evolution of the eastern volcanic ridge of the canary islands based on new kar data the results of 64 new k ar age determinations together with 32 previously published ages show that after a period of erosion of the basal complex miocene volcanic activity started around 20 ma in fuerteventura and 15 ma in lanzarote forming a tabular succession of basaltic lavas and pyroclastics with a few salic dykes and plugs this series includes five separate volcanic edifices each one with its own eruptive history in fuerteventura several miocene eruptive cycles have been identified in the central edifice one around 20 17 ma followed by two others centred around 15 and 13 ma in the southern edifice the maximum of activity took place around 16 14 ma whereas in the northern one the main activity occurred between 14 and 12 ma in lanzarote a first cycle of activity took place in the southern edifice between 15 5 and 14 1 ma followed by another between 13 6 and 12 3 ma in the northern edifice three pulses occurred 10 2 8 3 6 6 5 3 and 3 9 3 8 ma an important temporal gap greater in fuerteventura than in lanzarote separates series i from the plio quaternary series ii iii and iv formed by multi vent basaltic emissions in fuerteventura the following eruptive cycles have been identified 5 2 9 2 4 1 8 1 7 0 8 0 4 and 0 1 ma in lanzarote the activity was fairly continuous from 2 7 ma to historic times with a maximum in the lower pleistocene eruptive rates in the series i edifices were on the average 0 1 0 01 km3 ka comparable but slightly smaller than in similar edifices in tenerife and la gomera but much lower than in gran canaria average post miocene eruptive rates were about 0 013 0 027 km3 ka in lanzarote and 0 003 0 007 km3 ka in fuerteventura all these volcanic edifices show a similar general sequence fissural eruptions erosion multi vent volcanism repeated at different periods in different parts of the eastern islands of the canaries the model of growth of the series i edifices is comparable to those in tenerife and la gomera long periods of activity sometimes greater than 6 m y with pulses separated by gaps however salic and intermediate differentiates frequent in tenerife and la gomera are very scarce in these islands the fuerteventura lanzarote ridge shows a decrease in volcanic activity with time and also a certain ssw nne polarity in the temporal development of volcanism

the tectonically controlled emplacement of a vertically sheeted gabbro pyroxenite intrusion feeder zone of an ocean island volcano fuerteventura canary islands abstract the miocene px1 gabbro pyroxenite pluton fuerteventura canary islands is a 3 5 5 5 km shallow level intrusion 0 15 0 2 gpa and 1100 1120 c interpreted as the feeder zone to an ocean island volcano it displays a vertical magmatic banding expressed in five 50 to 100 metre wide nne ssw trending alkaline gabbro sequences alternating with pyroxenites this emplacement geometry was controlled by brittle to ductile shear zones generated by a regional e w extensional tectonic setting that affected fuerteventura during the miocene at a smaller scale the px1 gabbro and pyroxenite bands consist of metre thick differentiation units which suggest emplacement by periodic injection of magma pulses as vertical dykes that amalgamated similarly to a sub volcanic sheeted dyke complex individual dykes underwent internal differentiation following a solidification front parallel to the dyke edges this solidification front may have been favoured by a significant lateral horizontal thermal gradient expressed by the vertical banding in the gabbros the fractionation asymmetry within individual dykes and the migmatisation of the wall rocks pyroxenitic layers result from the fractionation and accumulation of clinopyroxene olivine plagioclase crystals from a mildly alkaline basaltic liquid they are interpreted as truncated differentiation sequences from which residual melts were extracted at various stages of their chemical evolution by subsequent dyke intrusions either next to or within the crystallising unit compaction and squeezing of the crystal mush is ascribed to the incoming and inflating magma pulses the expelled interstitial liquid was likely collected and erupted along with the magma flowing through the newly injected dykes clinopyroxene mineral orientation as evidenced by ebsd and micro x ray tomography investigations displays a marked pure shear component supporting the interpretation of the role of compaction in the generation of the pyroxenites conversely gabbro sequences underwent minor melt extraction and are believed to represent crystallised coalesced magma batches emplaced at lower rates at the end of eruptive cycles clinopyroxene orientations in gabbros record a simple shear component suggesting syn magmatic deformation parallel to observed nne ssw trending shear zones induced by the regional tensional stress field this emplacement model implies a crystallisation time of 1 to 5 years for individual dykes consistent with px1 emplacement over less than 0 5 my a minimum amount of approximately 150 km3 of magma is needed to generate the pluton part of it having been erupted through the central volcanic centre of fuerteventura if the regional extensional tectonic regime controls the px1 feeder zone initiation and overall geometry rates and volumes of magma depend on other source related factors high injection rates are likely to induce intrusion growth rates larger than could be accommodated by the regional extension in this case dyke intrusion by propagation of a weak tip combined with the inability of magma to circulate through previously emplaced and crystallised dykes could result in an increase of non lithostatic pressure on previously emplaced mushy dyke walls thus generating strong pure shear compaction within the pluton feeder zone and interstitial melt expulsion these compaction dominated processes are recorded by the cumulitic pyroxenite bands

catastrophic debris avalanche deposit of socompa volcano northern chile between 10 000 and 500 yr ago the socompa volcano in northern chile experienced a catastrophic collapse of a 70 deg sector of the original cone causing a debris avalanche that descended nearly 3000 m vertically and traveled more than 35 km from the volcano the deposits cover some 490 sq km and have a minimum volume of 15 cu km parts of the original cone slumped in a nearly coherent form and are now preserved as large blocks more than 400 m high the primary avalanche traveled northwestward over sloping ground before coming to rest transiently forming a prominent marginal ridge and then slid away northeastward to form a secondary flow overriding much of the primary avalanche deposit abundant prismatic jointed dacite blocks within the debris avalanche deposit and a thin fine grained pumiceous deposit beneath it suggest that the collapse was triggered by magmatic activity and may have been accompanied by a violent lateral blast collapse was followed by eruption of pumiceous pyroclastic flows and extrusion of voluminous dacite domes

