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

the role of partial melting in the 15 ma geochemical evolution of gran canaria a blob model for the canary hotspot the subaerial portion of gran canada canary islands was built by three cycles of volcanism a miocene cycle 8 5 15 ma a pliocene cycle 1 8 60 ma and a quaternary cycle 1 8 0 ma only the pliocene cycle is completely exposed on gran canaria the early stages of the miocene cycle are submarine and the quaternary cycle is still in its initial stages during the miocene sio2 saturation of the mafic volcanics decreased systematically from tholeiite to nephelinite for the pliocene cycle sio2 saturation increased and then decreased with decreasing age from nephelinite to tholeiite to nephelinite sio2 saturation increased from nephelinite to basanite and alkali basalt during the quaternary in each of these cycles increasing melt production rates sio2 saturation and concentrations of compatible elements and decreasing concentrations of some incompatible elements are consistent with increasing degrees of partial melting in the sequence melilite nephelinite to tholeiite the mafic volcanics from all three cycles were derived from co2 rich garnet lherzolite sources phlogopite ilmenite sulfide and a phase with high partition coefficients for the light rare earth elements lree u th pb nb and zr possibly zircon were residual during melting to form the miocene nephelinites through tholeiites phlogopite ilmenite and sulfide were residual in the source of the pliocene quaternary nephelinites through alkali basalts highly incompatible element ratios e g nb u pb ce k u nb pb ba rb zr hf la nb ba th rb nb k nb zr nb th nb th la and ba la exhibit extreme variations in many cases larger than those reported for all other ocean island basalts but these ratios correlate well with degree of melting survival of residual phases at higher degrees of melting during the miocene cycle and differences between major and trace element concentrations and melt production rates between the miocene and pliocene tholeiites suggest that the miocene source was more fertile than the pliocene quaternary source s we propose a blob model to explain the multi cycle evolution of canary volcanoes and the temporal variations in chemistry and melt production within cycles each cycle of volcanism represents decompression melting of a discrete blob of plume material small degree nephelinitic and basanitic melts are derived from the cooler margins of the blobs whereas the larger degree tholeiitic and alkali basaltic melts are derived from the hotter centers of the blobs the symmetrical sequence of mafic volcanism for a cycle from highly undersaturated to saturated to highly undersaturated compositions reflects melting of the blob during its ascent beneath an island in the sequence upper margin corelower margin volcanic hiatuses between cycles and within cycles represent periods when residual blob or cooler entrained shallow mantle material fill the melting zone beneath an island

a multichannel seismic study of lithospheric flexure across the hawaiian emperor seamount chain existing models assume that the thickened crust beneath seamounts is the result of a surface volcanic load flexing an elastic plate new results suggest that flexed oceanic crust beneath the hawaiian emperor seamount chain is underlain by a 4 km thick deep crustal body we intepret the body as a deep crustal sill complex associated with the tholeiitic stage of volcano building along the chain

seismic boundaries of the eastern central atlantic mesozoic crust from multichannel seismic data we report the results of a multichannel seismic study on eastern central atlantic oceanic crust unmigrated and migrated sections have been used to identify the main seismic boundaries within the crust the upper crust generally is seismically transparent except for a 20 km long continuous reflection which we interpret as associated with a long lived normal fault in the basement and with hydrothermal circulation short and discontinuous reflections in the upper crust have also been observed the lower crust is either transparent or variably reflective in form of subhorizontal layered reflection packages and or dipping reflections the reflectivity patterns are interpreted as magmatic in origin except for the dipping reflections that affect the whole crust which are interpreted as expressions of extensional faults the reflections dipping ridgeward are thought to have acted as detachment surfaces where plate separation took place the moho has been identified along most of the length of the seismic profiles either as the base of the reflective lower crust or as a sharp single reflection the igneous crust shows large variations in thickness sometimes associated with fracture zones in the cretaceous crust fracture zones in the jurassic crust do not show in general a crustal thinning this may be due to different accretionary processes during jurassic and cretaceous times

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

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

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

seismostratigraphy of the western flanks of el hierro and la palma canary islands a record of canary islands volcanism abstract a cruise carried out aboard the spanish r v hesperides using a 255 inch3 airgun allowed to identify three main seismostratigraphic units in the western submarine flanks of the islands of la palma and el hierro canary islands the time structure and thickness maps of each unit together with the interpretation of the seismic facies demonstrate that the evolution of the canary islands is recorded in the marine basin the structure maps show that the older reflectors dip to the nw in contrast to the present day sea floor which dips to the wnw the thickness maps also show that the depocentre moved from a position parallel to the northwest african margin to a position now occupied by the island of la palma despite the high sedimentation rates of hemipelagic background sedimentation in the study area the three seismic units can be interpreted in terms of their relation to the canarian volcanism unit i was deposited before the initiation of volcanism and the arrival of volcaniclastic flows and is thus mainly if not entirely composed of hemipelagic sediments unit ii seems to reflect the shield phases of the easternmost edifices and as such would be constituted by the distal products of erosion and mass wasting of these islands unit iii in contrast results mainly from the shield phase of the two westernmost islands la palma and el hierro and as such reflects more proximal conditions as demonstrated by the presence of lateral collapse deposits from these islands

experimental hydration of natural volcanic clinopyroxene phenocrysts under hydrothermal pressures 0 5 3 kbar water is a key parameter in mantle rheology magma genesis magma evolution and resulting eruption styles because it controls the density and the viscosity as well as the melting and crystallization behavior of a melt the water content in nominally anhydrous minerals nams such as clinopyroxene recently has been used as a proxy for magmatic water contents nams however may dehydrate during magma degassing and eruption we performed rehydration experiments on potentially degassed clinopyroxene phenocrysts from various volcanic settings the experiments were conducted in hydrogen gas at 1 atm or hydrothermal pressures ranging from 0 5 to 3 kbar to test the incorporation of water into natural clinopyroxene under water fugacities similar to those in a volcanic system our results show a dependence of the water content in the clinopyroxene crystals with pressure as the phenocrysts begin to dehydrate upon lower water fugacities in the experiments water loss or gain in a crystal occurs according to the relatively fast redox reaction oh fe 2 o 2 fe 3 h 2 which was confirmed by mossbauer spectroscopy the kinetics of this redox process are independent of pressure and thus water fugacity water contents in rehydrated clinopyroxene crystals can be related to magmatic water contents at various levels in a volcanic system our results thus show that the water content in erupted clinopyroxene phenocrysts cannot be taken for granted to be representative of magmatic water contents prior to magma degassing the conducted experiments indicate the simultaneous dehydration of clinopyroxene along with magma ascent and degassing rehydration experiments under hydrothermal pressures however may be able to reconstruct clinopyroxene water contents at crystallization prior to dehydration

