coeval giant landslides in the canary islands implications for global regional and local triggers of giant flank collapses on oceanic volcanoes abstract giant landslides are an important part of the evolution of most intra plate volcanic islands they often proceed in catastrophic events likely to generate voluminous debris avalanches and eventually trigger destructive tsunamis although knowledge of the timing of their recurrence is a key factor regarding the hazard assessment in coastal environments only a few of them have been well dated in this contribution we focus on the la orotava event on tenerife which we date with the unspiked k ar technique between 534 and 523 ka such narrow temporal interval is compatible within uncertainties with the age of the cumbre nueva collapse on the neighboring island of la palma we thus examine here the possible common triggering mechanisms at the global regional and local scales both events occurred shortly after the climax of the oxygen isotopic stage 14 during the rapid transition towards the interglacial stage 13 reinforcing the hypothesis of a control from global paleoclimatic changes on the destabilization of oceanic islands intense volcanic pulses at the regional scale also lead to the synchronous overgrowth of several volcanic islands in the archipelago but coeval destabilization on tenerife and la palma appears significantly controlled by the intrinsic morphology of the edifices with contrasted instability thresholds for shield volcanoes and volcanic ridges respectively finally we propose that the two events may be genetically linked dynamic transfer of voluminous debris avalanches during a giant landslide episode can induce isostatic readjustments generate significant ground acceleration and finally produce a large tsunami three processes which can concur to trigger large scale flank collapse on a neighboring mature unstable volcanic island

effusive history of the grande decouverte volcanic complex southern basse terre guadeloupe french west indies from new k ar cassignol gillot ages abstract the grande decouverte volcanic complex gdvc active since at least 0 2 ma is the most recent volcanic complex of the basse terre island guadeloupe lesser antilles arc a detailed geochronological study using the k ar cassignol gillot technique has been undertaken in order to reconstruct the history of effusive activity of this long lived volcanic system twenty new ages permit to suggest that the gdvc experienced at least six main effusive stages from 200 ka to present time to the north of the gdvc the gds grande decouverte soufriere volcano has been active since at least 200 ka and to the south the trmf trois rivieres madeleine field started to be emplaced 100 ka morphological investigations suggest that the whole trmf volcanism was emitted from vents distinct from the gds most probably a large e w fissure network linked to the marie galante rift the mean age of 62 5 ka obtained for the e w madeleine le palmiste alignment suggests that a fissure opening event occurred at that time however whole rock major and trace element signatures are similar for both systems suggesting that a common complex magma plumbing system has fed the overall gdvc we report very young ages for lava flows from the trmf which implies that

sensitivity analysis of the gravity geoid estimation a case study on the azores plateau abstract a numerical investigation into the effects of high resolution heterogeneous data on the estimation of the geoid is presented for the area of the azores plateau gravity data were complemented with high resolution digital terrain models mass density models from geophysical information and the most recent geopotential model from the champ mission ggm02 to derive a high precision gravity model gravity data were reduced from the residual terrain model effects and the ggm02c model and a grid with 1 5 spatial resolution was generated by least squares collocation the gravimetric geoid model was computed by the direct evaluation of stokes integral with a spherical cap radius of 0 8 with gravity data reduced by helmert s second condensation method the geoid model was evaluated over sea by comparison with 6 years of topex poseidon altimeter data and an absolute agreement of 14 cm rms was achieved after removing the bias over land the geoid was compared with a total of 223 gps levelling points corresponding to five different vertical datums locally adjusted solutions were determined for each island with a four parameter model and a maximum rms of 12 cm on pico and a minimum of 2 1 cm on faial were determined as a result of persistent volcanic and tectonic activity on most of the azores islands this geoid residual standard deviation must not be viewed as purely geoid error but containing in addition levelling and gps position errors and vertical displacement the effect on geoid accuracy of the digital terrain model resolution of the spatial density of gravity data and of the mass density was evaluated and two important conclusions were derived first the digital terrain model resolution has a clear effect on the geoid accuracy with a maximum rms of 3 4 cm on s miguel second the mass density model does not affect the accuracy of the geoid this second result indicates that the effect of variable density models on geoid determination may apply only to extensive areas of high terrain and not to smaller topographic units such as single volcanoes the high precision gravity model and gravimetric geoid for azores azgeod07 generated in this study will allow the conversion of old orthometric heights to ellipsoidal heights at precisions useful for the monitoring of vertical deformation the geoid will also have application to investigate ocean circulation modulation and dynamic processes of earth s mantle

giant quaternary landslides in the evolution of la palma and el hierro canary islands in the past large morphological escarpments in the canaries have been generally related to explosive and or erosive processes recent onshore and offshore investigations drastically changed this interpretation by providing evidence of the importance of giant lateral collapses in the evolution of the islands especially in their earlier stages of growth giant landslide scars and deposits are readily observed both onshore and offshore in the younger western canaries and seem to be a common feature of the development of the entire archipelago at least one catastrophic collapse is apparent on la palma the cumbre nueva giant landslide which occurred about 560 ka ago this collapse removed some 200 km3 of central western la palma forming a large embayment three successive giant landslides and evidence of an aborted attempt at another are seen in the island of el hierro the combined volume of those collapses estimated at about 400 500 km3 considerably exceeds the present subaerial volume of the island about 140 km3 giant landslides and erosion during the past million years have removed more than half of the total subaerial volume of la palma and el hierro

burial history and kinetic modeling for hydrocarbon generation part i the galo model this paper discusses the principles and applications of the galo computer program which generates numerical simulations of the evolution of a sedimentary basin the program calculates variations in the sedimentary bed thickness predicts the thermal regime in the sedimentary cover or in the basement and estimates the potential hydrocarbon yield of the source rocks alternative methods for determining the magnitude of tectonic subsidence of the basement surface within the framework of a local isostasy model are applied to provide a detailed model of the sequential tectonic thermal events involved in the development of the basin the program determines reaction parameters controlling the maturation of the organic matter in source rocks these parameters are based largely on the hydrocarbon pyrolysis yield data and the stage of maturation of the organic matter entered into the program neglecting this stage drastically displaces the reaction spectrum toward higher energies leading to considerable underestimation of hydrocarbon output

diagenesis provenance and reservoir quality of triassic tagi sandstones from ourhoud field berkine ghadames basin algeria the triassic tagi trias argilo greseux inferieur fluvial sandstones are the main oil reservoirs in the berkine basin algeria nonetheless their provenance and diagenesis and their impact on reservoir quality are virtually unknown samples from the ourhoud field representing the lower middle and upper tagi subunits were studied using a combination of petrographic mineralogical and geochemical techniques the lower tagi sandstones have an average framework composition of q98 3f0 6r1 1 and 95 of the quartz grains are monocrystalline by contrast the middle upper tagi sandstones have an average framework composition of q88 3f9 8r1 9 and 79 7 of the quartz grains are monocrystalline the lower tagi quartz arenites derived from paleozoic siliciclastic rocks whereas the middle upper tagi subarkoses originated mainly from metamorphic terrains this change in provenance is a potential criterion for correlation within the tagi also this change has contributed to the significantly different diagenetic paths followed by the lower tagi quartz arenites and the middle upper tagi subarkoses grain coating illitic clays are abundant in the lower tagi where they exert a critical control on reservoir quality these clays are interpreted as pedogenic and or infiltrated in origin and to have had in part smectitic precursors shallow burial fe dolomite cementation was favored in the downthrown block of the field bounding fault where it contributed to the poor reservoir quality magnesite siderite cements are multiphase the earliest generation is composed of fe rich magnesite that precipitated during shallow burial from hypersaline fluids with high mg ca ratios probably refluxed residual brines associated with the liassic evaporites later magnesite siderite generations precipitated during deeper burial from waters with progressively higher fe mg ratios authigenic vermicular kaolin largely consists of dickite that replaced previously formed kaolinite dickitization was followed by late stage illitization related to the dissolution of detrital and authigenic k feldspar quartz the most abundant cement was mainly sourced by the pressure or clay induced dissolution of detrital quartz and is a critical factor controlling the reservoir quality overall quartz cement is more abundant in the lower tagi than in the middle upper tagi and this increase correlates with a decrease in average porosity within the lower tagi quartz cement abundance is stratigraphically very variable which is in part related to facies controlled variations in grain coating clay resulting in major vertical variations in reservoir quality anhydrite and barite cements postdate quartz overgrowth the sulfate necessary for their formation was likely sourced by deep subsurface dissolution of late triassic liassic evaporites

