structural outline of a tertiary basement cored uplift inversion structure in western spitsbergen svalbard kinematics and controlling factors the tertiary fold and thrust belt of spitsbergen can be divided into a western basement involved fold thrust stack and a central eastern foreland fold and thrust belt in western nordenskiold land the first order structure is an ene verging basement cored fold and fault complex involving paleozoic to tertiary strata the northern part reveals an upright monocline geometry of east tilted sedimentary cover units with associated layer parallel to low angle thrusts and folds these structures consist of two populations oriented both parallel to nnw sse and oblique to wnw ese the general structural trend of the fold complex in the central and southern parts of west nordenskiold land the fold complex involves tilted basement cut by steep transverse faults and late normal faults the east limb of the fold complex displays repeated basement and paleozoic strata orustdalen formation in its core and mesozoic triassic strata influenced by map scale chevron folds and two decollement levels all located above an eastward rotated major detachment fault the kleivdalen thrust establishing fold fault relations includes a three stage structural history in the fold complex as follows 1 a phase of early nne ssw shortening associated with wnw ese folds and thrusts and 2 a dominant ene wsw basement involved shortening leading to the first order nnw sse striking fold complex followed by 3 approximately e w extension the resulting structures and structural variability along strike as well as across strike appear to have been controlled by basement and carboniferous basin structures underlying the permian cretaceous platform strata restored stratigraphic sections based on thrust repetition of basement and cover e g within a type section of the carboniferous orustdalen formation support such an interpretation a tentative inversion tectonic model reproduces the position s of local and major thrust ramps and associated folds as a result of inheritance from carboniferous basin structures

evolution of the central tertiary basin of spitsbergen towards a synthesis of sediment and plate tectonic history abstract the central tertiary basin of spitsbergen developed east of a strike slip boundary between the eurasian and greenland plates in response to the initiation of rifting and later seafloor spreading in the norwegian greenland sea using a new plate model for the opening of the north atlantic we attempt to relate the sediment history of the central tertiary basin to its plate tectonic framework and suggest a basin development in four phases the central tertiary basin was formed in the early paleocene during a right lateral strike slip phase after the plate boundary between greenland and svalbard had jumped eastward to the hornsund fault zone phase 1 the onset of seafloor spreading between greenland and eurasia and a drastic counterclockwise change in spreading direction between greenland and north america after chron 25 late paleocene induced compression dominated transpression between greenland and svalbard until chron 24 lower eocene phase 2 the first sedimentary evidence for tectonic uplift along the strike slip zone is found in a wedge shaped delta fan in the northwestern part of the basin strike slip dominated transpression prevailed from chron 24 to chron 21 lower middle eocene contemporaneous with successive basin narrowing and an eastward migration of the depocenter phase 3 after chron 21 lower middle eocene the relative motion between greenland and svalbard first changed to strike slip terminating the transpressional phase and then to transtension after chron 13 lower oligocene phase 4

precise p and s wave velocity structures in the kitakami massif northern honshu japan from a seismic refraction experiment the kitakami massif which is located in the eastern part of northern honshu japan is composed of two geological units the northern kitakami terrane is characterized as a jurassic accretionary complex while the southern kitakami terrane consists of pre silurian basement and silurian lower cretaceous marine sediments the boundary region of these two units called the hayachine tectonic belt htb is composed of mafic to ultramafic rocks the kitakami massif experienced intense granitic intrusions in the cretaceous we present a detailed crustal structure model for the eastern part of the massif derived from an extensive seismic refraction experiment conducted on a 194 km n s line the uppermost crust is covered with a very thin 0 5 1 km surface layer with a velocity of 3 1 5 4 km s the velocity structure below this layer shows remarkable lateral variation in the northern kitakami terrane the p wave velocity and vp vs at the top of the basement are 5 85 5 95 km s and 1 68 1 70 respectively the seismic attenuation in this region is high qp 150 200 and qs 70 100 in contrast the uppermost crust in the southern kitakami terrane is characterized by a high p wave velocity 6 05 6 15 km s and vp vs 1 74 1 77 the qp and qs also show high values of 300 400 and 150 200 respectively such a structural difference persists to 14 to 16 km depth at which the p wave velocity increases to 6 45 km s the low velocity and high attenuation in the northern kitakami terrane represent a highly deformed structure of the accretionary complex the high p wave velocity and vp vs in the southern kitakami terrane indicate the relatively mafic crustal composition which may result from the fragment of the oceanic crust incorporated by the accretion process or the uplifting in the latest jurassic early cretaceous a midcrustal interface determined from wide angle reflections shows an abrupt southward depth decrease from 25 to 20 km under the htb the p wave velocity and vp vs between 14 and 16 km depth and the midcrustal interface are 6 45 6 55 km s and 1 74 1 78 respectively the moho depth under the northern kitakami terrane decreases southward from 34 to 32 km in the southern kitakami terrane the moho dips slightly southward the p wave velocity and the vp vs ratio in the lower crust are 6 9 7 0 km s and 1 75 1 76 respectively the p wave velocity in the uppermost mantle is not well resolved but is probably less than 7 7 km s the s wave velocity derived from relatively clear sn is 4 35 4 40 km s our results show that the htb is a prominent structural boundary extending to the moho the crust of kitakami massif was not homogenized by the cretaceous granitic intrusions and the original structural difference remains in the upper crust

dating of late paleozoic rifting events in the north atlantic new biostratigraphic data from the uppermost devonian and carboniferous of east greenland the uppermost devonian and carboniferous sedimentary rocks in east greenland include eight spore pollen assemblages of early tournaisian tn1 to mid visean v3 and westphalian age the recognition of these assemblages provides the first firmly established biostratigraphic scheme of these sedimentary rocks and dates the earliest phase of late paleozoic extensional tectonics in east greenland as pre tournaisian the latest rift pulse of the paleozoic started in the westphalian and new half graben systems continued to develop along the basin margins until autunian time this new age information suggests that late paleozoic rifting events were synchronous in the entire north atlantic arctic region

deep seismic crustal structure beneath the bonin trough abstract the bonin trough and the bonin ridge are located in the fore arc region of the southern bonin arc system such a conspicuous trough ridge formation along an arc cannot be recognized in other trench island arc systems the southern bonin arc is characterized by other several unique geological and geophysical features the tectonics controlling their formation and evolution has attracted interest of many earth scientists but has not been understood well in 1987 we made a seismic refraction experiment across the bonin trough to clarify the structure of the crust and the upper mantle of this area which has not been known well to date high quality seismic data of airgun shooting and of explosive sources were acquired by ocean bottom seismograph and hydrophone obsh systems a detailed seismic velocity structure model was obtained by modeling of the observed travel times and amplitudes using a two dimensional ray tracing technique the structure is considerably variable across the bonin trough especially in the sedimentary layers in spite of its flat sea floor topography thinning of the upper crust is recognized in the trough suggesting that the bonin trough was formed by rifting of the island arc crust uplifting of the crust and the uppermost mantle beneath the bonin ridge is required in our structure model the depth to the moho boundary decreases from 18 km beneath the shichito ridge to 14 km beneath the bonin ridge this is in good agreement with the crustal structure expected from large positive gravity anomaly observed over the bonin ridge

backarc rifting constructional volcanism and nascent disorganised spreading in the southern havre trough backarc rifts sw pacific high resolution multibeam em300 and seabeam data of the southern havre trough sht combined with observations and sample collections from the submersible shinkai6500 and deep tow camera are used to develop a model for the evolution and magmatism of this backarc system the havre trough and the associated kermadec arc are the product of westward subduction at the pacific australian plate boundary detailed studies focus on newly discovered features including a seamount saito seamount and a deep graben ngatoroirangi rift 4000 m water depth floored with a constructional axial volcanic ridge 5 km in length and in excess of 200 m high both of which are characterised by pillow and lobate flows estimated at elongate volcanic ridges at 35 15 s and 34 30 s and backarc seamounts 35 30 s 178 30 e occur at the eastern margin of the sht similar seafloor morphology is observed in the central and western portions of the basin suggesting that recent volcanism may be broadly distributed across the backarc mass balance modelling indicates a maximum crustal thickness of 11 km to 4000 m spreading systems these discontinuous spreading systems are characterised by failed rifts rift segmentation and propagation successive episodes of magmatic intrusion into thinned faulted arc basement results in defocused asymmetrical accretion cross arc volcanic chains isolated volcanoes and underlying basement plateaus are interpreted to represent a cap of recent extrusives however they may also be composed entirely of newly accreted crust and the spatially extensive basement fabric of elongated volcanic ridges may be the surface expression of pervasive dike intrusion that has thoroughly penetrated and essentially replaced the original arc crust with newly accreted intrusives

