theoretical models of magnetic anisotropy to strain relationship revisited abstract mathematical modelling of the relationships between the low field magnetic anisotropy and strain are redeveloped and the calculated data are compared with the degree of anisotropy for various rock types it is found that the degree of anisotropy for realistic strain magnitudes is unrealistically high in the passive model the ductile model for which the degree of anisotropy depends on the magnetic grain the matrix viscosity ratio becomes realistic at high viscosity contrasts in the line plane model the theoretical degree of anisotropy corresponds well to the natural degree of anisotropy for rocks in which the carrier of magnetic anisotropy is either magnetite or phyllosilicate minerals by contrast in the case of haematite and pyrrhotite the modelled degree of anisotropy is much higher than the natural values in the viscous model the calculated degree of anisotropy corresponds well to that measured in sedimentary and volcanic rocks in the models imposing pure shear strain the natural logarithm of the degree of anisotropy to natural strain relationship can be approximately represented by a straight line at least for low to intermediate strains the proportionality constant varies according to the specific model and the specific carrier of the anisotropy of magnetic susceptibility

breakup of the newfoundland iberia rift abstract the newfoundland iberia rift is considered to be a type example of a non volcanic rift key features of the conjugate margins are transition zones tzs that lie between clearly continental crust and presumed normal penrose type oceanic crust that appears up to 150 180 km farther seaward basement ridges drilled in the iberia tz consist of exhumed serpentinized peridotite of continental affinity consistent with seismic refraction studies although the boundaries between continental crust and the tzs can be defined with relative confidence there are major questions about the position and nature of the change from rifting to normal sea floor spreading at the seaward edges of the tzs notably drilling of presumed oceanic crust in the young m series anomalies to investigate and potentially resolve these conflicts we analysed the tectonic history and deep pre cenomanian stratigraphy of the rift using seismic reflection profiles and drilling results rifting occurred in two main phases late triassic earliest jurassic and late jurassic early cretaceous the first phase formed continental rift basins without significant thinning of continental crust the second phase led to continental breakup with extension concentrated in three episodes that culminated near the end of berriasian hauterivian and aptian time the first two episodes appear to correlate with separation of continental crust in the southern and northern parts of the rift respectively suggesting that the rift opened from south to north in a two step process the third episode persisted through barremian and aptian time we suggest that during this period there was continued exhumation of subcontinental mantle lithosphere at the plate boundary and that elevated in plane tensile stress throughout the rift caused intraplate extension primarily within the exhumed mantle this rifting may have been interrupted for a time during the barremian when melt was introduced from the southern edge of the rift by plume magmatism that formed the southeast newfoundland ridge and j anomaly ridge and the conjugate madeira tore rise we propose that the rising asthenosphere breached the subcontinental mantle lithosphere in latest aptian earliest albian time initiating sea floor spreading this resulted in relaxation of in plane tensile stress i e a pulse of relative compression that caused internal plate deformation and enhanced mass wasting this aptian event produced a strong rift wide reflection that is unconformably onlapped by post rift sediments that were deposited as a stable sea floor spreading regime was established although previously considered to be a breakup unconformity associated with separation of continental crust the event instead marks the final separation of the subcontinental mantle lithosphere our analysis indicates that interpretation of tectonic events in a non volcanic rift must consider the rheology of the full thickness of the continental lithosphere in addition to spatial and temporal changes in extension that may occur from segment to segment along the rift

alteration mineralization and metamorphism in the area of the east south c ore zone 24th level of the dickenson mine red lake northwestern ontario the area of the east south c esc orebody of the dickenson mine red lake consists of variably altered and mineralized basalt basaltic volcaniclastic rocks minor sulphidic iron formation and

planktonic foraminiferal biostratigraphy of the neogene sequence in the adana basin turkey and its correlation with standard biozones the aim of this study is to describe the biostratigraphic chronostratigraphic and ecostratigraphic relationships of the neogene sequence in the adana basin the adana basin is located in southern turkey and bordered by the tauride orogenic belt to the north the amanos mountains to the east the mediterranean coast to the south and the ecemis fault zone to the west from base to top the neogene sequence consists of the gildirli formation continental redbeds the shallow marine kaplankaya formation the reefal limestones of the karaisali formation the shales of the guvenc formation slope to deep marine a thick submarine fan complex cingoz formation the shallow marine and fluvio deltaic kuzgun formation and the shallow marine lagoonal continental handere formation the planktonic foraminiferal biozones identified within the neogene sequence of the adana basin are globigerinoides trilobus and praeorbulina glomerosa curva burdigalian globorotalia fohsi peripheroronda orbulina suturalis langhian and globorotalia mayeri serravallian the late tortonian is characterized by the first occurrence of globorotalia suterae there are no planktonic foraminiferal zones in the messinian but this level may be correlated with a non distinctive zone in the mediterranean region the pliocene is represented by the sphaeroidinellopsis acme zone

magnetic susceptibility of the rock matrix related to magnetic fabric studies non ferromagnetic minerals constitute what is called the rock matrix whose susceptibility k1 is directly accessible using only high magnetic fields measurements on minerals and a wide range of rock types show that k1 is mainly due to paramagnetism and hardly exceeds 10 3 si with an anisotropy degree p less than 1 35 different methods to estimate the role of the matrix component in low field susceptibility k and its anisotropy include petrological and chemical analysis evolution of p vs k low temperature studies and comparison of k with remanent magnetizations

chronostratigraphic constraints on the genesis of archean greenstone belts northwestern superior province ontario canada abstract the paper reports new u pb zircon ages for supracrustal assemblages of the red lake mcinnes lake hornby lake north spirit lake and favourable lake greenstone belts of northwestern superior province and evaluates their significance within the regional stratigraphic and tectonic context the new data confirm and refine the existing picture of a multistage evolution lasting ca 300 m y initiated at ca 3000 ma by periods of coeval calc alkalic tholeiitic and komatiitic magmatic activity followed by the eventual accretion of a microcontinental nucleus by ca 2900 2800 ma and concluded by an intense period of extensive tholeiitic and calc alkalic volcanism and by widespread plutonism and tectonism between 2750 and 2680 ma volcanic sequences in the mcinnes lake and hornby lake greenstone belts of the berens river subprovince yield ages of 2974 2 2969 3 2928 2 and 2901 2 ma showing a correlation with the early stages of greenstone belt development in the region similarly a sedimentary unit in the northern red lake greenstone belt was probably deposited at ca 2900 ma as indicated by a range of detrital zircon ages between 2989 and 2916 ma and the absence of younger components by contrast a volcanic unit in the center of the red lake greenstone belt previously thought to be 2830 ma yields an age of 2745 7 4 ma which correlates with some of the latest volcanic episodes in the uchi subprovince a detrital zircon population in a sedimentary unit of the western favourable lake greenstone belt of the sachigo subprovince displays single grain ages ranging from 2843 to 2727 ma the youngest age corresponding to that of an unconformably underlying tonalite gneiss the geological and geochronological relationships suggest that the north spirit lake and favourable lake greenstone belts represent back arc basins that evolved between ca 2750 and 2730 ma in a transtensional setting within the older north caribou terrane sedimentation was initiated during opening and deepening of the basins and accompanied most of the concluding compression and imbrication stages the period between 2750 and 2680 ma was also characterized by widespread granitoid plutonism that enveloped the mcinnes lake and hornby lake greenstone belts and older tonalites and formed the bulk of the berens river subprovince

galicia bank ocean continent transition zone new seismic reflection constraints abstract the west iberia continental margin is a type locale for magma poor rifting and studies there have been instrumental in changing the classical view of the ocean continent transition oct from a discrete boundary juxtaposing continental and oceanic crust into a more complicated zone of varying width that can include exhumed mantle this study examines two new seismic lines in the galicia bank area extending west of the peridotite ridge showing high resolution images of five new ridges these ridges could be hyperextended continental crust exhumed continental mantle or rough ultra slow spreading oceanic crust there are no tilted fault blocks with pre syn rift stratigraphy that would indicate continental crust there are also no faults indicating mid ocean spreading with seismic layer stratigraphy indicating normal oceanic crust the ridges have no coherent internal seismic structure and some resemble the topographic profile of the peridotite ridge therefore it is likely the western ridges are also mainly composed of serpentinized mantle these western ridges are also similar to small oceanic core complexes observed along the active part of the mid atlantic ridge which also contain exhumed serpentinized mantle this implies that there is a gradual transition within our study area from continental extension to seafloor spreading exhumation of continental mantle results in the formation of peridotite ridges then transitions to episodic volcanism which produces local thin basaltic crust and exhumation of oceanic core complexes asymmetric processes during initial rifting and spreading result in contrasting structures on the two resulting margins

structure and development of the southeast newfoundland continental passive margin derived from screech transect 3 new seismic reflection data from the grand banks of newfoundland and the newfoundland basin add to the growing knowledge of the composition structure and history of this nonvolcanic margin geophysical imaging is now approaching the extent of that done previously on the conjugate margin along iberia providing a valuable database for the development of rifting models two parallel profiles over the shelf platform image deep crustal fabric representing precambrian or possibly appalachian deformation as well asmesozoic extension progressively more intense extension of continental crust is imaged oceanwards without the highly reflective detachments frequently seen on profiles off galicia a landward dipping event l is imaged sporadically and appears to be analogous to a similar event on the iberian iam9 profile the transition zone is probably exposed serpentinized mantle as interpreted off the iberian margin although there appears to be a difference in the character of ridge development and reflectivity the distinctive u reflection identified previously at the base of the newfoundland basin deep water sedimentary section and recently identified as one or more thin basalt sills is imaged on newly presented profiles that connect previously published profiles scr3 and scr2 showing that u is highly regular and continuous except where interrupted by basement highs u is also seen to have a major impact on the ability to image underlying basement a full transect beginning over completely unextended continental crust through to oceanic crust has provided a data set from which estimates of extension and the pre rifting location of the present continental edge can be made two estimates were obtained 85 km based on faulting and 120 km based on crustal thickness

