3 d seismic images of an extensive igneous sill in the lower crust when continents rift magmatism can produce large volumes of melt that migrate upwards from deep below the earth s surface to understand how magmatism impacts rifting it is critical to understand how much melt is generated and how it transits the crust estimating melt volumes and pathways is difficult however particularly in the lower crust where the resolution of geophysical techniques is limited new broadband seismic reflection data allow us to image the three dimensional 3 d geometry of magma crystallized in the lower crust 17 5 22 km depth of the northern north sea in an area previously considered a magma poor rift the sub horizontal igneous sill is 97 km long n s 62 km wide e w and 180 40 m thick we estimate that 472 161 km3 of magma was emplaced within this intrusion suggesting that the northern north sea contains more igneous intrusions than previously thought the significant areal extent of the intrusion 2700 km2 as well as presence of intrusive steps indicate sills can facilitate widespread lateral magma transport in the lower crust

three dimensional seismic imaging of paleogene dike fed submarine volcanoes from the northeast atlantic margin we use three dimensional seismic data to describe the architecture of shallow intrusive igneous sill and dike complexes intruded into the upper crust as well as the internal and external geometry of extrusive conical igneous mounds that were fed by the magma conduits the conical mounds accreted on the seabed directly above the tips of the basaltic dikes between 54 9 and 54 6 ma in plan view the mounds are broadly circular 1 1 7 km in diameter and have a relief of 50 300 m they occur above a complex network of linked cuspate shaped sills and dikes intruded into paleocene and cretaceous sediments of the faeroe shetland basin northeast atlantic margin the highly organized internal structure consisting of bulbous layers arranged concentrically around a central axis along with the clear vertical link to the underlying sills and dikes indicates that they most likely represent pillowed basaltic lava and hyaloclastite mounds that were fed by the dikes and extruded onto the seafloor mounds of similar external geometry have been described from sidescan sonar images above active spreading centers in oceanic settings however such structures are rarely recognized in passive margin settings and prior to this investigation our knowledge of their three dimensional internal geometry has been largely speculative

growth and destruction of gran canaria deduced from seismic reflection and bathymetric data the morphology and structure of the submarine flanks of gran canaria have been mapped using hydrosweep swath bathymetry and high resolution reflection seismic data the growth and destruction of the island has been characterized previously by three major periods of volcanic activity 16 9 ma 4 5 3 5 ma younger than 3 ma separatedby erosional intervals two major sector collapses along the west coast inferred from the coastal morphology are believed to have formed at the end of the shield building phase one is characterized by a 19 km wide reentrant along the northwestern coast that may have formed synchronously with the formation of the 20 km diametermiocene tejeda caldera high sedimentation rates around gran canaria 50 m myr tend to cover and bury major landslide blocks ssw off the island several canyons continue seaward into a major sediment fan a 9 5 km wide volcaniclastic ridge in this fan is interpreted to represent deposits of the pliocene subaerial roque nublo debris avalanche we tentatively interpret the slope break at a depth of 600 800 m as the transition between subaerial and subaqueous chilled lavas at the end of the shield building phase the subsidence caused by the volcanic load 30 000 km3 on the lithosphere may thus amount to no more than 800 m several canyons on the island can be traced down the submarine flanks to a depth of 3 5 km indicating that at least deeper portions below the level of subsidence were eroded by mass flows continuing seaward from the subaerial canyons four submarine volcanoes were identified west and northeast of the island

detection of miocene saucer shaped sills offshore senegal via integrated interpretation of seismic magnetic and gravity data the atlantic margin offshore senegal has been explored by seismic reflection and grav mag surveys high amplitude laterally transgressive seismic reflectors are found to coincide with gravimetric and magnetic highs once seismic data are integrated with potential fields modelling these reflectors can be safely interpreted as saucer shaped igneous sills up to some hundreds of metres thick some km wide the occurrence of hydrothermal vent complexes and forced folds in the stratigraphic sequence above the sills constrain the intrusion age to the miocene field observations and in situ magnetic susceptibility measurements of oligocene miocene and quaternary igneous rocks emplaced in coastal senegal support this interpretation

structure and emplacement of the pliocene roque nublo debris avalanche deposit gran canaria spain abstract collapse of the flanks of the pliocene roque nublo stratocone on gran canaria lead to large debris avalanches that traveled far beyond the coastline with velocities that may have exceeded 100 m s the deposits comprised at least 14 km 3 of debris and covered an area of about 180 km 2 in the southern half of the island the debris filled deep canyons are largely exhumed at present incomplete disintegration poor fluidization and a good preservation of megablocks are thought to be mainly due to the confinement of the debris avalanche within deep canyons the rheological behavior of lithologic domains varies with their size internal strength and relative position within the deposit the deformation structures indicate that distinct components flowed whereas others slid throughout the transport in a relatively dense mode the following factors are believed to have been important in generating the roque nublo debris avalanche deposit 1 unusual abundance of pyroclastic flow and other volcaniclastic deposits making up the upper roque nublo cone 2 highly asymmetric basement beneath the cone with a very high southern ridge and a steep erosional southern slope leading to major instabilities 3 intrusion of dikes and cryptodomes as well as hydrothermal alteration in the crater area further weakening the volcano

miocene igneous activity in the northern subbasin offshore senegal nw africa abstract more than 70 enigmatic discordant seismic anomalies of limited lateral extent associated with eye shaped structures and folds have been imaged on 2d seismic data from the offshore northern subbasin of the senegal basin nw africa in this paper we define their distribution characterise their morphology and compare them to similar features imaged by seismic data along the ne atlantic margin that have been demonstrated to be igneous sills hydrothermal vents and intrusion related forced folds we propose that the cretaceous and paleogene strata in the northernmost part of the offshore northern subbasin were heavily intruded by igneous sills during the miocene the proposed timing of intrusion is coincident with that previously suggested for the development of the cayar seamount located 100 km nnw of dakar and onshore volcanism in the cap vert area near dakar and in the cape verde islands this stage of miocene igneous activity is interpreted to be closely associated with the coeval collision between africa and europe the interpreted igneous sills give rise to an unexpected soft seismic response the preferred explanation for the soft appearance of the sills is that the majority of sills are thin

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

neogene igneous intrusions in the northern south china sea evidence from high resolution three dimensional seismic data igneous intrusions emplaced within the prospective intervals of sedimentary basins can exert a significant impact on petroleum systems and hence are of considerable interest particularly when risking exploration plays a number of discordant high amplitude seismic anomalies dsas with a range of geometries are documented in high resolution 3d seismic data in the northern south china sea their distribution and seismic characteristics are analysed and compared with similar seismic anomalies documented within sedimentary basins in the atlantic margins and other locations the dsas occur mainly within early miocene strata and are interpreted as igneous intrusions that were emplaced close to the palaeo seabed and are dated as early middle miocene using seismic stratigraphic methods a number of vents are also identified above the intrusions within early middle miocene strata several geometrical forms are observed referred to here as saucer shaped lensoid shaped stacked and composite intrusions the seismic expression of these is increasing complex towards the palaeo seabed with a tendency for the saucer shaped sills to be the deepest intrusive forms the igneous intrusions observed in this study only could be identified using 3d seismic data and they are important for the future evaluations of petroleum systems basin evolution and tectonic analysis in the pearl river mouth basin c 2014 elsevier ltd all rights reserved

structure and evolution of hydrothermal vent complexes in the karoo basin south africa the karoo large igneous province formed at c 183 ma is characterized by the presence of voluminous basaltic intrusive complexes within the karoo basin extrusive lava sequences and hydrothermal vent complexes these last are pipe like structures up to several hundred metres in diameter piercing the horizontally stratified sediments of the basin detailed mapping of two sediment dominated hydrothermal vent complexes shows that they are composed of sediment breccias and sandstone the breccias cut and intrude tilted host rocks and are composed of mudstone and sandstone fragments with rare dolerite boulders sandstone clasts in the breccias are locally cemented by zeolite which represents the only hydrothermal mineral in the vent complexes our data document that the hydrothermal vent complexes were formed by one or a few phreatic events leading to the collapse of the surrounding sedimentary strata we propose a model in which hydrothermal vent complexes originate in contact metamorphic aureoles around sill intrusions heating and expansion of host rock pore fluids resulted in rapid pore pressure build up and phreatic eruptions the hydrothermal vent complexes represent conduits for gases and fluids produced in contact metamorphic aureoles slightly predating the onset of the main phase of flood volcanism

influence of igneous sills on paleocene turbidite deposition in the faroe shetland basin a case study in flett and muckle sub basin and its implication for hydrocarbon exploration

structure emplacement mechanism and magma flow significance of igneous fingers implications for sill emplacement in sedimentary basins abstract field and seismic observations show that numerous sills exhibit lobate morphologies each lobe corresponds to a distinct igneous segment exhibiting a finger like shape the long axis of which is commonly interpreted as a magma flow indicator robust understanding of the emplacement mechanisms of finger shaped sills and direct observations supporting finger orientation as magma flow indicator are lacking in this paper we present the results of detailed structural mapping on an exceptional easily accessible 1 km long outcrop in the neuquen basin argentina that exhibits a sill its contacts and the structures in the finely layered sedimentary host rock we show that the sill is made of distinct segments that grew inflated or coalesced we also demonstrate that the fingers were emplaced according to the viscoelastic fingering or viscous indenter models with no field evidence of tensile elastic fracture mechanism as commonly assumed in mechanical models of sill emplacement we identified new structural criteria at the intrusion s contacts for inferring magma flow direction during the magma emplacement our small scale structural observations carried out on a seismic scale outcrop have the potential to considerably aid the structural interpretation of seismic data imaging igneous sills i e to fill the standard gap between outcrop scale field observations and seismic scale geophysical data

development and post depositional deformation of a middle eocene deep water sandy depositional system in the sorvestsnaget basin sw barents sea abstract three dimensional seismic data from the sorvestsnaget basin sw barents sea supported by well data are used to investigate a middle eocene deep water depositional system the system forms a nnw oriented sediment accumulation characterized by increased seismic amplitudes and abrupt western termination the data indicate that post depositional sand remobilization and injection led to formation of sub circular sediment blocks up to several km wide to the east of the main accumulation the deep water depositional system was deformed by wing like sandstone intrusions extending 200 400 m upwards from the margins of the parent sand bodies the intrusions have polygonal or broadly circular plan view geometries deformation is inferred to have been associated with overpressure of the sand bodies as a result of rapid burial fluid migration into the sealed sand bodies from deeper sources via synsedimentary faults and fluid drainage from the surrounding mudrock during early compaction the final triggering mechanism for sand remobilization and injection is inferred to have been fracture propagation due to differential compaction and or fault induced earthquakes the injectite complexes are often associated with folding of overlying strata which we relate to differential compaction intrusion of sand took place during the middle eocene post depositional sand remobilization and injection have important implications for hydrocarbon exploration because they cause changes in the reservoir primary architecture connectivity and structure

