detachment faulting mantle serpentinization and serpentinite mud volcanism beneath the porcupine basin southwest of ireland the porcupine basin southwest of ireland provides an opportunity to study the symmetry of rifting at stretching factors approaching continental breakup profiles across the basin image a bright reflection that appears to represent a detachment fault and may in part be a decollement at the top of partially serpentinized mantle although overall the basin appears symmetric the consistent westward structural dip of the detachment implies that at high stretching factors extension was asymmetric farther south the porcupine median high appears in cross section to be a triangular construction overlying tilted fault blocks and onlapped by postrift sediment despite no evidence for synrift magmatism this high has previously been interpreted as a basaltic structure however it may represent a serpentinite mud volcano or diapir we suggest that such structures produce the serpentinite breccias found within the rifted continent ocean transition of nonvolcanic margins

the complex 3 d transition from continental crust to backarc magmatism and exhumed mantle in the central tyrrhenian basin geophysical data from the medoc experiment across the northern tyrrhenian backarc basin has mapped a failed rift during backarc extension of cratonic variscan lithosphere in contrast data across the central tyrrhenian have revealed the presence of magmatic accretion followed by mantle exhumation after continental breakup here we analyse the medoc transect e f which extends from sardinia to the campania margin at 40 5 n to define the distribution of geological domains in the transition from the complex central tyrrhenian to the extended continental crust of the northern tyrrhenian the crust and uppermost mantle structure along this 400 km long transect have been investigated based on wide angle seismic data gravity modelling and multichannel seismic reflection imaging the p wave tomographic model together with a p wave velocity derived density model and the multichannel seismic images reveal seven different domains along this transect in contrast to the simpler structure to the south and north the stretched continental crust under sardinia margin abuts the magmatic crust of cornaglia terrace where accretion likely occurred during backarc extension eastwards around secchi seamount a second segment of thinned continental crust 7 8 km is observed two short segments of magmatically modified continental crust are separated by the 5 km wide segment of the vavilov basin possibly made of exhumed mantle rocks the eastern segment of the 40 5 n transect e f is characterized by continental crust extending from mainland italy towards the campania margin ground truthing and prior geophysical information obtained north and south of transect e f was integrated in this study to map the spatial distribution of basement domains in the central tyrrhenian basin the northward transition of crustal domains depicts a complex 3 d structure represented by abrupt spatial changes of magmatic and non magmatic crustal domains these observations imply rapid variations of magmatic activity difficult to reconcile with current models of extension of continental lithosphere essentially 2 d over long distances

structure and breakup history of the rifted margin of west antarctica in relation to cretaceous separation from zealandia and bellingshausen plate motion 1 geophysical data acquired using r v polarstern constrain the structure and age of the rifted oceanic margin of west antarctica west of the antipodes fracture zone the 145 km wide continent ocean transition zone cotz of the marie byrd land sector resembles a typical magma poor margin new gravity and seismic reflection data indicates initial continental crust of thickness 24 km that was stretched 90 km farther east the bellingshausen sector is broad and complex with abundant evidence for volcanism the cotz is 670 km wide and the nature of crust within the cotz is uncertain margin extension is estimated to be 106 304 km in this sector seafloor magnetic anomalies adjacent to marie byrd land near the pahemo fracture zone indicate full spreading rate during c33 c31 80 68 myr of 60 mm yr 1 increasing to 74 mm yr 1 at c27 62 myr and then dropping to 22 mm yr 1 by c22 50 myr spreading rates were lower to the west extrapolation towards the continental margin indicates initial oceanic crust formation at around c34y 84 myr subsequent motion of the bellingshausen plate relative to antarctica 84 62 myr took place east of the antipodes fracture zone at rates 40 mm yr 1 typically 5 20 mm yr 1 the high extension rate of 30 60 mm yr 1 during initial margin formation is consistent with steep and symmetrical margin morphology but subsequent motion of the bellingshausen plate was slow and complex and modified rift morphology through migrating deformation and volcanic centers to create a broad and complex cotz

crustal thinning in the northern tyrrhenian rift insights from multichannel and wide angle seismic data across the basin extension of the continental lithosphere leads to the formation of rift basins or rifted continental margins if breakup occurs seismic investigations have repeatedly shown that conjugate margins have asymmetric tectonic structures and different amount of extension and crustal thinning here we compare two coincident wide angle and multichannel seismic profiles across the northern tyrrhenian rift system sampling crust that underwent different stages of extension from north to south and from the flanks to the basin center tomographic inversion reveals that the crust has thinned homogeneously from 24 km to 17 km between the corsica margin and the latium margin implying a factor of 1 3 1 5 on the transect 80 km to the south the crust thinned from 24 km beneath sardinia to a maximum of 11 km in the eastern region near the campania margin factor of 2 2 the increased crustal thinning is accompanied by a zone of reduced velocities in the upper crust that expands progressively toward the southeast we interpret that the velocity reduction is related to rock fracturing caused by a higher degree of brittle faulting as observed on multichannel seismic images locally basalt flows are imaged intruding sediment in this zone and heat flow values locally exceed 100 mw m2 velocities within the entire crust range 4 0 6 7 km s which are typical for continental rocks and indicate that significant rift related magmatic underplating may not be present the characteristics of the pre tectonic syn tectonic and post tectonic sedimentary units allow us to infer the spatial and temporal evolution of active rifting in the western part of the southern transect thick postrift sediments were deposited in half grabens that are bounded by large fault blocks fault spacing and block size diminish to the east as crustal thinning increases recent tectonic activity is expressed by faults cutting the seafloor in the east near the mainland of italy the two transects show the evolution from the less extended rift in the north with a fairly symmetric conjugate structure to the asymmetric margins farther south this structural evolution is consistent with w e rift propagation and southward increasing extension rates

early stage rifting of the northern tyrrhenian sea basin results from a combined wide angle and multichannel seismic study extension of the continental lithosphere leads to the formation of rift basins and ultimately may create passive continental margins the mechanisms that operate during the early stage of crustal extension are still intensely debated we present the results from coincident multichannel seismic and wide angle seismic profiles that transect across the northern tyrrhenian sea basin the profiles cross the corsica basin france to the latium margin italy where the early rift stage of the basin is well preserved we found two domains each with a distinct tectonic style heat flow and crustal thickness one domain is the corsica basin in the west that formed before the main rift phase of the northern tyrrhenian sea opening 8 4 ma the second domain is rifted continental crust characterized by tilted blocks and half graben structures in the central region and at the latium margin these two domains are separated by a deep 10 km sedimentary complex of the eastern portion of the corsica basin travel time tomography of wide angle seismic data reveals the crustal architecture and a subhorizontal 15 17 1 km deep moho discontinuity under the basin to estimate the amount of horizontal extension we have identified the pre syn and post tectonic sedimentary units and calculated the relative displacement of faults we found that major faults initiated at angles of 45 50 and that the rifted domain is horizontally stretched by a factor of 1 3 8 10 mm a the crust has been thinned from 24 to 17 km indicating a similar amount of extension 30 the transect represents one of the best imaged early rifts and implies that the formation of crustal scale detachments or long lived low angle normal faults is not a general feature that controls the rift initiation of continental crust other young rift basins like the gulf of corinth the suez rift or lake baikal display features resembling the northern tyrrhenian basin suggesting that half graben formations and distributed homogeneous crustal thinning are a common feature during rift initiation

seismic stratigraphic record of the amundsen sea embayment shelf from pre glacial to recent times evidence for a dynamic west antarctic ice sheet studies of the sedimentary architecture and characteristics of the antarctic continental margin provide clues about past ice sheet advance retreat cycles and help improve constraints for paleo ice dynamic models since early glacial periods a first seismostratigraphic analysis of the amundsen sea embayment shelf and slope of west antarctica reveals insights into the structural architecture of the continental margin and shows stages of sediment deposition erosion and transport reflecting the history from pre glacial times to early glaciation and to the late pleistocene glacial interglacial cycles the shelf geometry consists of a large pre and syn rift basin in the middle shelf region between basement cropping out on the inner shelf and buried basement ridge and highs on the outer shelf a subordinate basin within the large basin on the mid shelf may be associated with motion along an early west antarctic rift system branch at least 4 km of pre glacial strata have been eroded from the present inner shelf and coastal hinterland by glacial processes six major sedimentary units ass 1 to ass 6 separated by five major erosional unconformities ass u1 to ass u5 are distinguished from bottom to top unconformity ass u4 results from a major truncational event by glacial advance to the middle and outer shelf which was followed by several episodes of glacial advance and retreat as observed from smaller scale truncational unconformities within the units above ass u4 some of the eroded sediments were deposited as a progradional wedge that extends the outer shelf by 25 to 65 km oceanward of the pre glacial shelf break we compare the observed seismic characteristics with those of other antarctic shelf sequences and assign an early cretaceous age to bottom sedimentary unit ass 1 a late cretaceous to oligocene age to unit ass 2 an early to mid miocene age to unit ass 3 a mid miocene age to unit ass 4 a late miocene to early pliocene age to unit ass 5 and a pliocene to pleistocene age to the top unit ass 6 buried grounding zone wedges in the upper part of unit ass 5 on the outer shelf suggest pronounced warming phases and ice sheet retreats during the early pliocene as observed for the ross sea shelf and predicted by paleo ice sheet models our data also reveal that on the middle and outer shelf the flow path of the pine island thwaites paleo ice stream system has remained stationary in the central pine island trough since the earliest glacial advances which is different from the ross sea shelf where glacial troughs shifted more dynamically this study and its stratigraphic constraints will serve as a basis for future drilling operations required for an improved understanding of processes and mechanisms leading to change in the west antarctic ice sheet such as the contemporary thinning and grounding line retreat in the amundsen sea drainage sector