an evaluation of criteria to deduce the sense of movement in sheared rocks some of the most useful criteria for the deduction of the sense of shear are summarized for use in areas where unequivocal field evidence is lacking apparently conflicting evidence from rotated pressure shadow regions around porphyroclasts and porphyroblasts is clarified the use of quartz crystallographic fabric asymmetry to deduce the shear sense in the bulk rock should be treated with caution and used only together with detailed microstructural observations

archaean gold mineralisation in a normal motion shear zone at harbour lights leonora western australia although many archaean greenstone hosted mesothermal gold deposits are in steep reverse motion fault zones other fault geometries are prospective for mineralization harbour lights is one of a number of deposits at leonora hosted in a normal motion shear zone probably related to movement off the adjacent domal granitoid the deposit is also atypical in that mineralization predates the last deformation to affect the mine sequence but formed by similar processes to other mesothermal deposits in all respects other than the detail of shear zone geometry kinematics and timing

magnetic fabric implications for the relationships between deformation mode and grain growth in slates from the borrowdale volcanic group in the english lake district abstract in the less chlorite rich slates from the borrowdale volcanic group chlorite magnetic fabric almost corresponds to fabric resulting from deformation following the march fernandez model but chlorite grain rotation could be related to the first stages of the tectonic deformation in the other slates the chlorite grains probably impinging after these stages upon one another and a simple grain rotation mechanism being therefore no longer possible

ocean continent boundary in the iberia abyssal plain from multichannel seismic data abstract the ocean continent boundary of the west iberia margin is marked by a basement ridge trending n s four segments of this ridge are recognized each of them being progressively offset westward from 40 n to 43 n because the setting and seismic character of the ridge in the iberia abyssal plain are similar to those of the galicia margin ridge which is made of serpentinized peridotite we think that the southern segments of the ridge are also made of the same mantle material the segmentation of the ridge suggests that the northward propagation of the continental break up during the north atlantic opening in early cretaceous times was discontinuous each segment possibly corresponding to a propagation step east of the ridge the basement of the whole iberia abyssal plain consists of highly thinned continental crust locally resting on a seismic reflector that resembles the s reflector previously recognized off galicia by analogy with the galicia margin we propose that the tilted crustal blocks lay on serpentinized peridotite derived from the upper mantle the s reflector corresponding to the contact between crustal rocks and serpentinite

the ocean continent boundary off the western continental margin of iberia crustal structure west of galicia bank a seismic refraction transect across the galicia bank continental margin shows that the original continental crust thins westward from 17 to 2 km immediately east of a margin parallel peridotite ridge pr immediately west of the pr oceanic crust is only 2 5 3 5 km thick but farther west oceanward it thickens to 7 km the pr caps a similar to 60 km wide lens shaped serpentinized peridotite body underlying both thinned continental and thin oceanic crust when superimposed on a reflection time version of the velocity model the s reflector is clearly intracrustal at its east end westward s cuts down to lower crustal levels eventually coinciding with the top of the serpentinized peridotite lens original crust mantle boundary these observations render almost impossible the seafloor exposure of the pr by s acting as a top to the west detachment fault numerical models of melting and borehole subsidence information constrain our rifting model the easternmost continental crust experienced a total stretching factor of 4 3 most likely in two stages it probably occurred over similar to 25 m y with the highest fate of stretching at the beginning of the main earlier rift phase valanginian 141 135 ma the 3 4 7 km thick continental crust depending on whether serpentinized peridotite is assigned to crust or mantle which may include melt products requires stretching factors 6 more than 11 7 and a rift duration of more than 25 13 m y the thin oceanic crust immediately west of the pr is explained by conductive cooling of the mantle during the long prebreakup stretching phase which temporarily caused reduced melting immediately after breakup

crustal structure and magmatism of north atlantic continental margins enormous variations exist along rifted margins of the north atlantic in the magmatic activity that accompanied continental breakup the north atlantic margins exhibit a full range of magmatic behaviour one end of the spectrum commonly termed volcanic margins is found in the northern north atlantic off greenland norway and northwest britain where huge volumes of igneous rock were added to the continental crust as it rifted and the adjacent oceanic crust is considerably thicker than normal the other end of the spectrum so called non volcanic margins occurs further south off france and spain where only minor volcanism accompanied rifting and the oceanic crust immediately adjacent to the continental margin is thinner than normal oceanic crust results from seismic profiles are used to determine the volume and distribution of igneous crust accumulated as the continents broke up and seafloor spreading commenced the volume of melt produced during rifting is controlled mainly by the temperature of the underlying asthenospheric mantle and by the amount and rate of decompression as it rises beneath stretching and thinning lithosphere large quantities of igneous rock were produced as the continents broke up to form the north atlantic where the newly initiated iceland plume brought abnormally hot mantle beneath the rift much smaller quantities of melt were produced further south where mantle temperatures were normal during rifting the distribution of igneous rocks across the continental margin and the adjacent oceanic crust is controlled by the rate at which melt is produced and by the ease with which it can intrude laterally in the crust where the rate of stretching is very slow and the rifting is spread over many millions or even tens of millions of years as is common during the initial stages of rifting then the rising asthenospheric mantle has time to cool by conduction heat is lost from the asthenospheric mantle both vertically into the overlying water layer and laterally into the colder wedges of continental lithosphere on either side of the rifted region as a consequence of the reduced mantle temperatures considerably less partial melting occurs in the slowly rising asthenospheric mantle than in mantle which rises rapidly beneath rifts this explains the abnormally thin oceanic crust found adjacent to the non volcanic rifted continental margins in the north atlantic as the new ocean widens the spreading centre becomes isolated from the continental margins on either side by newly formed warm oceanic lithosphere and the rate of rifting generally increases the oceanic crust then attains its equilibrium thickness as conductive heat loss from the rising asthenospheric mantle reduces and all the melt formed by decompression of the mantle solidifies close to the spreading axis basaltic melts can intrude continental crust far more easily than oceanic crust basaltic dykes may extend many hundreds of kilometres away from the magma source beneath continental rifts this redistributes melt laterally towards the continent in both volcanic and to a lesser extent in non volcanic margins and may be a contributory factor in leaving unusually thin crust in the first formed ocean immediately adjacent to some rifted margins it also allows melt formed under volcanic rifts to migrate large distances laterally as is seen in the rockall area northwest of britain

easternmost mediterranean evidence of the zanclean flooding event and subsequent surface uplift adana basin southern turkey according to the literature the adana basin at the easternmost part of the mediterranean basin in southern turkey records the pliocene stage with shallow marine to fluvial deposits our micropalaeontological analysis of samples from the adana basin reveal late lago mare biofacies with paratethyan ostracod assemblages pertaining to the loxocorniculina djafarovi zone grey clays rich in planktonic foraminifera lie above the lago mare deposits within the grey clays the continuous occurrence of the calcareous nannofossil reticulofenestra zancleana and the base of the reticulofenestra pseudoumbilicus paracme points to an early zanclean age 5 332 5 199 ma both ostracod and benthic foraminifera indicate epibathyal and bathyal environments 87 sr 86 sr measurements on planktonic and benthic foraminifera fall below the mean global ocean value for the early zanclean indicating potentially insufficient mixing of low 87 sr 86 sr mediterranean brackish lago mare water with the global ocean in the earliest pliocene we utilize the ages and palaeodepths of the marine sediments together with their modern elevations to determine uplift rates of the adana basin of 0 06 to 0 13 mm a 1 since 5 2 5 3 ma total uplift of 350 650 m from surface data and 0 02 0 13 mm a 1 since c 1 8 ma total uplift of 30 230 m from subsurface data

determination of stress from slip data faults and folds a new technique is derived to invert slickenside data for the stress field that caused the faulting episode this inversion is simplified by the assumption that the magnitude of the tangential traction on the various fault planes at the time of rupture is similar study of three normal faulting regimes shows that the inversion derived with this assumption yields results that closely match older inversions that did not include the assumption hence the assumption may be valid and is shown to be justified by analyzing a simple fracture criterion application of slip data inversions is extended from faulting regimes to the slip on bedding plane faults in folding regimes comparison of the inversion results with the geometry of the folds shows this application to be successful greatly increasing the number of data sets that can be used to find the paleostress field

gold quartz veins in metamorphic terranes and their bearing on the role of fluids in faulting gold quartz vein fields in metamorphic terranes such as greenstone belts provide evidence for the involvement of large volumes of fluids during faulting and may be products of seismic processes near the base of the seismogenic regime in the val d or district of the abitibi greenstone belt canada quartz tourmaline carbonate veins form a vein field 30 15 km in the hanging wall of a crustal scale fault zone which was the main channelway for upward migration of the deeply generated fluids the veins occur in small high angle reverse faults and in adjacent horizontal extensional fractures extending up to 75 m in intact rocks they have formed incrementally during active reverse faulting in response to crustal shortening at depths corresponding to those at the base of the seismogenic zone in actively deforming crust detailed structural and fluid inclusion studies provide evidence for generally lithostatic but fluctuating fluid pressures p of the order of 200 mpa and for cyclic stress reversals during vein formation and provide good support for the fault valve model a comparison of vein characteristics with standard earthquake rupture parameters suggests that each slip increment along veins in reverse faults was accompanied by a small earthquake 4 m 3 or less the large vein field thus represents both the extent of fluid dispersion in the hanging wall of a crustal scale channelway and the distribution of small earthquakes integrated over the lifetime of the hydrothermal system it is proposed that such small earthquakes along veins in reverse faults are related to large earthquakes m 6 nucleating near the base of the seismogenic regime along the nearby crustal scale fault either as aftershocks or as a precursory smarm