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

the occurence and paleolimnologic significance of cutthroat trout oncorhynchus clarki in pluvial lakes of the estancia valley central new mexico cutthroat trout oncorhynchus clarki fossils in the quaternary age lacustrine sediment of the estancia valley provide insight into the paleolimnologic history of the valley the presence of fish is evidence that a pluvial system overflowed into the pecos river watershed most likely the overflow occurred during the expansion of early lake estancia an illinoian or pre illinoian pluvial lake known only in subcrop once established in the estancia watershed trout occupied headwater streams and only intermittently migrated and resided in developing lake systems the headwater streams served as refugia through the sangamon and early and middle wisconsin time when a fresh water lake did not exist in the valley with the advent of full pluvial conditions during the late wisconsin trout migrated from headwater streams into the first of three fresh water phases of late lake estancia on two occasions climate shifted to warmer and drier conditions causing significant lake level drawdown salinity increased and trout were eliminated from the lake only to be reintroduced during the next fresh water phase near the close of the late wisconsin late lake estancia waned and desiccated but headwater streams remained as fish refugia following the interpluvial episode the basin again filled culminating in lake willard considered to be of latest wisconsin age with evolution into a fresh water body trout migrated into a lake environment for the last time ensuing hot dry conditions brought about the desiccation of lake willard and severely impacted the headwater streams this factor in possible combination with human fishing activity led to the elimination of fish from the estancia valley after a continuous occupation of at least 130 000 yr

magma transport through the crust via interconnected sill complexes three dimensional seismic data from the volcanic margin offshore norway have been used to map the complex three dimensional geometry of two major sill complexes these data show that the complexes consist of bowl shaped or inclined sheetlike discordant sills that intersect with one another over a vertical distance of 8 12 km and transect basement and sedimentary rocks of the middle to upper crust using a simple graphical technique we demonstrate the interconnectedness of the sill complex and hence the maximum time for sill emplacement we show that sills are interconnected by junctions occurring systematically at the lowest points of the overlying sills and hence that the sill complex could have acted as a single throughgoing magmatic plumbing system transporting mafic melts from mid lower crustal depths to near surface based on this imaging of the magmatic plumbing system we conclude that sills can form viable and efficient conduits for crustal magma transport in volcanic margins and may play a role in feeding large extrusive complexes

sill related seafloor domes in the zhongjiannan basin western south china sea abstract magmatism can exert significant impact on sedimentary basins such as the zhongjiannan basin zjnb western south china sea we have evaluated multibeam bathymetric and multichannel seismic reflection data acquired by the guangzhou marine geological survey in recent years in order to investigate the distribution the characteristics and the subsurface structures related to seafloor domes found in the northeastern zjnb our data revealed forty two domes at water depths between 2312 m and 2870 m which are clustered around volcanic mounds large seamounts and along the edge of the central depression in the study area these domes are generally circular to elongate or irregular in plan view with large basal areas and they also have gentler flanks dips of 1 46 7 73 with vertical reliefs ranging from tens to hundreds of meters in seismic sections majority of the domes are underlain by variably shaped and complex magmatic sills which provide a cause effect relationship between domes formation and igneous intrusions these intrusions heat surrounding organic rich sediments release hydrocarbons fluidize sediment pore waters and form gas rich fluids which fill in sediment and uplift overlying strata immediately above the sills to form forced folds which are manifested as seafloor domes these sill folds dome structures have important implications for understanding geomorphologic features caused by sills emplaced at depth

prolonged post rift magmatism on highly extended crust of divergent continental margins baiyun sag south china sea three dimensional 3d seismic borehole and geochemical data reveal a prolonged phase of post rift magmatism on highly extended crust of the baiyun sag south china sea two volcanic complexes are identified and described in the context of continental rifting and diachronous continental breakup of the south china sea biostratigraphic data from exploration wells by7 1 and by2 complemented by k ar datings from core samples confirm that magmatic activity in the baiyun sag occurred in two main stages 1 a first episode at the base of the miocene 23 8 ma and 2 a second episode occurring at the end of the early miocene 17 6 ma the relative location of volcanic complexes in the baiyun sag and their stratigraphic position reveals prolonged magmatism inboard of the ocean continent transition zone during continental breakup we suggest that magmatism in the baiyun sag reflects progressive continental breakup in the south china sea with the last volcanic episode marking the end of a breakup sequence representing the early post rift tectonic events associated with the continental breakup process seismic and borehole data from this breakup sequence records diachronous magma emplacement and complex changes in depositional environments during continental breakup c 2016 the authors published by elsevier b v

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

quaternary evolution of the ria de vigo spain abstract the seismic analysis of the sedimentary infill of the ria de vigo reveals that the infill comprises of a fifth order sequence 18 ky bounded by a major discontinuity surface within the holocene sequence several seismic units have been identified the oldest one originated after the wurm glaciation and the origin of its top discontinuity was eroded during the regression sea level at 120 m of this last glacial episode isotopic stages 2 to 4 18 ky b p in some places below this ria infill another sequence can be identified this older sequence is associated with the pre existing faults and troughs in the deepest parts of the ria and it was deposited during the wurm glaciation miocene pleistocene eroded sediments were moved from the rias area to deeper zones where they accumulated in the lowstand system tract the next sea level rise occured in two steps producing two transgressive units separated by an hiatus surface this cycle was interrupted by the next sea level fall to 55 m marked on the seismic records by another recognizable boundary the next sea level rise took place in several steps back stepping with some stillstands generating another transgressive system tract in the ria from that time on the relative sea level continued rising depositing the most recent unit which represents the highstand system tract separating the highstand system tract and the transgresive unit below there is a consensed section the analysis of 29 cores provides groundtruthing for our hypothesis the identified main lithologic units show a transgressive sequence a granitic rock base an overlying second unit locally wedge shaped and most recently a marine muddy unit covering the present ria seafloor

igneous sill and finger emplacement mechanism in shale dominated formations a field study at cuesta del chihuido neuquen basin argentina seismic reflection data and field observations have revealed the presence of voluminous igneous sill complexes emplaced into organic rich shale formations in sedimentary basins worldwide damage and structures associated with sills have major implications for fluid flow through basins constraining the distribution of these structures requires a good understanding of the sill emplacement mechanism however most mechanical models of sill emplacement assume elastic host behaviour whereas shale is expected to deform inelastically this contradiction calls for new field observations to better constrain sill emplacement mechanisms in this paper we report on detailed field observations of spectacularly exposed fingers and a sill emplaced in shale at cuesta del chihuido in the neuquen basin argentina exceptional outcrop conditions allow detailed descriptions of both 1 the entire cross section of the intrusions and 2 the deformation structures accommodating intrusion propagation in the host rock all intrusions exhibit irregular blunt or rectangular tips the structures accommodating the tip propagation are systematically compressional including reverse faults folding and imbricate thrust system our observations suggest that the studied intrusions have propagated by pushing the host rock ahead as a viscous indenter our observations suggest that the viscous indenter model is probably a dominant mechanism of sill emplacement in shale

the shallow depth emplacement of mafic intrusions on a magma poor rifted margin an example from the bight basin southern australia abstract three dimensional 3d seismic data has provided important insights into how magma is transported and stored in sedimentary basins much of our understanding is based on volcanic rifted margins in contrast the magma plumbing systems of magma poor rifted margins are less well studied this study uses 3d seismic data to describe the magma plumbing system of the bight basin igneous complex a volcanic province located along the magma poor southern australian margin here magma emplacement occurred in the mid eocene some 40 million years after the onset of seafloor spreading our data images a variety of 5 270 m thick 2 23 km diameter mafic intrusions that are confined to within 1200 m of the paleoseabed intrusions emplaced at 200 m depth formed hybrid and compound sills and are typified by elongate lava flow like morphologies intrusions emplaced at depths of 200 1200 m formed saucer shaped and compound sills as well as laccoliths approximately 60 of the intrusions have lava flows and volcanogenic vents above their shallowest tips as shown from previous studies this suggests that the intrusions played a crucial role in transporting magma to the paleoseabed furthermore many of the intrusions are overlain by forced folds highlighting the role of magma emplacement in inducing overburden deformation the sills and laccoliths rarely form interlinked complexes and instead most commonly occur as isolated bodies this suggests that they were fed by dykes we infer that high rates of magma ascent in the dykes prevented their transition into sills within sediments at 1 2 km depth our study highlights that the magma plumbing system of the bight basin igneous complex contains a diversity of magmatic intrusions the morphology of which is linked to their emplacement depth host sediment rheology and the physical properties of the magma this plumbing system contrasts markedly with those found along better studied volcanic rifted margins