present day stress orientations adjacent to active strike slip faults california and sumatra present day stress directions interpreted from well bore breakouts adjacent to two crastal scale active strike slip faults the san andreas fault in california and the great sumatran fault in sumatra indicate that the maximum horizontal stress direction sh is oriented at a high angle 70 90 to both faults the regionally defined stress fields spanning these faults show that adjacent young or actively growing folds have formed orthogonal to sh and are therefore in the thrust fault orientation these observations indicate a decoupling of the strike slip and compressional components of the deformation within these broadly transpressive zones borehole breakouts in 118 wells in western california indicate a regionally consistent stress pattern with sh generally oriented ne sw nearly perpendicular 80 90 to the strike of the san andreas fault the orientation of sh nearly perpendicular to the san andreas fault implies low shear stress on the fault and is consistent with geological interpretations of the coast and transverse ranges indicating active compressional deformation fault plane solutions for recent dip slip style earthquakes principal stress directions determined from inversion of earthquake focal mechanisms and induced hydraulic fracture orientations a stress trajectory map for western california is computed using an iterative statistical algorithm in which observed directional data such as breakout directions are used to obtain a model regional stress field analysis of well bore breakouts in 25 wells within the central and southern oil districts of sumatra indicates that the regionally defined sh adjacent to the active great sumatran strike slip fault is oriented at a high angle 70 80 to the fault this orientation of sh is consistent regionally with geologic stress indicators and focal mechanisms of dip slip earthquakes preliminary analysis of the stress field in the vicinity of the philippine and alpine faults suggests sh is also oriented at a high angle to these active strike slip faults similarly the minimum horizontal stress sh is oriented at a high angle to the the kane and dead sea transforms the observation of sh and sh in the vicinity of active strike slip faults being oriented nearly perpendicular and parallel to the faults suggests that large crustal scale strike slip faults may in general be inherently weak surfaces

linked thrust and strike slip faulting during late cretaceous terrane accretion in the san juan thrust system northwest cascades orogen washington the san juan thrust system makes up the western elements of the late cretaceous northwest cascades orogen of washington a stack of metamorphic nappes with terranes ranging in age from early paleozoic to middle cretaceous the tectonic development of the nappes is an unresolved issue important to understanding plate convergent processes operating in the north american cordillera in the creta ceous as well as at other times two terrane bounding fault zones were studied in this project the lopez and the rosario fault zones the fault zone rocks were affected by two cataclastic plastic late cretaceous deformational events d1 and d2 that included accretion and lateral motion during blueschist facies metamorphic conditions d1 produced upright folds and a subvertical axial planar s1 foliation fabric in the lopez fault zone and southwest vergent folds and gently northeast dipping axial planar s1 foliation in the rosario fault zone in the lopez fault zone d2 produced northwest striking and subvertical strike slip shear zones s2 with dominant sinistral displacements whereas in the rosario fault zone d2 generated low angle s2 shear zones and various slip crenulation fabrics formed by northwest directed thrust motion the d1 fabrics are inferred to be related to initiation of subduction related accretion of the nappes by orogen normal southwest northeast shortening and accretionary tectonics the subsequent d2 fabrics developed as temporally overlapping subduction related low angle thrusts in the rosario fault zone and high angle sinistral strike slip faults in the lopez fault zone in an overall transpressive setting due to oblique convergence this model suggests that the high angle lopez fault zone d2 was located above a gently northeast dipping thrust detachment s2 expressed by the rosario fault zone that allowed the accreted nappes to move parallel to the orogen the kinematic model cannot validate regional scale dextral terrane translation of the san juan thrust system as inferred by paleomagnetic data elsewhere in the western united states but addresses important tectonic processes caused by oblique subduction and changing plate conditions

crustal structure and seismicity of the havre trough at 26 s an ocean bottom seismographic obs experiment was carried out to investigate the present day tectonics at the northern end of the havre trough a backarc basin in the southwestern pacific hypocenter distribution shows no seismicity within 50 km of the obs array but two active regions outside the trough one is to the northeast of the array at a bathymetric high between the lau basin and havre trough the other is to the southeast of the array beneath the landward slope of the kermadec trench p wavespeed structure obtained from the refraction survey is characterized by a thinned island arc crust with a thickness of 9 10 km many volcanic intrusions shown in reflection profiles that support extension tectonics are covered by undisturbed sediments these suggest little present activity related to rifting and or spreading

from rifting to active spreading in the lau basin havre trough backarc system sw pacific locking unlocking induced by seamount chain subduction associated with pacific australia plate convergence the lau basin havre trough is an active back arc basin that has been opened since 5 5 ma by rifting and southward propagating oceanic spreading current back arc opening rates decrease from 159 mm yr 1 in the northern lau basin to 15 mm y 1 in the southern havre trough major tectonic changes occur at the transition between havre trough rifting and full oceanic spreading of the eastern lau spreading center elsc where the oblique to trench westward subducting louisville seamount chain lsc sweeps southwards along the tonga trench new swath bathymetry seismic reflection data and limited rock sampling in this area constrain a tectonic and kinematic back arc model that incorporates the effects of lsc subduction the elsc which extends southward to 24 55 s forms a deep rift valley propagating southward through older rifted arc basement present day seismicity and fresh and fractured pillow lavas at 23 42 s are consistent with rift valley neovolcanism conversely the northern havre trough has low seismicity and rifted volcanic basement ridges trending 25 45 oblique to the basin axis consistent with low levels of extensional tectonism and volcanism this latter structural fabric is interpreted as an early stage of rifting that is now locked due to compression on the arc exerted by lsc subduction while in the lau basin such effects have passed as the lsc swept along the tonga trench it is proposed that the lau havre back arc opening is controlled by tectonic constraints exerted at the limits of the system by the lsc subduction which determines the southward migration of the tonga arc pole of rotation and associated lau basin opening a discrete three stage back arc opening evolution is proposed comprising 1 an initial phase of back arc rifting along the whole length of the plate boundary beginning at 6 5 ma 2 a subsequent phase mostly present in the southern part of the back arc domain and still active in the havre trough of transpression and transtension starting at 4 ma in the north as the lsc starts to subduct and sweeps southward along the tonga trench and 3 a renewed opening phase in the northern segment of the back arc domain with rifting and spreading starting at 3 5 ma as subduction of the lsc along the northern tonga trench is progressively completed

model for late mesozoic early tertiary tectonics of coastal california and western mexico and speculations on the origin of the san andreas fault cretaceous and early tertiary arc and forearc rocks found along the coast in southern california and baja california have been shown by paleomagnetic measurements to have originated many hundreds or even several thousands of kilometers south of their current locations northward transport also is found in cretaceous batholithic rocks near the edge of the continent in washington and british columbia the consistency of this pattern suggests that slices of arc and forearc rock originating on the western edge of north america have been translated along the coast by strike slip faulting strike slip faults are shown to be an expected response to north oblique subduction of the farallon and or kula plates faulting and subduction probably were concurrent activities i e the arc and forearc grew and were displaced simultaneously because displacement was dominantly parallel to subduction related lithic belts arc and forearc rocks may have traveled large distances without producing either significant hiatuses in the rock record or conspicuous disruptions in the distribution of lithic belts subduction related strike slip faulting is shown to be favored by high angles of oblique convergence shallow dip of the subducting slab relatively easy slip on potential faults within the arc or forearc and the existence of a place for the moving sliver to go it is suggested that these conditions are not difficult to satisfy and that subduction related strike slip faulting may thus be a common feature of convergent orogens the location of the san andreas fault inboard from the continental margin may be attributable to localization of the pacific north american transform by a system of precollision subduction related faults