deep structure of the ocean continent transition in the southern iberia abyssal plain from seismic refraction profiles ocean drilling program legs 149 and 173 transect we present a wide angle seismic refraction study of an 80 40 km region of the southern iberia abyssal plain south of galicia bank an intersecting grid of two e w and four n s wide angle reflection refraction profiles is used to define variations of the basement velocity structure within this unusually wide ocean continent transition oct these structures can be systematically linked to variations in acoustic basement morphology and to results from ocean drilling program odp boreholes lateral changes in the velocity structure of the basement occur abruptly over distances of 20 km where complex variations may be found thinned upper continental crust 2 5 km thick with velocities of 5 0 6 6 km s is limited to a series of n s fault blocks immediately south of galicia bank this crust is underlain by a high velocity layer 7 3 7 9 km s of weakly serpentinized i e 0 25 peridotite which exists throughout the eastern part of the survey area basement within the oct appears to consist dominantly of a broad region of exposed upper mantle that has been serpentinized heterogeneously both vertically and horizontally in the southeast sector of our survey where basement topography deepens and becomes subdued continental fault blocks are absent instead basement contains an upper layer of more pervasively serpentinized i e 25 45 peridotite that is 2 km thick this layer is characterized by low velocity at the top of basement 4 2 km s that increases rapidly with depth and it probably corresponds to a seismically unreflective layer previously identified in reflection profiles to the south of our survey in the western section of our survey beneath a series of elevated basement ridges velocities are reduced within both the upper basement layer 3 5 6 0 km s and lower layer 6 4 7 5 km s these changes suggest that both upper and lower layers have become more highly serpentinized with values of 60 100 in the upper layer and 25 45 in the lower layer probably during the last stages of rifting and immediately before formation of oceanic crust a normal or slow spreading oceanic crustal structure is not found within the survey region thus it appears that the onset of seafloor spreading occurs in the region west of the peridotite ridge sampled at odp site 897 and east of the j magnetic anomaly

deep structure in the vicinity of the ocean continent transition zone under the southern iberia abyssal plain we present results from a seismic and magnetic study of acoustic basement beneath the southern iberia abyssal plain an ocean continent transition zone oct characterized by subdued basement relief and weak magnetization lies seaward of thinned continental crust its western edge is a region with isochron parallel ridges and generally higher basement magnetizations the width of the oct decreases to the north the seaward change in basement morphology coincides with changes in seismic velocity structure but in both regions anomalously high velocities at shallow depths within acoustic basement suggest that the oct consists largely of serpentinized peridotite our magnetic and seismic data support the hypothesis of exhumed upper mantle more than that of ultraslow sea floor spreading for the origin of the oct

total tectonic subsidence a parameter for distinguishing crust type at the u s atlantic continental margin total tectonic subsidence tts is the difference between the prerifting continental crust elevation and the present sediment unloaded basement depth in a sedimentary basin tts is calculated using observations of bathymetry and basement depth and assumptions about sediment density and the loading response of the lithosphere i use the extensional model for sedimentary basin formation to interpret the tts of a passive continental margin that model predicts that the tts on an old margin should define the major crust type boundaries and indicate the lateral distribution of extension within the extended continental crust tts analysis of the u s atlantic continental margin indicates that the boundary between extended continental and oceanic crusts lies along the east coast magnetic anomaly ecma to the north of the blake spur fracture zone bsfz and along the blake escarpment to the south there is no tts anomaly associated with the blake spur magnetic anomaly which seems to be underlain by normal oceanic crust the ecma appears to be associated with a tts minimum but i attribute that to artificially shallow estimates of depth to magnetic basement under the ecma tts estimates of extended continental crust thickness agree well with gravity models except where the problem with magnetic basement depth estimates interferes the amount of crust extension prior to seafloor spreading varies along the strike of the margin the most abrupt change is at the bsfz across the bsfz the amount of extension varies by 160 km but the volume of continental material does not vary the extension variation may be caused by lateral changes in the gross rheology of the continental lithosphere in the case of the bsfz it would be the suture of more ductile pre late paleozoic african craton with more brittle north american craton that could cause the abrupt change

porphyroclast systems as kinematic indicators porphyroclasts of relatively strong minerals in mylonites commonly have an internal monoclinic shape symmetry defined by tails of dynamically recrystallized material the geometry of a porphyroclast and its tails called a porhyroclast system can serve as a valuable indicator of the sense of vorticity porphyroclast systems have been divided into and types on the basis of the geometry of the tails types have wedge shaped recrystallized tails whose median lines lie on opposite sides of a reference plane parallel to the tails and containing the symmetry axis for the system types are further subdivided into a a types in which the porphyroclast is isolated in a relatively homogeneous matrix and b types in which the porphyroclast system is associated with a shear band foliation in the matrix types typically have narrow recrystallized tails whose median lines cross the reference plane adjacent to the porphyroclast consequently embayments of matrix material occur adjacent to the porphyroclasts and the tails display characteristic bends a porphyroclast system in a mylonite develops when the relatively weak dynamically recrystallized grain aggregate in the porphyroclast mantle changes its shape due to non coaxial flow in the adjacent matrix this behaviour has been modelled in shear box experiments passive marker lines around rigid cylinders embedded in silicone putty were subjected to simple shear the experiments were modified to simulate a change in recrystallization rate r with respect to rate of deformation by decreasing the diameter of the rigid cylinder during deformation at variable rates the ratio r appears to be one of the most important factors in determining which porphyroclast system will develop at high r values flow of recrystallized material away from the porphyroclast is continuously appended by the production of new grains and wedge shaped a type tails develop at low r values relatively few new grains are added to the tails which become thinned and deflected by drag due to the spinning motion of the porphyroclast in addition most porphyroclast systems at low shear strains are of a type or lack monoclinic symmetry whereas types are only developed at high shear strain values complex porphyroclast systems characterized by two generations of tails are observed in many of the natural and model shear zones studied and may form due to fluctuating r conditions that allow isolated a and type porphyroclast systems to be used as sense of vorticity indicators are the systems should have a monoclinic shape symmetry matrix grain size should be small with respect to porphyroclast size matrix fabric should be homogeneous deformation history should be simple and observations should be made on sections normal to the inferred bulk vorticity vector for the mylonite

compressional deformation at the ocean continent transition in the ne atlantic local zones of compressional deformation spatially coincident with the ocean continent transition occur in the ne atlantic off western iberia on the northern margin of the bay of biscay and in the southern rockall trough the deformation zones are typically broad oceanward facing monoclines several tens of kilometres in width the amount of shortening is small although the structures may also accommodate some strike slip motion deformation peaked during the mid late eocene in biscay off galicia bank and in rockall trough and in the mid miocene off western iberia these deformation pulses were contemporary with the pyrenean and betic orogenies in western europe and may have resulted from structural reorganizations within the evolving orogens driven by changes in plate motion possible mechanisms which might concentrate deformation at the ocean continent transition include slip within serpentinized peridotite underlying the transitional region and reactivation of a pre existing detachment fault within the thinned continental crust our observations may imply that rifted continental margins when reactivated can develop into new sites of plate subduction

determination of position gradient tensor from strain measurements and its implications for the displacement across a shear zone abstract a method is proposed for determination of the position gradient tensor from conventional strain measurements the position gradient tensor can be multiplicatively decomposed into two components left stretch and rotation tensors the former is readily supplied by field strain data whereas the latter is generally unknown in nature in order to determine the position gradient tensor using strain data it is assumed that structures within a shear zone are symmetric about the plane common to the transport direction and the pole to the shear zone or alternatively that the shear strain in the direction parallel to the pole to the shear zone on the plane normal to the transport direction in a parallel sided shear zone is negligible with these assumptions the position gradient tensor is fully determined from the attitude and principal ratios of the strain ellipsoid determined from field data this method has been applied to the strain data from deformed fragments in a succession of late triassic volcanic breccias abutting a large strike slip shear zone in north central british columbia the resulting position gradient tensor is then used to constrain the displacement across the shear zone suggesting 39 shortening normal to and dextral displacement of about 1700 m along the shear zone

syn tectonic magmatism and the development of compositional layering ungava orogen northern quebec canada abstract layer and foliation parallel emplacement of granitic veins was an important process in the regional development of compositional layering in now exhumed middle crustal sections of both archean and paleoproterozoic age in the northern ungava peninsula quebec canada in the archean superior province diorite and tonalite plutons were penetratively deformed and metamorphosed at granulite facies conditions coeval with voluminous granitic magmatism the paleoproterozoic narsajuaq arc contains evidence for contemporaneous magmatism transpressional deformation and granulite facies metamorphism prior to its collision with the superior province basement in both plutonic domains regional compositional layering is defined by 1 metre to kilometre scale alternation of generally well foliated tonalite and quartz diorite bodies and 2 centimetre to kilometre scale variably deformed granitic veins and sheets that lie parallel to layering tectonic foliation in the host rocks syn tectonic intrusion of a substantial portion of the veins along extension fractures sub parallel to layering foliation i e at high angle to the regional shortening direction is interpreted to have occurred due to the combination of a strong anisotropy and high magma pressures compositional layering generated and or enhanced by this process may contribute to the overall seismic reflectivity of the middle and lower crust

dominant symmetry of a conjugate southern australian and east antarctic magma poor rifted margin segment synthesis and modeling of published deep seismic and potential field data from the conjugate magma poor rifted margins of the great australian bight southern australia and central wilkes land east antarctica show that there is pronounced symmetry of structures in a 300 km wide zone straddling the axis of final breakup this symmetry is observed consistently for a distance of some hundreds of kilometers along strike from inboard to outboard both margins comprise a narrow zone of attenuation of the crystalline continental crust an approximately 4 km high basement ridge interpreted as unroofed peridotites at the location of maximum thinning of the continental crust and a 60 70 km wide continent ocean transition zone that contains a sedimentary basin that may be underlain by altered mantle and fragments of crystalline continental crust the marked breakup symmetry described here is in contrast to the asymmetry of the iberia newfoundland margin and is consistent with the operation of a symmetrical extensional detachment system deforming the whole crust in the center of the rift as envisaged by some numerical models for the continental rifting process

