onshore offshore potential field analysis of the more trondelag fault complex and adjacent structures of mid norway abstract the more trondelag fault complex mtfc is one of the most prominent fault complexes of scandinavia it exerted a strong control on the development of offshore basins of mid norway and onshore topography however the relationships between the faults observed in the field onshore and those identified by means of seismic profiling offshore remain obscure regional gravity and aeromagnetic data are used to map regional scale faults and in particular to delineate the main geophysical features related to the mtfc the advantage of potential field data is to provide an almost continuous coverage and to tie bedrock mapping onshore to seismic interpretation offshore in this paper we apply potential field transformations to focus on the regional and deep seated structures in order to extract new geological information also the tilt derivative technique tdr is applied to gravity and magnetic data with the aim of enhancing linear trends the results indicate the possible onshore offshore links of large scale structural elements like the mtfc and late caledonian detachments e g kollstraumen detachment the locations of different segments of the mtfc are detected and possible new faults lineaments are depicted correlating petrophysical data with gravity and magnetic maps explains the influence of the mtfc on the deformation and mineralisation of bedrock along its strike in addition the structural pattern seen in the enhanced lineaments is diagnostic for the sinistral strike slip movements that are known to have occurred in devonian time along the mtfc this confirms the important role of the mtfc in the tectonic setting and geological evolution of mid norway

high temperature deformation during continental margin subduction exhumation the ultrahigh pressure western gneiss region of norway abstract a new dataset for the high pressure to ultrahigh pressure western gneiss region allows the definition of distinct structural and petrological domains much of the study area is an e dipping homocline with e plunging lineations that exposes progressively deeper more strongly deformed more eclogite rich structural levels westward although eclogites crop out across the wgr scandian deformation is weak and earlier structures are well preserved in the southeastern half of the study area the scandian reworking increases westward culminating in strong scandian fabrics with only isolated pockets of older structures the dominant scandian deformation was coaxial e w stretching the sinistrally sheared more trondelag fault complex and nordfjord mylonitic shear zone bound these rocks to the north and south there was moderate top e amphibolite facies deformation associated with translation of the allochthons over the basement along its eastern edge and the nordfjord sogn detachment zone underwent strong lower amphibolite facies to greenschist facies top w shearing a northwestward increase in exhumation related melting is indicated by leucosomes with hornblende plagioclase and scandian sphene in the western 2 3 of the study area exhumation related amphibolite facies symplectite formation in quartzofeldspathic gneiss postdated most scandian deformation further deformation was restricted to slip along biotite rich foliation planes and minor local folding that the western gneiss region quartzofeldspathic gneiss exhibits a strong gradient in degree of deformation implies that continental crust in general need not undergo pervasive deformation during subduction

a multiproxy approach to reconstructing sea surface conditions using coral skeleton geochemistry 1 we use elemental ratio mg ca sr ca u ca and ba ca and oxygen isotope data from a porites lutea coral head collected from offshore amedee island new caledonia 22 29 s 166 28 e to assess the degree to which changes in these geochemical variables reflect variations in sea surface conditions we have assessed the robustness of each geochemical proxy by comparing 25 years 1992 1968 of monthly geochemical variations with a local record of sea surface temperature sst and with the appropriate 1 by 1 grid box from a global gridded sst data set we conclude from our comparison that the most consistent proxies of monthly sst variations at this site are 18o r2 0 84 p 0001 and sr ca r2 0 84 p 0001 the fidelity of the coral based sr ca sst proxy was assessed via calibration verification exercises at new caledonia and rarotonga the paleoclimate accuracy of the coral sr ca sst technique is judged to be robust and the precision of the technique is estimated to be 0 3 0 5 2 based on the calibration verification exercise in contrast monthly variations in mg ca and u ca ratios are only moderately correlated with monthly sst variations r2 0 55 p 0001 for mg ca and r2 0 47 p 0001 the strength of the correlation between sst and mg ca and u ca varies as a function of time suggesting that variations in these ratios are not a simple function of sst variations this variability in goodness of fit between u ca sst and mg ca sst may ultimately limit the use of these ratios as coral paleothermometers averaging or stacking individual proxy sst records sr ca mg ca and u ca to generate a composite proxy sst record does not necessarily improve the proxy record if the signal to noise ratio in each proxy is highly variable for example stacking of sr ca mg ca u ca records at new caledonia produces a proxy sst time series that has greater standard error than the individual sr ca sst time series cf ordinary least squares standard error of 1 16 c versus 0 86 c ba ca variations have little correlation with sst sr ca mg ca or u ca variations at new caledonia in conclusion variations in oxygen isotopic composition of seawater calculated by removing the sr ca based temperature component of the 18o signal agree reasonably well with observed variations in sea surface salinity especially at the interannual timescale