the three dimensional geometry and growth of forced folds above saucer shaped igneous sills forced folds formed at the seabed immediately overlying shallow 1 km saucer shaped sills along the ne atlantic margin during the early paleogene examples of this sill fold relationship are exceptionally well imaged by high resolution 3d seismic datasets from the ne rockall basin the forced folds are domal in shape 2 4 km in diameter exhibit a structural relief of up to 350 m and comprise sediment volumes of ca 1 km3 a comparison of the thickness distribution across and volume of a saucer shaped sill with a high intrusion diameter to depth ratio and the structural relief and volume of its associated forced fold shows a remarkable equivalence this has the important implication that the structural relief on intrusion related forced folds can be used as an estimate of the thickness of the underlying sill the analysed forced folds are interpreted to have formed through three continual growth stages that are directly linked to the mechanical emplacement of the underlying saucer shaped sills their growth was associated with an increase in faulting of the overlying strata and influenced coeval or subsequent development of polygonal fault systems within the overburden these structures represent a new type of four way dip closed hydrocarbon trap

zircon dating ties ne atlantic sill emplacement to initial eocene global warming abstract the earth experienced rapid greenhouse gas induced global warming during the palaeocene eocene thermal maximum petm the source of the gas is however debated we have for the first time determined the ages of magmatic sills in the voring basin offshore norway zircon u pb ages of 55 6 0 3 and 56 3 0 4 ma demonstrate that sill emplacement was synchronous with the petm within small errors this discovery strengthens the hypothesis that global warming was triggered by rapid release of greenhouse gases generated by heating of organic rich sediments around intrusions in the ne atlantic rather than from dissociation of gas hydrates supplementary material u pb data are available at http www geolsoc org uk sup18392

seismic characteristics and evolution of post rift igneous complexes and hydrothermal vents in the lingshui sag qiongdongnan basin northwestern south china sea abstract the study of morphology distribution and characteristics of igneous complexes has great significance to the understanding of magma plumbing processes geodynamics and tectonic evolution of continental margins previous studies concentrated partly on the magma rich rifted basins where the lateral magma transport mainly affects the igneous complexes connection and distribution however due to seismic wave shielding effects of the large shallow magmatic bodies the underlying igneous complexes and their corresponding magma plumbing systems in the magma poor rifted margins are still in debate in this study 2d 3d seismic data and well data are utilized to describe the morphology architecture and spatial temporal distribution of igneous complexes in the lingshui sag of the qiongdongnan basin northwestern south china sea margin the identified igneous complexes include 98 intrusive sills and feeder dykes beneath some of the isolated sills twenty six cone shaped mounds that overlie intruded sills through internal disturbed conduits were also described drilled well samples and seismic expressions suggest that these mounds are hydrothermal vents a uniform bottom mounds horizon of these vents suggests that they probably formed at the same time constrained by biostratigraphic data and sedimentation rate of underlying and overlying sedimentary layers the magma emplacement was dated to the middle miocene ca 14 6 ma most of the hydrothermal vents are distributed along the f2 fault zone and have direct linkage with the underlying sills while the large sill complexes that are connected with limited vents are mainly present above the hyperextended continental crust where the crust thins to 6 10 km the sills intruded into different layers from the lower oligocene to the lower miocene and the emplaced depth of sills is 1 2 6 3 km whether or not they feed any vents above unlike most of the large volume and laterally linked sills found in the magma rich rifted margins the scattered distribution of sills at different levels indicates that dykes probably play an important role in magma transport which might coexist with numerous polygonal or small faults and interference reflections this work highlights the critical role of basin structures in controlling the distribution of post rift igneous complexes in magma poor margins including thinned continental crust sedimentary thickness and faults

lithological controls on igneous intrusion induced ground deformation ground deformation commonly precedes volcanic eruptions although its relationship to underlying intrusion networks is complex we use 3d seismic reflection data to examine the link between a saucer shaped sill and an overlying forced fold formed at the contemporaneous palaeosurface our results highlight a disparity in size between the sill and fold which we attribute to accommodation of magma by overburden uplift and fluid expulsion from the host rock sill transgression occurred in response to plastic deformation of the host rock and did not produce seismically resolvable uplift inversion models of ground deformation should therefore acknowledge host rock behaviour during intrusion supplementary material uninterpreted seismic section and sill thickness fold amplitude data are available at www geolsoc org uk sup18663

the plio quaternary volcanic evolution of gran canaria based on new k ar ages and magnetostratigraphy the combined use of radiometric dating 51 new unspiked k ar ages magnetostratigraphy and field geology establishes a new time framework for the last two stages of the volcanic evolution of gran canaria most of the dated samples have ages coherent with their stratigraphic positions and magnetic polarities our new set of data extends the end of the roque nublo rn group one of the main posterosive stages of gran canaria which started about 4 9 ma ago to ages as young as 2 87 ma this is about 0 7 ma younger than previously thought moreover the dating of samples collected in well defined stratigraphic sequences supports the contemporaneity of the early stages of the post roque nublo group and the vanishing activity of the roque nublo stratovolcano between 3 7 and 2 9 ma the multiple lateral collapses of the roque nublo stratovolcano occurred during this period between 3 5 and 3 1 ma which corresponds to a main period of volcanic quiescence after 2 9 ma the effusive activity propagated along a well defined nw se rift until about 1 5 ma shifting progressively from a rifting propagation to platform forming lavas thereafter the activity is very disperse and belongs to the brunhes period with most of it before 500 ka

the holocene volcanic history of gran canaria island implications for volcanic hazards previous published data combined with our results of 13 new radiocarbon ages and extensive geological fieldwork indicate that during the past 11 ka 24 monogenetic basaltic eruptions occurred in the north sector of gran canaria these eruptions can be grouped into three periods of eruptive activity 1900 3200 14c a bp 5700 6000 14c a bp and an older period represented by only one eruption el draguillo dated at 10 610 190 14c a bp archaeological studies have shown that the more recent eruptions affected prehistoric human settlements on the island field studies demonstrate that the eruptions typically built strombolian cones 30 250 m in height and associated relatively long lava flows 100 10 350 m in length a few eruptions also produced tephra fall deposits the total erupted volume of these eruptions is about 0 388 km3 46 1 as tephra fall 41 8 as cinder cone deposits and 12 1 as lava flows the relatively low eruption rate 0 04 km3 ka 1 during the past 11 ka is consistent with gran canaria s stage of evolution in the regional volcano tectonic setting of the canary archipelago the results of our study were used to construct a volcanic hazards map that clearly delimits two sectors in the ne sector of gran canaria where potential future eruptions would pose a substantial risk for densely populated areas copyright 2009 john wiley sons ltd

submarine hydrothermal vent complexes in the paleocene of the faroe shetland basin insights from three dimensional seismic and petrographical data this work presents a new method of coarse grained sediment input into a deep sedimentary basin and presents a new example of igneous processes controlling sedimentary facies the mesozoic cenozoic faroe shetland basin sediments are intruded by late paleocene igneous sills and dikes sill intrusions are frequently expressed on the paleosurface as hydrothermal mounds and vents occurring directly above sill tips three dimensional seismic data are used to image a paleocene submarine mounded structure that has been penetrated by an exploration well drilled in a d 1984 seismic morphology is combined with petrographic data to show that the mound was erupted from a central vent as a series of sediment pulses consisting of sediments disaggregated and recycled from depth a submarine sediment volcano

geometry and controls on the development of igneous sill related forced folds a 2 d seismic reflection case study from offshore southern australia emplacement of magma in the shallow subsurface can result in the development of dome shaped folds at the earth s sur face these so called forced folds have been described in the fi eld and in subsur face data sets although the exact geometry of the folds and the nature of their relation ship to under lying sills remain unclear and in some cases controversial in this study we use high quality two dimensional 2 d seismic refl ection and borehole data from the ceduna sub basin offshore southern australia to describe the structure and infer the evolution of igneous sill related forced folds in the bight basin igneous complex thirty three igneous sills which were em placed 200 1500 m below the paleo seabed in upper cretaceous rocks are mapped in the ceduna sub basin the intrusions are expressed as packages of high amplitude refl ections which are 32 250 m thick and 7 19 km in diameter we observe fi ve main types of intrusion type 1 strata concordant sills type 2 weakly strata discordant trans gressive sills type 3 saucer shaped sills type 4 laccoliths and type 5 hybrid intru sions which have geometric characteristics of intrusion types 1 3 these intrusions are overlain by dome shaped folds which are up to 17 km wide and display up to 210 m of re lief the edges of these folds coincide with the margins of the underlying sills and the folds display the greatest relief where the underly ing sills are thickest the folds are therefore interpreted as forced folds that formed in response to emplacement of magma in the shallow subsurface the folds are onlapped by lutetian middle eocene strata indicat ing they formed and the intrusions were em placed during the latest ypresian ca 48 ma we demonstrate that fold amplitude is typi cally less than sill thickness even for sills with very large diameter to depth ratios suggest ing that pure elastic bending forced folding of the overburden is not the only process ac commodating magma emplacement and that supra sill compaction may be important even at relatively shallow depths based on the ob servation that the sills intruded a shallowly buried succession the discrepancy between fold amplitude and sill thickness may refl ect loss of host rock volume by fland pore fl uid expulsion from poorly lithifi ed water rich beds this study indicates that host rock composition emplacement depth and deformation mechanisms are important controls on the style of deformation that oc curs during intrusive igneous activity and that forced fold amplitude may not in all cases refl ect the thickness of an underlying igneous intrusion in addition the results of this study suggest that physical and numeri cal models need to model more complex host rock stratigraphies and rheologies if they are to capture the full range of deformation mechanisms that occur during magma em placement in the earth s shallow subsurface

