 a 1 this rate is similar to estimates from other african oceanic islands e g reunion and cape verdes but is significantly less than that which has been calculated at hawaii there is no evidence in either the seismic or gravity data that any significant amount of magmatic material has underplated the flexed oceanic crust the crustal and upper mantle structure at tenerife therefore differs from other oceanic islands such as hawaii and marquesas where 4 km of underplated material have been reported

s rich apatite hosted glass inclusions in xenoliths from la palma constraints on the volatile partitioning in evolved alkaline magmas the composition of s rich apatite of volatile rich glass inclusions in apatite and of interstitial glasses in alkaline xenoliths from the 1949 basanite eruption in la palma has been investigated to constrain the partitioning of volatiles between apatite and alkali rich melts the xenoliths are interpreted as cumulates from alkaline la palma magmas apatite contains up to 0 89 wt so3 3560 ppm s 0 31 wt cl and 0 66 wt ce2o3 sulfur is incorporated in apatite via several independent exchange reactions involving p5 ca2 vs s6 si4 na and ce3 the concentration of halogens in phonolitic to trachytic glasses ranges from 0 15 to 0 44 wt for cl and from 0 2 wt so3 dsapatite glass is only slightly dependent on the melt composition and can be expressed as so3 apatite wt 0 157 ln so3 glass wt 0 9834 the phonolitic compositions of glass inclusions in amphibole and hauyne are very similar to evolved melts erupted on la palma the lower sulfur content and the higher cl content in the phonolitic melt compared to basaltic magmas erupted in la palma suggest that during magma evolution the crystallization of hauyne and pyrrhotite probably buffered the sulfur content of the melt whereas the evolution of cl concentration reflects an incompatible behavior trachytic compositions similar to those of the water rich glass inclusions analyzed in apatite and clinopyroxene are not found as erupted products these compositions are interpreted to be formed by the reaction between water rich phonolitic melt and peridotite wall rock

unrest signals after 46 years of quiescence at cumbre vieja la palma canary islands abstract monogenetic eruptions are the most common volcanic activity in the world however unrest monitoring data are scarce due to the long intervening quiescence periods this study analyzes unrest signals recorded in one of the largest monogenetic fields in the canary islands cumbre vieja la palma two seismic swarms were registered in october 2017 and february 2018 with b values of 1 6 0 1 and 2 3 0 2 respectively suggesting an intense magmatic fluids contribution gas and or magma both swarms were linked to changes in gas emissions increases in hydrogen concentration and r ra c up to 7 52 0 05 were recorded before the first swarm at the sampling point closest to where seismicity was located indicating a deep gas input after the second swarm increases in r ra c and thoron soil concentration were recorded at two locations this dataset is compatible with a stalled magmatic intrusion at ca 25 km depth with an estimated volume between 5 5 10 4 km3 and 3 10 2 km3

deep volcanic morphology below lanzarote canaries from gravity inversion new results for timanfaya and implications abstract the deep roots of oceanic island volcanoes are poorly known and geophysical models can help to constrain processes such as magma storage and transport before and during eruptions lanzarote canary islands is a volcanic island in post erosional phase where in the 18th century one of the most important historical eruptions considering duration and volume of the canary islands took place in the timanfaya area to improve the knowledge on the structure of lanzarote and in timanfaya area we carry out a gravity determination of the subsurface anomalous 3d density structure using an improved quasi automatic inversion methodology the obtained model presents a 3d morphology of anomalous density bodies we describe the improvements of the inversion methodology the adjusted model and interpretative conclusions corresponding to the structure and the long term cumulative magmatic plumbing system of the island three high density sources are described as resulting in the inference of three main volcanic complexes a large central complex san bartolome and two smaller complexes one in the ne and a third smaller one located in the sw close to the timanfaya area the outcrops of miocene lava flows from the center of the island can be attributed to the top of the central intrusive model we infer the local plumbing system for timanfaya volcano area by means of strongly tilted successive branches of magma departing from the sw intrusive body the structural results show no evidence of any magma chamber below timanfaya as proposed by previous works we also present a comparison of the gravity results and geological observations showing different cases of correlation in the island they go from a good match between the gravity anomaly and the position of the central volcanic structure to no anomaly associated to the fissural quaternary volcanic activity

changing depths of magma fractionation and stagnation during the evolution of an oceanic island volcano la palma canary islands la palma canary islands represents an oceanic island volcano with an active rift zone inferred to have formed during the last 800 ka following southward growth of the former radial symmetrical stratovolcano taburiente we carried out clinopyroxene melt thermobarometry and microthermometry of fluid inclusions to reconstruct the evolution of the magma plumbing systems over time and to understand the genetic relationship between taburiente and the presently active cumbre vieja rift zone clinopyroxene melt equilibria of phenocryst rims and glassy groundmass indicate pressures of 0 60 1 04 gpa 19 34 km depth for taburiente 0 47 1 17 gpa 16 40 km for the former cumbre nueva rift arm of taburiente and 0 50 0 78 gpa 16 26 km for bejenado volcano that formed after collapse of the cumbre nueva rift these pressures are interpreted to reflect depths of magma storage and major crystal fractionation co2 dominated fluid inclusions hosted by clinopyroxenes and olivines indicate pressures of formation or re equilibration within an overall range of 0 25 0 61 gpa 8 19 km depth respective frequency maxima are at 0 41 0 50 gpa for taburiente dunite xenoliths 0 26 0 43 gpa for cumbre nueva ankaramites and 0 26 0 32 gpa for bejenado cumulate xenoliths these pressures are interpreted to reflect levels of temporary magma stagnation during ascent our data show that the magma pathways during all volcanic phases including the presently active cumbre vieja rift klugel a hansteen t h galipp k 2005 magma storage and underplating beneath cumbre vieja volcano la palma canary islands earth and planetary science letters 236 211 226 are characterized by two distinct storage levels a system of prolonged storage within the upper mantle and a system of short term stagnation within the lower crust or near to the moho both the mantle and crustal storage systems show a migration to shallower levels from 1 0 ma to present probably as a result of changing thermomechanical properties of the mantle and crust and possibly stoping our combined barometric data and field observations suggest that the extinct taburiente cumbre nueva and the active cumbre vieja represent two distinct volcanoes with separate magma plumbing systems in this case the present rift configuration does not reflect continuous growth of the taburiente shield volcano during the last 800 ka none of the la palma volcanoes shows any indicators of a long lived shallow magma reservoir where magmas fractionate and from which rift zones emanate which is an important difference to hawaiian shield volcanoes characterized by shallow subcaldera magma chambers