pull apart formation and strike slip partitioning in an obliquely divergent setting leka ophiolite norway abstract the leka ophiolite complex loc is located on the island of leka norway and belongs to the uppermost allochthon of the scandinavian caledonides the rocks of the adjacent mainland and most of the surrounding islands are basement gneisses and supracrustal rocks not related to the ophiolite complex paleostress analysis gravity inversion and regional geology support a fault bounded rhombochasm geometry for the loc the paleostress inversions revealed two types of tensors interpreted as small strains 1 horizontal extension generally e w to ne sw and 2 horizontal extension in the same direction with an added component of perpendicular horizontal contraction a strong positive gravity anomaly 25 mgal is centered on leka and gravity inversion indicates that the loc lies directly below its surface exposures with steep sided walls and a flat bottom located at 7 km depth the faults bounding the loc probably initiated during postorogenic extension in the scandinavian caledonides the faults are regional in scale and are parallel to other ne sw trending en echelon faults along the norwegian coastline and on the adjacent mainland a pull apart structure explains the down dropping and subsequent preservation of the loc as it is surrounded by rocks from lower structural positions within the nappe stack the paleostress directions from leka support a sinistral component of shear along these faults the gravity inversion is consistent with a fault bounded geometry this pull apart structure as uniquely recorded by the dense ophiolitic rocks suggests that strike slip partitioning was active in an obliquely divergent setting

late cretaceous cenozoic intraplate contractional deformation at the norwegian continental shelf timing magnitude and regional implications abstract contractional structures large anticlines and synclines reverse faults and inverted centres of deposition of assumed late cretaceous cenozoic age are common in cretaceous tertiary basins of the northwestern european margin the similarities in style orientation and timing of these structures are striking the present detailed analysis of one anticline the ormen lange dome of the mid norwegian continental shelf indicates that the total contraction is moderate less than 2 3 and that the analysed anticline has been growing almost continuously since its initiation in eocene till present inversion in the barents sea started already in the late cretaceous this episode is suggested to be related to far field effects of active plate margin processes and transfer of stresses across the plate as a consequence of the sub hercynian and paleocene laramide event of the alpine orogeny the development of co axial structures was facilitated by stress focusing along pre existing high relief n s and ne sw trending fault complexes far field plate tectonic stresses originating mainly from the alpine orogeny seem to have been the most important cause of contractional deformation on the nw european shelf in addition ridge push from the north atlantic spreading may have contributed significantly particularly during the neogene

resurgent strike slip duplex development along the hitra snasa and verran faults more trondelag fault zone central norway abstract lineament analysis of the ene wsw verran and hitra snasa faults of the long lived more trondelag fault zone mtfz has revealed the presence of a complex array of anastomosing faults and fractures this has the geometric configuration of a major dextral strike slip fault zone and compares well with characteristic patterns of braided wrench faulting e g the san andreas fault system of california the fault array recognized in conjunction with the verran fault is clearly post caledonian and is considered to define a dextral strike slip duplex system associated with the parallel hitra snasa fault are riedel like structures which tend to point to an earlier component of sinistral movement rock products present along the hitra snasa fault and its secondary faults comprise mylonites hydrothermally altered rocks and small scale recrystallized breccias along the main verran fault evidence of late polyphasal deformation is seen in several discrete episodes of brecciation hydrothermal alteration and locally pervasive prehnite and stilbite veining the fault structures occurring along the hitra snasa and verran faults are thought to have originated as a sinistral fault system of late devonian age especially for the hitra snasa lineament subsequently strike slip movement reversed in sense and shifted locus towards the verran fault system during the late jurassic or early cretaceous during this strike slip reversal some earlier fractures related to the sinistral system were rejuvenated within the stress field of the evolving dextral duplex system strike slip displacements of a similar age are known from fault complexes on the norwegian continental shelf and in the northern north sea the regional picture indicates that the mtfz was almost certainly linked to the fault systems of northern scotland prior to the opening of the viking graben