gully incision as a key factor in desertification in an arid environment the negev highlands israel abstract gully incision has been eroding the alluvial sediments and loess soils deposited and developed along the valleys in the arid and semiarid regions of israel this phenomenon is critical in the arid regions of the negev highlands where the agricultural fields the main floral biomass and the areas which have the highest grazing value are limited to narrow valleys filled with redeposited loessial sediments the headcut migration and gully development in the region were studied between 1990 and 2001 in three representative drainage basins zipporim revivim and sekher during flood events the runoff penetrates the alluvial cover of the valleys forming vertical headcuts which gradually retreat up the valley the runoff is channeled into narrow gullies preventing the floodwater from spreading over the whole width of the valley the change in irrigation efficiency along the valleys is reflected in a sharp estimated drop of 70 90 in the floral biomass causing the reduction of the range value by 83 99 during the monitoring time interval 1990 2001 the linear gully retreat in the study area ranged between 12 3 and 250 m an average rate of 1 12 22 7 m year 1 for each gully head the process is accompanied by erosion of soil which has high agricultural and range value the total soil losses in these sites ranged between 800 and 9000 m3 at an average rate of 81 818 m3 year 1 for each gully head which is equivalent to 121 1227 mg year 1 during the monitoring period approximately 0 11 0 87 ha of land lost its agricultural and range value in each basin under study at an average rate of 0 01 0 079 ha year 1 since the byzantine period 1400 bp approximately 6 5 ha which is 10 of the land that had high agricultural and range value in the zipporim valley lost its value due to gully erosion no recovery effects of the gully channels were found in the nearby region the soil erosion is generated by a long term natural dynamic change in the soil rock ratio evolving within the drainage basins through time since the termination of the last glacial phase the loessic sediments originally deposited within the drainage basins during the late pleistocene glacial stage are being removed under the present holocene climate in several erosion stages this ongoing phenomenon is causing degradation of soil and biomass and is severely reducing the agricultural and range potential of the region these parameters indicate that an ongoing process of desertification is active in the arid environment of the negev highlands and is advancing in proportion to the headcut retreat rates in the region the soil erosion and headcut retreat have been active in the negev highlands for the last few millennia if these processes continue in the future the negev highlands region will lose its agricultural potential within a few millennia however the fact that the ancient inhabitants of the region implemented successful long term land conservation techniques already 3000 years ago implies that a sustainable land management policy can be adapted to the negev highlands as well as to other semi arid regions in the middle east

continent ocean transition at the western barents sea svalbard continental margin the change in crustal type at the western barents sea svalbard margin takes place over a narrow zone related to primary rift and shear structures reflecting the stepwise opening of the greenland sea regionally the margin is composed of two large shear zones and a central rifted margin segment local transtension and transpression at the plate boundary caused the early cenozoic tectonism in svalbard and the western barents sea and might explain the prominent marginal gravity and velocity anomalies

the valu fa ridge the pattern of volcanic activity at a back arc spreading centre abstract the central valu fa ridge an active back arc spreading segment bounded by small overlapping spreading centres can be divided into three regions each 8 12 km long with distinct bathymetric morphological and magnetic characteristics these observations suggest that each region has a different volcanic history driven by variations in melt supply along axis two of the three regions are centred on small deviations of the ridge axis which appear to be the local foci of extrusion there appears to have been a recent re organisation of the magmatic supply to the ridge in the past the highest magmatic budget was at the southern end of the ridge but it has now switched to the northern end where it coincides with a small overlapping spreading centre this re organization may be associated with island are activity beneath the ridge a bright reflector which is interpreted as being from the roof of a magma chamber is laterally more continuous that the inferred volcanic segmentation this implies that mixing of magma within the chamber must be limited along strike the magmatic budget at various parts of the ridge inferred from axial morphology can be correlated with variations in the width and brightness of the reflector this correlation suggests that the size of the chamber is dynamic and changes in response to variations in supply from below or delivery upwards

the margin between senja and spitsbergen fracture zones implications from plate tectonics abstract analysis of multichannel seismic data from the continental margin off svalbard between the senja and spitsbergen fracture zones suggests that the transition between continental and oceanic crust is located at or close to the hornsund fault zone in the late paleocene early eoeene 57 m y the region between svalbard and northeast greenland was subjected to regional shear movements associated with a transform system between the young lofoten greenland basin and the arctic ocean approximately 50 m y ago the spreading axis migrated to the northeast creating a deep basin north of the greenland senja fracture zone forming the passive margin between bear island and 76 5 n north of 76 5 n the regional transform was maintained at the time of the main reorganization of relative plate motion 36 m y the northern margin evolved a continental fragment was possibly cut off from the svalbard margin forming a small microcontinent the microcontinent appears as the submarine ridge which has been associated with the hovgaard fracture zone it is suggested that the sediments west of the hornsund fault zone are not older than eocene in the south and mid oligocene in the north the position of the spreading axis has greatly influenced the margin sedimentation

along strike changes in fault array and rift basin geometry of the carboniferous billefjorden trough svalbard norway abstract the billefjorden fault zone bfz of svalbard norway is a long lived major tectonic lineament with significant influence on the structural style of the northwestern barents shelf the fault zone can be traced for around 2 300 km in an n s direction where it is made up of three major fault strands all dipping 50 70 to the east field and seismic data delineate gradual shifts in displacement between master faults northern odelfjellet balliolbreen and southern dronbreen faults and suggest that two c 20 km long 2 3 km wide relay zones exist along strike the western fault strand consistently has a pre carboniferous reverse character placing basement on top of devonian sedimentary units with a throw estimated at 10 km subsequent carboniferous extensional reactivation of segments of the bfz resulted in formation of the billefjorden trough with a rift basin showing a fairly consistent polarity for its length this suggests a profound control by the older devonian reverse faults on the extensional structural style the billefjorden trough extends for a minimum of 110 km along strike and is 20 30 km wide at the most a gentle north plunge of the basin axis in the south is mirrored by an opposite plunge in the north offering a depth thickness of around 2000 m in the central realm diminishing to 500 m in the south geometries of the trough suggest sedimentary response to fault growth with weak lithologies such as evaporites promoting fault monocline formation and associated lenticular basin geometries on the contrary wedged shaped fill geometries toward major faults is consistent with significant fault movement and growth sequences subsequent mild tertiary reactivation of fault segments of the bfz is suggested by local reverse faults and deep seated anticline syncline pairs

late cenozoic geomorphic evolution in response to inversion evidence from field and gpr studies in kim drainage basin western india abstract this study presents field and ground penetrating radar gpr data for understanding geomorphic evolution of the kim drainage basin in response to tectonic inversion of the narmada ankleshwar block of the cambay rift basin located on the western continental margin of india the narmada ankleshwar block underwent continuous sedimentation up to mio pliocene and subsequently was subjected to compressional inversion four geomorphic surfaces are recognised that formed in response to the varying degrees of tectonic activity related to phases of inversion these are the early pleistocene erosional surface epes late pleistocene depositional surface lpds early holocene erosional surface ehes and the late holocene depositional surface lhds the phases of increased tectonic activity relate to two erosional episodes while two depositional periods relate to waning tectonic activity or quiescent periods we show that the narmada ankleshwar block suffered inversion earlier than other parts of the cambay basin to the north of the nsf localisation of early inversion movements occurred in an area characterised by thinner crust and involved the development of new reverse faults and transformation of the nsf from a normal to a reverse fault gpr studies indicate the reverse nature of the various faults in the kim drainage basin and provide evidence of their late reactivation under compression the study demonstrates that the parts of a large sedimentary basin can undergo inversion at different times depending on the orientation of pre existing crustal discontinuities with respect to the controlling stress trajectories

tertiary tectonism and basin inversion of the st jonsfjorden region svalbard abstract deformed basement and cover rocks of the st jonsfjorden area further define the character of spitsbergen s tertiary fold and thrust belt three major thrusts comprise a folded ca n060 e directed foreland propagating thust stack with likely additional subsurface thrust faults the folded vegardbreen robertsonfjellet thrust is the most significant fault in the complex and re emerges in the core of a disrupted synclinal structure in triassic strata shortening across the area indicated from line length restoration is of the order of 13 km differences in stratigraphy between and within thrust sheets indicate the thrust stack initiated along the edge of a westward deepening carbonbiferous basin with a fault step margin and represents basin inversion early structures related to basin formation had a major control on later thrust sheet evolution and the complexity of inversion structures reflects the initial complexity of the basin geometry such basin inversion could characterize the length of the fold and thrust belt the st jonsfjorden structures are primarily contractional and together with areas farther southeast in the fold thrust belt indicate shortening took place perpendicular to the fold belt across much of the length of the evolving margin

tertiary or cretaceous age for spitsbergen s fold thrust belt on the barents shelf several publications propose that main phase fold thrust development on spitsbergen was late cretaceous and not tertiary as previously thought the question of timing is crucial to models for crustal response to transpressive plate motions involvement of tertiary strata in fold thrust structures the sedimentology of the tertiary basin strata and studies of paleo stress field evolution all indicate paleocene to eocene fold thrust development during opening of the norwegian greenland oceanic basin a regional angular unconformity of 1 between paleocene and early cretaceous strata is consistently disconformable to the eye and precludes any significant older deformation in the immediate area pre unconformity deformation was likely strike slip in character and concentrated in the west the proposal for late cretaceous fold thrust belt formation is inconsistent with the geology