reconstructing the architectural evolution of volcanic islands from combined k ar morphologic tectonic and magnetic data the faial island example azores the morpho structural evolution of oceanic islands results from competition between volcano growth and partial destruction by mass wasting processes we present here a multi disciplinary study of the successive stages of development of faial azores during the last 1 myr using high resolution digital elevation model dem and new k ar tectonic and magnetic data we reconstruct the rapidly evolving topography at successive stages in response to complex interactions between volcanic construction and mass wasting including the development of a graben we show that 1 sub aerial evolution of the island first involved the rapid growth of a large elongated volcano at ca 0 85 ma followed by its partial destruction over half a million years 2 beginning about 360 ka a new small edifice grew on the ne of the island and was subsequently cut by normal faults responsible for initiation of the graben 3 after an apparent pause of ca 250 kyr the large central volcano cv developed on the western side of the island at ca 120 ka accumulating a thick pile of lava flows in less than 20 kyr which were partly channelized within the graben 4 the period between 120 ka and 40 ka is marked by widespread deformation at the island scale including westward propagation of faulting and associated erosion of the graben walls which produced sedimentary deposits subsequent growth of the cv at 40 ka was then constrained within the graben with lava flowing onto the sediments up to the eastern shore 5 the island evolution during the holocene involves basaltic volcanic activity along the main southern faults and pyroclastic eruptions associated with the formation of a caldera volcano tectonic depression we conclude that the whole evolution of faial island has been characterized by successive short volcanic pulses probably controlled by brief episodes of regional deformation each pulse has been separated by considerable periods of volcanic inactivity during which the faial graben gradually developed we propose that the volume loss associated with sudden magma extraction from a shallow reservoir in different episodes triggered incremental downward graben movement as observed historically when immediate vertical collapse of up to 2 m was observed along the western segments of the graben at the end of the capelinhos eruptive crises 1957 58

growth destruction and volcanic facies architecture of three volcanic centres in the miocene usak gure basin western turkey subaqueous subaerial volcanism in a lacustrine setting abstract early to mid miocene extension in western anatolia related to plate tectonic motions resulted in the development of a number of normal fault bounded sedimentary basins as well as different styles and compositions of volcanic activity the usak and gure basins accumulated a thick fluvio lacustrine fill in which three distinct volcanic edifices elmadag itecektepe and beydagi and their deposits can overlap with each other and with the sediments produced by the background sedimentation in addition complete facies architectures of small volume monogenetic volcanoes have been recognised in association with the three large complex polygenetic volcanoes providing a complex mixed siliciclastic and volcaniclastic basin infill in the respective basins where volcanism took place all three volcanic centres display a complex succession of effusive and explosive volcanisms and their reworked deposits with abundant evidences of magma water interaction such as peperites for non explosive magma water interaction with the lacustrine water saturated sediment and standing water body in a large alkaline lake during the constructive phase proximal successions of pyroclastic flows pyroclastic falls and rarely surge deposits are associated with distally emplaced debris flow deposits sometimes of mixed volcanogenic and terrestrial origins and are interbedded with lacustrine sediments of the inay group all three volcanic centres then experienced a phase of volcano growth and degradation between 17 and 15 ma ago most likely related to a combination of tectonic movements on ne sw trending basement faults which triggered multiple flank collapses and volcanic debris avalanches elmadag and voluminous ignimbrite eruptions that triggered caldera formation itecektepe and beydagi volcanic centres lacustrine conditions persisted during the destruction and post destruction stages of the volcano s evolution as evidenced by indications of magma water interactions within the central collapse structures which also contain uplifted basement metamorphic rocks now exhumed in their eroded cores

the off shore continuation of an active basaltic volcano piton de la fournaise reunion island indian ocean structural and geomorphological interpretation from sea beam mapping abstract in 1984 a sea beam survey of the submarine east flank of piton de la fournaise was performed with r v jean charcot three main types of volcanic or volcano tectonic features have been identified 1 1 the subaerial ne and se volcanic rift zones of piton de la fournaise do not extend more than about five kilometers offshore unlike typical hawaiian rift zones which form narrow 2 4 km ridges extending tens of kilometers from the summit the active rift zones of piton de la fournaise widen downslope attaining more than 10 km at their front 2 2 the submarine extension of the grand brule slide is larger than the subaerial portion the entire slide forms a 7 24 km scar bounded by two ramparts to the north and south the slumped material may have moved as a debris flow forming a large talus downslope of the slide however the submarine counterpart of the south area of the grand brule seems to be composed by a slumped block whose structure is apparently not disturbed 3 3 another prominent feature is a conspicuous topographic high that occupies nearly all the center of the surveyed zone this cast flank submarine plateau cannot be associated with any active structure of piton de la fournaise its surface generally dips gently 2 3 and its northern and southern flanks are extensively cut by landslides cones of variable dimensions are observed on the plateau and farther to the east three hypotheses are examined to account for the origin of this morphology a remnant flank of an ancestral fournaise volcano associated with a large buried intrusion found by drilling beneath the grand brule b distinct volcanic massif or c material of a huge and ancient landslide the geophysical data show that the western part of this submarine plateau is reversely magnetized and associated with a moderate positive gravity anomaly this confirms that as suggested by the bathymetric analysis this part of the plateau is relatively coherent conversely the eastern portion of the plateau appears to be poorly magnetized and composed of low density material probably chaotic materials derived from landslides the reversed magnetization of the western part shows that the whole structure is older than 0 7 ma these results show that the volcanic history of piton de la fournaise is more complex than previously thought

caldera or flank collapse in the fogo volcano what age consequences for risk assessment in volcanic islands abstract the target of this study is the fogo island in cape verde where the hazards caldera and or flank collapse and the timing 120 ka or younger are still controversial using high resolution dem field geological and structural analysis and high precision k ar dating we produced an age calibrated volcanic stratigraphy of fogo s summit cha das caldeiras for the last ca 220 ka from this we infer the following evolution and associated processes 1 the fogo volcano formed during seven stages of construction and partial destruction 2 three flank collapses can be recognised the biggest of which occurred between 60 and 43 ka 3 this collapse occurred retrogressively producing at least two distinct collapse blocks 4 the innermost collapse was only partial forming a flat step where a new volcano pico do fogo grew and formed the cha das caldeiras literally flat of the calderas 5 the removal of the buttressing eastern flank by the outermost collapse can be responsible for the seemingly caldera structure 6 the growing load of the young volcano can produce a new flank failure following the innermost fault 7 the young and closely spaced collapse ages here reported indicate a significant risk for the inhabitants of fogo in particular and for the whole cape verde archipelago and atlantic seaboard if a tsunami is produced by a future catastrophic flank collapse