melt mineral fluid interactions in ultramafic nodules from alkaline lavas of mount etna sicily italy melt and fluid inclusion evidence abstract clinopyroxene phenocrysts and ultramafic nodules in the ancient alkaline lavas of mount etna contain melt and fluid inclusions which represent immiscible trapping of basaltic melt and co2 inclusions consist of glass vapor co2 hosted by clinopyroxene with kaersutite magnetite spinel and apatite daughter minerals type i and liquid co2 vapor co2 glass secondary inclusions type ii with highly variable fluid glass ratios electron microprobe investigations on type i melt inclusions indicate a glass of trachitic composition with extremely high chlorine contents 0 5 1 wt which we believe evolved from an initial melt composition of an alkali basalt homogenization temperatures th n 128 of type ii co2 glass inclusions display a bimodal fluid density distribution with high density 0 61 0 75 g cm3 co2 fluids in the nodules and low density 0 23 0 61 g cm3 co2 fluids in the phenocrysts a two step degassing process is proposed with high density immiscible co2 fluids formed at pressures of about 4 3 kbar the density distribution suggests interaction events between nodules ascending lavas and fluid phases with a peak around 3 5 kbar a second generation of lower density co2 is recorded around 2 8 kbar most likely prior to eruption

effect of shallow level contamination on the helium isotope systematics of ocean island lavas the bimodal distribution of helium isotope ratios in ocean island lavas has provided powerful constraints on the composition and evolution of the earth s mantle1 3 high 3he hotspot ratios 3he 4he greater than in mid ocean ridge basalt morb found on hawaii4 and iceland5 are thought to trace pristine plumes from the deep er mantle whereas low 3he hotspot values 3he 3he morb value at tristan da cunha6 and st helena7 are considered to characterize plumes composed in part of recycled oceanic or continental crust here we report the observation of both high 3he and 6low 3he characteristics8 in lavas from a single ocean island heard island in the indian ocean whereas the high 3he lavas provide unambiguous evidence for the involvement of a deep seated plume in their genesis we argue that the low 3he 4he ratios in other lavas result from shallow level contamination by radiogenic helium before eruption these observations call into question the presumed association between low 3he ratios at heard island and elsewhere and ancient crustal material recycled back into the mantle

re equilibration of glass and co2 inclusions in xenolith olivine a tem study co 2 rich fluid inclusions were observed in olivine from mantle xenoliths from the island of tenerife canary islands inclusions that are present in deformed olivine porphyroclasts consist of co 2 fluids minor high alkali silica rich glass ni fe sulfides homogenization temperature distributions reveal that most of the inclusions originally trapped at mantle conditions re equilibrated to lower density values transmission electron microscope tem studies indicate that most fluid inclusions appear as perfectly euhedral negative crystals with variable shape from prismatic to equant size from 2 diffusion consequently they should be taken into account for the correct interpretation of microthermometric results

emplacement of a xenolith rich sill lajitas texas abstract a 2 15 m thick hawaiite sill in the cretaceous boquillas formation west of the big bend national park texas locally contains a zone 1 12 m thick containing 25 vol xenoliths the inclusions ranging in size from 2 cm to 1 m are dominated by cumulate gabbros and white quartzite the mafic inclusions broke from the sidewall cumulates in a reservoir that fed the hawaiite sill many xenoliths show contacts between quartzite and igneous rock marked by clinopyroxene crystals perpendicular to the contacts the quartzite xenoliths are permeated variably by quenched mafic liquid now devitrified glass with plagioclase clinopyroxene smectite and some quartz grains are fringed by inverted tridymite stratigraphic reconstruction indicates that the sill was emplaced at a depth shallower than 0 5 km but the source of the paleozoic quartzite and sidewall cumulate xenoliths was at least 1 km below the sill the high concentration of xenoliths their lack of imbrication orientation or sorting the preservation of unbroken thin slabs of limestone and the absence of xenoliths at the top and bottom of the sill all support emplacement by plug flow of xenolith charged magma in the center lubricated by less viscous xenolith free magma at the margins crystal size distribution of plagioclase indicates that mean crystal residence time for cumulates was about 75 years and crystallization time at the aphyric upper margin of the sill was about 2 years

a general numerical model for surface waves generated by granular material intruding into a water body abstract surface water waves generated by large scale landslides have been a major concern of many geoscientists and coastal engineers because they may result in disastrous consequences this study presents an advanced two phase model for dry granular material intruding into an otherwise still water body as well as their resulting waves the water air interface both within and outside the granular material is captured by the volume of fluid method the inter granular stresses are formulated based on a general collisional frictional law developed for underwater granular flows and a modified k e model is adopted to describe the turbulence effect of the ambient fluid phase interaction is characterized by the drag force caused by the relative motion between the granular particles and the fluid the effect of the ambient fluid on the restitution coefficient of granular particles is also considered the newly proposed two phase model is validated following a reasonable agreement of the numerical results with measured data from small scale laboratory tests on surface waves caused by collapse of a subaerial granular column and by intrusion of a landslide into water generation and propagation of the waves as well as the motion and deformation of the granular body are all adequately represented by the numerical model a relatively more general applicability of the proposed model to the study of waves generated by granular landslides can thus be expected

the effects of flank collapses on volcano plumbing systems the growth of large volcanoes is commonly interrupted by episodes of flank collapse that may be accompanied by catastrophic debris avalanches explosive eruptions and tsunamis el hierro the youngest island of the canary archipelago has been repeatedly affected by such mass wasting events in the last 1 ma our field observations and petrological data suggest that the largest and most recent of these flank collapses the el golfo landslide likely influenced the magma plumbing system of the island leading to the eruption of higher proportions of denser and less evolved magmas the results of our numerical simulations indicate that the el golfo landslide generated pressure changes exceeding 1 mpa down to upper mantle depths with local amplification in the surroundings and within the modeled magma plumbing system stress perturbations of that order might drastically alter feeding system processes such as degassing transport differentiation and mixing of magma batches