surface expression of eastern mediterranean slab dynamics neogene topographic and structural evolution of the southwest margin of the central anatolian plateau turkey 1 the southwest margin of the central anatolian plateau has experienced multiple phases of topographic growth including the formation of localized highs prior to the late miocene that were later affected by wholesale uplift of the plateau margin our new biostratigraphic data limit the age of uplifted marine sediments at the southwest plateau margin at 1 5 km elevation to 7 17 ma and regional lithostratigraphic correlations imply that the age is 6 7 ma single grain ca tims u pb zircon analyses from a reworked ash within the marine sediments yield dates as young as 10 6 ma indicating a maximum age that is consistent with the biostratigraphy our structural measurements within the uplifted region and fault inversion modeling agree with previous findings in surrounding regions with early contraction followed by strike slip and extensional deformation during uplift focal mechanisms from shallow earthquakes show that the extensional phase has continued to the present broad similarities in the change in the tectonic stress regime after 8 ma and the onset of surface uplift after 7 ma imply that deep seated process es caused post 7 ma uplift the geometry of lithospheric slabs beneath the plateau margin pliocene to recent alkaline volcanism and the uplift pattern with accompanying normal faulting point toward slab tearing and localized heating at the base of the lithosphere as a probable mechanism for post 7 ma uplift of the southwest margin considering previous work in the region there appears to be an important link between slab dynamics and surface uplift throughout the anatolian plateau s southern margin

role and effects of pore fluid pressure in thrusting the case history of the umbria marche apennines central italy structure timing and rates of deformation and the aspect ratio of the external zones of the umbria marche thrust system umts have been investigated with the aim of comparing features and processes occurring during the growth of a tectonic wedge with those inferred from mechanically based model predictions the results of the umts test seem to support the idea that most of the characteristic features of a thrust system may be considered as the result of the incremental transient increase of the pore fluid pressure pf as a consequence of the amount of shortening of a crustal section the strong dependence of pf on strain rates and on the thickness of the rock mass involved in the deformation may also help to explain local and or regional variations in the aspect ratio of the deformed state profiles of different fold and thrust belts

early cretaceous motion of flemish cap with respect to north america implications on the formation of orphan basin and se flemish cap galicia bank conjugate margins bouguer gravity anomalies together with deep seismic reflection and magnetic data on both sides of the north atlantic are used to locate the hinge zones of the flemish cap and galicia bank within the iberian and north american plates regions across which there were abrupt changes in lithospheric extension the characteristic shape and alignment of these hinge zones suggest that they were conjugate features generated during chrons m25 m0 late jurassic early aptian around a distally located euler pole of rotation rifting between iberia and north america involved these two larger plates and the two smaller microplates the flemish cap and galicia bank microplates the motion of the microplates which were adjacent to eurasia was much more complex than those of the larger plates the motion between the microplates from chron m25 or older to chron m0 was complicated by the fact that they remained attached to each other for most of the time when regions to the south were rifting apart as a result continental regions landward of these segments were subjected to extension that created the orphan and flemish pass basins on the north american side and the galicia interior basin on the iberian side by comparing the hinge zones delineated off galicia bank and flemish cap using the bouguer anomalies we were able to infer that flemish cap rotated approximately 438 relative to galicia bank and iberia and moved 200 300 km se with respect to north america such motions of flemish cap and galicia bank agree remarkably well with extensional episodes deduced from industry multichannel seismic reflection data acquired in the orphan basin normal fault orientations identified in the west orphan basin trend n0208 and are approximately perpendicular to the flow lines of our proposed flemish cap north american motion during the m25 m0 period which provides an independent constraint on our proposed kinematic model therefore extensional events affected not only the galicia bank flemish cap conjugate margins but also the galicia interior and orphan basins and need to be taken into account in any assessment of the geological development of the iberian and north american continental margins during the intermargins workshop meeting modelling the extensional deformation of the lithosphere imedl held in pontresina in 2004 a benchmark exercise was proposed to model the crustal and mantle rifting processes between the western galicia bank and the se flemish cap conjugate margins where high quality seismic reflection and refraction data exist screech line 1 funck et al 2003 hopper et al 2004 and ise line 17 perez gussinye et al 2003 henning et al 2004 during the meeting it became apparent that additional boundary conditions and constraints were needed to correctly characterize the known extension across the iberian newfoundland margin the aim of this paper is to provide some of these conditions and constraints namely a knowledge of the initial positions of plates and microplates before their separation by sea floor spreading processes the positions of flemish cap and galicia bank are well constrained at chron m0 fig 1a because of the identification of correlatable sea floor magnetic anomalies in both the bay of biscay sibuet et al 2004b and in the north atlantic srivastava et al 2000 the resulting euler pole position was constrained by the geometry of the triple junction that had remained at the mouth of the bay of from karner g d manatschal g pinheiro l m eds imaging mapping and modelling continental lithosphere extension and breakup geological society london special publications 282 63 76 doi 10 1144 sp282 4 0305 8719 07 15 00 the geological society of london 2007 fig 1 a reconstruction of the north atlantic between africa af iberia ib and north america na at chron m0 with respect to eurasia eu as given by srivastava et al 2000 ib eu 43 858n 5 838w 244 768 af eu 43 618n 6 938w 240 898 na eu 69 678n 154 268e 23 178 m0 picks west of ib crosses and east of j c sibuet et al 64

insight into the nature of the ocean continent transition off west iberia from a deep multichannel seismic reflection profile a high quality multichannel seismic reflection profile across the west iberia margin confirms the existence of a 130 km wide transition zone between tilted continental fault blocks and unequivocal oceanic crust the zone is characterized by a 1 0 2 5 km thick seismically unreflective upper basement layer lying over reflective basement that contains major landward dipping reflectors that mostly truncate against the base of the upper layer and penetrate to depths of 10 19 km below the basement surface and minor seaward dipping reflectors moho reflections are absent in this zone we suggest that the unreflective layer represents tectonically exposed upper mantle that has undergone extensive serpentinization enhanced by vigorous seawater circulation about 40 km farther north the transition zone narrows to 35 km and the unreflective layer is less continuous and widespread

a revised stratigraphic framework for later cenozoic sequences in the northeastern mediterranean region this study describes the lithostratigraphic character of mid cenozoic oligocene pliocene sequences in different parts of the northeastern mediterranean area and offers a detailed stratigraphic correlation for this region the sequences concerned are drawn from the camardi area south central anatolia the adana basin the misis mountains and the kyrenia range northern cyprus and the submerged florence rise west of cyprus the stratigraphic relationships identified here indicate the following a following the middle eocene lutetian regression there was uplift throughout the entire region b episodes of fluvial and lacustrine deposition in intramontane settings ensued in most of this region during the late eocene early miocene interval c following a regionally extensive phase of tectonic compression major marine transgression commenced in the late oligocene in northern cyprus and in the early miocene in adjacent southern turkey with the exception of the ecemi fault zone where continental deposition continued d these oligo miocene transgressive sequences comprise a broadly diachronous complex of both shallow and deeper marine facies including reefal carbonates littoral clastics basinal shales and fan turbidites e deeper marine miocene facies persisted longer in the misis area and in northern cyprus f a regional regression occurred throughout most of the area during the late serravallian to tortonian interval and is marked by the abrupt locally discordant appearance of extensive shallow marine deltaic and fluvial deposits g continued regression in the messinian led to the formation of significant evaporite deposits in the western and southern parts of the region but localized uplift of the misis area is attested by the initial deformation of the neogene rocks there and the absence of messinian sediments from this area h in the pliocene there was extensive emergence of the northern parts of the region interrupted by brief marine incursions the present day drainage pattern was established at this time i marine conditions persisted longer in northern cyprus where emergence occurred only in the latest pliocene

vertical and lateral organization of a carbonate deep water slope marginal to a submarine fan system miocene southern turkey organization is recognized in the forereef deep water slope submarine fan system of the burdigalian langhian kaplankaya formation a basinwards transition from a prograding shelfal reef complex through forereef talus deep water slope and laterally encroaching bypass deep water clastic system is described although the deep water slope makes up the bulk of the succession considerable thickness variations occur between the reef and deep water clastic complexes these are controlled by sea floor topography carbonate foreslope gradient and degree of mass wasting off the platform and foreslope the vertical and lateral heterogeneity of the kaplankaya deep water slope system is described from a number of localities along a 40 km long and up to 3 km wide exposed section of the northern margin of the miocene adana basin a foreland basin setting resulting from thrust sheet loading from the north during the tauride orogeny detailed field mapping is supplemented with vertical sedimentary logs photomosaics palaeontological and petrological data to investigate stratal variation diagnostic architectural elements controls on slope progradation differential timing of basinward encroachment of the reefal complex and lateral onlap of the deep water clastic system onto the slope three dimensional models are presented showing the vertical and lateral facies associations in different parts of the deep water slope system and provide a basis for architectural prediction of geometry and relative position in such environments

evidence for 1 5 km of uplift of the central anatolian plateau s southern margin in the last 450 kyr and implications for its multiphased uplift history

a deep seismic investigation of the flemish cap margin implications for the origin of deep reflectivity and evidence for asymmetric break up between newfoundland and iberia summary seismic reflection and refraction data were acquired along the southeast margin of flemish cap at a position conjugate to drilling and geophysical surveys across the galicia bank margin the data document first order asymmetry during final break up between newfoundland and iberia an abrupt necking profile of continental crust observed off flemish cap contrasts strongly with gradual tapering on the conjugate margin there is no evidence beneath flemish cap for a final phase of continental extension that resulted in thin continental crust underlain by a strong s like reflection which indicates that this mode of extension occurred only on the galicia bank margin compelling evidence for a broad zone of exhumed mantle or for peridotite ridges is also lacking along the flemish cap margin instead anomalously thin 3 4 km thick oceanic crust is observed this crust is highly tectonized and broken up by high angle normal faulting the thin crust and rift structures that resemble the abandoned spreading centre in the labrador sea suggest that initial seafloor spreading was affected by processes observed in present day ultra slow spreading environments landwards flemish cap is underlain by a highly reflective lower crust the reflectivity most likely originates from older palaeozoic orogenic structures that are unrelated to extension and break up tectonics

