crustal structure of the labrador sea conjugate margin and implications for the formation of nonvolcanic continental margins wide angle seismic studies have determined the detailed velocity structure along a 350 km long profile across the labrador margin combination of this model with a previously published cross section for the southwestern greenland margin constitutes the first combined conjugate margin study based on seismic velocity structure the results indicate three distinct zones across the labrador margin similar to the structure of the conjugate greenland margin zone 1 represents 27 to 30 km thick continental crust thinning gradually seaward over 100 km distance farther seaward zone 2 is 70 80 km wide characterized by a distinct lower crust 4 5 km thick in which velocity increases with depth from 6 4 to 7 7 km s interpretation for this lower crustal block favors an origin by serpentinized peridotite rather than by magmatic under plating zone 3 represents two layered normal oceanic crust the cross sections from both margins are reconstructed to an early drift stage at chron 27 this demonstrates that the serpentinites in zone 2 are symmetrically distributed between previous identifications of chrons 31 and 33 on both margins zone 1 shows a marked asymmetry with a gradual thinning of continental crust off labrador contrasted with a rapid thinning off greenland the abundant serpentinization of upper mantle peridotite in zone 2 and the asymmetric shape of zone 1 are both probably related to a very slow rate of continental rifting which produced little if any melt

timing of kimberlite carbonatite and ultramafic lamprophyre emplacement in the alkaline province located 64 67 n in southern west greenland abstract the timing and duration of kimberlite and related magmatism in southern west greenland have been investigated by determining precise u pb perovskite pyrochlore and rb sr phlogopite ages for 37 samples collected in the sisimiut sarfartoq and maniitsoq regions a summary of these results indicate that this magmatism occurred during three main periods within a time span of more than 1 b y 1 mesoproterozoic 1284 1209 ma 2 neoproterozoic 604 555 ma and 3 jurassic 166 158 ma rb sr phlogopite ages were determined for four mesoproterozoic ultramafic lamprophyre samples collected 50 km ese to sse of sisimiut and they have broadly similar ages between 1284 and 1209 ma the most precise ages are between 1246 and 1209 ma and are interpreted to be a distal manifestation of alkaline and ultrapotassic magmatism related to the 1300 1130 ma gardar rift 800 km further south the majority of the new dates 28 are from dykes and sheets emplaced over an 50 m y time span during the neoproterozoic a period dominated by ultramafic lamprophyres some of which are transitional into kimberlites initiation of this alkaline magmatism occurred at 604 ma however the majority of dykes and sheets were emplaced in the period between 585 555 ma with possible pulses at 578 7 1 4 and 556 7 1 2 ma calcite kimberlites in the maniitsoq region and the sarfartoq carbonatite are constrained to the youngest period of magmatism at 560 ma many of the kimberlites and ultramafic lamprophyres in the neoproterozoic west greenland alkaline province were emplaced following the opening of the iapetus ocean at about 615 ma and are interpreted to be linked to continental rifting the youngest alkaline and ultrapotassic magmatism in west greenland mesozoic to paleogene extends for more than 300 km along the coast and the ages obtained in this study for two jurassic carbonatite complexes the 165 ma qaqarssuk complex near maniitsoq and the 158 ma tikiusaaq complex east of nuuk indicate that carbonatites are also an integral part of this jurassic alkaline province there is a peak in alkaline and ultrapotassic magmatism in west greenland during the period 165 145 ma possibly indicating a period of increased extension during the opening of the north atlantic ocean

lithospheric structure of the labrador sea from constrained 3 d gravity inversion regional inversions of free air gravity data constrained by bathymetric and sediment thickness information were undertaken over the labrador sea and its margins to generate 3 d density anomaly models to investigate broad scale crustal structural variations across the extinct spreading centre benchmarked against independent seismic moho depth constraints a density anomaly isosurface within the inverted volumes was selected as a moho proxy and regional maps of moho structure were developed inversions using two different sources for depth to basement constraints revealed similar moho structures with a depth to moho of 12 km beneath the labrador sea which deepens to 20 km and greater towards davis strait and beneath the offshore extension of the grenville province density anomaly slices through the models corresponding to seismic lines show good agreement between the inverted moho proxy and the seismic moho with the only exceptions occurring where a high velocity lower crustal zone or underplate has been modelled from wide angle reflection refraction profiling studies the inverted depth to moho estimates were combined with depth to basement constraints to investigate crustal thickness both for the full crust and for individual crustal layers revealing that the crust of the labrador sea is generally 5 10 km thick but thickens to 20 25 km towards davis strait and beneath the offshore extension of the grenville province not taking into account high density underplates or anomalously high density lower crust sediment and crustal thickness variations were investigated to compute stretching factors across the labrador sea and to identify zones which deviate from local isostatic compensation assuming both an initial unstretched crustal thickness of 35 km and using a variable unstretched crustal thickness model much of the labrador sea has experienced 70 90 per cent thinning the derived values suggest that embrittlement of the entire crust and serpentinization of the upper mantle are likely to have occurred for large portions of the central and southern labrador sea inboard of known oceanic crust isostatic considerations reveal sediment excess and deficiency on the labrador and greenland margins respectively possibly reflecting fundamental rheological asymmetry with the greenland margin appearing weaker than the labrador margin a strong gradient from sediment deficiency to excess exclusive to the labrador margin may reveal the southwestern limit of a regional graben bounding listric detachment or of a zone of distributed faults and detachments

the structure evolution and symmetry of the magma poor rifted margins of the north and central atlantic a synthesis abstract magma poor rifted margins consistently show extreme crustal thinning accompanied by normal faulting the serpentinization of the mantle beneath crust thinned to less than 8 2 km and the unroofing of a broad zone of mantle within the continent ocean transition accompanied by the development of detachment and other large offset faults these observations are the logical result of the progressive extension of cool lithosphere away from thermal anomalies such as plumes although the paucity of magmatism may be explained by depth dependent extension of the lithosphere and by pre depleted sub crustal lithosphere rifting above initially cool sub lithospheric mantle also may explain the subsidence deficit observed at some margins synrift subsidence is buffered by the simultaneous influx of warmer oceanic asthenosphere as it extends thins and cools ductile creeping layers in the mid and deep crust become progressively more brittle resulting in increased coupling between the upper and lower crust and eventually the embrittlement of the entire crust faults cutting from the surface across the moho bringing water into the mantle and causing its serpentinization increased coupling and the development of serpentine detachments predict the development of late stage asymmetry once the entire crust is brittle such detachments are imaged on some margins and inferred on others analysis of the crustal structure across conjugate margins shows that these are approximately symmetric until this late stage when they become markedly asymmetric similar analyses show that depth dependent stretching of the crust is insufficient to explain the discrepancy between the amount of the visible extension along faults and the amount of crustal thinning instead this extension discrepancy may be related to the complex evolution of brittle deformation through multiple phases and styles of faulting related to the changes in the rheological character and strength of the lithosphere as it is thinned complex polyphase faulting continues after complete crustal separation resulting in the exhumation of broad expanses of peridotitic basement the top of which is everywhere marked by an exhumed slip surface similar to the corrugated surface observed at mid ocean ridges the similarity in processes between mantle unroofing and seafloor spreading makes the distinction between the cot and true oceanic crust difficult and possibly moot

understanding potential pressure regimes in undrilled labrador deep water by use of global analogues in recent years new deepwater seismic based exploration work has resulted in the revision of existing basin boundaries and identification of new potentially oil bearing basins in the deepwater labrador region the petroleum potential in this deepwater area has also been encouraged by the identification of slick and seepage locations using 2d seismic data and satellite imagery the importance is that surface slicks possibly are related to subsurface hydrocarbon migration thus all recent data collated together show strong evidence for an active petroleum system in deep water many of the wells in shallow water have been drilled with low mud weights suggestive of low pore pressures however where thick shale packages are present significant overpressure is observed by significant kicks clearly there is a close association between thick and deep shale packages and high pore pressure thus one of the key risks in developing the deepwater potential is to understand the pressure regime the success of this approach has been highlighted recently by successful discoveries such as

the continental margin off southern greenland along strike transition from an amagmatic to a volcanic margin the southern part of the continental margin off southern west greenland is an amagmatic margin that may have taken at least 30 and possibly more than 60 million years to form during the cretaceous at an average extension rate of between 8 7 and 4 4 mm a 1 to its northwest and east are volcanic continental margins formed in the early tertiary when sea floor spreading started above the hot north atlantic plume head the survival of the amagmatic margin means that plume head material could never have been present under it and therefore the plume head could not have had the circularly symmetric shape commonly depicted in the literature