deep intrusions lateral magma transport and related uplift at ocean island volcanoes abstract oceanic intraplate volcanoes grow by accumulation of erupted material as well as by coeval or discrete magmatic intrusions dykes and other intrusive bodies within volcanic edifices are comparatively well studied but intrusive processes deep beneath the volcanoes remain elusive although there is geological evidence for deep magmatic intrusions contributing to volcano growth through uplift this has rarely been demonstrated by real time monitoring here we use geophysical and petrological data from el hierro canary islands to show that intrusions from the mantle and subhorizontal transport of magma within the oceanic crust result in rapid endogenous island growth seismicity and ground deformation associated with a submarine eruption in 2011 2012 reveal deep subhorizontal intrusive sheets sills which have caused island scale uplift of tens of centimetres the pre eruptive intrusions migrated 15 20 km laterally within the lower oceanic crust opening pathways that were subsequently used by the erupted magmas to ascend from the mantle to the surface during six post eruptive episodes between 2012 and 2014 further sill intrusions into the lower crust and upper mantle have caused magma to migrate up to 20 km laterally resulting in magma accumulation exceeding that of the pre eruptive phase a comparison of geobarometric data for the 2011 2012 el hierro eruption with data for other atlantic intraplate volcanoes shows similar bimodal pressure distributions suggesting that eruptive phases are commonly accompanied by deep intrusions of sills and lateral magma transport these processes add significant material to the oceanic crust cause uplift and are thus fundamentally important for the growth and evolution of volcanic islands we suggest that the development of such a magma accumulation zone in the lower oceanic crust begins early during volcano evolution and is a consequence of increasing size and complexity of the mantle reservoir system and potentially the lithospheric stresses imposed by increasing edifice load

features of crustal structure under the canary islands abstract the data and interpretation of a seismic refraction project carried out in the canary islands in 1977 and 1979 are presented the moho is reached at about 15 km under fuerteventura gran canaria and tenerife whereas under lanzarote a value of 11 km has been found the velocity at the surface varies even within one island from 2 8 to 4 4 km s there are variations in the velocity of the main crustal layer under the volcanic deposits a continuous velocity depth function seems to be more appropriate for the island of tenerife contrary to fuerteventura lanzarote and gran canaria which seem to have a layered structure there is evidence for pronounced structural differences between lanzarote and fuerteventura the mantle velocity has a value of about 8 0 km s under the western islands whereas a very low value of 7 4 km s has been found under lanzarote and fuerteventura despite the clear structural differences between the islands our results leave little doubt about the oceanic character of all the islands the differences between the eastern and western group may be due to the islands being situated close to the african continental margin the seismic velocities under the volcanic deposits do not support the idea of a common basement for all the islands they rather suggest independent volcanic edifices finally a comparison of the structure of the crust under the canary islands with that under other volcanic islands reveals remarkable similarities

thermal model of successive dike injections and implications for the development of intraplate volcanoes abstract temperatures in the root zones of volcanoes play a critical role in the development and persistence of shallow level magmatic reservoirs in the crust here we present a 1d thermal model allowing evaluation of the thermal impact of magma travelling in conduits to the surface on the root zone of a volcano this thermal model has been developed to better understand the formation of a vertical intrusion located in the root zone of a dismembered miocene volcano on fuerteventura canary archipelago this intrusion named px1 constitutes an almost pure amalgamation of dikes of either clinopyroxenitic or gabbroic composition both types of dikes display cumulate textures and are interpreted as resulting from the protracted crystallization of a mafic magma the formation of clinopyroxenitic in contrast to gabbroic dikes requires that the residual melt was extracted at high temperature 1050 to avoid plagioclase crystallization simulations of multiple dike injections show that the temperature in the root zone increases significantly with the addition of dikes but the maximum temperature reached in the system depends on the duration of magma flow in the conduits and the time interval between dike injections i e repose period active flow is the critical parameter that distinguishes instantaneous dike injection from a magmatic conduit without significant magma flow 1 month high temperature conditions 1000 c cannot be maintained in the pluton unless dikes are very thick and the repose period is extremely small on the other hand magma flow times of one to several months combined with short time intervals between dike injections persistent high temperature in the vicinity of magma conduits limits the differentiation of melts in transit to the surface providing a potential explanation for why lavas of mafic to intermediate composition predominate in intraplate volcanoes such as fuerteventura or fogo island cape verde archipelago in extreme cases when temperatures over 1000 1050 c in the central part of the feeding zone are maintained for years the remaining magma in the conduit does not solidify but is preserved in a mushy state new pulses of magma would not be able to cross this zone but would rather amalgamate in the incipient magma reservoir the present model differs from previous models of sill intrusion in that magmas do not need to pond at depth to create a reservoir but merely supply heat while travelling to the surface depending on the time interval between dike injections and the duration of magma flow through the crust magma rising in vertical conduits could directly feed the volcanic edifice or could lead to the formation of magma reservoirs this process may explain why some volcanoes erupt mafic or differentiated magmas during distinct periods of activity