the warnie volcanic province jurassic intraplate volcanism in central australia abstract the cooper and eromanga basins of south australia and queensland are the largest onshore hydrocarbon producing region in australia igneous rocks have been documented infrequently within end of well reports over the past 34 years with a late triassic to jurassic age determined from well data however the areal extent and nature of these basaltic rocks were largely unclear here we integrate seismic well gravity and magnetic data to clarify the extent and character of igneous rocks preserved within eromanga basin stratigraphy overlying the nappamerri trough of the cooper basin we recognise mafic monogenetic volcanoes that extend into tabular basalt lava flows igneous intrusions and more locally hydrothermally altered compound lava flows the volcanic province covers 7500 km2 and is proposed to have been active between 180 160 ma we term this jurassic volcanic province the warnie volcanic province wvp after the warnie east 1 exploration well drilled in 1985 the distribution of extrusive and intrusive igneous rocks is primarily controlled by basement structure with extrusive and intrusive igneous rocks elongate in a nw se direction finally we detail how the wvp fits into the record of jurassic volcanism in eastern australia the wvp is interpreted as a product of extension and intraplate convective upwelling above the subducting pacific slab the discovery of the wvp raises the possibility of other yet unidentified volcanic provinces worldwide

syndepositional forced folding and related fluid plumbing above a magmatic laccolith insights from outcrop lower cretaceous basque cantabrian basin western pyrenees emplacement of shallow magmatic laccoliths can result in the development of dome shaped forced folds and fractures in the overburden and at the depositional surface these folds and fractures have been described from both outcrop studies and seismic interpretation however the main controls on fold growth and fracture development remain unclear and in some cases controversial this paper presents a new approach in the analysis of the growth of laccolith intrusions and forced folds in this study deep water growth deposits at an outcrop in the basque cantabrian basin north iberia record the coeval formation and evolution of a late albian forced fold and related clastic dike system above the igneous larragan laccolith the vertical succession allows field mapping and characterization of the growth deposits the underlying forced fold and the forcible larragan laccolith at depth the larragan laccolith is 600 m wide and 40 m thick and intrudes an organic rich unit at an original decompacted depth of 450 m a multidisciplinary study sedimentology structure petrology and geochemistry of the growth deposits reveals that the emplacement of the laccolith created a dome shaped upward widening fold which had a final relief of 18 36 m and a width of 850 m at the paleoseabed simultaneously in the hinge zone of the fold local tensional stress induced the formation of a fracture system which subsequently acted as conduits for overpressured ascending fluids methane and water and fluidized sediments originating from the metamorphic aureole of the laccolith this plumbing system reached the paleoseabed where extruded sediments were deposited and methane derived carbonates precipitated a comprehensive model is proposed in which incremental emplacement of magma sheets induced pulsating contact metamorphism folding and fracturing of the overburden and episodic activity of the fluid plumbing system

geometric characterization of igneous intrusions 3 d seismic insights from the campos basin se brazil abstract igneous intrusions are important for the exploration and appraisal phases of an oilfield due to their impact on petroleum systems their presence can be associated with the generation migration accumulation and entrapment of hydrocarbons in particular 1 sills with low permeability might form barriers to fluid flow and migration 2 sills may re use fracture networks providing insights on fluid migration and interaction s 3 sills may influence source rock maturation 4 sill induced uplifting of overburden and faulting may generate traps and 5 their geometric complexities enables the understanding of the interconnectedness of sill complexes which is the focus of this study therefore we provide a systematic characterization of sill geometries and their morphometric parameters we used three dimensional seismic data calibrated with well logs to interpret sills in the southern campos basin brazil throughout the late cretaceous until the paleogene sills intruded into the cretaceous to the eocene post salt sedimentary sequence including shallow platform carbonates transgressive marls and shales a morphometric analysis assisted by seismic attributes allowed the geometric characterization of sills namely 1 saucer shaped 2 slightly saucer shaped 3 climbing saucer shaped 4 transgressive and 5 rough layer parallel the documented sills comprise a wide range of sizes 0 43 14 35 km2 that increase with depth up to 3 18 km extend vertically from 0 06 to 0 23 km and vary from low 1 82 3 31 to high dip 6 05 15 74 the sill complex area extends over 67 35 km2 this study suggests that a thorough characterization of sill intrusions may have a substantial influence on the prediction of other igneous occurrences the mapped sills might have implications not just on the acoustically similar shallow platform albian carbonates of the macae group but may also provide insightful geometric constraints on the brazilian pre salt igneous intrusions

structural style of buried ediacaran basins in saudi arabia on seismic reflection data abstract several isolated ediacaran basins subcrop phanerozoic strata in saudi arabia the structural styles of these subcropping basins are reviewed here based on interpretation of 2d and 3d seismic reflection data and comparison with arabian shield outcrops the basins are distinguished by layered seismic reflectors that are interpreted as sedimentary and volcanic strata due to limited well penetrations these packages cannot be directly dated but a relative chronology is established anchored by constraints from the arabian shield and regional studies most of the basins are bound by extensional faults and the basin fills show growth architectures and angular unconformities the bounding faults trend broadly north south and are interpreted to be late to post orogenic reactivations of oceanic terrane margins based on their structural characteristics in comparison with sub basins exposed on the shield the basin fills are correlated with the ediacaran jibalah group an equivalent of the omani nafun group these sub basins experienced inversion and exhumation prior to ongoing volcanism and unconformable deposition of late ediacaran to earliest cambrian kurayshah group sediments the kurayshah group is disconformably overlain by the widespread tayma group siliciclastics this disconformity correlates to the angudan unconformity in oman the kurayshah group includes a late ediacaran stratovolcano over 40 km in diameter in the eastern basins evaporitic structural styles indicate the presence of hormuz ara evaporites with local igneous intrusions that correlate at least in part to the kurayshah group the tayma group infills significant accommodation space variations and was affected by ongoing but declining differential subsidence and reactivation of the underlying basin bounding faults

cenozoic sill intrusion in the central and southern east china sea shelf basin abstract cenozoic igneous rocks dominated by basalts are exposed sporadically onshore east china and they provide important information about the cenozoic evolution of the region importantly their geometries and distribution are still not well constrained in the 200 600 km wide offshore continental shelf region based on seismic profiles this study presents the geometric characteristics of 133 igneous sills that are widely distributed in the central and southern regions of the east china sea shelf basin ecssb sills in high amplitude continuous seismic reflections mostly occur in a time interval of 1 1 3 3 s in multiple seismic profiles corresponding to a depth range of 1 1 4 8 km they can be classified into five types saucer shaped sills strata concordant sills laccoliths inclined sheets and hybrid sills of these the saucer shaped sills predominate strata deformation associated with these igneous sills indicate that sill intrusion has become intense since the miocene and it potentially affected petroleum systems in the ecssb forced folds induced by the sills are prospective petroleum traps we infer that sill intrusion in the ecssb was due to magma upwelling caused by dehydration and or small scale convection in a large mantle wedge above the stagnant pacific slab the subduction of the philippine sea plate resulted in tectonic inversion in the ecssb and extension in the okinawa trough since the early miocene triggered more magmatism in the tectonically thinned ecssb thick sedimentary strata over a thin crust in the ecssb may have induced more intrusive than extrusive cenozoic magmatism

a critical analysis of the structure and tectonic significance of rift oblique lineaments transfer zones in the mesozoic cenozoic succession of the faroe shetland basin ne atlantic margin abstract nw se trending rift oblique lineaments transfer zones9 occur along the length of the ne atlantic margin previous workers have suggested that these lineaments played an important role in providing conduits and or barriers to sedimentation during the cretaceous and palaeocene it has also been suggested that they were active as discrete basin wide strike slip faults this study uses a well calibrated 3d seismic survey of regional extent to critically assess the structural and stratigraphic evidence for three rift oblique lineaments in the uk sector of the faroe shetland basin victory clair and judd lineaments structures previously attributed to basin wide strike slip deformation can be more simply explained as igneous intrusions hydrothermal vent complexes gas chimneys and or faults that transfer extensional strain between en echelon rift segments there is little evidence to suggest that activity along discrete basin wide lineaments controlled palaeocene sedimentation within the faroe shetland basin rather sediment transport and deposition at this time are likely to have been controlled by along and across strike variations in the magnitude of thermal subsidence which in turn reflect the 3d nature of the underlying mesozoic rift architecture

a large volcanic debris avalanche in the pliocene roque nublo stratovolcano gran canaria canary islands abstract during the second magmatic cycle of gran canaria between 5 and 3 ma the roque nublo stratovolcano rns achieved its almost total development reaching a height of 2500 2600 m and spreading about 100 km 3 of products over a surface area of at least 250 km 2 in the last growth stage of the rns and probably in connection with the paroxysmic genesis of the roque nublo explosive caldera a sector of the volcanic edifice suffered a gravitational collapse of significant importance the data reported here show that the collapse was accompanied by a great avalanche the roque nublo debris avalanche deposit rndad composed mainly of block facies the last explosive emissions of the rns were restricted to ignimbrites and some explosive breccias that locally overlap the avalanche deposits the features of the outcrops along the course of the avalanche make it possible to distinguish between the proximal intermediate and distal deposits the debris avalanche 3 4 km 3 moved sw then s and finally sse part of the deposit mainly formed by large megablocks remained very near the source area halfway along the course the avalanche was channelled by broad and steep paleovalleys in the most distal areas the rndad opens into a fan shape reaching a distance of 28 30 km a simplified kinematical physical model is used to understand the movement of the rndad the model is based on the speculative reconstruction of the rns edifice based in turn on its scarce peripheral remains an arbitrary avalanche path was selected with a total travel distance from the source area top of the stratovolcano of 28 km with these assumptions it is possible to calculate the speed at each point v m 90 m s and other parameters that show that the rndad is very similar to other well known volcanic avalanches

