tectonic history of the lunksoos composite terrane in the maine appalachians several ordovician volcanic terranes are preserved between the paleozoic north american margin and the avalon terrane in the northern appalachians of maine they have been interpreted as remnants of an island arc on the basis of their current position in the appalachians or as ocean islands near the margin of avalon on the basis of paleontologic data a study of one of these terranes the lunksoos terrane in northern maine was undertaken through a combination of paleomagnetic and structural analyses in order to understand its tectonic evolution paleomagnetic study of the pre caradoeian pre late ordovician stacyville volcanics revealed three components of magnetization the final magnetization removed d 90 i 36 95 11 8 is interpreted to be primary and yields a paleolatitude of approximately 20 s however a late ordovician remagnetization cannot be excluded the stacyville volcanics now overlie a cambrian and lower ordovician sequence the grand pitch and shin brook formations that is believed to have been deposited at the southern side of iapetus possibly near the margin of avalon during the middle and late ordovieian avalon was at paleolatitude s higher than 40 s while the volcanics were either formed or remagnetized at a paleolatitude of 20 s the pre caradocian stacyville volcanics therefore could not have been deposited directly on the grand pitch shin brook sequence but must have been tectonically emplaced the rockabema diorite which intrudes the entire cambro ordovician sequence constrains the timing of this emplacement to be pre late early silurian these relationships indicate that the lunksoos area is a composite terrane within the maine appalachians the tectonic emplacement scenario is unnecessary if the grand pitch and shin brook formations were not located on the south side of iapetus during the ordovician this alternative however poses conflicts with the interpretation of faunal affinities

pre folding magnetization reconfirmed for the late ordovician early silurian dunn point volcanics nova scotia johnson r j e and van der voo r 1990 pre folding magnetization reconfirmed for the late ordovician early silurian dunn point volcanics nova scotia tectonophysics 178 193 205 paleomagnetic results have been obtained for three new sites in steeply inclined subarea1 volcanic flows of the dunn point formation from the avalon terrane of nova scotia demagnetization analysis reveals a characteristic magnetization carried by hematite which is similar to that reported in previous studies of this unit a new and improved fold test for the characteristic component combining paleomagnetic and structural data from the present study with paleomagnetic data for vertically dipping flows and laterites studied previously by the authors is significantly positive the new fold test reconfirms the prefolding age of the characteristic component a primary age of magnetization is inferred based on field evidence for early oxidation of the flows the overall mean direction for the characteristic component of d 344o i 60 k 68 6 ass 4 1 paleopole at 2on 130 e corresponds to a late ordovician earliest silurian paleolatitude for avalon of 41 s the latter is much higher than that predicted for the area on the basis of the cratonic north america apparent polar wander path implying a substantial post ordovician displacement 1700 km of avalon with respect to the craton the dunn point result supports previous paleogeographic reconstructions that show avalon together with the continental blocks of hercynian europe and northwestern gondwana

synchronous development of type 2 and type 3 fold interference patterns evidence for recumbent sheath folds in the allendale area broken hill nsw australia abstract synchronous development of type 2 and type 3 fold interference patterns occur in the poly deformed broken hill inlier the interference patterns have resulted from the superposition of recumbent f2 folds and n s oriented upright f3 folds the synchronous development of type 2 and type 3 fold interference patterns is attributed to variation in the hinge of f2 folds by as much as 90 suggesting the development of a regional scale sheath like fold geometry during d2 overprinting relationships along the eastern limb of the pap synform suggests that it formed part of a recumbent fold hinge that was flattened during horizontal crustal shortening this has resulted in the development of a modified type 3 fold interference pattern the results of this study show that the type 2 and type 3 fold interference patterns can develop during the same deformation event in an evolving orogen

heat flow and geothermal model of the black sea depression abstract the black sea basin is a deep depression within the alpine folded belt the total thickness of cretaceous quaternary sediments in the central part reaches 14 18 km the earth s crust thickness is reduced to 22 28 km the depression is featured by low heat flow minimal

an offshore onland transect across the north eastern black sea basin crimean margin evidence of paleocene to pliocene two stage compression abstract the tectonic evolution of the black sea bs is a subject of debate there are several unsolved questions 1 the timing and the spatial progression of the bs basin opening and 2 the timing of cenozoic shortening along the northern margin of the eastern bs basin the timing of the main compressional deformations related to the inversion of the greater caucasus gc basin is assumed to be oligo miocene however late cretaceous early paleocene shortening linked to the final closure of the northern branch of the neotethys is also suggested the crimean mountains cm to the north of the eastern bs is one of the key areas to investigate in order to fix the tectonic evolution of the bs to precise the timing of the cenozoic shortening of the eastern bs we focus on an integrated onshore offshore transect from the eastern cm to the sorokin trough north of eastern bs we use newly collected stratigraphic and structural data from the eastern cm and a new interpretation of multichannel seismic lines we define 1 the offshore seismic stratigraphy and constrain the relative chronology of deformations 2 the age of seismic units by correlation of the seismic data with the subbotina 403 well log and 3 we construct an on to off shore transect of eastern cm northern eastern bs region our results evidence a polyphased cenozoic compression in the northern part of the eastern bs 1 paleocene earliest eocene and 2 oligocene miocene maikopian normal faults appear to be related to a formation of the foreland basin instead of evidencing the eastern bs cretaceous rifting finally this study allows precising the shortening phases within eastern cm and eastern bs since the early paleocene linking them to the neotethys closure and the gc tectonic evolution

tectono metamorphic evolution of syros and sifnos islands cyclades greece abstract miocene exhumation of metamorphic rocks in the aegean sea is partly a consequence of post orogenic extension if the post orogenic mechanism of exhumation is rather well understood the earlier syn orogenic eocene exhumation is still largely enigmatic previous authors have argued in terms of extension or compression new structural and petrological data on sifnos and syros islands show that exhumation of high pressure low temperature hp lt rocks involves crustal scale extensional ductile shear zones during the eocene we observe a continuum of top to the ne and e ductile shear from the eocene in the blueschist facies to the miocene in the greenschist facies this deformation is distributed in the eclogites and blueschists whereas it is rather localised along ductile shear zones in the greenschists eclogites which are preserved only at the top of the structural pile are exhumed with a cold retrograde p t path in the lower part of the structural pile we observe a progressive retrogression of eclogites in blueschist then greenschist facies this lower part of pile is subsequently exhumed with p t paths showing a nearly isothermal decompression before cooling p t t deformation data suggest that the cycladic blueschists are progressively exhumed by a continuum of accretion at the base of the orogenic wedge and by a partly non coaxial extensional deformation above distributed during the syn orogenic stage then localised during the post orogenic stage we then compare the mechanism of syn orogenic exhumation of crete and the cyclades and we discuss a simple geodynamic scenario for the aegean domain and the external hellenides which accounts for 1 the southward migration of the hellenic trench and arc during the cenozoic 2 the p t t deformation data for the cycladic blueschists and the phyllite quartzite nappe and 3 the transition from syn orogenic to post orogenic in the cyclades

late neoproterozoic paleogeography of the southeastern new england avalon zone insights from u pb geochronology and paleomagnetism integrated geochronologic and paleomagnetic investigation of the arc related lynn and mattapan volcanic complexes around boston massachusetts establishes a neoproterozoic paleopole for the southeastern new england avalon zone four new u pb zircon dates obtained using isotope dilution and thermal ionization mass spectrometry id tims methods range from 597 4 1 5 ma to 595 7 1 6 ma in agreement with published lynn mattapan results of ca 596 ma the mean direction calculated from the a component of magnetization at nine lynn mattapan sites has a declination d of 319 9 and an inclination i of 57 0 95 7 4 the paleopole based on this mean direction is 206 e 60 n these results pass both reversals and fold tests and are regionally consistent among lithologies that include basalt andesite rhyodacite and rhyolite which represent both volcanic and subvolcanic phases most sites also contain stable b and c magnetic components with directions that suggest ordovician to permian remagnetizations a broadly comparable a component direction with d 109 0 and i 63 4 95 9 4 n 11 samples was obtained from one site in the squantum member of the roxbury conglomerate maximum age of 593 ma overlying the volcanic sequence the lynn mattapan results indicate that southeastern new england occupied a mid latitude position at ca 595 ma similar to those reported from avalonian terranes in maritime canada the most likely peri gondwanan position for avalonia consistent with these paleomagnetic data lies off the west african margin using poles from the east sahara craton egypt and the rio de la plata craton brazil has permitted reconstruction of west gondwana without recourse to laurentian proxies

topography of the crust mantle boundary beneath the black sea basin abstract a map of moho depth for the black sea and its immediate surroundings has been inferred from 3 d gravity modelling and crustal structure has been clarified beneath the basin centre the thickness of the crystalline layer is similar to that of the oceanic crust in the western and eastern black sea basins the moho shallows to 19 and 22 km respectively below the tuapse trough northeastern margin adjacent to the caucasus orogen the base of the crust is at 28 km whereas in the sorokin trough it is as deep as 34 km the base of the crust lies at 29 and 33 km depths respectively below the southern and northern parts of the mid black sea ridge for the shatsky ridge between the tuapse trough and the eastern black sea basin the moho plunges from the northwest 33 km to the southeast 40 km the arkhangelsky ridge south of the eastern black sea basin is characterised by a moho depth of 32 km the crust beneath these ridges is of continental type

age and geodynamic evolution of the black sea basin tectonic evidences of rifting in crimea the timing and direction of opening of the black sea basin are debated however parts of its margins were inverted during cenozoic and can be studied onshore the crimean mountains are located in the middle of the northern margin of the basin and at the onshore prolongation of the mid black sea high we present the first detailed mapping of large striated normal faults in crimea these faults define graben structures that trend parallel to the continental margin kinematic analysis of the faults combined with new biostratigraphic data show that the syn rift sequence is valanginian to late albian in age it consists of siliciclastic deposits with limestone olistoliths in contrast the post rift late cretaceous carbonaceous sequence of crimea is devoid of normal faults or olistoliths it unconformably overlies the graben structures the onset ages and the trends of extension are quite similar in the northern crimea and the southern turkey inverted margins of the basin the early cretaceous extension directions are normal to the mid black sea high and the black sea margins we conclude that rifting of black sea basin occurred from the valanginian to the late albian 39 ma and drifting during the late cretaceous based on the directions of rifting on the lack of evidence of strike slip motions near the mid black sea high and on published paleomagnetic data we propose that the black sea opened with rotations accommodated by transform faults at its western and eastern margins as a response to asymmetric slab rollbacks of the neo tethys plate the inversion of the crimean margin results from two successive shortening events early eocene ne sw compression eocene to present se nw compression their timing support the idea that compressional stresses generated by continental collisions in turkey were transmitted through the strong black sea lithosphere up to crimea