magma evolution of the sete cidades volcano sao miguel azores the sete cidades volcano sao miguel azores is situated at the eastern end of the ultraslow spreading terceira rift axis the volcano comprises several dominantly basaltic pre caldera eruptions a trachytic caldera forming stage and a post caldera stage consisting of alternating trachytic and basaltic eruptions the post caldera flank lavas are more primitive 5 wt mgo than the pre caldera lavas implying extended fractional crystallization and longer crustal residence times for the pre caldera shield building lavas thermobarometric estimates show that the ascending alkali basaltic magmas stagnated and crystallized at the crust mantle boundary similar to 15 km depth whereas the more evolved magmas mainly fractionated in the upper crust similar to 3 km depth the caldera forming eruption was triggered by a basaltic injection into a shallow trachytic magma chamber lavas from all stages follow a single continuous liquid line of descent from alkali basalt to trachyte although slight differences in incompatible element e g ba nb la nb and sr isotope ratios imply some heterogeneity of the mantle source major and trace element data suggest similar partial melting processes throughout the evolution of the volcano slight geochemical differences between post and pre caldera stage lavas from the sete cidades volcanic system indicate a variation in the mantle source composition with time the oxygen fugacity increased from the pre caldera to the post caldera stage lavas probably as a result of the assimilation of crustal rocks this is supported by the presence of crustal xenoliths in the lavas of the flank vents the lavas from the sete cidades volcano generally have low sr isotope ratios however rocks from one post caldera vent on the western flank indicate mixing with magmas resembling the lavas from the neighbouring agua de pau volcano having higher sr isotope ratios the different magma sources at sete cidades and the adjacent agua de pau volcano imply that despite their close proximity there is only limited interaction between them

olivine clinopyroxenite xenoliths in the oslo rift se norway olivine clinopyroxenite xenoliths in a basalt flow at krokskogen in the oslo rift consist mainly of al ti rich clinopyroxene and alteration products after olivine possibly also orthopyroxene the clinopyroxene contains primary inclusions of cr al bearing titanomagnetite pyrite and devitrified glass and secondary fluid inclusions rich in co2 on the basis of petrography mineral compositions and bulk major and trace element chemistry it is concluded that the xenoliths represent cumulates with about 5 trapped liquid formed from a mildly alkaline basaltic magma microthermometrical analysis of secondary or pseudosecondary fluid inclusions give a minimum pressure of formation of 5 5 to 6 kbars that is a depth greater than 16 17 km the host lava has initial nd 4 16 0 17 and sr 5 50 0 26 which is believed to reflect the isotopic composition of the lithospheric mantle source region under south norway in early permian time the isotopic character of the magma which gave rise to the xenoliths is preserved in clinopyroxenes which have ndt 1 9 to 2 6 and srt 1 1 to 1 8 the isotopic differences between the host magma and the xenoliths reflect some degree of crustal contamination of the xenolith s parent magma

barometry of lavas from the 1951 eruption of fogo cape verde islands implications for historic and prehistoric magma plumbing systems fogo is one of the most active oceanic volcanoes in the world the island was affected by a prehistoric giant lateral collapse that decapitated the summit of the former monte amarelo volcano subsequent volcanism has partly filled the collapse scar and built up the present day cha das caldeiras plain and the pico do fogo stratovolcano we have conducted a thermobarometric study of historic and prehistoric basanitic to tephritic rocks in order to gain insight into fogo s magma plumbing system and the impact of the collapse event on fractionation depths a main focus was the penultimate 1951 eruption which produced basanites to tephrites 5 0 8 2 wt mgo at two sites south and northwest of pico do fogo clinopyroxene melt barometry of phenocrysts yields a well confined pressure range of 480 650 mpa for the final crystallization level microthermometric data of co2 dominated fluid inclusions in olivine and clinopyroxene phenocrysts yield systematically lower pressures of 250 430 mpa inclusions in cumulate xenoliths yield pressures of 100 290 mpa the combined data indicate pre eruptive magma storage in the uppermost mantle between 17 and 22 km depth and syn eruptive short term magma stalling within the lower crust at 8 13 km depth the lower pressures revealed by fluid inclusions in xenoliths may indicate that they originate from pre 1951 magma pulses that stalled and crystallized at variable levels in the crust there is however no petrologic evidence for persistent crustal magma chambers clinopyroxene melt barometric data of other historic and prehistoric eruptions indicate that magma storage and differentiation occurred in the uppermost mantle at pressures between 420 and 870 mpa 15 30 km depth throughout the subaerial evolution of fogo our data indicate that fractionation depths decreased significantly during a period of about 100 ka representing a strong growth phase of fogo edifice leading up to the giant monte amarelo flank collapse at 123 62 ka this trend seems to have been interrupted by the flank collapse as early post collapse magmas stagnated at deeper levels than late pre collapse ones historic eruptions show shallower and broader pressure ranges indicating an increase in complexity of the magma storage systems thus petrologic data indicate that flank collapse events may significantly influence deep seated magma plumbing systems beneath ocean islands

a giant landslide on the north flank of tenerife canary islands the extent of mass wasting along the north flank of tenerife has been mapped using swath bathymetry gloria side scan sonar and 3 5 khz echo sounder data the marine surveys show that north of tenerife a giant landslide is exposed over an area of 5500 km2 of the seafloor more than twice the surface area of the island the landslide truncates an older ridge and valley topography that is associated with the shield building basalts on tenerife we interpret the ridge and valley topography as the result of subaerial erosion the landslide is estimated to have a length of 100 km a width of up to 80 km and a volume of about 1000 km3 it extends onshore into the orotava and icod valleys which have been interpreted as of landslide origin k ar dating of basaltic flows in the steep headwall of orotava suggests an age of formation for the valley is younger than 0 78 ma and may even be younger than 0 27 ma the icod valley is located immediately to the north of the most recent volcano on tenerife las canadas and has been associated with the collapse of its caldera between 1 2 and 0 2 ma a young age for the landslide is supported by the 3 5 khz echo sounder data which show that the landslide is draped by a thin 10 m layer of younger sediment the landslide did not form however during a single catastrophic event but represents the amalgamation of a number of separate landslides the occurrence of the ridge and valley topography in water depths of up to 2 5 km suggests that the shield building basalts have subsided by at least this amount since they formed 3 3 8 0 ma we speculate that this subsidence is caused by some form of stress relaxation that occurs in the underlying lithosphere the giant landslide imaged in our sonar data is associated with the late stages in the development of the most recent volcano on tenerife las canadas which only began at about 1 8 ma thus landsliding may be a particular feature of the time soon after emplacement when because of incomplete isostatic adjustment oceanic volcanoes have their greatest elevations above sea level and therefore are most susceptible to slope failure