tectonic significance of present day stress relief phenomena in formerly glaciated regions abstract investigations were conducted in several regions of norway with the purpose of detecting and measuring stress relief features and to derive from them valuable information on the shallow crustal stress state stress relief features are induced by blasting and sudden rock unloading in road construction and quarrying operations and are common in norway and probably in other regions of fennoscandia as they are in ne america stress relief at the earth9s surface is diagnostic of anomalously high stress levels at shallow depths in the crust and characterizes the formerly glaciated baltic and canadian precambrian shields the mean orientation of the maximum horizontal compressive stress axis as deduced from the orientation of stress relief features was found to be nw se consistent with north atlantic ridge push forces we show that our determined stress orientations are in excellent agreement with other kinds of stress data as a final step we estimate ridge push force magnitudes from gravity data in the north atlantic region our computations suggest that strong ridge push forces characterize the baltic and canadian shields we conclude from this quantitative analysis and our fieldwork results that present day stress relief in fennoscandia and ne america is mostly triggered by plate scale ridge push forces and not by residual glacial loading stresses

structure and seismic stratigraphy of the innermost mid norwegian continental shelf an example from the frohavet area abstract the frohavet basin a newly discovered sedimentary basin on the innermost mid norwegian continental shelf occurs in an area 60 20 km and contains a stratal sequence up to 1000 m thick dating by ice transported erratic blocks suggests a jurassic age the sequence is preserved in half grabens downthrown to the north west and is cut by numerous faults some of which are interpreted as syndepositional the sequence reflects an upward change from continental deposition with the frohavet area acting as a local depocentre to more widespread continental and marine deposition the predominant sediment transport direction was towards the north west the frohavet sequence was deformed during a phase of extensional tectonism probably in late jurassic early cretaceous times

regional tectonic interpretation of image enhanced gravity and magnetic data covering the mid norwegian shelf and adjacent mainland abstract gravity and magnetic field data covering mid norway and the norwegian sea were processed in order to enhance tectonic features on various scales the local features were subjected to an unconventional processing technique involving a non linear adaptive wallis filter designed to enhance the smallest wave lengths when compared with recent structural information derived from seismic data the processed gravity and magnetic maps show the main structural trends major fault zones and basin boundaries thus proving their worth for regional tectonic mapping previously undetected nw se trending offshore crustal lineaments are revealed a landward prolongation of the bivrost lineament appears to continue subparallel towards proterozoic shear zones below the caledonian nappes in the rana area either along the western margin of the transscandinavian granite porphyry belt or the nw se trending mala skelleftea tectonic zone a large lineament is also observed as a landward prolongation of the surt lineament indicating a relationship with the storsjon edsbyn deformation zone a major deep crustal shear zone in the precambrian of sweden a slightly increased seismic activity which is possibly related to the present ridge push force is observed along parts of the previously unknown transfer zones combined gravity and magnetic modelling indicates a low crustal thickness in the northwesternmost part of the voring basin between the surt and the jan mayen lineaments the lack of correlation between the gravity and the magnetic patterns observed on the residual field maps suggests the presence of a shallow curie isotherm situated above or within the uppermost basement

three dimensional modelling of alteration zones based on geochemical exploration data an interpretable machine learning approach via generalized additive models abstract the inference of deep alterations plays an important role in the analysis of deep geological processes and the targeting of buried mineral resources however the construction of three dimensional 3d models of alteration zones based on geochemical data is challenging due to the diverse geological processes and scarcity of information related to deep alterations in this paper we propose an interpretable machine learning method to infer 3d geological models of alteration zones based on geochemical data from the dayingezhuang area china to expose the information hidden in geochemical data that is indirectly and weakly related to alteration zones a generalized additive model gam is used it learns a nonlinear intelligible model associating geochemical anomalies extracted by pca with alteration features the model learned via gam and is then combined with a bayesian framework to infer the thickness of alterations in a no drilling area thus enabling 3d modelling of deep alteration zones with such an intelligible model geologists are capable of inspecting the reliability of the model and better understanding the association between the distribution of geochemical elements and deep alterations the inference results show that the relationship between geochemical anomalies and alteration depth is significant while the relationship with alteration thickness is complex the results of this study provide the underlying insights needed to guide the analysis of deep geological mineralization processes