role of crustal stretching on subsidence of the continental crust abstract the principal areas of subsidence of the continental crust are wide intracontinental basins and passive continental margins in many intracontinental basins crustal extension amounts to only a few percent and is unable to explain their subsidence as shown for the timan pechora pre caspian and west texas basins the deep black sea and south caspian basins are underlain by highly attenuated continental crust having velocities in the 7 km s range that shows no evidence for significant extension in passive margins upper crustal extension ranges between 10 and 40 whereas the lower crust is attenuated by 2 3 times e g campos basin north biscay margin large discrepancy between upper crustal stretching and lower crustal attenuation is seen in the crustal configuration of many intracontinental grabens e g baikal and dniepr prypyat basins only in highly extended areas such as the basin and range province and the east china rift system does crustal stretching account for the observed crustal thinning the observed discrepancy between upper extension and crustal thinning across intracontinental rifts and passive margins and particularly in some wide intracontinental basins suggests that crustal stretching alone cannot account for the subsidence of these basins phase transformations in the lower crust probably facilitated by the presence of hydrous fluids can cause rapid 1 ma as well as long term 200 1500 ma upward displacement of the moho discontinuity resulting in high amplitude subsidence of the crust in areas of crustal extension this mechanism can overprint subsidence induced by thermal relaxation of the lithosphere the case of the black sea and south caspian basins shows that density increase of the lithosphere can also occur independently of crustal stretching

geological structure of the northern part of the eastern black sea from regional seismic reflection data including the dobre 2 cdp profile the authors thank the chief editor of this special publication marc sosson university of nice sophia antipolis france and reviewers rs acknowledges support from the royal society of edinburgh for facilitating the collaboration that has led to the production of this paper this work was partly supported within the statutory activities no 3841 e 41 s 2015 of the ministry of science and higher education of poland

fractionation of bulk rock composition due to porphyroblast growth effects on eclogite facies mineral equilibria pam peninsula new caledonia chemically zoned porphyroblasts in metamorphic rocks indicate that diffusional processes could not maintain equilibrium conditions on a grain scale during porphyroblast growth or establish it afterwards an effect of this inability to maintain equilibrium is the progressive removal of elements forming garnet cores from any metamorphic reaction that occurs at the porphyroblast boundaries or in the matrix of the rock to examine this effect on mineral assemblages the bence albee matrix correction was applied to x ray intensity maps collected using eclogite samples from northern new caledonia in order to determine the chemical composition of all parts of the sample the manipulation of these element maps allows a quantitative analysis of the fractionation of the bulk rock composition between garnet cores and the matrix a series of calculated equilibrium volume compositions represents the change in matrix chemistry with progressive elemental fractionation as a consequence of prograde garnet growth under high p conditions pressure temperature pseudosections are calculated for these compositions in the cao na2o feo mgo al2o3 sio2 h2o system assemblages modal proportions and mineral textures observed in the new caledonian eclogites can be closely modelled by progressively removing elements forming garnet cores from the bulk rock composition the pseudosections demonstrate how chemical fractionation effects the peak metamorphic assemblage prograde textures and the development of retrograde assemblages

structural and depositional evolution of the east balkan thrust belt bulgaria analysis of structural and sedimentologic data from onshore outcrops offshore wells and offshore seismic profiles indicates that the thrust belt geometry in eastern bulgaria from the paleocene to the holocene is characterized by a southeastward plunge toward the western black sea basin this plunge was caused by 1 a combination of eastward thinning continental crust in the west and oceanic crust in the east 2 a postrift thermal subsidence of the continental crust 3 buttressing and no buttressing of the moesian platform against the thrust belt in its western and eastern parts respectively and 4 northeastward thrust belt advance these factors controlled the overall eastward diminishing uplift of the thrust belt and associated eastward sediment funneling into the black sea evidence for the eastward fading uplift and buttressing includes the 1 eastward decreasing amount of shortening along constructed cross sections yielding 30 10 5 11 and 4 km 18 6 6 5 6 8 and 2 5 mi respectively from west to east respectively 2 eastward trend of more complete stratigraphic sections and shallower erosional levels and 3 eastward increase in decollement depths being 3 7 3 8 9 5 to 13 5 and 12 3 to 14 1 km 2 3 2 4 5 9 8 4 and 7 6 8 8 mi the age of the last thrusting is progressively younger toward the east from the middle eocene through the late eocene to the oligocene from west to east respectively onshore parts of the thrust belt which were significantly affected by buttressing against the moesian platform exhibit thrusting followed by late eocene gravitational collapse oligocene quiescence and neogene extension the thrust belt part farther east exhibits thrusting followed by oligocene neogene extension a paleocene middle eocene piggyback basin formed in the onshore part of the thrust belt centered in the east balkan zone with a southeastward plunging axis which migrated northeastward with basin shortening and filling the development of the east balkan thrust belt and its later extensional modification had a dominant control over sediment transport lithofacies and depositional patterns developing thrust belt fold structures together with the orogenic hinterland and highs in the foreland formed a northeastward and eastward expanding system of sediment input southeastward plunging axes of the foreland basin and the paleocene middle eocene piggyback basin were the principal sediment transport pathways together with subordinate internal synclinal axes these depressions funneled sediments toward and into the western black sea basin as orogenesis advanced to the northeast former depositional areas were uplifted and eroded providing local sources of sediment

deciphering the neoproterozoic history of the hollow fault avalon terrane mainland nova scotia abstract recognition and deciphering of the early history of fault zones is difficult because younger fabrics commonly overprint and obscure older ones the hollow greendale fault system in the avalon terrane of the northern antigonish highlands in mainland nova scotia has suffered many episodes of motion in the paleozoic during development of the appalachian orogen field relationship and petrographic observations indicate that its neoproterozoic history is preserved as ca 610 ma ne and nw trending ductile shear zones within the georgeville group contact aureole of the intrusive syn to late tectonic greendale complex kinematic indicators within the ne trending shear zone along the southwestern contact indicate dextral shear and are compatible with dextral shear indicators within the greendale complex and with the orientation of coeval regional f1 fold structures within the antigonish highlands the nw trending shear zone along the northeastern contact represents either a step over fault within a dextral shear zone or a zone of localized transpression associated with the emplacement of the greendale complex local preservation of neoproterozoic shear zone fabrics within the georgeville group host rocks is attributed to the shielding effects of the proximal greendale complex which acted as a rigid unit during paleozoic deformation so that subsequent motion along the hollow fault was partitioned along the northeastern and southwestern contact of the complex the neoproterozoic history combined with paleocontinental reconstructions indicates that the hollow greendale fault system was part of an important regional strike slip fault zone within a volcanic arc regime along the periphery of gondwana murphy et al 1999a murphy et al 1999b

three dimensional interpretation of gravity data from sedimentary basins using an exponential density depth function in mapping the topography of the basement of deep sedimentary basins by gravity modelling the accuracy can be improved by incorporating an exponential increase in density with depth for calculating the gravity effect of a three dimensional 3d structure with such an exponential density depth relation a frequency domain forward algorithm based on series expansion is presented the numerical evaluation of which can be performed efficiently by fast fourier transform the algorithm can be applied in a recursive procedure to give the inverse solution in terms of basement relief the inversion procedure is satisfactorily tested on a 2d synthetic example and a 3d field example of gravity data from the western margin of the pannonian basin in eastern austria where up to 2 2 km of tertiary sediments overlie an igneous or metamorphic basement the results are confirmed by basement intersections in several wells

on application of three dimensional interactive modeling in gravity and magnetics by h j gotze and bernd lahmeyer geophysics 53 1096 1108 august 1988 gotze and lahmeyer present the main principles and results new automatic system for the interactive modeling of three dimensional 3 d gravity and magnetic fields the high efficiency of the system is demonstrated convincingly on a practical example of a geologic study in the northwest german basin the importance and timeliness of this work are beyond doubt nonetheless a few remarks on the analytical results seem to be appropriate

crustal s wave structure beneath eastern black sea region revealed by rayleigh wave group velocities abstract in this study the crustal s wave structure beneath the eastern black sea region including the eastern black sea basin ebsb and eastern pontides ep has been revealed using inversion of single station fundamental mode rayleigh wave group velocities in the period range of 4 40 seconds we used digital broadband recordings of 13 regional earthquakes that recently occurred in the easternmost ebsb recorded at stations of the kandilli observatory and earthquake research institute koeri the average group velocity dispersion curves were generated from 26 paths for the ebsb and 16 paths for the ep and they were inverted to determine the average 1 d shear wave structure of the region we have created a pseudo section roughly depicting the crustal structure of the region based on the group velocity inversion results of all station earthquake paths the thickness of the sedimentary layer reaches 12 km in the center of ebsb vs 2 5 3 1 km s and decreases 4 km in the ep there is a thin sedimentary layer in the ep vs 2 7 km s a consolidated thin crust that exists in the ebsb possesses a high seismic velocity vs 3 8 km s while a thin 26 km and transitional crust exists beneath the ebsb a thick about 42 km continental crust exists beneath the ep where the conrad is clearly seen at about a 24 km depth thick continental crust in the ep region is clearly distinguished from a gradational velocity change vs 3 4 3 8 km s the moho dips approximately southwards and the vs velocity 4 25 4 15 km s beneath the moho discontinuity decreases from the ebsb to the ep in the n s direction this may be an indication of a southward subduction