trace element distribution among rock forming minerals from metamorphosed to partially molten basic igneous rocks in a contact aureole fuerteventura canaries abstract low pressure partial melting of basanitic and ankaramitic dykes gave rise to unusual zebra like migmatites in the contact aureole of a layered pyroxenite gabbro intrusion in the root zone of an ocean island basal complex fuerteventura canary islands these migmatites are characterised by a dense network of closely spaced millimetre wide leucocratic segregations their mineralogy consists of plagioclase an 32 36 diopside biotite oxides magnetite ilmenite amphibole dominated by plagioclase in the leucosome and diopside in the melanosome the melanosome is almost completely recrystallised with the preservation of large relict igneous diopside phenocrysts in dyke centres comparison of whole rock and mineral major and trace element data allowed us to assess the redistribution of elements between different mineral phases and generations during contact metamorphism and partial melting dykes within and outside the thermal aureole behaved like closed chemical systems nevertheless zr hf y and rees were internally redistributed as deduced by comparing the trace element contents of the various diopside generations neocrystallised diopside in the melanosome leucosome and as epitaxial phenocryst rims from the migmatite zone are all enriched in zr hf y and rees compared to relict phenocrysts this has been assigned to the liberation of trace elements on the breakdown of enriched primary minerals kaersutite and sphene on entering the thermal aureole major and trace element compositions of minerals in migmatite melanosomes and leucosomes are almost identical pointing to a syn or post solidus reequilibration on the cooling of the migmatite terrain i e mineral melt equilibria were reset to mineral mineral equilibria

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

volcanic and morphological evolution of la gomera canary islands based on new k ar ages and magnetic stratigraphy implications for oceanic island evolution the spatial and chronological evolution of canary islands volcanism is due to eastward progression of the slow moving african plate over a mantle plume la gomera is located between the western shield stage islands 12 ma with 23 k ar ages and palaeomagnetic data we can constrain the timing of the main subaerial volcanic phases of la gomera the shield volcano c 9 4 8 0 ma the postshield peripheral lava flows c 7 4 5 0 ma the postshield horizontal lava flows c 5 4 4 3 ma and late intra canyon lava flows c 1 9 ma the horizontal lava flows fill a 10 km wide depression formed by a giant landslide garajonay the entire structure of la gomera is in relief inversion declining volcanic construction rates from the shield to the postshield stages are correlated with increasing erosion rates whereas the period of volcanic quiescence hiatus has low erosion rates the succession and duration of the hotspot volcanic stages in the canary islands are compared with those in the hawaiian islands thus underlining differences between slow moving and fast moving plate settings

low pressure water assisted anatexis of basic dykes in a contact metamorphic aureole fuerteventura canary islands oxygen isotope evidence for a meteoric fluid origin migmatites produced by low pressure anatexis of basic dykes are found in a contact metamorphic aureole around a pyroxenite gabbro intrusion px2 on fuerteventura dykes outside and inside the aureole record interaction with meteoric water with low or negative 18o whole rock values 0 2 to 3 4 decreasing towards the contact recrystallised plagioclase diopside biotite and oxides from within the aureole show a similar evolution with lowest 18o values 2 8 4 2 4 4 and 7 6 respectively in the migmatite zone close to the intrusion relict clinopyroxene phenocrysts preserved in all dykes retain typically magmatic 18o values up to the anatectic zone where the values are lower and more heterogeneous low 18o values decreasing towards the intrusion can be ascribed to the advection of meteoric water during magma emplacement with increasing fluid rock ratios higher dyke intensities towards the intrusion acting as fluid pathways and higher temperatures promoting increasing exchange during recrystallisation

small vertebrate taphonomy of la cueva del llano a volcanic cave on fuerteventura canary islands spain palaeoecological implications abstract cueva del llano is a volcanic tube of pleistocene age on fuerteventura island a strand of it ramal nuevo contains a complex sedimentary infill which has been divided into three sedimentary units and contains at least eight fossiliferous levels of holocene age the taphonomic analysis of small vertebrates found in the sediments revealed a scatological origin for the vertebrate assemblage and that the barn owl tyto alba is the main agent responsible for this concentration of bone remains furthermore the taphonomic analysis allows to reconstruct the changes in the palaeodiet of barn owls during the holocene of fuerteventura canary islands and infer the alterations produced in the vertebrate comunity during that time in the upper units of the sedimentary infill the appearance of the house mouse mus musculus is observed this immigration is correlated that is associated to a decrease of the lava mouse malpaisomys insularis proportions in the fossil assemblage also the study of small vertebrate accumulation in ramal nuevo shows that volcanic tubes can be referred to as very useful concentration trap for taphonomic studies

stable isotope δ18o δ13c and δd signatures of recent terrestrial communities from a low latitude oceanic setting endemic land snails plants rain and carbonate sediments from the eastern canary islands abstract stable isotopes of oxygen and carbon extracted from fossil land snail shells have been used increasingly to interpret past environments to evaluate the utility of this approach for low latitude oceanic islands populations of the modern helicid land snail theba geminata a species also abundant in the quaternary fossil record of the region were sampled at ten low altitude d and 2 v smow for 18 o ranging from 11 to 2 v smow and from 2 6 to 0 7 v smow respectively the local vegetation is heterogeneous including c 3 c 4 and cam plants 13 c values vary from 13 0 to 29 0 v pdb across plant species of the 24 species five are c 4 15 are c 3 and four are cam plants the 18 o values for shells represent a narrow range of values from 0 3 to 2 5 v pdb which is consistent with the low climate seasonality typifying low latitude oceanic settings hypothetical model of the expected 18 o value for shell aragonite precipitated in equilibrium suggests that the most negative 18 o shell represent the closest estimate for 18 o rain water the 13 c values of shells range from 9 4 to 1 7 v pdb the most positive 13 c values are attributed to a diet based on c 4 plants the comparison of 13 c values of soft tissues and shells suggests that snails ingested notable amounts from 20 up to 40 of foreign carbonates consequently fossil shells with the most negative 13 c values should be selected for radiocarbon dating in future geochronological studies of the region the 13 c values of body tissues vary from 12 0 to 27 2 v pdb indicating that land snails consumed c 3 and c 4 plants indiscriminately the mean carbon isotopic composition averaged across multiple fossil specimens may thus provide a useful tool for reconstructing paleoclimates and paleoenvironments throughout the quaternary history of the canary islands and other comparable low latitude oceanic settings

shear zones as a result of intraplate tectonics in oceanic crust the example of the basal complex of fuerteventura canary islands ductile shear zones affecting igneous rocks pyroxenites syenites gabbros and carbonatites belonging to the basal complex of the island of fuerteventura are described here they develop typical mylonites with their cortege of structures and crystallographic fabrics an evolution from brittle to ductile conditions has been recognized and interpreted as being due to the ascent of alkaline magmas and related fluids and subsequent emplacement of weak rocks carbonatites syenites along the shear zones local metamorphic changes favour the ductile behaviour via a reaction enhanced softening mechanism the shear zones are arranged in a nearly orthorhombic pattern kinematic criteria suggest an extensional tectonic scenario with a bulk irrotational nonplane deformation the long axis of the finite deformation ellipsoid is e w and horizontal the available data allow us to establish this deformation as being from the late oligocene to the early miocene this is tentatively related to the plate tectonics evolution and mantle anomalies in the northwestern corner of the african plate