crustal structure flexure and subsidence history of the hawaiian islands seismic reflection profile data have been used to estimate the long term 106 years mechanical properties of the oceanic lithosphere underlying the hawaiian islands the data show prominent reflectors associated with the top of the oceanic crust reflector 2 the m discontinuity and the base of the crust reflector 3 the two way travel time to the reflectors has been depth converted using velocity depth functions derived from seismic refraction expanding spread profile data and compared to calculated depths based on simple three dimensional elastic plate models a good fit to the reflector depths was obtained for a model with an effective elastic thickness of the lithosphere te of 40 km the main discrepancies with the refraction data occur beneath oahu and molokai where the predicted depth of the base of the flexed crust is too shallow and beneath the southeast flank of hawaii where it is too deep we attribute the thickened crust beneath oahu to ponding of magma at the base of the crust following the last phases of tholeiitic shield building and the thinned crust beneath the flanks of hawaii to crustal melting beneath the youngest part of the chain the effective te of 40 km is higher than expected for 80 m y oceanic lithosphere possibly due to the effects of subsurface loads that act at or near the base of the flexed crust according to free air gravity anomaly and bathymetry data te does not change significantly along the island chain retaining a similar value for hawaii as it does for oahu we have used this result to estimate the pattern of subsidence and uplift that would be expected along the hawaiian islands because of flexural loading of hawaii the observed depth of the haleakala wave cut terrace northeast of maui can be generally explained by the flexure model the main discrepancies between observed and the predicted depths occur northwest of hawaii where they suggest a somewhat higher value of te possibly due to incomplete adjustment of the lithosphere we suggest that the addition of loads to the end of a volcanic chain generated as a plate moves over a mantle hotspot is accommodated by progressive flexing downstream causing subsidence of preexisting volcanos that lie in the flexural moat and uplift of islands on the flanking bulge the progressive flexure model predicts a characteristic pattern of offlap and onlap in the regions flanking the hawaiian islands that is generally similar to stratigraphic relationships observed along previously published seismic profiles of the moat a progressive flexure model may also apply to the case of a continental plate moving over a mantle hotspot and could explain the observations of 1 a clinoform pattern of stratigraphy in some flood basalt provinces and 2 a seaward dipping reflector sequence at some passive continental margins

the chemically zoned 1949 eruption on la palma canary islands petrologic evolution and magma supply dynamics of a rift zone eruption the 1949 rift zone eruption along the cumbre vieja ridge on la palma involved three eruptive centers 3 km spaced apart and was chemically and mineralogically zoned duraznero crater erupted tephrite for 14 days and shut down upon the opening of llano del banco a fissure that issued first tephrite and after 3 days basanite hoyo negro crater opened 4 days later and erupted basanite tephrite and phonotephrite while llano del banco continued to issue basanite the eruption ended with duraznero erupting basanite with abundant crustal and mantle xenoliths the tephrites and basanites from duraznero and llano del banco show narrow compositional ranges and define a bimodal suite each batch ascended and evolved separately without significant intermixing as did the hoyo negro basanite which formed at lower degrees of melting the magmas fractionated clinopyroxene olivine kaersutite ti magnetite at 600 800 mpa and possibly 800 1100 mpa abundant reversely zoned phenocrysts reflect mixing with evolved melts at mantle depths probably as early as 1936 hoyo negro basanite entered the deep rift system at 200 350 mpa some shallower pockets of this basanite evolved to phonotephrite through differentiation and assimilation of wall rock a few months prior to eruption a mixing event in the mantle may have triggered the final ascent of the magmas most of the erupted tephrite and basanite ascended from mantle depths within hours to days without prolonged storage in crustal reservoirs the cumbre vieja rift zone differs from the rift zones of kilauea volcano hawaii in lacking a summit caldera or a summit reservoir feeding the rift system and in being smaller and less active with most of the rift magma solidifying between eruptions

the pliocene seamount series of la palma canary islands a pliocene submarine series of alkali basaltic pillow lavas hyaloclastites and breccias a a sheeted dike swarm b and a basal suite of gabbro and ultramafic rocks c from la palma canary islands is interpreted as a cross section through an uplifted seamount this series has been tilted to its present orientation of 50 230 plunge and azimuth probably by upwarping due to intrusions in the central portion of the island the basal plutonic complex c also includes intrusives coeval with up to 2000 m of younger subaerial alkali basaltic lavas unconformably overlying the submarine series the plutonic suite c is overlain abruptly by more than 1800 m of sills b 0 4 1 m thick on average with minor screens of lavas and breccias extrusives a form a 1750 m thick sequence of pillow lavas breccias and hyaloclastites the clastic rocks increase in abundance upward and are of four main types 1 breccias consisting of partly broken pillows formed nearly in situ 2 heterolithologic pillow fragment breccias 3 hyaloclastites composed dominantly of highly vesicular lapilli and ash sized shards the latter thought to have formed by near surface explosive eruptions and been subsequently transported downslope by mass flows 2 and 3 being interpreted to have been resedimented and 4 pillow scoria breccias from the upper 700 m of the extrusive section consisting of amoeboidal highly vesicular pillows and lava stringers and local bombs probably formed by cracking and bleeding of gas rich expanding pillow lava and some shallow submarine subaerial lava fountaining the extrusive series is chemically and mineralogically crudely zoned with the most differentiated rocks metatrachytes and mugearites at the base and most picritic lavas occurring near the top of the series subsequent to emplacement the entire extrusive and intrusive series has been hydrothermally altered the lower part to greenschist and the upper part to smectite zeolite facies mineral assemblages the la palma succession combined with evidence from surface studies of seamounts suggests that seamounts are formed by intrusive and extrusive processes in approximately equal portions the nature of eruptive clastic and depositional mechanisms changes drastically during growth of a seamount if the critical depth for major magmatic degassing is surpassed and especially if magmatic explosive processes can occur at very shallow water depth the critical depth depending on magma and thus volatile composition changes in slopes of a seamount influence depositional processes based on these factors at least three major depositional sites develop as a seamount grows summit flank and apron facies nonexplosive extrusive processes prevail in the deep water stage dominantly producing pillow lavas 75 these consist of individual pillow volcanoes up to 200 m high with large pillows near the base and decreasing pillow size toward the top of a volcano pillow breccias and pillow fragment breccias comprise approximately 20 of this facies the deep water flank and apron facies are characterized by debris flow deposits with possibjy rather dense matrix material the shallow water shoaling stage is reached when the seamount top reaches the critical depth for drastic increase in exsolution of magmatic volatiles about 800 m for the alkali basaltic seamount of la palma resulting in formation of mainly clastic rocks 70 in situ pillow rind breccias and scoriaceous amoeboidal breccias and pillows are formed in the summit regions of the seamount by repeated expansion and leaking of frothy pillow lava possibly by lava fountaining resedimented heterolithologic pillow fragment breccias lapilli breccias and hyaloclastites are deposited on the flanks and aprons of the seamount pillow lavas comprise 30 of these deposits