repeat ridge jumps and microcontinent separation insights from ne arabian sea abstract microcontinents separate due to ridge jumps associate either asymmetric sea floor spreading or plume ridge interactions india separated from seychelles at 64 ma by asymmetric sea floor spreading initially when the spreading centre in the mascarene basin jumped towards the indian sub continent between magnetic chrons c29 and c28 the subsequent tectonics is difficult to comprehend since laxmi ridge another microcontinent formed during the later phase most of the studies considered the laxmi ridge as a sliver others considered it to be oceanic crust high resolution deep 25 km seismic data reveals that i the ridge possesses 15 km deep sea ward dipping reflector sdr packages ii normal faulted rift valleys devoid of syn rift sedimentary packages and iii axial magma chambers 5 7 km beneath the ridge top additionally from 2d forward gravity models we deduce that the ridge most possibly comprises of high density oceanic crust we conclude the laxmi ridge to be indeed composed of oceanic crust and a fossil spreading centre we thus identified the ridge jumps and their relation to the seychelles microcontinent separation previous numerical models suggest that the time required for a ridge jump is controlled by magmatic heating spreading rate at the ridge and plate ages for repeated ridge jumps the additional factor is the dynamic relation between the plume and lithosphere in terms of melt transfer and heating we find that the medium spreading rates and high magmatic heating due to the reunion plume and young plates favoured rapid and repeated ridge jumps towards the plume

wide angle seismic transect across the torngat orogen northern labrador evidence for a proterozoic crustal root a refraction wide angle reflection seismic transect across the labrador peninsula covers the core zone of the se churchill province the paleoproterozoic torngat orogen and the archean nain province including a portion of the labrador continental margin an airgun array was used as source and 11 ocean bottom seismometers and 16 land stations recorded the shots forward modeling of travel times and amplitudes reveals a deep asymmetric crustal root beneath the torngat orogen with a crustal thickness of 49 km and with p wave velocities of 6 9 7 0 km s the geometry of the velocity model and the root can be best explained by either westward dipping subduction or westward underthrusting of the nain crust gravity modeling suggests a correlation of the crustal root with a gravity low that extends 100 km in an e w direction and 200 km from north to south the preservation of the crustal root is attributed to the lack of postorogenic heating and ductile reworking consistent with the lack of abundant postcollisional magmatism in the se churchill province a discontinuity possibly cutting through the entire crust is interpreted as a zone of major transcurrent shearing associated with the main phase of deformation west of the torngat orogen the crustal thickness in the core zone of the churchill province varies between 35 and 38 km p wave velocities of 5 8 7 0 km s east of the orogen the crystalline crust in the nain province is 38 km thick velocities from 5 8 to 6 9 km s but thins to 9 km in the shelf area of the labrador margin where it is covered with up to 8 km of sediments no high velocity zone was found beneath the thinned continental crust at the margin

an organic geochemical assessment of oceanographic conditions at manop site c over the past 26 000 years eleven sediment samples taken downcore and representing the past 26 kyr of deposition at manop site c 0 57 2 n 138 57 3 w were analyzed for lipid biomarker composition biomarkers of both terrestrial and marine sources of organic carbon were identified in general concentration profiles for these biomarkers and for total organic carbon toc displayed three common stratigraphic features in the time series 1 a maximum within the surface sediment mixed layer 4 ka 2 a broad minimum extending throughout the interglacial deposit and 3 a deep pronounced maximum within the glacial deposit using the biomarker records a simple binary mixing model is described that assesses the proportion of terrestrial to marine toc in these sediments best estimates from this model suggest that 20 of the toc is land derived introduced by long range eolian transport and the remainder is derived from marine productivity the direct correlation between the records for terrestrial and marine toc with depth in this core fits an interpretation that primary productivity at site c has been controlled by wind driven upwelling at least over the last glacial interglacial cycle the biomarker records place the greatest wind strength and highest primary productivity within the time frame of 18 to 22 kyr b p diagenetic effects limit our ability to ascertain directly from the biomarker records the absolute magnitude that different types of primary productivity have changed at this ocean location over the past 26 kyr

lower crustal intrusion on the north atlantic continental margin near the faroe islands in the north atlantic the majority of basalt is intruded into the continent ocean transition rather than extruded onto the surface this melt is intruded into the lower crust as sills which cross cut the continental fabric rather than as an underplate of 100 melt as has often been assumed when continents break apart the rifting is sometimes accompanied by the production of large volumes of molten rock1 2 3 the total melt volume however is uncertain because only part of it has erupted at the surface furthermore the cause of the magmatism is still disputed specifically whether or not it is due to increased mantle temperatures we recorded deep penetration normal incidence and wide angle seismic profiles across the faroe and hatton bank volcanic margins in the northeast atlantic here we show that near the faroe islands for every 1 km along strike 360 400 km3 of basalt is extruded while 540 600 km3 is intruded into the continent ocean transition we find that lower crustal intrusions are focused mainly into a narrow zone 50 km wide on the transition although extruded basalts flow more than 100 km from the rift seismic profiles show that the melt is intruded into the lower crust as sills which cross cut the continental fabric rather than as an underplate of 100 per cent melt as has often been assumed evidence from the measured seismic velocities and from igneous thicknesses are consistent with the dominant control on melt production being increased mantle temperatures with no requirement for either significant active small scale mantle convection under the rift or the presence of fertile mantle at the time of continental break up as has previously been suggested for the north atlantic ocean4 5 6

sea surface temperature and productivity records for the past 240 kyr in the arabian sea abstract deep sea sediments of two cores from the western ty93 929 p and the southeastern md900963 arabian sea were used to study the variations of the indian monsoon during previous climatic cycles core ty93 929 p was located between the sw monsoon driven upwelling centres off somalia and oman which are characterized by large seasonal sea surface temperature sst and particle flux changes by contrast core md900963 was situated near the maldives platform an equatorial ocean site with a rather small sst seasonality less than 2 c for both cores we have reconstructed sst variations by means of the unsaturation ratio of c37 alkenones which is compared with the 18o records established on planktonic foraminifera in general the sst records follow the 18o variations with an sst maximum during oxygen isotope stage 5 5 the last interglacial at about 120 130 kyr and a broad sst minimum during isotope stage 4 and 3 3 approximately 40 50 kyr the sst difference between the holocene and the last glacial maximum lgm is of the order of 2 c in both cores the ssts during isotope stage 6 are distinctly higher by 1 2 c than the cold sst minima during the last glacial cycle lgm and stage 3 to reconstruct qualitatively the past productivity variations for the two cores we used the concentrations and fluxes of alkenones and organic carbon together with a productivity index based on coccolith species florisphaera profunda relative abundance within each core there is a general agreement between the different palaeoproductivity proxies in the southeastern arabian sea core md900963 glacial stages correspond to relatively high productivity whereas warm interstadials coincide with low productivity all time series of productivity proxies are dominated by a cyclicity of about 21 23 kyr which corresponds to the insolation precessional cycle a hypothesis could be that the ne monsoon winds were stronger during the glacial stages which induced deepening of the surface mixed layer and injection of nutrients to the euphotic zone by contrast the records are more complicated in the upwelling region of the western arabian sea core ty93 929 p this is partly due to large changes in the sedimentation rates which were higher during specific periods isotope stages 6 5 4 5 2 3 and 2 unlike core md900963 no simple relationship emerges from the comparison between the 18o stratigraphy and productivity records the greater complexity observed for core ty93 929 p could be the result of the superimposition of different patterns of productivity fluctuations for the two monsoon seasons the sw monsoon being enhanced during interglacial periods whereas the ne monsoon was increased during glacial intervals a similar line of reasoning also could help explain the sst records by the superimposition of variations of three components global atmospheric temperature and sw and ne monsoon dynamics

glacial and interglacial wind regimes over the eastern subtropical atlantic and north west africa analysis of aeolo marine dust deposits in the subtropical eastern atlantic enables the strength of the major wind patterns during the late quaternary to be evaluated and gives an insight into the climate of north africa

crustal plumbing system of post rift magmatism in the northern margin of south china sea new insights from integrated seismology abstract the origin and evolution of magmatism in rifting margins are a fundamental geological subject and remain the focus of intense studies unlike the classical magma poor and magma rich rifting margins the northern margin of the south china sea scs exhibits a strong post rift magmatism but the evolution and mechanism of this behavior are still poorly understood in this work we investigate the detailed structural features of the post rift magmatism in the crust of the scs northern margin our analysis is based on wide angle and multichannel reflection seismic data combined with previous seismological results our results show a wide distribution of shallow igneous sills and intrusions these features are spatially and tectonically linked to the lower crustal high velocity bodies hvbs and submarine volcanism indicating a causative connection between the three features considering the existence of an obvious low velocity branch of the hainan plume in the northern scs and uplift of the lithosphere asthenosphere boundary we propose that the hvbs reflect consolidated mafic intrusions which formed the lower crustal reservoirs feeding the overlying igneous sills and intrusions in the scs northern margin where abundant extensional and detachment faults can act as magmatic channels such a dynamic process might cause post rift volcanism our results suggest that the crustal magmatic system of post rift volcanism has a multilevel upward migration mode and the hvbs in the lower crust could be the product of post rift magmatism further indicating that the scs northern margin had a magma poor property at the rifting phase but has undergone a strong magmatic rejuvenation by the subsequent mantle plume