oligocene to lower pliocene deposits of the norwegian continental shelf norwegian sea svalbard denmark and their relation to the uplift of fennoscandia a synthesis abstract this study provides the results of the first integrated study of oligocene pliocene basins around norway within the study area three main depocentres have been identified where sandy sediments accumulated throughout the oligocene to early pliocene period the depocentre in the norwegian danish basin received sediments from the southern scandes mountains with a general progradation from north to south during the studied period the depocentre in the basinal areas of the uk and norwegian sectors of the north sea north of 58 n received sediments from the scotland shetland area because of the sedimentary infilling there was a gradual shallowing of the northern north sea basin in the oligocene and miocene a smaller depocentre is identified offshore northern nordland between ranafjorden approximately 66 n and vesteralen approximately 68 n where the northern scandes mountains were the source of the oligocene to early pliocene sediments in other local depocentres along the west coast of norway sandy sedimentation occurred in only parts of the period shifts in local depocentres are indicative of changes in the paleogeography in the source areas in the barents sea and south to approximately 68 n the oligocene to early pliocene section is eroded except for distal fine grained and biogenic deposits along the western margin and on the oceanic crust this margin was undergoing deformation in a strike slip regime until the eocene oligocene transition the early oligocene sediments dated in the vestbakken volcanic province and the forlandssundet basin represent the termination of this strike slip regime the change in the plate tectonic regime at the eocene oligocene transition affected mainly the northern part of the study area and was followed by a quiet tectonic period until the middle miocene when large compressional dome and basin structures were formed in the norwegian sea the middle miocene event is correlated with a relative fall in sea level in the main depocentres in the north sea formation of a large delta in the viking graben frigg area and uplift of the north and south scandes domes in the norwegian danish basin the sorgenfrei tornquist zone was reactivated in the early miocene possibly causing a shift in the deltaic progradation towards the east a late pliocene relative rise in sea level resulted in low sedimentation rates in the main depositional areas until the onset of glaciations at about 2 7 ma when the scandes mountains were strongly eroded and became a major source of sediments for the norwegian shelf whilst the frigg delta prograded farther to the northeast

deep crustal structure off akita eastern margin of the japan sea deduced from ocean bottom seismographic measurements abstract a seismic exploration was carried out to detect the heterogeneity of the seismic wavespeed structure associated with the plate convergence at the eastern margin of the japan sea two airgun obs ocean bottom seismograph profiles were shot off akita japan where a seismic gap seems to exist but the location of the plate boundary has not been confirmed one of the profiles was 60 km long trending nne ssw named line obs 9 at the northeastern end of the yamato basin and the other was 170 km long trending wnw ese line nt95 1 parallel to the direction of the supposed plate convergence the crustal structure beneath line obs 9 consists of six layers the uppermost layer is sediment three layers are identified beneath the top sedimentary layer and their p wavespeeds are estimated to be 3 3 3 4 km s 5 1 5 4 km s and 5 8 6 3 km s which corresponds to the upper crust underneath these layers a layer with p wavespeed ranges of 6 3 7 2 km s comprises the middle and lower crust the depth of moho is inferred to be 19 km these wavespeed values are comparable with those of the present japanese island arc while the thickness of the crust is one half of that of the japanese arc the crustal model supports the scenario that the yamato basin is formed by extension of the island arc the crustal model for line nt95 1 shows a transition from the extended island arc structure beneath the yamato basin to a thicker crust similar to the japanese arc p wavespeed heterogeneity related to the plate boundary is not detected however a significant change in the structural model along the profile is found around the region where the largest change in the seafloor topography exists in that region the wavespeeds in the middle crust have lower values than those of the neighboring area and the moho begins to deepen towards the japanese island arc from comparison with the relationship between p wavespeed structure and aftershock distribution of the 1993 hokkaido nansei oki earthquake southwest of hokkaido m jma 7 8 the region may correspond to a possible fault position of the pending earthquake

structure and structural development of the havre trough sw pacific northeast of new zealand the pacific plate is obliquely subducted beneath the overriding australian plate major differences appear in the oblique convergence driven structures that occur along the plate boundary while strike slip component of convergence is accommodated in the forearc domain to the south at the eastern north island margin we here substantiate that at least part of the strike slip component is accommodated within the back arc havre trough to the north offshore new zealand new swath bathymetry and structural data collected in the havre back arc domain show that the basin as a whole displays oblique to basin axis structures that allow considering the basin to be the loci of extensive tectonics associated with dextral displacement of the kermadec arc block relative to the australian plate therefore where the two plates are oceanic the oblique convergence between pacific and australian plates is partitioned at the subduction trench for its normal to trench component and at the rear of the kermadec arc block for part or all of its along strike component where it is intimately associated with extensional rifting within the back arc domain the kinematic pattern of australian pacific plate boundary northeast of new zealand that straddles a limit between continental and oceanic lithosphere allows addressing the specificity of the structural development the deformation distribution and the assessment of movement components that occur in a back arc basin associated with oblique convergence

a geophysical interpretation of the secular displacement and gravity rates observed at ny alesund svalbard in the arctic effects of post glacial rebound and present day ice melting summary we have analysed the ny alesund very long baseline interferometry vlbi data over the period 1994 august to 2004 may and we obtain secular displacement rates relative to a nnr nuvel 1a reference frame of 0 2 0 5 mm yr 1 1 7 0 5 mm yr 1 and 4 8 1 1 mm yr 1 for the north east and vertical directions respectively the corresponding global positioning system gps station displacement rates relative to the same reference frame for the north east and vertical directions are 0 2 0 6 mm yr 1 2 3 0 6 mm yr 1 and 6 4 1 5 mm yr 1 at nya1 and 0 1 0 5 mm yr 1 1 6 0 5 mm yr 1 and 6 9 0 9 mm yr 1 at nall where these gps rates were derived from the itrf2000 velocity solution of heflin from the comparison at 25 globally distributed collocated sites we found that the difference in uplift rate between vlbi and gps at ny alesund is mainly due to a gps reference frame scale rate error corresponding to 1 6 mm yr 1 in the gps vertical rates the uplift rate was estimated to be 5 2 0 3 mm yr 1 from the analysis of the tide gauge data at ny alesund hence the uplift rates obtained from three different kinds of data are very consistent each other the absolute gravity ag measurements at ny alesund which were carried out four times period 1998 2002 by three different fg5 absolute gravimeters lead to a decreasing secular rate of 2 5 0 9 gal yr 1 1 gal 10 8 ms 2 in this analysis the actual data obtained from a superconducting gravimeter at ny alesund were used in the corrections for the gravity tide including the ocean tide effect and for the air pressure effect we have

analysis of fault populations in western spitsbergen implications for deformation partitioning along transform margins mesoscale faults expressed in the paleogene central basin and cretaceous basement along the west spitsbergen orogenic belt are used to define the history of continental deformation associated with the development of the transform system that accompanied the opening of the eurasian basin and the norwegian greenland sea a fundamental change in the orientation of faults from dominantly north south in the basal part of the basin to northeast striking in the upper units broadly correlates with a major shift in plate motion during late paleocene early eocene time the two main populations of faults are interpreted as extension fractures that were variably reactivated as shear fractures and formed in response to north south compression followed by northeast southwest compression paleostress stratigraphy or the analysis of striated faults measured in successive stratigraphic units of the central basin corroborates this interpretation and allows a time sequence of paleostress tensors to be defined results show that a late cretaceous early paleocene north south compression consistent with plate motion was followed by three relatively short lived and regionally limited faulting events leading up to a change in plate motion during late paleocene time post chron 25 major transpressive tectonism followed producing northeast trending fractures that were reactivated as dextral and sinistral faults defining a prolate shape paleostress ellipsoid with a horizontal 1 this regionally reproducible tensor consistent with the prediction of dextral transpression along the paleotransform was probably initiated at approximately the paleocene eocene boundary finally a post early eocene deformation pervasively recorded in the study area by an oblate shape paleostress ellipsoid with horizontal 3 is tentatively correlated with the dextral transtension that characterized the post chron 13 opening of the norwegian greenland sea and eurasian basin this study offers documentation of deformation partitioning during the evolution of a transform margin the late cretaceousearliest paleocene compression associated with the prototransform did not involve substantial partitioning and a north south maximum principal stress pervaded the continental crust away from the transform in contrast the late paleocene eocene transpression reflects total partitioning of deformation along the evolved mature transform margin oblique plate motion was presumably partitioned into a strikeslip zone s offshore whereas the onshore central basin recorded only the orthogonal component of oblique convergence and divergence a pattern similar to modern orogenic belts developed in zones of oblique plate motion