a reappraisal of the stratigraphy of cueva del llano fuerteventura and the chronology of the introduction of the house mouse mus musculus into the canary islands abstract major ecological changes related to anthropogenic activities begin on islands with initial human settlement key factors to understanding insular holocene ecological changes are the arrival dates of both humans and alien species to the islands in this context finely stratified fossil sites are powerful tools to study the chronology and causes of these changes previous work based on conventional 14c ages of land snails coming from the finely stratified site cueva del llano at fuerteventura canary islands eastern atlantic ocean indicates that one of the major ecological changes that took place in this archipelago the arrival of house mouse mus musculus occurred around 7000 yrs ago thus before the first arrival of humans to the islands to extend these studies we obtained 14c ages by accelerator mass spectrometer ams directly on bone collagen from selected bones of rodents lava mouse malpaisomys insularis and house mouse from seven sites cueva del llano cueva de villaverde and malpais de la arena i ii fuerteventura el bebedero and jameo de la puerta falsa lanzarote and barranco de la baranda la palma the new ages derived from the upper levels of cueva del llano cll 9 1 9 2 indicate a very young age for these materials between 1667 1949 and 1261 1391 cal ad these results support a more recent and very different chronology for the holocene ecological changes that occurred on these islands compared to previous studies explanations for the stratigraphically anomalous age shown in previous papers are put forward on the other hand the available 14c ages indicate that the house mouse arrived on the eastern canary islands some time between 756 cal bc 313 cal ad and probably from there spread to the other islands before european contact

loess like and palaeosol sediments from lanzarote canary islands spain indicators of palaeoenvironmental change during the late quaternary abstract on lanzarote canary islands quaternary saharan dust and weathered local volcanic material were trapped in miocence to pliocene valleys dammed by younger volcanic edifices these sediments show sequences of alternating reddish clayey and loess like yellowish silty material in order to investigate if reddish clayey layers contain material derived from local pedogenesis and if so which pedogenetic processes were active we performed sedimentological micromorphological and environmental magnetic analyses the analyses demonstrate that these layers contain material derived from local soils these soils were characterised by clay formation rubefication and the formation of superparamagnetic particles during periods of enhanced soil moisture thus they can serve as natural archives in order to reconstruct the terrestrial palaeoclimatic history of lanzarote the distribution of soil material in the profiles shows that cold periods of the late quaternary were characterised by more humid conditions than today using palaeontological remains and a comparison with recent soils on tenerife we can roughly estimate maximal palaeoprecipitation values during more humid periods

volcanic evolution of the island of tenerife canary islands in the light of new k ar data new age determinations from tenerife together with those previously published 93 in all provide a fairly comprehensive picture of the volcanic evolution of the island the oldest volcanic series with ages starting in the late miocene are formed mainly by basalts with some trachytes and phonolites which appear in anaga teno and roque del conde massifs in anaga ne three volcanic cycles occurred one older than 6 5 ma a second one between 6 5 and 4 5 ma with a possible gap between 5 4 and 4 8 ma and a late cycle around 3 6 ma in teno nw after some undated units the activity took place between 6 7 and 4 5 ma with two main series separated by a possible pause between 6 2 and 5 6 ma in the zone of roque del conde s the ages are scattered between 11 6 and 3 5 ma between 3 3 and 1 9 ma the whole island underwent a period of volcanic quiescence and erosion the large canadas volcano made up of basalts trachytes and phonolites was built essentially between 1 9 and 0 2 ma to the ne of this central volcano linking it with anaga is a chain of basaltic emission centers with a peak of activity around 0 8 ma the canadas caldera had several collapse phases associated with large ignimbrite emissions there were at least an older phase more than 1 ma old on the western part of the volcano and a younger one less than 0 6 ma old in the eastern side the two large valleys of guimar and la orotava were formed by large landslides less than 0 8 ma ago and probably before 0 6 ma ago the present canadas caldera was formed by another landslide less than 0 2 ma ago this caldera was later filled by the huge teide volcano which has been active even in historic times during the same period a series of small volcanoes erupted at scattered locations throughout the island the average eruptive rate in tenerife was 0 3 km3 ka with relatively small variations for the different eruptive periods this island and la gomera represent a model of growth by discontinuous pulses of volcanic activity separated by gaps often coinciding with episodes of destruction of the edifices and sometimes extended for several million years the neighbouring gran canaria on the other hand had an initial rapid shield building phase during which more than 90 of the island was built and a series of smaller pulses at a much later period a comparison between these three central islands indicates that the previously postulated westward displacement in time of a gap in the volcanic activity is valid only as a first approximation several gaps are present on each island overlapping in time and not clearly supporting either of the models proposed to explain the evolution of the canaries

hotspot volcanism close to a passive continental margin the canary islands the canarian archipelago is a group of volcanic islands on a slow moving oceanic plate close to a continental margin the origins of the archipelago are controversial a hotspot or mantle plume a zone of lithospheric deformation a region of compressional block faulting or a rupture propagating westwards from the active atlas mountains fold belt have been proposed by different authors however comparison of the canarian archipelago with the prototypical hotspot related island group the hawaiian archipelago reveals that the differences between the two are not as great as had previously been supposed on the basis of older data quaternary igneous activity in the canaries is concentrated at the western end of the archipelago close to the present day location of the inferred hotspot this is the same relationship as seen in the hawaiian and cape verde islands the latter archipelago associated with a well defined but slow moving mantle plume shows anomalies in a plot of island age against distance which are comparable to those seen in the canary islands these anomalies cannot therefore be used to argue against a hotspot origin for the canaries individual islands in both archipelagoes are characterized by initial rapid growth the shield building stages of activity followed by a period of quiescence and deep erosion erosion gap which in turn is followed by a post erosional stage of activity the absence of post shield stage subsidence in the canaries is in marked contrast with the major subsidence experienced by the hawaiian islands but is comparable with the lack of subsidence evident in other island groups at slow moving hotspots such as the cape verdes comparison of the structure and structural evolution of the canary islands with other oceanic islands such as hawaii and reunion reveals many similarities these include the development of triple mercedes star rift zones and the occurrence of giant lateral collapses on the flanks of these rift zones the apparent absence of these features in the post erosional islands may in part be a result of their greater age and deeper erosion which has removed much of the evidence for their early volcanic architecture we conclude that the many similarities between the canary islands and island groups whose hotspot origins are undisputed show that the canaries have been produced in the same way