geochronology and stratigraphy of the roque nublo cycle gran canaria canary islands the roque nublo cycle of pliocene age is the second main cycle of subaerial volcanic activity in gran canaria during this cycle a stratovolcano at least 2500 m high developed in the central part of the island its volcanic products covered an area of about 540 km 2 the detailed stratigraphy of the roque nublo cycle together with a magnetostratigraphic study and six new k ar dates which complement 22 previously published ones have led to the reconstruction of the volcanic history of this cycle in which six main stages have been distinguished the revised chronology of the roque nublo cycle implies an overlap in age with the earliest rocks of the third cycle of subaerial activity in gran canaria no volcanic hiatus occurred between the second and third cycles as was previously thought to be the case

discovery of lower cretaceous hydrothermal vent complexes in a late rifting setting southern north sea insights from 3d imaging we present data for 31 kilometre scale hydrothermal vent complexes and associated sand remobilization that have formed as a consequence of magmatic intrusions within salt strata southern north sea dutch sector this study uses 3d seismic data tied to three wells and artificial neural networks to describe conical and cylindrical vent structures located in the ne part of the broad fourteens basin the structures are composites of 58 subvertical pipes that form complexes and are 951 364 m in height and 487 426 m in diameter interactions of magma and fluids at depth triggered successive fluid pressure build ups in triassic sandstones resulting in upward propagated ruptures followed by the collapse of overlying deposits and the injection and extrusion of fluidized sand the relationship between vent tops and their overlying deposits indicates a mid hauterivian age unusual for volcanic activity in the north sea area this event could have a significant impact on hydrocarbon exploration as the hydrothermal vent complexes bypass a regional source rock and seal offering new migration routes and connectivity between potential reservoirs the intrusions also raise questions about the influence of transform tectonics on the focusing of volcanic activity during the late rifting phase of the north sea supplementary material tables of seismic attributes and the geometry of the vent complexes as well as a 3d visualisation of the vents are available at https doi org 10 6084 m9 figshare c 3571593

anomalous lower crustal structure and origin of magmatism in the southeastern margin of the south china sea abstract late cenozoic continental rifting and breakup separated the southern margin of the south china sea scs from the northern margin it remains unknown whether the high density velocity zones hvzs in the lower crust extend southwards from the northeastern margin of the scs to the conjugate southern margin we integrated two newly acquired and processed multichannel seismic reflection profiles with gravity and magnetic data across the liyue reed bank and north palawan basin to clarify the characteristics of crustal structure and their relationship to post rift magmatism our results show an asymmetric distribution of the hvzs in the conjugate margins the lower crust anomalous reflections are isolated and mostly restricted in the areas of the ocean continent transition oct and the distal sag in gravity modeling the crustal thickness decreases from 20 km in the proximal sag to a minimum of 6 km in the distal sag and these anomalous reflections spatially correspond to high density zones no more than 4 km in thickness the magmatic features are presented by igneous intrusions at the top of the basement that deform post rift strata in the early miocene these hvzs above which the crustal stretching factor is 3 3 5 8 support that an anomalously hot asthenospheric mantle persisted during lithospheric thinning resulting in magmatic underplating and density drop in the uppermost mantle during early breakup

distribution 14c chronology and paleomagnetism of latest pleistocene and holocene lava flows at haleakalā volcano island of maui hawai i a revision of lava flow hazard zones 1 new mapping and 60 new radiocarbon ages define the age and distribution of latest pleistocene and holocene past 13 000 years lava flows at haleakal volcano island of maui paleomagnetic directions were determined for 118 sites of which 89 are in lava flows younger than 13 000 years the paleomagnetic data in conjunction with a reference paleosecular variation psv curve for the hawaiian islands are combined with our knowledge of age limitations based on stratigraphic control to refine age estimates for some of the undated lava flows the resulting volumetric rate calculations indicate that within analytical error the extrusion rate has remained nearly constant during the past 13 000 years in the range 0 05 0 15 km3 kyr only about half the long term rate required to produce the postshield strata emplaced in the past 1 myr haleakal s eruptive frequency is similar to that of hual lai volcano on the island of hawai i but its lava flows cover substantially less area per unit time the reduced rates of lava coverage indicate a lower volcanic hazard than in similar zones at hual lai

seismic characteristics of basaltic extrusive and intrusive rocks transient voluminous basaltic volcanism is frequently associated with continental breakup forming so called volcanic rifted continental margins until recently most rifted margins were considered nonvolcanic however the improvement in seismic imaging techniques has shown that breakup volcanism is a common phenomenon at the november 1997 volcanic margin workshop in potsdam it was shown that at least 70 of the atlantic margins are volcanic a number which may apply to the indian ocean margins as well

submarine volcanic mounds in the pearl river mouth basin northern south china sea a number of enigmatic km scale mound structures have been discovered in the baiyun sag of the pearl river mouth basin using high resolution 2d and 3d seismic data combined with multi beam bathymetry based on detailed seismic characterization we interpret these as sill fed volcanic mounds associated structures include igneous sills trans tensional faults lava flows and compactional drape folds the igneous intrusions and associated mounds were emplaced in the late early miocene c 18 5 ma or shortly thereafter constrained by the onlap relationship between the mounds and their overburden the volcanic mounds are preferentially developed above or adjacent to basement highs indicating a structural control on the igneous plumbing system we propose that the fractures and tectonic faults above the raised basement follow pre existing zones of weakness and may have acted as feeding conduits for the magmatic material the discovery of the early miocene igneous province has important implications for the understanding of the evolution of the pearl river mouth basin and for regional hydrocarbon prospectivity c 2014 elsevier b v all rights reserved

carbon release by off axis magmatism in a young sedimented spreading centre continental rifting creates narrow ocean basins where coastal ocean upwelling and enhanced silicate weathering remove carbon dioxide from the atmosphere evidence from seismic data sonar backscatter and seafloor images and geochemical water analyses suggest that in young sedimented rifts active magmatism occurs in a broader region than appreciated and releases carbon from the sediments

reply to comment by k thomson on the three dimensional geometry and growth of forced folds above saucer shaped sills by d m hansen and j cartwright

absolute paleointensity from hawaiian lavas younger than 35 ka abstract paleointensity studies have been conducted in air and in argon atmosphere on nine lava flows with radiocarbon ages distributed between 3 3 and 28 2 ka from the mauna loa volcano in the big island of hawaii determinations of paleointensity obtained at eight sites depict the same overall pattern as the previous results for the same period in hawaii although the overall average field intensity appears to be lower since the present results were determined at higher temperatures than in the previous studies this discrepancy raises questions regarding the selection of low versus high temperature segments that are usually made for absolute paleointensity the virtual dipole moments are similar to those displayed by the worldwide data set obtained from dated lava flows when averaged within finite time intervals the worldwide values match nicely the variations of the sint 200 synthetic record of relative paleointensity and confirm the overall decrease of the dipole field intensity during most of this period the convergence between the existing records at hawaii and the rest of the world does not favour the presence of persistent strong non dipole components beneath hawaii for this period

new technique for dating igneous sills three dimensional seismic interpretation of tertiary sills within the northeast atlantic margin demonstrates that shallow level 20 km long the fill of the minibasin is dated biostratigraphically as 54 6 55 ma which fits well with radiometric dates for the timing of intrusion of sills around this basin ca 53 55 ma the recognition and dating of onlap fill seismic reflector packages that are delimited by forced folds form a new and useful method for dating shallow level igneous intrusions in sedimentary basins a method that provides independent constraints on radiometric dating techniques similar forced folds are recognized from other basins that have shallow level sills suggesting that the technique presented here may be similarly applicable in comparable geologic settings

influence of crystallised igneous intrusions on fault nucleation and reactivation during continental extension abstract continental rifting is commonly accommodated by the nucleation of normal faults slip on pre existing fault surfaces and or magmatic intrusion because crystallised igneous intrusions are pervasive in many rift basins and are commonly more competent i e higher shear strengths and young s moduli than the host rock it is theoretically plausible that they locally intersect and modify the mechanical properties of pre existing normal faults we illustrate the influence that crystallised igneous intrusions may have on fault reactivation using a conceptual model and observations from field and subsurface datasets our results show that igneous rocks may initially resist failure and promote the preferential reactivation of favourably oriented pre existing faults that are not spatially associated with solidified intrusions fault segments situated along strike from laterally restricted fault intrusion intersections may similarly be reactivated this spatial and temporal control on strain distribution may generate 1 supra intrusion folds in the hanging wall 2 new dip slip faults adjacent to the igneous body or 3 sub vertical oblique slip faults oriented parallel to the extension direction importantly stress accumulation within igneous intrusions may eventually initiate failure and further localise strain the results of our study have important implications for the structural of sedimentary basins and the subsurface migration of hydrocarbons and mineral bearing fluids

crustal structure of northern gran canaria canary islands deduced from active seismic tomography seismic p wave travel times collected during meteor cruise m24 are inverted to derive a three dimensional model of the p wave velocity structure of the northern part of gran canaria canary islands the data consist of 6689 p wave travel times from 1487 offshore air gun shots which were recorded by both land based seismometers and ocean bottom hydrophones the crustal structure is well imaged by the data set as demonstrated by analysis of the resolution and tests with synthetic data the volcanic island is characterized by generally high p wave velocities 5 5 km s and a heterogeneous structure with large lateral velocity variations high p wave velocities are found around the centers of the miocene shield volcanoes in the vicinity of aguimes san nicolas and agaete as well as the center of the pliocene roque nublo volcano the velocity structure suggests a high percentage of dense intrusive rocks some of the intrusive rocks were emplaced during the eruption of 1000 km3 of miocene felsic magmas following the basaltic shield phase the velocity structure beneath la isleta peninsula and its submarine continuation is interpreted as a volcanic rift zone with abundant dikes the velocities decrease to 5 km s north of the coastline a high velocity zone thinning away from the central edifice is interpreted as the massive island flank extending up to 50 km off the coast which is underlain by prevolcanic neogene jurassic sediments the igneous part of the oceanic crust exhibits an anomalous structure with a relatively small thickness 3 km layer 3 and a 2 4 km thick layer 2 probably reflecting a modification of the crust due to long lasting magmatic intrusive activity during the evolution of the canary islands the moho north of gran canaria is found at a depth of 15 km the structure of gran canaria and the adjacent ocean basin is thought to be the result of a diffuse mantle upwelling under a slowly moving plate