petroleum generation and migration in the ghadames basin north africa a two dimensional basin modeling study the ghadames basin contains important oil and gas producing reservoirs distributed across algeria tunisia and libya regional two dimensional 2 d modeling using data from more than 30 wells has been undertaken to assess the timing and distribution of hydrocarbon generation in the basin four potential petroleum systems have been identified 1 a middle upper devonian frasnian and triassic triassic argilo greseux inferieur tag i system in the central western basin 2 a lower silurian tannezuft and triassic tag i system to the far west 3 a lower silurian tannezuft and upper silurian acacus system in the eastern and northeastern margins and 4 a lower silurian tanezzuft and middle upper devonian frasnian system to the east southeast the lower silurian tanezzuft source rock underwent two main phases of hydrocarbon generation the first phase occurred during the carboniferous and the second started during the cretaceous generating most hydrocarbons in the eastern libyan basin the frasnian shales underwent an initial minor generative phase in the central depression during the carboniferous however the main generation occurred during the late jurassic cenozoic in the western and central depression the frasnian shales are currently only marginally mature in the eastern part of the basin modeling indicates that the alpine eocene exhumation of the eastern libyan basin margin had a significant control on the timing of hydrocarbon generation from the lower silurian source rock the preferred burial history model calibrates source rock maturity data by incorporating late exhumation and reduced subsidence prior to the hercynian carboniferous orogeny as a result the tannezuft shales preserve their generative potential into the mesozoic cenozoic with renewed hydrocarbon generation during subsequent reburial which can migrate to post hercynian carboniferous traps hence favoring the preservation of hydrocarbon accumulations

morpho structural evolution of a volcanic island developed inside an active oceanic rift s miguel island terceira rift azores the evolution of volcanic islands is generally marked by fast construction phases alternating with destruction by a variety of mass wasting processes more specifically volcanic islands located in areas of intense regional deformation can be particularly prone to gravitational destabilisation the island of s miguel azores has developed during the last 1 myr inside the active terceira rift a major tectonic structure materializing the present boundary between the eurasian and nubian lithospheric plates in this work we depict the evolution of the island based on high resolution dem data stratigraphic and structural analyses high precision k ar dating on separated mineral phases and offshore data bathymetry and seismic profiles the new results indicate that 1 the oldest volcanic complex nordeste composing the easternmost part of the island was dominantly active between ca 850 and 750 ka and was subsequently affected by a major south directed flank collapse 2 between at least 500 ka and 250 ka the landslide depression was massively filled by a thick lava succession erupted from volcanic cones and domes distributed along the main e w collapse scar 3 since 250 kyr the western part of this succession furnas area was affected by multiple vertical collapses associated plinian eruptions produced large pyroclastic deposits here dated at ca 60 ka and less than 25 ka 4 during the same period the eastern part of the landslide scar was enlarged by retrogressive erosion producing the large povoacao valley which was gradually filled by sediments and young volcanic products 5 the fogo volcano in the middle of s miguel is here dated between ca 270 and 17 ka and was affected by at least one southwards flank collapse 6 the sete cidades volcano in the western end of the island is here dated between ca 91 and 13 ka and experienced mutliple caldera collapses a landslide to the north is also suspected from the presence of a subtle morphologic scar covered by recent lava flows erupted from alignments of basaltic strombolian cones the predominance of the n150 and n75 trends in the island suggest that the tectonics of the terceira rift controlled the location and the distribution of the volcanism and to some extent the various destruction events

corrigendum to gps and tectonic evidence for a diffuse plate boundary at the azores triple junction earth planet sci lett 381 2013 177 187

flank collapse and large scale landsliding in the cape verde islands off west africa large scale landslides occur on the flanks of many volcanic oceanic islands worldwide none have taken place in historical time but their geohazard potential especially their ability to generate tsunamis is large the cape verde islands are a group of 10 large and several smaller volcanic islands off the coast of west africa between 15 and 17 n a single flank landslide has previously been described from the island of fogo but systematic analysis of the cape verde group has until now been lacking this paper describes and interprets a multibeam bathymetry data set covering the slopes of the western cape verde islands including those of the islands with the most recent volcanic activity fogo in the southwest and santo antao in the northwest all of the larger islands show evidence of large flank landslides although only fogo and the southwest part of santo antao have failed in the last 400 ka tope de coroa the volcano at the southwest end of santo antao has been inactive for the past 170 ka and is judged to have a low landslide potential unless volcanic activity resumes in contrast there would seem to be a high probability of a future east directed landslide on fogo from the area of the highly active pico do fogo volcano although it is impossible to predict a timescale for such an event a tsunami generated by such a landslide could have a catastrophic effect on the adjacent island of santiago and possibly even farther afield on the west african coast

large scale flank collapse events during the activity of montagne pelee martinique lesser antilles 1 a horseshoe shaped structure already identified on the southwestern flank of montagne pelee martinique lesser antilles arc was previously interpreted as resulting of a flank collapse event but no debris avalanche deposits were observed at the time new offshore high resolution bathymetry and geophysical data aguadomar cruise december 1998 to january 1999 r v l atalante lead us to identify three debris avalanche deposits on the submarine western flank of montagne pelee extending down to the grenada basin they display morphological fronts and hummocky morphology on bathymetric data speckled pattern on backscatter data and hyperbolic facies on 3 5 khz and seismic profiles new on land geological studies lead us to identify two other horseshoe shaped structures on the same flank of the volcano the three submarine deposits have been traced back to the structures identified on land which confirms the occurrence of repeated flank collapse events during the evolution of montagne pelee the ages of the last two events are estimated at 9 ka and 25 ka on the basis of 14c and 238u 230th dates every flank collapse produced debris avalanches which flowed down to the caribbean sea we propose that the repeated instabilities are due to the large asymmetry of the island with western aerial and submarine slopes steeper than the eastern slopes the asymmetry results from progressive loading by accumulation of volcanic products on the western slopes of the volcano and development of long term gravitational instabilities meteoric and hydrothermal fluid circulation on the floor of the second flank collapse structure also creates a weakened hydrothermalized area which favors the recurrence of flank collapses

radiometric dating of three large volume flank collapses in the lesser antilles arc abstract it is now recognised that flank collapses are a recurrent process in the evolution of the lesser antilles arc volcanoes large magnitude debris avalanche deposits have been identified off the coast of dominica martinique and st lucia with associated volumes up to 20 km 3 deplus c le friant a boudon g komorowski j c villemant b harford c segoufin j cheminee j l 2001 submarine evidence for large scale debris avalanches in the lesser antilles arc earth planet sci lett 192 145 157 we present new radiometric dating of three major events using the k ar cassignol gillot technique in the qualibou depression of st lucia a collapse has been constrained by dome emplacement prior to 95 2 ka in dominica where repetitive flank collapse events have occurred le friant a boudon g komorowski j c deplus c 2002 l ile de la dominique a l origine des avalanches de debris les plus volumineuses de l arc des petites antilles c r geoscience 334 235 243 the plat pays event probably occurred after 96 2 ka inside the depression caused by this event scotts head which is interpreted as a proximal megabloc from the subsequent soufriere avalanche event has been dated at 14 1 ka providing an older bound for this event on martinique three different domes within the carbets structure dated at 337 5 ka constrain the age of this high magnitude event finally these results obtained from three of the most voluminous flank collapses provide constraints to estimate the recurrence of these events which represent one of the major hazards associated with volcanoes of the lesser antilles arc