time evolution of deformation using time series of differential interferograms application to la palma island canary islands differential interferometry is a very powerful tool for detecting changes in the earth s crust where coherence conditions are good but is difficult to employ in some volcanic areas due to dense vegetation we apply two differential insar methods using the time series associated with the interferograms to perform a phase analysis on a data set for la palma island canary islands from the ers 1 and ers 2 european space agency esa satellites for the time period 1992 to 2000 both methods involve choosing a master image from the database and creating a series of interferograms with respect to this image the coherent pixel time series cpts technique chooses pixels with good average coherence aligns the unwrapped interferograms with a stable area and then performs an inversion to calculate the linear velocity to quantify the deformation the coherent target modeling ctm method calculates the temporal coherence of each pixel to identify stable targets and then determines the best velocity for each pixel by using a linear fit that maximizes the temporal coherence using these two methods we have been able to detect deformation on la palma island that has been previously undetectable by conventional insar methods there is a roughly circular region on the southern part of the island that is actively deforming at 4 to 8 mm yr this region is located near the teneguia valcano the host of the last known eruption on la palma in 1971 a thorough investigation of the possible sources for this deformation revealed that it was most likely created by a subsurface thermal source

dating of the upper pleistocene holocene volcanic activity of la palma using the unspiked k ar technique abstract combined unspiked k ar dating and detailed mapping have established the eruptive chronology of the cumbre vieja volcano in the canary islands the cv volcano is a large polygenetic volcano subaerial area 220 km2 subaerial volume 125 km3 elevation above sea level 2000 m which rests on the southern flank of the older taburiente cumbre nueva volcano we defined two stratigraphic units by their relationship to the development of coastal cliffs developed around the cumbre vieja volcano a cliff forming series and a scree forming series which is draped over the cliffs and forms the coastal platforms at their bases k ar ages were measured from 20 samples from the two series there are no discrepancies between k ar ages and the stratigraphy the k ar ages of one flow compare well with 14 c determinations 14 c 3 2 0 1 ka k ar 4 2 ka the ages of the scree forming series range from 3 2 ka to 21 2 ka the cliff forming series ages range from 20 2 ka to 123 3 ka but as the base of the sequence is not exposed the growth of the cumbre vieja volcano must have begun substantially earlier the boundary between the two coincides with the low sea level stand in the last glacial maximum which we infer to have been a period of intense coastal erosion dated samples from the upper part of the taburiente cumbre nueva volcano range in age from 853 10 ka to 566 8 ka the age of the youngest taburiente cumbre nueva volcano sample provides an upper bound on the age of the subsequent cumbre nueva giant lateral collapse

melt extraction pathways and stagnation depths beneath the madeira and desertas rift zones ne atlantic inferred from barometric studies the madeira and desertas islands eastern north atlantic show well developed rift zones which intersect near the eastern tip of madeira sao lourenco peninsula we applied fluid inclusion barometry and clinopyroxene melt thermobarometry to reconstruct levels of magma stagnation beneath the two adjacent rifts and to examine a possible genetic relationship during their evolution densities of co2 dominated fluid inclusions in basanitic to basaltic samples from sao lourenco yielded frequency maxima at pressures of 0 57 0 87 gpa 23 29 km depth and 0 25 0 32 gpa 8 10 km whereas basanites basalts and xenoliths from the desertas indicate 0 3 0 72 gpa 10 24 km and 0 07 0 12 gpa 2 3 km clinopyroxene melt thermobarometry applied to ti augite phenocryst rim and glass groundmass compositions indicates pressures of 0 45 1 06 gpa 15 35 km sao lourenco and 0 53 0 89 gpa 17 28 km desertas islands which partly overlap with pressures indicated by fluid inclusions we interpret our data to suggest a multi stage magma ascent beneath the madeira archipelago main fractionation occurs at multiple levels within the mantle 15 km depth and is followed by temporary stagnation within the crust prior to eruption depths of crustal magma stagnation beneath sao lourenco and the desertas differ significantly and there is no evidence for a common shallow magma reservoir feeding both rift arms we discuss two models to explain the relations between the two adjacent rift systems madeira and the desertas may represent either a two armed rift system or two volcanic centres with separate magma supply systems for petrological and volcanological reasons we favour the second model and suggest that madeira and the desertas root in distinct regions of melt extraction magma focusing into the desertas system off the hotspot axis may result from lithospheric bending caused by the load of the madeira and porto santo shields combined with regional variations in melt production due to an irregularly shaped plume

control of regional sea level by surface uplift and subsidence caused by magmatic underplating of earth s crust magmatic underplating of the crust is a common feature of major basalt provinces the emplacement of magma within the lithosphere leads to surface uplift with a magnitude of the order of 10 of the thickness of the underplated material the composition of associated igneous rock samples suggests that much of the underplated material is made of gabbro this gabbro is denser than the magma from which it crystallizes so uplift of earth s surface caused by the emplacement of magma at the crust mantle boundary must be followed by subsidence as the magma solidifies this subsidence is equal to approximately half the original uplift and takes place within 0 1 m y of injection of the magma the association of magmatic underplating with surface uplift followed by subsidence provides a mechanism for changes of sea level including previously unexplained episodic highstands of sea level

