controls on the distribution of calcareous foraminifera in the lower carboniferous of ireland abstract microfacies analyses of thin sections from over 650 samples of asbian and brigantian late visean platform carbonates from ireland shows that foraminiferal assemblages are controlled by the relative abundance of echinoderms mainly crinoids bryozoans and calcareous algae koninckopora ungdarella and palaeoberesellids archaediscidae valvulinella and tetrataxidae thrived in algal poor crinoid and bryozoan thickets at or below fair weather wavebase late visean algal limestones contain abundant endothyridae and palaeotextulariidae and are interpreted to have been deposited at depths between 5 and 10 m the morphology of the foraminifera studied is related closely to their facies distribution many taxa inhabited high energy shallow marine algal meadow facies these include bibradya cribrospira nevillella and bradyina with cribrate apertures and other specialised test features that protected the protoplasm from damage gigasbia omphalotis globoendothyra and pseudoendothyra with large rotund or keeled multilayered tests and forschiidae with large thick walled tests infaunal taxa such as the lituotubella nevillella gigasbia and the palaeotextulariids are recorded from algal facies and appear to have been unable to survive on bryozoan and crinoidal substrates pseudoammodiscus and earlandia characterized by simple morphologies and single layered walls and endothyranopsis endothyra and eostaffella planispirally coiled with multilayered micritic tests are regarded as the least facies controlled of the taxa studied the encrusting nature of pseudolituotuba and scalebrina ensured survival in a wide range of platformal palaeoenvironments though algal meadows were not generally suitable substrates for the pseudolituotubidae the secondary deposits in the umbilical region of the asteroarchaediscinae may have been an adaptation for survival in the dense crinoidal bryozoan thickets where they lived delicate planoarchaediscus occurs in algal poor wackestone to packstone facies typical of low energy palaeoenvironments possibly at depths below 20 m howchinia which occurs with fasciella a probable alga in intraclastic wackestone facies may also have lived in water deeper than 20 m major changes in foraminiferal assemblages through the asbian and brigantian stages of the late visean are attributed to changes in associated biotic constituents early asbian endothyrid and forschiid dominated assemblages were controlled by the relative abundance of bryozoans koninckopora and palaeoberesellids by the late asbian the foraminiferal assemblages were controlled by the presence or absence of palaeoberesellids ungdarella and to a lesser extent bryozoans asbian assemblages were similar although foraminifers such as bradyinids cribrospira and globoendothyra became abundant in the late asbian a switch to predominantly echinoderm mainly crinoid and bryozoan substrates in the brigantian may have caused the major change from late asbian endothyrid and palaeotextulariid assemblages to archaediscid and tetrataxid dominated assemblages

paleoenvironmental reconstruction of microbial mud mound derived boulders from gravity flow polymictic megabreccias visean sw spain abstract the upper visean outcrops from the guadiato valley cordoba sw spain provide a well preserved record of the mud mound factory which was developed in a mainly siliciclastic synorogenic foreland basin during the oblique sinistral collision of two terranes ossa morena and central iberian blocks the first onset of mud mound development has been recorded as microbial mud mound derived boulders in polymictic megabreccias as result of strong tectonic activity the upper visean record from the mississippian central band at guadiato valley starts with lower heterolithic units up to 180 m thick and shows two major tectonically controlled cycles a fining upwards interval fu followed by a coarsening upwards interval cu these cycles are linked to two active margins with gravelly fan delta development and different source areas mud mound derived boulders occur in the cu interval and are formed by peloidal primary and secondary reworked automicrites and allomicrites showing a diverse faunal and floral assemblage although never as the main skeletal framebuilders however the observed coeval richness in sponges lyssacinose hexactinellids and non lithistid demosponges and the diverse calcareous algae assemblage in mud mound derived boulders are not common in other visean buildups the growth cavities display changes in the geopetal relationships between fillings and the secondary cavities containing sand to gravel fillings reflecting a complex pre boulder and mud mound derived boulder history detailed mapping sampling stratigraphic and microfacial analyses have allowed the reconstruction of the mud mounds sedimentary environment prior to the collapse transport and emplacement as boulders with polymictic gravels