oligo miocene rift of sardinia and the early history of the western mediterranean basin the geodynamic evolution of the western mediterranean basin in spite of many studies is still uncertain there is some consensus for interpreting this basin as a kind of small oceanic marginal basin its opening has generally been related to a subduction process which was active during the oligocene miocene somewhere east of sardinia corsica1 7 as the margins of the basin are deeply buried below miocene to present sediments direct lithological and stratigraphical data which could explain the events responsible for its formation are rare8 10 or missing altogether to obtain such data detailed field studies have been undertaken in sardinia fig 1 and the first results are presented here this approach is justified by the fact that in that island oligocene and miocene sediments were deposited in a rift fossa tettonica sarda of verdabasso11 which is the easternmost arm of the complex rift system that affected the european plate during oligocene and miocene times one of these arms evolved towards a small oceanic basin the western mediterranean or algero provencal basin while others such as the gulf of valencia and the sardinia rift aborted and remained at the rift stage its exceptional exposures make it possible to examine the sardinia rift to clarify the sequence of events which created it and to establish a sedimentological model which we believe is directly applicable to the western mediterranean basin

seismic structure of the central tyrrhenian basin geophysical constraints on the nature of the main crustal domains in this work we investigate the crustal and tectonic structures of the central tyrrhenian back arc basin combining refraction and wide angle reflection seismic was gravity and multichannel seismic mcs reflection data acquired during the medoc mediterraneo occidental 2010 survey along a transect crossing the entire basin from sardinia to campania at 40 n the results presented include a 450 km long 2 d p wave velocity model obtained by the traveltime inversion of the was data a coincident density model and a mcs poststack time migrated profile we interpret three basement domains with different petrological affinity along the transect based on the comparison of velocity and velocity derived density models with existing compilations for continental crust oceanic crust and exhumed mantle the first domain includes the continental crust of sardinia and the conjugate campania margin in the sardinia margin extension has thinned the crust from 20 km under the coastline to 13 km 60 km seaward similarly the campania margin is also affected by strong extensional deformation the second domain under the cornaglia terrace and its conjugate campania terrace appears to be oceanic in nature however it shows differences with respect to the reference atlantic oceanic crust and agrees with that generated in back arc oceanic settings the velocities depth relationships and lack of moho reflections in seismic records of the third domain i e the magnaghi and vavilov basins support a basement fundamentally made of mantle rocks the large seamounts of the third domain e g vavilov are underlain by 10 20 km wide relatively low velocity anomalies interpreted as magmatic bodies locally intruding the mantle

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

extension discrepancy at north atlantic nonvolcanic rifted margins depth dependent stretching or unrecognized faulting rifted margins show an apparent discrepancy between the amount of extension measurable from faults and the amount of crustal or lithospheric thinning determined from wide angle data or subsidence this extension discrepancy has been interpreted in terms of depth dependent stretching in which the upper crust is extended and thinned far less than the rest of the lithosphere here i show that at those nonvolcanic margins where the velocity structure is well known the upper and lower crust appear to thin equally toward the margin implying that the discrepancy is not due to depth dependent stretching but more likely due to unrecognized polyphase and top basement faulting

deep crustal roots beneath the northern apennines inferred from teleseismic receiver functions abstract teleseismic waveforms recorded by a regional array crossing the northern italian peninsula and northern corsica are analyzed using the receiver function technique to determine the first order crustal structure the receiver function approach is used to isolate receiver side ps conversions generated at the crust mantle boundary and any major velocity discontinuity beneath the stations we used the time delay between the direct p wave and the ps wave converted at the moho discontinuity to infer crustal thickness beneath the stations the crust mantle boundary is estimated at 25 1 km of depth in northern corsica 20 2 km beneath the elba island and 20 to 24 2 km beneath tuscany in the eastern portion of the array moho depth increases from 28 2 km beneath the adriatic coast to 49 3 km beneath the apennine chain in a distance of about 100 km a double ps conversion produced beneath the val tiberina graben to the west of the apennines corresponds to interfaces as deep as 20 2 and 52 2 km this observation supports the hypothesis of partial overlapping between the shallow tuscan moho and the deeper adriatic moho the westward deepening of the adriatic moho beneath the northern apennines can be explained by lithosphere delamination that has dragged downward the adriatic lower crust the deep crustal root estimated beneath the northern apennines indicates that this portion of the chain is isostatically overcompensated

extent and dynamics of the west antarctic ice sheet on the outer continental shelf of pine island bay during the last glaciation abstract swath bathymetry and topas sub bottom profiler acoustic data reveal the presence of a major cross shelf bathymetric trough containing streamlined subglacial bedforms formed in soft till that extends to the continental shelf edge of outer pine island bay amundsen sea west antarctica the new data indicate that the west antarctic ice sheet wais extended to the shelf edge of pine island bay during the last glaciation and was drained by a grounded fast flowing palaeo ice stream through this outer shelf trough topography and subglacial geology are likely to have exerted a strong control on the development and location of palaeo ice streams in pine island bay topas records show that mega scale glacial lineations are formed in an acoustically transparent sediment layer interpreted to be soft till and are inferred to be the product of subglacial sediment deformation beneath the palaeo ice stream the flat to irregular nature of the basal reflector of the acoustically transparent layer of soft till implies that a combination of groove ploughing of the substrate and subglacial sediment deformation were important processes beneath the palaeo ice stream in the outer trough of pine island bay as well as palaeo ice streams elsewhere in antarctica therefore the formation of the soft till layer and possibly associated subglacial bedforms are likely to be a function of these palaeo ice stream processes in a regional context the wais extended to the continental shelf edge of the bellingshausen amundsen and ross seas and was drained by a number of palaeo ice streams during the last glaciation

evidence for extensional shear zones in the mantle offshore britain and their implications for the extension of the continental lithosphere deep seismic profiles recorded in the seas around the british isles have revealed bands of seismic reflections in the uppermost mantle on the basis of their appearance geophysical characteristics and association with major crustal faults these features are best interpreted as mantle shear zones furthermore in the north sea the mantle reflectors appear to follow an extensional trend and when interpreted as extensional shear zones help explain the regional stratigraphy of the overlying basin the crosscutting relationships between mantle reflections to the west of scotland and a major strike slip fault the great glen fault ggf suggest that the mantle structure postdates the ggf and hence is probably related to subsequent extension furthermore kinematic analysis of lithospheric deformation to the north of scotland is consistent with the structure observed on the seismic data if the flannan mantle reflection is an extensional shear zone reconstruction of the lithosphere prior to permian extension restores the flannan to the edge of the rockall trough a rift probably initiated in the carboniferous thus the flannan fault may have developed during carboniferous rifting it is concluded that most of the mantle reflections are some form of extensional shear zone in the mantle and the role of such structures during lithospheric extension is considered

uranium isotopes and dissolved organic carbon in loess permafrost modeling the age of ancient ice abstract the residence time of ice in permafrost is an indicator of past climate history and of the resilience and vulnerability of high latitude ecosystems to global change development of geochemical indicators of ground ice residence times in permafrost will advance understanding of the circumstances and evidence of permafrost formation preservation and thaw in response to climate warming and other disturbance we used uranium isotopes to evaluate the residence time of segregated ground ice from ice rich loess permafrost cores in central alaska activity ratios of 234 u vs 238 u 234 u 238 u in water from thawed core sections ranged between 1 163 and 1 904 due to contact of ice and associated liquid water with mineral surfaces over time measured 234 u 238 u values in ground ice showed an overall increase with depth in a series of five neighboring cores up to 21 m deep this is consistent with increasing residence time of ice with depth as a result of accumulation of loess over time as well as characteristic ice morphologies high segregated ice content and wedge ice all of which support an interpretation of syngenetic permafrost formation associated with loess deposition at the same time stratigraphic evidence indicates some past sediment redistribution and possibly shallow thaw among cores with local mixing of aged thaw waters using measures of surface area and a leaching experiment to determine u distribution a geometric model of 234 u 238 u evolution suggests mean ages of up to 200 ky bp in the deepest core with estimated uncertainties of up to an order of magnitude evidence of secondary coatings on loess grains with elevated 234 u 238 u values and u concentrations suggests that refinement of the geometric model to account for weathering processes is needed to reduce uncertainty we suggest that in this area of deep ice rich loess permafrost ice bodies have been preserved from the last glacial period 10 100 ky bp despite subsequent fluctuations in climate fire disturbance and vegetation radiocarbon 14 c analysis of dissolved organic carbon doc in thaw waters supports ages greater than 40 ky bp below 10 m doc concentrations in thaw waters increased with depth to maxima of 1000 ppm despite little change in ice content or cryostructures these relations suggest time dependent production of old doc that will be released upon permafrost thaw at a rate that is mediated by sediment transport among other factors