the role of density in the accumulation of basaltic melts at mid ocean ridges it is commonly assumed that magma ponds at a level of neutral buoyancy in the shallow crust where melt densities are equal to the bulk density of the surrounding crust at the east pacific rise this neutral buoyancy level lies only 100 400 m below the sea floor significantly shallower than the depths 1 2 km of the magma bodies imaged in multichannel reflection data suggesting that other factors must control the collection of melt in these reservoirs the apparent inverse relationship between magma chamber depth and spreading rate at intermediate and fast spreading ridges suggests that the thermal structure of the rise axis not the buoyancy of melt is the primary factor that controls the depth at which melt ponds in crustal magma chambers beneath mid ocean ridges

reflection seismic investigations in the volcaniclastic apron of gran canaria and implications for its volcanic evolution high resolution reflection seismic data obtained around gran canaria allow a detailed and consistent correlation of seismic reflectors of the northern and southern canary basins with the lithology drilled by dsdp leg 47a sse of gran canaria as well as with major phases of volcanic activity on gran canaria as mapped onshore two prominent reflectors were chosen as marker horizons and correlated with the drilled lithology the results indicate that reflector r7 above the miocene volcaniclastic debris flows v1 v3 reflects the shield building phase of gran canaria reflector r3 is interpreted as corresponding with the pliocene roque nublo formation the top of the massive island flank of gran canaria defined by seismically chaotic facies extends 44 to 72 km off the coast of gran canaria west of gran canaria the flank of tenerife onlaps the steeper and older flank of gran canaria which in turn is onlapping the older flank of fuerteventura to the east in a similar way erosional channels which can also be traced up to 50 km from the area between gran canaria and fuerteventura into the deeper northern basin have been identified in the bathymetry the data presented provide new detailed information for modelling the submarine and subaerial evolution of the central canary islands of gran canaria and tenerife i e the timing of their shield building phases and later stages of major volcanic activity as reflected by the position of prominent seismic reflectors in the seismic stratigraphy

rates of magma ascent and depths of magma reservoirs beneath la palma canary islands peridotitic mantle xenoliths from historic and prehistoric eruptions on la palma show many similarities prolonged reactions of the xenoliths with their host magmas have been used to place constraints on the magma transport system beneath the island all xenoliths show crystalline selvages and 0 9 2 6 mm wide diffusion zones in olivine along most of their surface diffusion kinetics in olivine combined with fluid inclusion barometry document that selvages and diffusion zones formed at crustal levels within 8 to about 100 years some xenolith fractures lack selvages and were in contact with the host magma for less than 4 days a multistage magma ascent is proposed i peridotite wall rock was fragmented and became incorporated into the ascending magma years to decades prior to the eruption ii the xenoliths were rapidly transported to and deposited in crustal magma reservoirs forming selvages and diffusion zones at the xenolith rims iii renewed fragmentation of the xenoliths occurred days to hours prior to eruption possibly by decompressive strain fracturing during rapid ascent

magma storage and migration associated with the 2011 2012 el hierro eruption implications for crustal magmatic systems at oceanic island volcanoes 1 starting in july 2011 anomalous seismicity was observed at el hierro island a young oceanic island volcano on 12 october 2011 the process led to the beginning of a submarine nw se fissural eruption at 15 km from the initial earthquake loci indicative of significant lateral magma migration here we conduct a multifrequency multisensor interferometric analysis of spaceborne radar images acquired using three different satellite systems radarsat 2 envisat and cosmo skymed constellation of small satellites for mediterranean basin observation the data fully captures both the pre eruptive and coeruptive phases elastic modeling of the ground deformation is employed to constrain the dynamics associated with the magmatic activity this study represents the first geodetically constrained active magmatic plumbing system model for any of the canary islands volcanoes and one of the few examples of submarine volcanic activity to date geodetic results reveal two spatially distinct shallow crustal magma reservoirs a deeper central source 9 5 4 0 km and a shallower magma reservoir at the flank of the southern rift 4 5 2 0 km the deeper source was recharged explaining the relatively long basaltic eruption contributing to the observed island wide uplift processes and validating proposed active magma underplating the shallowest source may be an incipient reservoir that facilitates fractional crystallization as observed at other canary islands data from this eruption supports a relationship between the depth of the shallow crustal magmatic systems and the long term magma supply rate and oceanic lithospheric age such a relationship implies that a factor controlling the existence depth of shallow crustal magmatic systems in oceanic island volcanoes is the lithosphere thermomechanical behavior

emplacement of dikes sills and crustal magma chambers at divergent plate boundaries abstract a model of dike emplacement at divergent plate boundaries is developed which predicts that below the uppermost 1 3 km of the oceanic crust the number and lengths of dikes in any particular swarm should increase but that the thickness should decrease with depth in the crust these predictions are supported by field observations it is proposed that rapid injections of dikes at divergent plate boundaries may temporarily alter the normal stress field in such a way that at a certain level in the crust subsequent dikes change into sills such sills may develop into crustal magma chambers either when many nearby sills combine into a large one or when an initial sill absorbs the magma of many dikes that enter it in a rapid succession while the sill is liquid for the fastest spreading ridges the initial thickness of a sill that is to develop into a crustal chamber need only attain 20 m whereas at the slowest spreading ridges the initial thickness must exceed 170 m because thin sills are much more likely to form than thick sills the probability of sills developing into crustal chambers increases with dike intrusion frequency hence with spreading rate furthermore the model predicts first that with increasing spreading rate the length of the chamber along the ridge axis should increase and second that the most likely site for magma chambers is at depths of 2 4 km both these predictions are supported by available data