seismicity analysis at the prestige oil tanker wreck area galicia margin nw of iberia an evaluation of the geological hazard related to the sinking of the prestige oil tanker in november 2002 in the galicia margin nw of iberia was supported by the spanish research agency it included a specific seismic study of the local activity and of the regional seismicity in this margin results of which are presented here published global catalogues show that diffuse seismicity of moderate magnitude events up to 5 6 mb can be associated with the northern flank of the galicia margin with a roughly e w distribution however event locations in this area are poorly constrained due to the inappropriate geometry of permanent seismic networks we collected and analyzed new data from a dense deployment of 10 obs around the wreck site and from a network of 12 land stations at the nw corner of iberia during a 7 months operation period the land network permitted location of 120 events with magnitudes ranging from 1 6 to 4 8 more than 30 of which were not reported by the spanish permanent array confirming the existence of a moderate seismicity in this area five new focal solutions have been obtained for events on land providing additional information about the active faults in the region the obs network ran for 1 month and allowed the location of three earthquakes of magnitude 2 5 near the sinking site four more events have been identified with just a rough determination of their epicenters based on polarization of the p wave arrivals besides these earthquakes the obs data recorded numerous seismic events of different types they include i groups of very short and regularly spaced pulses that can be explained as acoustic calls generated by finback whales ii a large number of short duration seismic events 2 3 s long identified only at individual obs iii local intense monochromatic signals lasting for up to 4 h that can be described as harmonic tremors these last two types of seismic events might be related to hydrothermal activity within the uppermost sediments and deserve additional studies to appropriately establish the seismic hazard of this area 2007 elsevier b v all rights reserved

quantification and restoration of extensional deformation along the western iberia and newfoundland rifted margins 1 many recent papers describe the structure of the iberia and newfoundland rifted margins however none of them propose kinematic restorations of the complete rift system to quantify the amount of extension necessary to exhume mantle and initiate seafloor spreading in our study we use two pairs of cross sections considered as conjugate lines one across the galicia bank flemish cap and the other across the southern iberia abyssal plain flemish pass both transects have been imaged by reflection and refraction seismic methods and have been drilled during ocean drilling program legs 103 149 173 and 210 drilling penetrated parts of the rift stratigraphy and the underlying basement the cross sections can therefore be considered as the best documented conjugate transects across present day hyperextended magma poor rifted margins the aim of this paper is threefold 1 provide a detailed description of the crustal architecture of the two conjugate sections 2 define the extensional structures and their ages and 3 quantify the amount of strain and strain rate accommodated along these lines this paper proposes a quantitative description of extension along the iberia newfoundland rift system and discusses the limitations and problems in quantifying extensional deformation along hyperextended rifted margins

distribution anisotropy the cause of ams in igneous rocks understanding of ams in pristine basic igneous rocks in terms of flow orientation of ellipsoidal magnetite grains is thwarted by the fact that these grains 1 typically are irregularly equant or skeletal rather than distinctly ellipsoidal and 2 usually crystallize interstitially and late after magma flow has ceased however the distribution of such grains will be relatively anisotropic if they grew in residual liquid volumes within a preferredly oriented by flow silicate template this constraint may impose a slight preferred shape orientation to the irregular magnetite grains during their growth but in addition we suggest it is the anisotropic magnetic interaction between the grains which is the basic cause of ams experiments involving the casting of magnetite epoxy mixtures in various foliated or lineated glass templates have yielded samples with the expected ams symmetry i e k3 perpendicular to glass plates or k1 parallel to glass rods slicing of near isotropic synthetic blank and natural rock cores and interleaving with glass slides showed a progressive increase in anisotropy of the blank from 0 4 to 2 and the natural rock from 0 9 to 2 9 in both the k3 axis migrates to be perpendicular to the glass slides

geochronological constraints on the timing of magmatism deformation and gold mineralization in the red lake greenstone belt northwestern ontario the paper presents u pb ages on zircon baddeleyite titanite rutile and monazite from volcanic and plutonic rocks of the red lake greenstone belt in the northern superior province the purpose of the study was to refine a previously outlined time frame for the volcanic evolution of the belt define the time of major plutonism and deformation and constrain the age of formation of gold deposits volcanism spanned at least 270 ma between 3000 and 2730 ma new ages of 2989 3 and 2894 2 ma for units of a lower volcanic sequence and and 2744 1 ma for units of an upper volcanic sequence corroborate and refine the previously established relationships local gabbroic and felsic intrusions cutting through the lower sequence yield ages of 2870 15 and respectively volcanism was succeeded by major plutonism deformation alteration and metamorphism between about 2730 and 2700 ma these processes were interrelated and progressed as a relatively continuous sequence of events accentuated by major activity d

block rotations along the strike slip finlay ingenika fault north central british columbia implications for paleomagnetic and tectonic studies structure developed in association with oblique motions on the dextral strike slip finlay ingenika fault fif in the mcconnell creek area north central british columbia is dominated by subvertical to vertical strike slip faults some of the faults cut the area into discrete fault bounded blocks several kilometres wide stress tensors for 24 sites were inverted from the regional cleavage which predates the block bounding faults the site mean stress tensors indicate that the fault bounded blocks were rotated clockwise about a subvertical axis during progressive oblique motions on the fif rotation varies systematically being maximal 58 7 3 3 close to the fif and minimal 0 0 1 6 about 20 km away paleomagnetic samples were collected from 13 sites in the widespread early jurassic to cretaceous plutonic rocks interpretable magnetic components of presumed late cretaceous age were obtained from six sites the observed paleopole is significantly different from the late cretaceous reference pole for cratonal north america cna after corrections for the local block rotations the precision is much improved k increased from 48 to 383 and the paleopole moves closer to the reference pole but is not coincident with it rotation about the eulerian pole for the best fitting small circle to the tintina trench and northern rocky mountain trench fault zone however brings the observed pole into coincidence with that for cna and requires 670 km of dextral displacement on the fault zone it is evident therefore that local structures associated with large dextral strike slip faults could account for at least part of the paleomagnetic disparity between some western parts of the canadian cordillera and cna

archean tectonic and metallogenic evolution of the superior province of the canadian shield abstract the superior province of the canadian shield has mainly experienced an archean tectonic history comprising several cycles of volcanism plutonism and tectonism although the rocks of the superior province span more than 500 million years of archean time most mineral deposits formed in an interval of 100 million years or less corresponding to a period of accretion of oceanic and pre existing continental fragments in the late archean at 2 7 ga in accord with recent tectonic syntheses which argue for the accretionary origin of the superior province the metallogenic history of the superior province can also be interpreted in the same context provided secular anomalies in the early history of the earth are acknowledged for relatively unique deposit types such as komatiitic nickel deposits and voluminous iron formations volcanogenic massive sulphide iode gold and granitoid associated deposits as well as ni cu pge cr and ti deposits associated with mafic ultramafic intrusions are readily interpreted in terms of the construction and accretion of late archean island arcs

the origin of s c mylonites and a new fault zone model abstract this paper presents a synthesis of experimental data on mechanical behaviour and deformation textures of simulated halite shear zones with special regard to the internal structures of s c mylonites and their mechanical implications halite is the only mineral so far for which a complete transition between brittle shearing deformation to fully ductile shearing flow in the dislocation glide regime has been studied experimentally under large shear strains that may be encountered along faults or plate boundaries moreover deformation textures in the shear zones are similar to those of mylonites and cataclasites thus the experimental results provide an insight into the petrogenesis of fault rocks mylonites in particular and the establishment of a realistic fault model between the brittle regime and the fully ductile regime i e pressure insensitive inelastic regime there exists a wide and distinct regime called semiductile in which deformation textures are nearly identical to those developed in the ductile regime yet the shear resistance is pressure dependent and potentially unstable fault motion can occur in the low pressure part in cooking salt shear zone experiments the characteristic texture in the semiductile and ductile regimes is foliation resembling mylonitic foliation which formed in the direction of maximum elongation in the semiductile regime nearly homogeneous shearing deformation characterized by the formation of uniform and pervasive foliation changes into heterogeneous deformation after a critical shear strain and this strain localization induces potentially unstable fault motion the primary mode of internal slip after the strain localization is slip along y riedel shears parallel to the shear zone boundary interconnected with r 1 and some p riedel shears these shear surfaces of concentrated deformation are very similar to the internal structures of so called s c mylonites hence the semiductile regime is the primary candidate for the formation of s c mylonites and at least some s c mylonites must have formed at seismogenic depths this interpretation is consistent with recently reported interlaced pseudotachylytes and mylonites it is also shown that the size of recrystallized halite grains presumably mostly postdeformational decreases with increasing shear strains but not with the shear stress and this is consistent with the grain size reduction with strain concentration which has been confirmed for many mylonites in the world thus estimation of flow stress from recrystallized grains needs to be done with great care and might often be erroneous existing fault models are critically examined from the viewpoint of the halite experiments and a new fault model is proposed whereby fault zones are divided into brittle semibrittle semiductile and ductile regimes with increasing depth the shear resistance of faults is highest in the semiductile regime and the seismogenic depth is likely to extend down to the upper part of this regime the semiductile regime thus emerges as an area of primary interest with regard to the petrogenesis of many s c mylonites modelling of large and great shallow earthquakes along pre existing faults and plate boundaries and quantitative evaluation of the mechanical interactions of plates across their boundaries

anisotropy of complex magnetic susceptibility as an indicator of strain and petrofabric in rocks bearing sulphides abstract a new method anisotropy of complex magnetic susceptibility acms for determining the petrofabric of specimens with conductive minerals is developed the method uses the same induction coil equipment and techniques that can be used for the measurement of the anisotropy of magnetic susceptibility ams however a higher 100 khz operating frequency emphasizes the electrical conductivity response and thus yields a measure of the anisotropy of electrical conductivity of the specimen the method was tested on variably deformed plasticine samples containing aluminium fabric markers and on synthetic aggregates of pyrrhotite and talc pyrrhotite mixtures deformed triaxially at a confining pressure of 200 mpa 2 kbar by up to 35 homogeneous shortening acms successfully defines the petrofabric and permits prediction of the principal directions of finite strain the intensity of ams and to a lesser extent of acms correlate with the strain ratio in these simple coaxial flattening plane strain experimental deformations on selected materials