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

regional uplift gas hydrate dissociation and the origins of the paleocene eocene thermal maximum much of the north atlantic region experienced hundreds of metres of transient uplift during the latest paleocene regional uplift should cause dissociation of gas hydrates stored in marine sedimentary strata and the subsequent release of carbon to the atmosphere should enhance warming through the greenhouse effect we have developed models of the spatial distribution of uplift to match observational constraints from sedimentary basins fringing the north atlantic in order to provide quantitative estimates of the carbon released upon uplift these models are coupled to a simple parameterisation of carbon storage in sub seafloor gas hydrates results of modelling indicate that large quantities of carbon can be released by uplift with some models generating over 2000 gt of carbon release the possibility that latest paleocene regional uplift occurred over the same time interval as onset of the paleocene eocene thermal maximum petm around 30 kyr cannot be ruled out using current stratigraphical observations or mantle convection models in this case the uplift mechanism alone can account for the magnitude and timing of the carbon isotope excursion associated with the petm alternatively if the duration of latest paleocene uplift was closer to the upper bound of around 1 myr or if other paleocene uplift events were equally significant then gas hydrate dissociation upon uplift could have contributed to longer term changes in ocean temperature and carbon isotope composition through the late paleocene these temperature changes in combination with development of the north atlantic land bridge during the latest paleocene culmination of uplift may be able to force rapid changes in ocean circulation and cause phenomena such as the petm

evolution of shelf margin clinoforms and deep water fans during the middle eocene in the sorvestsnaget basin southwest barents sea interpretation of seismic data from the sorvestsnaget basin southwest barents sea demonstrates gradual middle eocene basin infilling from the north generated by southward prograding shelf margin clinoforms the basin experienced continued accommodation development during the middle eocene because of differential subsidence caused by the onset of early eocene sea floor spreading in the norwegian greenland sea faulting salt movement and different tectonic activity between the sorvestsnaget basin and veslemoy high during this time the margin shows transformation from an initially high relief margin to a progradation in the final stage the early stage of progradation is characterized by the establishment of generally oblique clinoform shifts creating a flat shelf edge trajectory that implies a gentle falling or stable relative sea level and low accommodation to sediment supply ratio 1 in the topsets during the early stage of basin development the high relief margin narrow shelf stable or falling relative sea level seismicity and presumably high sedimentation rate caused accumulation of thick and areally extensive deep water fans seismic scale sandstone injections deform the fans a fully prograding margin developed when the shelf to basin profile lowered apparently because of increased subsidence of the northern part this stage of the basin development is generally characterized by the presence of sigmoid clinoform shifts creating an ascending shelf edge trajectory that is implying steady or rising relative sea level with an accommodation to sediment supply ratio of greater than 1 implying sand accumulation on the shelf this study suggests that some volume of sand was transported into the deep water during relative sea level rise considering the narrow shelf and inferred high rates of sediment supply

magma and sediment i emplacement mechanism of late carboniferous tholeiite sills in northern britain president s anniversary address 1981 like other great tholeiite sheets of the world the midland valley sill and whin sill were emplaced in thick accumulations of sediments which at the time of intrusion were not much older nor had been orogenically deformed however the carboniferous sediments of northern britain had been deposited under the influence of continuous differential subsidence so that they were already disposed in syn sedimentary basins and swells when intrusion began by drawing palinspastic contours of the sills relative to a late westphalian marine band approximating to the surface at the time of emplacement it is established that the dolerites mainly follow bedding planes dipping at angles of as much as 5 down to the bottoms of the basins isopachs of the sills indicate a further relationship for the intrusions are thickest at the bottoms of the basins these facts are not explained by any intrusion mechanism previously postulated though there seems to be broad agreement as to the processes which have given rise to thinning and en echelon lensing at leading edges as well as to step and stair transgression of sediment bedding it is proposed that emplacement must have been controlled in part by gravitational flow down dip from feeder dykes which extended to between 0 5 and 1 0 km below the contemporary surface thereafter hydrostatic equilibrium was attained first by accumulation at the bottom of the basins and then by further advance up dip under pressure of head the sheets are so similar in aspect to flood basalts that it must be assumed that the sediments offered only low frictional resistance to splitting and flow

conspicuous seismic reflections in upper cretaceous sediments as evidence for black shales off south africa abstract the upper cretaceous is commonly associated with greenhouse climate oceanic anoxic events oae and the ongoing break up of gondwana which resulted in strong variations of the ocean s currents flow paths and climate change little is known about these changing conditions in particular south of south africa a high resolution seismic reflection data set from the submarine transkei basin off south africa revealed various depositional stages for this region for the past 90 ma in these seismic sections a recurrently appearing high amplitude horizon within weak to homogeneous upper cretaceous reflections was observed due to the inaccessibility of any drill hole data from the transkei basin and adjacent regions the origin of this reflector is difficult to specify it is roughly dated at 80 85 ma which falls within the last big oae in upper cretaceous oae 3 a seismostratigraphic analysis led to an exclusion of several features as the origin for this reflector such as gas hydrates opal bearing horizons or biogenic oil other possible features such as lithologic variations intrusions or black shales are discussed in more detail according to its appearance and reflection characteristics it could possibly be the first report of black shales in this region

fluvial dissection isostatic uplift and geomorphological evolution of volcanic islands gran canaria canary islands spain abstract digital analysis of torrential gullies barrancos deeply incised into the volcanic island of gran canaria canary islands allows us to extract the longitudinal profiles and pre incision surfaces for individual basins from which morphometric parameters length elevation area slope have been calculated other derived parameters such as ridgeline profiles maximum incision values volume removed by fluvial erosion geophysical relief and isostatic uplift have also been computed based on k ar ages for the island well constrained incision uplift rates have been calculated by means of the combination of different methodological approaches commonly used in orogens and large mountain ranges the geomorphological and morphometric analyses reveal that the island is clearly divided into four environmental quadrants determined by the combination of a couple of key factors the age of the volcanic surfaces and the climatic conditions these factors determine a young sector covered with plio quaternary platform forming lavas finished at 1 9 1 5 ma evolving under contrasting wet ne to dry se climates and an older sector conserving the residual surfaces of the miocene shield building 14 5 8 7 ma at the ridgelines also subjected to wet nw and dry sw climates incision is related to the age zonation of the island maximum incisions

effects of canary hotspot volcanism on structure of oceanic crust off morocco analysis of over 6400 km of multichannel seismics mcs and 50 sonobuoy reflection and refraction experiments reduced both in the domain of x t and tau p shows that a region within the jurassic quiet zone off morocco underwent dramatic changes as a result of the passage of the lithosphere over the canary hotspot commencing approximately 60 ma a seismic unit ucf interpreted as volcanic in origin is observed within the sediments in a region characterized by a broad bathymetric swell it shows diffractions from its upper surface and an internally chaotic seismic facies and pinches out between sedimentary units of continuous subparallel facies a velocity inversion is noted between the ucf 4 7km s and the underlying sediment 3 1 km s the ucf is time transgressive it lies near the cretaceous s tertiary boundary in the northern portion of the study area and is younger to the south kinematic studies of the movement of the canary hotspot relative to africa show that the hotspot first appeared off nw africa about 60 ma and was located beneath oceanic crust in the region where the ucf is observed depth to basement measurements in areas not effected by the hotspot show a consistent linear trend of increased depth with age in areas effected by the hotspot the thermal rejuvenation is evident as basement depths shoal with increased proximity to the present hotspot the reheating of the crust resets the thermal age of the lithosphere with many of the properties of crust of a younger age subsidence curves of the reheated crust off morocco show good correlation to subsidence curves of other reheated crust on a global basis a zone characterized by high crustal velocities 7 1 7 4 km s and greater crustal thicknesses by 1 2 km is observed in an area that corresponds to the bathymetric swell the region of the ucf and the reelevated basement the high velocities and increased crustal thickness are interpreted to be the result of underplating and assimilation of existing oceanic crust caused by the canary thermal anomaly the presence of high crustal velocities coupled with a thickened crustal section has been noted on various passive margins of the world they have generally been attributed to the thermal processes associated with continental rifting off morocco we believe that similar thermally induced phenomena have occurred but that here the heat anomaly was the midplate volcanism associated with the canary hotspot