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

time and temperature in petroleum formation application of lopatin s method to petroleum exploration n v lopatin in the soviet union has developed a method for taking both time and temperature into account as factors in thermal maturation of kerogen lopatin s time temperature index of maturity tti values correlate with the thermal regimes corresponding to generation and preservation of hydrocarbons because such information is potentially of great interest for oil exploration a calibration and evaluation have been made of lopatin s method within the limitations of the data presently available the following statements can be made 1 the rate of the chemical reactions involved in thermal maturation of organic material appears to double with every 10 c 18 f rise in temperature 2 threshold values of lopatin s time temperature index of maturity tti are 15 onset of oil generation 75 peak oil generation 160 end oil generation 500 40 oil preservation deadline 1 000 50 oil preservation deadline 1 500 wet gas preservation deadline 65 000 dry gas preservation deadline 3 tti values calculated from lopatin reconstructions consistently agree with other maturation parameters commonly used by petroleum geochemists potential applications of lopatin s method for oil exploration include timing of oil generation calculation of volume of hydrocarbons generated within a basin and determination of economic deadlines

the giant submarine alika debris slide mauna loa hawaii probably represent multiple subsidence events before during and after the debris avalanches lower slopes of the slide contain distinctive lobate terraced deposits that are interpreted as having been emplaced more slowly prior to the debris avalanches estimated thicknesses of 50 200 m suggest volumes of 200 600 km 3 for the two lobes the combined volume of the entire slide and slump terrane is probably 1500 2000 km 3 the slide deposits predate a 13 ka coral reef and probably postdate the block faulted ninole basalt roughly dated as a few hundred thousand years old the alika slide or a similar deposit recognized on gloria images further north along the hawaiian ridge probably triggered a giant wave that washed 325 m high on lanai at about 100 ka slumping on mauna loa has been most intense adjacent to the large arcuate bend in its southwest rift zone as the rift zone migrated westward away from the growing kilauea volcano slumping events were probably triggered by seismic activity accompanying dike injection along the rift zone such massive slumps landslides and distal submarine turbidity flows appear to be widespread on the flanks of hawaiian volcanoes

eruptive response of oceanic islands to giant landslides new insights from the geomorphologic evolution of the teide pico viejo volcanic complex tenerife canary large sector collapses are a major component of oceanic islands evolution here we show that voluminous events such as the icod landslide on tenerife canary islands cause dramatic changes on the magma feeding system and control the subsequent volcanic and geomorphologic evolution of the eruptive complex over a period of more than 150 kyr instantaneous unloading by the icod landslide is marked by the development of a large phonolitic explosive eruption dated at 175 3 ka and interpreted as reflecting the immediate emptying of a shallow pre existing magma chamber geochronological geomorphological and geochemical analyses carried out on the post landslide volcanic succession sampled in a 4 4 km long underground water recovery gallery provide further evidence for an enhanced extrusion of primitive lavas starting in the 10 kyr time interval following the failure rapid construction 40 kyr of a thick basaltic volcano in the landslide scar at high eruptive rates up to 8 km3 kyr 1 increased the lithostatic pressure which then favored the intermittent storage of basic magma under the edifice this resulted in more episodic construction evidenced by a significant decrease in output rates and the increasing occurrence of lavas with intermediate composition from 117 7 to 52 7 ka an apparent volcanic gap is observed between 52 7 and 18 1 ka after which highly differentiated lavas have been dominantly erupted we propose that part of the gap can be explained by the individualization of a shallow magma reservoir a few kilometers below the base of the teide volcano during recent periods vertical and lateral extrusions of trachytic and phonolitic viscous bodies from this storage area contributed to increase the slope of the main edifice up to 35 overall favoring its present day instability

large scale catastrophic flank collapses in a steep volcanic ridge the pico faial ridge azores triple junction abstract large scale flank collapses are common in the geological evolution of volcanic ocean islands in the atlantic to date catastrophic lateral collapses in the azores islands have been difficult to identify leading to suggestions that a lack of events may relate to the relatively small size of the islands here we show evidence for two major collapses on the northern flank of pico island pico faial volcanic ridge central azores suggesting that this island had a collapse incidence similar to that of other atlantic volcanic islands the study is based on the analysis of 1 offshore and onshore high resolution digital elevation models 2 field data focused on the n flank and 3 new k ar ages on selected lava flow samples pico sub aerial northern flank is marked by two conspicuous arcuate shaped depressions concave towards the sea here interpreted as landslide scars a main debris field is observed offshore the largest depression this deposit has 20 km of maximum length covers ca 150 km2 is composed of meter to hectometer blocks and has an exposed volume here estimated between 4 and 10 km3 though the actual volume probably exceeds 10 km3 debris flow towards the ese was apparently determined by the slope of the narrow wnw ese s jorge channel young lava flows cascade over the interpreted scars thus concealing the older volcanic sequence s affected by the landslide s new k ar ages measured on these lava flows provide a minimum age of ca 70 ka for the large scale collapse s in pico s northern flank

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

offshore evidence for a huge landslide of the northern flank of tahiti nui french polynesia a bathymetric analysis of the flanks of tahiti nui french polynesia reveals the existence of a major catastrophic north directed landslide during its eruptive history the related debris avalanche da deposits extend north 70 km from the island shore and have a total volume of about 800 km3 two contrasted facies of the debris are recognized 1 relatively small sized material including a few blocks with well developed flow structures elongate downslope directed ridges and transversal pressure ridges and 2 a scattering of large kilometer sized individual blocks that form in part a prominent bathymetric hummock in the proximal central part of the landslide deposits bathymetric analyses suggest that the tahitian failure evolved through two main successive shots the da debris were rapidly overlain by subsequent volcanic material producing a smooth surface down to 1500 m below sea level the on land and offshore structures indicate a listric fault geometry for the landslide scar the volume removed by the landslide is thus estimated between 400 km3 and 450 km3 discrepancy in the volume of the scar and the debris derived from it is due in part to expansion of the debris to fragmentation of the avalanche and to incorporation of sediments comparison with a recently recognized southern tahitian landslide clouard et al 2001 and with landslides recognized around the hawaiian islands and the canary islands shows that the huge northern tahitian landslide described here has a reduced mobility in its central part perhaps the older tetiaroa eruptive complex to the north acted as a buttress to inhibit movement of the da products the northern and southern tahiti nui landslides moved in opposite directions away from the main central e w directed rift zone that served as the main magma feeding structure then the huge northern landslide strongly controlled the later volcano structural evolution by capturing subsequent volcanic activity to the north despite the northwestward displacement of the pacific plate over the society hot spot

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

processes that control mineral and element abundances in shales abstract a shale s composition can be used to infer physical chemical and biological processes that have acted on it over its life history and this knowledge is used to surmise conditions at the time when each process was active this review lists the most important processes that control shale mineral and element abundances during each of the five stages of its life history 1 during weathering transport and deposition the most important processes are chemical weathering hydraulic sorting and mixing adsorption reverse weathering and incorporation of organic matter and biominerals 2 during early diagenesis the most important processes are exchange across the water sediment interface compaction microbial respiration mineral transformations and concretion formation 3 during burial diagenesis the most important processes are compaction catagenesis and metagenesis and mineral transformations 4 during exhumation the most important processes are decompaction brine invasion groundwater penetration and microbial respiration 5 during weathering the most important processes are organic matter oxidation mineral oxidation and hydrolysis groundwater transport and disaggregation this classification of processes provides a way to envision how concurrent and consecutive processes that occurred over a shale s life history have affected its mineralogy and chemical composition