u pb zircon ages for magmatism in the red lake greenstone belt northwestern ontario u pb dating was carried out on nine volcanic rocks and two felsic intrusions from the red lake greenstone belt in order to establish an absolute time framework for the magmatic evolution of the area and yield first indications on the time of deformation and gold mineralization the data indicate a protracted period of igneous activity spanning at least 270 ma felsic volcanic rocks near the top of the tholeiitic to komatiitic sequence in the eastern part of the belt yield ages of and a third unit dated at contains inherited zircons older than 2982 ma which casts some uncertainty on the validity of the inferred intercept age rocks in the western part of the belt previously believed to form a relatively young calc alkalic sequence but now known to be dominantly tholeiitic are shown to be relatively old with ages of and these two dates also bracket the age of stromatolites occurring in chemical sediments that are under and overlain by the dated units another volcanic horizon in the centre of the b

application of the critical coulomb wedge theory to hyper extended magma poor rifted margins the critical coulomb wedge theory ccwt has been extensively used in compressional tectonics to resolve the shape of orogenic or accretionary prisms while it is less applied to extensional and gravitational wedges despite the fact that it can be described by the same equation in particular the hyper extended domain at magma poor rifted margins forming the oceanward termination of extended continental crust satisfies the three main requirements of the ccwt 1 it presents a wedge shape 2 the rocks forming the wedge are completely brittle frictional and 3 the base of the wedge corresponds to a low friction decollement however hyper extended margins present a fully frictional behaviour only for a very thin crust therefore this study is limited to the termination of hyper extended continental crust which deforms in the latest stage of continental rifting in this paper we define a method to measure the surface slope and the basal deep of this wedge that we apply to 17 hyper extended magma poor rifted margins in order to compare the results to the values predicted by the ccwt because conjugate pairs of hyper extended magma poor rifted margins are commonly asymmetric due to detachment faulting the wedges in the upper and lower plate margins corresponding respectively to the hanging wall and footwall of the detachment system are different while the stress field in the upper plate wedge corresponds to a tectonic extensional wedge the one in the lower plate matches that of a gravity extensional wedge using typical frictional properties of phyllosilicates e g clays and serpentine the shape of the hyper extended wedges can be resolved by the ccwt using consistent fluid overpressures our results show that all lower plate margins are gravitationally stable and therefore have a close to critical shape whereas the tectonic extensional wedges at upper plate margins are critical sub or sup critical due to the detachment initial angle and the duration of the tectonic activity in this paper we discuss the geometry and structural evolution of the most distal parts of hyper extended continental margins and the formation of extensional allochthons during hyper extension using the ccwt theory

tectonic controls on stratigraphic evolution of the adana basin turkey the neogene adana basin of se turkey was initiated after thrust emplacement of the tauride belt to the north of the basin seismic reflection profiles across the southern part of the adana basin provide information on structural and stratigraphic evolution of the basin based on seismic character and the identification of unconformities three megasequences and two mega sequence boundaries are identified the first megasequence is partly coincident with an early miocene rifting event and it comprises reefs that have grown on fault footwall crests with fore and back reef sediments in intervening lows subsequent rapid flexurally induced subsidence generated an underfilled basin which was then passively filled by turbiditic sediments megasequence 2 showing aggradational character on seismic profiles further extensional faulting and coupled sinistral wrench faulting took place after the deposition of megasequence 2 erosional truncation of its upper part is followed by the deposition of continental and shallow marine sediments of megasequence 3 which shows localized progradational sequences characteristic of shallow water deposition further minor extensional faulting took place after the deposition of megasequence 3

variations in heat flow across the goban spur and galicia bank continental margins we present the results of 44 new heat flow stations which were taken in 1984 and 1989 in profiles across the goban spur and galicia bank continental margins nw atlantic ocean simple extensional models indicate that the heat flow across both these early cretaceous rifted margins should increase from values of 45 50 mw m2 over oceanic crust to 65 80 mw m2 on the continents the rate of this increase should help to constrain the mechanism simple versus pure shear by which the upper more radiogenic continental crust is thinned measurements across goban spur increase from values of 40 45 mw m2 over oceanic crust to 50 55 mw m2 near the continental shelf they follow the predicted trend for pure shear rifting but only if the value of upper crustal radiogenic heating is low 1 2 mu w m3 otherwise they would require the upper crust to thin more rapidly than the total crustal thickness as with a lower plate simple shear margin measurements across galicia bank show a very different pattern with similar values over oceanic crust but much lower values 30 35 mw m2 nearer land this is difficult to reconcile with any simple single rifting event but is more compatible with an origin as a pure shear or lower plate rather than upper plate margin we also note that oceanic values of heat flow require asthenospheric temperatures 100 degrees c lower than normal for both margins this indicates that the triple junction in existence between these margin segments during the breakup of iberia europe and north america was not the site of a major mantle plume

how does the continental crust thin in a hyperextended rifted margin insights from the iberia margin the discovery of hyperthinned continental crust and exhumed mantle on present day deep water rifted margins leads to two fundamental questions 1 in detail how does the crust thin in extension and 2 what controls extreme crustal thinning and mantle exhumation reflection and refraction seismic lines across the iberian margin show decoupling levels in the crust cut by structures that eventually transfer deformation to mantle levels the region of decoupled extension appears to be more broadly distributed on the northern iberian margin and more localized on the southern margin based on drill hole data the transition from decoupled to coupled deformation occurred during tithonian time ca 145 ma this evolution from decoupled to coupled deformation may help explain the crustal architecture of the iberian margin an apparent delay of subsidence across the hyperextended coupled zone of the iberian margin may indicate that crustal thinning had to occur simultaneously with lithospheric necking and the advection of heat related to lithospheric mantle thinning

sedimentology of a late cenozoic collisional sequence the misis complex adana southern turkey abstract this study is concerned with miocene sequences formed within part of the cukurova basin of southern turkey a major downwarp created during the early stages of collision between the afro arabian plate and the tauride anatolian microplate assemblage we report here the results of a combined stratigraphical sedimentological structure and geochemical study of the misis complex a structurally elevated segment of cukurova basin fill this analysis has demonstrated the structurally imbricated nature of the misis sequences and the tectonic juxtaposition of originally well separated coeval facies the initial discernible phase of basin filling pre burdigalian was marked by deep marine conditions and marginal tectonic instability probably related to a late phase of tauride nappe advance the subsequent phase of crustal extension burdigalian early tortonian produced expansion of the cukurova basin limits and an upwards shoaling succession in which sediment transport towards the southwest gradually became dominant as a result of earlier suturing and uplift in northeasterly sectors of the collision zone the miocene arenites of the misis complex are petrographically diverse with common siliciclastic and carbonate detrital admixtures and mineralogically immature and their position in petrotectonic fields indicates a compound provenance from both recycled orogen and magmatic arc sources a noteworthy petrographic feature is the compositional similarity of arenites from both shallow and deep marine facies the general succession of neogene facies observed in the cukurova basin and misis complex is consistent with their evolution within a perisutural foreland basin but this interpretation is complicated by petrographic and geochemical features attributed to remnants of an older magmatic arc later stages of basin filling are also marked by the local occurrence of anomalous palaeoenvironmental associations including olistostromic units attributed to contemporaneous intra basinal tectonism

timing of gold mineralization at red lake northwestern ontario canada new constraints from u pb geochronology at the goldcorp high grade zone red lake mine and the madsen mine the goldcorp high grade zone at the red lake mine has reserves proven and probable established at 1 775 million tons mt at an average grade of 80 6 g t au new u pb geochronologic data combined with detailed mapping and crosscutting relationships provide timing constraints and new insights into the formation of the exceptionally rich goldcorp high grade zone the results show that the main stage of the high grade mineralization in the high grade zone formed before 2712 ma and that a second stage of gold mineralization much smaller in terms of total gold content but spectacular in terms of grade formed after 2702 ma this second stage is attributed to gold remobilization caused by the enhanced thermal gradient and deformation associated with the emplacement of the cat island pluton 2699 ma approximately 7 km east of the deposit or by the ca 2 63 to 2 66 ga postorogenic regional thermal event indicated by hornblende muscovite and biotite ar ar cooling ages from the uchi subprovince it is proposed that the main stage of high grade mineralization formed between ca 2723 to 2712 ma possibly synchronous with emplacement of the dome and mckenzie island stocks the abino granodiorite and hammell lake batholith as well as with penetrative d2 main stage regional deformation lamprophyre dikes spatially associated with the deposit postdate main stage mineralization by at least 10 m y a postore granodiorite dike from the madsen mine the second largest deposit in the district was dated at 2698 1 ma this age is similar to a postalteration and late deformation diorite dike at the creek zone showing near the former starratt olsen mine which was dated at 2696 2 ma the crosscutting relationships confirm that the main stage of mineralization at the madsen mine is pre 2698 ma a folded and metamorphosed polymictic conglomerate located stratigraphically above the campbell red lake deposit and deposited after ca 2747 but before 2712 ma is correlated with the newly recognized huston assemblage crosscutting and overprinting relationships between the conglomerate and the alteration indicate protracted multistage aluminous and iron carbonate quartz veining and or alteration event s before and after deposition of the conglomerate the age of the conglomerate confirms that the campbell red lake deposit is proximal to a folded regional unconformity consistent with the empirical relationship between large gold deposits and unconformities elsewhere in archean greenstone belts this paleosurface represents a key first order exploration target and it is proposed that areas of high potential for gold exploration in red lake occur in the balmer assemblage rocks within 500 m to 1 km of the unconformity