amount of extension on small faults an example from the viking graben extension estimates based on palinspastic restoration of only the largest faults in a deformed terrane may be significantly deficient due to neglect of small faults i e unsampled faults most of which have smaller displacements than do sampled faults small faults individually account for little extension but there may be large numbers of them the cumulative extension on small faults can be calculated from the fractal size distributions of fault displacements independent extension estimates support the inference from fault population statistics that small faults account for significant amounts of extension for example restorations of mesozoic faults interpreted from seismic reflection profiles across the viking graben in the north sea yield extension estimates that are only 40 75 of independent estimates the fractal size distribution of fault displacements in the viking graben is consistent with the hypothesis that the remaining 25 60 of extension resulted from displacements on small faults

deep structure of the north tyrrhenian sea from multi channel seismic profiles and on land wide angle reflection refraction seismic recording lisa cruise geodynamical implications we present a lithospheric section of the northern tyrrhenian basin based on principal observations along a transect from corsica island to tuscany margin offshore crustal structure observations come from the lisa deep seismic cruise composed by multi channel seismic profiles and wide angle reflection refraction seismic data other parts of the section are constrained by published data from different geophysical sources a great detachment between alpine corsica and hercynian corsica constitutes the base of the corsica basin the end of this detachment is probably located below the elba island in the ductile lower crust where we observed an east dipping reflector interpreted as ductile shear zone similar detachments have been observed beneath the punta ala basin on the tuscany margin our section shows a thin crust below corsican basin 15 km thick and a thicker crust below the pianosa ridge 25 km between elba island and the tuscany coast the moho reflections shallow to 23 km depth as identified on the mcs profiles and from the modelling of the wide angle reflection refraction seismic date an asthenospheric mantle uplift produces a significant heat flow below the tuscany margin the base of the lithosphere is located at 75 km depth below the corsica margin at 50 km below the corsica basin and as shallow as 30 km below the tuscany margin the shift observed between the corsica basin and the tuscany coast suggests an asymmetric lithospheric thinning which involves a detachment fault located at the base of the corsican basin

grounding line retreat of the west antarctic ice sheet from inner pine island bay ice loss from the marine based potentially unstable west antarctic ice sheet wais contributes to current sea level rise and may raise sea level by 3 3 m or even 5 m in the future over the past few decades glaciers draining the wais into the amundsen sea embayment ase have shown accelerated ice flow rapid thinning and fast retreat of the grounding line gl however the long term context of this ice loss is poorly constrained limiting our ability to accurately predict future wais behavior here we present a new chronology for wais retreat from the inner continental shelf of the eastern ase based on radiocarbon dates from three marine sediment cores the ages document a retreat of the gl to within 100 km of its modern position before ca 10 000 calibrated cal yr b p this early deglaciation is consistent with ages for gl retreat from the western ase our new data demonstrate that in contrast to the ross sea wais retreat from the ase shelf was largely complete by the start of the holocene our results further suggest either slow gl retreat from the inner ase shelf throughout the holocene or that any episodes of fast gl retreat must have been short lived thus today s rapid retreat may be exceptional during the holocene and may originate in recent changes in regional climate ocean circulation or ice sheet dynamics

cenozoic prograding sequences of the antarctic continental margin a record of glacio eustatic and tectonic events abstract sedimentary sections up to 6 14 km thick lie beneath many areas of the antarctic continental margin the upper parts of the sections contain up to 6 km of cenozoic glacial and possibly non glacial sequences that have prograded the continental shelf up to 85 km we describe the cenozoic sequences using two general categories based on their acoustic geometries type ia sequences which account for most prograding of the antarctic continental shelf have complex sigmoidal geometries and some acoustic characteristics atypical of low latitude margins such as troughs and mounds lying parallel and normal to the shelf edge and high velocities 2 0 2 6 km s for flat layers within 150 m of the seafloor type iia sequences which principally aggrade the paleoshelf lie beneath type ia sequences and have mostly simple geometries and gently dipping reflections the prograding sequences are commonly located near the seaward edges of major mesozoic and older margin structures relatively rapid cenozoic subsidence has occured due to the probable rifting in the ross sea thermal subsidence in the antarctic peninsula and isostatic crustal flexure in wilkes land in prydz bay and the weddell sea prograding sequences cover mesozoic basins that have undergone little apparent cenozoic tectonism grounded ice sheets are viewed by us and others as the principal mechanism for depositing the antarctic prograding sequences during the initial advance of grounded ice the continental shelf is flexurally overdeepened the inner shelf is heavily eroded and gently dipping glacial strata are deposited on the shelf i e type iia sequences the overdeepened shelf profile is preserved a during glacial times by grounded ice sheets episodically crossing the shelf eroding sediments from onshore and inner shelf areas and depositing sediments at the front of the ice sheet as outer shelf topset banks and continental slope foreset aprons i e type ia sequences and b during interglacial times like today by little or no clastic sedimentation on the continental shelf other than beneath retreated ice shelves lying far from the continental sheld edge ice streams carve broad depressions across the shelf and carry abundant basal sediments directly to the continental shelf edge thereby creating troughmouth fans and sheet like prograding sequences i e type ia sequences numerous acoustic unconformities and multiple overcompacted layers within the prograding sequences suggest major fluctuations of the antarctic ice sheet the available drilling and seismic interpretations provide the following history 1 cenozoic ice sheets have existed in places near the continental shelf since middle to late eocene time 2 a grounded antarctic ice sheet first expanded to the continental shelf edge with probable overdeepening of the outer shelf in late eucene to early oligocene time in prydz bay possibly in early miocene time in the ross sea and at least by middle miocene time in the weddell sea 3 the relative amounts of shelf prograding and inferred ice volume variations and related sea level changes have increased since middle to late miocene time in the eastern ross sea prydz bay and possibly weddell sea our analysis is preliminary further acoustic surveys and scientific drilling are needed to resolve the proximal antarctic record of glacio eustatic climatic and tectonic events recorded by the prograding sequences

deep seismic structure of the tonga subduction zone implications for mantle hydration tectonic erosion and arc magmatism we present the first detailed 2d seismic tomographic image of the trench outer rise fore and back arc of the tonga subduction zone the study area is located approximately 100 km north of the collision between the louisville hot spot track and the overriding indo australian plate where 80 ma old oceanic pacific plate subducts at the tonga trench in the outer rise region the upper oceanic plate is pervasively fractured and most likely hydrated as demonstrated by extensional bending related faults anomalously large horst and graben structures and a reduction of both crustal and mantle velocities the 2d velocity model presented shows uppermost mantle velocities of 7 3 km s 10 lower than typical for mantle peridotite 30 mantle serpentinization in the model tonga arc crust ranges between 7 and 20 km in thickness and velocities are typical of arc type igneous basement with uppermost and lowermost crustal velocities of 3 5 and 7 1 km s respectively beneath the inner trench slope however the presence of a low velocity zone 4 0 5 5 km s suggests that the outer fore arc is probably fluid saturated metamorphosed and disaggregated by fracturing as a consequence of frontal and basal erosion tectonic erosion has most likely been accelerated by the subduction of the louisville ridge causing crustal thinning and subsidence of the outer fore arc extension in the outer fore arc is evidenced by 1 trenchward dipping normal faults and 2 the presence of a giant scarp 2 km offset and several hundred kilometers long indicating gravitational collapse of the outermost fore arc block in addition the contact between the subducting slab and the overriding arc crust is only 20 km wide and the mantle wedge is characterized by low velocities of 7 5 km s suggesting upper mantle serpentinization or the presence of melts frozen in the mantle

soil movements on permafrost slopes near fairbanks alaska many north facing slopes in the yukon tanana uplands of alaska show signs of downhill movements in the form of hummocky surface and leaning trees measurements of movements and pore pressures were made at several sites in the caribou poker creek research watershed it was found that on slopes with inclinations near 30 most of the movements occurred immediately after thaw when pore pressures were high to evaluate the slope stability the soil strength was measured by direct shear tests the strength of the moss layer and tree roots was evaluated by performing tension tests on the roots and the moss root complex results of stability analyses show that local failures involving individual wedges are likely the displacements associated with a wedge slide would result in a hummock or step the strength of the moss root complex was found to be a significant factor in the stability of the wedge and of the step key words moss roots permafrost pore pressure shear strength slope stability thaw