burial history and thermal evolution of the southern and western saharan basins synthesis and comparison with the eastern and northern saharan basins a quasi two dimensional analysis of burial history and thermal evolution was carried out along eight profiles for sedimentary sections in 24 wells in the southern and western saharan basins with the aid of one dimensional nonsteady numerical reconstructions the modeling shows that thermal activation during the permian triassic jurassic was most intense in the timimoun basin and the northern part of the ahnet and mouydir basins with a heat flow of about 70 80 mw m2 and a lithosphere thickness of 40 50 km activation was more moderate in the sbaa subbasin and reggane basin with a heat flow of approximately 63 67 mw m2 and a crustal thickness of 55 60 km these values are comparable to those for the eastern saharan basins where the intensity of the triassic activation decreased considerably from north to south the present day thermal regime of the ahnet and reggane basins and the central part of the timimoun basin is comparable to that of the illizi basin where the present day lithosphere is as thin as 25 km and recent volcanism has occurred moderate extension of the lithosphere with a maximum total amplitude of about 1 16 during the cenozoic is assumed in our modeling in the reggane basin and the southern half of the timimoun basin as well as in the central and eastern part of the illizi basin thermal analysis of the saharan basins has shown that the hercynian erosion can account for only a minor part of the jumps observed in the vitrinite profiles ro intrusive activity and the associated hydrothermal heat transfer during the triassic and early jurassic accurately explain the steplike character of maturation profiles in the saharan basins in particular the lower level of catagenesis and conservation of oil deposits in the relatively hot sbaa subbasin are the result of less intensive hydrothermal intrusive heating of the basin during the jurassic as compared to that in neighboring basins this could also be ascribed to a deeper location of the lithosphere and probably deeper intrusions in the sbaa subbasin this relatively moderate thermal regime of the sbaa subbasin might be connected to its structural position of as it was a shoulder to neighboring deeper depressions

discovery of a huge sector collapse at the nisyros volcano greece by on land and offshore geological structural data abstract this study uses on land and offshore geological and structural data to demonstrate that a huge lateral collapse involved the se flank of nisyros volcano the collapse beheaded the summit part of the volcano and also involved the submarine portion of the slope producing a large debris avalanche deposit with a volume of about 1 km3 which has been recognized on the sea floor on land stratigraphic and structural data indicate that a thick succession of lava flows nikia lavas was emplaced in a huge horseshoe shaped depression open seaward and extending below the sea the magma feeding system in the volcano pre dating and following the collapse was structurally influenced by a dominant ne sw direction which is perpendicular to the newly recognised sector collapse the ne sw structural trend is consistent with the regional tectonic structures found offshore around nisyros and with the related nw se extension direction we suggest that the lateral magma pressure produced by repeated magma injections along tectonic discontinuities contributed to destabilise the volcano flank the occurrence of a pyroclastic deposit that mantled the scar left by the collapse suggests that a magma batch might have been injected inside the volcano and triggered the collapse the lavas of the pre collapse edifice have been deposited in alternating submarine and subaerial environments suggesting that vertical movements might also be a major triggering mechanism for large lateral collapses recognition of this phenomenon is particularly important in recent active island or coastal volcanoes as it can trigger tsunamis

geology and 40ar 39ar geochronology of the medium to high k tanaga volcanic cluster western aleutians we used geologic mapping and geochemical data augmented by 40 ar 39 ar dating to establish an eruptive chronology for the tanaga volcanic cluster in the western aleutian arc the tanaga volcanic cluster is unique in comparison to other central and western aleutian volcanoes in that it consists of three closely spaced active volumetrically significant edifices sajaka tanaga and takawangha the eruptive products of which have unusually high k 2 o contents thirty five new 40 ar 39 ar ages obtained in two different laboratories constrain the duration of pleistocene holocene subaerial volcanism to younger than 295 ka the eruptive activity has been mostly continuous for the last 150 k y unlike most other well characterized arc volcanoes which tend to grow in discrete pulses more than half of the analyzed tanaga volcanic cluster lavas are basalts that have erupted throughout the lifetime of the cluster although a considerable amount of basaltic andesite and basaltic trachyandesite has also been produced since 200 ka major and trace element variations suggest that magmas from sajaka and tanaga volcanoes are likely to have crystallized pyroxene and or amphibole at greater depths than the older takawangha magmas which experienced a larger percentage of plagioclase dominated fractionation at shallower depths magma output from takawangha has declined over the last 86 k y at ca 19 ka the focus of magma flux shifted to the west beneath tanaga and sajaka volcanoes where hotter more mafic magma erupted

burial history and kinetic modeling for hydrocarbon generation part ii applying the galo model to saharan basins the galo basin evolution model described in makhous et al 1997 is applied to evaluate hydrocarbon generation and migration histories in several saharan basins three basins the oued el mya ghadames and illizi are located in the central and eastern parts of the saharan platform and are investigated in detail the ahnet mouydir timimoun reggane and other basins located in the southern and western parts of the platform are also studied the modeling results combined with geochemical data are used in a synthesis of the regional framework the thermal gradients in the ghadames and illizi basins are greater than those in the oued el mya basin this difference is attributed to differences in sedimentation and subsidence rates to less hercynian erosion and to fewer occurrences of evaporates in the akfadou region of the ghadames basin and in the mereksen region of the illizi basin in the southern and western parts of the illizi province the major subsidence occurred before hercynian uplift very moderate hercynian uplift in the ghadames and illizi basins did not involve a significant decrease of temperatures and organic matter maturation continued but at slower rates as a result the realization of hydrocarbon potential appears to be higher than would be expected favorable traps are located near subsided areas where the source shales particularly the devonian were not subjected to uplift and erosion in this respect the eastern sahara including the ghadames and illizi basins is a favored province analysis of the distribution of present day temperatures and paleotemperatures in the paleozoic sediments of the triassic province oued el mya ghadames trias and north illizi basins combined with effective source rock occurrences shows that favorable conditions for hydrocarbon generation during the paleozoic occurred essentially in the southern and southwestern parts of the province hydrocarbon generation during the mesozoic took place mainly in the central and northern parts of this province however some of the hydrocarbon accumulations in the northern and northeastern parts of oued el mya basin and in the northern and western ghadames basin were subsequently destroyed by the hercynian orogeny in the illizi basin ordovician and devonian structures are the most likely traps for hydrocarbons generated during the paleozoic whereas in the ghadames and oued el mya basins structures formed prior to the late cretaceous are preferentially favorable for oil accumulation gas accumulations are found in traps formed in the late cretaceous or later when source shales were buried to 3 3 3 5 km and more

40ar 39ar constraints on the temporal evolution of graciosa island azores portugal lava flows spanning the eruptive record of graciosa island azores archipelago and a gabbro xenolith were dated by 40ar 39ar in order to constrain the pleistocene and holocene volcanic evolution of the island the results range from 1 05 ma to 3 9 ka whereas prior published k ar and 14c ages range from 620 to 2 ka the formation of the serra das fontes shield volcano started at minimum 1 05 ma and the magmatic system was active for ca 600 ky as suggested by the formation of the gabbro xenolith by magmatic differentiation evolved magmas making up the serra das fontes serra branca composite volcano were generated at ca 450 ka after a period of ca 110 ky of volcanic inactivity and erosion of volcanic edifices volcanism was reactivated with the formation of the vitoria unit nw platform later the development of the vulcao central unit started with the formation of monogenetic cones located to the south of the serra das fontes serra branca vitoria unit this volcanism became progressively more evolved and was concentrated in a main eruptive center forming the vulcao central stratovolcano with an age older than 50 ka the caldera related to this stratovolcano is older than 47 ka and was followed by effusion of basaltic magmas into the caldera resulting in the formation of a lava lake which ultimately spilled over the caldera rim at ca 11 ka the most recent eruptions on graciosa formed two small pyroclastic cones within the caldera and the pico do timao cone within the vitoria unit at ca 3 9 ka