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

slope failures on the flanks of the western canary islands abstract landslides have been a key process in the evolution of the western canary islands the younger and more volcanically active canary islands el hierro la palma and tenerife show the clearest evidence of recent landslide activity the evidence includes landslide scars on the island flanks debris deposits on the lower island slopes and volcaniclastic turbidites on the floor of the adjacent ocean basins at least 14 large landslides have occurred on the flanks of the el hierro la palma and tenerife the majority of these in the last 1 million years with the youngest on the northwest flank of el hierro as recent as 15 thousand years in age older landslides undoubtedly occurred but are difficult to quantify because the evidence is buried beneath younger volcanic rocks and sediments landslides on the canary island flanks can be categorised as debris avalanches slumps or debris flows debris avalanches are long runout catastrophic failures which typically affect only the superficial part of the island volcanic sequence up to a maximum thickness of 1 to 2 km they are the commonest type of landslide mapped in contrast slumps move short distances and are deep rooted landslides which may affect the entire thickness of the volcanic edifice debris flows are defined as landslides which primarily affect the sedimentary cover of the submarine island flanks some landslides are complex events involving more than one of the above end member processes individual debris avalanches have volumes in the range of 50 500 km3 cover several thousand km2 of seafloor and have runout distances of up to 130 km from source overall debris avalanche deposits account for about 10 of the total volcanic edifices of the small relatively young islands of el hierro and la palma some parameters such as deposit volumes and landslide ages are difficult to quantify the key characteristics of debris avalanches include a relatively narrow headwall and chute above 3000 m water depth on the island flanks broadening into a depositional lobe below 3000 m debris avalanche deposits have a typically blocky morphology with individual blocks up to a kilometre or more in diameter however considerable variation exists between different avalanche deposits at one extreme the el golfo debris avalanche on el hierro has few large blocks scattered randomly across the avalanche surface at the other icod on the north flank of tenerife has much more numerous but smaller blocks over most of its surface with a few very large blocks confined to the margins of the deposit icod also exhibits flow structures longitudinal shears and pressure ridges that are absent in el golfo the primary controls on the block structure and distribution are inferred to be related to the nature of the landslide material and to flow processes observations in experimental debris flows show that the differences between the el golfo and icod landslide deposits are probably controlled by the greater proportion of fine grained material in the icod landslide this in turn relates to the nature of the failed volcanic rocks which are almost entirely basalt on el hierro but include a much greater proportion of pyroclastic deposits on tenerife landslide occurrence appears to be primarily controlled by the locations of volcanic rift zones on the islands with landslides propagating perpendicular to the rift orientation however this does not explain the uneven distribution of landslides on some islands which seems to indicate that unstable flanks are a weakness that can be carried forward during island development this may occur because certain island flanks are steeper extend to greater water depths or are less buttressed by the surrounding topography and because volcanic production following a landslide my be concentrated in the landslide scar thus focussing subsequent landslide potential in this area landslides are primarily a result of volcanic construction to a point where the mass of volcanic products fails under its own weight although the actual triggering factors are poorly understood they may include or be influenced by dyke intrusion pore pressure changes related to intrusion seismicity or sealevel climate changes a possible relationship between caldera collapse and landsliding on tenerife is not in our interpretation supported by the available evidence

crustal architecture and deep structure of the ninetyeast ridge hotspot trail from active source ocean bottom seismology a 550 km long transect across the ninetyeast ridge a major indian ocean hotspot trail provided seismic refraction and wide angle reflection data recorded on 60 ocean bottom instruments about 24 000 crustal and 15 000 upper mantle arrivals have been picked and used to derive an image of the hotspot track two approaches have been chosen i a first arrival tomographic inversion yielding crustal properties and ii forward modelling of mantle phases revealing the structure at the crust mantle boundary region and of the uppermost mantle away from the volcanic edifice seismic recordings show the typical phases from oceanic crust that is two crustal refraction branches pg a wide angle reflection from the crust mantle boundary pmp and a wave group turning within the upper mantle pn approaching the edifice three additional phases have been detected we interpret these arrivals as a wide angle reflection from the base of material trapped under the pre hotspot crust pm2p and as a wide angle reflection pnp and its associated refraction branch pn from a layered upper mantle the resulting models indicate normal oceanic crust to the west and east of the edifice crustal thickness averages 6 5 7 km wide angle reflections from both the pre hotspot and the post hotspot crust mantle boundary suggest that the crust under the ridge has been bent downwards by loading the lithosphere and hotspot volcanism has underplated the pre existing crust with material characterized by seismic velocities intermediate between those of mafic lower crustal and ultramafic upper mantle rocks 7 5 7 6 km s 1 in total the crust is up to 24 km thick the ratio between the volume of subcrustal plutonism forming the underplate and extrusive and intrusive volcanism forming the edifice is about 0 7 an important observation is that underplating continued to the east under the wharton basin during the shield building phase however ninetyeast ridge was located adjacent to the broken ridge and was subsequently pulled apart along a transform fault boundary therefore underplating eastwards of the fracture zone separating the edifice from the wharton basin suggests that prolonged crustal growth by subcrustal plutonism occurred over millions of years after the major shield building stage this fact however requires mantle flow along the fossil hotspot trail the occurrence of pnp and pn arrivals is probably associated with a layered and anisotropic upper mantle due to the preferential alignment of olivine crystals and may have formed by rising plume material which spread away under the base of the lithosphere

geodetic and structural research in la palma canary islands spain 1992 2007 results we review the results of the geodetic and structural studies carried out on la palma island using geodetic and geophysical data during the period 1992 2007 insar and gps observation techniques were applied to study the existence of deformation on the island and gravity observations were carried out for structural studies gravity data were inverted using a nonlinear three dimensional gravity inversion approach to obtain the geometry of the anomalous bodies constructed in a random growth process with respect to an exponentially stratified background the main structural feature is a large central body under the caldera de taburiente with high density which was interpreted as the pliocene age uplifted seamount and a relatively dense intrusive plutonic complex magma body the cumbre vieja series is characterized by elongated minima distributed according to the rift structure insar results show a clear subsidence located on the teneguia volcano where the last eruption took place in 1971 a thermal source is the most probable origin for this deformation a gps network composed of 26 stations covering the total island surface was set up vertical displacements determined comparing the gps coordinates obtained in 2007 with coordinates determined in 1994 are consistent with the insar results obtained in the southern part of the island this is not the case for the northern part from the comparison of 2006 and 2007 coordinates it is clear that more time is needed to obtain significant displacements but observed trends are also consistent with insar results all the observed significant displacements are in stations located outside of the large high density central body

the emergence of volcanic oceanic islands on a slow moving plate the example of madeira island ne atlantic the transition from seamount to oceanic island typically involves surtseyan volcanism however the geological record at many islands in the ne atlantic all located within the slow moving nubian plate does not exhibit evidence for an emergent surtseyan phase but rather an erosive unconformity between the submarine basement and the overlying subaerial shield sequences this suggests that the transition between seamount and island may frequently occur by a relative fall of sea level through uplift eustatic changes or a combination of both and may not involve summit volcanism in this study we explore the consequences for island evolutionary models using madeira island portugal as a case study we have examined the geologic record at madeira using a combination of detailed fieldwork biostratigraphy and 40ar 39ar geochronology in order to document the mode timing and duration of edifice emergence above sea level our study confirms that madeira s subaerial shield volcano was built upon the eroded remains of an uplifted seamount with shallow marine sediments found between the two eruptive sequences and presently located at 320 430 m above sea level this study reveals that madeira emerged around 7 0 5 6 ma essentially through an uplift process and before volcanic activity resumed to form the subaerial shield volcano basal intrusions are a likely uplift mechanism and their emplacement is possibly enhanced by the slow motion of the nubian plate relative to the source of partial melting alternating uplift and subsidence episodes suggest that island edifice growth may be governed by competing dominantly volcanic and dominantly intrusive processes