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

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

palaeobiogeographic context in the development of shallow water late visean early bashkirian benthic foraminifers and calcareous algae in the cantabrian mountains spain abstract the late visean to early bashkirian shallow water carbonate valdediezma platform in the picos de europa province of the cantabrian zone has been subdivided into eight microbiotic intervals by means of similarity clusters using the morisita coefficient the most complete visean bashkirian interval is represented in the valdediezma valley jitu l escarandi road to tresviso where only the steshevian to lower part of the protvian middle serpukhovian is missing this interval is better represented in the pompedrei bridge to la hermida composite section and also in the deeper water section at vegas de sotres these intervals contain a succession from the mikhailovian upper visean up to the krasnopolyanian lower bashkirian the assemblages of the valdediezma limestone show comparatively low similarity indices with the neighbouring basins in the collisional front in the western extremity of the palaeotethys during the progression of the variscan orogeny in this mobile belt two domains are recognized a western domain composed of outcrops in south western spain and in the moroccan meseta and an eastern domain comprising basins located in southern france some basins such as the betic cordillera initially had more influence from the western domain but later during the late serpukhovian it is considered as being part of the eastern domain the valdediezma platform foraminiferal and algal content is coincident with its location as an isolated platform surrounded by deep water seas and with higher similarities with the eastern domain regional tectonic events are recognized from the late visean onward and they are mostly masked by the overprint of latest pennsylvanian events facies changes are commonly observed particularly at the base of the intervals suggesting that facies control is the most important factor controlling the assemblages it is considered that eustatic sea level changes exerted a certain control on the assemblages

rock mass strength and slope stability of the hilina slump kīlauea volcano hawai i abstract stability of the hilina slump on the south flank of k lauea volcano hawai i is investigated using slope stability analyses based on rock mass mechanics the hilina slump is an active example of the giant landslides that are observed around submarine flanks of ocean island volcanoes based on edifice topology along with derived rock mass strength and deformability parameters slope stability analyses predict that the geometries of present day failure surfaces of the hilina slump are shallow located at less than 3 5 km depth below the upper surface of the edifice the failure surfaces at the base of the hilina slump are predicted to be structurally independent from a previously interpreted subjacent detachment at the contact between the k lauea edifice and the oceanic crust based on these model results the hilina slump is envisioned to ride atop the south flank of k lauea as it spreads seaward along this slipping basal detachment under present day slope and sea level configurations local horizontal ground accelerations greater than 0 4 0 6 g are predicted to cause slip along failure surfaces within hilina slump therefore dynamic stress changes due to slip along the subjacent detachment may potentially trigger slip along failure surfaces of the hilina slump model derived stability and failure surface geometries can account for the distinct observed distribution of slip along specific hilina faults following the m fa 7 9 1868 ka u and m s 7 2 1974 kalapana earthquakes further the spatial distribution of south flank aftershocks m 1 5 recorded between 1950 and 1976 are consistent with the predicted distribution of potential earthquake induced slip of the hilina faults

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

rapid deformation of kilauea volcano global positioning system measurements between 1990 and 1996 campaign global positioning system gps measurements from 1990 to 1996 are used to calculate surface displacement rates on kilauea volcano hawaii the gps data show that the south flank of the volcano which has generated several large earthquakes in the past 3 decades is displacing at up to 8 cm yr to the south southeast the summit and rift zones are subsiding with maximum subsidence rates of 8 cm yr observed a few kilometers south of the summit caldera elastic dislocation modeling of the gps data suggests that the active sources of deformation include deep rift opening along the upper east and east rift zone fault slip along a subhorizontal fault near the base of the volcano and deflation near the summit caldera a nonlinear optimization algorithm was used to explore the parameter space and to find the best fitting source geometry there is a broad range of model geometries that fit the data reasonably well however certain models can be ruled out including those that have shallow rift opening or shallow fault slip some offshore aseismic slip on a fault plane that dips between 258 north northwest and 88 south southeast is required best fitting slip and rift opening rates are 23 28 cm yr although rates as low as 10 cm yr are permitted by the data