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

construction and destruction of a volcanic island developed inside an oceanic rift graciosa island terceira rift azores abstract there is a great lack of knowledge regarding the evolution of islands inside active oceanic rifts in particular the meaning of the different evolutionary steps therefore we conducted an investigation in graciosa island which lies at the northwestern end of the terceira rift in the azores triple junction with the objective of constraining the evolution of the island in terms of volcanic growth and mass wasting in particular the meaning and age of the destruction events from digital elevation model dem analysis stratigraphic and tectonic observations k ar dating on key samples and available bathymetry and gravity data we propose that graciosa comprises five main volcanic complexes separated by major unconformities related to large scale mass wasting 1 the older volcanic edifice serra das fontes complex grew until ca 700 ka and was affected by a major flank collapse towards the southwest which removed the whole sw flank the summit and a part of the ne flank 2 the baia do filipe complex developed between at least 472 ka and 433 ka in two different ways in the sw presently offshore as a main volcano and in the ne unconformably over the sub aerial remnants of the serra das fontes complex as secondary volcanic edifices 3 the baia do filipe complex was affected by a major flank collapse towards the sw again removing most of the edifice 4 the remnants of the baia do filipe complex were covered in unconformity by the serra dormida complex between ca 330 and 300 ka which in turn was unconformably covered by the younger basaltic cover complex between ca 300 ka and 214 ka these two units were affected by a third major sector collapse that removed the whole western flank the summit and part of the eastern flank of the serra dormida and basaltic cover complexes 5 despite the relatively young age of graciosa the collapse scars are not well preserved and not active anymore 6 a central type volcano has been growing since at least 60 ka at the southeastern end of the island inside the scar left by a fourth sector collapse towards the se which affected most previous complexes contemporaneously parasitic strombolian cones formed all over the island despite the location of graciosa inside the active terceira rift the new data indicate that the evolution of the island has been driven by a competition between volcano growth and repeated destruction by catastrophic sector collapses rather than by slow incremental faulting associated with the tectonics of the rift

causal link between quaternary paleoclimatic changes and volcanic islands evolution 1 giant landslides and resulting tsunamis represent the main geologic hazards linked to volcanic island evolution from offshore and onland studies flank failures have been identified around numerous islands in most geodynamic contexts however the triggering conditions are still poorly understood and several causes may act simultaneously to reach a critical threshold here we show that most large volume 10 km3 landslides occur at glacial stages termination and we propose that a causal relationship between flank collapse of volcanic islands and global climatic changes has existed at least since 900 kyr moreover ages reported here favour the hypothesis that major collapses occurred during the onset of glacial to interglacial transitions when sudden influx of melt water from polar ice caps causes rapid sea level rise we propose that rapid sea level rise induces enhanced coastal erosion and sudden changes of pore pressure conditions within basal layers which favour edifice failure

k ar dating extended into the last millennium application to the youngest effusive episode of the teide volcano spain less than one thousand years dating of the youngest volcanic episode of the teide volcano canary islands spain has been performed using the k ar cassignol technique analyses of about 20 g of pure alkali feldspar yielded a weighted mean age of 800 300 years stratigraphic historic and archeomagnetic dating validate this age and rule out the hypothesis of the presence of significant excess argon contamination for this flow our result shows that the last effusive activity of the teide volcano took place shortly before european settlement in tenerife island this study confirms that the cassignol technique can be applied with success for historic dating and demonstrates that it can now even be extended to the last millennium

the iapetus model a plate tectonic concept for the variscan belt of europe abstract a plate tectonic model is presented explaining the evolution of the variscan belt of europe it regards the iapetus ocean and its branch the tornquist sea as the only ocean involved in the caledonian variscan and alleghenian mega orogen the iapetus and its marginal basins disappeared through oblique subduction and collision in the following sequence 1 1 northeastern iapetus including the tornquist sea caledonian orogeny 2 2 central iapetus acadian orogeny 3 3 adjacent marginal basins variscan orogeny and 4 4 southwestern iapetus alleghenian orogeny the area of the variscides was part of the continental margin of gondwana made up of ridges and ensialic basins no ocean lay within the variscan area during the palaeozoic although patches of oceanic crust probably existed in rift basins e g the lizard ophiolite after the silurian early devonian closure of northwestern and central iapetus the variscan area was surrounded by cratons on three sides in a manner similar to that around the modern mediterranean sea the subsequent variscan orogeny was essentially an ensialic thrusting and folding induced by a further approach of gondwana toward laurentia after the variscan collision gondwana rotated clockwise to the west by moving along a strike slip zone this rotation during the carboniferous opened the palaeo tethys in the east and caused the alleghenian collision in the west the middle ordovician to permian palaeogeography is presented on a series of maps modelling tectonic displacement and plate motions avalonia is interpreted as the ordovician volcanic island arc of gondwana separated from mainland gondwana by an oceanic gulf or a back arc basin the iberian arc may have originated by a continental escape of iberia from the center of collision into the oceanic gulf the variscan austro alpine and southern alpine units are today located near their earliest early carboniferous position

ghadames basin southern tunisia a reappraisal of triassic reservoirs and future prospectivity recent discoveries of oil and gas in triassic reservoirs of the ghadames basin eastern algeria suggest that similar potential exists to the east in the southern tunisian part of the province for decades southern tunisia has remained an underexplored part of the basin in large part owing to older geological interpretations that focus on paleozoic reservoirs and to limitations in seismic data quality resulting from statics problems that have rendered trap identification inaccurate or tenuous new analyses of previously and recently acquired geological and geochemical data as well as improvements in seismic data acquisition and processing have begun to reverse older notions regarding limited hydrocarbon presence in southern tunisia log correlations indicate that productive sand rich intervals of the major triassic reservoir in the region the trias argilo greseux inferieur tagi can be correlated over large distances suggesting significant continuity into lightly drilled and undrilled areas analyses of geochemical data reveal a more complex multistage history of hydrocarbon maturation and migration than previously believed much greater volumes of petroleum have been generated and a larger variety of traps have been created than can be accounted for by older interpretations where added to the use of new field and processing parameters for seismic surveys these factors have together led to important upgraded evaluations of basin potential in southern tunisia

large scale active slump of the southeastern flank of pico island azores we report evidence for ongoing lateral slump of part of the southeastern flank of the pico volcanic ridge in the azores data from a high resolution digital elevation model field work gps and radar interferometry show that 1 the slumping sector is several cubic kilometers in size 2 the structure involves several curved scars with normal fault kinematics 3 the central part is undergoing little horizontal displacement toward the southeast 1 6 1 3 mm yr but significant downward movement 5 12 mm yr and 4 the outer part of the southeastern flank of pico is subsiding faster than the inner parts this likely reflects recent individualization of a steep seaward dipping fault in the moving mass the slump shares similarities with active slumps recognized elsewhere although the studied area may represent only the proximal part of a much larger complex potentially affecting the deep submarine base of the island displacement of the subaerial part of the southeastern flank of pico seems to be accommodated by the movement and rotation of large blocks along listric normal faults