a tectonic model for the norwegian passive margin with implications for the ne atlantic early cretaceous to break up a sub regional tectonic study of the mid norwegian margin has been assimilated into a broader regional study of the ne atlantic margin the ne atlantic margin experienced several extensional events between devonian post orogenic collapse and break up in early tertiary this paper focuses on the extensional events between early cretaceous and early tertiary it is suggested that ne trending early cretaceous rifting followed the entire margin from the southern rockall trough to the bjornoya basin of the sw barents sea this rift had a markedly different trend than the preceding n trending late jurassic rift of e g the north sea seamounts may have been emplaced in the highly thinned basin axes during early cretaceous rifting subsequent rift events followed the early cretaceous rift trend an enigmatic 9mid9 cretaceous event probably extensional is observed in the northern part of the mid norwegian margin the event is expressed by faulting in the inner voring basin and by uplift of the outer voring and lofoten margins uplift is associated with a widespread unconformity uplift of the gjallar ridge in the voring basin culminated during the latest cretaceous to early tertiary rifting with structural geometries broadly similar to those seen in core complexes a new tectonic model for ne atlantic margin is proposed based on these observations and builds on analogues from the modern rift system in the red sea and woodlark basin of papua new guinea

high strain zones from mesoto macro scale at different structural levels central norwegian caledonides abstract high strain shear zones of diverse character metamorphic grade and scale occur in different tectonic settings in the caledonides of central norway three specific examples are described strain products range from high pt granulite to amphibolite facies thrust related scandian mylonites at deep structural levels to ultracataclasites and mylonites generated in the ductile to ductile brittle transition regimes along the multiply reactivated orogen oblique more trondelag fault complex in another example geochemical data from a transformation of granite to mylonite at an intermediate structural level indicate that the high strain change over probably occurred as an open volume gain system involving silicification in the case of the more trondelag fault complex a sinistral strike slip regime during devonian time was coeval with regionally extensive top to the sw shear in the country rocks outside the fault zone later components of movement along the multiphase fault zone from latest palaeozoic to cenozoic time were mainly of brittle dip slip to dextral strike or oblique slip character

a simplified model of stress slip relationships application to the froy field northern north sea abstract we apply an analytical method sortan to determine fault slip as induced by far field stress the sortan method is based on the wallace bott hypothesis the method is applied to all major faults of the froy oil field located at the eastern margin of the southern viking graben north sea the purpose was to quantify the most likely senses of motion experienced by the faults during the late jurassic early cretaceous rifting event because strike slip displacement is generally difficult to determine based on classical exploration methods particular attention was paid to the simulated strike slip component along the major faults depth converted structural maps were used to determine fault attitudes the presence at the northern edge of the field of a major syn rift dextral strike slip fault the north froy fault allowed us to constrain the most likely characteristics of the prevailing stress field during rifting according to different possible stress states different models were run the results from the sortan modelling indicate that the strike slip component of motion was in general minor on the major faults within the oil field the inferred stress state is found consistent with rifting involving fault related displacement strongly dependent on 3 orientation this stress state prevailed at least during the latest stages of rifting latest jurassic early cretaceous of the northern north sea this case study shows that where paleostress inversion methods cannot be applied in the absence of direct observation the sortan method has the potential to constrain the slip behaviour of the brittle structure it also enables one to rapidly check the overall mechanical consistency of tectonic interpretations

associated water and organic compounds in coral skeletons quantitative thermogravimetry coupled to infrared absorption spectrometry 1 samples from coral skeletons belonging to six species have been submitted to thermogravimetric analysis in the temperature range between 20 and 550 c weight losses are interpreted on the basis of simultaneously recorded infrared absorption spectra at specific wavelengths for water and co2 the organic water content of coral skeletons represents up to 2 5 of the total weight additionally it is shown that during heating the main part of water remains linked to organic compounds up to 275 330 c suggesting organic materials associated with the skeleton are hydrated