the morphology of intrusion related vent structures and their implications for constraining the timing of intrusive events along the ne atlantic margin intrusion related vent structures found within palaeocene sediments and near the palaeocene eocene transition in basins along the ne atlantic margin have been studied in detail using 3d seismic data the vents formed at the palaeo seabed as a result of sill intrusion and the vent fill ranges in composition from entirely remobilized sedimentary to dominantly magmatic the vents are commonly developed above sill edges and crests in sills to which they are linked by pipe and diatreme like structures the vents also develop above the upper tips of deep seated faults and at fault intersections the vents can be used to constrain the approximate timing of igneous sill intrusion and duration of hydrothermal activity it is estimated that using the seismically constrained stratigraphic context of these vents to establish the timing of sill emplacement is associated with an uncertainty of 100 ka and up to as much as 800 ka interpretation of the vents indicates that sill intrusion took place during a number of discrete phases within the palaeocene and earliest eocene these structures and their timing of formation have important implications for climate change studies basin scale processes including fluid flow and diagenesis as well as hydrocarbon exploration

flow dynamics in mid jurassic dikes and sills of the ferrar large igneous province and implications for long distance magma transport abstract magma flow paths in sill fed dikes of the ferrar large igneous province lip contrast with those predicted by classic models of dike transport in lips and magmatic rift settings we examine anisotropy of magnetic susceptibility ams flow paths in dike networks at terra cotta mountain and mt gran which intruded at paleodepths of 2 5 and 1 5 km these intrusions up to 30 m thick exhibit irregular interconnected dike sill geometries and adjoin larger sills 200 300 m thick at different stratigraphic levels both shallowly dipping and sub vertical magma flow components are interpreted from ams measurements across individual intrusions and often match macroscopic flow indicators and variations in dike attitudes flow paths suggest that intrusive patterns and magma flow directions depended on varying stress concentrations and rotations during dike and sill propagation whereas a regional extensional tectonic control was negligible or absent unlike giant dike swarms in lips elsewhere e g 1270 ma mackenzie lip dikes of the ferrar lip show no regionally consistent vertical or lateral flow patterns suggesting these intrusion were not responsible for long distance transport in the province in the absence of regionally significant colinear dike swarms or observed intrusions at crustal depths 4 km we suggest that long distance magma transport occurred in sills within beacon supergroup sedimentary rocks this interpretation is consistent with existing geochemical data and thermal constraints which support lateral magma flow for 3 500 km across the gondwana supercontinent before freezing

synrift magmatism in a cenozoic rift basin from 3d seismic data wichianburi sub basin phetchabun basin thailand part 1 distribution and timing of intrusions and forced folds the late oligocene pliocene wichianburi sub basin phetchabun rift thailand has undergone three phases of development late oligocene early miocene c 16 ma east west extension on predominantly nnw sse to north south striking faults 16 ma c 3 ma ne extension on nnw sse north south and ne sw trending faults and 3 ma to present post rift subsidence the basin was also affected by intrusive and extrusive igneous activity from 24 to 2 ma the relationships among the structure rift basin stratigraphy and sheet intrusions are unusually well documented as a result of extensive hydrocarbon exploration drilling and 3d seismic data together with the production of hydrocarbons from igneous sills the oldest igneous activity c 24 13 ma lies sw of the wichianburi sub basin where extrusive rocks exposed at the surface have been dated by k ar and 40ar 39ar methods the overall igneous activity youngs from the south of the basin to the north 11 9 ma numerous domal folds occur across the basin the sill and laccolith dimensions the rate of fold development the variable timing of fold formation and the fold geometry all indicate that the folds are related to magma emplacement not tectonic inversion fold formation occurred at c 16 15 and 12 11 ma in single or multiple stages the timing of folding coupled with the radiometric dating of some sills k ar 39ar 40ar indicates that the greatest amount of intrusive activity occurred between 16 and 11 ma the 16 ma date coincides with the switch from east west to nw se extension which promoted dilatancy within the upper crust along a range of synrift fault orientations and some pre rift trends the burial history of the main depocentre shows that miocene sill emplacement occurred at depths

igneous activity in the bornu basin onshore ne nigeria implications for opening of the south atlantic the structure of igneous plumbing systems in circum south atlantic intra continental rift basins e g the west and central african rift systems remains enigmatic owing to poor subsurface data coverage and quality how magmatism in these basins related to the opening of the south atlantic is thus poorly understood we integrate 2d and 3d seismic reflection data c 27 600 km 2 data from 23 boreholes and field observations from the bornu basin and upper benue trough onshore ne nigeria to examine the timing and development of igneous bodies possibly related to opening of the south atlantic we identify numerous sills which typically have saucer shaped and en echelon morphologies and extrusive volcanic cones the igneous rocks are alkali basalts and dolerites seismic stratigraphic relationships indicate that emplacement occurred in the early cretaceous albian to cenomanian c 120 ma late cretaceous santonian to early campanian c 83 ma and cenozoic miocene c 22 ma magmatism was broadly coeval with major plate boundary interactions characterized by major azimuthal changes in fracture zones in the developing south atlantic ocean the broad temporal correlation between intra continental rift basin magmatism and plate boundary interactions suggests that periods of magma emplacement may have in some way been instigated by stress dissipation into intra continental rift basins

geomorphological reconstruction and morphometric modelling applied to past volcanism accurate and precise morphometric modelling can be extended to past eruptions after a careful palaeogeomorphological reconstruction of volcanic landforms in an oceanic island this reconstruction was used to derive the pre post eruption and present day digital elevation models dem the correct pixel size interpolation method and quality of these dems are discussed the process in a geographical information system framework of the geological information of cone lava flow and tephra fall deposits together and the aforementioned dems allowed the determination of main morphological features of these volcanic landforms and their derivatives the calibration and validation of morphometric modelling were performed on simulated volcanic landforms and verified by a case study a typical holocene monogenetic basaltic eruption at gran canaria island spain

seismic volcanostratigraphy of large volume basaltic extrusive complexes on rifted margins large volume extrusive basaltic constructions have distinct morphologies and seismic properties depending on the eruption and emplacement environments the presence and amount of water is of main importance while local rift basin configuration erosion and resedimentation determine the overall geometry of the volcanic constructions we have developed the concept of seismic volcanostratigraphy a subset of seismic stratigraphy to analyze volcanic deposits imaged on seismic reflection data the method places special focus on identification and mapping of seismic facies units and the volcanological interpretation of these units interpretation of seismic reflection data along the atlantic and western australia rifted margins reveals six characteristic volcanic seismic facies units named 1 landward flows 2 lava delta 3 inner flows 4 inner seaward dipping reflectors inner sdr 5 outer high and 6 outer sdr these units are interpreted in terms of a five stage tectonomagmatic volcanic margin evolution model comprising 1 explosive volcanism in a wet sediment broad basin setting 2 subaerial effusive volcanism forming gilbert type lava deltas along paleoshorelines 3 subaerial effusive volcanism infilling a fairly narrow rift basin 4 shallow marine explosive volcanism as the injection axis is submerged below sea level and finally 5 deep marine sheet flow or pillow basalt volcanism further erosion and resedimentation processes are particularly important during the shallow marine stages seismic volcanostratigraphy provides important constraints on rifted margin development in particular on the prevolcanic basin configuration relative timing of tectonomagmatic events total amount of volcanic rocks location of paleoshorelines and margin subsidence history these parameters give key boundary conditions for understanding the processes forming volcanic margins and other large volume basaltic provinces

inelastic deformation during sill and laccolith emplacement insights from an analytic elastoplastic model numerous geological observations evidence that inelastic deformation occurs during sills and laccoliths emplacement however most models of sill and laccolith emplacement neglect inelastic processes by assuming purely elastic deformation of the host rock this assumption has never been tested so that the role of inelastic deformation on the growth dynamics of magma intrusions remains poorly understood in this paper we introduce the first analytical model of shallow sill and laccolith emplacement that accounts for elasto plastic deformation of the host rock it considers the intrusion s overburden as a thin elastic bending plate attached to an elastic perfectly plastic foundation we find that for geologically realistic values of the model parameters the horizontal extent of the plastic zone lp is much smaller than the radius of the intrusion a by modeling the quasi static growth of a sill we find that the ratio lp a decreases during propagation as 1 a 4 p with p the magma overpressure the model also shows that the extent of the plastic zone decreases with the intrusion s depth while it increases if the host rock is weaker comparison between our elasto plastic model and existing purely elastic models shows that plasticity can have a significant effect on intrusion propagation dynamics with e g up to a doubling of the overpressure necessary for the sill to grow our results suggest that plasticity effects might be small for large sills but conversely that they might be substantial for early sill propagation 2

experimental modelling of shallow magma emplacement application to saucer shaped intrusions abstract saucer shaped dolerite and sandstone intrusions are common in sedimentary basins world wide we have conducted a series of scaled experiments simulating the process of magma emplacement in sedimentary basins with particular attention on the formation of saucer shaped sills the model materials were 1 cohesive fine grained silica flour representing brittle crust and 2 molten low viscosity oil representing magma the experiments were performed in both homogeneous and layered models in all the experiments oil injection resulted in doming of the surface in the homogeneous models the injected oil formed cone sheets and sub vertical dykes cone sheets formed for shallow injection 1 3 cm and vertical dykes formed for deeper injection 4 5 cm in layered models the injected oil always formed saucer shaped intrusions our experimental results show that 1 sill intrusion results in the formation of a dome with melt erupting at the rim 2 layering controls the formation of sills and saucer shaped sills 3 saucer shaped sills are fed from the bottom and the fluid flows upward and outward and 4 the diameter of saucer shaped sills increase with increasing emplacement depth the systematic relation between domes and sills and the depth dependence of sill diameters show that saucer shaped intrusions result from the interaction between a growing flat lying shallow sill and doming of the free surface we conclude that saucer shaped intrusions represent fundamental geometries formed by shallow magma intrusion in stratified basins