old marine seismic and new satellite radar data petroleum exploration of north west labrador sea canada abstract this paper presents some new concepts in the petroleum systems of the northern labrador and southern baffin island offshore region of eastern canada the focus of this work is the region of the hekja o 71 gas discovery of 1979 by aquitaine one of only five wells drilled between 1976 and 1980 within an area covering some 166 000 square kilometers within the saglek basin this study emerged from a broad scale re examination of the petroleum potential of this area from the crust up using regional reflection refraction and potential field data an opportunity to use sar synthetic aperture radar data from the radarsat 1 earth observation satellite was taken to incorporate alternative data sources to support this exploratory review and resource assessment examination of the final map of interpreted slick like features on the sea surface revealed a close correlation of some of these occurrences to several bathymetric features which have underlying seismic signatures similar to previously identified gas hydrate pipes or chimney anomalies as seen in data from offshore nova scotia and in the irish sea globally many active marine hydrocarbon seeps appear on the seafloor as pockmarks in this case no seafloor depressions were seen on conventional multi channel 2 d seismic data associated with active seepage instead very distinct mound like structures are seen associated with seeps at two locations east of hudson strait the presence of significant cold water coral in close proximity to the active seepage sites may show a link between seafloor petroleum seepage and coral reef development similar to that observed offshore norway close examination of the near surface seismic character led to the interpretation of what was originally seen as seismic noise in vintage data as likely being fluid escape chimneys or gas pipes along the eastern edge of the hekja structural complex where favourable hydrocarbon trapping conditions are present no active seeps were seen there this may be due to other factors such as the nature of the fluids that are escaping or the possibility of self sealing activity by biological agents such as bacterial matting with associated carbonate hard ground formation one seep anomaly was noted relatively close to the major basaltic eruptive complex near the gjoa g 37 well this may be due to the presence of volcaniclastic hosted hydrocarbons similar in style to those recently discovered at the rosebank field in paleocene volcanics in the faroe shetland basin the occurrence of an active seep in a volcanically dominated terrain raises the potential for a radical shift in accepted types of petroleum leads and where they may occur the presence of apparent oil seepage versus the past history of finding only gas prone accumulations is a strong indicator that a second oil prone petroleum system exists in the saglek basin the signs of active petroleum systems as shown by oil seep anomalies with confirming seismic evidence of discrete sea floor structures in close proximity makes a compelling argument for re examining these areas with an eye towards stratigraphic instead of structural plays

age of tertiary volcanic rocks on the west greenland continental margin volcanic evolution and event correlation to other parts of the north atlantic igneous province radiometric ages for undated parts of the volcanic succession and intrusions in west greenland were obtained by the 40ar 39ar incremental heating method acceptable crystallization ages were obtained for 27 samples combined with published results the new data provide a volcanic stratigraphy correlatable throughout the nuussuaq basin the thick onshore volcanic pile consists of four widespread formations 62 5 61 ma picrites vaigat formation 61 60 ma depleted basalts malig t formation and the hellefisk 1 well 60 58 ma less depleted basalts svartenhuk formation and 56 54 ma enriched basalts naqerloq formation two local successions comprise 53 5 ma alkali basalts erqua formation and 38 7 ma transitional basalts talerua member a central volcano developed on ubekendt ejland leading to the sarq ta qaq gabbro granophyre intrusion at 57 55 ma pre break up volcanism took place further south as early as 64 63 ma the offshore volcanic succession most probably comprises the known onshore succession plus some younger lavas the change in spreading direction near the paleocene eocene boundary took place west of the nuussuaq basin c 56 2 ma some tectonomagmatic events are correlatable across the entire north atlantic igneous province a quiescent 58 56 ma period correlates with similar periods in east greenland and the faroes and the naqerloq formation is coeval with the eocene basalts in east greenland the paleocene and eocene tholeiitic basalts are distinguishable chemically in early eocene time mantle typical of the iceland plume seems to have extended beneath the whole west greenland margin as well as the central east greenland margin

the oceanic crustal structure at the extinct slow to ultraslow labrador sea spreading center two seismic refraction lines were acquired along and across the extinct labrador sea spreading center during the seismic investigations off greenland newfoundland and labrador 2009 cruise we derived two p wave velocity models using both forward modeling rayinvr and traveltime tomography inversion tomo2d with good ray coverage down to the mantle slow spreading paleocene oceanic crust has a thickness of 5 km while the eocene crust created by ultraslow spreading is as thin as 3 5 km the upper crustal velocity is affected by fracturation due to a dominant tectonic extension during the waning stage of spreading with a velocity drop of 0 5 to 1 km s when compared to paleocene upper crustal velocities 5 2 6 0 km s the overall crustal structure is similar to active ultraslow spreading centers like the mohns ridge or the south west indian ridge with lower crustal velocities of 6 0 7 0 km s an oceanic core complex is imaged on a 50 km long segment of the ridge perpendicular line with serpentinized peridotites 7 3 7 9 km s found 1 5 km below the basement the second ridge parallel line also shows extremely thin crust in the extinct axial valley where 8 km s mantle velocity is imaged just 1 5 km below the basement this thin crust is interpreted as crust formed by ultraslow spreading which was thinned by tectonic extension

climatic changes along the northwestern african continental margin over the last 30 kyrs two sediment cores were investigated to study the regional climatic variability of the nw african upwelling over the late quaternary biomarker data and sea surface temperatures ssts predicted from alkenones at 25 n and 21 n exhibited distinct features the amplitude of the last deglaciation was estimated to 4 5 c at 25 n and 2 2 5 c at 21 n at 25 n terrestrial and marine glacial inputs were higher than holocene ones as a result of a strengthening of the trade winds and intensification of oceanic production in contrast at 21 n warmer ssts and lower organic carbon and alkenone productions during the last glacial suggest a regression of the upwelling and therefore a change of wind regime low glacial n alkanols are consistent with the migration of the vegetation belt during the maximum of african aridity while their decrease towards the core top may be indicative of anthropogenic disturbances

tectonic evolution of southern baffin bay and davis strait results from a seismic refraction transect between canada and greenland 1 wide angle reflection refraction seismic data were acquired on a 450 km long transect in southern baffin bay extending from baffin island to greenland dense air gun shots were recorded on 22 ocean bottom seismometers apwave velocity model was developed from forward and inverse modeling of the observed travel times beneath the baffin island shelf a three layered continental crust is observed with velocities of 5 5 to 6 9 km s typical for transform margins there is a sharp transition between continental and oceanic crust off baffin island 7 km thick oceanic crust is interpreted to lie in a major transform fault identified on the gravity map beneath the deep baffin bay basin 9 km thick oceanic crust is encountered but thins to 6 km within an assumed fracture zone the thicker than normal oceanic crust indicates an ample magma supply possibly related to melt extracted from a mantle plume seaward of the greenland continental crust 20 km thick igneous crust 6 3 to 7 3 km s is encountered in a 25 km wide zone interpreted as a leaky transform fault that can be correlated southward through davis strait the igneous crust is bounded by a 20 km wide basin to the west underlain by 4 km thick crust of unknown affinity this structure is probably associated with transform movements a high velocity lower crustal layer 7 1 km s of 8 km thickness is indicated beneath the greenland crust and can be correlated into the adjacent thick igneous crust both the thick igneous and greenland crust are covered by up to 4 km of paleogene volcanics 5 2 to 5 7 km s

lateral flow and ponding of starting plume material many mantle plumes started with voluminous heads of hot material that ascended as diapirs through the mantle flood basalts radial dike swarms and frequently continental breakup are associated with the impingement of starting plume heads on the base of the lithosphere the buoyant plume head material ponds at the base of the lithosphere and then flows laterally relief on the base of the lithosphere acts as an upside down drainage pattern with enclosed catchments for this flow that is plume material preferentially collects beneath regions where the lithosphere is locally thin such as thermally subsiding sedimentary basins an example is uplift associated with the iceland starting plume which inverted the mesozoic irish sea basin additional relief at the base of the lithosphere is associated with rifting and seafloor spreading in the case of the northern north sea material from the iceland starting plume ponded beneath a basin with locally thin lithosphere rifting breached the enclosed catchment allowing the ponded plume material to drain across the new passive margin toward very thin lithosphere produced by seafloor spreading rifting also creates a conduit for the flow of plume material away from the region underlain by the starting plume head an example is the volcanic passive margin off nova scotia which is 2000 km from the center of the bahama starting plume head numerical and analytical calculations indicate that lateral flow of plume material consistent with this observation is expected if its viscosity is around 1018 pa s