geometry and subcrop maps of shallow jurassic basins along the mid norway coast abstract interpretation of new seismic data from four inshore nearshore areas along the coast of mid norway yields important information on the geometry and stratigraphy of downfaulted jurassic sedimentary rocks three seismic units have been identified these are interpreted to be of middle to late jurassic age fangst group and melke formation half graben geometries related to normal fault movement are common for the areas although the beitstadfjorden basin and the griptarane area also record possible strike slip movements the structural development of the four areas can be related to tectonic movements along the more trondelag fault complex the jurassic basins along the coast of mid norway are directly comparable in size and geometry with previously unmapped deep seated basins in the voring basin we suggest that the inshore nearshore and offshore basins originated during the same extensional event in late jurassic early cretaceous times and that this basin forming event was regionally very extensive

numerical modeling of cenozoic stress patterns in the mid norwegian margin and the northern north sea numerical modeling of cenozoic stress patterns in the northern north sea and the mid norwegian margin is presented and the sense of potential slip along major fault planes belonging to the two areas is restored we assume that the main regional source of stresses is the atlantic ridge push as demonstrated by previous studies furthermore we also assume a nearly consistent nw se strike for the far field stress from continental breakup between greenland and norway earliest eocene to present day first we applied the commercial two dimensional distinct element method udec to simulate cenozoic stress and displacement patterns in the study area variations in rheology and major fault zones were introduced into the model the more trondelag fault complex and its inferred continuation into the shetland platform forms the major mechanical discontinuity in the model second we used the sortan method developed at the university of paris vi to predict the sense of potential slip along major fault planes the input for the sortan model was constrained by the geometry of the selected fault planes and local principal stress directions extracted from the udec modeling our results show that the more trondelag fault complex and its inferred continuation into the shetland platform act as a weak fault zone this fault zone divides the study area into two different stress provinces the continental margin and the northern north sea this result agrees well with the observed differences in cenozoic structural evolution of the two areas compressive structures are observed along the continental margin whereas relative tectonic quiescence characterizes the northern north sea during the tertiary the restored stress patterns in the northern north sea and the mid norwegian margin also agree well with the observed present day stress configuration our analysis demonstrates a method to reconstruct the sense of slip on major fault planes by combining two complementary numerical tools udec and sortan as a result it is demonstrated that oblique slip motions are mainly expected in particular strike slip and reverse dip slip faulting are simulated

mesozoic sedimentary rocks in edoyfjorden and beitstadfjorden central norway implications for the structural history of the more trondelag fault zone abstract a seismic reflection profiling survey has indicated the existence of downfaulted mesozoic sequences in edoyfjorden south of smola trondheimsleia and in beitstadfjorden these rocks are preserved in halfgrabens within the more trondelag fault zone mtfz which is interpreted as an important structural element in central norway the mtfz probably originated in the palaeozoic and at least two phases of reactivation can be recognized in the mesozoic sequences

the role of fault reactivation and growth in the uplift of western fennoscandia new structural data published aft data and topographic data suggest that the latest cretaceous cenozoic uplift of western norway was associated with normal reactivation of the more trondelag fault complex reactivation focused along the base of today9s topographic rise with maximum displacements in the order of 2 3 km structural and aft data indicate that reactivation occurred along a displacement gradient with least normal displacement in the ne and increasing displacements towards the sw reactivation commenced in connection with the triassic to earliest cretaceous phases of rifting on the norwegian margin and probably continued through most of the tertiary the late cretaceous to cenozoic topographic development of the scandes mountains followed structurally induced templates such as those described from other areas of active normal faulting a fault model for the cenozoic uplift of the norwegian mainland provides a framework for provenance erosion and transport of sediments eventually deposited in the offshore post rift basins in the latest cretaceous palaeogene and neogene the asymmetric topographic profile of fennoscandia is reflected in the aft data and suggests that lithospheric flexure places a first order control on the shape of the scandes mountains and the central fennoscandian craton

the role of structural inheritance in the development of high displacement crustal faults in the necking domain of rifted margins the klakk fault complex froya high offshore mid norway abstract the role of inherited structures during the development of normal faults in continental rifts and proximal domains of passive margins have been extensively studied few studies however have a focus on deciphering the role of inheritance in the development of high displacement 10 km low angle 25 km is present during rifting