history of subduction and back arc extension in the central mediterranean summary geological and geophysical constraints to reconstruct the evolution of the central mediterranean subduction zone are presented geological observations such as upper plate stratigraphy hp lt metamorphic assemblages foredeep trench stratigraphy arc volcanism and the back arc extension process are used to define the infant stage of the subduction zone and its latest back arc phase based on this data set the time dependence of the amount of subducted material in comparison with the tomographic images of the upper mantle along two cross sections from the northern apennines and from calabria to the gulf of lyon can be derived further the reconstruction is used to unravel the main evolutionary trends of the subduction process results of this analysis indicate that 1 subduction in the central mediterranean is as old as 80 myr 2 the slab descended slowly into the mantle during the first 20 30 myr subduction speeds were probably less than 1 cm year x1 3 subduction accelerated afterwards producing arc volcanism and back arc extension and 4 the slab reached the 660 km transition zone after 60 70 myr this time dependent scenario where a slow initiation is followed by a roughly exponential increase in the subduction speed can be modelled by equating the viscous dissipation per unit length due to the bending of oceanic lithosphere to the rate of change of potential energy by slab pull finally the third stage is controlled by the interaction between the slab and the 660 km transition zone in the southern region this results in an important re shaping of the slab and intermittent pulses of back arc extension in the northern region the decrease in the trench retreat can be explained by the entrance of light continental material at the trench

the zuccale fault elba island italy a new perspective from fault architecture the zuccale fault central eastern elba island has been regarded since the 1990s as a low angle normal fault that records neogene crustal extension in the inner tyrrhenian side portion of the northern apennines the flat lying attitude of the fault zone and the strong excision of thick nappes were the main reasons for this interpretation previous structural and petrographic studies have focused primarily on the fault rocks themselves without map scale investigation of the structural setting and deformation structures in the hanging wall and footwall blocks furthermore despite the complex history proposed for the zuccale fault the timing of deformation has not yet been constrained by radiometric age data we present the findings of recent geological studies on eastern elba island that provide significant new insight on the nature and tectonic significance of the zuccale fault we document in detail the architecture of breccias and cataclasites that comprise the zuccale fault our new observations are consistent with a purely brittle deformation zone that crosscuts older early middle and late miocene regional and local tectonic structures the activity on the fault postdates emplacement of the late miocene porto azzurro pluton and it displaces a previously formed nappe stack 6 km eastward without any footwall exhumation or hanging wall block rotation these new data raise questions about the development of misoriented faults in the upper crust

ice flow of the antarctic ice sheet we present a reference comprehensive high resolution digital mosaic of ice motion in antarctica assembled from multiple satellite interferometric synthetic aperture radar data acquired during the international polar year 2007 to 2009 the data reveal widespread patterned enhanced flow with tributary glaciers reaching hundreds to thousands of kilometers inland over the entire continent this view of ice sheet motion emphasizes the importance of basal slip dominated tributary flow over deformation dominated ice sheet flow redefines our understanding of ice sheet dynamics and has far reaching implications for the reconstruction and prediction of ice sheet evolution

retreat history of the ross ice sheet shelf since the last glacial maximum from deep basin sediment cores around ross island abstract radiocarbon dated sediment cores from deep basins beneath the mcmurdo ice shelf and seasonally open water north of ross island mcmurdo sound display a characteristic succession of sedimentary facies that document the retreat of the ross ice sheet at the last glacial maximum to its present ice shelf configuration the facies succession records a transition from a nearly grounded ice sheet to open marine environments north of ross island that comprises in ascending stratigraphic order 1 slightly consolidated clast rich muddy diamict dominated by basement clasts from the transantarctic mountains and interpreted as melt out from the basal layer debris proximal to a retreating grounding zone 2 sparsely fossiliferous reworked diatom frustules and non bioturbated mud lacking lonestones interpreted as a sub ice shelf facies and 3 diatom mud and diatom ooze indicative of open marine conditions with evidence of iceberg rafting the succession in the open marine lewis basin north of ross island is similar though the diamict is much sandier and sedimentation rates 1 2 orders of magnitude higher we present a radiocarbon chronology from total organic carbon which implies that lift off of grounded ice in the 900 m deep marine basins surrounding ross island occurred by 10 100 14c years bp following lift off an ice shelf was maintained to the north of ross island until 8900 14c years bp we identify a phase of accelerated retreat at that time between the drygalski trough and ross island immediately preceding the timing of meltwater pulse 1b at 8900 14c years bp the calving line became pinned to ross island significantly decoupling from the grounding line and marking the transition from a retreating ice sheet to the development of the present ice shelf

deglacial history of the west antarctic ice sheet in the western amundsen sea embayment abstract the amundsen sea embayment ase drains approximately 35 of the west antarctic ice sheet wais and is one of the most rapidly changing parts of the cryosphere in order to predict future ice sheet behaviour modellers require long term records of ice sheet melting to constrain and build confidence in their simulations here we present detailed marine geological and radiocarbon data along three palaeo ice stream tributary troughs in the western ase to establish vital information on the timing of deglaciation of the wais since the last glacial maximum lgm we have undertaken multi proxy analyses of the cores core description shear strength x radiographs magnetic susceptibility wet bulk density total organic carbon nitrogen carbonate content and clay mineral analyses in order to 1 characterise the sedimentological facies and depositional environments and 2 identify the horizon s in each core that would yield the most reliable age for deglaciation in accordance with previous studies we identify three key facies which offer the most reliable stratigraphies for dating deglaciation by recording the transition from a grounded ice sheet to open marine environments these facies are i subglacial ii proximal grounding line and iii seasonal open marine in addition we incorporate ages from other facies e g glaciomarine diamictons deposited at some distance from the grounding line such as glaciogenic debris flows and iceberg rafted diamictons and turbates into our deglacial model in total we have dated 78 samples mainly the acid insoluble organic aio fraction but also calcareous foraminifers which include 63 downcore and 15 surface samples through careful sample selection prior to dating we have established a robust deglacial chronology for this sector of the wais our data show that deglaciation of the western ase was probably underway as early as 22 351 calibrated years before present cal yr bp reaching the mid shelf by 13 837 cal yr bp and the inner shelf to within c 10 12 km of the present ice shelf front between 12 618 and 10 072 cal yr bp the deglacial steps in the western ase broadly coincide with the rapid rises in sea level associated with global meltwater pulses 1a and 1b although given the potential dating uncertainty additional more precise ages are required before these findings can be fully substantiated finally we show that the rate of ice sheet retreat increased across the deep up to1600 m basins of the inner shelf highlighting the importance of reverse slope and pinning points in accelerated phases of deglaciation

sequential faulting explains the asymmetry and extension discrepancy of conjugate margins rifted continental margins are the sites that record the thinning and break up of continents to form new oceans cesar ranero and marta perez gussinye use seismic imaging to accurately measure fault extension at the conjugate west iberia and newfoundland margins and compare this to crustal thinning they use these observations to create a balanced kinematic model of rifting that resolves the extension discrepancy in which crustal thinning appears to be greater than the extension caused by brittle faulting by producing both fault controlled crustal thinning which progresses from a rift basin to the asymmetric structure and extreme thinning of conjugate rifted margins these authors use seismic imaging to accurately measure fault extension at the conjugate west iberia and newfoundland margins and compare this with crustal thinning they use these observations to create a balanced kinematic model of rifting that resolves the extension discrepancy where crustal thinning seems to be greater than the extension caused by brittle faulting during early extension cold continental lithosphere thins and subsides creating rift basins if extension continues to final break up the split and greatly thinned plates subside deep below sea level to form a conjugate pair of rifted margins although basins and margins are ubiquitous structures the deformation processes leading from moderately extended basins to highly stretched margins are unclear as studies consistently report that crustal thinning is greater than extension caused by brittle faulting1 2 3 4 this extension discrepancy might arise from differential stretching of brittle and ductile crustal layers2 but that does not readily explain the typical asymmetric structure of conjugate margins5 6 in cross section one margin displays gradual thinning accompanied by large faults and the conjugate margin displays abrupt thinning but smaller scale faulting5 whole crust detachments active from early in the rifting could in theory create both thinning and asymmetry1 but are mechanically problematical furthermore the extension discrepancy occurs at both conjugate margins leading to the apparent contradiction that both seem to be upper plates to a detachment fault7 8 alternative models propose that much brittle extension is undetected because of seismic imaging limitations caused either by subseismic resolution faulting9 invisible deformation along top basement 100 km scale detachments8 or the structural complexity of cross cutting arrays of faults3 here we use depth migrated seismic images to accurately measure fault extension and compare it with crustal thinning the observations are used to create a balanced kinematic model of rifting that resolves the extension discrepancy by producing both fault controlled crustal thinning which progresses from a rift basin to the asymmetric structure and extreme thinning of conjugate rifted margins contrary to current wisdom the observations support the idea that thinning is to a first degree explained by simple andersonian faulting that is unambiguously visible in seismic data