nature of the s reflector beneath the galicia banks rifted margin preliminary results from prestack depth migration beneath the tilted fault blocks of the galicia rifted margin a bright reflection termed s has been interpreted as the master detachment fault controlling the extension of the margin however on time migrated sections s appears to be locally offset by the steep faults of the upper section we investigate the true geometry of s and its relation to the overlying faults through iterative prestack depth migration we conclude that it is not significantly offset by the faults which instead appear to stop abruptly at s thus we interpret s as the master detachment and consider its role during extension

deep structure of the ocean continent transition in the southern iberia abyssal plain from seismic refraction profiles the iam 9 transect at 40 20 n we present a crust and mantle velocity structure for the west iberia passive continental margin derived from a 320 km long wide angle seismic profile acquired in the southern iberia abyssal plain we observe a 170 km wide ocean continent transition zone which includes a pair of overlapping peridotite ridges and is bounded by oceanic crust and landward by fault bounded blocks of continental crust the profile lies 40 km south of the transect sampled by ocean drilling program odp legs 149 and 173 the transition zone structure can be divided into an upper layer 2 4 km thick with velocities of between 4 5 and 7 0 km s 1 and generally a high velocity gradient 1 s 1 and a lower layer up to 4 km thick with a velocity of 7 6 km s 1 and a low velocity gradient a weak moho reflection in this zone was seen only on wide angle profiles at an offset of 30 km the upper layer has a distinctly lower velocity than thinned continental crust adjacent to the continental slope conversely the lower layer has too high a velocity to be magmatically intruded or underplated lower continental crust on the coincident seismic reflection profile fault bounded crustal blocks identified in unequivocal extended continental crust are not observed in the transition zone the upper layer has velocity bounds and gradient similar to oceanic layer 2 observed west of the peridotite ridges but no oceanic layer 3 velocity structure is present while magnetic anomalies have been identified within the transition zone they have not been modeled successfully as seafloor spreading magnetic anomalies nor do they generally form long linear margin parallel features finally odp boreholes 40 km north of our profile and within the interpreted transition zone have recovered up to 140 m thick sections of serpentinite and serpentinized peridotites with little evidence of mafic igneous material we conclude that the transition zone cannot be dominantly composed of either extended continental crust or oceanic crust although current melting models predict a considerably thicker crust of decompression melt products we interpret this region as exposed upper mantle peridotite with little or no synrift extrusive material and limited amounts of synrift material intruded within the serpentinized peridotite

linking slab break off hellenic trench retreat and uplift of the central and eastern anatolian plateaus abstract the central and eastern anatolian plateaus are integral parts of the world s third largest orogenic plateau in the past decade geophysical surveys have provided insights into the crust lithosphere and mantle beneath eastern anatolia these observations are now accompanied by recent surveys in central anatolia and new data constraining the timing and magnitude of uplift along its northern and southern margins together with predictions from geodynamic models on the effects of various processes on surface deformation and uplift the observations can be integrated to identify probable mechanisms of anatolian plateau growth a changeover from shortening to extension along the southern margin of central anatolia that is coeval with the start of uplift can be most easily associated with oceanic slab break off and tearing this interpretation is supported by tomography deep seismicity or lack thereof and gravity data based on the timing of uplift geophysical and geochemical observations and model predictions slab break off likely occurred first beneath eastern anatolia in middle to late miocene time and propagated westward toward cyprus by the latest miocene alternatively the break off near cyprus could have occurred in late pliocene to early pleistocene time in association with collision of the eratosthenes seamount continental fragment with the subduction zone uplift at the northern margin of central anatolia appears to result from crustal shortening starting in the late miocene or early pliocene which has been linked to the broad restraining bend of the north anatolian fault the uplift history of the interior of central anatolia since the late miocene is unclear although shortening there appears to have ended by the late miocene followed by ne sw extension this change in the deformation style broadly coincides with faster retreat of the hellenic trench as well as uplift of the northern and southern margins of central anatolia these different events throughout the plateau may be linked as faster retreat of the hellenic trench has been predicted to occur after slab break off which could have induced extension of central anatolia and helped to form the north anatolian fault through accelerated westward movement of anatolia relative to eurasia correlative geochronologic evidence that we summarize here supports the hypothesis that the geodynamic activity throughout the aegean anatolian domain starting in latest miocene to early pliocene time defines a series of events that may all be linked to slab break off

determination of the tectonic stress tensor from slip along faults that obey the coulomb yield condition a new method to calculate the stress tensor associated with slip along a population of faults is derived here the method incorporates two constraints first the stresses in the slip direction satisfy the coulomb yield criterion and second the slip occurs in the direction of maximum shear stress along the fault the computations provide the complete stress tensor normalized by the vertical stress and evaluation of the mean coefficient of friction and the mean cohesion of the faults during the time of faulting the present method is applied to three field cases dixie valley nevada wadi neqarot israel and yuli microearthquakes taiwan it is shown that the coefficieet of friction of the three cases varies between 0 1 to 0 8 further it is demonstrated that previous stress inversion methods implicitly assume zero friction along the faults

quantitative subsidence analysis of the mesozoic evolution of the lusitanian basin western iberian margin abstract quantitative subsidence analysis of 26 wells in the lusitanian basin provides new constraints on the western iberian mesozoic passive margin development backstripped tectonic subsidence curves show a three fold subdivision of vertical motions from late triassic onward continental rifting was initiated during the late triassic and early jurassic from middle jurassic onward a distinct different behaviour is expressed in the subsidence curves for the north and the south lusitanian basin during the middle jurassic the south lusitanian basin records a stretching episode with stretching factors of about 1 08 while the north lusitanian basin typically has a middle jurassic hiatus this different development is also expressed in the late jurassic and early cretaceous sedimentary sequence when both the north and south lusitanian basin are subjected to another stretching episode with a more pronounced development of the southern than of the northern part of the basin the stretching factors for this last phase are about 1 03 for the northern part and 1 08 for the southern part of the area this north south difference during the middle jurassic to early cretaceous for which the transition roughly coincides with the location of the nazare fault zone is probably a result of differences in pre rift crustal composition or thickness late cretaceous sediments are mostly absent in the analysed wells in the southern part of the basin the absence of the cretaceous record is a consequence of erosion due to cenozoic inversion of the basin the generally low estimates for stretching factors suggest that the analysed eastern part of the lusitanian basin forms the distal part of the mid cretaceous continental breakup a comparison with subsidence curves of neighbouring basins of iberia reflects general patterns in mesozoic basin development and confirms the generally held view that the extension leading to continental breakup migrated from south to north during the middle jurassic to early cretaceous in west iberia

structure and rifting evolution of the northern newfoundland basin from erable multichannel seismic reflection profiles across the southeastern margin of flemish cap we present the results from processing and interpreting five lines from the 1992 erable multichannel seismic reflection experiment extending from the southeastern margin of flemish cap into the northern newfoundland basin these profiles reveal significant along strike variations in the rifting styles experienced by flemish cap in the southwest a 100 km wide transition zone is identified between thinned continental crust and thin oceanic crust similar to the conjugate galicia bank and iberian margins this transition zone contains a section of deep basement adjacent to a series of shallower ridges and is interpreted as exhumed serpentinized mantle along strike towards the northeast this transition zone pinches out completely within 100 km and is replaced by thin oceanic crust directly adjacent to thinned continental crust by interpreting nearby seismic profiles and profiles on the conjugate margins using the same classification criteria we construct regional maps of the distribution of crustal domains on both sides of the north atlantic these maps reveal significant variations in rifting style on the conjugate margins and along strike of each margin and also highlight the role of ancient transfer zones in compartmentalizing these rifting variations into four distinct regions we propose that the limited localization of shallow topographically high serpentinized peridotite ridges on the newfoundland iberia and flemish cap galicia bank conjugate margins was directly related to an increase in the rate of extension following the separation of flemish cap and galicia bank which exhumed deeper less serpentinized mantle

tectonic analysis of fault slip data sets using data that include the direction and the sense of motion on individual fault surfaces determined by slickenside lineations it is possible to reconstruct reduced stress tensors that correspond to the orientation of stress axes and to the ratio 2 3 1 3 between principal stress values 1 2 3 compression being positive no assumption is made concerning the orientation of fault planes relative to stress axes so that reactived faults are taken into account as well as newly created ones qualitative and quantitative methods for analysis of fault slip data were developed during the last 10 years the practical limitation of the methods and the necessity for critical field observations are emphasized these methods can be applied to focal mechanisms of earthquakes a more complex analysis of heterogeneous data sets involving an iterative separation of different stress systems is also discussed this analysis enables one to distinguish successive faulting events careful qualitative study in the field is in all cases essential

azimuthal seismic anisotropy in a zone of exhumed continental mantle west iberia margin summary p wave azimuthal seismic anisotropy of the uppermost mantle has been shown to indicate directions of extension both recent and fossil in oceanic and continental settings we have determined the p wave anisotropy of a zone of exhumed continental mantle beneath the southern iberia abyssal plain as a possible indication of the initial direction of separation of iberia from north america in a region where there are no magnetic lineations or fracture zone lineations adjacent to the margin with which to constrain this direction over 10 000 airgun shots were recorded by 11 ocean bottom seismometers hydrophones from which 24 900 arrivals that had traversed unaltered weakly serpentinized upper mantle were picked complete 360 azimuthal coverage was attained between the shots and receivers for ranges up to 55 km p wave raypaths through the zone of exhumed continental mantle were ray traced through a velocity model that incorporated the 3 d relief of the seabed and acoustic basement time residuals with respect to this model were fitted using an azimuthally dependent function small anisotropy 7 per cent with a fast direction of 143 was determined to exist between 3 1 and 6 7 km below the top of the basement although the fast direction suggests that the post breakup mantle stretching between iberia and north america was northwest southeast this hypothesis is hard to reconcile with other observations instead we conclude that motion along concave downward faults during the exhumation of the upper mantle could have been sufficient to change an initially roughly east west margin normal fast direction to the 143 azimuth observed today the degree of serpentinization was estimated to decrease from 20 to 0 per cent between 3 and 7 km depth into the basement in the zone of exhumed continental mantle the degree of upper mantle anisotropy is similar to that observed in other oceanic and continental settings where similar degrees of serpentinization are inferred from mean p wave velocities