high temporal resolution mg ca and ba ca records in modern porites lobata corals 1 secondary ion mass spectrometry sims was used to determine mg ca and ba ca variations across two skeletal structures the fasciculi and the centers of calcification cocs in two porites lobata corals of different linear extension rates from oahu hawaii both corals exhibit large mg and ba heterogeneity which is not related to sea surface temperature sst or composition higher concentrations of ba occur in the fasciculi and higher mg in the cocs of the slowly extending coral compared to the fast growing coral mg and ba concentrations are significantly higher in the cocs of both corals compared to the fasciculi trace element variations may reflect changes in the calcifying fluid composition or changes in skeletal trace element incorporation regressions between mg ba and sr reported in a prior publication indicate that the skeletal incorporation of each element is affected by a different factor or combination of factors smoothed sims records of ba ca variations across the fasciculi of the fast growing coral follow the seasonal trend predicted from sst and expected seawater chemistry variations smoothed sims mg ca records do not correlate with sst indicating that sims mg ca records cannot be used to estimate past ssts

devonian orogen parallel opposed extension in the central norwegian caledonides late orogenic early to middle devonian extension in the scandinavian caledonides was unidirectional in western norway new data from two detachment zones hoybakken and kollstraumen north of the more trondelag fault complex show that bidirectional opposed orogen parallel extension dominated in this region at this time the fault complex acted as a transfer zone for the hoybakken detachment extension and uplift in central norway triggered significant magmatic activity in contrast to the lack of granite intrusions during exhumation of western norway

styles of extension offshore mid norway and implications for mechanisms of crustal thinning at passive margins 1 eocene magmatic breakup along the mid norway rifted margin was preceded by extreme jurassic cretaceous crustal thinning in a magma poor environment along the se borders of the rift top basement detachment faults with heaves on the order of 15 40 km evolved in at least two stages to become the boundaries between moderately thinned 20 30 km thick crust and a 100 200 km wide highly extended area with crustal thicknesses generally between 2 and 12 km under the present day more and voring basins in the footwalls of the basin flank detachments lower and middle crust was exhumed in extensional domes that became incised by a younger set of normal faults under the most highly thinned areas a more distal set of deep seated basin floor detachments incised and extended remnant crust and probably the upper mantle leaving as little as 5 km of continental crust to be preserved under thick synrift and postrift deposits we suggest that basin flank detachments such as the ones described above hold the potential to reduce the crustal thickness down to the critical value required for embrittlement of continental crust thus they prepare the ground for incision by the basin floor detachments which may become responsible for exhumation of deep crust or continental mantle if extension is allowed to proceed

a discussion of structural and thermal control of magnetic anomalies on the mid norwegian margin we discuss the correlation between the depth extent of magnetic sources the curie temperature depth and crustal structures on the mid norwegian margin spectral methods can be used to estimate the depth extent of magnetic sources even if the bottom is located in the lower crust however only with limited resolution the bottom of the magnetic surfaces is often regarded to represent the depth to the curie isotherm however comparison with a 3d model based on the interpretation of potential field and seismic reflection data and thermal modelling shows that the depth extent of the magnetic sources is merely controlled by the overall geometry of the crystalline crust and not the temperature distribution the observed changes in the magnetic field between the inner and outer part of the mid norwegian margin appears not to reflect as previously assumed the depth to the curie temperature but the geometry of the basement and lower crust our 3d model of the mid norwegian margin reveals a basement configuration that involves a basement with different petrophysical properties which can be connected with lithological basement units of onshore norway