neogene evolution of the southwestern tyrrhenian sea sardinia basin and western bathyal plain abstract the reprocessing of mcs reflection lines and sampling data across the sw tyrrhenian basin from the sardinia tunisia strait sts to the orosei canyon line ocl show that the acoustic basement of the area is made by variscan crystalline metamorphic rocks covered by a thick sequence of sediments including the messinian interval the pre messinian sequence can be subdivided into three seismic intervals or subunits largely calibrated by sampling data the oldest pre messinian subunit is strongly deformed by compressional and or transpressional structures and the recovered samples are deep water arkosic sediments aquitanian in age however the whole interval may encompass a wider time span probably from late oligocene to langhian this subunit was laid down in a fore arc basin located between a volcanic arc sardinia and an accretionary wedge calabrian peloritanian kabilide or ck units prior to the collision of the latter elements with the continental margin of africa in sicily and tunisia along the so called drepano thrust front dtf coeval to collision the generation of the main sardinia thrust mst occurred carrying the sardinia basement rocks over the ck units and deforming the fore arc basin sediments the intermediate pre messinian sedimentary subunit spans from part of serravallian to part of tortonian it is post tectonic with respect to the underlying subunit but it represents a pre rift succession if related to the overlying one it consists of terrigenous deposits prograding from sardinia to the ene into a basin some hundreds of meters deep which was left in the area after collision the youngest pre evaporitic subunit late tortonian early messinian in age displays wedge shaped reflectors in the sardinia basin and forms the lower portion of a syn rift complex including the messinian and part of the pliocene sediments this succession records the onset of extensional tectonics in the area as also testified by the tortonian age of exumation of the basement while in the tyrrhenian basin north of the ocl intra tortonian to intra pliocene rifting was strong but discontinuous and migrating with time to the east in the sw tyrrhenian basin in contrast rifting was less severe but continuous during the same time interval this emphasizes the role played by the ocl a inherited mesozoic discontinuity reactivated as a transfer zone during the neogene these new data allow correlation of the main miocene deformational events observed in the study area to those of the adjacent emerged areas namely the peloritani and maghrebian units in sicily prior to the pliocene quaternary full development of the southern tyrrhenian sea

topographic and ecologic controls on root reinforcement shallow landslides are a significant hazard in steep soil mantled landscapes during intense rainfall events the distribution of shallow landslides is controlled by variations in landscape gradient the frictional and cohesive properties of soil and roots and the subsurface hydrologic response while gradients can be estimated from digital elevation models information on soil and root properties remains sparse we investigated whether geomorphically controlled variations in ecology affect the spatial distribution of root cohesion by measuring the distribution and tensile strength of roots from soil pits dug downslope of 15 native trees in the southern appalachian mountains north carolina united states root tensile strengths from different hardwood tree species were similar and consistently higher than the only native shrub species measured rhododendron maximum roots were stronger in trees found on noses areas of divergent topography relative to those in hollows unchanneled convergent topography coincident with the variability in cellulose content this cellulose variability is likely related to topographic differences in soil water potential for all species roots were concentrated close to the soil surface with roots in hollows being more evenly distributed in the soil column than those on noses trees located on noses had higher mean root cohesion than those in hollows because of a higher root tensile force r maximum had the shallowest weakest roots suggesting that recent expansion of this species due to fire suppression has likely lowered the root cohesion of some hollows quantification of this feedback between physiologic controls on root growth and slope hydrology has allowed us to create a curvature based model of root cohesion that is a significant improvement on current models that assume a spatially averaged value

mechanisms of extension at nonvolcanic margins evidence from the galicia interior basin west of iberia 1 we have studied a nonvolcanic margin the west iberia margin to understand how the mechanisms of thinning evolve with increasing extension we present a coincident prestack depth migrated seismic section and a wide angle profile across a mesozoic abandoned rift the galicia interior basin gib the data show that the basin is asymmetric with major faults dipping to the east the velocity structure at both basin flanks is different suggesting that the basin formed along a paleozoic terrain boundary the ratios of upper to lower crustal thickness and tectonic structure are used to infer the mechanisms of extension at the rift flanks stretching factor 2 the ratio is fairly constant indicating that stretching of upper and lower crust was uniform toward the center of the basin 3 5 5 5 fault block size decreases as the crust thins and faults reach progressively deeper crustal levels indicating a switch from ductile to brittle behavior of the lower crust at 3 5 faults exhume lower crustal rocks to shallow levels creating an excess of lower crust within their footwalls we infer that initially extension occurred by large scale uniform pure shear but as extension increased it switched to simple shear along deep penetrating faults as most of the crust was brittle the predominant brittle deformation might have driven small scale flow 40 km of the deepest crust to accommodate fault offsets resulting in a smooth moho topography the gib might provide a type example of nonvolcanic rifting of cold and thin crust

basement control on past ice sheet dynamics in the amundsen sea embayment west antarctica abstract the development of landscapes and morphologies follows initially the tectonic displacement structures of the basement and sediments such fault zones or lineaments are often exploited by surface erosional processes and play therefore an important role in reconstructing past ice sheet dynamics observations of bathymetric features of the continental shelf of the amundsen sea embayment and identification of tectonic lineaments from geophysical mapping indicate that the erosional processes of paleo ice stream flows across the continental shelf followed primarily such lineaments inherited from the tectonic history since the cretaceous break up between new zealand and west antarctica three major ice flow trends correspond to different tectonic phases in east west northwest southeast and north south directions east west oriented basement trends correlate with coastline trends and overlay tectonic lineaments caused by former rift activities directional trends with northwest southeast orientation are observed for the glacial troughs of the western embayment outer shelf the western pine island bay coastal zones and the inner pine island glacial trough and are associated with a distributed southern plate boundary zone of the former bellingshausen plate the north south trend of the main pine island glacial trough and the north northeast trend of the abbot ice shelf trough on the outer shelf follow the predicted lineation trend of an eastern branch of the west antarctic rift system extending from the thwaites drainage basin northward into pine island bay an understanding of this context helps better constrain the geometries and sea bed substrate conditions for regional paleo ice sheet models

splitting a continent insights from submarine high resolution mapping of the moresby seamount detachment offshore papua new guinea the moresby seamount detachment in the woodlark basin east of papua new guinea is arguably the best exposed active detachment fault in the world we present the results of a high resolution autonomous underwater vehicle survey of bathymetry bottom water temperature and turbidity in combination with dredging and existing drillhole data a synthesis of the tectonic geomorphology kinematics and mechanics of the detachment is provided the detachment surface which has a 30 northward dip and 8 km post pliocene displacement is well preserved two major smooth areas are tectonically created and megascopic kilometer scale slickensides indicate downdip direction of movement the detachment is transected by a major sinistral strike slip fault suggesting deformation partitioning in the detachment zone in response to the 500 k y change in plate kinematics the mainly gabbroic protoliths and cataclasites from the fault show pervasive syntectonic alteration leading to large increases in abundance of quartz and more important calcite resulting quartz rich and calcite rich mylonites play a crucial role as weak fault rocks and ductile microstructures point to detachment operation at low differential stress a kilometer sized anomaly in bottom water temperature and turbidity is found at the downdip end of the detachment zone indicating that it hosts an active hydrothermal system probably fed by overpressured fluids from a deep crustal source

finite extension and low angle normal faulting andersonian theory for infinitesimal strains predicts that normal faults will form at high angles to the surface in extensional terranes in contrast low angle normal faults are sometimes observed on which tens of kilometers of slip has occurred and moderate angle faults with slip of 5 to 15 km are common a simple extension of the theory to account for the stresses required to drive finite deformation shows that low angles are preferred for large extension on individual faults the formation of low angle faults may require inhomogeneities in stress or material properties but once slip begins on a low angle fault it is likely to continue whereas slip on high angle faults is likely to end after modest slip to be replaced by the formation of new high angle faults

distribution of glacial geomorphic features on the antarctic continental shelf and correlation with substrate implications for ice behavior surveys were conducted seaward of all the major drainage outlets of the antarctic ice sheet from the pennell coast north victoria land to marguerite bay antarctic peninsula the results show that the ice sheet extended onto the outer shelf glacial troughs occur offshore of all major glacial outlets where the substrate is crystalline bedrock ice flow tended to follow the structural grain of the bedrock deposited little sediment and eroded the underlying bedrock where ice flowed over relatively soft more easily eroded sedimentary strata the direction of ice flow was more directly offshore and depositional features characterize the sea floor in these areas the signature of the grounded ice consists of till deposits and large scale geomorphic features drumlins occur within the region of contact between crystalline and sedimentary substrates the different geological substrates are interpreted to have exerted a fundamental control on the behavior of past ice sheets the troughs in the areas of bedrock composed of sedimentary substrate are interpreted to have been occupied by relatively fast flowing ice ice streams and the troughs in the areas of crystalline substrate are interpreted to have been occupied by slower moving ice the area between these two zones was characterized by ice acceleration and is marked by drumlins