evaluation of solutions for deep constant head boreholes estimation of the field saturated hydraulic conductivity kfs is essential for ground water management and for numerical modeling of ground water flow and contaminant transport the constant head borehole test can be used to measure kfs of deep soils for a deep borehole of ha 10 500 where h is the water height in the borehole and a is the radius the accuracy of the estimated kfs varies depending on the shape factor associated with ha many analytical solutions have been obtained on the basis of approximate boundary conditions available to evaluate the shape factor to find the best solution that provides an accurate shape factor the accuracy of the different solutions was evaluated using a series of numerical simulations that satisfy the pressure boundary condition of the borehole test our comparison on the basis of the analytical and numerical solutions shows that for homogeneous soils the kfs calculated by xiang s solution xiang 1993 eos trans am geophys union 74 43 285 and that by reynolds et al 1983 soil sci 136 250 268 are almost identical to the numerical results xiang s solution however was found to be more accurate for evaluating the flow distribution than was that of reynolds et al

seismic imaging of hotspot related crustal underplating beneath the marquesas islands volcanism in active continental rift zones1 2or on rifted continental margins3is frequently associated with unusually high lower crustal seismic velocities indicating the presence of large igneous intrusions at the base of the crust the only comprehensive investigation of crustal underplating at an oceanic hotspot beneath hawaii4 6 has yielded controversial results7 here we report the results of seismic refraction experiments across the marquesas islands hotspot trace which show that the island chain is underlain by crust 15 17 km thick and that a large lower crustal region 275 km wide and 2 8 km thick has seismic velocities 7 3 7 75 km s 1 indicative of crustal underplating wide angle reflections occur near the base of the normal lower crustal velocities and at the base of the underplating complex we interpret these reflectors as the relict pre hotspot moho and the current post hotspot moho respectively the high velocity material may be purely intrusive or may consist of a mixture of intrusive and preexisting rocks the volume of the high velocity body is impressive amounting to nearly twice the volume of volcanics erupted at the surface

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

contrasting magmatic cannibalism forms evolved phonolitic magmas in the canary islands volcanic sequences on ocean islands record the temporal evolution of underlying magmatic systems and provide insights into how silicic crust is produced away from convergent margins assimilation has often been suspected to contribute but the detection of such a process and its evolving maturity during migration across a mantle plume is less well documented here we present new major and trace element and sr nd pb u th ra pa isotope data that facilitate comparison of basanite to phonolite evolution on tenerife canary islands with that shown by published data from la palma on both islands 230th 238u ratios decrease with differentiation from parental magmas with 230th excess toward different silicic contaminants in secular equilibrium on la palma this is inferred to reflect assimilation of small amounts of mafic wall rock on tenerife both 230th 238u and 231pa 235u ratios decrease toward 1 with increasing differentiation and this is accompanied by a subtle increase in pb isotope ratios at the same time 226ra 230th ratios change from 1 a hitherto unreported magnitude the tenerife assimilant is thus constrained to be a partial melt of syenite formed in equilibrium with residual feldspar the differences reflect a primarily deeper more mafic magma system beneath la palma during its late shield building stage whereas recent magmatic evolution at tenerife occurs primarily at lower temperatures in small shallower magma systems formed during its post basaltic shield stage differentiation takes millennia or less

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

thermal nature of mantle upwellings below the ibero western maghreb region inferred from teleseismic tomography independent models of p wave and s wave velocity anomalies in the mantle derived from seismic tomography help to distinguish thermal signatures from those of partial melt volatiles and compositional variations here we use seismic data from sw europe and nw africa spanning the region between the pyrenees and the canaries in order to obtain a new s sks relative arrival time tomographic model of the upper mantle below iberia western morocco and the canaries similar to previous p wave tomographic results the s wave model provides evidence for 1 subvertical upper mantle low velocity structures below the canaries atlas ranges and gibraltar arc which are interpreted as mantle upwellings fed by a common lower mantle source below the canaries and 2 two low velocity anomalies below the eastern rif and betics that we interpret as the result of the interaction between quasi toroidal mantle flow induced by the gibraltar slab and the mantle upwelling behind it the analysis of teleseismic p wave and s wave arrival time residuals and the conversion of the low velocity anomalies to temperature variations suggest that the upwellings in the upper mantle below the canaries atlas ranges and gibraltar arc system may be solely thermal in nature with temperature excesses in the range 100 350 c our results also indicate that local partial melting can be present at lithospheric depths especially below the atlas ranges the locations of thermal mantle upwellings are in good agreement with those of thinned lithosphere moderate to high heat flow measurements and recent magmatic activity at the surface

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

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

constructive and destructive episodes in the building of a young oceanic island la palma canary islands and genesis of the caldera de taburiente the results of new field observations 23 new k ar determinations and sixteen previously published determinations provide the basis for the reconstruction of the subaerial volcanic history of the island of la palma after the seamount activity represented by the materials of the basal complex an eruptive phase between 2 0 and 1 3 ma formed a large shield a period of volcanic quiescence followed until around 1 ma during which a large lateral collapse partly destroyed the former edifice between 1 05 and 0 7 ma activity was renewed in the shield and a n s ridge was built in the southern part of the island around 0 7 ma two new large lateral collapses affected the western part of both edifices and they were followed by eruptions between 0 71 and 0 65 ma which built a new edifice that partly filled the depressions thus created the caldera de taburiente constitutes the eroded remnants of the depression formed in the northern shield from 0 65 ma to present activity has been restricted to the n s ridge which has continued to grow southwards there was a general n s migration of volcanic activity with time but in the shield the trend was northwest to southeast eruptive rates seem to have been fairly constant during the different eruptive phases considered between 0 15 and 0 37 km3 ka a very similar succession of constructive and destructive episodes has been obtained for the neighboring island of hierro but in this case the activity started around 0 8 ma and eruptive rates were about 0 5 km3 ka

the geological history of maio cape verde islands the oldest igneous rocks on maio are pillow lavas of mid ocean ridge pillow basalts character which have been tilted and uplifted about 4 km from the ocean floor to outcrop as a partial ring dipping steeply away from a central plutonic complex made up of pyroxenites essexites syenites and carbonatites the ocean floor volcanic rocks are overlain conformably by a stratigraphically continuous pelagic carbonate succession which demonstrates a shallowing depositional environment from the upper jurassic to upper cretaceous times when tuffaceous beds indicate renewed volcanism the tuffs are associated with rudites demonstrating the emergence of the island and amongst the clasts are plutonics indicating upper cretaceous magmatism and the unroofing of the volcano to a substantial depth deformation under compressive stress resulted in the folding and local repetition by thrusting of this sedimentary cover which together with the plutonic core had been intensively injected by major sills the mesozoic succession has been planed off and overlain with marked unconformity by a largely neogene sequence of volcanic and terrestrial sedimentary rocks there is a hiatus throughout the palaeogene and constructional activity appears to recommence with ankaramitic hyaloclastite and lava deltas and subaerial ankaramitic flows these are overlain by fluvial sediments and tuffs stratigraphically above these is an extensive plateau of silica undersaturated lavas olivine melilitites and nephelinites which rest on a planed and locally lateritized surface at topographically higher levels in the eastern part of the island there are thick ankaramitic lavas and pyroclasts which evidently flowed eastward through valleys cut down into the mesozoic strata and appear to be of pliocene age the subsequent history of the island appears to be non volcanic