cenozoic evolution of the eastern black sea a test of depth dependent stretching models abstract subsidence analysis of the eastern black sea basin suggests that the stratigraphy of this deep extensional basin can be explained by a predominantly pure shear stretching history a strain rate inversion method that assumes pure shear extension obtains good fits between observed and predicted stratigraphy a relatively pure shear strain distribution is also obtained when a strain rate inversion algorithm is applied that allows extension to vary with depth without assuming its existence or form the timing of opening of the eastern black sea which occupied a back arc position during the closure of the tethys ocean has also been a subject of intense debate competing theories called for basin opening during the jurassic cretaceous or paleocene eocene our work suggests that extension likely continued into the early cenozoic in agreement with stratigraphic relationships onshore and with estimates for the timing of arc magmatism further basin deepening also appears to have occurred in the last 20 myr this anomalous subsidence event is focused in the northern part of the basin and reaches its peak at 15 10 ma we suggest that this comparatively localized shortening is associated with the northward movement of the arabian plate we also explore the effects of paleowater depth and elastic thickness on the results these parameters are controversial particularly for deep water basins and margins but their estimation is a necessary step in any analysis of the tectonic subsidence record stored in stratigraphy

jurassic cretaceous low paleolatitudes from the circum black sea region crimea and pontides due to true polar wander article in a recent study paleomagnetic and paleoenvironmental data from adria as part of the african plate suggest a trend toward much lower 15 latitudes from early jurassic to earliest cretaceous at the position of adria than suggested by the apparent polar wander apw paths the smoothing of existing apw paths has most likely caused this low latitude episode to be overlooked in this study we test if the low paleolatitudes in the jurassic to early cretaceous can also be found in eurasia i e crimea ukraine and the pontides turkey that are situated in the present day black sea region our eurasian data suggest the same low late jurassic to early cretaceous paleolatitudes as shown for africa the jurassic to lower cretaceous time span is characterized by tethys subduction between the african and eurasian continents and these subduction zones likely functioned as an anchor in the mantle therefore we regard it unlikely that both the african and eurasian plates moved by n1500 km south and subsequently north with respect to the mantle as suggested by the paleomagnetic results true polar wander tpw provides a mechanism that rotates the earth s crust and mantle with respect to its core and it was recently quantified the period from 195 135 ma early jurassic to earliest cretaceous is subject to clockwise tpw which could well explain our results we conclude that tpw rather than plate tectonics is the cause of low late jurassic to early cretaceous african and eurasian paleolatitudes in the eastern mediterranean area

the moho in extensional tectonic settings insights from thermo mechanical models the lithospheric memory is key for the interplay of lithospheric stresses and rheological structure of the extending lithosphere and for its later tectonic reactivation other important factors are the temporal and spatial migration of extension and the interplay of rifting and surface processes the mode of extension and the duration of the rifting phase required to lead to continental break up are to a large extent controlled by the interaction of the extending plate with slab dynamics the finite strength of the lithosphere has an important effect on the formation of extensional basins this applies both to the geometry of the basin shape as well as to the record of vertical motions during and after rifting we demonstrate a strong connection between the bulk rheological properties of europe s lithosphere and the evolution of some of europe s main rifts and back arc systems the thermo mechanical structure of the lithosphere has a major impact on continental break up and associated basin migration processes with direct relationships between rift duration and extension velocities thermal evolution and the role of mantle plumes compressional reactivation has important consequences for post rift inversion borderland uplift and denudation as illustrated by poly phase deformation of extensional back arc basins in the black sea and the pannonian basin region

sources of fluids and gases expelled at cold seeps offshore georgia eastern black sea four seep sites located within an 20 km2 area offshore georgia batumi seep area pechori mound iberia mound and colkheti seep show characteristic differences with respect to element concentrations and oxygen hydrogen strontium and chlorine isotope signatures in pore waters as well as impregnation of sediments with petroleum and hydrocarbon potential all seep sites have active gas seepage near surface authigenic carbonates and gas hydrates cokheti seep iberia mound and pechori mound are characterized by oil stained sediments and gas seepage decoupled from deep fluid advection and bottom water intrusion induced by gas bubble release pechori mound is further characterized by deep fluid advection of lower salinity pore fluids the pechori mound pore fluids are altered by mineral water reactions at elevated temperatures between 60 and 110 c indicated by heavier oxygen and lighter chlorine isotope values distinct li and b enrichment and k depletion strontium isotope ratios indicate that fluids originate from late oligocene strata this finding is supported by the occurrence of hydrocarbon impregnations within the sediments furthermore light hydrocarbons and high molecular weight impregnates indicate a predominant thermogenic origin for the gas and oil at pechori mound iberia mound and colkheti seep c15 hydrocarbons at the oil seeps are allochtonous whereas those at the batumi seep area are autochthonous the presence of oleanane an angiosperm biomarker suggests that the hydrocarbon source rocks belong to the maikopian formation in summary all investigated seep sites show a high hydrocarbon potential and hydrocarbons of iberia mound colkheti seep and pechori mound are predominantly of thermogenic origin however only at the latter seep site advection of deep pore fluids is indicated

stretching lineations in transpressional shear zones an example from the sierra nevada batholith california abstract ductile shear zones and associated stretching lineations are generally considered to be the result of two dimensional simple shear deformations with stretching lineations interpreted to rotate into parallelism with the direction of tectonic transport with increasing deformation however stretching lineations perpendicular to the inferred tectonic transport direction are displayed by some shear zones field studies in the sierra nevada batholith have revealed a single shear zone the rosy finch gem lake shear zone that contains both steeply plunging stretching lineations in older metamorphosed sedimentary and granitic rocks and shallowly plunging stretching lineations in syntectonic granitoids dextral sense of shear indicators are found in all these units and deformation occurred simultaneously along the length of the shear zone theoretical strain modeling indicates that stretching lineations can be either horizontal or vertical within transpressional shear zones to investigate the kinematics of three dimensional deformation we examine the role of stretching lineations which form as a result of finite strain including the possibility of partitioning a component of the strike slip movement onto shear bands comparing the field data with the strain modeling we interpret the along strike variation in lineation behavior within the rosy finch gem lake shear zone to be a result of the differences in finite strain recorded by different units the older units showing steeply plunging lineation have recorded more finite strain across a narrower shear zone than the syntectonic granites which record shallowly plunging lineations we conclude that the orientation of the lineation within transpressional shear zones does not necessarily correlate with the transport direction but may reflect along strike variations in finite strain and or strain partitioning

structural geology across a proposed archaean terrane boundary in the eastern yilgarn craton western australia abstract the eastern goldfields province of the archaean yilgarn craton western australia can be divided into several nw se trending terranes with different stratigraphic signature at least two main phases of penetrative ductile deformation affect the terranes d1 is a phase of nappe type transport mainly to the north along gently dipping ductile shear zones it is interpreted as a phase of regional extension contemporaneous with intrusion of massive granitoid plutons and possibly contemporaneous with deposition of felsic volcanics and metasediments in the greenstone belts terrane boundaries were probably formed during d1 d2 gave rise to steep nw se to n s trending foliations and upright folds d2 is strongly partitioned over the area for strain and vorticity the pattern of partitioning seems to be dependent on the position of granitoid plutons which give rise to development of d2 strain shadows d1 structures have been preserved mainly in these strain shadows terrane boundaries are transected by boundaries of d2 structural domains minor intrusion of granitoids continued during and after d2 d1 is possibly associated with arrival of a mantle plume below the yilgarn craton and d2 may be a phase of regional shortening in a thinned lithosphere weakened by the thermal event

seismic model of the crust and upper mantle in the scythian platform the dobre 5 profile across the north western black sea and the crimean peninsula the scythian platform scp with a heterogeneous basement of baikalian variscan cimmerian age is located between the east european craton eec on the north and the crimean caucasus orogenic belt and the black sea bs basin on the south in order to get new constrains on the basin architecture and crustal structure of the scp and a better understanding of the tectonic processes and evolution of the southern margin of the eec during mesozoic and cenozoic time a 630 km long seismic wide angle refraction and reflection warr profile dobre 5 was acquired in 2011 october it crosses in a w e direction the fore dobrudja trough the odessa shelf of the bs and the crimean plain the field acquisition included eight chemical shot points located every 50 km and recorded by 215 stations placed every 2 0 km on the land in addition the offshore data from existing profile 26 placed in the odessa shelf were used the obtained seismic model shows clear lateral segmentation of the crust within the study region on four domains the fore dobrudja domain km 20 160 an offshore domain of the karkinit trough at the odessa shelf of the bs km 160 360 an onshore domain of the central crimean uplift crimean plain km 360 520 and the indolo kuban trough at the kerch peninsula km 520 620 that is the easternmost part of the crimea two contrasting domains of the scp within the central part of the dobre 5 profile the karkinit trough and the central crimean uplift may represent different stages of the scp formation a deep karkinit trough with an underlying high velocity 7 16 km s 1 lower crust body suggests its rifting related origin during early cretaceous time the central crimean uplift represents a thick up to 47 km crustal domain consisting of three layers with velocities 5 8 6 4 6 5 6 6 and 6 7 7 0 km s 1 which could be evidence of this part of the scp originating on the crust of precambrian craton eec the thick heterogeneous basement of the central crimean uplift shows inclusions of granitic bodies associated with magmatic activity related with variscan orogeny within the scp general bending and crustal scale buckling of the central crimean uplift with a wavelength of 230 km could be an effect of the alpine compressional tectonics in the adjacent crimean mountains the extended rifted continental margin of the scp eec at the odessa shelf and buckling uplifted domain of the central crimean uplift affected by compressional tectonics are separated by the n s oriented western crimean fault the crust of the southern margin of the eec is separated from the scp which originated on the eec crust tectonised and reworked during the palaeozoic mesozoic by the crustal fault of w e orientation which corresponds with the golitsyn fault observed at the surface between the eec and the scp the fore dobrudja domain with a thick 10 km heterogeneous basement and two subhorizontal layers in the crystalline crust with velocities 6 2 6 3 and 6 4 6 65 km s 1 differs from the scp crust and its origin could be very similar to that of the trans european suture zone and palaeozoic west european platform