continental rifting and initial sea floor spreading in the woodlark basin our understanding of the processes by which continents rift and sea floor spreading initiates is derived primarily from studies either of old passive margins and oceanic crust or of young regions of intra continental extension where spreading has not yet started it has been thought that continental rifting ceases when sea floor spreading begins1 2 that oceanic fracture zones develop from transfer or transform faults within continental rifts3 4 and that linear magnetic anomalies correlate with the onset of sea floor spreading during times of magnetic reversals5 6 here we present a marine geophysical survey of one of the few active examples of continental rifting and spreading initiation the western woodlark basin papuan peninsula region of new guinea which shows that in detail these assumptions do not hold the data confirm models of the rifting to spreading transition that invoke both ridge propagation and nucleation of discrete spreading cells7 10 and provide an unambiguous example of a spreading centre reorienting by synchronous jumping rather than propagation

polyphase faulting during the development of the west galicia rifted margin rifted margins are commonly characterised by an extension discrepancy the amount of extension measurable from the observed faulting is far less than that required to explain the crustal thinning it is shown here that polyphase faulting may provide a simple explanation for this paradox but can be very hard to recognise on seismic sections however at the west galicia rifted margin the galicia interior basin between the galicia bank and the mainland and the deep galicia margin to the west of the galicia bank a combination of high quality depth images seismic velocity information and stratigraphic control through odp drilling and submersible sampling provide complementary evidence for polyphase faulting berriasian hauterivian rifting in the galicia interior basin occurred along two sets of faults the first unroofed deep crustal rocks evidenced by high seismic velocities close to top basement the second cut and dismembered these early faults further rifting up until the aptian then focussed west of the galicia bank where two further phases of faulting can be inferred from the diachronous nature of seismostratigraphic units tilted within fault blocks removal of the latest phase of faulting aligns discontinuous reflections within the fault blocks into an anastomosing network of earlier faults restoration along these brings the crust back to its early hauterivian state similar to the present structure of the interior basin

antarctic and southern ocean influences on late pliocene global cooling the influence of antarctica and the southern ocean on late pliocene global climate reconstructions has remained ambiguous due to a lack of well dated antarctic proximal paleoenvironmental records here we present ice sheet sea surface temperature and sea ice reconstructions from the andrill and 1b sediment core recovered from beneath the ross ice shelf we provide evidence for a major expansion of an ice sheet in the ross sea that began at 3 3 ma followed by a coastal sea surface temperature cooling of 2 5 c a stepwise expansion of sea ice and polynya style deep mixing in the ross sea between 3 3 and 2 5 ma the intensification of antarctic cooling resulted in strengthened westerly winds and invigorated ocean circulation the associated northward migration of southern ocean fronts has been linked with reduced atlantic meridional overturning circulation by restricting surface water connectivity between the ocean basins with implications for heat transport to the high latitudes of the north atlantic while our results do not exclude low latitude mechanisms as drivers for pliocene cooling they indicate an additional role played by southern high latitude cooling during development of the bipolar world

ice sheet retreat dynamics inferred from glacial morphology of the central pine island bay trough west antarctica abstract pine island glacier drains portions of the west antarctic ice sheet into the amundsen sea during the last glacial maximum the glacier extended nearly 500 km from its present location onto the outer continental shelf unusually restricted sea ice cover during the austral summer of 2010 allowed for a systematic multibeam swath bathymetric and chirp sonar survey of the mid shelf section of pine island trough the mapped glacial landforms reveal new information about the paleo pine island ice stream s dynamic retreat from the mid shelf area and confirm previous suggestion of a retreat in distinct steps the periods of grounding line stability during the overall retreat phase are marked by sediment accumulations i e grounding zone wedges these wedges are here mapped in sufficient detail to characterize spatial dimensions and estimate the volume of deposited sediment considering a range of sediment flux rates from the paleo pine island ice stream we estimate that the largest and most clearly defined grounding zone wedge located at about 73 s in the surveyed area took between 600 and 2000 years to form the ice stream retreated landward of this wedge before 12 3 cal ka bp the swath bathymetric imagery of landforms in pine island trough includes glacial features that suggest that retreat between periods of grounding line stability may be associated with episodes of ice shelf break up the depths of grounding line wedges decrease in a landward direction from 740 to 670 m and record elevation of the grounding line as it stepped landward in all the grounding line elevation varied by only 80 m over a distance of just over 100 km implying a low ice sheet profile during retreat finally we revisited seismic reflection profile nb9902 acquired along pine island trough in 1999 in combination with the newly acquired swath bathymetric imagery from 2010 together these data show that the ice stream paused during its retreat to form grounding zone wedges at an area in central pine island trough where a high in dipping bedrock strata exists and the glacial trough is narrow forming a bathymetric bottle neck

deciphering tectonic phases of the amundsen sea embayment shelf west antarctica from a magnetic anomaly grid abstract the amundsen sea embayment ase with pine island bay pib in the eastern embayment is a key location to understanding tectonic processes of the pacific margin of west antarctica pib has for a long time been suggested to contain the crustal boundary between the thurston island block and the marie byrd land block plate tectonic reconstructions have shown that the initial rifting and breakup of new zealand from west antarctica occurred between chatham rise and the eastern marie byrd land at the ase recent concepts have discussed the possibility of pib being the site of one of the eastern branches of the west antarctic rift system wars about 30 000 km of aeromagnetic data collected opportunistically by ship based helicopter flights and tracks of ship borne magnetics were recorded over the ase shelf during two rv polarstern expeditions in 2006 and 2010 grid processing euler deconvolution and 2d modelling were applied for the analysis of magnetic anomaly patterns identification of structural lineaments and characterisation of magnetic source bodies the grid clearly outlines the boundary zone between the inner shelf with outcropping basement rocks and the sedimentary basins of the middle to outer shelf distinct zones of anomaly patterns and lineaments can be associated with at least three tectonic phases from 1 magmatic emplacement zones of cretaceous rifting and breakup 100 85 ma to 2 a southern distributed plate boundary zone of the bellingshausen plate 80 61 ma and 3 activities of the wars indicated by nne ssw trending lineaments 55 30 ma the analysis and interpretation are also used for constraining the directions of some of the flow paths of past grounded ice streams across the shelf

geothermal structure of the tyrrhenian sea over 200 heat flow measurements have been carried out in the tyrrhenian sea mostly since 1977 as part of the heat flow map for italy and surrounding seas italian program as well as part of the french italian tyrrhenia program all data have been corrected for the influence of the plio quaternary sedimentation measured heat flow values were evaluated according to the sedimentary environment following criteria outlined by sclater et al 1980 in this way areas affected mainly by shallow thermal effects in the zones with maximum density of data have been displayed filtering out these shallow contributions the major regional geothermal trends were obtained the tyrrhenian basin can be divided in two distinct regions with different geothermal characteristics the northern part of the basin appears to be connected with the continental structures involved in the interaction between the corsica and tuscan margins the maximum heat flow area located offshore civitavecchia is related to the tensile structures of the tuscan geothermal province the most important thermal features of the central and southern part are located along the central belt trending nw se the lowest heat flow values are located in the peri tyrrhenian areas and are related to the continental margins of the basin while the maxima are connected with the stretched and thinned area localized in the bathyal plain taking into account the heat flow data as well as other geological and geophysical information an evolutionary model for the tyrrhenian sea is presented suggesting a generalized stretching of an initially continental crust accompanied by intensive rifting phases which may have favoured the onset of oceanic type crust

active tectonics of the adriatic region from gps and earthquake slip vectors 1 to investigate the kinematics of the adriatic region we integrate continuous and episodic gps measurements with mw 4 5 earthquake slip vectors selected from the regional centroid moment tensor catalogue coherent motion of gps sites in the po valley in apulia and in the hyblean plateau allows us to estimate geodetically constrained angular velocities for these regions the predictions of the gps inferred angular velocities are compared with the earthquake slip vectors showing that the seismically expressed deformation at the microplate boundaries is consistent with the observed geodetic motion the remarkable consistency between geodetic seismological and geological evidence of active tectonics suggests that active deformation in the central adriatic is controlled by the relative motion between the adria and apulia microplates the microplates angular rotation rates are then compared with the rotation rates calculated with a simple block model supporting the hypotheses 1 that apulia forms a single microplate with the ionian sea and possibly with the hyblean region and 2 that adria and apulia rotate in such a way as to accommodate the eurasia nubia relative motion we suggest that the present day microplate configuration follows a recent fragmentation of the adriatic promontory that during the neogene rigidly transferred the africa motion to the orogenic belts that now surround the adriatic region