deep seismic reflection data across the conjugate margins of the labrador sea a deep seismic reflection transect of the conjugate margins of the labrador sea is described which represents one of the few data sets of this kind a characteristic reflectivity is ascribed to a 120 km wide ribbon of very thin crust that may be either thinned continental crust which has perhaps been intruded or oceanic crust perhaps modified by the proximity of the continent most of the major changes in crustal thickness and in the subsidence and sedimentation patterns on the margins occur landward of these transitional zones which are found on both margins an interpretation of these regions as continental in origin is compatible with other seismic observations on the west greenland margin but does not match the magnetic anomaly interpretation which requires the transitional crust to be oceanic in origin models that satisfy the gravity anomalies and the subsidence history have been used to assist in interpreting the seismic data the subsidence models include the effects of decompression meltin

structural characteristics of the ocean continent transition along the rifted continental margin offshore central labrador abstract studies of the structural deformation and the nature of the ocean continent transition zone at the rifted continental margin offshore central labrador and its conjugate off west greenland have been conducted over several decades and helped to define our understanding of the controlling factors in the development of magma poor margins globally new two dimensional seismic reflection data are now available across the labrador margin which can help to modify and refine this understanding in this paper we describe some of these new seismic data and the corresponding potential field data in relation to earlier studies including an existing deep seismic crustal velocity profile these data cross the three major structural and compositional zones below the sedimentary wedge defined in earlier deep seismic experiments as 1 extended zone of continental crust including the hyper extended region partly underlain by serpentinized mantle 2 exhumed and serpentinized continental mantle zone and 3 zone of oceanic crust we are able to extend these zones laterally over 200 km along the margin the rifted continental crust is hyper extended over tens of kilometers landward of the breakup location where many varieties of normal faults and possible low angle detachment surfaces are present some of which are near or at the base of the crust further seaward mantle was serpentinized and likely exhumed and possesses a seismic character very different from the continental crust basement in this zone may locally form prominent ridges within the oceanic zone we define a further sub division into a proto oceanic domain with thin variable oceanic crust of about 70 65 ma in age magnetic chrons 27 to 31 and a steady state seafloor spreading region further seaward thus seafloor spreading starts at about chron 31 time potential field data and models are broadly consistent with these zones a strongly reflective post rift volcanic event is present across much of the region especially over the exhumed mantle zone and parts of the oceanic crust these results are discussed and compared to earlier studies of the west greenland conjugate margin and to other well studied magma poor margins given that this rift occurred in thick cold cratonic lithosphere the results are remarkably similar to those off iberia and newfoundland suggesting that a long rift history and or mantle metasomatism may have weakened the lithosphere prior to the main rifting event

transition from amagmatic to volcanic margin mantle exhumation in the voring basin before the icelandic plume influence abstract the outer voring basin norwegian sea is an abnormally deep and distal part of the norwegian passive margin known as magma rich yet the lastest borehole drilled in its northernmost part led to a drastic change in the interpretation of seismic reflection data this update motivates a new model for the entire mesozoic eocene rifting period here i evaluate the link between tectonics serpentinization and magmatism in the norwegian margin from the ryazanian valanginian to the palaeocene eocene magmatic breakup maps of the regional nise sandstones and main regional unconformities specifically highlight the fundamental role of the nyk vema structure to understand the basin and to question the deformation timing related to deep structures the top of partially serpentinized mantle is supported by high amplitude reflectors clearly visible on certain seismic lines known as t reflector covered with gravity driven pre exhumation sediments and further deposits a new structural scheme based on the interpretation of 2d and 3d seismic data shows the complex organization of fault networks and constrains a major deformation period between the late campanian and the late palaeocene ocean scale complementary arguments are in good agreement with lower cretaceous mantle exhumation before becoming a volcanic margin in the palaeocene this segment of the norwegian margin appears as amagmatic until the late campanian at least i propose an integrated model since the onset of hyperextension in the end of the jurassic until the cessation of activity of the aegir ridge in the miocene this model has implications regarding the context dependent interpretation of lower crustal bodies the ubiquity of serpentinization and mantle exhumation worldwide and on the hydrocarbon system

seismic volcanostratigraphy of the gascoyne margin western australia abstract integrated interpretation of seismic gravity and magnetic data has revealed the presence of a large breakup related volcanic complex on the rifted gascoyne margin western australia using the concept of seismic volcanostratigraphy we have identified three main volcanic seismic facies units related to the extrusive volcanism 1 landward flows 2 seaward dipping reflections sdr and 3 volcanic protrusions additionally we have identified four seismic facies units related to the tectonomagmatic evolution of the margin 4 domes 5 moho 6 top underplating and 7 sill intrusions the galah rise comprises the majority of the volcanic complex and is dominated by 100 200 km long ne striking volcanic ridges surrounded by multiple sets of deep marine emplaced sdrs an estimated excess crustal volume of the 50 000 km 2 large galah rise is 350 000 km 3 the volcanic complex is located at the outer corner of a shear rift margin setting the magmatism is sparse on the shear margin massive near the outer corner and decreases ne wards along the rifted margin segment and away from the fracture zone the gascoyne margin is comparable to the volcanic voring margin ne atlantic in terms of dimensions structural setting and distribution of the volcanic seismic facies units however the along margin variations in magmatism are more prominent on the gascoyne margin

western davis strait a volcanic transform margin with petroliferous features abstract we present a compilation of the western davis strait region offshore southeastern baffin island nunavut canada with new subsurface geological structural details and observations regarding past hydrocarbon occurrences from scientific and commercial exploration this consists of seismic mapping with archival data correlated with a filtered marine bouguer anomaly gravity compilation and magnetic data sets covering northern saglek basin the western part of the lady franklin basin and the ungava fault zone from south of baffin bay a regional seismic horizon for mapping basin architecture comes from the top of the paleogene volcanic syn magmatic zone where pervasive volcanic flows and intrusions are intermingled with the sedimentary section the seismic depth map to the top of the regional volcanic seismic horizon shows pre rift sedimentary basins having maximum depths of approximately 4 5 km flanking the shallower ungava fault zone correlation of bouguer anomaly gravity and magnetic data interpretations with the seismic mapping indicate that over some areas true crystalline basement is deeper than can be determined by reflection seismic as the base of the syn magmatic section is not resolvable for seismic mapping extensive paleogene mafic intrusives and extrusive basalts dominate the architecture of this volcanic rifted margin as seen by the dominant high amplitude magnetic anomalies associated with many deeper structures the over 250 km long davis strait fault is recognised as the key structural element of the ungava fault zone ufz and valley complex the adjoining davis strait high maps on seismic as a continuous structure running the length of davis strait plunging southwards to a bouguer gravity high feature that terminates the western end of the extinct eocene spreading zone south of davis strait this horn shaped structural feature establishes the presence of an accommodation zone with multiple faults and localised thrust faulting as required to fit the complex mechanics for strike slip motion that occurs along the south end of this transform fault system the revised marine bouguer anomaly gravity data set also defines two new near shore grabens east of cumberland sound the southern tariut basin and the northern imaqpik basin each extending over 100 km in length with sediment thicknesses of at least 4 km these pre rift basins most likely originate from the paleozoic based on seafloor dredge and nearby shallow drill cores from previous studies the hydrocarbon charge of a previously unexplained petroliferous shallow marine drill core that is adjacent the eastern edge of the tariut basin is attributed to paleozoic source rocks that have undergone enhanced thermal maturation from sill intrusion associated with rifting the imaqpik basin shows strong evidence of a hydrocarbon system from the proximity of clustered interpreted sea surface oil slicks mapped from satellite radar images and a local zone of anomalously high dissolved methane measured within the water column that originates from the seafloor immediately east of cape dyer at the northern limit of that basin the overlying cape dyer flood basalt field extends from limited onshore exposures into the offshore and maps with magnetic data over an area of approximately 13 000 km2 this extrusive feature and it s implicit underlying intrusive components are likely the unconventional heat source for the anomalous enhanced thermal maturation of paleozoic to paleogene source rocks in these pre rift basins that host this previously unrecognised petroleum system

wide angle seismic imaging of a mesoproterozoic anorthosite complex the nain plutonic suite in labrador canada the mesoproterozoic nain plutonic suite nps of labrador canada one of the largest anorogenic plutonic terranes was studied by a refraction wide angle seismic experiment four ocean bottom seismometers and 18 land stations were deployed along a 330 km profile and recorded air gun shots from the easternmost 160 km with the nps located in the center of the line at the suture of the nain and churchill provinces p and s wave velocity models were developed by forward modeling of travel times and amplitudes upper and middle crustal p wave velocities outside and beneath the nps range from 5 9 to 6 5 km s lower crustal p wave velocities range from 6 55 to 7 0 km s within the anorthositic rocks velocities are as high as 6 8 km s and reflections define the base of the nps to be 8 km deep in the se churchill province and 11 km in the nain province a variation that may be the result of lateral density changes within the country rocks or the anorthosites the total crustal thickness is 39 km west of the nps but is only 32 34 km beneath the nps some 5 km less than nain province crust distal from the nps the inferred crustal thinning is possibly related to anatexis of the lowermost crust by a thermal plume that generated the plutonism the poisson s ratios are 0 275 within the anorthosite plutons 0 27 in the upper and middle crust and 0 285 in the lower crust these values are some 0 03 higher than in the archean nain crust distal to the nps indicating a higher plagioclase content at all crustal levels as result of the plutonism we postulate that a crustal root similar to the root observed farther north in the torngat orogen was completely removed by anatexis and the silicic and basic magmas probably ascended to midcrustal levels along preexisting zones of weakness at the nain churchill boundary