environments of crystallization and compositional diversity of mauna loa xenoliths two picrite flows from the sw rift zone of mauna loa contain introduction xenoliths of dunite harzburgite lherzolite plagioclase bearing xenoliths hosted in mauna loa s tholeiitic stage lavas lherzolite and harzburgite troctolite gabbro olivine gabbro and provide a rare opportunity to glimpse into the volcano s gabbronorite textures and olivine compositions preclude a mantle magma chambers and plumbing system in hawaii source for the xenoliths and rare earth element concentrations of xenoliths are much more abundant in alkalic lavas than xenoliths and clinopyroxene indicate that the xenolith source is in tholeiitic lavas as a result of reconfiguration of the not old oceanic crust but rather a hawaiian tholeiitic stage conduit and storage system as magma supply rate demagma pyroxene compositions phase assemblages and textural creases clague 1987 each xenolith records the chemrelationships in xenoliths indicate at least two different crys ical and physical environment in a small part of the tallization sequences calculations using the pmelts algorithm magma chamber at a particular time similarly the show that the two sequences result from crystallization of primitive individual crystals that compose xenoliths hosted in a mauna loa magmas at 6 kbar and 2 kbar independent single flow or series of flows may reflect the changes in calculations of olivine ni fo compositional variability in the magma composition over time textural and complagioclase bearing xenoliths over these crystallization sequences positional features of xenoliths preserve evidence for are consistent with observed olivine compositional variability variation in geochemical petrological and physical contwo parents of similar bulk composition but which vary in ni ditions within the magma system content are necessary to explain the olivine compositional compositions of mauna loa xenoliths range widely variability in the dunite and plagioclase free peridotitic xenoliths and include pyroxenite peridotite troctolite and dunite xenoliths probably crystallized in a small magma storage area as well as gabbroic lithologies many exhibit distinctive beneath the rift zone rather than the large sub caldera magma cumulate or laminated textures previous studies of reservoir primitive picritic magmas are introduced to isolated mauna loa xenoliths are few white 1966 jackson et rift zone storage areas during periods of high magma flux al 1982 so the initial objective of this study is to subsequent eruptions reoccupy these areas and entrain and characterize the petrography and geochemistry of a reptransport xenoliths to the surface resentative collection of samples the second objective is to analyze textures mineral assemblages phase relationships and compositions to identify genetic relationships among the xenoliths as well as with the host to construct a crystallization history of the magmas that are parental to the xenoliths and ultimately to model the

later stages of volcanic evolution of la palma canary islands rift evolution giant landslides and the genesis of the caldera de taburiente the islands of la palma and el hierro form the western end of the hotspot induced canary islands chain both islands are at present in the earliest and fastest shield building stage of growth and show many similarities with the hawaiian islands la palma shows two very distinct phases of volcanic construction 1 a pliocene submarine volcanic and intrusive series interpreted as an uplifted seamount at least 1500 m above present sea level and 2 a subaerial volcanic series erupted in the past 2 m y taburiente volcano initially formed the northern part of the island and then extended to the south forming a ridge cumbre nueva ridge that was partially destroyed about 560 ka by a giant lateral collapse the cumbre nueva collapse possibly involving 180 200 km 3 of subaerial volcanic material the northwest boundary of the cumbre nueva collapse formed a vertical scarp that enlarged by headward erosion formed the spectacular depression of caldera de taburiente cumbre vieja volcano a north south elongated rift forms the southern half of la palma and constitutes its last stage of growth including all eruptive activity in the past 125 k y detailed field observations mapping and high precision radiometric dating have allowed reconstruction of the growth and structural changes of the cumbre vieja volcano interactions between eruption rates coastal erosion and glacio eustatic sea level change allow stratigraphic subdivision of the edifice the structure of the volcano has been controlled for most of its history by a rift system with a clearly dominant north south and less distinct north east and north west volcanic rift zones the rift reorganization of the volcano to a single north south rift since 7 ka and the opening of faults during the 1949 eruption probably reflect increasing instability of the west flank of the volcano

origin of xenoliths in the trachyte at puu waawaa hualalai volcano hawaii rare dunite and 2 pyroxene gabbro xenoliths occur in banded trachyte at puu waawaa on hualalai volcano hawaii mineral compositions suggest that these xenoliths formed as cumulates of tholeiitic basalt at shallow depth in a subcaldera magma reservoir subsequently the minerals in the xenoliths underwent subsolidus reequilibration that particularly affected chromite compositions by decreasing their mg numbers in addition olivine lost cao and plagioclase lost mgo and fe2o3 during subsolidus reequilibration the xenoliths also reacted with the host trachyte to form secondary mica amphibole and orthopyroxene and to further modify the compositions of some olivine clinopyroxene and spinel grains the reaction products indicate that the host trachyte melt was hydrous clinopyroxene in one dunite sample and olivine in most dunite samples have undergone partial melting apparently in response to addition of water to the xenolith these xenoliths do not contain co2 fluid inclusions so common in xenoliths from other localities on hualalai which suggests that co2 was introduced from alkalic basalt magma between the time co2 inclusion free xenoliths erupted at 106 6 ka and the time co2 inclusion rich xenoliths erupted within the last 15 ka

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

vertical movements of ocean island volcanoes insights from a stationary plate environment abstract uplift reconstructions based on the cape verde s geological record provide a unique opportunity to study the long term isostatic movements associated with hotspot activity on a stationary plate environment the archipelago is considered stationary with respect to its melting source so the hotspot driven isostatic effects affecting the ocean islands are expected to be enhanced in this study ar ar and u th geochronology techniques were used to date a set of palaeo markers of sea level from santiago s and sao nicolau s edifices two of the main cape verde islands a comparison between relative sea level and eustatic sea level from a modern eustatic curve was established to extract the vertical displacement undergone by the markers and to reconstruct the uplift subsidence history of each island the resulting uplift reconstructions confirm that both santiago and sao nicolau experienced a general uplift trend over the last 6 ma seemingly synchronous with the vigorous volcanic activity that built their exposed edifices these islands however exhibit different uplift histories despite their common uplift trend several uplift mechanisms were tested and a local rather than regional mechanism is proposed as the main cause of uplift generally unrelated with far field effects of surface loading this mechanism is probably associated with magmatic additions at crustal level

vertical movements of ocean island volcanoes insights from a stationary plate the origin of hotspot swells is still controversial and their development is at present poorly constrained and strongly model dependent however since islands are built on top of these structures the role of swell development in island uplift subsidence should be assessed

comment on the insular shelves of the faial pico ridge azores archipelago a morphological record of its evolution by quartau et al