western versus eastern black sea tectonic evolution pre rift lithospheric controls on basin formation abstract we demonstrate the key role of pre rift rheology on the kinematics of basin formation in the western and eastern black sea basins constraints on modelling results are provided by a large data set based on more than 50 000 km of multichannel seismics offshore and onshore wells regional gravity and magnetic surveys refraction seismics and field studies the model supports the presence of important differences in the thickness and in the thermal state of the lithosphere which rifted to form the western middle barremian and the eastern middle paleocene black sea subbasins a 200 km and a 80 km thick pre rift lithosphere appear to have driven the deformation in the western and in the eastern black sea respectively differences in the geometry and in the mechanical properties of the pre rift lithosphere have a strong control on the depth of necking and thus on the basin morphology the model sheds light on palaeotectonic and palaeogeographic reconstructions duration of rifting events location of subsiding areas and erosional surfaces the western and the eastern parts of the black sea appear to be two distinct basins characterised by different evolutionary paths determined by different pre rift conditions

polar wander and paleomagnetic reference pole controversies the purpose of this paper is to review the progress made over the past four years in studies of phanerozoic and precambrian polar wander with an emphasis on the contributions made by u s scientists we perceive a general theme embracing the notion that the accuracy of cratonic reference poles and therefore of apparent polar wander apw paths is not as good as was generally believed four years ago a renewed interest in research concerning cratonic reference poles is largely the result of paleomagnetic studies in orogenic belts namely the western cordillera and appalachians of north america the andes of south america and elsewhere which seek to document the existence or non existence of displacements of suspect terranes i e rotation and or translation with respect to their presently associated cratons some of the results of this research are reviewed in this volume by hillhouse and mcwilliams an important realization of which paleomagnetists have long been aware but which was demonstrated recently by a number of sobering examples for both the paleozoic and mesozoic apw paths for north america is that the reliability of concordance discordance parameters that define terrane displacement is dependent not only on the precision and accuracy of the individual paleomagnetic study but also on the precision and accuracy of the appropriate cratonic reference pole

rare earth and trace element mobility in mid crustal shear zones insights from the mont blanc massif western alps the behaviour of rare earth elements ree during fluid rock interaction in mid crustal shear zones has received little attention despite their potential for mass balance calculation and isotopic tracing during deformation in this study several cases of large ree mobility during alpine fluid driven shear zone development in the pre alpine granitic basement of the mont blanc massif are considered on a regional scale the undeformed granite compositions range within 5 wt sio2 70 5 75 3 wt and magmatic chemical variations are of the order of 10 20 ascribed to minor effects of crystal fractionation major and trace element mobility observed in shear zones largely exceeds these initial variations shear zones developed a range of mineral assemblages as a result of shearing at mid crustal depths at not vert similar0 5 gpa 400 c five main shear zone assemblages involve muscovite chlorite epidote actinolite and calcite respectively as major phases in most cases selective enrichments of light or heavy ree and y ta hf are observed ree mobility is unrelated to deformation style cataclastic mylonitic the intensity of strain and to the shear zone s major metamorphic mineral assemblages instead the changes in ree concentrations are ascribed to the alteration of pre existing magmatic ree bearing minerals during deformation related fluid rock interaction and to the syntectonic precipitation of metamorphic ree bearing minerals mainly monazite bastnasite aeschynite and tombarthite minor proportions 2 of these accessory phases with grain sizes mostly 20 m account for enrichments of up to 5 1 compared to the initial granite whole rock ree budget the stability of the ree phases appears to be largely dependent on the altering fluid composition ree mobility is ascribed to changes in ph and to the availability of co32 po42 and so42 ligands in the fluid such processes are likely to influence the mobility of ree y hf and ta in shear zones

porphyroblast nucleation growth and dissolution in regional metamorphic rocks as a function of deformation partitioning during foliation development in regional metamorphic rocks the partitioning of deformation into progressive shearing and progressive shortening components results in strain and strain rate gradients across the boundaries between the partitioned zones these generate dislocation density gradients and hence chemical potential gradients that drive dissolution and solution transfer phyllosilicates and graphite are well adapted to accommodating progressive shearing without necessarily building up large dislocation density gradients within a grain because of their uniquely layered crystal structure however most silicates and oxides cannot accommodate strain transitions within grains without associated dislocation density gradients and hence are susceptible to dissolution and solution transfer as a consequence zones of progressive shearing become zones of dissolution of most minerals and of concentration of phyllosilicates and graphite exceptions are mylonites where strain rates are commonly high enough for plastic deformation to dominate over diffusion rates and therefore over dissolution and solution transfer porphyroblastic minerals cannot nucleate and grow in zones of active progressive shearing as they would be dissolved by the effects of shearing strain on their boundaries however they can nucleate and grow in zones of progressive shortening and this is aided by the propensity for microfracturing in these zones which allows rapid access of fluids carrying the material presumed to be necessary for nucleation and growth zones of progessive shortening also have a number of characteristics that help to lower the activation energy barrier for nucleation this includes a build up of stored strain energy relative to zones of progressive shearing in which dissolution is occuring porphyroblast growth is generally syndeformational and previously accepted criteria for static growth are not valid when the role of deformation partitioning is taken into account porphyroblasts in a contact aureole do not grow statically either as microfracturing associated with emplacement allows access of fluids in a fashion that is similar to microfracturing in zones of progressive shortening the criteria used for porphyroblast timing can be readily accommodated in terms of deformation partitioning reactivation of deforming foliations and a general lack of rotation of porphyroblasts with the spectacular exception of genuinely spiralling garnet porphyroblasts

the recognition of reactivation during continental deformation reactivation involves the accommodation of geologically separable displacement events intervals 1 ma along pre existing structures the definition of a significant period of quiescence is central to this phenomenological definition and the duration of the interval chosen represents the resolution limit of reactivation criteria found in most ancient settings in neotectonic environments reactivation can be further defined as the accommodation of displacements along structures that formed prior to the onset of the current tectonic regime this mechanistic definition cannot always be applied to ancient settings due to the uncertainties in constraining relative plate motion vectors four sets of criteria may be used to recognize reactivation in the geological record stratigraphic structural geochronological and neotectonic some structural criteria may not be reliable if used in isolation to identify reactivated structures much of the previously published evidence cited to invoke structural inheritance is equivocal as it uses similarities in trend dip or three dimensional shape of structures numerous fault and shear zone processes can cause significant weakening both synchronously with deformation and in the long term and may be invoked to explain reactivation the collage of fault bounded blocks forming most continents therefore carries a long term architecture of inheritance which can explain much of the observed complexity of continental deformation zones

a new crustal model of the anatolia aegean domain evidence for the dominant role of isostasy in the support of the anatolian plateau the engines of surface deformation in the anatolia aegean region are a matter of debate including the origin of the high elevations of the anatolian plateau recent publications based on geological and thermomechanical modelling emphasize the role of dynamic topography in the plateau uplift however quantitative estimates of the contribution of dynamic topography are affected by large uncertainties due to insufficient knowledge of the crustal structure in particular crustal thickness and density to reduce these uncertainties we provide a new accurate crustal thickness map of the anatolia aegean domain computed from a large volume of broadband seismic data in addition we display high resolution seismic sections of the internal structure of the crust in western and central anatolia density contrasts are derived from the same seismic data set and bouguer gravity anomaly computed from the egm2008 model our crustal thickness model is highly correlated with the topography suggesting that the anatolian plateau is close to isostatic equilibrium the average density difference between crust and upper mantle computed from our crustal model and bouguer gravity anomaly is low compared to the global average 0 315 10 3 kg m 3 the ratio of surface elevation to crustal thickness is lower than average 1 9 4 which also indicates a low density crust differences between isostatic topography and observed topography are overall small 500 m the east to west gradients of crustal thickness and topography changes are nearly constant in between the taurides and pontides at the northern and southern borders of anatolia the observed constant crustal thickness gradient may indicate a low viscosity lower crust supported by the thin mantle lithosphere evidenced by seismic tomography beneath the anatolian plateau we propose that viscous flow in the lower crust has smoothed out lateral changes in the crustal structure expected for such a heterogeneous collage of continental fragments this flow may originate from gravitational potential energy differences between eastern anatolia thick crust high elevations and the aegean sea thin crust low elevations suggesting that gravity plays an integral part in the westward escape of anatolia

the dynamics of the eastern mediterranean and eastern turkey summary in this study we investigate the dynamics of the region that includes greece the aegean sea and asia minor in a least squares inversion we solve for a continuous strain rate field and corresponding velocity field that satisfies 872 gps data the estimate of the geodetic strain rate field provides constraints for our dynamic analysis next we separately solve the depth integrated 3 d force balance equations for depth integrated deviatoric stresses within the lithosphere in which body force input comes from differences in vertically integrated vertical stress or differences in gravitational potential energy per unit area gpe these gpe estimates calibrate the absolute magnitudes of deviatoric stresses that are acting within the lithosphere further we investigate the sensitivity of our stress field solutions by using two different crustal structure models one from compiled crustal structure estimates obtained primarily from relatively recent seismic observations and the other from the crust 2 0 model in an iterative least squares inversion we then solve for stress field boundary conditions that when added to the contribution of deviatoric stresses associated with gpe differences provides a best fit to the directions of principal axes and relative magnitudes of the principal axes of the rates of strain obtained in the kinematic analysis robust features that arise from the boundary condition solution are nne forcing along the southern boundary east of about 33 e 0 5 1 2 1012 n m 1 with a rapid anticlockwise rotation of forces to the west of this along with an outward pulling force 0 4 1012 n m 1 directed ssw along the entire hellenic arc segment this force system along the hellenic arc can be interpreted as a result of slab rollback the total depth integrated 3 d deviatoric stresses in the final dynamic solution provides an excellent match to the deformation indicators throughout the region with vertically integrated stress magnitudes of order 0 5 2 5 1012 n m 1 we use constraints from derived stress magnitudes together with gps defined scalar values of strain rate magnitude to define bulk effective viscosities of the lithosphere depth averaged effective viscosities for the entire lithosphere are high within the black sea of order 0 7 3 1023 pa s relative to surrounding continental lithosphere north anatolian shear zone northern aegean sea and gulf of corinth are characterized by low depth averaged viscosities of order 1 5 1021 pa s deviatoric stresses from gpe differences and boundary condition effects combine in surprising ways in some regions resulting in near total stress cancellation in areas such as the southern aegean sea and portions of the central anatolian block gpe differences combine with boundary condition effects along the eastern segment of the north anatolian fault naf in a way that is compatible with the hypothesis that motion on the naf was facilitated by slab detachment beneath east anatolia and dynamic uplift of east anatolian plateau in general gpe differences play a nearly equal role as boundary condition influences in their contribution to the total deviatoric stress field the low depth integrated deviatoric stress magnitudes throughout the region suggest that zones of active deformation are facilitated by dramatic weakening mechanisms throughout the lithosphere