eurekan transpressive deformation in the wandel hav mobile belt northeast greenland 1 besides the w e trending kap cannon thrust zone and harder fjord fault zone the 300 km long and nw se striking wandel hav mobile belt represents the third major fault zone in north greenland structural analyses in several areas of this belt suggest that compressive deformation is characterized by transpressive dextral strike slip kinematics this is demonstrated by a combination of folding around w e axes approximately north and south directed reverse faulting and dextral strike slip displacements along nw se trending fault lines the initial formation of the long linear faults is interpreted to be related to deformational events in late paleozoic triassic jurassic and late cretaceous times due to the lack of structural evidence we assume that deformations led to the generation of extension faults which probably were reactivated during dextral strike slip tectonism it is suggested that dextral transpressive deformation was coeval with n s compression at the harder fjord fault zone and cap cannon thrust zone and took place during eocene eurekan times dextral strike slip tectonism in the wandel hav mobile belt was the result of n s compression due to a general northward movement of the greenland plate as a zone of crustal weakness the belt can be interpreted as the onshore equivalent of the main transcurrent fault zone de geer fault which caused the intracontinental dextral slip of svalbard barents shelf relative to north greenland during early tertiary eurekan times and prior to their separation in this configuration it represents one part of the belt of eurekan deformation which extends from the canadian arctic islands over north greenland to the barents shelf where compressive deformation is recorded in the west spitsbergen fold and thrust belt

lineament domain of regional strike slip corridor insight from the neogene transtensional de geer transform fault in nw spitsbergen lineaments on regional scale images represent controversial features in tectonic studies published models explain the presence of the lineament domains in most geodynamic environments as resulting from the enhanced erosion along strikes normal to the upper crustal regional extension despite their success in many tectonic frameworks these models fail to explain the existing lineament domains in the regional strike slip corridors that separate regional blocks including the transform faults the present paper investigates the lineament distribution in such environments and specifically presents the results from a study along the shear corridor of the de geer transform fault in the north atlantic responsible for the separation and drifting away between northern greenland and the svalbard archipelago since oligocene times the study spans from satellite image analysis and outcrop scale investigations to a more regional analysis on a digital bathymetric model of the north atlantic arctic ocean lineaments were automatically detected in the spectral band 8 0 52 0 9 m of a landsat 7 image 15 m pixel resolution a total of 320 image lineaments were extracted from both the regional and the local scale investigations and statistically analyzed results from the multi scalar lineament analyses revealed the existence of a main n s lineament domain regionally persistent from the de geer corridor to the western margin of northern spitsbergen where it relates to the youngest post oligocene tectonics observed onshore this is confirmed by field observations showing that the n s faults represent the youngest brittle deformation system and systematically cut the deformations associated with the building of the tertiary west spitsbergen fold and thrust belt the n s lineament domain is the result of the activity of a larger regional scale tectonic feature nw se oriented and responsible for the localized extension within its deformation corridor the de geer transform fault a model is presented that involves the presence of a thin upper crust with brittle behavior lying above a deeper crustal layer characterized by a more ductile deformation the lower layer suffers more diffuse homogeneous strain this strain is transmitted to the upper brittle layer forming clusters of enhanced fracturing zones aligned following the induced stress trajectories lineaments develop along these weaker fractured zones preferentially etched by erosional processes and align perpendicular to the least horizontal compression sigma3 which in turn forms an angle to the shear kinematics in the western part of spitsbergen this angle is smaller than 45 due to the transtensional tectonic regime the proposed model for lineament domain origin in strike slip environments well integrates the existing models in literature and could be applied to other similar geodynamic contests

the lau havre taupo back arc basin a southward propagating multi stage evolution from rifting to spreading abstract the lau havre taupo lht system is an active 2000 km long back arc basin associated with pacific australian plate convergence in the sw pacific data from the lht back arc system include odp drillhole swath bathymetric and side scan imagery seismic reflection rock geochemistry magnetic anomaly heat flow shallow seismicity gravity and seismic refraction data the lht forms a longitudinal transect from southward propagating true oceanic spreading in the lau basin near tonga similarly southward propagating arc rifting in the havre trough and southward propagating continental rifting in the taupo volcanic zone tvz in northern new zealand four transitional tectonic settings are identified along the lht north to south between the continuum of spreading to rifting and comprise 1 oceanic spreading of the central lau spreading centre clsc propagating into oceanic crust formed by the eastern lau spreading centre elsc 2 oceanic spreading of the elsc propagating into rifted lau havre arc crust 3 rifting within havre arc crust propagating into rifting new zealand continental crust and 4 rifting of continental crust propagating into as yet non rifted but flexurally subsiding continental crust the enhanced spatial and temporal resolution of observed tectonic and magmatic processes along the strike of the lht is used to constrain a model for the evolution of back arc rifting to back arc spreading a sequence of five stages is identified and comprise 1 a combination of incipient simple and pure shear 2 early distributed and spatially heterogeneous half graben rifting with low angle synthetic and antithetic structures associated with rapid graben sediment infilling ephemeral early morb like rift magmatism and the initial trenchward migration of the arc front 3 a latter phase of half graben rifting mostly confined to a contiguous axial zone with continued ephemeral morb like rift magmatism and further trenchward migration of the arc front 4 initial oceanic spreading with evolving steady state morb magmatism along the axial rift graben system and 5 the reconfiguration of ridge geometry in response to changes in opening orientation leading to the development of ridge propagation into newly created oceanic crust rifting stages 2 and 3 can produce at least 120 km wide back arc crust by a balance of crustal extension with an estimated factor of 3 with rift and constructional arc magmatism in the lht system depending on latitude rates of widening during stages 2 and 3 vary between 15 and 45 mm yr 1 whilst stages 4 and 5 have full spreading rates of 90 mm yr 1

the eurekan deformation in the arctic an outline the evolution of the eurekan deformation zones in the arctic is closely related to the development of the circum greenland plate boundaries in early cenozoic times 53 34 ma mostly the eurekan orogeny or deformation has been interpreted as a predominantly compressive tectonic event but the eurekan deformational history in the arctic was not the result of a single tectonic episode it rather represents a complex sequence of successive tectonic stages which produced a number of intra continental deformation zones with changing sometimes opposing lateral oblique and convergent kinematics in the canadian arctic archipelago north and ne greenland and svalbard the interaction between the continental plates especially in combination with the development of transform faults resulted onshore in the formation of several complex deformation zones and areas of eurekan deformation the eurekan deformation can be divided into two major tectonic stages the first phase in the early eocene was dominated by orthogonal compression in the west spitsbergen fold and thrust belt along the west margin of the barents shelf and contemporaneous sinistral strike slip tectonics along the wegener fault and on ellesmere island whereas the second phase in the late eocene was characterized by dextral strike slip and compression on ellesmere island and contemporaneous dextral transpression and transtension along the de geer fracture zone or hornsund fault complex between ne greenland and spitsbergen

crustal structure of the kermadec arc from mango seismic refraction profiles three active source seismic refraction profiles are integrated with morphological and potential field data to place the first regional constraints on the structure of the kermadec subduction zone these observations are used to test contrasting tectonic models for an along strike transition in margin structure previously known as the 32 s boundary we use residual bathymetry to constrain the geometry of this boundary and propose the name central kermadec discontinuity ckd north of the ckd the buried tonga ridge occupies the forearc with vp 6 5 7 3 km s 1 and residual free air gravity anomalies constrain its latitudinal extent north of 30 5 s width 110 20 km and strike 005 south of 25 s south of the ckd the forearc is structurally homogeneous down dip with vp 5 7 7 3 km s 1 in the havre trough backarc crustal thickness south of the ckd is 8 9 km which is up to 4 km thinner than the northern havre trough and at least 1 km thinner than the southern havre trough we suggest that the eocene arc did not extend along the current length of the tonga kermadec trench the eocene arc was originally connected to the three kings ridge and the ckd was likely formed during separation and easterly translation of an eocene arc substrate during the early oligocene we suggest that the first order crustal thickness variations along the kermadec arc were inherited from before the neogene and reflect mesozoic crustal structure the cenozoic evolution of the tonga kermadec hikurangi margin and along strike variations in the duration of arc volcanism