burial history and thermal evolution of the northern and eastern saharan basins the numerical one dimensional reconstruction of the burial history and thermal evolution of the sedimentary section and basement was conducted for 32 wells in the east algerian basins with the help of the galo basin modeling system these reconstructions allowed the performance of a quasi two dimensional analysis of the burial history of the basins changes in rock temperatures the lithosphere thickness and maturation conditions of organic matter during basin development along the four profiles crossing the study region the modeling assumed that the highest thermal activation in the history of the saharan basins with the heat flow more than 100 mw m2 and the thinnest lithosphere on the order of 25 35 km took place during the late carboniferous to permian in the dahar and oued el mya basins the uplift responsible for this activation caused erosion of 2000 3000 m of ordovician to lower carboniferous strata the ghadames and illizi basins were subjected at the same time to more moderate erosion and thermal activation with heat flow less than 75 mw m2 in the triassic cretaceous interval maximum subsidence occurred in the northern areas which were characterized by maximal thermal activation and the thinnest lithosphere in the permian at present the situation is opposite to that in the permian the highest thermal regime occurs in the southern areas of the study region and especially in the illizi basin where heat flow reaches and even exceeds 100 mw m2 and the thickness of the lithosphere decreases as much as 30 km the modeling also assumes stretching of the lithosphere in the northeastern and central parts of the illizi basin with maximal amplitude of about 1 16 during the cenozoic the analysis shows that the hercynian erosion could account for only a few of the abrupt changes in vitrinite profiles in the saharan basins and that triassic and later intrusive activity and associated hydrothermal heat transfer accurately explain the steplike character of maturation profiles

plate tectonics and cratonal geology in northeast africa egypt sudan the stratigraphical interpretation of the strata of nubia allows for the first time in connection with structural petrological and sedimentological investigations to reconstruct the geological development of this cratonal area after cratonization during the panafrican event extensional trends in wsw ene direction caused a structural relief striking nnw sse the collision between gondwana and the northern continents during the carboniferous resulted in the uplifting of large parts of the northeast african plate and was accompanied by more or less east west striking faults and magmatic intrusions erosion of paleozoic sediments in middle and southern egypt and reversal of the main drainage direction was the consequence this caused deposition of karroo type strata in northern sudan including glacial deposits at the base along the sudanes egyptian border

a giant landslide on the southern flank of tahiti island french polynesia we present evidence for an ancient and voluminous subaerial landslide of the southern flank of tahiti society islands during a marine geophysical survey in 1996 submarine mass wasting deposits were mapped as far as 60 km from the southern shore of the island acoustic imagery reveals a surface of 2950 km of debris avalanche and hummocky terrain based on bathymetric data the volume of the debris is estimated to be 1150 km in comparison with hawaiian and other oceanic island landslides it can be classified as a giant rapid and cataclysmic event tahiti morphology and the distribution of volcanic ages over the island strongly suggest that the slope failure initiated near the top of the southern island flank between 650 and 850 ka the landslide scar was subsequently filled by eruptions the estimated volume of the subaerial removed material exhibits a large discrepancy with the volume of the submarine deposits that can be explained by recurrent slide events

gps and tectonic evidence for a diffuse plate boundary at the azores triple junction abstract we use gps bathymetric structural and seismic data to define the pattern of present deformation along the northern half of the azores plateau where the nubia eurasia plate boundary terminates at the axis of the mid atlantic ridge mar new and existing campaign gps velocities from the azores islands reveal extension oblique to a series of en echelon volcanic ridges occupied by terceira s jorge pico and faial islands in a frame of reference defined by 69 continuous gps stations on the eurasia plate terceira island moves 2 1 mm yr away from eurasia consistent with the island s location within the terceira rift and plate boundary structure the volcanic ridges south of the terceira rift move toward wsw at progressively faster rates reaching a maximum of 3 5 0 5 mm yr 2 for the pico faial volcanic ridge the hypothesis that the terceira rift accommodates all nubia eurasia plate motion is rejected at high confidence level based on the motions of sites on s jorge island just west of terceira rift all of the islands move relative to the nubia plate with pico island exhibiting the slowest motion only 1 0 5 mm yr 2 detailed bathymetry from the interior of the hypothesized azores microplate reveals faults that crosscut young mar seafloor fabric these observations and the gps evidence for distributed deformation described above argue against the existence of a rigid or semi rigid azores microplate and instead suggest that nubia eurasia plate motion is accommodated by extension across a 140 km wide zone east of the mar axis most likely bounded to the north by the northern shoulder of the terceira rift the mar spreading rate along the western end of the azores deformation zone 38 5 n 39 5 n is intermediate between the eurasia north america rate measured at 39 5 n and the nubia north america rate measured at 38 5 n consistent with the joint conclusions that the nubia eurasia boundary is broad where it intersects the mar and the azores triple junction is diffuse rather than discrete

acoustic bed velocity and bed load dynamics in a large sand bed river 1 development of a practical technology for rapid quantification of bed load transport in large rivers would represent a revolutionary advance for sediment monitoring and the investigation of fluvial dynamics measurement of bed load motion with acoustic doppler current profilers adcps has emerged as a promising approach for evaluating bed load transport however a better understanding of how adcp data relate to conditions near the stream bed is necessary to make the method practical for quantitative applications in this paper we discuss the response of adcp bed velocity measurements defined as the near bed sediment velocity detected by the instrument s bottom tracking feature to changing sediment transporting conditions in the lower missouri river bed velocity represents a weighted average of backscatter from moving bed load particles and spectral reflections from the immobile bed the ratio of bed velocity to mean bed load particle velocity depends on the concentration of the particles moving in the bed load layer the bed load layer thickness and the backscatter strength from a unit area of moving particles relative to the echo strength from a unit area of unobstructed bed a model based on existing bed load transport theory predicted measured bed velocities from hydraulic and grain size measurements with reasonable success bed velocities become more variable and increase more rapidly with shear stress when the transport stage defined as the ratio of skin friction to the critical shear stress for particle entrainment exceeds a threshold of about 17 this transition in bed velocity response appears to be associated with the appearance of longer flatter bed forms at high transport stages

structure of the mobile south flank of kilauea volcano hawaii how do huge landslides occur in hawaii we can begin to address this question by examining an incipient landslide structure on the mobile south flank of kilauea volcano between 1970 and 1989 this part of the south flank moved in a southeast direction seaward by 4 m on its eastern end and by 10 m on its western end parallel to the western boundary of a large oifshore topographic bench we show that abrupt decreases in cumulative flank movement correspond to abrupt decreases in hypocenter concentration most of the earthquakes occur in a 7 to 10 km deep band beneath the south flank and relative relocation of a subset of these events shows that they are derived from a single horizontal plane which appears to be a decollement focal mechanisms for this deep seismicity are dominated by thrust fault mechanisms with the overlying block moving seaward a comparison of south flank bathymetry with decollement structures on other volcanoes suggests that the distal end of this decollement coincides with the distal end of the offshore topographic bench 30 50 km from shore and 5 km below sea level the fault system forming the hilina pali is connected with this decollement so that slip on the hilina pali s normal faults coincides with slip of the decollement and with reverse faulting of the distal end of the bench this interpretation is supported by studies of the events associated with the m7 2 kalapana earthquake in 1975 when the hilina pali is connected to the outer bench with a decollement inferred from seismicity a wedge 8 km thick adjacent to kilauea s magma system and 1 2 km thick along the edge of the outer bench an area over 3000 km2 is defined the thickness adjacent to the magma system decreases eastward along kilauea s east rift zone and southwestward from kilauea caldera whereas the thickness of the lip of the outer bench decreases only eastward geologic observations and geophysical studies of the subaerial flank reveal an extensive magma system beneath the koae fault system as well as beneath kilauea caldera and its east rift zone we infer that the boundary of the proximal end of the mobile flank is the southern boundary of this magma system and that this boundary coincides with the southern boundaries of both the koae fault system and kilauea s east rift zone