lithosphere structure of the ukrainian shield and pripyat trough in the region of eurobridge 97 ukraine and belarus from gravity modelling abstract the southern segment of the seismic profile eurobridge eurobridge 97 eb 97 located in belarus and ukraine crosses the suture zone between two main segments of the east european craton fennoscandia and sarmatia as well as sarmatia itself at the initial stage of our study a 3 d density model has been constructed for the crust of the study region including the major part of the osnitsa mikashevichi igneous belt omib superimposed by sediments of the pripyat trough pt and three domains in the ukrainian shield the volhyn domain vd with the anorthosite rapakivi korosten pluton kp the podolian domain pd and the ros tikich domain rtd the model comprises three layers sediments with maximum thickness 6 km in the pt and two heterogeneous layers in the crystalline crust separated at a depth of 15 km 3 d calculations show the main features of the observed gravity field are caused by density heterogeneities in the upper crust allocation of density domains deeper than 15 km is influenced by moho topography fitting the densities here reveals an increase up to 2960 kg m 3 in the modelled bodies accompanied by a moho deepening to 50 km in contrast a moho uplift to a level of 35 37 km below the kp and major part of the pt is associated with domains of reduced densities an important role for the deep odessa gomel tectonic zone dividing the crust into two regions one of basically archean consolidation in the west pd and rtd and one of proterozoic crust in the east kirovograd domain was confirmed 2 d density modelling on the eb 97 profile shows that in the upper crust three main domains of different precambrian evolution the omib with the superimposed pt the vd with the kp and the pd can be distinguished deeper in the middle and lower crust layered structures having no connection to the surface geology are dominant features of the models least thickness of the crust was obtained below the kp greatest crustal thickness more than 50 km was found below the pd characterised also by maximum deviation of velocity density relation in the rocks from a standard one the velocity and density models along the eb 97 profile have been interpreted together with inferred v p v s ratios to estimate crustal composition in terms of sio 2 content in the course of the modelling the status of the pd as a centre of archean granulitic consolidation has been confirmed the crustal structure of the anorthosite rapakivi kp is complex for the first time a complicated structure for the lower crust and lower crust upper mantle transition zone beneath the kp has been determined the peculiarities of the crustal structure of the kp are quite well explained in terms of formation of rapakivi anorthosite massifs as originating from melt chambers in the upper mantle and lower crust an important role for the south pripyat fault spf repeatedly activated during proterozoic palaeozoic times has been ascertained at the subplatform stage of crustal evolution the spf was probably a magma channel facilitating the granitic intrusions of the kp in the palaeozoic the fault was reactivated during rifting in the pt

3d crustal and lithospheric model of the arabia eurasia collision zone three dimensional joined inversion of topography gravity and geoid data was carried out in the collision zone between the eurasian and arabian plates comprising central and eastern anatolia the black sea basin and the caucasus region the 3d algorithm first introduced by motavalli anbaran et al 2013 is based on a bayesian approach with gaussian density functions in which the targeted area is divided into vertical columns each comprised of four layers namely water of known thickness i e bathymetry if present crust lithospheric mantle and asthenosphere the inversion results are moho depth average crustal density and depth to the lithosphere asthenosphere boundary defined here as the 1350 c isotherm existing seismic moho depths were used as a priori information in order to constrain crustal thicknesses thickest crust up to 50 km was found underneath the great caucasus mountains thinnest crust 22 25 km underneath the black sea basin the east anatolian plateau is underlain by relatively thick crust up to 45 km thinning to less than 40 km towards the central anatolian plateau eastern anatolia and the eastern part of central anatolia are underlain by strongly thinned lithosphere up to 100 km thickest lithosphere up to 200 km underlies the caspian basin and the russian platform

the impact of climate change tectonism and hydrology on the formation of carboniferous tropical intermontane mires the springhill coalfield cumberland basin nova scotia abstract both climate and tectonism are influential in determining basin and mire hydrology in the rapidly subsiding intermontane basins of euramerica which formed in response to the variscan hercynian alleghenian orogeny however the record of climate change has been muted and may therefore go unrecognized the complex interplay of climate and tectonism in a tropical continental setting is recorded in the 4 km thick westphalian a b fill of the cumberland basin thick peat accumulation was favoured at the southern basin margin where rheotrophic forested mires 4 9 km wide flourished between basin axis rivers and coalesced alluvial fans derived from the cobequid highlands as a result of their geomorphic setting the thicker coals 4 3 m exhibit distinct areal zones piedmont inner mire and riverine evidence that the forest swamps were nourished both by rainfall and by groundwater discharge from alluvial fans includes the stratigraphic affinity of thick coals and basin margin conglomerates interfingering of distal fan sheetflood and mire deposits petrographic evidence of elevated ph partial gelification of tissues and predominance of the arboreous lycopsids lepidodendron and paralycopodites whereas such groundwater supply is crucial to maintenance of modern wetlands in drier periods a subhumid climate is implied coals at joggins further removed from groundwater discharge at the basin margin are less well developed a 600 m thick coal window within the fining and reddening upward basin fill sequence at springhill is inferred to represent a coincidence of optimal groundwater supply and net subsidence the ultimate decline of peat accumulation in the basin may reflect decrease in catchment area and fan size and loss of rainshadow as the cobequid massif was denuded and the basin filled the coal window ca 6 9 10 5 yr is punctuated by non marine cyclothems of coal grey sideritic mudrock and multistorey sandstone that share similar time frames with astronomic cycles of axial precession ca 1 4 10 4 yr the stress of related climate change is inferred to have caused peat accumulation to fall into disequilibrium with sediment flux and basin subsidence the late quaternary history of certain african mires illustrates the dramatic impact of climate change especially temperature and seasonality and orographic effects on tropical continental peat accumulation aspects of the groundwater recharge model may be applicable to the westphalian stephanian intermontane mires of spain and mesozoic coal basins of northern china

dobre 2 warr profile the earth s upper crust across crimea between the azov massif and the northeastern black sea the dobre 2 wide angle reflection and refraction profile was acquired in june 2007 as a direct southwestwards prolongation of the 1999 dobrefraction 99 that crossed the donbas foldbelt in eastern ukraine it crosses the azov massif of the east european craton the azov sea the kerch peninsula the easternmost part of crimea and the northern east black sea basin thus traversing the entire crimea caucasus compressional zone centred on the kerch peninsula the dobre 2 profile recorded a mix of onshore explosive sources as well as airguns at sea a variety of single component recorders were used on land and ocean bottom instruments were deployed offshore and recovered by ship the dobre 2 datasets were degraded by a lack of shot point reversal at the southwestern terminus and by some poor signal registration elsewhere in particular in the black sea nevertheless they allowed a robust velocity model of the upper crust to be constructed along the entire profile as well as through the entire crust beneath the azov massif a less well constrained model was constructed for much of the crust beneath the azov sea and the kerch peninsula the results showed that there is a significant change in the upper crustal lithology in the northern azov sea expressed in the near surface as the main azov fault this boundary can be taken as the boundary between the east european craton and the scythian platform the upper crustal rocks of the scythian platform in this area probably consist of metasedimentary rocks a narrow unit as shallow as about 5 km and characterized by velocities typical of the crystalline basement bounds the metasedimentary succession on its southern margin and also marks the northern margin of the northern foredeep and the underlying successions of the crimea caucasus compressional zone in the southern part of the azov sea a broader and somewhat deeper basement unit about 11 km with an antiformal shape lies beneath the northern east black sea basin and forms the southern margin of the crimea caucasus compressional zone the depth of the underlying moho discontinuity increases from 40 km beneath the azov massif to 47 km beneath the crimea caucasus compressional zone

age thermal evolution and history of the black sea basin based on heat flow and multichannel reflection data abstract multichannel reflection data tugolessov et al 1985 have revealed two deeps in the basement topography of the black sea which are filled with sediments from 12 to 15 km thick the deeps lack the granitic layer and are underlain by oceanic type crust which we assume to be generated by seafloor spreading processes the age of the deeps was interpreted previously in a highly controversial manner as being from the paleozoic early mesozoic to the recent in the paper age estimations were undertaken using surficial heat flow data assuming that they are related to deep seated age dependent heat flow generated by the cooling oceanic lithosphere but that they are strongly distorted by the heating of continuously accumulating sediments as well as by additional heat input from radiogenic production within sediments using reliable thermophysical parameters of compacting sediments the distorted heat flow in the sediments was evaluated numerically this allowed us to estimate the age of the black sea deeps floor the results show that the west black sea deep is 130 to 95 m y old and the east black sea deep is nearly 110 m y old these figures support an interpretation of the black sea deeps as remnants of a late mesozoic back arc basin that evolved behind the lesser caucasian pontide island arc the inferred middle cretaceous age of the deeps is the first estimate obtained quantitatively and corresponds well with available heat flow and multichannel reflection data