uniform sense normal simple shear of the continental lithosphere geophysical studies suggest that the thin crust characteristic of the basin and range province extends eastward beneath the west margin of the colorado plateau and rocky mountain regions in arizona and utah zones perhaps over 100 km wide may be defined bounded on the west by the east limit of upper crustal normal faults that account for more that 10 extension and on the east by the east limit of thinning beneath the colorado plateau a discrepancy exists within these zones between the negligible extension measurable in the upper crust and the substantial extension apparent from crustal thinning assuming the discrepant zone crust was as thick as or thicker than the colorado plateau rocky mountain crust prior to extensional tectonism if various theories appealing to crustal erosion are dismissed mass balance problems evident in the discrepant zones are most easily resolved by down to the east normal simple shear of the crust moving lower and middle crustal rocks that initially were within the zones up and to the west to where they now are locally exposed in the basin and range province west of the discrepant zones in both arizona and utah east directed extensional allochthons with large displacement are exposed these geophysical and geological observations complement one another if it is accepted that the entire crust in both arizona and utah failed during extension on gently east dipping east directed low angle normal faults and shear zones over a region several hundred kilometres wide large scale uniform sense normal simple shear of the crust suggests the entire lithosphere may do the same such a hypothesis predicts major lithospheric thinning without crustal thinning will occur in plateau areas in the direction of crustal shear in the case of the arizona utah and red sea extensional systems and possibly the death valley extensional terrain a broad topographic arch typically 1500 2000 m higher than the extended terrain is present suggesting lithospheric thinning in areas predicted by the hypothesis

extreme crustal thinning in the south porcupine basin and the nature of the porcupine median high implications for the formation of non volcanic rifted margins the southern porcupine basin is characterized by axial stretching factors that are greater than six and typical of rifted margins as such the basin can be regarded as a natural laboratory to investigate the evolution and symmetry of rifting leading towards continental separation and breakup a bright reflection here named p cuts down to the west from the base of the sedimentary section is overlain by small fault blocks and appears to represent a detachment fault p may in part follow the top of partially serpentinized mantle this interpretation is consistent with gravity modelling and with numerical models of crustal embrittlement and mantle serpentinization during extension furthermore p closely resembles the s reflection west of iberia where such serpentinites are well documented although overall the basin remains symmetrical the consistent westward structural dip of the detachment implies that at high stretching factors extension became asymmetric farther south the porcupine median high appearing lens shaped in cross section overlies the tilted fault blocks and is onlapped by postrift sediment despite no evidence for synrift magmatism this high has previously been interpreted as a basaltic structure however it develops above the line of intersection of the crust mantle boundary with the p detachment and hence may be related to the spatial limit of serpentinization the median high may represent a serpentinite mud volcano or diapir we suggest that such structures produce the serpentinite breccias found within the rifted continent ocean transition of nonvolcanic margins

geometry and development of glacial continental margin depositional systems in the bellingshausen sea we present multi channel seismic mcs reflection profiles and bathymetry data acquired across a remote and poorly surveyed part of the antarctic continental margin in the bellingshausen and amundsen seas this new information has been combined with published data and used to interpret the style of sedimentation on the continental shelf slope and rise and to describe sedimentation processes which have been active in this region most seismic reflection profiles crossing the continental margin show prograded sequences beneath the outer shelf and upper slope and we infer that the stratal characteristics of these sequences indicate that grounded ice sheets reached the shelf edge during previous glacial times although there are general similarities in stratal geometry on these profiles in detail they reveal significant longitudinal variations in sediment input from the shelf to the upper slope on several profiles we found evidence of mass wasting of the continental slope in the form of slump and debris flow deposits at greater depth turbidity flows bottom currents and coriolis force have controlled the further transportation and deposition of sediment which has resulted in the development of mounds channels and sediment wave fields the distribution and variations in the size and geometry of the mounds reflect sediment input and the relative contribution of these other factors which control sedimentation on the continental rise

glaciomarine sedimentation dynamics of the abbot glacial trough of the amundsen sea embayment shelf west antarctica sedimentary sequences of the continental shelf of the eastern amundsen sea embayment in west antarctica represent records of past outlet glaciers and ice streams the former flow of ice streams was channelled through glacial troughs which now form large bathymetric depressions we therefore selected one of the largest troughs the abbot glacial trough in the outer shelf to analyse its glacial depositional and erosional history based on horizon stratigraphy derived from seismic data several basement highs channellized the delivery of sediment and controlled the grounded ice sheet in early glacial periods both pre glacial and full glacial seismic facies were identified glacially transported and deposited sediments extended the shelf break by 75 km from the pre glacial shelf edge the main abbot glacial trough contains sediment from confluent ice flows of the pine island thwaites cosgrove and abbot glacier systems as well as smaller contributions from local ice streams emanating from thurston island sherman island of peacock sound played an important role in the dynamics of the abbot glacier by dividing the ice flow into two ice streams which interfered with the main glacial sediment transport paths from the south this study contributes to an understanding of the formation of the amundsen sea shelf and the extent of past ice sheet advances

evidence for abundant subglacial meltwater beneath the paleo ice sheet in pine island bay antarctica marine geological and geophysical data collected from the continental shelf in pine island bay antarctica reveal a complex paleo subglacial drainage system controlled by bedrock topography and subglacial meltwater discharge significant amounts of freely flowing meltwater existed beneath former ice sheets in pine island bay subglacial drainage is characterized by descriptions of glacial landforms imaged on the sea floor and sedimentary deposits collected in piston cores bedrock geology is characterized using seismic data large scale landforms on the shelf include channels and cavities incised into impermeable crystalline bedrock there is a transition from randomly oriented channels on the inner shelf to a dendritic pattern of elongate channels on the middle shelf on the outer shelf a change in basal conditions occurs where sedimentary deposits bury crystalline bedrock no evidence for flowing meltwater exists on sedimentary substrates instead meltwater formed a the ice sediment contact was incorporated into the sediments contributing to development of a deforming lied which was sampled in piston cores characterization of subglacial meltwater processes that occurred in the past may aid in understanding the role meltwater plays in stability of the west antarctic ice sheet today

odp leg 107 in the tyrrhenian sea insights into passive margin and back arc basin evolution leg 107 of the ocean drilling program drilled a west northwest east southeast transect of seven sites across the tyrrhenian sea the youngest of the sub basins of the mediterranean sea sites 654 653 652 and 656 document the rifting and subsidence of the sardinia passive continental margin on the upper margin site 654 we cored a classic transgressive sequence subaerial conglomerates overlain by oyster bearing sands overlain by marine marl comparison between the recovered lithologies and seismic reflection profiles suggests that the synrift sediments on the upper margin are tortonian late miocene to messinian latest miocene in age whereas synrift sediments on the lower margin are messinian to pliocene in age during the messinian desiccation of the mediterranean sites 654 and 653 now on the upper sardinian margin apparently occupied a basinal setting where they received nannoplankton bearing clays interbedded with laminated gypsum sites 656 and 652 now on the lower sardinia margin were apparently higher standing during the desiccation event their messinian facies are subaerial and lacustrine respectively we infer from these lines of evidence that tilting and subsidence occurred more than a million years earlier on the upper margin than on the lower margin such diachroneity can be interpreted in terms of migration of the zone of maximum extension above a rolling back subduction zone or in terms of extension of continental crust by shear along a deep detachment fault sites 655 651 and 650 were drilled into two small basalt floored basins of the central and eastern tyrrhenian emplacement of basaltic crust in the central tyrrhenian vavilov basin apparently began more than a million years before emplacement of basaltic crust in the eastern tyrrhenian marsili basin this observation is compatible with previous suggestions that the tyrrhenian has grown southeastward in response to rollback of the down going slab that currently dips northwestward under the toe of italy at the easternmost site high vesicularity of the basalt and benthic foram assemblages in the oldest sediments imply that the basalt erupted in water shallower than 2 500 m it has apparently subsequently subsided to its present depth of 4 100 m below sea level nearly three times as fast as normal subsidence of crust formed at a mid ocean ridge

the variability of root cohesion as an influence on shallow landslide susceptibility in the oregon coast range decades of quantitative measurement indicate that roots can mechanically reinforce shallow soils in forested landscapes forests however have variations in vegetation species and age which can dominate the local stability of landslide initiation sites to assess the influence of this variability on root cohesion we examined scarps of landslides triggered during large storms in february and november of 1996 in the oregon coast range and hand dug soil pits on stable ground at 41 sites we estimated the cohesive reinforcement to soil due to roots by determining the tensile strength species depth orientation relative health and the density of roots 1 mm in diameter within a measured soil area we found that median lateral root cohesion ranges from 6 8 23 2 kpa in industrial forests with significant understory and deciduous vegetation to 25 6 94 3 kpa in natural forests dominated by coniferous vegetation lateral root cohesion in clearcuts is uniformly 10 kpa some 100 year old industrial forests have s