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

development of a late visean mississippian mixed carbonate siliciclastic platform in the guadalmellato valley southwestern spain abstract the penas rubias syncline southwestern spain exposes a well preserved shallow water platform succession containing a spectrum of facies corresponding to inner platform intertidal to supratidal environments across to deeper water middle to outer platform environments nineteen microfacies are recognized which are grouped into seven facies association corresponding to siliciclastic deltaic bars mixed carbonate siliciclastic shoals carbonate mud mound boundstones background platform carbonates background platform siliciclastics mixed tempestites and deep water siliciclastic shales and sandstones the age of the succession was determined mainly by foraminiferans and calcareous algae which permit the succession to be assigned to the late brigantian latest visean this upper brigantian platform is the only record of sedimentation of this age in the region and thus is key for interpreting the sedimentary and tectonic evolution of the carboniferous rocks in sierra morena biotic and sedimentological features were analyzed in order to assess the controls on the sedimentation several factors have influenced sedimentological changes turbidity subsidence siliciclastic discharges storms and bioturbation the siliciclastic discharges exerted a considerable control on the basal deposits mostly in their percentage of quartz sand grains and as microconglomerates however they did not develop as large deltaic deposits and their influence can be considered as virtually negligible in regards to the remaining part of the succession turbidity as a result of higher percentage of silt and mud in suspension seems to be the main factor controlling the change between the older intertidal deposits in the inner platform to the younger subtidal deposits of the middle and outer platform as a result of the increase of the mud and silt in suspension facies changed first to marlstones and nodular argillaceous limestones and second to predominantly calcimicrobial boundstones and shales in the uppermost part of the carbonate succession as well as showing a marked change from photic controlled benthic faunal and microfloral assemblages to assemblages more tolerant or better adapted to muddier dysphotic substrates bioturbation is also interpreted as one of the main controls influencing the different type of boundstones in the middle platform permitting the vertical growth of dome shaped mud mounds or as sheet like deposits storm influences seem to have exerted some control on the positive relief of the dome shaped boundstones which are usually capped by tempestites the differential subsidence observed in the northwestern sector of the platform allowed the accumulation of many stacked dome shaped mounds a feature not recognized in southeastern parts the general stratigraphical sequence seems to be controlled by eustasy and synsedimentary tectonics the overall succession exhibits a pronounced deepening upwards transgressive sequence from siliciclastic delta bars mixed shoals carbonates and shales of the middle platform with the growth of calcimicrobial boundstones and dark green shales passing up into black shales at the top of the sequence in the outer platform and possibly submarine slope settings although this transgressive sequence is in harmony with the 3rd order glacioeustatic cycle defined for the late brigantian in the western palaeotethys all these brigantian rocks accumulated in a synsedimentary extensional regime which is related to the initiation of a sinistral strike slip regime previously recognized as affecting only serpukhovian and younger rocks in sierra morena these synsedimentary faults allow us to recognize significant lateral variations in thickness over short distances

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

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

distributed deformation close to the azores triple point abstract terceira rift and the northern and southern branches of the mid atlantic ridge mar form a triple junction close to 39 n known as the azores triple junction new swath bathymetric data are used to investigate the surface expression of faulting close to the triple junction by the systematic mapping of mar generated abyssal hills it is shown that close to the geometrical intersection between the three spreading axes there exists no single transform fault connecting terceira rift to the mar but a distributed tectonic deformation area characterized by mesoscale brittle deformation close to the surface covering approximately 90 km by 100 km and almost no volcanism which links terceira rift to the mar accommodating the relative displacement of the three plates close to the geometrically triple point magnetic chrons are used to compute the spatial variation of spreading velocity at the mid atlantic ridge and confirm the above interpretation they show a progressive increase of spreading velocity along a single mar segment between pure nubian at 38 30 n and pure eurasian at 39 25 n without the development of a transform fault that would integrate the eurasia nubia plate boundary the comparison of similar triple junctions where a slower axis joins two faster ridges shows that the slower arm does not reach the triple point and that there is always a finite triple junction area highly tectonized in which size is dependent on the angle between the two faster arms and consequently on the relative spreading velocity of the slower arm