evolution of nonvolcanic rifted margins new results from the conjugate margins of the labrador sea the crust across each margin of the labrador sea a conjugate rift margin pair consists of three well defined zones thinned continental crust 70 80 km wide transitional crust and oceanic crust the transition zone is characterized by a low velocity upper crust 4 5 km s underlain by a 6 4 7 7 km s layer we propose that the lower layer is serpentinized upper mantle it is less likely to be gabbroic igneous lower crust the low velocity upper crust may be either an oceanic basaltic layer or very thin 2 km continental crust results from this first combined seismic reflection and refraction study of a conjugate margin pair support very slow initial continental rifting 1 mm yr on average resulting in an asymmetric crustal thinning profile with breakup occurring against the west greenland shelf this asymmetry may be an important feature of rifting at nonvolcanic margins and may be related to strain hardening of the cooling and thinning lithosphere or to small scale convection in the lower lithosphere and asthenosphere at the sides of the rift the thin crust in the transition zone implies that the amount of melt generated in the upwelling mantle is negligible consistent with slow spreading or rifting the transition from this slow formational period to normal oceanic accretion processes is marked by a sharp decrease in basement depth signaling an increase to normal oceanic crustal thickness

eocene continental breakup in baffin bay abstract we question the timing of continental breakup and early oceanization in baffin bay north east atlantic north of the ungava fault zone the breakup was syn magmatic and led to the development of conjugate volcanic passive margins vpms we investigated the innermost part of the w greenland vpm where a remarkable inner sdr is fully exposed in the svartenhuk area our new radiometric ages and paleomagnetic data from syn tectonic basaltic lavas indicate that continental stretching and thinning spanned the c26r to at least the c24r period giving an eocene lower boundary age for continental breakup in baffin bay these results contradict the proposed flooring of baffin bay by a paleocene oceanic crust older than c24n and also question the accretion of oceanic crust before c22 we confront our results to the dynamics of the northward oceanic rift propagation across the ungava transform fault system and we suggest that plate breakup in baffin bay occurred 8 m y later than in n labrador sea as a result of the thermal and mechanical barrier effect induced by the ungava transform zone

geophysical characteristics of the continental crust along the lithoprobe eastern canadian shield onshore offshore transect ecsoot a review the eastern canadian shield onshore offshore transect ecsoot of the lithoprobe program included 1200 km of normal incidence seismic profiles and seven wide angle seismic profiles across archean and proterozoic rocks of labrador northern quebec and the surrounding marine areas archean crust is 33 44 km thick p wave velocity increases downwards from 6 0 to 6 9 km s there is moderate crustal reflectivity but the reflection moho is unclear archean crust that stabilized in the proterozoic is similar except for greater reflectivity and a well defined moho proterozoic crust has similar or greater thickness variable lower crustal velocities and strong crustal reflectivity geodynamic processes of paleoproterozoic growth of the canadian shield are similar to those observed in modern collisional orogens the suturing of the archean core zone and superior provinces involved whole crustal shearing top to west in the core zone linked to thin skinned deformation in the new quebec orogen the torngat orog

margin segmentation and volcano tectonic architecture along the volcanic margin off argentina uruguay south atlantic abstract some 25 000 kilometers of regional multichannel seismic data acquired by bgr along the continental margins off argentina and uruguay document that the early cretaceous south atlantic continental breakup and initial sea floor spreading were accompanied by large scale transient volcanism emplacing voluminous extrusives manifested in the seismic data by huge wedges of seaward dipping reflectors sdrs the emplacement of the deeply buried 60 120 km wide sdrs was probably episodic as documented by at least three superimposed sdrs units distinct along margin variations in architecture volume and width of the sdrs wedges are probably related to margin segmentation it is suggested that the margin can be divided at least in four compartments bounded by the falkland fracture zone falkland transfer the colorado transfer the ventana transfer and the salado transfer the individual margin segments reflect in the distribution and thickness of the post rift sediments the individual transfer zones may have acted as rift propagation barriers selectively directing rift segments in left stepping patterns along the western south atlantic margin although we found extensive variations in the architecture style and extent of the seaward dipping reflector sequences a general trend is that the largest volumes are emplaced close to the proposed transfer zones and the width of the sdrs wedges decreases northward within the individual margin segments we suggest that mainly adiabatic decompression and melt generation from shallow sources can explain distinct along margin variations in the volcano tectonic architecture and volumes of extruded magmas

tectonic control of the oil rich large igneous carbonate salt province of the south atlantic rift abstract the early cretaceous south atlantic magmatic province samp which includes the parana etendeka lip produced about 8 million km 3 of tholeiitic basalt and diabase over an area of 4 million km 2 huge pre salt oil reserves discovered in 2007 by petrobras in non marine carbonates are estimated at more than 45 billion barrels here we show the close causal relationship of the southward increasing width of the wedge shaped south atlantic rift with the similarly southward increase in igneous activity in the thicknesses of non marine carbonate and salt and in the size of oil reserves all controlled mainly by south america s early clockwise rotation away from africa about a pole in its northeast large diabase dike swarms transversal to the rift witness to south america s rotation that opened in its wake the southward widening south atlantic rift westward increasing pressure on the equatorial margin by south america s clockwise rotation forced open the benue trough and created pre late aptian folds in the demerara plateau and in brazil s solimoes upper amazonas basin prerift and synrift volcanic activity increases southward culminating in the parana etendeka lip and in the offshore volcanic sdrss that continue southward to the cape basin berriasian valanginian rift sediments deposited from about 145 ma 10 ma before the flood basalts of the parana etendeka lip the largest transversal dike swarm continued in the proto walvis ridge that separated the central south atlantic endorheic rift basin from the sea in the south erosion and leaching of basalts supplied ca mg and sio 2 to the endorheic basin for the deposition of non marine carbonates and authigenic clays basalt flows intercalated with carbonates nearly until salt deposition about 113 ma hypogenic leaching of carbonates by mantle derived co 2 created optimal reservoirs supergiant oil deposits occur where the widest endorheic basin and the volcanic province overlap

sedimentary response to mantle plumes implications from paleocene onshore successions west and east greenland the uplift history of the upper cretaceous paleocene sedimentary successions underneath the extensive tertiary flood basalts of west and east greenland supports recently described models for the generation of flood basalt provinces in response to rising hot mantle plumes however the sedimentary development indicates that the period of plume related uplift prior to eruption of volcanic rocks was very short 5 m y substantial regional uplift and faulting took place in west and east greenland in the early paleocene to earliest late paleocene resulting in a basinwide unconformity in west greenland the uplift was associated with fluvial peneplanation valley incision and catastrophic deposition in east greenland it was associated with fluvial peneplanation the cumulative uplift in west greenland is probably on the order of several hundred meters whereas in east greenland the observed uplift cannot be quantified in both west and east greenland this phase was shortly followed by rapid major subsidence associated with extensive volcanism it is suggested that this sequence of events reflects the arrival of the north atlantic mantle plume or plumes

molecular stratigraphy of cores off northwest africa sea surface temperature history over the last 80 ka the molecular stratigraphy of biogeochemical oceanic flux study core 31k 19 n 20 10 w and ocean drilling program hole 658c 20 45 n 18 35 w has been studied for c37 alkenone abundances over the past 80 ka at high resolution circa 200 500 years the derived uk37 sea surface temperature record for both cores shows a range of temperatures from about 18 c during the last glacial to 21 5 c during the early holocene both records also reveal changes in sea surface temperature as much as 2 4 c over a few hundred years which correlate well with similar abrupt climatic changes observed in cores from elsewhere in the ne atlantic associated with heinrich events our results indicate that meltwater produced by these ice rafting events was transmitted southward by the canary current where it had considerable impact on sea surface temperatures in the subtropical eastern atlantic