tectonosedimentary evolution of the deep iberia newfoundland margins evidence for a complex breakup history most of the conceptual ideas concerning sedimentary architecture and tectonic evolution of deep rifted margins are based on either intracontinental rift basins or proximal margins both of which underwent only small amounts of crustal thinning in this paper we investigate the tectonosedimentary and morphotectonic evolution related to continental breakup of the highly extended deep iberia newfoundland margins our results show that continental breakup is a complex process distributed in time and space on the basis of mapping of dated seismic units and borehole data we are able to identify two major phases of extension during a first phase dated as tithonian to barremian 145 128 ma deformation is related to exhumation of mantle rocks basins become younger oceanward and fault geometry changes from upward to downward concave resulting in complex sedimentary structures and basin geometries a second phase dated as latest aptian 112 ma overprints previously exhumed mantle and accreted juvenile oceanic crust over more than 200 km leading to the formation of basement highs the observed complex breakup history challenges classical concepts of rifting and leads to new interpretations for the tectonosedimentary evolution of deep rifted margins

structural evolution of auriferous deformation zones at the campbell mine red lake greenstone belt superior province of canada abstract the campbell mine the largest gold mine in the red lake camp lies within the regional first order nw trending foliation parallel cochenour gullrock lake deformation zone the auriferous veins at the mine are hosted by subvertical second order deformation zones within the cochenour gullrock lake deformation zone these second order deformation zones strike nw nnw and e w across the foliation parallel nw trending ore zones a f f2 and nl ore zones the rock and magnetic foliations show progressive increase in strain intensity but their orientations do not change this together with the absence of other shear sense indicators within the foliated rocks strongly suggests that the foliation parallel nw trending ore zones were developed during ne sw subhorizontal shortening foliation oblique ore zones strike nnw g and p zones and e w part of a and l zones they display shear sense indicators such as asymmetrical folding of thin gold bearing quartz carbonate veins and progressive rotation of petro and magnetic fabrics these shear sense indicators indicate that nnw and e w trending ore zones are dextral and sinistral strike slip shear zones respectively the intersection of these second order shear zones is approximately parallel to the subvertical boudin axis of foliation parallel veins in the nw trending deformation zones and the nw trending deformation zones bisect the nnw and e w trending shear zones these suggest that the nnw and e w trending shear zones are conjugate shear zones developed in association with the ne sw subhorizontal shortening which is normal to the nw trending deformation zones cross cutting relationships the deformation recorded in post ore lamprophyre dykes and stress tensors inverted from the fault slip data suggest that the ne sw compression deformation spanned a prolonged period auriferous veining under the compression regime is followed by lamprophyre dyke intrusion then by brittle ductile faulting under ne sw compression the mode of deformation may characterize other parts of cochenour gullrock lake deformation zone and is of significant importance in gold exploration in the eastern part of the red lake greenstone belt field data from the cochenour gullrock lake deformation zone and the margin of the trout lake batholith suggest that the ne sw shortening is likely related to the batholith emplacement and that the cochenour gullrock lake deformation zone corresponds to a highly attenuated limb of a nw trending regional fold which overprints earlier ne trending folds in the area

structural comparison of archetypal atlantic rifted margins a review of observations and concepts abstract in this study we compare three pairs of conjugate rifted margins that are often referred to as archetypes of rift systems despite numerous differences a remarkable first order structural similarity appears between the magma poor iberia newfoundland the magma rich mid norway east greenland and the sediment rich angola brazil rifted margins typical is the seaward arrangement of distinct domains proximal necking distal and outer that each present specific comparable structural characteristics our study also suggests that magma rich systems may go through a stage of hyper extension indicating that extreme crustal thinning does not preclude a magmatic breakup in this contribution we clarify the definition of a number of terms introduced recently in rifted margin studies we review the major features constitutive of these key referenced systems discuss their similarities and differences and examine how the related deformation modes develop in the life cycle of a rift that goes to seafloor spreading we conclude that the distinct domains observed in the margin architecture represent distinct stages in the evolution of rifted margin independently of their later evolution into magma poor or magma rich environments

seismic constraints on the three dimensional geometry of low angle intracrustal reflectors in the southern iberia abyssal plain several lines of evidence suggest that simple shear rifting of the continental crust in the form of low angle detachment faulting occurred during the final stages of continental breakup between west iberia and the grand banks the primary evidence for such faulting is the occurrence of low angle high amplitude reflectors within the basement adjacent to the ocean continent transition zone here we present a series of intersecting depth migrated seismic reflection profiles that image one such reflector the h reflector located on the southern edge of galicia bank h lies beneath several boreholes drilled during odp legs 149 and 173 in a region where the oceanward extent of extended continental crust steps at least 150 km westward from its location in the southern iberia abyssal plain to its location off the relatively shallow galicia bank in our profiles h appears to define a surface that extends over a region of at least 200 km2 and that dips down 19 to the north towards galicia bank the profiles show that a close affinity exists between h and the most seaward continental crust based on geophysical data and odp drilling results we infer that the basement above h is composed of continental crust deformed by extensional faults into a series of wedge shaped blocks and thin slivers these basement wedges have a complex 3 d geometry h rises to the basement surface on a number of the seismic profiles and appears to define locally the oceanward extent of continental fault blocks

tectonic implications of exposure of lower continental crust beneath the iberia abyssal plain northeast atlantic ocean geophysical evidence we present new seismic data from a basement high beneath the southern iberia abyssal plain that appears from the latest ocean drilling program odp results and indirectly from various seismic observations to consist of lower continental crustal material this is a unique opportunity to use seismic profiles and other geophysical evidence to investigate the tectonic process which led to the exhumation of these rocks we infer that the lower crust was exhumed at the seafloor and then uplifted toward the end of rifting our results lead to the following new observations low angle detachment faults previously reported along the east west lusigal 12 profile across the southern iberia abyssal plain penetrate both the 3 10 km thick continental crust and unusually the uppermost mantle processing of new multichannel seismic reflection profiles across the basement high on which odp sites 900 1067 and 1068 are located reveals that the high is bounded by a previously unsuspected steep landward dipping normal fault on its east flank basement cores from the above odp sites also reveal that the high is not capped by the previously predicted early syn rift sediment but by rocks from the lower continental crust these unexpected observations are incorporated into a new tectonic model of the development of this part of the west iberia margin which is also consistent with other geophysical observations a novel feature of this model is the proposal that the seaward edge of the continental crust is thinned to 3 6 km by a currently poorly understood process the model implies three stages of deformation 1 lithospheric extension principally by symmetric pure shear which leads to a 10 km thick crust in which the lower crust is largely absent over the axial zone and the crust mantle boundary forms a shear zone 2 further thinning and then dissection of the most distal continental crust by seaward dipping low angle normal faults 3 inception of a high angle landward dipping normal fault that offsets the tectonized crust mantle boundary and uplifts the lower crust to the crest of the basement high on which odp sites 900 1067 and 1068 were drilled

micropaleontology and paleoecology of the neogene sediments in the adana basin south of turkey this paper analyses the stratigraphical features and fossil associations ostracod and planktonic foraminifer of the late miocene deposits in the adana basin in this research numerous samples were collected from the sediments both below and above the messinian evaporitic layers which cropped out in the western and middle part of the adana basin due to paleoenvironmental changes during the messinian salinity crisis the fine grained sediments below the gypsum layers surrounding topcu and karayayla villages located in the western part of the basin are sterile nodular anhydrite and enterolithic structures are well developed in these selenitic gypsum layers which are supposed to represent a sabkha environmental condition in the middle part of the adana basin some re sediment detritic gypsum deposits cropped out around semiramis village houses the lithological characteristics and faunal assemblages of the sediments both below and above these evaporites are more or less similar to each other fossil fauna ostracod and planktonic foraminifera demonstrate that these sediments are not older than latest tortonian as suggested by the presence of neogloboquadrina humerosa and not younger than earliest messinian as suggested by the last occurrence of globigerinoides bulloideus similar planktonic assemblages were found in the drill log bored east of the adana basin where there was no evaporitic occurrence both the planktonic species and the presence of globorotalia suterae from 7 81 ma to 7 24 ma point that also these fine granied sediments a late tortonian early messinian in age the quantity of kaolinite recorded is relatively higher in the tortonian early messinian than in the late messinian sediments all data show that during the latest tortonian earliest messinian time interval the area was characterised by shallow marine environments and humid climatic conditions

exhumed upper mantle within the ocean continent transition on the northern west iberia margin evidence from prestack depth migration and total tectonic subsidence analyses 1 the west iberia continental margin contains an enigmatic north south ridge of serpentinized peridotite located within the ocean continent transition we used prestack depth migration and total tectonic subsidence analysis to constrain the basement type adjacent to the ridge in order to learn more about its emplacement prestack depth migration was performed on segments of the nine east west lines from the iberia seismic experiment ise 97 and total tectonic subsidence analyses were performed on the depth sections the seismic data and subsidence analyses are consistent with exhumed upper mantle occurring immediately landward of the ridge suggesting that the ridge is located within a broad zone of exhumed mantle that has been serpentinized the subsidence analyses also provide minimum bounds on the thickness of the serpentinized layer which extends from the zone of exhumed mantle landward under thinned continental crust exhumed upper mantle has previously been identified in the wider ocean continent transition to the south in the southern iberia abyssal plain and we conclude that similar but narrower exposures occur to the north in the galicia bank area while upper mantle appears to have been tectonically exhumed along all the ise 97 lines it does not always form a distinct basement ridge there is no well defined ridge on three seismic profiles in the middle of the ise 97 survey where it is well developed the peridotite ridge parallels a deeply penetrating west dipping normal fault and the three middle lines appear to represent a transfer zone where this normal fault is not well developed