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

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

recurrent large scale landsliding on the west flank of la palma canary islands a large area of debris avalanche deposits has been discovered on the western submarine flanks of the island of la palma multibeam bathymetry and its derivative backscatter data towed ocean bottom instrument tobi sidescan sonar images and 3 5 khz and airgun seismic reflection data have been used to identify at least two and possibly as many as four major landslide events the youngest of the events the cumbre nueva debris avalanche extends onshore into the valleys bounded by the caldera de taburiente and cumbre nueva ridge which mark the degraded collapse scars radiometric dating of the volcanic flows in the headwall indicate an age of between 536 and 125 ka for this landslide the debris avalanche covers an area of 780 km2 has a maximum thickness of 500 m and has an estimated volume of 95 km3 older deposits collectively referred to as the playa de la veta debris avalanche complex are probably as the name indicates an amalgamation of at least two or three events rather than the result of a single catastrophic failure the playa de la veta debris avalanche complex is associated onshore with an unconformity dated as late matuyama 1 ma to 800 ka it covers an area of 1200 km2 has a maximum thickness of 1300 m and may represent a total volume of up to 650 km3 the greater thicknesses and limited areas occupied by debris avalanches on the western flank of la palma compared to other landslides in the canary archipelago suggest that the la palma landslide masses have relatively low mobility the different debris avalanche lobes formed by each landslide event are separated by channels 2 2 5 km wide the clear relationship between channel position and the boundaries of each debris avalanche lobe indicates that debris avalanches control later channel formation and pathways the relief of the submarine flanks of the la palma volcanoes in the areas of island slope unaffected by landslides is mainly the result of constructional volcanic processes however the older submarine slopes such as in the northern taburiente volcano may also have been modified by smaller scale submarine mass wasting and sediment flows

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

upper mantle magma storage and transport under a canarian shield volcano teno tenerife spain we use clinopyroxene liquid thermobarometry aided by petrography and mineral major element chemistry to reconstruct the magma plumbing system of the late miocene largely mafic teno shield volcano on the island of tenerife outer rims of clinopyroxene and olivine phenocrysts show patterns best explained by decompression induced crystallization upon rapid ascent of magmas from depth the last equilibrium crystallization of clinopyroxene occurred in the uppermost mantle from 20 to 45 km depth we propose that flexural stresses or alternatively thermomechanical contrasts create a magma trap that largely confines magma storage to an interval roughly coinciding with the moho at 15 km and the base of the long term elastic lithosphere at 40 km below sea level evidence for shallow magma storage is restricted to the occurrence of a thick vitric tuff of trachytic composition emplaced before the teno shield volcano suffered large scale flank collapses the scenario developed in this study may help shed light on some unresolved issues of magma supply to intraplate oceanic volcanoes characterized by relatively low magma fluxes such as those of the canary madeira and cape verde archipelagoes as well as hawaiian volcanoes in their postshield stage the data presented also support the importance of progressive magmatic underplating in the canary islands

the distribution of basaltic volcanism on tenerife canary islands implications on the origin and dynamics of the rift systems abstract one of the most characteristic features of volcanic islands is the existence of rift zones defined commonly as orientated eruptive fissures or parallel rows of elongate cinder cones and dyke swarms occasionally these rifts can appear at the birth of the volcanic island and persist until the last episodes of its constructions controlling the form and structure of the island e g azores islands in the case of tenerife canary islands it is possible to observe two rift zones santiago del teide and dorsal rifts running nw se and ene wsw marked by parallel rows of aligned cones and eruptive fissures additionally at the southern part of the island southern volcanic zone basaltic volcanism is characterized by scattered vents and apparently non coherently orientated eruptive fissures some authors relate the existence of the latter volcanism to a n s running rift zone that defines the third branch of a three armed rift system in the island in the present paper we first investigate the tectonic controls on the distribution of basaltic volcanism at the southern volcanic zone and their relation with the nw se and ene wsw rifts the numerical results obtained suggest that basaltic volcanism of the southern part of tenerife can be easily explained as the result of a extensional stress field derived from the combined effects of the nw se and ene wsw rifts as a second objective we have also investigated the origin of the santiago del teide and dorsal rift zones and their role on the formation of the original shield volcano and the subsequent evolution of the whole island our numerical results contrast with previously published explanations on the origin of the tenerife rifts that included fracturing due to volcano spreading or to deformation of the volcano due to magma intrusion we consider that volcanic activity in tenerife began throughout fissural volcanism along these structures that were already present in the oceanic basement progressively accumulating the basaltic series that gave rise to the construction of the composite shield volcano

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

hawaiian magma reservoir processes as inferred from the petrology of gabbro xenoliths in basalt kahoolawe island gabbro xenoliths in a tholeiitic lava of kahoolawe island hawaii a 1 3 1 4 ma shield volcano are 1 3 cm in size and comprised of plagioclase clinopyroxene and orthopyroxene gabbro textures while intergranular and in part subophitic are open due to 28 48 vol of vesicular basalt occupying xenolith space vesicles in and around the xenoliths are lined or filled with rhyolitic glass segregation vesicles the host is evolved tholeiite mgo 6 1 wt with phenocrysts microphenocrysts and glomerocrysts of olivine clinopyroxene orthopyroxene and plagioclase and megacrysts 1 cm of plagioclase the sr isotope ratio of one xenolith is 0 70489 the host basalt ratio is 0 70460 xenolith isotope composition grain resorption and clinopyroxene fs12 5 15wo38 35 5 orthopyroxene fs19 5 24wo4 1 and plagioclase an68 65or0 8 1 2 compositions suggest that these gabbros crystallized from kahoolawe tholeiitic magma of essentially the same composition as the host basalt but pre dating the magma represented by the host based on the absence of intergranular fe ti oxide phases from the pl cpx opx assemblages and the open vuggy textures we envision crystallization on a reservoir roof at temperatures 1100 c entrainment of gabbro assemblages and plagioclase megacrysts from a roof mush suspension zone occurred during convection associated with replenishment of the magma reservoir these open textured gabbro xenoliths are therefore not fragments of preexisting coarse grained bodies such as sills or segregation veins rhyolitic glass in vesicles represents a gas effervescence filtration process that forced fractionated residual liquids from the groundmass into voids associated with the xenoliths