bathymetric prediction from dense satellite altimetry and sparse shipboard bathymetry the southern oceans south of 30 s are densely covered with satellite derived gravity data track spacing 2 4 km and sparsely covered with shipboard depth soundings hundreds of kilometers between tracks in some areas flexural isostatic compensation theory suggests that bathymetry and downward continued gravity data may show linear correlation in a band of wave lengths 15 160 km if sediment cover is thin and seafloor relief is moderate at shorter wave lengths the gravity field is insensitive to seafloor topography because of upward continuation from the seafloor to the sea surface at longer wavelengths isostatic compensation cancels out most of the gravity field due to the seafloor topography we combine this theory with wiener optimization theory and empirical evidence for gravity noise to signal ratios to design low pass and band pass filters to use in predicting bathymetry from gravity the prediction combines long wavelengths 160 km from low pass filtered soundings with an intermediate wavelength solution obtained from multiplying downward continued band pass filtered 15 160 km gravity data by a scaling factor s s is empirically determined from the correlation between gravity data and existing soundings in the 15 160 km band by robust regression and varies at long wave lengths we find that areas with less than 200 m of sediment cover show correlation between gravity and bathymetry significant at the 99 level and s may be related to the density of seafloor materials in these areas the prediction has a horizontal resolution limit of 5 10 km in position and is within 100 m of actual soundings at 50 of grid points and within 240 m at 80 of these in areas of very rugged topography the prediction underestimates the peak amplitudes of seafloor features images of the prediction reveal many tectonic features not seen on any existing bathymetrie charts because the prediction relies on the gravity field at wavelengths 160 km it is insensitive to errors in the navigation of sounding lines but also cannot completely reproduce them therefore it may be used to locate tectonic features but should not be used to assess hazards to navigation the prediction is available from the national geophysical data center in both digital and printed form

microearthquakes and tectonics in an active back arc basin the lau basin abstract an ocean bottom seismograph obs array was deployed for 20 22 days in late 1984 to investigate the precise locations of microearthquakes and their tectonic implications for active back arc opening in the northern lau basin using p and s wave arrival times from four or more obss the hypocenters of 300 shallow earthquakes were located with a high confidence level the magnitudes of most obs located earthquakes were estimated to be less than four in the northern half of the survey area a narrow linear zone of microearthquakes trending nnw sse has been identified the northern part of the narrow seismic zone is within a central axial depression at the southern end of the peggy ridge further south the trend of the seismic zone becomes more n s the narrow seismic zone seems to be composed of at least six seismic segments offset by short aseismic zones most of the seismic segments trend nnw sse suggesting a system of left stepping en echelon spreading ridges where the spreading ridge segment is seismically inactive and the transform fault is active the spreading ridges appear to strike n s or nnw sse but the direction of the back arc opening is considered to be nw se no hypocenters were located with a high level of precision in the area south of latitude 18 s except a small isolated zone of shallow earthquakes at the southeastern part of the survey area we suggest that the shallow earthquakes in this isolated seismic zone were intraplate events in the tonga platelet this platelet is separated from the major indo australian plate by the back arc opening system in the lau basin

tertiary west spitsbergen fold and thrust belt on broggerhalvoya svalbard structural evolution and kinematics the tertiary fold and thrust belt on broggerhalvoya is characterized by a ne vergent pile of nine thrust sheets the basal sole thrust of the pile is located in precambrian phyllites and climbs up section to the ne the lower thrust sheets consist predominantly of post caledonian cover sediments two thrust sheets in the central part of the pile contain a syncline and anticline on a kilometer scale the kilometer scale fold is cut by juxtaposed thrusts giving rise to the formation of four structurally higher basement dominated thrust sheets a five stage kinematic model is proposed 1 in sequence foreland propagating formation of the lower thrust sheets with ramp flat geometries in response to n s subhorizontal bedding parallel movements 2 change in tectonic transport to more east northeasterly directions and first out of sequence thrusting inversion and uplift of the basement in the hinterland formation of the kilometer scale fold structure 3 truncation of the kilometer scale fold by a thrust fault and stacking of the highest basement dominated thrust sheets by hindward propagating mode of thrust generation 4 n s extension due to extensional collaps of the stack 5 w e extension the strain of the thrust sheets is predominantly compressive with the exception of the structurally highest thrust sheet reflecting a temporal change to a more transpressive regime ramping of some thrust faults is suggested to be in part controlled by reactivated carboniferous normal faults the basal sole thrust of the thrust sheet stack also follows the trend of the kongsvegen fault which showed enhanced activity during late mesozoic early tertiary extension the curvature of the west spitsbergen fold and thrust belt on broggerhalvoya is interpreted to be controlled mainly by oblique ramping on the kongsvegen fault associated with pinning on the nordfjorden block as well as by along strike lithological and thickness variations of the post caledonian strata in addition this suggests that pre existing structures have controlled the tertiary geometry the temporal change in the kinematics during thrust tectonics can be linked with the plate tectonic framework in the arctic during tertiary times

discussion on pre ocean opening compression of the northwestern atlantic margin evidence from eastern greenland journal vol 157 2000 707 710 scientific editing by nick rogers h d maher jr s bergh alvar braathen write manby lyberis 2000 argue for a cretaceous palaeocene age and a convergent setting for both the fold structures of the wandel sea basin and for the west spitsbergen fold thrust belt as an alternative to models of decoupling during palaeocene eocene transpressive motions between greenland and the barents shelf in this context we discuss evidence on the timing and kinematics of the west spitsbergen fold thrust belt and constraints on the timing of deformation in the wandel sea basin multiple lines of evidence constraining the timing of fold thrust formation in spitsbergen are discussed in maher et al 1995 and clearly indicate major fold thrust development in the palaeocene eocene space limitations prevent their description here the nature of additional late cretaceous deformation on spitsbergen is another question it is partly constrained by the unconformity at the base of the tertiary sequence which is well exposed in many places and is consistently disconformable to the eye this unconformity involves differential uplift to the north with a regional tilt of a degree or less has a character inconsistent with previous fold thrust development along the islands western margin and can be related to a second pulse within the high arctic large igneous province maher 2001 more recent work confirms a palaeocene eocene age for the spitsbergen contractional structures manby lyberis refer to blythe kleinspehn 1998 as indicating a late cretaceous age for spitsbergen fold thrust belt uplift in their summary figure blythe kleinspehn indicate uplift and erosion of source terranes initiating at 70 ma and continuing until c 43 ma six detailed thermal histories generated from track length modelling of samples taken from the tertiary foreland basin sediments provide particular insight as the authors note three samples with depositional ages of

tectonic inversion in the wandel sea basin a new structural model of kilen eastern north greenland the seminunatak kilen in eastern north greenland with its complexly deformed carboniferous cretaceous strata is a key area to understand the tectonic history of the transform plate boundary between eastern north greenland and svalbard detailed 3 d geological mapping from oblique photogrammetry along with limited ground fieldwork and interpretation of previously published data forms the basis for a new structural model of kilen previous structural models interpreted rhombic shaped fault patterns as the evidence for strike slip tectonics these structures are here interpreted to be the result of a post coniacian ne sw extension with nw se trending normal faults followed by later n s compression of presumable paleocene eocene age folding the faults passively and suggesting the presence of a basal detachment furthermore two thrust sheets have been distinguished on kilen a lower kilen thrust sheet and an upper hondal elv thrust sheet separated by a subhorizontal fault the central detachment the style of deformation and the structures described are interpreted as the result of paleocene eocene n s directed compression resulting in basin inversion with strike slip faults only having minor status this indicates that the greenland margin as exposed on kilen and the conjugate svalbard margin in the west spitsbergen fold and thrust belt are more similar than previously anticipated

seismic images of a magma chamber beneath the lau basin back arc spreading centre we present normal incidence seismic reflection profiles from a back arc spreading centre in the southern lau basin which show a bright mid crustal reflector beneath the ridge axis analysis of wide angle seismic data collected simultaneously with the reflection profiles shows that the reflector coincides with the top of a low seismic velocity zone we interpret the reflector as the top surface of a magma chamber the lau basin is one of only two places where a magma body has been clearly imaged beneath a spreading centre the other being the east pacific rise between 9 and 13 n ref 1 the lau basin reflector is imaged beneath an entire 35 km long ridge segment it is also present beneath both ridges and the overlap basin of a small overlapping spreading centre this is the first observation of a widespread magma body beneath an overlapping spreading centre and indicates that the offset here is not related to a break in continuity of the magma chamber