550 580 ma magmatism in cape breton island nova scotia canada the product of nw dipping subduction during the final stage of amalgamation of gondwana abstract cape breton island is host to widespread magmatic activity dated between 550 and 580 ma in the south its products include the capelin cove pluton and host coastal volcanic belt both are composed of bimodal tholeiitic calc alkaline suites that were emplaced on a thin sialic crust in a volcanic arc system their trace element and nd isotope variations are consistent with fractional crystallization accompanied by lower crustal contamination in a compositionally zoned magma chamber in contrast the indian brook and kerrs brook plutons and price point volcanic rocks in central cape breton island have higher contents of strongly incompatible trace elements and resemble modern arc related calc alkaline rocks emplaced on a moderately thick continental crust comparison with available data for other 550 580 ma igneous rocks across cape breton island indicates that they were produced above a nw dipping subduction zone this convergence was synchronous with the final stage of globalscale orogenic activity that culminated with the final amalgamation of gondwana available detrital zircon ages in late neoproterozoic 650 545 ma sediments in the antigonish highlands avalon composite terrane suggest derivation from the amazon craton it is proposed that the avalon composite terrane formed off northwestern south america during the late neoproterozoic

eocambrian paleomagnetism of the boston basin evidence for displaced terrane a paleomagnetic study of the late precambrian roxbury formation consisting of extrusives and clastic sediments has yielded a steeply downward directed and pre folding characteristic magnetization d i 219 71 95 5 k 311 paleopole at 13 n 267 e n 4 sites which indicates a significantly higher paleolatitude 55 than would be expected if the boston basin were part of the equatorial north american craton in the latest precambrian and earliest paleozoic this characteristic magnetization reveals dual polarities and is further supported by a positive conglomerate test a ubiquitous post folding late paleozoic overprint is present in nine sites d i 183 14 95 8 k 42 with a paleopole at 41 s 285 e the pre folding magnetization resides in hematite which is inferred to have formed during early oxidation of the rocks the high stability of this hematite may have prevented its magnetization from being reset during the late paleozoic chemical event responsible for the magnetic overprint the boston basin has a marked geological similarity to the avalon basement terranes in nova scotia and newfoundland as well as the armorican massif in france and the high paleolatitudes observed for all these terranes suggest a common paleogeographical affinity a likely paleolocation is near the northwestern margin of gondwana which was located at the southpole in the latest precambrian and early cambrian

tectonic setting of the north gondwana margin during the early ordovician a comparison of the ollo de sapo and famatina magmatic events abstract this paper presents a comparison of compiled geochronological and geochemical data from the ollo de sapo and famatina magmatic events the ollo de sapo magmatic sequence is located in northwest iberia and was emplaced during the early ordovician from 495 to 474 ma the famatina complex is a magmatic sequence located in northern argentina that was emplaced during the early to mid ordovician from 483 to 463 ma these magmatic events are currently interpreted to have been emplaced in different tectonic settings despite both having occurred along the north gondwana margin geochronological data indicates that these magmatic events occurred contemporaneously over at least 9 m y and therefore can provide a snapshot of the northern gondwana margin during the mid ordovician major element data indicates that both magmatic suites are calc alkaline to alkali calcic and trace element and ree data show magmatic signatures that are indistinguishable this study highlights the similarity between the ollo de sapo and the famatina magmatic suites and discusses alternative models for their emplacement based on paleomagnetic and paleobiogeographical data these data indicate that the ollo de sapo was likely emplaced in a subduction zone setting while the famatina magmatic suite may be of parautochthonous origin to gondwana implying that the pampeanan margin may not have been active during the early to mid ordovician

jurassic arc volcanism on crimea ukraine implications for the paleo subduction zone configuration of the black sea region article i nfo the early cretaceous and younger opening of the black sea has obliterated much of the older record of tethyan subduction below southeastern europe the earlier mesozoic evolution was dominated by opening and closure of tethyan oceans between gondwana and laurasia with their consumption at least in part accommodated along the southern eurasian margin crimea ukraine a peninsula in the northern black sea represents the northernmost region of southeastern europe that exposes a record of a pre cretaceous tethyan active margin to shed new light on the paleosubduction zone configuration of the southeastern european margin in the jurassic we report 40

the black sea back arc basin insights to its origin from geodynamic models of modern analogues the black sea is generally thought to be a back arc basin with active extension rifting beginning in late early cretaceous times although some fundamental issues such as the presence or absence of a related magmatic arc and the orientation of the related driving subduction zone remain vaguely defined at best however as shown here the regional structure of the black sea is consistent with that predicted by geodynamic models of modern back arc basin formation in which extension is driven by slab roll back this includes an asymmetric distribution of horst and graben structures in the back arc basin the distribution and spacing of which is related to the strength of the underlying lithosphere which forms the hanging wall of the subduction zone by analogy the intrabasinal structure of the black sea as a whole is explicable as the consequence of a single phase of asymmetric back arc basin formation not two separate phases independently responsible for its western and eastern segments and its underlying lithosphere is rheologically strong as predicted by recent models of precambrian europe and present day tomography

the moho depth map of the european plate summary the european plate has a 4 5 gy long and complex tectonic history this is reflected in the present day large scale crustal structures a new digital moho depth map is compiled from more than 250 data sets of individual seismic profiles 3 d models obtained by body and surface waves receiver function results and maps of seismic and or gravity data compilations we have compiled the first digital high resolution map of the moho depth for the whole european plate extending from the mid atlantic ridge in the west to the ural mountains in the east and from the mediterranean sea in the south to the barents sea and spitsbergen in the arctic in the north in general three large domains within the european plate crust are visible the oldest archean and proterozoic crust has a thickness of 40 60 km the continental variscan and alpine crust has a thickness of 20 40 km and the youngest oceanic atlantic crust has a thickness of 10 20 km

fault controlled emplacement of arc related magmas along the neoproterozoic northern gondwanan margin an example from the antigonish highlands nova scotia abstract in the antigonish highlands nova scotia neoproterozoic ca 620 605 ma magmatism is a local representative of regional arc related tectonothermal activity that typifies avalonia and related terranes located along the northern gondwanan margin three distinct types of coeval magma are represented by volcanic rocks of the georgeville group and by syn to post tectonic plutons e g greendale complex i calc alkalic subduction related basaltic andesites and andesites ii crustally derived rhyodacites and rhyolites and iii fe ti rich continental tholeiites derived from the melting of subcontinental lithosphere these magmas were probably generated in an extensional arc regime with deep seated faults providing conduits for rising magmas the georgeville group was polydeformed by thrusts isoclinal folds and upright folds associated with movement along ne trending faults very soon after it was deposited a 85 km long 1 2 km wide magnetic anomaly transects georgeville group strata and connects outcrops of fe ti rich continental tholeiites and ultramafic cumulate rocks of the greendale complex the n s orientation of this anomaly is compatible with coeval sinistral shear along ne trending faults and its magnetic signature suggests that it is a shallow regional studies indicate that the kinematic reversal and the cessation of magmatism is a local expression of the neoproterozoic early paleozoic termination of subduction and generation of a transform fault along the northern gondwanan margin possibly by ridge trench collision analogous to the cenozoic evolution of the san andreas fault system in the western united states

transfer of deformation in back arc basins with a laterally variable rheology constraints from analogue modelling of the balkanides western black sea inversion the balance between extension and contraction in back arc basins is very sensitive to a number of parameters related to on going subduction and collision processes this leads to complex back arc geometries where a lateral transition between crustal blocks with contrasting rheologies is often recorded one good example is the back arc region of the balkanides pontides orogens where lateral variations in rheologies are observed between the balkanides moesian block and the pontides western black sea basin the latter opened during cretaceous eocene and has been inverted together with the former starting during late middle eocene the inversion generated contrasting geometries along the orogenic strike with a narrow zone of high deformation in the balkanides moesia region wide areas of thrusting with low offsets in the pontides western black sea basin and a transitional zone characterized by highly curved geometries this overall type of inversion is investigated here by the means of analogue modelling testing the role of inherited crustal geometries during inversion our modelling suggests that the contrasting architecture of inverted structures observed in the balkanides pontides domain are the result of pre existing crustal stretching geometries of various blocks inherited from the cretaceous eocene extension the stretched and weak back arc basins can transfer contraction deformation at large distances explaining structures derived by observational studies the collisional deformation recorded in the pontides was transmitted at large distances that are in the range of the contraction structures observed in the centre and northern part of the western black sea in the light of analogue modelling results we argue that the western black sea was a rheologically weaker domain when compared with the adjacent western onshore at the beginning of the inversion in contrast with previous results derived from numerical modelling studies that argued for a strong west black sea domain at the beginning of inversion

complex plumbing systems in the near subsurface geometries of authigenic carbonates from dolgovskoy mound black sea constrained by analogue experiments targeted sampling on the dolgovskoy mound northern shatsky ridge revealed the presence of spectacular laterally extensive and differently shaped authigenic carbonates the sampling stations were selected based on sidescan sonar and profiler images that show patchy backscatter and irregular and discontinuous reflections in the near subsurface the interpretation of acoustic data from the top part of the mound supports the seafloor observations and the sampling that revealed the presence of a complex subsurface plumbing system characterized by carbonates and gas the crusts sampled consist of carbonate cemented layered hemipelagic sedimentary unit 1 associated with several centimetres thick microbial mats three different carbonate morphologies were observed a tabular slabs b subsurface cavernous carbonates consisting of void chambers up to 20 cm3 in size and c chimney and tubular conduits vertically oriented or forming a subhorizontal network in the subsurface the methanogenic origin of the carbonates is established based on visual observations of fluids seepage structures 13c depletion of the carbonates 13c varying between 36 7 and 27 4 and by thin carbonate layers present within the thick microbial mats laboratory experiments with a hele shaw cell were conducted in order to simulate the gas seepage through contrasting grain size media present on the seafloor combined petrography visual observations and sandbox simulations allowed a characterization of the dynamics and the structures of the plumbing system in the near subsurface based on sample observations and the experiments three observed morphologies of authigenic carbonates are interpreted respectively as a darcian porous flow through the finely laminated clayey coccolith rich layers b gas accumulation chambers at sites where significant fluid escape was impeded by thicker clayey layers forming the laminated unit1 and c focussed vertical fluid venting and subhorizontal migration of overpressured fluids released from b the hele shaw cell experiments represent a promising tool for investigating shallow fluid flow pathways in marine systems