submarine landslides around the canary islands the morphology and structure of the submarine flanks of the canary islands were mapped using the gloria long range side scan sonar system bathymetric multibeam systems and sediment echosounders twelve young 2 ma giant landslides have been identified on the submarine flanks of the canary islands up to now older landslide events are long buried under a thick sediment cover due to high sedimentation rates around the canary islands most slides were found on the flanks of the youngest and most active islands of la palma el hierro and tenerife but young giant landslides were also identified on the flanks of the older 15 20 ma but still active eastern islands large scale mass wasting is an important process during all periods of major magmatic activity the long lived volcanic constructive history of the islands of the canary archipelago is balanced by a correspondingly long history of destruction resulting in a higher landslide frequency for the canary islands compared to the hawaiian islands where giant landslides only occur late in the period of active shield growth the lower stability of the flanks of the canaries is probably due to the much steeper slopes of the islands a result of the abundance of highly evolved intrusive and extrusive rocks another reason for the enhanced slope instability is the abundance of pyroclastic deposits on canary islands resulting from frequent explosive eruptions due to the elevated volatile contents in the highly alkalic magmas dike induced rifting is most likely the main trigger mechanism for destabilization of the flanks flank collapses are a major geological hazard for the canary islands due to the sector collapses themselves as well as triggering of tsunamis in at least one case a giant lateral blast occurred when an active magmatic or hydrothermal system became unroofed during flank collapse

caldera formation at volcan colima mexico by a large large holocene volcanic debris avalanche abstract about 4 300 years ago 10 km 3 of the upper cone of ancestral volcan colima collapsed to the southwest leaving a horseshoe shaped caldera 4 km in diameter the collapse produced a massive volcanic debris avalanche deposit covering over 1550 km 2 on the southern flanks of the volcano and extending at least 70 km from the former summit the avalanche followed a steep topographic gradient unobstructed by barriers resulting in an unusually high area volume ratio for the colima deposit the apparent coefficient of friction fall height distance traveled for the colima avalanche is 0 06 a low value similar to those of other large volume deposits the debris avalanche deposit contains 40 75 angular volcanic clasts from the ancestral cone a small proportion of vesicular blocks that may be juvenile and in distal exposures rare carbonate clasts plucked from the underlying surface by the moving avalanche clasts range in size to over 20 m in diameter and are brecciated to different degrees pulverized and surrounded by a rock flour matrix the upper surface of the deposit shows prominent hummocky topography with closed depressions and surface boulders a thick coarse grained compositionally zoned scoria fall layer on the upper northeastern slope of the volcano may have erupted at the time of collapse a fine grained surge layer is present beneath the avalanche deposit at one locality apparently representing an initial blast event most of the missing volume of the ancestral volcano has since been restored at an average rate of 0 002 km 3 yr through repeated eruptions from the post caldera cone as a result the southern slope of volcan colima may again be susceptible to collapse over 200 000 people are now living on primary or secondary deposits of the debris avalanche and a repetition of this event would constitute a volcanic disaster of great magnitude ancestral volcan colima grew on the southern trenchward flank of the earlier and larger volcano nevado de colima trenchward collapse was favored by the buttressing effect of nevado the rapid elevation drop to the south and the intrusion of magma into the southern flank of the ancestral volcano other such trenchward younging paired volcanoes are known from mexico guatemala el salvador chile and japan the trenchward slopes of the younger cones are common sites for cone collapse to form avalanche deposits as occurred at colima and popocatepetl in mexico and at san pedro volcano in chile

the contribution of landslides to landscape evolution in europe abstract after a review of some analytical and conceptual models of slope evolution with the intervention of mass movements a proposal is made of a series of indicators for the quantitative description of landscape evolution in relation to mass movements the ratio between landslide mobilisation rate and downwearing rate is proposed as a quantitative measure of the significance of mass movements in landscape evolution a subdivision of european regions with respect to their susceptibility to landsliding as a process of landscape evolution is proposed the role of landsliding for the evolution of landscape in some regions is described the data presented show that landsliding may in some cases be the main contributor to landscape change

modelling of crustal anomalies of lanzarote canary islands in light of gravity data the application of a gravity inversion method enables us to obtain a 3 d density contrast model of the upper crustal anomalies of the volcanic island of lanzarote canary islands for this we use a network of 296 gravity stations distributed over the whole island and a digital terrain model of about 45 000 terrestrial and oceanic data to determine the corresponding terrain correction a density value of 2480 kg m 3 is chosen for this correction by means of a new approach the resulting bouguer anomaly is analysed by means of a least squares prediction which gives us a mean level of uncorrelated observational noise of about 1 2 mgal this anomaly is considered in order to obtain independent information about the inner anomalous mass density distribution by means of a 3 d gravity inversion based on a systematic exploration on a prismatic partition of the subsoil volume and adopting et priori values of the density contrast positive and negative to determine the geometry of the anomalous bodies the problem of non uniqueness of the solution is avoided by using a minimization mix condition on the weighted residuals and the weighted whole anomalous mass the structural solution is finally presented by means of horizontal sections and vertical profiles a main intrusive body is located under the central eastern area and could correspond to a dilated volcanic activity of shield formation it shows a prismatic form of more than 15 km depth subducted with only the ridges remaining as horst blocks moreover the sw and ne extreme areas of the island show smaller and shallower positive bodies interpreted as less developed magmatic intrusions conversely several density lows offer interesting shallow alignments 45 degreesn ene wsw and 125 degreesn wnw ese which could be associated with a fracture system corresponding to structural stress and also correlate with historic eruptions such as for instance the timanfaya eruption the monitoring of several geophysical parameters at two underground geodynamic stations in the ne zone of the island and timanfaya shows characteristic differences between the two zones which confirm crustal anomalies in the second station