seismic study of the transform rifted margin in davis strait between baffin island canada and greenland what happens when a plume meets a transform 1 the davis strait transform margin was studied using a 630 km long wide angle reflection refraction seismic transect extending from se baffin island to greenland dense airgun shots were recorded by 28 ocean bottom seismometers deployed along the line a p wave velocity model was developed from forward and inverse modeling of the wide angle data and incorporation of coincident deep multichannel reflection seismic data off baffin island in the saglek basin 7 to 11 km thick two layered continental crust 5 8 6 6 km s is observed off greenland continental crust is divided into three layers 5 4 6 8 km s with a maximum thickness of 20 km farther offshore greenland the crust thins to 7 12 km and the lower crust disappears between the continental blocks a 140 km wide zone with oceanic crust layer 2 is 5 4 6 2 km s and layer 3 is 6 7 7 0 km s is located the western half of this zone is interpreted to be part of a volcanic margin with seaward dipping reflectors the eastern part is associated with the ungava fault zone ufz the major transform fault in davis strait the ufz thus acted as leaky transform fault during phases of transtension southward flow of material from the iceland plume created a 4 to 8 km thick underplated layer 7 4 km s beneath the thinned portions of the continental crust and beneath previously emplaced oceanic crust plume related paleogene volcanism is indicated by an up to 4 km thick layer 4 3 5 8 km s with basalts and interbedded sediments that can be traced from se baffin island 400 km toward the east

new evidence on the structure of the labrador sea greenland continental margin a 275 km section of a regional seismic reflection profile from the greenland side of the labrador sea has been reprocessed and interpreted three zones of different structural style have been identified the innermost of which is block faulted magnetic modelling based on the seismic line shows that sea floor spreading anomalies are confined to the outermost zone and the oldest identified anomaly is 27n all attempts to model the area landward of anomaly 27n as a series of remanent magnetizations of alternating polarity failed however a model in which the innermost zone is interpreted as extended and block faulted continental crust and the intermediate zone as continental crust intruded and overlain by reversely magnetized igneous material fits the magnetic and seismic data it is concluded that at least in the northern labrador sea sea floor spreading started in palaeocene times chron 27 and large areas formerly thought to be underlain by oceanic crust should now be considered to be continental one plate kinematic consequence may be a reduced need to postulate large strike slip movements along nares strait

interaction of rifting and hot horizontal plume sheets at volcanic margins we have explored the idea that observations of large igneous crustal thickness at volcanic rifted continental margins may be explained by the interaction of rift driven flow in the lithosphere with an underlying sublithospheric hot plume sheet this concept is assessed by numerical modeling of the viscous flow caused by divergent plate motions using a viscous temperature and pressure dependent nonlinear fluid the plume sheet consists of an initially hot layer just below the lithosphere which responds to the overlying lithospheric motions for reasonable values of input parameters we can successfully predict the observed thickness of igneous crust at the margin its formation time inferred average mantle melt fractions and importantly the eventual transition to normal oceanic crustal thicknesses observations are selected from the north atlantic region with an emphasis on the recent results from the east greenland volcanic margin the best fitting models suggest that relatively little small scale convection is needed after the initial strong pulse of mantle upflow due to the presence of moderately hot 1450 c buoyant plume material under the rift the results favor a thin 50 km plume sheet layer this hot mantle reservoir is soon depleted and replaced by normal temperature mantle unless the rift lies directly over the deep source of plume material

seismic evidence for plume derived volcanism during formation of the continental margin in southern davis strait and northern labrador sea the crustal structure in the southern davis strait and the adjacent ocean continent transition zone in ne labrador sea was determined along a 185 km long refraction wide angle reflection seismic transect to study the impact of the iceland mantle plume to this region a p wave velocity model was developed from forward and inverse modelling of dense airgun shots recorded by ocean bottom seismographs a coincident industry multichannel reflection seismic profile was used to guide the modelling as reflectivity could be identified down to moho the model displays a marked lateral change of velocity structure the sedimentary cover velocities 1 8 3 9 km s 1 is up to 4 km thick in the north and thins to 1 km in the south the segment of the line within southern davis strait is interpreted to be of continental character with a two layered 13 km thick crust with p wave velocities of 5 6 5 8 and 6 4 6 7 km s 1 in the upper and lower crust respectively the crust is underlain by a 2 to 4 km thick high velocity layer 7 5 km s 1 this layer we interpret as underplated material related to the iceland plume the southern segment of the line in labrador sea displays a 2 km thick layer with a velocity of 4 5 km s 1 this layer can be correlated to a well about 100 km to the west of the line where palaeocene basalts and interbedded sediments were drilled underneath is a 12 km thick crust with a 2 km thick upper layer 5 8 6 6 km s 1 and a 10 km thick lower layer 6 8 7 2 km s 1 this crust is interpreted to be of oceanic character s wave modelling yields a poisson s ratio of 0 28 for the lower crust compatible with a gabbroic composition the igneous crust is 5 km thicker than normal oceanic crust we suggest that the increased magma production was created by buoyancy driving flow

crustal structure of the rifted volcanic margins and uplifted plateau of western yemen from receiver function analysis we analyse p wave receiver functions across the western gulf of aden and southern red sea continental margins in western yemen to constrain crustal thickness internal crustal structure and the bulk seismic velocity characteristics in order to address the role of magmatism faulting and mechanical crustal thinning during continental breakup we analyse teleseismic data from 21 stations forming the temporary young conjugate margins laboratory yocmal network together with gfz and yemeni permanent stations analysis of computed receiver functions shows that 1 the thickness of unextended crust on the yemen plateau is 35 km 2 this thins to 22 km in coastal areas and reaches less than 14 km on the red sea coast where presence of a high velocity lower crust is evident the average vp vs ratio for the western yemen plateau is 1 79 increasing to 1 92 near the red sea coast and decreasing to 1 68 for those stations located on or near the granitic rocks thinning of the crust and by inference extension occurs over a 130 km wide transition zone from the red sea and gulf of aden coasts to the edges of the yemen plateau thinning of continental crust is particularly localized in a 30 km wide zone near the coastline spatially co incident with addition of magmatic underplate to the lower crust above which on the surface we observe the presence of seaward dipping reflectors sdrs and thickened oligo miocene syn rift basaltic flows our results strongly suggest the presence of high velocity mafic intrusions in the lower crust which are likely either synrift magmatic intrusion into continental lower crust or alternatively depleted upper mantle underplated to the base of the crust during the eruption of the sdrs our results also point towards a regional breakup history in which the onset of rifting was synchronous along the western gulf of aden and southern red sea volcanic margins followed by a second phase of extension along the red sea margin

the volcanic margins of the northern labrador sea insights to the rifting process 1 a new interpretation of seismic reflection data on the continental margin of northern labrador shows basement structures similar to those observed on other volcanic rifted margins seaward dipping reflections inner flows volcanic plateaus and lava deltas are observed on these data magnetic chron 27n 61 ma is coincident with the volcanic plateaus connecting these features to the paleocene volcanism farther north in davis strait therefore we are able to extend the region of volcanism about 500 km south along the margin similar structures are also observed on the conjugate west greenland margin below the volcanic plateaus gravity and wide angle seismic data show thick igneous crust which is fairly symmetrically distributed across the conjugate margins however the geometry of the thinned continental crust is not symmetrical a narrower zone of thinning is observed off northern labrador the thick igneous crust lies seaward of thinned continental crust which exhibits little or no underplating by the magmatic event this observation is compatible with recent models for the formation of nonvolcanic margins followed by a magmatic event late in the rift evolution in mesozoic time rifting of the cold thick cratonic lithosphere occurred between greenland and north america with minimal volcanic activity then in late cretaceous time the zone of rifting narrowed and localized seaward of the shelf creating a relatively narrow zone of lower lithospheric thinning and mantle upwelling into which the paleocene magmas were eventually channeled this scenario is supported by studies of mesozoic igneous rocks on land in coastal west greenland and labrador

structure of archean crust and passive margin of southwest greenland from seismic wide angle data to investigate the structure and composition of the archean crust beneath the shelf of southwest greenland parallel to the passive margin we conducted an onshore offshore seismic wide angle experiment in 1989 one of our goals was to obtain a velocity depth profile along the thinned continental or transitional crust to place constraints on the magmatic rifting history in the northern labrador sea seismic recording instruments at four locations along the coast recorded energy from an air gun array up to 400 km distance due to the dense shot spacing of 100 to 150 m we were able to identify continuous reflected and refracted phases from the upper to lower crust results from a one dimensional extremal inversion indicated a high velocity zone hvz with p wave velocities of more than 7 2 km s at the bottom of the transitional crust combined two dimensional travel time forward modeling and inversion produced a velocity depth model that contains midcrustal and lower crustal discontinuities between 12 and 25 km depth and a moho dipping northward at 30 to 42 km depth an average crustal velocity of about 6 6 km s indicates a high portion of mafic components in the crust the lowermost crust consists of a hvz with a maximum thickness of 8 km and temperature corrected velocities of 7 5 to 7 85 km s the hvz may be explained by an underplated igneous complex often observed under passive margins worldwide metamorphism to garnet pyroxene granulite during postrift isobaric cooling of the 30 to 40 km deep thinned continental crust could explain the velocities that are higher than on other margins a large volume of magmatic material must have been added to the crust but did not produce extrusions magmatic underplating of the thinned continental or transitional crust of sw greenland is likely associated with a possible hot spot magmatism in the davis strait and baffin bay region magmatism associated with continental rifting was found to reach farther south along the northern and central part of the archean block than previously thought