along strike variations in the composition of sandstones derived from the uplifting western greater caucasus causes and implications for reservoir quality prediction in the eastern black sea oligo miocene outcrops along the southern margin of the western greater caucasus preserve a record of sediments shed from the range into the northern and central parts of the eastern black sea sandstones in the russian western caucasus are significantly more quartz rich than those located farther se in western georgia the latter contain appreciably more mudstone and volcanic rock fragments oligo miocene turbidite systems derived from the russian western caucasus in the tuapse trough and central eastern black sea may therefore form better quality reservoirs at shallow to moderate depths than sediments derived from west georgian volcaniclastic sources in the easternmost part of the basin palynomorph analysis indicates sediment derivation predominantly from jurassic and cretaceous strata in the russian western caucasus and from eocene strata and an increasing proportion of cretaceous strata upsection in western georgia an eocene volcaniclastic source is proposed for the increased rock fragment component in west georgian sandstones eocene volcaniclastic rocks are no longer exposed in the greater caucasus but similar rocks form the inverted fill of the adjara trialet basin farther south in the lesser caucasus the former presence of a northern strand of this basin in the west georgian caucasus is supported by earlier thermochronological work

avalonian proximity of the ordovician miramichi terrane northern new brunswick northern appalachians paleomagnetic evidence for rifting and back arc basin formation at the southern margin of iapetus a paleomagnetic investigation of the middle ordovician tetagouche group in northern new brunswick was undertaken to determine the paleogeo aphi position of the miramichi terrane stepwise thermal demagnetization of pillow basahs reveals a high temperature characteristic gnet tion with a mean direction of b w z 69 k 22 aas 13 tih corrected n 7 sites 73 samples a positive fold test and the presence of antipodal normal and reversed polarity directions indicate that this ancient direction is ordovician in age with a paleopole position of 52 n 352 e the corresponding pateolatitude of 535 places these vokanic rocks near the southern margin of the iapetus ocean at paleolatitudes similar to those revealed by avalon for the middle to late ordovician the mafic and felsic volcanic rocks and marine sedimentary rocks of the tetagouche and fournier groups have been interpreted to be remnants of a rifted continental margin and a middle ordovician back arc basin our results show that the process of rifting and back arc basin formation occurred at the avalonian margin of iapetus which implies that ordovician subduction was not restricted to the laurentian margin but also marks the southern margin of japetus

paleomagnetism of the late precambrian fourchu group cape breton island nova scotia volcanogenic sediments of the fourchu group and a gabbroic intrusion which are found in the avalonian terrane of south eastern cape breton island have been sampled for paleomagnetic analysis upo

the black sea basins structure and history new model based on new deep penetration regional seismic data part 1 basins structure and fill abstract this work is based upon results of interpretation of about 8872 km long regional seismic lines acquired in 2011 within the international project geology without limits in the black sea the seismic lines cover nearly the entire black sea basins including russia turkey ukraine romania and bulgaria sectors a new map of acoustic basement relief and a new tectonic structure scheme are constructed for the black sea basins the basement of the black sea includes areas with oceanic crust and areas with highly rifted continental crust a chain of buried seamounts which were interpreted as submarine volcanoes of late cretaceous santonian to campanian age has been identified to the north of the turkish coast on the shatsky ridge probable volcanoes of albian age have also been recognized synorogenic turbidite sequences of paleocene eocene and oligocene ages have been mapped in the cenozoic numerous compressional and transpressional structures were formed in different parts of the black sea basin during the pleistocene quaternary turbidites mass transport deposits and leveed channels were formed in the distal part of the danube delta

paleomagnetic reconnaissance of early mesozoic carbonates from williston lake northeastern british columbia canada evidence for late mesozoic remagnetization three classic sections of middle and late triassic fossiliferous limestones cropping out around williston lake in british columbia canada were sampled for paleomagnetic study the objective was to test the suitability of these units for detailed magnetobiostratigraphic study with the aim of improving the reference triassic geomagnetic polarity time scale the williston lake characteristic magnetizations differ however from any triassic north america cratonic reference directions a satisfactory agreement is found instead with cretaceous early cenozoic north america cratonic reference directions the exclusive occurrence of normal polarity suggests that remagnetization likely occurred during the cretaceous long normal superchron remagnetizations may have been triggered by connate brines which moved along aquifers of porous sandstones and carbonates in the early stages of laramide folding resume trois sections fossiliferes classiques de calcaires trias moyen et tardif affleurant autour du lac williston en colombie britannique ont ete echantillonnees pour une etude paleomagnetique l objectif etait de s assurer de la pertinence de ces unites pour une etude magneto bio stratigraphique detaillee visant a ameliorer l echelle referentielle de temps de la polarite geomagnetique au trias les magnetisations caracteristiques du lac williston different toutefois de toute direction cratonique referentielle au trias en amerique du nord toutefois une correlation satisfaisante est etablie avec les directions cratoniques referentielles du cretace cenozoique precoce en amerique du nord l occurrence exclusive d une polarite normale suggere qu il y eut probablement une remagnetisation au cours du long superchron normal du cretace les remagnetisations peuvent avoir ete declenchees par des saumures connees qui se sont deplacees le long d aquiferes de gres et de carbonates poreux dans les premieres phases du plissement laramide

diachronous demise of the neotethys ocean as a driver for non cylindrical orogenesis in anatolia continent continent collision drives crustal deformation topographic rise and geodynamic change africa eurasia convergence accommodated in the eastern mediterranean involved subduction of the neotethyan oceanic lithosphere in anatolia subduction was followed by collision of continental crust of greater adria with eurasia to form the izmir ankara erzincan suture zone discerning the effects of this collision from pre collisional ophiolite obduction related orogeny of greater adria is notoriously difficult estimates on the timing of collision in central anatolia are based on a forearc to foreland basin transition along the eurasian margin and suggest a 60 ma age of initial collision here we assess whether this age is also representative for collision in eastern anatolia and across the cenozoic sivas basin that straddles the greater adria europe suture to this end we retro deform regional block rotations in the pontides the kirsehir block and the taurides building a first order regional block circuit around the sivas basin we show that up to 700 km of convergence must have been accommodated across the sivas basin after central anatolian kirsehir pontide collision at 60 ma an order of magnitude more than estimated crustal shortening and that wholesale lithospheric subduction must have occurred throughout much of the cenozoic paleocene collision would require that this subduction consumed continental lithosphere which is unlikely we consequently infer that oceanic subduction continued much longer in eastern anatolia perhaps well into the miocene we postulate that prolonged oceanic subduction and slab pull drew the eastern taurides north relative to the central taurides leading to shortening and oroclinal bending in central anatolia the diachronous demise of the neotethys ocean in anatolia as a function of its paleogeography is thus a likely driver for the strong non cylindricity of the cenozoic anatolian collisional orogen

geochemical and isotopic characteristics of early silurian clastic sequences in antigonish highlands nova scotia canada constraints on the accretion of avalonia in the appalachian caledonlde orogen avalonia is a terrane that accreted to laurentia baltica during the development of the appalachian caledonide orogen interpretations of the timing of accretion have been constrained by comparing faunal affinities overstep sequences age and kinematics of inferred accretionary deformational events and controversial paleomagnetic data we show that the time of accretion of avalonia may also be constrained by contrasts in the geochemical and isotopic signatures of its igneous rocks which reflect the characteristics of the underlying continental basement and mantle and sedimentary rocks which reflect provenance early silurian clastic sedimentary rocks of the beechill cove formation antigonish highlands nova scotia were deposited on avalonian crust the formation predominantly consists of approximately 80 m of siltstones and shales deposited in a nearshore environment and derived from the northeast their age is constrained by paleontological data and by directly underlying late ordovician early s

paleomagnetism of the moreton s harbour group northeastern newfoundland appalachians evidence for an early ordovician island arc near the laurentian margin of iapetus paleomagnetic results have been obtained from mafic volcanic units in the upper part of the moreton s harbour group which is part of an accreted island arc terrane that is preserved in the notre dame bay subzone of the central mobile belt of the newfoundland appalachians detailed thermal and alternating field demagnetization reveals a stable characteristic component of magnetization carried by magnetite at a large number of sites in pillow basalts and coeval basaltic dikes the intrusives contain both polarities and a primary age for the characteristic magnetization is indicated by a positive contact test for one of the dikes and by a positive structural test involving a correction for block rotations strike correction the overall mean direction for the characteristic component after tectonic tilt and strike correction flows and intrusives d 171 i 22 k 22 6 95 6 5 pole 29 n 135 e flows d 166 i 22 k 33 2 95 6 5 corresponds to an early ordovician paleolatitude for the arc of 11 s which is indistinguishable from the expected paleolatitude of the north american margin this implies that the arc formed at or near the margin of the craton in contrast the avalon block which formed the other margin of iapetus was widely separated from the arc and the craton at this time the early ordovician paleolatitude of the arc terrane supports a tectonic model in which coeval ophiolitic sequences inboard of the arc were formed in a narrow ocean basin between the arc and the craton subsequent convergence between the arc and laurentia in middle ordovician time resulted in closure of this narrow ocean basin and obduction of the back arc basin oceanic crust onto the ancient margin of the craton thus giving rise to the taconic orogenic pulse in the newfoundland appalachians

high strain zones a unified model abstract where a shear zone is bounded by undeformed wall rocks and there is no volume change the deformation path within the zone on the bulk scale approximates a simple shear where the zone boundaries are stretched and the shear direction between the two boundaries is parallel to one of the principal stretching directions of the boundaries the deformation path within the zone is not a simple shear but still has monoclinic symmetry both simple shear and general monoclinic deformation paths should be regarded as special cases in nature because generally not only are the zone boundaries stretched but also the shear is oblique to the principal stretching directions of the boundaries in this general case the deformation path is triclinic we establish a model which includes this general case also taking into consideration volume change five independent parameters are required to characterize the rate of deformation of the flow four are sufficient to characterize the flow kinematics the model is generally triclinic and orthorhombic and monoclinic deformations are subgroups by varying the values of the characterizing parameters the various types of high strain zones can be represented the kinematics of flow within such zones and the accumulated finite deformation geometry are investigated many field observations such as for example lineations in transcurrent shear zones that vary between vertical and horizontal cleavage transected folds and the absence of sheath folds in some shear zones where folds have been significantly rotated can sometimes be better interpreted in the context of our general model