re evaluation of the petroleum potential of the kufra basin se libya ne chad does the source rock barrier fall abstract the kufra basin is a large underexplored palaeozoic intracratonic sag basin in se libya and ne chad with extensions into nw sudan and sw egypt the basin fill consists of shallow marine to fluvial deposits ranging in age from infracambrian to cretaceous geologically the basin is very similar to the murzuq basin in sw libya which recently presented libya with its largest oil discovery for over a decade most of the hydrocarbon play elements known from the murzuq basin also occur in the kufra basin thick porous cambro ordovician sandstones are present and would form good reservoirs lower silurian shales may act as effective seals and there are potential structural traps in seismically defined fault blocks however the source rock availability in the kufra basin is currently unclear one of the two main source rock candidates in the basin is a lower silurian shale unit tanezzuft formation the tanezzuft shales have been described as being up to 130 m thick in outcrops at the basin margins but the shales were found to be replaced by siltstones and sandstones in two dry exploration wells drilled in the northern part of the basin by agip between 1978 and 1981 hot shales developed at the base of this widespread silurian shale unit form important source rocks in many areas of north africa and arabia these hot shales are interpreted to have been deposited in palaeodepressions such as incised valleys of the preceding lowstand or intrashelf basins during the initial transgression after the melting of the late ordovician ice cap the areal distribution of the organic rich unit is therefore discontinuous fieldwork in the kufra basin has shown that the basal tanezzuft horizon is not exposed on the northern and eastern margins of the basin deep infracambrian rift grabens have been interpreted on seismic lines from the kufra basin and in analogy to oman and algeria could contain organic rich infracambrian deposits the infracambrian succession in the kufra basin may contain a second major potential source rock and warrants further investigation

constraining burial history and petroleum charge in exhumed basins new insights from the illizi basin algeria intracratonic sag basins commonly have relatively simple tectonic histories however later tectonic activity involving exhumation can make reconstructing the burial history a challenging task this is important because the relative timing of hydrocarbon generation and trap formation can be a key factor in risk assessment if trap formation postdates peak hydrocarbon generation exploration plays are typically downgraded mechanisms for charge in such exhumed basins are critical factors for understanding exploration risk this study uses data collected from an ordovician gas condensate field in the illizi basin of algeria to document the charging of a trap formed or modified during exhumation of the basin following maximum burial integrated analysis of sonic compaction data thermal history indicators and stratigraphic well data was used to constrain the burial and thermal history of the region hydrocarbon generation in the lower silurian source rock is interpreted to have occurred during the carboniferous prior to hercynian exhumation and during the late cretaceous early eocene maximum burial prior to eocene exhumation structural reconstructions indicate that the field was initially located on the southern flank of a long lived intrabasinal paleozoic paleohigh the large low relief structural closure that defines the present day accumulation formed as a result of northward tilting of the illizi basin during eocene uplift of the hoggar massif the study demonstrates that the timing of trap formation at the ordovician field postdates the main local hydrocarbon generation events within the basin suggesting that alternative hydrocarbon charge mechanisms are required this study indicates considerable potential to charge updip traps on the flanks of exhumed petroliferous basins via redistribution of the preexisting hydrocarbons within the basin

the 1998 faial earthquake azores evidence for a transform fault associated with the nubia eurasia plate boundary abstract with very few exceptions m 4 tectonic earthquakes in the azores show normal fault solution and occur away from the islands exceptionally the 1998 shock was pure strike slip and occurred within the northern edge of the pico faial ridge fault plane solutions show two possible planes of rupture striking ene wsw dextral and nnw sse sinistral the former has not been recognised in the azores but is parallel to the transform direction related to the relative motion between the eurasia and nubia plates therefore the main question we address in the present study is do transform faults related to the eurasia nubia plate boundary exist in the azores knowing that the main source of strain is related to plate kinematics we conclude that the sinistral strike slip nnw sse fault plane solution is not consistent with either the fault dip ca 65 which is typical of a normal fault or the ca ene wsw direction of maximum extension both are consistent with a normal fault as observed in most major earthquakes on faults striking around nnw sse in the azores in contrast the dextral strike slip ene wsw fault plane solution is consistent with the transform direction related to the anticlockwise rotation of nubia relative to eurasia altogether tectonic data measured ground motion observed destruction and modelling are consistent with a dextral strike slip source fault striking ene wsw furthermore the bulk clockwise rotation measured by gps is typical of bookshelf block rotations observed at the termination of such master strike slip faults therefore we suggest that the 1998 earthquake can be related to the wsw termination of a transform ene wsw fault plane solution associated with the nubia eurasia diffuse plate boundary

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

volcan tancitaro michoacan mexico 40ar 39ar constraints on its history of sector collapse abstract volcan tancitaro is a 97 3 km3 stratovolcano located in the michoacan guanajuato volcanic field mgvf part of the trans mexican volcanic belt prior to this study there was only one k ar date 530 60 ka ban m hasenaka t delgado granados h takaoka n 1992 k ar ages of lavas from shield volcanoes in the michoacan guanajuato volcanic field mexico geofisica internacional 31 4 467 473 and one sector collapse event reported for this volcano in the literature garduno monroy v h corona chavez p israde alcantara i mennella l arreygue e bigioggero b chiesa s 1999 carta geologica de michoacan scale 1 250 000 universidad michoacana de san nicolas de hidalgo capra l macias j l scott k m abrams m garduno monroy v h 2002 debris avalanches and debris flows transformed from collapses in the trans mexican volcanic belt mexico behavior and implications for hazard assessment journal of volcanology and geothermal research 113 81 110 twenty six new 40ar 39ar ages indicate that volcan tancitaro became active 793 22 ka and that the most recent effusive activity occurred at 237 34 ka two catastrophic sector collapse events are identified and dated the first one occurred on the west side between 694 and 571 ka whereas the second one occurred on the east side between 261 and 238 ka the older collapse produced a 2 3 3 4 km3 debris avalanche and laharic deposit spread over 567 km2 whereas the more recent collapse left a 3 km wide horseshoe shaped scar on the eastern flank and produced a 3 6 7 0 km3 debris avalanche and laharic deposit that covers 654 km2 reconstruction of the main edifice of volcan tancitaro using arcgis software and digital elevation models indicates that the volume removed during the eastern sector collapse was 4 7 km3

volcano tectonic and geochemical evolution of an oceanic intra plate volcano tahiti nui french polynesia abstract geological mapping accurate k ar dating and geochemical analyses of lavas allow a detailed reconstruction of the geological history of tahiti nui island french polynesia the exposed volcanic activity is first characterized by the construction of a main shield from 1 4 ma to 870 ka with a maximum aerial eruptive rate around 2 km3 kyr lavas from this early building stage are alkaline slightly silica undersaturated with 87sr 86sr and 143nd 144nd compositions rather constant and close to the enriched mantle ii type vent locations were first concentrated along a main e w rift zone which was responsible for the lateral collapse of the northern and southern flanks of the main shield around 0 87 ma ago the subsequent activity was first restricted to the northern depression corresponding to an eruptive rate of about 5 km3 kyr in the period 850 760 ka significant variations in la sm 87sr 86sr and 143nd 144nd occur in lavas erupted immediately after the main northern landslide indicating a sudden increase in the extent of partial melting likely caused by the decompression subsequent to collapse however the later activity declined and the lavas exhibit a gradual change toward strongly silica undersaturated basanites likely indicating a decreasing extent of partial melting of the upper mantle the evolution of radiogenic isotope ratios over time indicates a change in the source toward more depleted compositions until around 500 ka post erosion volcanic activity following an apparent hiatus of 240 kyr exhibits similar major and trace element and isotope compositions the volcano structural and geochemical evolution of tahiti nui and the overall alkaline character of the lavas from other eruptive complexes of the society alignment suggest a relative weakness low temperature and low eruptive rate of the society plume compared to the hawaiian hot spot