contrasting rifted margin styles south of greenland implications for mantle plume dynamics abstract we present new and reprocessed seismic reflection data from the area where the southeast and southwest greenland margins intersected to form a triple junction south of greenland in the early tertiary during breakup at 56 ma thick igneous crust was accreted along the entire 1300 km long southeast greenland margin from the greenland iceland ridge to and possibly 100 km beyond the triple junction into the labrador sea however highly extended and thin crust 250 km to the west of the triple junction suggests that magmatically starved crustal formation occurred on the southwest greenland margin at the same time thus a transition from a volcanic to a non volcanic margin over only 100 200 km is observed magmatism related to the impact of the iceland plume below the north atlantic around 61 ma is known from central west and southeast greenland the new seismic data also suggest the presence of a small volcanic plateau of similar age close to the triple junction the extent of initial plume related volcanism inferred from these observations is explained by a model of lateral flow of plume material that is guided by relief at the base of the lithosphere plume mantle is channelled to great distances provided that significant melting does not take place melting causes cooling and dehydration of the plume mantle the associated viscosity increase acts against lateral flow and restricts plume material to its point of entry into an actively spreading rift we further suggest that thick archaean lithosphere blocked direct flow of plume material into the magma starved southwest greenland margin while the plume was free to flow into the central west and east greenland margins the model is consistent with a plume layer that is only moderately hotter 100 200 c than ambient mantle temperature and has a thickness comparable to lithospheric thickness variations 50 100 km lithospheric architecture the timing of continental rifting and viscosity changes due to melting of the plume material are therefore critical parameters for understanding the distribution of magmatism

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

the role of inherited lithospheric heterogeneities in defining the crustal architecture of rifted margins and the magmatic budget during continental breakup during the final stage of continental rifting stretching localizes in the future distal domain where lithospheric necking occurs resulting in continental breakup in magma poor margins the lithospheric necking is accompanied by crustal hyperextension serpentinization and exhumation of mantle lithosphere in the continent ocean transition domain cot in magma rich margins the necking is accomplished by the emplacement of large amounts of volcanics in the cot in the form of seaward dipping wedges of flood basalts sdrs this study examines the factors controlling the final crustal architecture observed in rifted margins and the magmatic budget during continental breakup using observations from the labrador sea the latter shows magma rich breakup with sdrs documented in the north and magma poor breakup with a wide domain of exhumed serpentinized mantle recorded in the south the pre rift strength of the lithosphere defined by the inherited thermal structure composition and thickness of the lithospheric layers controls the structural evolution during rifting while variations in the magmatic budget associated with breakup are controlled primarily by the interaction between the pre rift inheritance the timing and the degree of mantle melting in relation to lithospheric thinning and mantle hydration

timing and duration of volcanism in the north atlantic igneous province implications for geodynamics and links to the iceland hotspot abstract we combine new and published 40 ar 39 ar age determinations from incremental heating experiments on whole rocks and mineral separates to assess the timing duration and distribution of volcanic activity during construction of the north atlantic igneous province we use these ages together with volume estimates of erupted magmas and their cumulates to calculate melt production rates for the early tertiary flood basalts of east greenland and the faeroes islands the lavas lie at opposite ends of the greenland iceland faeroes ridge the postulated iceland hotspot track and record volcanic activity leading up to during and following continental breakup between greenland and europe dominantly basaltic but also alkalic and picritic magmas were erupted from beneath thick continental lithosphere simultaneously at 61 ma from baffin island to the western and eastern margins of greenland to the faeroe islands and the western british isles a roughly circular area 2000 km in diameter volcanic activity was increasingly intermittent by 57 56 ma but at 56 1 0 5 ma the average melt production rate increased by more than an order of magnitude over previous levels from 3000 km 3 km of rift my coinciding with continental rifting and shallow decompressional melting of the mantle that fed subaerial volcanic activity along most of the eastern margin of greenland and its complement on the northwestern european margin offshore abnormally thick oceanic crust was produced along the line of plate separation the upper part of this crust comprises seismically imaged seaward dipping subaerially erupted lavas by 50 ma eruption rates had diminished drastically and volcanic activity had narrowed to a much restricted portion of the east greenland margin at the western end of the greenland iceland ridge that subsequently connected in an age progressive trend to present hotspot activity in southeastern iceland the startup mantle plume head and tail model with moderate excess temperature t 100 c and active upwelling best explains the time space and compositional aspects of volcanism in this province

margin segmentation of baffin bay davis strait eastern canada based on seismic reflection and potential field data abstract the continental margin of baffin island was interpreted from a compilation of seismic reflection and potential field data based on these data it was divided into volcanic and non volcanic segments in the northernmost area coast parallel grabens and continental basement highs are superseded beneath the slope by irregular basement topography in combination with the velocities from refraction data and the lack of a magnetic slope anomaly we propose a non volcanic margin in the central region the seismic data show a limited region with a seaward dipping reflector sequence that may be intercalated with a sedimentary section both north and south of cape dyer extensive volcanic rocks are interpreted at and below seabed consistent with a volcanic margin in the southern region the depth to basement drops rapidly offshore a thick prograding sedimentary wedge produces a high amplitude long wavelength free air gravity anomaly that was previously confused with the continent ocean boundary although some volcanic rocks are mapped in the region this area is adjacent to the non volcanic labrador sea margin and is interpreted to be of similar structure segmentation of the margin by major faults can explain the abrupt transitions from volcanic to non volcanic margin segments the continent ocean boundary for the region is determined based on the potential field and seismic data along the greenland plate in davis strait the continent ocean boundary coincides with the ungava fault zone the continent ocean boundary is used in conjunction with published poles of rotation to evaluate plate reconstructions at chrons 33n and 27n the earlier reconstruction produces an extensive overlap of boundaries in the north the later reconstruction shows a gap in the southern region thus additional information is required to refine the reconstructions

an 18 000 year long eruptive record from volcan chaiten northwestern patagonia paleoenvironmental and hazard assessment implications abstract the 2008 eruption of volcan chaiten vcha in northwestern patagonia was the first explosive rhyolitic eruption to have occurred within a century and provided an unprecedented scientific opportunity to examine all facets of the eruption ranging from magma rheology ascent rates to ash fall effects on biota and infrastructure up to very recently it was thought that the latest eruption prior to the 2008 event occurred c 9750 cal a bp although a number of researchers have recognised additional eruptive products but their stratigraphy age and geochemical attributes have not been systematically described and or recorded in this study we provide a detailed examination of andic cover beds and tephra bearing lake sequences located both proximally and distally to vcha which record a series of hitherto unknown rhyolitic eruptive products and place all previous observations firmly within a coherent stratigraphic framework through major and trace element glass shard geochemistry we are able to confidently verify eruptive source a total of 20 discrete tephra beds are recognised with at least 10 having widespread areal distributions and or depositional imprints broadly comparable to or greater than the 2008 tephra event this record indicates that vcha has been continuously but intermittently active as far back as the end of the last glacial maximum c 18 000 cal a bp with two dominant genetically related magma types and an intermediary mixed type before this the eruptive record has been largely obscured and or erased by widespread andean piedmont glaciation however based on the tempo of vcha activity over the last c 18 000 years older vcha eruptives can be anticipated to occur as well as future hazardous explosive events the new eruptive inventory will ultimately be useful for correlating equivalent aged sequences and refining long term eruptive tempo as well as corresponding temporal changes in magmatic evolution

dynamical modelling of lithospheric extension and small scale convection implications for magmatism during the formation of volcanic rifted margins summary enhanced melt productivity as a consequence of buoyant upwelling and small scale convection of the mantle during rifting may play an important role in determining the fundamental structure of igneous crust produced during and following continental breakup this paper investigates the relationship between rift related decompression melting and the influence of small scale mantle convection and rift geometry on the subsequent production and distribution of melt related crust extension of the lithosphere is modelled numerically using a 2 d plane strain finite element method for viscous plastic creeping flows the evolving temperature and pressure fields within the model are coupled to an algorithm that predicts the amount and timing of decompression melting of upwelling mantle predicted melt fractions are converted to equivalent thicknesses of igneous crust and the predicted crustal thicknesses for a series of models are compared to the observed crustal structure of rifted margins inferred from seismic data models characterized by small scale mantle convection can to first order reproduce the general architecture of most volcanic rifted margins that is a relatively narrow band of thick 12 13 km igneous crust inferred to occur along strike of the margin juxtaposed with thinner oceanic crust farther offshore the variability in thickness 4 7 km predicted for the later stage thinner igneous crust is however difficult to reconcile with global observations of oceanic crustal thickness 7 1 km also the peak 13 km thickness of igneous crust predicted for models with convectively enhanced upwelling fails to match the great thicknesses 20 km of igneous crust observed at many volcanic margins composite models that include both small scale convection and a small increase to mantle potential temperature predict large pulses in initial magmatism and generation of 17 to 21 km thick crust followed by unstable production of thinner igneous crust the results indicate that models with small scale convection and no temperature anomaly may play a role in explaining the formation of volcanic margins with only moderately thick 11 15 km igneous crust further convection coupled with small increases to mantle temperature may be important during the initial phase of very thick igneous crust generation at some volcanic margins predicted distributions of igneous crust are moderately sensitive to asymmetric rifting of the lithosphere prior to breakup igneous crust accretion is asymmetric subsequent to breakup symmetry in the thermal structure of the upwelling sublithospheric mantle is the dominant control on the final distribution of igneous crust