the history of intrusive activity on the island of la palma canary islands abstract the island of la palma located in the northwest of the canary archipelago consists of two main geological units 1 the subaerial extrusive coberta series covers most of the island and consists of alkali basaltic lavas phonolitic plugs and pyroclastic rocks erupted between 1 61 ma and the recent 2 the basement complex is exposed in the barranco de las angustias and the caldera de taburiente and consists of the submarine intrusive and extrusive seamount series and a basal plutonic complex alkali basaltic dikes of different ages and orientations intruded in both units three groups of dikes and sills can be distinguished based on their field relationships petrography geochemistry and ages the oldest group i represent the feeder dikes to the seamount series intruded between 2 9 and 4 0 ma b p they were originally steep with a n05 w strike and perpendicular to the originally nearly flat bedding of the layered seamount series subsequent to emplacement group i dikes and the extrusives of the seamount series were rotated into their present orientation group ii sills intruded parallel to the bedding of the seamount series 45 230 are coeval with or younger than group i but older than the erosional unconformity separating the coberta and the basement complex i e 1 6 ma 50 vol of the volcanic edifice of the la palma seamount and highlight the importance of intrusive processes for island growth intrusions into central oceanic volcanoes like la palma may result in an uplift and rotation of more than 30 km 3 by up to 45

magma storage and underplating beneath cumbre vieja volcano la palma canary islands we have conducted a barometric study of basaltic lavas and mafic to ultramafic xenoliths from cumbre vieja volcano la palma in order to reconstruct magma storage plumbing and related intrusive island growth the samples were collected both along the volcano s rift zone and from its subaerial and submarine flanks up to 30 km off the rift axis clinopyroxene melt barometry of lavas yields a well defined pressure range of 410 770 mpa average 600 mpa and shows no systematic variation with sample locality this pressure range reflects a major fractionation level at ca 15 26 km depth within the uppermost mantle where phenocrysts and melt last equilibrated in contrast microthermometry of co2 dominated fluid inclusions in phenocrysts and xenoliths gives pressure estimates of 240 to 470 mpa average 330 mpa within the lower oceanic crust these pressures are interpreted to reflect an underplating zone at 7 14 km depth where ascending magmas become ponded prior to eruption and where passing magmas temporarily stagnate during eruption the underplating zone is inferred to extend to a radius of ca 30 km at least and its depth appears to increase slightly with distance to the rift axis our data thus show a remarkable pressure bimodality for long term and short term storage of magma that appears to be characteristic for cumbre vieja by using a simple model based on the cumulative volume of material added to the crust we have estimated uplift rates of 0 5 m ka due to underplating that occurs on the island scale on a time scale of some 10 ka these uplift rates are of similar magnitude as global changes in sea level a second more local mode of uplift and related faulting is caused by shallow intrusions into the volcanic edifice as is indicated by the highly irregular morphology of the cumbre vieja we stress that intrusion related uplift should be qualitatively considered when reconstructing the evolution of oceanic island volcanoes since most of the underplated material is inferred to consist of cumulate rocks being intimately mixed and juxtaposed with the lower oceanic crust and having similar densities it is probably impossible to detect such an underplating zone seismically

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

source effects on strong motion records and resolving power of strong motion arrays for source inversion abstract source effects are dominant in near source strong motion seismograms even in the high frequency range and source inversion is the most powerful tool for investigating source effects first source effects that are closely related to damage and intensity patterns are briefly shown large inconsistencies have been seen among source inversion results the cause seems to come mainly from insufficient station distribution for earthquake source studies however the deployment strategy of strong motion seismographs has been only poorly explored secondly three kinds of simulations conducted for the last several years are shown in order to indicate the vulnerability of the resolving power of strong motion arrays to a source inversion the simulations are 1 1 to obtain a relationship between the accuracy of the source inversion and fault array parameters 2 2 to present the optimum array geometry for the source inversion and 3 3 to describe the relative significance of various seismic waves in the source inversion thirdly basic guidelines on strong motion array layout for source inversion are provided and general comments are given on actual source inversion methods we find that the physical wave is a key concept for understanding the optimum array configuration and for choosing the most pertinent inversion method frequency consideration which is a remaining problem is required to decide the best inversion method and the best array layout we can design strong motion array for source inversion on the condition that frequency contents fault mechanism the spatial resolution and the inversion accuracy are prescribed

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

basanite to phonolite differentiation within 1550 1750 yr u th ra isotopic evidence from the a d 1585 eruption on la palma canary islands u th ra disequilibria of basanites tephrites and phonolites from the a d 1585 eruption on la palma canary islands constrain magma differentiation times in an ocean island rift zone the insignificant difference in 230th 232th implies differentiation from basanite to phonolite in 15 k y 226ra has a half life of 1600 yr however and permits higher temporal resolution 226ra 230th disequilibria are highest in the phonolites 46 54 and basanites 44 47 and lowest in the tephrites 38 41 the higher 226ra excesses in the end member compositions model basanite phonolite differentiation within 1550 1750 yr at a rate of 0 04 fractional crystallization per year such a short time interval is in sharp contrast to the 200 k y proposed for phonolite differentiation on the neighboring island of tenerife and could reflect different volcanic systems with a mantle fed rift system on la palma versus a crustal magma reservoir on tenerife

spatial distribution of hotspot material added to the lithosphere under la reunion from wide angle seismic data wide angle seismic lines recorded by ocean bottom and land seismometers provide a pseudo three dimensional investigation of the crust and upper mantle structure around the volcanically active hotspot island of la reunion the submarine part of the edifice has fairly low seismic velocities without evidence for intrusives an upper unit with a velocity depth gradient is interpreted as made of material erupted subaerially then transported and compacted downslope between this unit and the top of the oceanic plate imaged by normal incidence seismic reflection a more homogeneous unit indicated by shadow zones on several wide angle sections may correspond to lavas of a different nature extruded underwater in the earlier phase of volcanism coincident wide angle and normal incidence reflections document that the oceanic plate is not generally downwarping toward the island but doming instead toward its southeastern part with limited evidence for some intracrustal intrusion deeper in the lithosphere the presence of a layer of intermediate velocity between the crust and mantle is firmly established it is interpreted as resulting from the advection of hotspot magmatic products possibly partially molten and of a composition for which the crust is a density barrier the extensive wide angle coverage constrains the extent of this body it does not show the elongated shape expected from plate drift above a steady hotspot supply alternative propositions can hence be considered for example that la reunion is caused by a solitary wave of hotspot material or by a young hotspot the size of the underplate 140 km wide and up to 3 km thick corresponds to less than half the volume of the edifice on top of the plate