svartfjella eidembukta and daudmannsodden lineament tertiary orogen parallel motion in the crystalline hinterland of spitsbergen s fold thrust belt within metamorphic basement rocks of the hinterland of spitsbergen s tertiary fold thrust belt a 35 km long zone of notably deformed carboniferous strata and cretaceous intrusives forms a major orogen parallel lineament from svartfjella to eidembukta to daudmannsodden sedl orientations and geometries of map scale fault duplexes and associated fault plane striae populations of folds and associated cleavage and of tension gashes all indicate orogen parallel motion occurred along the sedl structural analyses indicates three phases 1 ene directed overthrusting 2 sinistral motion with a backthrust component and 3 dextral strike slip motion this history indicates a change from orogen perpendicular to orogen parallel movements orogen parallel movement was likely coeval with orogen perpendicular fold thrust transport to the ene in the foreland a model where dextral transpressive motion between greenland and svalbard was decoupled explains the hinterland foreland difference basement fabric aligned with carboniferous carbonates on the steep foreland face of an antiformal stack provided a through going weak surface a prerequisite for decoupling sinistral orogen parallel motion is explicable by short lived episode of sinistral plate motion or by local wedge extrusion during dextral transpression the evolution of decoupling patterns has significant implications for deducing plate motions from local kinematic and paleostress studies

thrust tectonics on broggerhalvoya and their relationship to the tertiary west spitsbergen fold and thrust belt the tertiary fold and thrust belt on broggerhalvoya is characterized by a ne vergent pile of nine thrust sheets the sole thrust of the pile is located in precambrian phyllites and climbs up section to the northeast four lower thrust sheets consisting predominantly of upper palaeozoic sediments are overlain by two thrust sheets in the central part of the stack which contain a kilometre scale syncline and anticline the fold is cut by juxtaposed thrusts giving rise to the formation of three structurally higher basement dominated thrust sheets a multiple stage kinematic model is proposed including 1 in sequence foreland propagating formation of the lower thrust sheets in response to n s subhorizontal bedding parallel movements 2 a change in tectonic transport to ene and out of sequence thrusting and formation of the kilometre scale fold structure followed by 3 truncation of the kilometre scale fold and stacking of the highest basement dominated thrust sheets by hind ward propagating out of sequence thrusting the strain of the thrust sheets is predominantly compressive with the exception of the structurally highest thrust sheets reflecting a temporal change to a more transpressive regime thrusting was followed by 4 n s extension and 5 w e extension comparison of the structural geometry and kinematic evolution of broggerhalvoya with the data reported for the fold belt further south allows us to assume a coeval evolution with the fold belt a latest paleocene early eocene age for the main phase of thrusting is suggested for the west spitsbergen fold and thrust belt the main phases therefore pre date the separation of svalbard and greenland due to right lateral movements along the hornsund fault zone the fold belt s temporal evolution followed by the formation of the forlandsundet graben can be linked with the plate kinematic framework in the span between latest paleocene and middle eocene times

lateral asthenospheric viscosity variations and postglacial rebound a case study for the barents sea the effect of lateral asthenospheric viscosity variations on observable signatures related to postglacial rebound in the barents sea is studied using a finite element approach to discretize the problem a comparison between a laterally homogeneous reference earth model and a laterally heterogeneous earth model is performed the results indicate that a change in asthenospheric viscosity of about three orders of magnitude influences predictions of land uplift up to 10 20 m present day velocities up to 0 5 1 5 mm a and present day gravity anomalies up to 0 4 0 8 mgal in the northwestern part of the barents sea region

the origin of the west spitsbergen fold belt from geological constraints and plate kinematics implications for the arctic abstract the west spitsbergen fold belt which extends for 300 km along the western margin of svalbard and is up to 80 km wide has much in common with foreland fold and thrust belts the near foreland segment of the fold belt exhibits ramp flat thrust trajectories whilst structurally higher nappes are typified by more listric thrusts higher nappes to the west contain imbricated carboniferous and basement rocks showing that the latter were actively involved in the fold belt deformation and a minimum of 80 km total shortening perpendicular to the western margin of svalbard is estimated the early stages of the eurekan deformation in north greenland can be linked to that of the west spitsbergen fold belt and the combined shortening across the two fold belts may exceed 80 km in ellesmere island eurekan structures are distributed in an arc like belt which records between 50 to 100 km of shortening since the late cretaceous kinematic reconstructions suggest that before the opening of the eurasian basin and norwegian greenland sea chron 25 svalbard was linked to north america in the late cretaceous palaeocene interval the motion across the greenland svalbard margin was mainly convergent giving rise to the west spitsbergen fold belt and the eurekan structures of north greenland the dextral separation of greenland and svalbard in post chron 24 time was accompanied by extension followed by pure extension in post chron 13 time

bathymetry and magnetic anomalies in the havre trough and southern lau basin from rifting to spreading in back arc basins abstract the havre trough and lau basin are active back arc basins related to pacific australian plate convergence these back arc basins provide insight into the evolution of rifting through various stages including a final stage of oceanic spreading we carried out a swath bathymetry and magnetic anomaly survey focused on the less studied havre trough and southern lau basin the western portion of the whole havre trough is deeper and more thickly sedimented whereas shallow bathymetry and volcanic edifices are dominant in the east we suggest that crustal rifting progresses asymmetrically with respect to the trough axis the active tectono magmatic zone migrates trenchward during ongoing widening rifting along normal faults trending in the longitudinal trough strike occurs in the southern havre trough volcanism is restricted to a line along the normal faults circular or elongated knolls in the northern havre trough indicate that en echelon type segmented rifting of short strike length and successive volcanic intrusion takes place volcanism in this area is dominated by diapir like magma intrusion into an extended and thinned arc crust the southernmost tip of the spreading center of lau basin is defined by the deep graben striking at n20 e located at 24 00 s 177 10 w

seismicity and state of stress within the overriding plate of the tonga kermadec subduction zone 1 to reassess the main tectonic units and to quantify the slip partitioning within the overriding plate of the tonga kermadec subduction zone a seismotectonic study was performed using global seismicity and focal mechanisms catalogs 1 new tectonic features were identified within the lau basin and the volcanic arc by remarkable shallow hypocenters alignments 2 the centroid moment tensor solutions catalog was processed in order to map the stress tensor variation in the upper plate we found the tectonic features characterized by a diffuse seismicity are subjected to a composite stress regime and they are interpreted as diffuse immature plate boundaries controlled by the high thermal anomaly lying beneath the lau basin 3 we quantified the margin parallel rates of motion using the azimuth of the maximum compressive stress component computed within the interplate zone the results highlight a major tectono kinematic segmentation related to the subduction of the louisville seamount chain

crustal and upper mantle structure in the ryukyu island arc deduced from deep seismic sounding summary in 1984 an extensive geophysical investigation was conducted in the northernmost part of the ryukyu island arc south of kyushu island japan the aim of this investigation was to obtain new information on the nature of crust and upper mantle at the continental margin through various geophysical measurements seismic profiling gravity magnetism sea beam and heat flow this paper presents the crust and upper mantle structure deduced from ocean bottom seismographic profiling conducted along two lines one line 190 km long was taken behind the northernmost part of the ryukyu island arc parallel to the major tectonic units i e the okinawa trough ryukyu arc and ryukyu trench the other 295 km long was perpendicular to the tectonic units along these profiles we deployed ocean bottom seismograms spaced 10 20km apart as a controlled source we used both explosives and an airgun array the experiment was successful and provided quite important information on the tectonics of a trenchisland arc back arc system the velocity structure obtained for the profile behind the ryukyu islands has continental properties the sediment thickness is 3 4 km although it shows lateral variations due to basement undulation the velocities of the upper and lower crust are 5 8 6 2 and 6 6 6 8 km s respectively the total crustal thickness decreases southwestward from 27 30 to 23 24 km this is direct evidence for crustal thinning associated with the process of back arc spreading the velocity structure along the profile from the trench to the island arc clearly shows the subduction accretion and deformation at this margin the crust beneath the trench has oceanic properties the sediment thickness is 1 3 3 0 km beneath which the igneous basement shows severe undulation the total crustal thickness is 7 8 km the p velocity is slightly less than 8 0 km s our seismic data revealed a huge sedimentary wedge located 50 150 km landward of the trench the maximum thickness of this wedge exceeds 12 km the origin of this wedge may be oceanic because the p wave velocity in its eastern half is almost comparable to that obtained for the trench area the velocity structure landward of the wedge is continental and similar to that obtained for the profile behind the island arc