an empirical phase diagram for a part of the n2co2 system at low temperature abstract microthermometric and chemical raman analysis data for 23 inclusions from triassic dolomites and evaporites northern tunisia are used to generate a t x section of the n2 co2 binary system most observed features including some metastable homogenizations are consistent with a simple topology well known in many binary and notably in the co2 ch4 system

boron concentrations of volcanic fields in different geotectonic settings abstract whole rock boron and other mobile and immobile element concentrations are reported for the alkaline maar volcanic rocks from the bakony balaton highland volcanic field bbhvf hungary and for three other geographically distinct maar volcanic fields from diverse tectonic settings spain canary islands tenerife new zealand waipiata otago and mexico pinacate sonora and ceboruco cone field boron concentrations along with other fluid immobile and incompatible element concentrations are used to study the fluid enrichment of the above mentioned intraplate volcanic materials the fluid addition was the highest in the trans mexican volcanic belt ceboruco cone field which is associated with recent subduction the bbhvf also shows high fluid enrichment the average b content of the tenerife canary islands samples 6 4 g g is similar to that of the bbhvf 6 9 g g the fluid enrichment is higher in the bbhvf than in the waipiata volcanic field wvf the magmatic source regions for all the investigated volcanic rocks were affected by fluid components to different degrees and despite the distant relationship to subduction zones all show evidence of a subduction derived fluid component

infrastructure and mechanics of volcanic systems in iceland the divergent plate boundary in iceland consists of more than two dozen systems where most of the volcano tectonic activity takes place at the surface the volcanic systems are characterised by 5 20 km wide and 40 100 km long swarms of tension fractures 102 m long normal faults 103 m long and volcanic fissures the holocene fissure swarms are confined to less than 10 000 year old basaltic lava flows mostly pahoehoe occurring near the centre of the active rift zone in any particular swarm the number of tension fractures exceeds that of normal faults all tension fractures and normal faults are vertical at the surface indicating that the surface parts were generated by an absolute tension in addition to a fissure swarm many volcanic systems have a central volcano some of which have developed collapse calderas in the late tertiary and pleistocene lava pile of iceland extinct volcanic systems are represented by local sheet swarms and regional dyke swarms the sheet swarms are normally circular or slightly elliptical several kilometres in radius and are confined to the extinct central volcanoes many swarms are associated with large plutons exposed at 1 2 km depth beneath the initial top of the rift zone and presumably the uppermost parts of extinct crustal magma chambers and in short traverses up to 90 of the rock may consist of sheets the sheets have a very variable strike dip on average 45 65 mostly towards the centre of the associated volcano and have an average thickness of about 1 m the regional dykes occur outside central volcanoes in swarms that are commonly 50 km long and 5 10 km wide in several kilometre long traverses commonly 1 5 of the rock consist of dykes but occasionally as much as 15 28 most regional dykes are subparallel and subvertical the average dyke thickness in the pleistocene swarms is less than 2 m but 4 6 m in the tertiary swarms while active the volcanic systems in the rift zone are supplied with magma from reservoirs located at the depth of 8 12 km at the boundary between the crust and upper mantle the reservoirs are partially molten with totally molten top regions and of cross sectional areas similar to those of the volcanic systems that they feed some active volcanic systems especially those that develop central volcanoes high temperature areas and calderas have in addition to the deep seated magma reservoirs shallow crustal magma chambers located at 1 3 km depth which in turn are fed by the deeper magma reservoirs it is proposed that the regional dyke swarms are supplied with magma largely from the deep seated reservoirs whereas the local sheet swarms are mainly fed from the associated crustal magma chambers because the volume of a crustal chamber is less than that of its deeper source reservoir a single magma flow dyke intrusion from the reservoir may trigger tens of magma flows sheet intrusions from the chamber which is one explanation for the enormous number of sheets associated with many central volcanoes the sheets follow the stress trajectories of the local stress fields around the source chambers whereas the regional stress field associated with the divergent plate movements controls the emplacement of the regional dykes it is suggested that many dykes develop as self affine some as self similar structures when applied to the krafla volcanic system in northern iceland model calculations suggest that a magma flow from the krafla reservoir with regional dyke formation should occur on average once every several hundred years and that tens of sheets might be injected from the shallow krafla chamber and triggered by a single magma flow from the krafla reservoir these results are in broad agreement with the available data

mechanical re equilibration of fluid inclusions in san carlos olivine by power law creep fluid inclusions in san carlos olivine stretch via plastic mechanisms when heat treated at 1400 c and 0 1 mpa in controlled f o 2 atmospheres for several days measurable changes in both inclusion dimensions and fluid densities occur densities decrease from 1 0 to 0 7 g cc stretching is fastest along 100 and slower along 001 and 010 the dislocation microstructure around the inclusions suggests that creep mechanisms operate uncertainties in the experimental determinations of stretching rates result from optical resolution limits errors inherent in measuring homogenization temperatures uncertainties in the fluid equation of state and changes in fluid chemistry during the heat treatment inclusion stretching by dislocation creep can be treated using a model developed for hot isostatic pressing in this model we assume spherical symmetry of plastic flow that the material yields by steady state power law creep and that the parameters for the constitutive law and fluid equation of state are known stretching rates are predicted to depend on the difference between the fluid pressure and the external pressure the temperature the constitutive law governing power law creep and geometry predicted stretching rates show fair but not exact agreement with experimentally measured rates the amount of stretching predicted by the model is in rough agreement with estimates based on dislocation microstructures around natural inclusions if xenolith ascent rates are of the order of 1 cm s or faster