geomorphological investigations of sediment traps on lanzarote canary islands as a key for the interpretation of a palaeoclimate archive off nw africa abstract on lanzarote canary islands late quaternary saharan dust and volcanic material were trapped in miocence to pliocene valleys dammed by volcanic lava flows these trapped sediments are potentially interesting as they can be natural archives useful to reconstruct the terrestrial palaeoclimate history of the nw african margin nevertheless slope wash processes altered the primarily eolian deposits making climatic interpretation not straightforward geomorphological mapping gis calculations and sedimentological investigations were used to unravel these processes influencing the temporal resolution of the palaeoclimatic archive demonstrating that they average the palaeoclimatic signal by some ka thus despite the colluvial geomorphic environment the valley fillings can be used for palaeoclimatic interpretation of events with a length of at least some ka the youngest sediments deposited since at least 2 5 ka are anthropogenically triggered and thus cannot be used for palaeoclimatic interpretation the results show that the input of saharan dust at lanzarote increased during the last 1 0 ka and especially during the early middle holocene

k ar chronology of the volcanic eruptions in the canarian archipelago island of la gomera a geochronological study of the island of la gomera canaries has been carried out by the k ar method the 26 new ages obtained together with the 17 previous determinations show that above the main unconformity of the island separating the basal complex from the later volcanic series there is a unit of lower old basalts more than 10 m y old polymictic volcanic breccias were emplaced between 10 and 9 m y ago the upper old basalts above them were formed between 9 and 6 m y ago with a peak of activity around 7 m y after a period of erosion 6 5 m y a thick series of young basalts associated with trachytic and phonolitic domes and flows were rapidly emplaced between 4 5 4 m y ago finally local basaltic activity took place 2 8 m y ago the age of the basal complex is not well known although three ages 14 6 15 5 and 19 3 m y have been obtained for some alkaline intrusives which seem to represent the youngest events in the complex

complexity of quaternary aeolian dynamics canary islands abstract carbonate aeolianites are important quaternary archives at the point of intersection between marine and terrestrial systems since they are composed of alternating aeolian sediments and several paleosol units these sequences are highly suitable to reconstruct palaeoenvironmental conditions in northern fuerteventura at least five different areas are characterised by successions of different dune generations and paleosols few studies have addressed the stratigraphic order of individual dune areas therefore a comprehensive consideration spanning several dune fields is needed here we aim to present a detailed stratigraphy of two different dune areas and to identify the contribution of different materials shelf origin dust origin volcanic origin along with processes accumulation soil formation erosion preservation that build up these archives four key sections were selected and sampled for laboratory analyses texture elemental composition caco3 content palaeoenvironmental magnetics luminescence dating and gastropod assemblages based on main stratigraphic features five major sedimentary sequences were identified indicating differences in prevailing sediment supply humidity and volcanic activity first luminescence dating irsl of the sequences revealed sedimentation ages between 360 ka and 15 ka finally we are able to demonstrate that different dune areas show comparable stratigraphic patterns but each studied site is defined by certain characteristics depending on the respective features of the closer surrounding the knowledge of these peculiarities and the underlying background is essential in order to correlate different sites and to attempt an appropriate environmental interpretation of the sedimentary sequences

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

using a genetic algorithm for 3 d inversion of gravity data in fuerteventura canary islands the use of genetic algorithms in geophysical inverse problems is a relatively recent development and offers many advantages in dealing with the non linearity inherent in such applications we have implemented a genetic algorithm to efficiently invert a set of gravity data employing several fixed density contrasts this algorithm determines the geometry of the sources of the anomaly gravity field in a 3 d context the genetic algorithms based on darwin s theory of evolution seek the optimum solution from an initial population of models working with a set of parameters by means of modifications in successive iterations or generations this searching method traditionally consists of three operators selection crossover and mutation acting on each generation but we have added a further one which smoothes the obtained models in this way we have designed an efficient inversion gravity method confirmed by both a synthetic example and a real data set from the island of fuerteventura in the latter case we identify crustal structures related to the origin and evolution of the island the results show a clear correlation between the sources of gravity field in the model and the three volcanic complexes recognized in fuerteventura by other geological studies

evidence of historic infilling of valleys in lanzarote after the timanfaya eruption ad 1730 1736 canary islands spain the timanfaya eruption 1730 1736 was the most important volcanic event on the canary islands during historical times after the 15th century ad it produced lava flows and pyroclastic layers tha

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

evidence of a modern deep water magmatic hydrothermal system in the canary basin eastern central atlantic ocean new seismic profiles bathymetric data and sediment rock sampling document for the first time the discovery of hydrothermal vent complexes and volcanic cones at 4800 5200 m depth related to recent volcanic and intrusive activity in an unexplored area of the canary basin eastern atlantic ocean 500 km west of the canary islands a complex of sill intrusions is imaged on seismic profiles showing saucer shaped parallel or inclined geometries three main types of structures are related to these intrusions type i consists of cone shaped depressions developed above inclined sills interpreted as hydrothermal vents type ii is the most abundant and is represented by isolated or clustered hydrothermal domes bounded by faults rooted at the tips of saucer shaped sills domes are interpreted as seabed expressions of reservoirs of ch4 and co2 rich fluids formed by degassing and contact metamorphism of organic rich sediments around sill intrusions type iii are hydrothermal volcanic complexes originated above stratified or branched inclined sills connected by a chimney to the seabed volcanic edifice parallel sills sourced from the magmatic chimney formed also domes surrounding the volcanic cones core and dredges revealed that these volcanoes which must be among the deepest in the world are constituted by oib type basanites with an outer ring of blue green hydrothermal al rich smectite muds magmatic activity is dated based on lava samples at 0 78 0 05 and 1 61 0 09 ma k ar methods and on tephra layers within cores at 25 237 ky the subvent hydrothermal volcanic complex constitutes the first modern system reported in deep water oceanic basins related to intraplate hotspot activity