a physical model for metal extraction and transport in shallow magmatic systems 1 the highest concentrations of metals e g cu au ag mo in the earth s crust are found in porphyry type deposits the metals are ultimately sourced from magmas and appear to be concentrated hundred to thousand fold from typical magmatic contents ppm ppb in the exsolved volatile phase to better quantify the purging and transport of metals we develop a physical model of volatile evolution in an incrementally built upper crustal magma reservoirs that considers 1 partitioning of metals from the melt to an exsolved volatile phase and 2 advection of the buoyant volatile phase using a single dimensionless parameter the peclet number pe ratio of advection rate over diffusion rate we propose that metal extraction and segregation from magmas can occur in 3 stages with different pe 1 during exsolution of the magmatic volatile phase in shallow crystal poor magma bodies slow volatile advection pe 1 2 during the growth of volatile channels that develop in the reservoir as crystallinity increases pe 1 and 3 during advection in connected channels rapid volatile advection high pe 1 for each stage a metal enrichment factor can be calculated allowing insight into the optimal conditions to maximize metal mass flux into the overlying hydrothermal system the model predicts that the most efficient purging of metals occurs for magmas with intermediate volatile contents and is enhanced during late stage magmatic activity as the reservoirs reach high crystallinity and are not disturbed by volcanic venting in agreement with natural observations suggesting that ore formation post dates volcanic activity

magmatic underplating in the canary archipelago abstract the location of the canary archipelago at the east edge of the north atlantic a few hundred kilometres from the west african coast has for years posed a serious difficulty in understanding the complex interaction between long lasting volcanic activity and one of the oldest seafloor basements 150 ma on earth many different hypotheses have been proposed in the last two decades to understand the genesis of the canary archipelago there is an increasing acceptance to explain the archipelago as the product of the slow passage of the african plate over a mantle hotspot in rival tectonic models stretching and thinning of the lithosphere would determine the islands as independent volcanic blocks we review recent geophysical and geological evidence supporting a mantle plume origin for the canary islands based on the recognition of crustal thickening by mafic intrusions produced by the interaction between the mantle plume and the old oceanic lithosphere beneath the canary archipelago

evidence for a persistent uplifting of la palma canary islands inferred from morphological and radiometric data abstract the morpho structural evolution of la palma canary islands is characterized by vertical movements responsible for or favoring large landslides in its northern part conglomerate terraces nowadays topographically hanged and re incised by the present day barranco de las angustias reveal a recent ongoing uplift process lava flows covered by this geological unit have been sampled and dated by the k ar cassignol technique at a mean age of 507 11 ka the minimum rate of uplift inferred of about 0 4 mm yr is similar to the one deduced from the abnormal elevation of the early submarine series staudigel and schmincke j geophys res 89 1984 11195 11215 this indicates that the northern shield may have experienced a global rise fairly constant throughout most of its geological history it probably results from the combination of regional atlas tectonic processes and the existence of a swell at the island scale this global rise together with the existence of a north south fault in the basement may have controlled triggering of the sw flank collapse of the northern shield and the subsequent concentration of magma along a southern still active topographic ridge the cumbre vieja cv morphological asymmetry of this structure may result from the destabilization of its distal western part favored by strong injections at the axis tilting processes along lateral listric faults can then explain the existence of slope break ups especially on the western side of the ridge such tectonic processes are likely responsible for local superimposed uplifting contributing to the genesis and development of huge western coastal cliffs even in sub historic and historic times we show that unlike many oceanic islands la palma island has experienced important positive vertical movements rather than subsidence

coastal evolution on volcanic oceanic islands a complex interplay between volcanism erosion sedimentation sea level change and biogenic production abstract the growth and decay of oceanic hotspot volcanoes are intrinsically related to a competition between volcanic construction and erosive destruction and coastlines are at the forefront of such confrontation in this paper we review the several mechanisms that interact and contribute to the development of coastlines on oceanic island volcanoes and how these processes evolve throughout the islands lifetime volcanic constructional processes dominate during the emergent island and subaerial shield building stages during the emergent island stage surtseyan activity prevails and hydroclastic and pyroclastic structures form these structures are generally ephemeral because they can be rapidly obliterated by marine erosion with the onset of the subaerial shield building stage coastal evolution is essentially characterized by rapid but intermittent lateral growth through the formation of lava deltas largely expanding the coastlines until they typically reach their maximum extension with the post shield quiescence in volcanic activity destructive processes gradually take over and coastlines retreat adopting a more prominent profile mass wasting and marine and fluvial erosion reshape the landscape and if conditions are favorable biogenic processes assume a prominent role post erosional volcanic activity may temporarily reverse the balance by renewing coastline expansion but islands inexorably enter in a long battle for survival above sea level reef growth and or uplift may also prolong the island s lifetime above the waves the ultimate fate of most islands however is to be drowned through subsidence and or truncation by marine erosion

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

textural constraints on the kinetics of crystallization of igneous rocks natural systems provide time controlled experiments on scales unreachable in the laboratory and with complexities unapproachable by computer experiments since temperature undercooling cannot be directly scaled with time in situ crystallization experiments provide information unavailable by other means the kinetics of crystallization in simple silicate systems have been studied extensively for glass ceramic systems e g uhlmann 1982 james 1982 but predictive models for nucleation behavior in particular remain inadequate part of the problem in creating models of nucleation lies in the difficulty of experimentally isolating the nucleation process crystal growth measurements are more accessible experimentally and for this reason crystal growth is better understood e g dowty 1980 kirkpatrick 1981 james 1982 baronnet 1984 however predictive models of crystal growth e g lasaga 1982 require accurate models for the temperature and compositional dependence of both the thermodynamic and kinetic driving forces for crystallization information that is currently limited the cse parameterization of the position of ymax as a function of t tl and t suggested by dearnley 1983 provides a potentially useful model that requires further testing similarly application of the adiabatic nucleation model of meyer 1986 to simple systems suggests that the position of tmax relative to tl has an approximately constant value of 0 55 0 60 exceptions are low dsf minerals such as albite and quartz additionally while experimental crystallization rate data is a necessary link between processes in natural melts and numerical models experimental growth rate data is confined to simple systems and conditions of moderately large undercooling while growth rate estimates in complex natural systems suggest that under most conditions undercoolings remain very small quantitative textural studies of dikes suggest a pronounced dependence of growth rate on total crystallization time e g ikeda 1977 which is in turn related to effective undercooling a function of both total dike width and distance from the dike margin by analogy minimum crystallization rates may be estimated from programmed cooling experiments if a temperature interval of crystallization is assumed growth rates determined in this way show the same relationship between growth rate and total crystallization time seen in the dike studies reflecting a systematic relationship between growth rate and cooling rate effective undercooling for plagioclase in basaltic systems while the data are not available for other mineral systems there is no reason to believe that similar patterns would not exist for other silicate minerals i e the similarity in dendritic olivine growth rates estimated by fowler et al 1989 using fractal analysis to the growth rates of plagioclase under conditions of rapid cooling estimated from programmed cooling rate experiments analysis of measured crystal size frequencies provides a means of extracting effective bulk kinetic information from geologic systems that can help to constrain the dynamic feedback between physical models of magmatic systems and rates of chemical change