kinematics of back arc inversion of the western black sea basin 1 back arc basin evolution is driven by processes active at the main subduction zone typically assuming the transition from an extensional back arc during the retreat of a mature slab to a contractional basin during high strain collisional processes such a transition is observed in the black sea where the accurate quantification of shortening effects is hampered by the kinematically unclear geometries of cenozoic inversion by means of seismic profiles interpretation quantified deformation features and associated syn tectonic geometries on the romanian offshore this study demonstrates that uplifted areas observed by exploration studies form a coherent thick skinned thrust system with n ward vergence thrusting inverted an existing geometry made up by successive grabens that were inherited from the cretaceous extensional evolution the shortening started during late eocene times and gradually affected all areas of the western black sea basin during oligocene and miocene times deformation being coherently correlated across its western margin the mechanism of this generalized inversion is the transmission of stresses during the collision recorded in the pontides balkanides system syn tectonic sedimentation in the western black sea demonstrates that this process was continuous and took place through the onset of gradual shortening migrating northward although the total amount of shortening is roughly constant in an e w direction individual thrusts have variable offsets deformation being transferred between structures located at distance across the strike of the system the black sea example demonstrates that the vergence and offset of thrusts can change rapidly along the strike of such a compressional back arc system this generates apparently contrasting geometries that accommodate the same orogenic shortening

tectonic significance of a llanvirn age for the dunn point volcanic rocks avalon terrane nova scotia canada implications for the evolution of the iapetus and rheic oceans abstract the paleozoic evolution of avalonia is crucial to the understanding of the development of the appalachian orogen and the iapetus and rheic oceans paleomagnetic faunal structural and isotopic data indicate that avalonia had accreted to laurentia by the early silurian in the avalon terrane of nova scotia ordovician early devonian rocks consist of bimodal volcanic rocks at the base dunn point formation disconformably overlain by a thick sequence of fossiliferous siliciclastics arisaig group which contain llandoverian to lochkovian fossils until now the only published age data for the volcanic rocks yielded an imprecise rb sr whole rock isochron age of 421 15 ma and the volcanism has been interpreted to reflect local extension and basin development related to the oblique collision between avalonia and laurentia after closure of the iapetus ocean we present u pb zircon data from a rhyolite which indicate an age of 460 0 3 4 ma for the dunn point formation an age that requires a re interpretation of its tectonic setting the dunn point volcanism probably developed on the avalonian microcontinent outboard from both laurentia and gondwana possibly in a rifted arc setting analogous to the modern taupo zone in northern new zealand a llanvirn age for these felsic rocks also reconciles apparently conflicting paleomagnetic data and inferred paleolatitude for avalonia in the ordovician silurian and implies 10 northward movement of avalonia between 460 and 440 ma and about 5 5 cm year for the latitudinal component of the convergence between avalonia and laurentia i e the destruction of the iapetus ocean and divergence between gondwana and avalonia development of the rheic ocean during this interval

evidence and timing of crustal extension versus shortening in the early tectonothermal evolution of a proterozoic continental rift sequence at broken hill australia 1 low pressure p high temperature t metamorphism previously attributed to crustal thickening accompanying nappe emplacement in the paleoproterozoic willyama supergroup at broken hill is reinterpreted as a response to crustal extension d1 and bimodal magmatism commencing circa 1700 ma d1 deformation occurred under amphibolite granulite facies conditions producing layer parallel fabrics s1 and metapelitic mineral assemblages in which andalusite dominated over sillimanite crustal extension ceased soon after 1640 ma to be followed by crustal thickening higher pressure metamorphism and northeast vergent recumbent folding d2 attendant on inversion of the original d1 extensional structures d2 recumbent folding has previously gone unrecognized but probably peaked around 1600 ma before further amphibolite facies metamorphism between 1600 and 1590 ma accompanying upright folding and northwest directed thrust faulting d3 in the light of this revised tectonothermal history geodynamic models erected to explain elevated thermal gradients and low p high t granulite facies metamorphism in tectonically thickened crust may not be as relevant to broken hill as once thought above average crustal temperatures and low p high t metamorphism in the willyama supergroup more likely occurred in response to voluminous magmatic intrusion accompanying crustal thinning mantle upwelling and emplacement and unroofing of midcrustal rocks along a major detachment surface a second major structural and or stratigraphic break in the willyama supergroup is indicated by the absence of d1 fabrics from the uppermost part of the sequence

3 d gravity analysis of the dniepr donets basin and donbas foldbelt ukraine abstract the dniepr donets basin ddb is a linear nw se trending late palaeozoic and younger sedimentary basin on the east european platform separating the ukrainian shield from the voronezh massif its northwestern dniepr segment has the characteristics of a typical rift basin to the southeast through a transition zone of approximately 200 km length the ddb is progressively uplifted and compressionally deformed into the correlatable donbas foldbelt df along the axis of the dniepr segment a series of gravity highs has been previously explained by high density crystalline crust beneath the axis of the basin caused by intrusion of mafic and ultramafic rocks in this paper the results of a 3 d gravity analysis using a gravity backstripping technique is described that investigates the crustal and upper mantle structure in the region of the ddb df transition zone and df a residual gravity field i obtained by subtracting the gravity influence of the sedimentary succession of the ddb from the observed field reveals a distinct positive anomaly along the axis of the rift basin increasing in amplitude to the southeast in concert with increasing sedimentary thickness a residual gravity field ii derived by removing the gravity effects of a modelled homogeneous crystalline crust from residual field i reaches 200 and 100 mgal amplitude in the df for two respective moho models based on different interpretations of the published crust and upper mantle seismic velocity models the first of these model a assumes crustal thickening beneath the transition zone and df to a moho depth up to 50 km whereas the second model b assumes a moho shallowing to depths in the range 35 37 km along the whole basin axis for each residual anomaly ii the best fitting 3 d distribution of average density in the crystalline crust has been computed both models indicate the existence of a high density body in the crystalline crust along the ddb axis increasing in density from the dniepr segment to the df with higher average crustal density required in the case of moho model a 3 17 103 kg m 3 versus 3 06 103 kg m 3 for model b the preferred interpretation of the density models is one in which the denser crystalline crust underlying the ddb df transition zone and df is explained by intrusion of mafic and ultramafic rocks during late palaeozoic rifting processes invocation of processes related to the uplift and inversion in the df are not required to explain the observed gravity field although reworking of the crust during permian and younger tectonism in the df cannot be ruled out

an integrated gravity model for europe s crust and upper mantle we present an integrated gravity model of the european lithosphere based on an analysis of a number of new data sets leading to a much higher resolution than provided by previous models first of all a recent crustal model eucrust 07 is used to quantify the crustal contribution to the observed gravity field and to identify the effect of mantle heterogeneity the new gravity field model is based on a combination of satellite champ and grace and terrestrial data we also use these data sets to estimate residual mantle gravity anomalies and residual topography reflecting the effect of mantle density variations induced by temperature and compositional heterogeneity the separation of these effects is vital for a proper assessment of mantle structure and evolution in addition we utilize a new tomographic model for p and s velocity anomalies beneath europe which is a priori corrected for crustal structure using eucrust 07 the seismic velocity anomalies were subsequently converted into temperature anomalies using a mineral physics approach we estimate the effect of temperature variations on the gravity field and subtract it from the total mantle field the residual fields point to an important role of compositional density anomalies in the upper mantle a number of key features of the compositional density distribution so far invisible in seismic tomography data are detected for the first time

retracted structural complexity in the curnamona province south australia polyphase strain partitioning and reactivation in this paper we examine the apparent timing relationships between the structural and metamorphic events of the amphibolite facies sequence in the walter outalpa shear zone wosz area in the southwestern part of the palaeo to mesoproterozoic curnamona province the local structural geometry and style are largely due to heterogeneous non coaxial flow in which foliation development is related to the superposition of two main independent structural events d2 and d3 strain was progressively partitioned into high strain zones in the southern part of the study area in contrast to the low strain areas in the north of the study area d2 deformation developed under amphibolite facies conditions and is partitioned between zones of thrusting and flattening folding related to nappe formation d3 deformation developed under greenschist facies conditions and is partitioned between strike slip faulting and folding d3 high strain zones form discontinuous nw trending anastomosing strands that contain relics of the d2 thrust related foliation these relicts preserve the higher grade mineral assemblages that are partially overprinted by d3 retrograde assemblages strike slip movement along the wosz is therefore interpreted to have re used the pre existing d2 thrust such that d2 strain partitioning influenced renewed d3 strain partitioning the high grade metamorphism and phase of pervasive deformation d2 m2 are ascribed to the d2 mesoproterozoic olarian orogeny that occurred in the curnamona province between ca 1600 and 1590 ma the tectonic context of the d3 m3 shearing event is highly uncertain recent geochronological sm nd isotope ages from garnet from within the wosz shear zone yield ca 520 490 ma delamerian ages dutch r a hand m clark c 2005 cambrian reworking of the southern australian proterozoic curnamona province constraints from regional shear zone systems geol soc london 162 5 763 775 however the d3 m3 shear foliation are truncated by the neoproterozoic unconformity flooring the adelaide rift complex stratigraphy suggesting pre delamerian orogeny activity along the shear zone it is thus likely that the d3 movement along the shear zone records a combination of late olarian orogenic movement with a component of reactivation during the delamerian orogeny 2005 elsevier b v all rights reserved

a fundamental problem with the kinematic interpretation of geological structures abstract non steady flows are ubiquitous in nature not only do imposed boundary conditions vary with time and rock rheology change during the course of deformation but also deformation is generally heterogeneous and all of these conditions lead to non steady flow histories in modern kinematic analysis flow apophyses the instantaneous stretching axes and the vorticity vector collectively referred to as the eigen directions of deformation are used in place of bruno sander s kinematic axes for deformation with a steady flow history this practice is well justified and has led to great advances in structural geology but for non steady flow histories the geometrical relationships among eigen directions flow pattern vary with time this makes it inappropriate to correlate an association of structures and fabrics with certain time invariant flow patterns and hence raises the question how should we interpret geological structures and fabrics kinematically without the assumption of homogeneous and steady deformation we suggest that the answer lies primarily in forward modeling of deformation based on a knowledge of rock properties