the primitive volcano of mount pelee its construction and partial destruction by flank collapse abstract the geology of mount pelee the active volcano of martinique lesser antilles has been actively studied during the past decade this paper reviews the current knowledge about the oldest least well known part of the volcano here called paleo pelee and the relations between paleo pelee and the mont conil volcanic complex paleo pelee consists mostly of volcanic breccias with a few lava flows it differs in this respect from neighbouring active volcanoes such as the grande decouverte soufriere in guadeloupe and the soufriere in st vincent the oldest products of which are mainly lava flows paleo pelee initially formed a regular cone which was comparable in size with the present edifice it is now largely eroded and its products form prominent radial ridges on the western flank of mount pelee these are buried under younger deposits on the eastern flank the uniformly andesitic breccias of paleo pelee are for the most part brecciated lava flows it is inferred that the activity of mount pelee was less explosive at this stage than during following periods neo pelee the paleo pelee formations overlap those of mont conil the geology of mont conil is poorly known however its lowest exposed products are submarine andesitic breccias cut by many dikes this contrasts with paleo pelee where all breccias are of subaerial origin pleistocene limestones are interbedded within the mont conil breccias between 120 and 150 m above sea level though mont conil seems to be closely linked to mount pelee on the basis of available petrological data a major uplift must have occurred sometime during or after the construction of mont conil and forms a recognizable geological boundary between the two volcanic systems the paleo pelee edifice was partially destroyed by a flank collapse event that occurred on the southwest flank during the early stage 40 000 20 000 y b p of neo pelee this event is evidenced by a large 6 2 5 km horseshoe shaped structure which is limited by well preserved morphological scarps on land and by a 300 m offshore scarp as shown by seabeam bathymetry paleo pelee breccias and lava flows are truncated by the boundary of the collapse structure lava domes occupied the upslope part of the structure at a later time these domes are intersected by the present crater etang sec which has probably been the active vent for at least 2000 years the active crater is located at the intersection between the flank failure depression and an older caldera formed at the paleo pelee stage but probably enlarged later the flank failure structure appears as a major structure of the volcano and creates a strong structural asymmetry in the edifice this fact should be considered when dealing with such various aspects as the hydrogeology of the volcano the structural control of past and future eruptions and the volcanic hazards

diverse basalt types from loihi seamount hawaii loihi seamount is the southeasternmost active volcano in the hawaiian emperor volcanic chain the seamount is considered representative of the early phase of hawaiian volcanism because of its youth small size and location near the melting anomaly seventeen dredge stations recovered transitional basalt alkalic basalt and basanite in addition to the expected tholeiitic basalt four flows of alkalic basalt contain common small dunite xenoliths the recovered samples have thin palagonite rinds and almost no manganese on the glassy surfaces we estimate that the lavas are less than about 4 000 yr old and many are less than 1 000 yr old loihi seamount is apparently in a transitional growth phase between the early eruption of alkalic lavas and the commonly observed subaerial tholeiitic eruptive phase previously thought to dominate hawaiian volcanism from inception until the postcaldera collapse alkalic stage

climatic cycles inferred from the aminostratigraphy and aminochronology of quaternary dunes and palaeosols from the eastern islands of the canary archipelago aminochronological and aminostratigraphical methods have been used to study the quaternary a e o l i a n deposits f r om the islands located east of the canary archipelago fuerteventura and lanzarote islands and la graciosa montana clara and alegranza islets t h e extent of racemisation epimerisation of four amino acids isoleucine aspartic acid phenylalanine and glutamic acid was measured in land snail shells of the genus theba the age calculation algorithms of these amino acids h a v e b e e n determined to permit t he numerical dating of these deposits eight a m i n o z o n e s e a ch defining dune palaeosol formation episodes have been distinguished and dated at 4 8 6 6 4 42 5 6 0 37 8 4 6 29 4 4 8 22 4 4 5 14 9 3 6 11 0 4 0 and 5 4 1 1 ka b p t h e first f i ve of t h em defining c y c l e s of 5 7 ka the alternation of palaeosols and a e o l i a n deposits w h i c h are related to abrupt transitions from humid to arid conditions are t he reflection of globally induced changes in north africa palaeoenvironmental conditions linked to the effect of african palaeomonsoons on the trade w i n d s and the saharan air layer probably these a eolian cycles with a recurrence neriod of 5 7 ka are t he expression of multiples of the 2 4 ka solar cycle

geochronology of some canarian dike swarms contribution to the volcano tectonic evolution of the archipelago we present new conventional k ar and 39ar 40ar age data and geometric observations on dike swarms which intrude the islands of la gomera tenerife and fuerteventura canary archipelago the younger dated dikes of la gomera 5 4 5 2 ma were emplaced by a radial fissural structure independently superimposed on an older one dated between 10 5 and 7 0 ma the dated dike swarms of both the anaga and teno peninsula of tenerife are contemporaneous 5 8 3 6 ma while ages of 0 43 ma were measured on two dikes intruding the pedro gil ridge the dikes of the basal complex of fuerteventura give well defined 39ar 40ar plateaus when they are situated far away from basic and ultrabasic plutons and disturbed 39ar 40ar age spectra when they are situated in the vicinity of the plutons these disturbances are probably due to a thermal metamorphism the results of both the conventional k ar and 39ar 40ar stepwise heating methods show the existence of an important magmatic phase between 24 and 17 ma the dike swarms of the basal complex are partly contemporaneous with other dike systems intruding the basaltic series i of fuster et al 1968a this phase seems to correspond to the final stages of activity on the main nne ssw volcano tectonic axis following this a volcanic edifice was built on the nw part of jandia peninsula mainly between 15 4 and 14 2 ma the similarity of the ages obtained on dikes and lava flows shows the importance of fissural volcanism in these islands this study shows that dating of dike swarms reveals the existence of major eruptive phases an important part of the products of which have been eroded brief episodes of fissural volcanic activity sometimes probably as short as 200 000 years may be correlated with the migration of the lithosphere over a fixed hot spot the north south 3 5 ma old present and the nne ssw 24 17 ma old oriented dike swarms of la palma staudigel et al in prep and fuerteventura may represent the regional paleostress orientation plane 1 2 which affected the lithosphere during their intrusion although other phenomena may control the orientation of dikes these directions are concordant with the known contemporaneous nw african tectonics

stress dependent morphological features on fracture surfaces of quartz and glass abstract stress dependent morphological features have been found on tensile fracture surfaces of natural brazilian quartz and synthetic quartz specimens which were flexed in air at room temperature these features are similar to stress dependent morphological features found on fracture surfaces of pyrex soda lime and lead glass when deformed in similar experiments for glass the relevant morphological feature is the fracture mirror a planar region surrounding the initial flaw stress dependent index features chosen for measurement in quartz depend upon the crystallographic orientation on the fracture surface their development is related to the crack system energy but in contrast to glass the features are not directly related to crack branching the experimental results follow an equation of the form a f r 1 2 where f is the fracture stress r is the size of a particular morphological feature e g the mirror radius in the case of glass and a is a constant from the magnitudes of a and the fracture toughness determined in these experiments we conclude that the natural brazilian quartz used in this study has significantly higher resistance to fracture than synthetic quartz