the miocene of pianosa island key to understanding the opening of the northern tyrrhenian back arc basin central mediterranean the only place where neogene quaternary rocks crop out for the entire tuscan archipelago in the northern tyrrhenian sea is the island of pianosa in particular the miocene deposits record the depositional and tectonic evolution of the northern tyrrhenian region during this time period these deposits are subdivided into two successions separated by a low angle unconformity the older middle burdigalian succession represents a calciturbidite shallow marine system whereas the younger late tortonian early messinian succession comprises a continental alluvial system that evolves upwards into a lagoonal marginal marine environment here we present sedimentological palaeontological and petrographical data that support a new stratigraphic and palaeogeographical framework for reconstructing the opening of the northern tyrrhenian back arc basin the early miocene succession records a pre rift marine depositional phase followed by a late burdigalian langhian erosional phase this was followed by a period of synrift continental marginal deposition as recorded by the late miocene succession terminated by an important phase of uplift probably induced by the start of magmatic activity in the tuscan archipelago area

oligocene development of the west antarctic ice sheet recorded in eastern ross sea strata seismic reflection data from the easternmost ross sea image buried scour and fill troughs and flat topped ridges interpreted as having formed by glacial erosion and deposition during the oligo cene the nnw sse orientation of the troughs and lack of similar oligocene glacial features within the central ross sea suggests that the ice issued from the highlands of marie byrd land located 100 km away and that portions of the west antarctic ice sheet formed earlier than previously accepted existing global climate models gcms do not produce west antarctic ice caps for the oligocene in part due to low elevations modeled for that time evidence for oligocene ice beyond the paleocoast suggests a higher elevation for the early cenozoic marie byrd land and ross embayment than at present

neogene and quaternary rollback evolution of the tyrrhenian sea the apennines and the sicilian maghrebides reconstruction of the evolution of the tyrrhenian sea shows that the major stage of rifting associated with the opening of this basin began at similar to10 ma it involved two episodes of back arc extension which were induced by the rollback of a west dipping subducting slab the first period of extension 10 6 ma was prominent in the northern tyrrhenian sea and in the western part of the southern tyrrhenian sea the second period of extension mainly affected the southern tyrrhenian sea began in the latest messinian 6 5 ma and has been accompanied by subduction rollback at rates of 60 100 km myr 1 slab reconstruction combined with paleomagnetic and paleogeographic constraints indicates that in the central apennines the latest messinian 6 5 ma arrival of a carbonate platform at the subduction zone impeded subduction and initiated a slab tear and major strike slip faults these processes resulted in the formation of a narrow subducting slab beneath the ionian sea that has undergone faster subduction rollback and induced extreme rates of back arc extension

late oligocene to recent episodes of magmatism in and around the tyrrhenian sea implications for the processes of opening in a young inter arc basin of intra orogenic mediterranean type abstract five episodes of magmatic activity as deduced from geochronological data affected the tyrrhenian and peri tyr rhenian areas from the late oligocene 32 ma to recent times the episodes of w e migration of magmatism from the islands of sardinia and corsica to the eolian islands and the roman comagmatic region of central italy are related to the anti clockwise drift movements of the apenninic chain and clockwise drifting of the sicilian part of the maghrebian chain magmatic activity in the tyrrhenian sea initiated in late miocene times 8 5 6 5 ma in concomitance with a significant change of the geodynamic regime from compressional to tensional the tyrrhenian bathyal plain was affected by two episodes of spreading the first episode occurred around 7 ma and the second from about 1 9 to 1 3 ma these spreading events apparently developed during times of magmatic quiescence in the peri tyrrhenian areas two subsequent episodes of volcanism of the seamount type occurred in the bathyal plain one from 5 to 1 8 and the other from 1 3 to recent they are contemporaneously with extensive manifestations in the peri tyrrhenian areas the different types of magmatism of the late miocene back arc spreading in the central bathyal plain and acidic manifestations of intra crustal anatectic origin in the northern continental platform and slope i e islands of capraia elba and montecristo and seamount vercelli are possibly related to movements of upwelling of the astenosphere which in the southern tyrrhenian sea developed with a much stronger intensity timing of the volcanism in relationship with the overall structural evolution through time in the basin and neighbouring lands is considered

three dimensional moho topography in italy new constraints from receiver functions and controlled source seismology in complex tectonics regions seismological geophysical and geodynamic modeling require accurate definition of the moho geometry various active and passive seismic experiments performed in the central mediterranean region revealed local information on the moho depth in some cases used to produce interpolated maps in this paper we present a new and original map of the 3 d moho geometry obtained by integrating selected high quality controlled source seismic and teleseismic receiver function data the very small cell size makes the retrieved model suitable for detailed regional studies crustal corrections in teleseismic tomography advanced 3 d ray tracing in regional earthquake location and local earthquake tomography our results show the geometry of three different moho interfaces the european adriatic ionian and tyrrhenian the three distinct moho are fashioned following the alpine and apennines subduction collision and back arc spreading and show medium to high frequency topographic undulations reflecting the complexity of the geodynamic evolution

normal fault growth displacement localisation and the evolution of normal fault populations the hammam faraun fault block suez rift egypt abstract fault segment linkage migration of the locus of fault activity and displacement localisation were important processes controlling the late oligocene recent evolution of the normal fault population of the hammam faraun fault block suez rift initial fault activity was distributed across the fault block on fault segments that had attained their final length within 1 2 my of rifting these initial segments then either grew by increasing displacement and linked to form longer segmented fault zones or died during a rift initiation phase that lasted 6 8 my following this rift initiation phase displacement became localised onto 25 km long border fault zones bounding the fault block and many of the early high displacement intra block fault zones died following displacement localisation onto the major faults bounding the fault block the locus of maximum displacement continued to migrate with post middle miocene displacement focused on the western margin of the fault block this migration of fault activity between major crustal scale normal faults can be viewed in terms of strain localisation at the rift scale the results from this study question conventional fault growth models based on final displacement distributions and highlight the sequential nature of faulting on major normal faults bounding domino style tilted fault blocks

reconstruction of the west antarctic ice sheet in pine island bay during the last glacial maximum and its subsequent retreat history abstract marine geological and geophysical studies were conducted to determine the late quaternary glacial history of the west antarctic ice sheet in pine island bay antarctica the data set includes sea floor imagery in the form of multibeam swath bathymetry and deep tow side scan sonar surveys distribution of sedimentary deposits and basal surface conditions are revealed through intermediate resolution seismic data and chirp 3 5 khz sub bottom profiles sedimentary deposits were sampled with piston cores and calcareous material was dated using ams radiocarbon techniques results from the study indicate the ice sheet was grounded on the outer shelf during its maximum extent sometime in the past thick ice flowing slowly and resting on crystalline bedrock was influenced by significant amounts of subglacial meltwater on the inner shelf thinner but more rapidly flowing ice characterized the seaward extent of the ice sheet which was grounded on a sedimentary substrate deglaciation occurred in two phases beginning soon after the last glacial maximum the outer most extension of the ice sheet retreated gradually pausing on a bathymetric high on the middle shelf by 16 000 14c years ago between 16 000 and 12 000 14c years ago ice sheet retreat resumed and may have proceeded rapidly to reach a present day position by 10 000 14c years ago

asymmetric rifts due to asymmetric mohos an experimental approach large scale asymmetries in structures and in the uplift width and volcanism of pairs of conjugate passive margins have been documented in various parts of the world these asymmetries reflect the dominant mode of extension preceding the break up of the continental lithosphere of the many parameters involved the pre rift crustal structure has been shown to play a fundamental role in controlling the process of continental rifting in this work we have used analogue models to show how initial asymmetric moho configurations are prone to produce asymmetric rifting with prominent asymmetries in the amount of extension accommodated by boundary faults in the patterns of lithospheric thinning asthenospheric upwelling and in the trajectories of magma migration after continental break up these deformative patterns are expected to lead to the development of a pair of asymmetric passive margins with one narrow strongly volcanic margin and a wider less volcanic or with areas of concentrated volcanic activity counterpart

antarctic topography at the eocene oligocene boundary we present a reconstruction of the antarctic topography at the eocene oligocene ca 34 ma climate transition this provides a realistic key boundary condition for modeling the first big antarctic ice sheets at this time instead of using the present day bedrock topography which has changed significantly from millions of years of tectonism and erosion we reconstruct topography using a set of tools including ice sheet erosion models models of thermal subsidence and plate movement erosion estimates are constrained with offshore sediment volumes estimated from seismic stratigraphy maximum and minimum topographic reconstructions are presented as indicators of the range of uncertainty our results point to a significant upland area in the ross sea marie byrd land and weddell sea sectors in addition east antarctic coastal troughs are much shallower than today due to the restoration of material that has been selectively eroded by the evolving ice sheets parts of east antarctica have not changed since the e o boundary because they were protected under non erosive cold based ice the reconstructions provide a better defined boundary condition for modeling that seeks to understand interaction between the antarctic ice sheet and climate along with more robust estimates of past ice volumes under a range of orbital settings and greenhouse gas concentrations

tectonics dynamics and plio pleistocene magmatism in the central tyrrhenian sea insights from the submarine transitional basalts of the ventotene volcanic ridge pontine islands italy