a past giant lateral collapse and present day flank instability of fogo cape verde islands fogo island is a large and extremely steepsided oceanic island volcano in the cape verde archipelago it has a large ca 9 km across east facing summit collapse structure the monte amarelo collapse with a probable volume of at least 150 200 km3 for most of its history the monte amarelo volcano had a small but productive central vent complex and radial rift zones fed by laterally propagating dykes shortly before the collapse the latter were replaced by north south trending arrays of en echelon vertically propagating dykes since the monte amarelo collapse the scar has partly filled with a new volcano the cha das caldeiras volcano the summit cone of this volcano the pico do fogo is a very young feature but has been abandoned in the most recent phase of activity from the 18th century onwards the same period has also seen the abandonment of earlier radial rift zones with laterally propagating dykes and their replacement with en echelon arrays of vents fed by vertically propagating dykes these form an n s trending array within the older collapse structure and are associated with seaward displacement of the eastern flank of the volcano within the old collapse structure the most recent eruptions those of 1951 and 1995 appear to be associated with episodes of flank instability manifested in n s surface fissuring and east facing normal faults these recent structural changes in the volcano parallel those which took place in the monte amarelo volcano prior to its collapse

island edifice failures and associated tsunami hazards volcanic ocean islands are prone to structural failure of the edifice that result in landslides that can generate destructive tsunamis these island landslides range enormously in size varying from small rock falls to giant sector failures involving tens of cubic kilometers of debris a survey of literature has allowed us to identify twenty three processes that contribute to edifice collapse these have been divided into endogenetic and exogenetic sources of edifice failure endogenetic sources of instability and failure include unstable foundations volcanic intrusions thermal alteration edifice pore pressures unbuttressed structures and buried faults exogenetic sources of instability and failure include collapse of subaerial or submarine deposits endo upwelling karst megaporosity fractures oversteepening overloading sea level change marine erosion weathering including hurricanes glacial response volcanic activity regional uplift or subsidence tectonic seismicity and anthropogenic agents while the endogenetic sources dominate during periods of active volcanism and cone building the exogenetic sources may cause failure at any time tsunamis both small and large are associated with these edifice failures

catastrophic flank collapses and slumping in pico island during the last 130 kyr pico faial ridge azores triple junction abstract the pico island constitutes the easternmost sub aerial domain of a steep wnw ese volcanic ridge which has developed within the nubia eurasia diffuse plate boundary azores triple junction the island comprises three volcanic systems from older to younger the topo volcano the fissural system and the pico stratovolcano from a high resolution digital elevation model 10 m and new bathymetric stratigraphic structural and high precision k ar data we reconstruct the main successive stages of growth and partial destruction of the island over the last 200 kyr we especially concentrate on the central sector of the island which has recorded gradual movements through slumping and catastrophic flank collapses since ca 130 kyr the remmants of the topo volcano are partly exposed on pico s se flank and are here dated between 186 5 and 115 4 ka topo was significantly destroyed by n and s directed large scale flank collapses between ca 125 and 70 ka on pico s n flank collapse seems to have removed all the unstable material but in the s the collapse structure is composite including a major flank collapse and a remnant slump complex that is still active a first episode of deformation occurred between ca 125 and 115 ka along the master fault of the slump between ca 115 and 69 ka most of the unstable material was removed by a major flank collapse leaving behind a still considerable volume of unstable material that comprises the active slump this first collapse was catastrophic and generated a large debris deposit recognized on the high resolution bathymetry with a minimum run out of ca 17 km the scar was partially filled by volcanic products erupted from volcanic cones developed within the slump depression and possibly also from the early wnw ese fissural system subsequent deformation in the slump area affected in part the filling units leading to the individualization of secondary curved faults younger volcanic products have gradually masked the mass wasting scars unlike the well known hilina slump hawaii pico s slump evolution might be controlled by an active regional tectonics