reconstruction of the differentiated long term exhumation history of fuerteventura canary islands spain through fission track and u th sm he data miocene intrusives and lower cretaceous siliciclastic sedimentary rocks from the basal complex in western fuerteventura were analyzed with low temperature thermochronometric methods such as fission track and u th sm he dating in order to reveal the evolution of the island s exhumation history the obtained thermochronometric data yields a very slow rate of cooling in the order of 1 5 3 c myr from 50 to 20 ma for the early cretaceous siliciclastic rocks these sedimentary units have never been heated significantly above 240 c after deposition and still record the submarine onset of the island s formation in the eocene intrusive bodies associated with the early miocene magmatic activity of the central volcanic complex of the island show rapid initial cooling rates of 50 70 c myr from 20 to 14 ma contemporaneous with the intrusions the cooling rate of the cretaceous sedimentary units increased to 25 35 c myr and it is inferred that this increase is associated with enhanced uplift and erosion of the central volcanic complex after 14 ma rates slowed down to 3 6 c myr palaeosols overlying the sedimentary units are themselves covered by pliocene basalt flows and reveal that the sedimentary rocks reached the surface before 5 ma the thermochronometric data obtained in this study for central fuerteventura is difficult to reconcile with the cooling history derived from previously obtained fission track and k ar data from the north western part of the island this inconsistency is likely to indicate that the exhumation history of fuerteventura is more complex and regionally subdivided than previously believed

oxygen and hydrogen isotope studies on the basal complexes of the canary islands implications on the conditions of their genesis 18o 16o and d h ratios have been measured in rocks and mineral separates from the basal complexes of fuerteventura gomera and la palma these complexes comprise alkali plutonic rocks ranging from olivine gabbros to syenites and dikes of various mineralogy cutting them all metamorphosed under greenschist conditions k ar determinations gave ages from 48 to 17 my the 18o s and d s of these rocks range from 1 4 to 11 and 113 to 45 respectively with a majority of rocks depleted in heavy isotopes relative to normal deep seated values these values do not correspond to those found in ophiolitic sequences which for a comparable temperature range give minimum 18o s 3 these values are explained in terms of water rock interactions involving limited amounts of meteoric waters from high elevations this implies the existence of a very important volcanic edifice over fuerteventura in the miocene oligocene period with elevations between 2 500 and a maximum of more than 4 000 m

the role of climate and aeolian dust input in calcrete formation in volcanic islands lanzarote and fuerteventura spain calcretes are widely described in non marine settings with carbonates in their catchment or vicinity areas but in volcanic islands without carbonates in their substrate calcretes are not very common in lanzarote and fuerteventura canary islands characterized by impressive volcanic landscapes the sedimentary carbonate rocks are rare except for some recent marine and aeolian deposits in these settings very well developed calcretes cover large areas of the present landscape the source of calcium required for the formation of these calcretes has not been discussed in much detail till now although its role is critical to an understanding of the climatic conditions in which calcium was transported and fixed and of the calcrete formation processes the petrological and geochemical studies 87sr 86sr ratios 13c 18o major trace and ree carried out in this paper do confirm the important role of aeolian dust input in the formation of these calcretes canarian calcretes were mainly generated by pedogenic processes and are composed of various irregular carbonate lamina interbedded with fine clastic deposits our study indicates that these interbeddings were the result of several stages in which during dry periods aeolian dust deposition alternated with leaching and calcite precipitation during wetter periods when plants insects and bacteria played an important role in carbonate precipitation the 18o 2 70 to 2 22 vpdb and 13c 8 21 to 0 24 vpdb values indicate that calcretes were formed by pedogenic processes comparison of calculated 18o values for the canary calcretes with continental mid latitude calcrete values reflects the more homogeneous temperature regimes of calcrete formation in island oceanic settings calcrete87sr 86sr ratios 0 706357 to 0 709208 show strong affinity with those obtained in aeolian carbonate dust and marine deposits and are relatively different from those obtained in basalts ree major and trace element concentrations show that ca bearing minerals from volcanic host rock contributed little to calcrete formation and most of the calcium was supplied by aeolian deposits such as the aeolian dust coming from the sahara and sahel or sand dunes

the generation at hot springs of sedimentary ore deposits microbialites and life abstract notwithstanding the current fashion which favours an epigenetic origin for what used to be termed sedex deposits there are several lines of evidence to indicate that phanerozoic base metal orebodies of this type have at least some exhalative aspects the fossil polychaete worms which occur in lower carboniferous pyrite mounds at tynagh and silvermines in ireland have affinities to paralvinella an organism that lives attached to hydrothermal chimneys at the juan de fuca hot spring site in the northeast pacific in addition fossil tube worms and their moulds occur both in silica masses underlying the carboniferous giant red dog sulphide orebody in alaska and in devonian barite and base metal deposits in north america and in russia respectively the development of sulphide and carbonate fossil microbialites over exhalative centres further supports generation of some mineral deposits on sea or lake floors carbonate microbialite mounds are also developing today over warm springs and seepages the existence of an environment in which sulphide mineralisation developed at the sea floor has implications also in a different sphere life itself may have emerged in a similar milieu at 4 2 ga from iron monosulphide bubbles a primitive metabolism could have been driven by the high long lived and constant redox potential of 300 mv made available across an iron monosulphide membrane which would have been spontaneously generated where sulphide bearing submarine alkaline springs issued into the acidic iron bearing hadean ocean the alkaline spring provided bisulphide to the iron rich carbonic acid ocean for the precipitation of iron monosulphide bubbles probotryoids as well as acetate shock 1992 the feeder to the biochemical krebs cycle driven in reverse by the high partial pressure of co2 in addition to its scientific significance an understanding of these beginnings may well benefit research into many aspects of economic geology even more extreme redox contrasts are revealed by the presence of sedimentary jasper or iron formation in three of the major carboniferous sulphide orebodies in ireland pyritic sulphide microbialites also grew over some of the associated fossil hot spring sites and may be recognised by their bacteriogenic 34s values 20 to 40 recognition of such fossil hot spring sites could lead to further discoveries of sedex deposits