statistical analyses and controls of root zone soil moisture in a large gully of the loess plateau soil moisture variability and controls are little known in large gullies of the loess plateau which represent complex topography with steep slopes this study analyzed spatial temporal variability of soil moisture at the 0 20 20 40 40 60 and 60 80 cm depths in a large gully of the loess plateau based on root zone soil moisture measurements for 3 years 2009 2011 the result showed that mean soil moisture standard deviation sd and coefficient of variation were highly dependent on depth the highest mean value was observed at the 20 40 cm depth while the lowest one was at the 0 20 cm depth the sd increased with mean soil moisture for various depths as soil moisture was relatively wet however a transition that sd decreased with mean soil moisture occurred when soil moisture was relatively dry positive correlations exist between moisture contents over different depths and that the relationships of the neighboring layers are relatively high with r2 from 0 70 to 0 76 correlation analysis principle component analysis and stepwise multiple regression analysis showed that soil particle size distribution and topography slope and elevation were the main environmental factors controlling soil moisture variability in the large gully

seismic mapping of a magma chamber beneath the valu fa ridge lau basin we analyze a dense grid of seismic normal incidence and wide angle data collected over an active back arc spreading center in the lau basin of the southwest pacific our survey area covers the whole of a 35 km long morphological segment and a small overlapping spreading center a bright reflector which is coincident with a velocity inversion at a depth of 3 2 0 2 km below the seafloor is observed on every one of the 40 across axis profiles we interpret this reflector as being the roof of a crustal magma chamber the widest magma chamber reflector occurs beneath the overlapping spreading center where it extends up to 4 km being imaged beneath both ridges and in places beneath the overlap basin elsewhere the width of the reflector varies between 0 6 and 2 3 0 4 km the narrowest reflectors are observed beneath deviations devais of the ridge axis in addition to being observed on each of the kilometer spaced across axis profiles the reflector is also seen as a continuous event for at least 10 km on a profile along the ridge axis the reflection coefficient of the event is between 0 34 and 0 65 this requires the melt at the top of the chamber to have a p wave velocity less than 2 7 km s if the interface is planar or less than 3 8 km s if the interface is layered

intensive water content and discharge measurement system in a hillslope gully in china abstract an automatic monitoring system was constructed to intensively study the water profile runoff interactions during rain events of a hillslope gully the system was installed on the loess plateau in the shaanxi province in northern china the primary goal was to obtain a better understanding of soil erosion processes in this district to aid in better management to accomplish this infiltration and runoff data for running calibrating and validating the lisem erosion model was needed the system presented here consisted of 29 time domain reflectometry tdr water content sensors that monitored the water content variation in time sensors were installed in different subsystems throughout the gully geometry such as in the cropland surrounding the gully in some gully slopes and in the gully floor at the outflow point of the gully an h flume was installed in order to measure the actual discharge of the gully system and to measure directly the sediment concentration in the discharge the monitoring system was programmed in this way so that more measurements were recorded when a rainstorm occurred installation took place in april 1998 and it was used until september 2000 in 1998 five major rain events were recorded which generated runoff and erosion in 1999 and 2000 only one cropland measurements showed high water contents and high infiltration rates all through the measuring period and also showed a strong reaction to precipitation the sidewalls of the gully showed much lower water contents where only very shallow parts showed some infiltration during rain showers while steep parts of the gully such as pipes and vertical walls showed an extremely low water content and practically no water content variation with time simulation results confirmed the suspicion that these areas are an important source for hortanian overland flow within the gully system model simulations further showed that most of the sediment being eroded from the gully system was coming from rills and smaller gullies being cut into the main gully bottom saturation excess overland flow proved to be dependent on the characteristic of the rain event as well as on the water content of the soil at the beginning of the event

a transpressional origin for the west spitsbergen fold and thrust belt insight from analog modeling 1 the west spitsbergen fold and thrust belt formed along the transform plate boundary between greenland and the western barents sea during paleocene eocene breakup in the northern north atlantic approximately 20 40 km margin perpendicular shortening accumulated in the belt has been attributed to transpression and strain partitioning in a restraining bend but also to head on collision we have applied scaled analog tectonic modeling to test the former hypothesis a pack of brittle quartz sand with a shallow thin layer of silicon putty was deformed by transpression at a 15 convergence angle by movement of a basal plate the kinematics was quantified by means of digital particle image velocimetry the result was a doubly vergent transpressional wedge consisting of a steeply tapered retrowedge and a strongly internally deformed steeply tapered prowedge separated by a central strike slip zone and an adjacent low taper thin skinned fold and thrust belt the doubly vergent wedge evolved through several kinematic phases three main stages were identified namely 1 initial distributed deformation 2 development of an oblique doubly vergent wedge with progressive evolution of local strain partitioning along the marginal shear zones and finally 3 a stage of full strain partitioning between a central strike slip zone and reverse displacement along marginal shear zones with folding and thrusting in a thin skinned belt on the proside the analog model convincingly reproduced the geometry and the kinematic evolution of the west spitsbergen fold and thrust belt supporting the hypothesis of its formation by strain partitioning in transpression with a small angle of convergence and significant lateral displacement

graben inversion in nature and experiments the inversion of crustal scale basement grabens is studied here through laboratory experiments on small scale models and available oil industry seismic lines from the southern north sea two basic configurations are considered first both the basement and the sedimentary cover are brittle and inversion does not involve any potential decollement between them second the basement and sedimentary cover are separated by a weak ductile layer e g salt which can allow decollement of the cover during both extension and later compression and inversion the second configuration is more complicated and can lead to a large variety of geological structures laboratory experiments were carried out on brittle ductile models built with sand to represent brittle layers basement and sedimentary cover and silicone putty to simulate the decollement layer between basement and cover a mechanically based classification of inversion structures is proposed the effects of some crucial parameters are investigated including obliquity between the direction of shortening and normal faults as well as strength profiles and the presence or absence of salt diapirs the experimental investigation leads to the following conclusions 1 the inversion of the graben by reactivation of normal faults implies that the angle between the direction of compression and the graben is less than 45 2 if there is a superficial decollement e g basement cover interface inversion initiates low dipping thrust faults in the cover localized at graben borders 3 salt diapirs or salt walls localized along the graben borders in the cover are preferential sites for the development of thrust faults and 4 when the cover is decoupled from the basement by a decollement layer inversion induced deformation in the cover which is partitioned between thrust faults along the graben borders and strike slip faults within the graben trending oblique to the graben borders experimental results are compared with field examples in particular from the southern north sea

state of stress and tectonic evolution of the west spitsbergen fold belt abstract the west spitsbergen fold belt is the result of a e w to ene wsw oriented compression which affected the whole of spitsbergen a late cretaceous palaeocene age for the fold belt deformation is indicated by the involvement of only the basal tertiary conglomerates in the folding and thrusting in western spitsbergen this compressional event was followed by a strike slip stress pattern with nw se oriented extension and ne sw compression which generated micro structures within the tertiary rocks on the map scale normal faults produced by a ne sw oriented extension overprint the compressional structures the later strike slip and extensional stress patterns correspond to the svalbard greenland dextral motion along the de geer zone in latest palaeocene eocene time the latest tectonic event which affected the whole of svalbard was an e w oriented extension related to the spreading along the knipovich ridge in oligocene neogene time

tectonic wedges geometry and kinematic interpretation abstract the geometry of several tectonic wedge combinations was studied in an outcrop in the basque basin western pyrenees three types of tectonic wedges were distinguished simple double and triple wedge on the surface the geometry of the observed tectonic wedges is always highly elemental emergent thrust horse or klippe the final stage in the evolution of a tectonic wedge is its delamination this can occur by the spreading of the thrusts which conform the wedge or by the development of back thrusts associated to them the relative age of the back thrust with respect to the thrust indicates whether the original structure was a simple thrust or a tectonic wedge if this criterion is applied to the pyrenean orogen this range corresponds to a tectonic wedge

transform normal extension and asymmetric basins an alternative to pull apart models continental transforms are commonly associated with relatively small scale pull apart basins however much larger scale basins which are not consistent with the pull apart model commonly exist adjacent to transforms structures associated with several basins along the dead sea rift and el pilar fault illustrate this these basins are remarkably asymmetric bounded by essentially linear transform segments on one side and subparallel normal faults on the other suggesting simultaneous strike slip motion and transform normal extension this observation which is incompatible with classical faulting theory can be explained along divergent plate boundaries if the transform fault is much weaker than the adjacent crust analysis of the orientation of the horizontal principal stress direction near a weak transform fault embedded in an otherwise strong crust shows that convergent and divergent plate motion results in a stress field characterized by nearly fault normal compression and extension respectively structural styles along the san andreas dead sea and el pilar transform systems show that predictable changes between these two states have occurred through time along strike of the transforms