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

dating the giant zhuxi w cu deposit taqian fuchun ore belt in south china using molybdenite re os and muscovite ar ar system abstract the recently discovered zhuxi w cu ore deposit is located within the taqian fuchun ore belt in the southeastern edge of the yangtze block south china its inferred tungsten resources based on new exploration data are more than 280 mt by 2016 at least three paragenetic stages of skarn formation and ore deposition have been recognized prograde skarn stage retrograde stage and hydrothermal sulfide stage secondly greisenization marmorization and hornfels formation are also observed scheelite and chalcopyrite are the dominant metal minerals in the zhuxi deposit and their formation was associated with the emplacement of granite stocks and porphyry dykes intruded into the surrounding carboniferous carbonate sediments huanglong and chuanshan formations and the neoproterozoic slate and phyllites the scheelite was mostly precipitated during the retrograde stage whereas the chalcopyrite was widely precipitated during the hydrothermal sulfide stage a muscovite 40ar 39ar plateau age of about 150 ma is interpreted as the time of tungsten mineralization and molybdenite re os model ages ranging from 145 9 2 0 ma to 148 7 2 2 ma for the subsequent hydrothermal sulfide stage of activity as the time of the copper mineralization our new molybdenite re os and muscovite 40ar 39ar dating results along with previous zircon u pb age data indicate that the hydrothermal activity from the retrograde stage to the last hydrothermal sulfide stage lasted up to 5 myr from 150 6 1 5 to 145 9 1 ma and is approximately coeval or slightly later than the emplacement of the associated granite porphyry and biotite granite the new ages reported here confirm that the zhuxi tungsten deposit represents one of the mesozoic magmatic hydrothermal mineralization events that took place in south china in a setting of lithospheric extension during the late jurassic 160 150 ma it is suggested that mantle material played a role in producing the zhuxi w cu mineralization and associated magmatism

the palaeoecological distribution of the endothyroids foraminifera in the guadiato area sw spain mississippian abstract this paper focusses on the distribution and methodological problems that are observed in the palaeoecological analyses of the endothyroids from the guadiato area in the southwestern part of the iberian peninsula in spite of a long history of taxonomical and biostratigraphical studies on endothyroids there have been few investigations of their palaeoecology and taphonomy the guadiato area contains a sequence of upper visean to pendleian marine carbonates the upper visean units were deposited in a storm dominated ramp the pendleian strata were deposited in a tectonically controlled shelf with narrow platform facies supra inter and subtidal and a wide area of slope deposits some of the foraminiferal assemblages of this succession typify intertidal facies and incipient shoals and are regarded as para autochthonous other assemblages such as the endothyroids in the higher part of the pendleian slope are of doubtful allochthony it is likely that endothyroids did not live in slope facies it was too deep but the extent of their transportation cannot be determined since their tests do not show signs of abrasion several factors controlled the endothyroid distribution such as salinity and depth deposits formed in high energy environments such as shoals and tidal flats were not favourable for the endothyroids particular palaeoecological factors also determine the distribution of certain families subfamilies or genera one of these factors is relative environmental stability for example some endothyroids that lack secondary deposits the archaediscinae and endothyra priscella were more abundant in stable environments in contrast other genera with secondary deposits the asteroarchaediscinae omphalotis and the evolved endothyra were more abundant in unstable or fluctuating microfacies this factor however did not control the distribution of every genus because this difference is not observed in some species of genera with or without secondary deposits e g globoendothyra

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

defining the plate boundaries in the azores region abstract the azores archipelago occupies the boundary zone where three major tectonic plates eurasia nubia and north america meet to form the azores triple junction repeat observations from six campaigns carried out between 1993 and 2001 for the tango network of gps sites now allow reliable estimations of the current motions of the involved plates at millimeter scale resolution analysis of these space geodetic data demonstrates that during the observation period santa maria island followed the average nubian plate movement and graciosa island mimicked the average eurasian plate behavior all other gps sites display intermediate behavior consistent with their locations within the active inter plate deformation area the active deformation area is well modeled by an elastic half space approach with the segmentation of the eurasian nubian plate boundary constrained by other geophysical data

a mid tournaisian late visean carbonate ramp reconstructed from nappes and olistolites in the southern montagne noire france abstract the mainly calcareous succession from the mid tournaisian to the lower part of the upper visean in the southern montagne noire mont peyroux nappes and cabrieres slices is sedimentologically revised from the late visean the variscan orogeny affected the area and the studied mississippian part of the succession was considered as part together with the devonian of a period of tectonic quiescence later included as nappes and olistolites in a wildflysch this study presents the facies from pelagic limestones calciturbidites bioclastic limestones and microbial limestones and the relationship between platform and calciturbidites in the pre orogenic context of the montagne noire basin during the mississippian the differences in the lithostratigraphy is analyzed by means of four tectonostratigraphical units mont peyroux nappe roquessels band cabrieres area and la serre band previously defined by other authors that together with the deep water vieussan caragnas unit not studied here due to the poverty in chronostratigraphical data allow reconstructing the original carbonate platform the latter seems to correspond to a ramp for the latest tournaisian to early visean and a distally steppened ramp from the middle visean to the early late visean including basin plain to slope as the deepest water environments and middle ramp as the shallowest except for the uppermost part of the succession where the inner ramp is recognized during this period the shallowing tendency in the tectonostratigraphic units is well marked mont peyroux nappe roquessels band cabrieres area la serre band from deeper to shallower which differs from the shallowing trend defined by previous authors during the devonian strong similarities are observed with the preserved mississippian carbonates in the mouthoumet massif to the south which might represent the shallowest water deposits of the ramp not preversed in the cabrieres la serre areas