the continent ocean crustal transition across the southwest greenland margin this paper examines the complete crustal transition across the nonvolcanic southwest greenland continental margin of the labrador sea using wide angle and coincident vertical incidence seismic profiles six ocean bottom seismometers and a sonobuoy record p and s wave first and multiple arrivals from the crust and upper mantle which are analyzed by two dimensional dynamic ray tracing and one dimensional reflectivity modeling the resulting seismic velocity model requires that the preexisting 30 km thick continental crust is thinned abruptly to 3 km across the continental slope primarily by removal of the lower crust farther seaward the crust thickens to 6 km primarily through the addition of a high velocity 7 0 7 6 km s layer in the lower crust this lower crustal layer is 4 5 km thick extends for a horizontal distance of 80 km and is interpreted as partially serpentinized upper mantle it is overlain by a low velocity 4 0 5 0 km s upper layer which is interpreted as highly fractured upper continental crust our model suggests that seafloor spreading did not start until chrons 27 28 13 ma younger than previously suggested this interpretation is supported by two dimensional modeling of gravity and magnetic data along the refraction line our results are consistent with a simple shear mechanism for the initial rifting with the sw greenland margin as the upper plate however a full characterization of the rifting mechanism must await comparison with a seismic model for the conjugate margin east of labrador

seismic volcanostratigraphy of the norwegian margin constraints on tectonomagmatic break up processes voluminous volcanism characterized early tertiary continental break up on the mid norwegian continental margin the distribution of the associated extrusive rocks derived from seismic volcanostratigraphy and potential field data interpretation allows us to divide the more voring and lofoten vesteralen margins into five segments the central more margin and the northern voring margin show combinations of volcanic seismic facies units that are characteristic for typical rifted volcanic margins the lofoten vesteralen margin the southern voring margin and the area near the jan mayen fracture zone show volcanic seismic facies units that are related to small volume submarine volcanism the distribution of subaerial and submarine deposits indicates variations of subsidence along the margin vertical movements on the mid norwegian margin were primarily controlled by the amount of magmatic crustal thickening because both the amount of dynamic uplift by the icelandic mantle plume and the amount of subsidence due to crustal stretching were fairly constant along the margin thus subaerial deposits indicate a large amount of magmatic crustal thickening and an associated reduction in isostatic subsidence whereas submarine deposits indicate little magmatic thickening and earlier subsidence from the distribution of volcanic seismic facies units we infer two main reasons for the different amounts of crustal thickening 1 a general northward decrease of magmatism due to increasing distance from the hot spot and 2 subdued volcanism near the jan mayen fracture zone as a result of lateral lithospheric heat transport and cooling of the magmatic source region furthermore we interpret small lateral variations in the distribution of volcanic seismic facies units such as two sets of inner seaward dipping reflectors on the central voring margin as indications of crustal fragmentation

late quaternary high resolution biomarker and other sedimentary climate proxies in a northeast atlantic core we studied variations in terrigenous input and sea surface temperature over the last 208 ka using a multiproxy approach involving direct comparison of terrigenous and marine molecular biomarker foraminiferal abundance and other sedimentological data for the same horizons in a single northeast atlantic core core t88 9p 48 23 n 25 05 w 3193 m water depth 790 cm core length with a well resolved 18o stratigraphy the abundances of three land derived long chain compound classes the n alkanes c27 c29 and c31 the n alkanoic acids c24 c26 and c28 and the n alkanols c24 c26 and c28 show glacial interglacial related changes in the past 208 ka which generally parallel the weight percent noncarbonate the abundances of these three compound classes are higher in glacial than in interglacial sediments such changes are consistent with the expected higher dust inputs during glaciations as well as enhanced advection of particulate matter in current systems ice rafted debris heinrich events may also contribute to the terrigenous biomarker record the sea surface temperature sst signals derived from the alkenone unsaturation index uk 37 give an average sst during interglacial periods of 13 c which is about 3 4 c higher than the average glacial sst estimate the uk 37 derived sst values dropped markedly in some heinrich layers while sometimes leading the onset of the layer the percent neogloboquadrina pachyderma s which is another frequently used qualitative temperature proxy generally shows maxima coinciding with the layers our results show that most heinrich layers were produced during times of intensely cold waters in the eastern north atlantic they demonstrate that sufficient alkenones are present in the sediments for alkenone stratigraphy to be used as a tool for the assessment of short term variations in sea surface temperatures even in these oligotrophic north atlantic waters

assessment of sea surface temperature variations in the central north atlantic using the alkenone unsaturation index u37k abstract a high resolution record of u37k derived sst estimations has been obtained in a core from the central north atlantic ocean su90 08 43 30 n 30 24 w spanning a time period of 280 ky the general trend of the u37k profile parallels closely the 180 signal and represent an independent confirmation that the sst variations in the glacial interglacial time scales are correlated with the northern ice sheets evolution in contrast to the climap 1984 conclusions based on the foraminiferal transfer function technique the sst during the last interglacial period lip isotopic stage 5 5 are 2 3 c warmer than during the holocene this result is in good agreement with many studies based in coastal and continental records that strongly suggest warmer climatic conditions over north america and europe finally the sst estimates during the last glacial maximum lgm 18 ky bp where 4 5 c cooler than during the previous glacial period pgp stage 6 we argue that this difference is caused by a northward position of the polar front during the pgp in the central north atlantic

tectonostratigraphic evolution of the labrador margin atlantic canada abstract the labrador continental margin provides a rich source of data with which to study the relationships between stratigraphy tectonics and paleoenvironment we have completed a regional seismic interpretation and integrated this with new biostratigraphic data based on analyses of palynomorphs from wells in the hopedale and saglek basins which occur on this margin our results are summarized in a tectonostratigraphic chart which displays new and consistent age control for the major lithostratigraphic units and provides more precise evaluation of their depositional and paleoenvironmental history we have identified and dated six regional unconformities in the wells and we can recognize several others on the seismic data the older unconformities cretaceous are related to the tectonics of rifting and seafloor spreading and may delineate the onset of different stages of the rift process in the paleocene early eocene unconformity development was influenced by episodic volcanism due to the passage of the proto iceland hotspot to the north and to a major change in spreading direction in the labrador sea many of these unconformities are also identified in offshore southwest greenland and the grand banks suggesting widespread controlling mechanisms during the post seafloor spreading stage the effects of mass wasting and slumping and of paleoenvironmental controls on the stratigraphy were more pronounced we discuss the petroleum potential of the hopedale basin in terms of the structures we see on the seismic data and highlight the bjarni formation which likely contains the most prospective source and reservoir rocks in this basin

mantle thermal structure and active upwelling during continental breakup in the north atlantic seismic reflection and refraction data acquired on four transects spanning the southeast greenland rifted margin and greenland iceland ridge gir provide new constraints on mantle thermal structure and melting processes during continental breakup in the north atlantic maximum igneous crustal thickness varies along the margin from s 30 km in the near hotspot zone 6 500 km from the hotspot track to v18 km in the distal zone 500 1100 km magmatic productivity on summed conjugate margins of the north atlantic decreases through time from 1800 300 to 600 50 km 3 km ma in the near hotspot zone and from 700 200 to 300 50 km 3 km ma in the distal zone comparison of our data with the british faeroe margins shows that both symmetric and asymmetric conjugate volcanic rifted margins exist joint consideration of crustal thickness and mean crustal seismic velocity suggests that along margin changes in magmatism are principally controlled by variations in active upwelling rather than mantle temperature the thermal anomaly vt at breakup was modest v100 125 c varied little along the margin and transient data along the gir indicate that the potential temperature anomaly 125 50 c and upwelling ratio v4 times passive of the iceland hotspot have remained roughly constant since 56 ma our results are consistent with a plume impact model in which 1 a plume of radius v300 km and vt of v125 c impacted the margin around 61 ma and delivered warm material to distal portions of the margin 2 at breakup 56 ma the lower half of the plume head continued to feed actively upwelling mantle into the proximal portion of the margin and 3 by 45 ma both the remaining plume head and the distal warm layer were exhausted with excess magmatism thereafter largely confined to a narrow 6 200 km radius zone immediately above the iceland plume stem alternatively the warm upper mantle layer that fed excess magmatism in the distal portion of the margin may have been a pre existing thermal anomaly unrelated to the plume fl 2001 elsevier science b v all rights reserved