the tjellefonna fault system of western norway linking late caledonian extension post caledonian normal faulting and tertiary rock column uplift with the landslide generated tsunami event of 1756 abstract on february 22 1756 approximately 15 7 million cubic meters of bedrock were catastrophically released as a giant rockslide into the langfjorden subsequently three 40 meter high tsunami waves overwhelmed the village of tjelle and several other local communities inherited structures had isolated a compartment in the hanging wall damage zone of the fjord dwelling tjellefonna fault because the region is seismically active in oblique normal mode and in accordance with scant historical sources we speculate that an earthquake on a nearby fault may have caused the already weakened tjelle hillside to fail from interpretation of structural geomorphic and thermo chronological data we suggest that today s escarpment topography of more og trondelag is controlled to a first order by post rift reactivation of faults parallel to the mesozoic passive margin in turn a number of these faults reactivated late caledonian or early post caledonian fabrics normal sense reactivation of inherited structures along much of coastal norway suggests that a structural link exists between the processes that destroy today s mountains and those that created them the paleozoic more trondelag fault complex was reactivated as a normal fault during the mesozoic and probably throughout the cenozoic until the present day its ne sw trending strands crop out between the coast and the base of a c 1 7 km high nw facing topographic great escarpment well preserved kinematic indicators and multiple generations of fault products are exposed along the tjellefonna fault a well defined structural and topographic lineament parallel to both the langfjorden and the great escarpment the slope instability that was formerly present at tjelle and additional instabilities currently present throughout the region may be viewed as the direct product of past and ongoing development of tectonic topography in more og trondelag county in the langfjorden region in particular structural geometry suggests additional unreleased rock compartments may be isolated and under normal fault control although post glacial rebound and topographically derived horizontal spreading stresses might in part help drive present day oblique normal seismicity the normal fault controlled escarpments of norway were at least partly erected in pre glacial times cretaceous to early tertiary post rift subsidence was interrupted by normal faulting at the innermost portion of the passive margin imposing a strong tectonic empreinte on the developing landscape

approximating edges of source bodies from magnetic or gravity anomalies cordell and grauch 1982 1985 discussed a technique to estimate the location of abrupt lateral changes in magnetization or mass density of upper crustal rocks the final step of their procedure is to identify maxima on a contoured map of horizontal gradient magnitudes we attempt to automate their final step our method begins with gridded magnetic or gravity anomaly data and produces a plan view of inferred boundaries of magnetic or gravity sources the method applies to both local surveys and to continent wide compilations of magnetic and gravity data e g zietz 1982 simpson et al 1983a kane et al 1982

diagenesis and remanence acquisition in the lower pliocene trubi marls at punta di maiata southern sicily palaeomagnetic and rock magnetic observations three new profiles lcm pmd and cmd through the lower cochiti polarity zone enable comparison of the effects of weathering and diagenesis on the magnetic properties of the early pliocene trubi marls these marls have been well dated by means of astronomical calibration and are of particular interest in terms of polarity zonation and regional tectonics the freshest exposures lcm profile carry a remanence associated with pyrrhotite which is particularly enhanced in some grey layers this is the first time that occurence of pyrrhotite as the mam remanence carrier in the trubi marls is documented sd magnetite was previously recognised as the fundamental ferromagnetic phase the mean chrm direction from the lcm record does not show the expected 30 35 clockwise rotation found in other studies and does not record the normal cochiti interval either i e is reverse throughout the sampled interval suggesting a relatively late origin for the nrm standard rock magnetic techniques are used to investigate the nature of the magnetization in the three laterally equivalent profiles at punta di maiata the actual data set seems to be better explained by a complex diagenetic history involving a multistage redox history that invokes a late anoxia event the previously postulated iron migration model van hoof et al 1993 was put forward for the suboxic situation and does not take into account the presence of magnetic sulfides which are clearly demonstrated in the zone under study the extended diagenetic model inferred here proposes a pathway that accounts for most of the new observations the salient feature is the postulated existence of a diagenetic phase that has altered the original nrm in some areas dissolution of magnetite resulting in a later stage acquisition of chemical remanence that does not date to the timing of deposition of the sediments the extension and the detailed mechanisms by which such a process has taken part deserve further research nonetheless the present investigation accounts for previously unrecognised features in the trubi marls from sicily and outlines how intricate the nature of the mechanisms contributing to the blocking of remanence in sediments can be