stratigraphic constraints on the timing and emplacement of the alika 2 giant hawaiian submarine landslide abstract previous work has found evidence for giant tsunami waves that impacted the coasts of lanai molokai and other southern hawaiian islands tentatively dated at 100 and 200 ka by u series methods on uplifted coral clasts seafloor imaging and related work off hawaii island has suggested the alika phase 2 debris avalanche as the source of the 100 ka giant wave deposits although its precise age has been elusive more recently a basaltic sand bed in odp site 842 300 km west of hawaii estimated at 100 20 ka has been suggested to correlate with this or another large hawaiian landslide our approach to the timing and linkage of giant submarine landslides and paleo tsunami deposits is a detailed stratigraphic survey of pelagic deposits proximal to the landslide feature beginning with a suite of seven piston gravity and box cores collected in the vicinity of the alika 2 slide we used u series dating techniques including excess 230 th and 210 pb profiling high resolution paleomagnetic stratigraphy including continuous u channel analysis 18 o stratigraphy visual and x ray sediment lithology and the petrology and geochemistry of the included turbidites and ash layers minimum ages for the alika phase 2a slide from detailed investigation of two of the cores are 112 15 ka and 125 24 ka 2 based on excess 230 th dating a less precise age for the alika phase 1 and or south kona slide is 242 80 ka 2 consistent with previous geological estimates oxygen isotope analyses of entrained planktonic foraminifera better constrain the alika phase 2a maximum age at 127 5 ka which corresponds to the beginning of the stage 5e interglacial period it is proposed that triggering of these giant landslides may be related to climate change when wetter periods increase the possibility of groundwater intrusion and consequent phreatomagmatic eruptions of shallow magma chambers our study indicates the contemporaneity of the alika giant submarine landslides and distal deposits from enormous turbidity currents as well as coral clasts reported to be tsunami deposits on lanai and molokai through direct dating and compositional analysis of the landslide deposits

the 1980 1997 and 1998 azores earthquakes and some seismo tectonic implications abstract we have studied the focal mechanisms of the 1980 1997 and 1998 earthquakes in the azores region from body wave inversion of digital gdsn global digital seismograph network and broadband data for the 1980 and 1998 shocks we have obtained strike slip faulting with the rupture process made up of two sub events in both shocks with total scalar seismic moments of 1 9 1019 nm mw 6 8 and 1 4 1018 nm mw 6 0 respectively for the 1997 shock we have obtained a normal faulting mechanism with the rupture process made up of three sub events with a total scalar seismic moment of 7 7 1017 nm mw 5 9 a common characteristic of these three earthquakes was the shallow focal depth less than 10 km in agreement with the oceanic type crust from the directivity function of rayleigh lr waves we have identified the nw se plane as the rupture plane for the 1980 and 1998 earthquakes with the rupture propagating to the se slow rupture velocity about of 1 5 km s has been estimated from directivity function for the 1980 and 1998 earthquakes from spectral analysis and body wave inversion fault dimensions stress drop and average slip have been estimated focal mechanisms of the three earthquakes we have studied together with focal mechanisms obtained by other authors have been used in order to obtain a seismotectonic model for the azores region we have found different types of behaviour present along the region it can be divided into two zones zone i from 30 w to 27 w zone ii from 27 w to 23 w with a change in the seismicity and stress direction from zone i in zone i the total seismic moment tensor obtained corresponded to left lateral strike slip faulting with horizontal pressure and tension axes in the e w and n s directions respectively in zone ii the total seismic moment tensor corresponded to normal faulting with a horizontal tension axis trending ne sw normal to the terceira ridge the stress pattern for the whole region corresponds to horizontal extension with an average seismic slip rate of 4 4 mm yr