multi stage magma ascent beneath the canary islands evidence from fluid inclusions gabbroic and ultramafic xenoliths and olivine and clinopyroxene phenocrysts in basaltic rocks from gran canaria la palma el hierro lanzarote and la gomera canary islands contain abundant co2 dominated fluid inclusions inclusion densities are strikingly similar on a regional scale histogram maxima correspond to one or more of the following pressures 1 minimum 0 55 to 1 0 gpa within the upper mantle 2 between 0 2 and 0 4 gpa the moho or the lower crust 3 at about 0 1 gpa upper crust fluid inclusions in several rocks show a bimodal density distribution the lower density maximum comprising both texturally early and late inclusions this is taken as evidence for an incomplete resetting of inclusion densities and simultaneous formation of young inclusions at well defined magma stagnation levels for gran canaria pressure estimates for early inclusions in harzburgite and dunite xenoliths and olivine phenocrysts in the host basanites overlap at 0 9 to 1 0 gpa indicating that such magma reservoir depths coincide with levels of xenolith entrainment into the magmas magma chamber pressures within the mantle inferred to represent levels of mantle xenolith entrainment are 0 65 0 95 gpa for el hierro 0 60 0 68 gpa for la palma and 0 55 0 75 gpa for lanzarote the highest density fluid inclusions in many canary island mantle xenoliths have probably survived in situ near isobaric heating at the depth of xenolith entrainment inclusion data from all islands indicate ponding of basaltic magmas at moho or lower crustal depths and possibly at an additional higher level strongly suggestive of two main crustal accumulation levels beneath each island we emphasize that repeated magmatic underplating of primitive magmas and therefore intrusive accretion are important growth mechanisms for the canary islands and by analogy for other ocean islands comparable fluid inclusion data from primitive rocks in other tectonic settings including iceland etna and continental rift systems hungary south norway indicate that magma accumulation close to moho depths shortly before eruption is not however restricted to oceanic intraplate volcanoes lower crustal ponding and crystallization prior to eruption may be the rule rather than the exception independent of the tectonic setting

magmatic feeding system and crustal magma accumulation beneath vulcano island italy evidence from co2 fluid inclusions in quartz xenoliths 1 pure co2 fluid inclusions are observed in quartz xenoliths from four lava flows in the island of vulcano corresponding to distinct activity stages during the last 120 kyr xenoliths which consist of aggregates of quartz grains are present in lavas of contrasting composition ranging from basaltic andesites to rhyolites two main generations of co2 inclusions are observed early type i inclusions were trapped prior to the ascent of the host xenoliths while type ii inclusions were trapped during the ascent into the host magma fluid inclusions show a bimodal distribution of homogenisation temperatures corresponding to two distinct density intervals 0 89 0 52 g cm 3 type i and 0 42 0 13 g cm 3 type ii type i inclusions indicate pressures of 0 56 0 33 gpa 21 13 km relating to the levels of xenolith entrapment in the host lavas type ii fluid inclusions show considerably lower pressures ranging from 0 14 to 0 03 gpa 5 5 3 km present data suggest ponding of mantle derived magmas in at least two distinct reservoirs located at lower crustal depths and at shallow levels respectively combined fluid inclusion and petrological data suggest that the deep reservoirs were the sites of extensive fractional crystallization mixing with source derived magmas and various degrees of crustal assimilation evolutionary processes also occurred inside shallow magma chambers in which deep magma mixed with residing melts and rested for short periods of time before being erupted to the surface index terms 5480 planetology solid surface planets volcanism 8450 8414 volcanology eruption mechanisms 8434 volcanology magma migration

unravelling the magma feeding system of a young basaltic oceanic volcano abstract a multidisciplinary approach combining petrological geochemical and fluid inclusion studies with seismic monitoring data was used to build a model of the magma feeding system of pico volcano azores islands north atlantic ocean we explore how magma has ascended to the surface in the last 10 ka and how this ascent is associated with the selective activation of the three tectonic systems intersecting the volcano the deepest and most important ponding level for all ascending magmas is located at 17 3 17 7 km and corresponds to the moho transition zone mtz which marks the transition from mantle rocks to ultramafic cumulates at shallower depth ascending magmas carry 30 vol of clinopyroxene and olivine each magma ascent followed a distinct path and ponded often for a limited period ponding levels common to all feeding systems are present at 16 3 16 7 km 12 1 14 5 km 9 4 9 8 km and 7 7 8 1 km these depths mark important discontinuities where magmas formed stacked sills and evolved through fractional crystallisation dense and un decrepitated fluid inclusions show rapid ascent from the mtz along the lomba do fogo sao joao fault n150 system and along the n120 regional transtensive system despite multiple intrusions magma ponding at 5 6 6 8 km occurs where the n150 and n60 tectonic systems intersect each other here magma evolves towards plagioclase rich and is only erupted at the summit crater and subterminal vents this region is the source of the frequent microseismicity recorded at 4 to 7 km beneath the southern flank of pico volcano which might be associated with the early stages of formation of a more complex magma reservoir the local and regional tectonics are of paramount importance in the activation of the different magma feeding systems over time this new information is fundamental to improve the knowledge on the future eruptive behaviour of pico volcano and can have significant implications on the mitigation of volcanic risk this multidisciplinary approach can be applied not only to other volcanoes of the azores but also to poorly monitored oceanic volcanoes where magma ascent strongly depends on the activation of tectonic systems

nitrogen rich fluid in the upper mantle fluid inclusions in spinel dunite from lanzarote canary islands fluid inclusions ranging from pure n2 to pure co2 occur in olivine porphyroclasts in spinel dunite xenoliths chrome diopside suite from two localities within the quaternary to historic alkaline lavas of lanzarote canary islands this is the first report of fluid inclusions containing major amounts of n2 in mantle xenoliths the nitrogen rich fluid inclusions predate at least one generation of nitrogen free carbon dioxide inclusions textural evidence indicates that the inclusions were trapped within the upper mantle some of the nitrogen rich fluid inclusions are intimately associated with solid inclusions of spinel the nitrogen rich fluid was most likely produced in situ by oxidation dehydration reactions destabilizing ammonium bearing silicate minerals phlogopite amphibole increasing oxygen fugacity or possibly increasing temperature of the mantle this process could be related to an event of co2 and silicate melt injection at 6 8 kbar neumann et al in press or to some earlier event in the evolution of the mantle beneath lanzarote the existence of a n2 rich fluid phase in at least some mantle lithology ies at certain conditions is demonstrated by these data this discovery has consequences for the understanding of the evolution of the mantle below the canary islands as well as for the global nitrogen budget