paleomagnetic determinations on lanzarote from magnetic and gravity anomalies implications for the early history of the canary islands the bouguer and aeromagnetic anomaly maps of lanzarote show a gravity high and a dipolar magnetic anomaly over the central part of the island indicating one isolated source assuming that the structure responsible for both anomalies is the same a methodology has been designed to estimate the total magnetization vector of the source which is interpreted as a large intrusive body mafic core positioned as a result of magma rising to the surface during the early stages of growth of lanzarote considering its geometry to be known from a previous three dimensional 3 d gravity model the approach proposed in this paper is based on the delineation of magnetic contacts through analysis of the horizontal gradient of the reduced to the pole anomaly map comparison between the gravity and the pseudogravity anomalies and 3 d forward magnetic modeling the total magnetization vector obtained by this method is defined by a module of 4 5 a m 1 and a direction d 20 degrees and i 30 degrees comparing the paleomagnetic pole obtained from this direction with the apparent polar wander path of africa for the last 160 myr it is concluded that the main component of the total magnetization vector is probably a primary natural remanent magnetization nrm which could have been acquired between 60 and 100 ma this result suggests that the emplacement of magmas at shallow depths linked to the beginning of volcanism in lanzarote took place during the upper cretaceous thus providing the first evidence of a timeline for the early formative stages of this volcanic island

seismic properties of the upper mantle beneath lanzarote canary islands model predictions based on texture measurements by ebsd abstract we present a petrophysical analysis of upper mantle xenoliths collected in the quaternary alkali basalt fields series iii and iv from the island of lanzarote the samples consist of eight harzburgite and four dunite nodules 5 to 15 cm in size and exhibit a typical protogranular to porphyroclastic texture an anomalous foliation resulting from strong recovery processes is observed in half of the specimens the lattice preferred orientations lpo of olivine orthopyroxene and clinopyroxene were measured using electron backscatter diffraction ebsd in most samples olivine exhibits lpos intermediate between the typical single crystal texture and the 100 fiber texture occasionally the 010 fiber texture was also observed simultaneous occurrence of both types of fiber textures suggests the existence of more than one deformation regime probably dominated by a simple shear component under low strain rate and moderate to high temperature orthopyroxene and clinopyroxene display a weaker but significant texture the lpo data were used to calculate the seismic properties of the xenoliths at pt conditions obtained from geothermobarometry and were compared to field geophysical data reported from the literature the velocity of p waves 7 9 km s obtained for a direction corresponding to the existing seismic transect is in good agreement with the most recent geophysical interpretation our results are consistent with a roughly w e oriented fastest p wave propagation direction in the uppermost mantle beneath the canary islands and with the lithosphere structure proposed by previous authors involving a crust mantle boundary at around 18 km in depth overlaid by intermediate material between 11 and 18 km

anomalously shallow palaeomagnetic inclinations and the question of the age of the canarian archipelago summary extensive geological geophysical and geochronological data available from the canary islands establish conclusively that formation of the oldest subaerial volcanic structure of the islands began during the miocene a mid cretaceous age for these volcanic formations has been postulated in previous works on the basis of palaeomagnetic determinations the results obtained in the present palaeomagnetic study of lanzarote include analysis of the record of variations of magnetic inclination in boreholes that penetrate the whole of the oldest volcanic series they show that the excessive age previously assigned to these formations is due to the utilization of volcanic units with abnormally low 15 magnetic inclinations lgis in lanzarote lavas exhibiting lgis appear interbedded in a volcanic series that overall shows a typical miocene inclination 45 the units stratigraphically beneath and above the lgi horizons give in fact directions consistent with the middle upper miocene field direction d 359 i 45 with k 29 a95 6 7 and a palaeopole of 87 n 178 e thereby confirming the miocene age of the oldest subaerial volcanics of lanzarote short excursions of the geomagnetic field seem likely to be the explanation for these lgis since other factors such as tectonic tilting post eruptive modification of the primary remanence or errors in sample orientation can be disregarded the detection in the canary archipelago of volcanic units with abnormally low magnetic inclinations seems to be related to the relatively continuous record of the geomagnetic field in rapidly growing volcanic edifices as seems to be indicated by the presence of a few usually one or two short polarity events in volcanic suites of several hundred metres thickness

emergent littoral deposits in the eastern canary islands abstract k ar ages a abdel monem p d watkins and p w gast 1971 american journal of science 271 490 521 this paper and revised paleontological determinations j meco 1977 los strombus neogenos y cuatenarios del atlantico euroafricano las palmas ediciones del excmo cabildo insular de gran canaria show that quaternary r crofts 1967 quaternaria 9 247 260 g lecointre k j tinkler and g richards 1967 academy of natural science of philadelphia proceedings 119 325 344 littoral deposits on lanzarote and fuerteventura are early pliocene and late pleistocene early and middle pleistocene strand lines are not represented early pliocene littoral and marine deposits contain a characteristic fossil assemblage strombus coronatus nerita emiliana gryphaea virleti patella cf intermedia and rothpletzia rudista differences in elevation record differential post pliocene uplift of the coastal platforms on which they lie late pleistocene beach deposits at low elevations belong to two groups an older with strombus bubonius and a younger without differences in elevation of early pliocene littoral deposits are reflected by differences in elevation of late pleistocene beach deposits nearby

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

quaternary laminar calcretes with bee nests evidences of small scale climatic fluctuations eastern canary islands spain thick laminar calcrete profiles are common on the surface of the eastern canary islands of lanzarote and fuerteventura this paper reports the study of one profile from lanzarote macher profile and one from fuerteventura tef a profile these profiles are about 2 m thick the macher profile is developed on basaltic host rocks and consists of two main horizons a lower horizon in which white veins of laminated micrite penetrate cracks and an upper laminar horizon the tef a profile is cumulative and consists from base to top of massive laminar and massive and laminar brecciated horizons highlighted in the study of these profiles are the presence of ooids the complex structure of the laminar horizons and the occurrence of fossil bee nests celliforma ooids consist of a nucleus of clay micrite and etched grains coated with envelopes of micrite and clay mainly palygorskite organic films favoured both the precipitation of carbonate and the adhesion of clays when the ooids formed in the soil the laminar horizons consist of a centimetre scale alternation of massive micrite with varied amounts of ooids and detrital grains with laminated micrite this alternation indicates the small scale periods of sedimentation erosion and soil formation in the upper part of a relatively stable surface these small scale alternations may reflect climatic vegetation changes in which arid periods are represented by micrite with ooids while laminated micrite reflects a better developed vegetation of the wet periods celliforma occur as ovoid larval cells with more or less rounded bases and a flat top the cells are about 3 cm long and 1 5 cm in diameter their wall is about 5 mm thick and is commonly laminated celliforma is interpreted as fossil nests of solitary bees their presence in the laminar horizon is evidence for the existence of a vegetation cover containing angiosperms