the middle to late devonian hoybakken detachment central norway 40ar 39ar evidence for prolonged late post scandian extension and uplift the regionally significant 0 5 2 km thick hoybakken detachment in central norway bounds the southern margin of the central norway basement window and exhibits a well developed top to the wsw fabric characteristic of late scandian devonian ductile extension 40 ar 39 ar data obtained from hornblende mica and k feldspar mineral separates of rocks collected in a transect through the hoybakken detachment yield well defined plateau and isochron mineral ages early devonian exhumation and cooling of the hoybakken detachment footwall is recorded by hornblende ages of 400 ma and mica ages of 390 ma the mylonitic fabric overlying the footwall records younger middle devonian mica crystallization ages of 384 381 ma that are among the youngest extensional ductile fabrics dated in the caledonides and suggest prolonged extensional activity on the hoybakken detachment after inferred cessation of ductile extension at 381 ma the rate of uplift and cooling was reduced and the footwall records late devonian to early carboniferous k feldspar ages of 371 356 ma prolonged extensional activity at hoybakken is compatible with recent u pb ages of deformed titanite crystals and established rb sr ages of white mica in shear related pegmatites both from the southwestern part of the fosen peninsula and 40 ar 39 ar ages of syn tectonic mica overgrowth from the adjacent hitra snasa fault together these ages suggest the onset of ductile extension soon after 401 ma and with the middle devonian crystallization ages determined here suggest that ductile extension on the hoybakken detachment had a duration of 11 20 ma the youngest age of 320 ma was obtained from a k feldspar in a cataclastic granite of the hoybakken detachment s hangingwall and is considered to date a phase of post scandian brittle deformation that overprinted the mylonitic shear fabric

tectonic development of the mid norway continental margin abstract the area reviewed covers the mid norway continental margin between latitudes 62 n and 68 n main structural elements as defined at the base cretaceous level are the trondelag platform underlying the inner shelf the more and voring basins located beneath the outer shelf and slope and the more platform and the outer voring plateau forming a base of slope trend of highs sediments contained in the mid norway basin range in age from late palaeozoic to cenozoic the basement was consolidated during the caledonian orogenic cycle devonian and early carboniferous wrench movements along the axis of the arctic north atlantic caledonides are thought to have preceded the namurian onset of crustal extension rifting processes were intermittently active for some 270 my until crustal separation between greenland and fennoscandia was achieved during the early eocene during the evolution of the norwegian greenland sea rift system a stepwise concentration of tectonic activities to its axial zone the area of subsequent continental separation is observed during the late palaeozoic to mid jurassic a broad zone was affected by tensional faulting during the late jurassic and cretaceous the trondelag platform was little affected by faulting whilst major rift systems in the more and voring basins subsided rapidly and their shoulders became concomitantly upwarped during the latest cretaceous and early palaeogene terminal rifting phase only the western more and voring basins were affected by intrusive and extrusive igneous activity following the early eocene crustal separation and the onset of sea floor spreading in the norwegian greenland sea the voring segment of the mid norway marginal basin subsided less rapidly than the more segment during the early and mid tertiary minor compressional deformations affected the voring basin and to a lesser degree the more basin tensional forces dominated the late palaeozoic to early cenozoic evolution of the mid norway basin and effected strain mainly in the area where the crust was weakened by the previous lateral displacements the lithosphere thinned progressively and the effects of the passively upwelling hot asthenospheric material became more pronounced massive dyke invasion of the thinned crust preceded its rupture

kinematics of the hoybakken detachment zone and the more trondelag fault complex central norway the tectonic disintegration of the caledonian orogen through combined extension contraction and strike slip was characterized by spatial and temporal strain partitioning through a period of at least 30 ma early to mid devonian exhumation of the central norway basement window was associated with retrograde top to the sw extensional shearing in the hoybakken detachment zone sinistral shearing along the more trondelag fault complex and formation of extension parallel folds progressive exhumation led to increasing strain localization and to the transition from ductile to brittle deformation in the interval between c 370 and 320 ma the hoybakken detachment fault cut previously folded detachment mylonites capturing mylonites in its hanging wall 40 ar 39 ar mica and k feldspar ages indicate a late devonian or younger age for the uppermost parts of the adjacent old red basin gentle folding of this stratigraphic level attests to the continuation of shortening and orogen oblique extension into late devonian carboniferous time shortening was intensified along strands of the more trondelag fault complex as shown by mutually cross cutting reverse and strike slip faults flower structures may be particularly common in constrictional strain systems where strike slip faults develop parallel to the principal elongation trend but normal to the principal axis of shortening