constraining the depth and timing of large scale conical sandstone intrusions kilometer scale sandstone intrusions a recently recognized end member of the spectrum of soft sediment deformation structures are important components of many deep water sandstone reservoirs they result from the remobilization of considerable volumes of sand during early stages of burial this paper uses three dimensional seismic data calibrated to nearby wells to describe an extensive system of large downward tapering conical sandstone intrusions from the faeroe shetland basin on the uk atlantic margin the intrusions are derived from a middle eocene submarine fan and are injected vertically upward through overlying highly faulted claystones to form conical bodies that interconnect across the 700 m thick claystone interval to feed a set of shallow intrusions located within a few hundred meters of the paleoseabed the forcible intrusion of these shallow sandstone bodies produced complementary folding of the contemporaneous seabed the subsequent onlap of these seabed domal folds took place immediately after the intrusion event and by correlation to biostratigraphic data from nearby wells we date these intrusions as late miocene this is the first time that both the age and emplacement depth range of a system of large scale sandstone intrusions have been constrained

post rift submarine volcanic complexes and fault activities in the baiyun sag pearl river mouth basin new insights into the breakup sequence of the northern south china sea abstract post rift volcanisms and fault activities are significant for understanding the tectonic sedimentary evolution of rifted continental margins and associated hydrocarbon entrapments in this study a series of post rift fault associated volcanic activities have been found in the northern continental margin of the south china sea scs however their episodes and relationships with the progressive continental breakup are still doubtful here new 2d 3d seismic borehole dating and biostratigraphic data are used to investigate the characteristics of the post rift volcanism and fault activities in the baiyun sag bys pearl river mouth basin the newly found fault associated volcanic complexes include thirteen submarine volcanic mounds and associated lava flows together with igneous sills that are mainly composed of basalts and tuffs seismic stratigraphic analysis combined with k ar dating from cores confirms that post rift volcanism in the bys climaxed along with the breakup of the scs mainly in three episodes 1 the first episode near oligocene miocene boundary 23 3 ma 2 the second at the middle early miocene 17 6 ma and 3 the new found third episode at the late early miocene 17 1 ma also fifty three syn sedimentary faults are interpreted which are characterized by a wnw trending normal fault group separated by an ene trending transcurrent fault group and there is evidence that these fifty three faults were long lived from ca 32 17 1 ma and served as important conduits for the upward migration of the magma the three episodes of volcanism and tectonic fault activities are related to the progressive continental breakup in the northern scs margin and they represent the tectonic signature of the early stage of the post rift subsidence after the lithospheric breakup which extends to the top of a hypothetical breakup sequence 32 17 1 ma in the bys furthermore this study proves that the diachronous continental breakup in the scs margin can result in corresponding changes in depositional architectures along with a breakup sequence characterized by the deposition of a sandstone carbonate shale regressive transgressive cycle the sedimentological changes and associated tectonic features recorded in the baiyun sag suggest an exceptionally active tectonic setting in the time of the formation of the breakup sequence early oligocene early miocene along the northern scs margin

lateral evolution of the rift to drift transition in the south china sea evidence from multi channel seismic data and iodp expeditions 367 368 drilling results the south china sea margins represent a critical natural laboratory to study the processes and parameters controlling the rift to drift transition high quality seismic data previously suggested the occurrence of a relatively sharp transition between the continental and oceanic domains a hypothesis recently validated by the results of the iodp expedition 367 368 drilled in the northern south china sea distal margin drilling results in this transition cored mid ocean ridge type basaltic basement site u1502 while its lateral equivalent showed continental affinities site u1499 seismic data document the lateral evolution of this narrow transition zone 15 to 25 km wide and tectono magmatic context related to breakup a short period magmatic event occurred during the latest stage of continental rifting and intruded the edge of the thinned continental crust triggering crustal breakup and onset of steady state seafloor spreading the architecture of the transitional domain documented in this work is in marked contrast with those interpreted as either magma starved or magma rich at breakup time suggesting that the continental margin of the scs is intermediate between the classical end member magmatic archetypes we propose that the magmatic event triggering continental breakup is related to decompression melting linked to the ascending asthenosphere it is assumed that this event was rapid at geological time scale 10 ma and was favored by a high mantle temperature

craters of elevation revisited forced folds bulging and uplift of volcanoes the eighteenth nineteenth century craters of elevation theory required magma to uplift strata doming the surface and creating a central down fallen crater or graben exponents of craters of elevation attempted to apply it to explain the origin of all volcanoes and rapidly the contemporary competing craters of eruption theory replaced it as the paradigm for volcano construction several historic examples have shown that intrusions can cause uplift termed bulges and can create features like those proposed for craters of elevation e g at usu 1944 bezymianny 1955 and mt st helens 1980 work on sedimentary basins that have had igneous activity has shown that intrusions create forced folds that uplift and deform strata in a similar way to that originally proposed for craters of elevation in view of the above we investigate large scale intrusion related topographic changes at two sites where the craters of elevation theory was developed the monogenetic volcanoes of the chaine des puys france and the teide stratovolcano tenerife we combine observations of such features with examples of forced folding to integrate the two fields of research our observations in the chaine des puys show that 1 the petit puy de dome has a bulge of up to 150 m uplift the uplift has a central depressed area a graben a dense network of normal faults basal thrusts and an aborted landslide 2 the grosmanaux volcano is a forced fold created by uplift of a previously flat lying area and has dense faulting and a graben on the resultant topographic bulge it was the site also of a major vulcanian eruption from the associated kilian crater 3 the gouttes volcano was uplifted by an intrusion like the petit puy de dome but then collapsed to generate a landslide and lateral blast 4 excavation in the lemptegy volcano exposes intra eruption intrusions with associated uplift providing examples in cross section of the internal deformation likely to be found inside other chaine des puys uplifted bulges on teide a bulge near the summit shows similar structures and surface tilting as seen on the petit puy de dome and this bulging may have formed during the eruption of the lavas negras the most recent activity on the summit area fault scarps on teide also expose small cryptodomes like those seen at lemptegy these examples coupled with field studies on eroded intrusions data on forced folds in basins and analogue models show how large scale topographic remodelling and structural change can be created by intrusions these can rapidly and significantly change the volcanic edifice a crater of elevation bulge or forced fold that is stabilised by the cooling of the intrusion will remain an important structural element in a volcano this process starts even at the small scale of monogenetic volcanoes and could occur through the lifetime of any growing stratovolcano such activity may be commonplace but may be masked by concomitant eruption or removed by subsequent collapse monitoring and hazard strategies should be ready to deal with such large scale events that will seriously modify the eruptive activity and stability of a volcano within days or weeks

the morphology of the submarine flanks of volcanic ocean islands a comparative study of the canary and hawaiian hotspot islands the submarine flanks of volcanic islands are shaped by volcanic constructional processes landslides erosion sediment deposition and tectonic movements we use a newly acquired multibeam sonar dataset from the westerly canary islands el hierro la palma and tenerife to develop a comparison with the hawaiian islands which suggests differences in the processes constructing and modifying their flanks landslides affect the flanks of both island groups debris avalanches fast moving shallow landslides have left smooth chutes and blocky deposits in both cases but blocks within some hawaiian avalanche deposits are markedly larger we attribute the larger block sizes in the hawaiian islands to the fact that their avalanches were relatively unconfined whereas many canary and hawaiian avalanches with small block sizes appear to have been constrained down narrow chutes forcing interactions between blocks within the flows and encouraging disintegration furthermore the hawaiian avalanches with the largest blocks initiated near sea level whereas many of the canary avalanches initiated above sea level so hydraulic resistance of water entering cracks may be an additional factor in resisting block disintegration during flow slow moving deep seated slumps or volcanic spreading have produced submarine benches and tabular escarpments due to thrust faulting adjacent to several hawaiian rift zones but are not well developed in the canaries although volcanic morphology is partly obscured by sedimentation in the canaries we are able to interpret lava terraces around the deep flanks of el hierro which are similar to those found in the hawaiian islands however cones rather than terraces are the most common volcanic forms in the canary islands implying that flank eruptions have involved magma with significant volatile contents assuming that volatile contents dictate whether cones or terraces are formed these differences may ultimately originate from the different building rates of the two island groups for example the lack of evidence for high level magma chambers in the canaries associated with their lower outputs implies that there is less possibility for degassing of magma below the summit before lateral intrusion down rift zones hence cones rather than lava terraces are more commonly observed the apparent lack of slumping or volcano spreading could also reflect a lack of driving pressure from extensive high level magma chambers in the canaries

interconnected sills and inclined sheet intrusions control shallow magma transport in the ferrar large igneous province antarctica field observations and structural data from intrusive complexes at allan hills and terra cotta mountain south victoria land antarctica demonstrate that interconnected sills and inclined sheets transported magma through the shallow subsurface these sills and sheets represent the upper crustal top 4 km plumbing system of the 183 ma ferrar large igneous province the sheets are short in length

release of methane from a volcanic basin as a mechanism for initial eocene global warming a 200 000 yr interval of extreme global warming marked the start of the eocene epoch about 55 million years ago negative carbon and oxygen isotope excursions in marine and terrestrial sediments show that this event was linked to a massive and rapid approximately 10 000 yr input of isotopically depleted carbon it has been suggested previously that extensive melting of gas hydrates buried in marine sediments may represent the carbon source and has caused the global climate change large scale hydrate melting however requires a hitherto unknown triggering mechanism here we present evidence for the presence of thousands of hydrothermal vent complexes identified on seismic reflection profiles from the voring and more basins in the norwegian sea we propose that intrusion of voluminous mantle derived melts in carbon rich sedimentary strata in the northeast atlantic may have caused an explosive release of methane transported to the ocean or atmosphere through the vent complexes close to the palaeocene eocene boundary similar volcanic and metamorphic processes may explain climate events associated with other large igneous provinces such as the siberian traps approximately 250 million years ago and the karoo igneous province approximately 183 million years ago