palaeomagnetic evidence for block rotations in the western greek rhodope summary the rhodope massif has been traditionally considered to be a pre mesozoic element that remained stable during the tertiary this idea has been partly supported by previous palaeomagnetic results on plutonic and volcanic rocks ranging in age from palaeocene to oligo miocene however new palaeomagnetic data from additional sites on tertiary magmatic rocks of the western greek rhodope show declination values indicating in most cases a clockwise rotation whereas inclinations are systematically lower than those corresponding to the actual latitudinal position of the rhodope our results together with previously published ones are discussed in the light of recent ideas proposed for the rhodope and the north aegean region we suggest that at least the western part of the greek rhodope has been clockwise rotated after the oligocene north south to ne sw extension tilted the formations towards the north or north east producing apparently high inclinations if the alternative pole position for eurasia proposed by westphal 1990 is adopted

e i corrected paleolatitudes for the sedimentary rocks of the baja british columbia hypothesis paleomagnetic inclinations from sediments of the western terranes of canada are consistently too shallow for their reconstructed paleogeographic positions two contradicting explanations for these discrepancies are 1 terranes have been displaced northward with respect to the stable american craton by several thousands of kilometres between the late cretaceous 75 ma and the eocene 50 ma and 2 sedimentary inclination error has caused a shallow bias in the paleomagnetic directions here we apply the elongation inclination e i method to paleomagnetic data sets from sedimentary rocks of supposedly allochtonous terranes of western north america to correct for inclination flattening our results indicate that the paleomagnetic directions from the continental silverquick sediments 95 92 ma of southern british colombia are not seriously affected by inclination error because the magnetic signal most likely concerns a chemical remanent magnetisation crm in contrast the marine sediments of the nanaimo group 84 72 ma of vancouver island region appear seriously affected by inclination flattening f 0 7 and the e i corrected mean inclinations are about 98 steeper than the original data we arrive at corrected inclinations paleolatitudes of i 578 k 388n for the silverquick and i 558 k 368n for the nanaimo sediments our corrected paleolatitudes indicate that the canadian terranes were indeed located adjacent to the baja californian margin during the late cretaceous thus supporting the baja bc hypothesis d 2005 elsevier b v all rights reserved

paleomagnetic evidence for neogene rotational deformations in the aegean domain new paleomagnetic data are reported from the islands of skyros and lesbos in central aegea and the izmir foca region in western anatolia together with previous results obtained in northwestern greece and with results from northern aegea reported by others authors these data suggest that the lower miocene arc was almost rectilinear trending e w and that the curvature was acquired by opposed rotational deformations at each termination moreover the observed inclinations which are shallower than those expected on the basis of a geocentered dipole field suggest a large northward drift since middle miocene

discrete plio pleistocene phases of tilting and counterclockwise rotation in the southeastern aegean arc rhodos greece early pliocene formation of the south aegean left lateral strike slip system the island of rhodos represents an uplifted block in the largely submerged southeastern aegean forearc it has a complex history of subsidence uplift and counterclockwise rotation during the plio pleistocene in response to the interplay between large scale geodynamic processes in this paper we present a new chronostratigraphic framework for the continental pliocene apolakkia basin of southwestern rhodos we combine these time constraints with recently published chronostratigraphic data from the marine plio pleistocene basins of northeastern rhodos to reconstruct rotational and vertical motions our palaeomagnetic results identify two rotation phases for rhodos c 10 9 6 counterclockwise ccw rotation between 3 8 and 3 6 ma and c 17 6 ccw rotation since 0 8 ma between these phases rhodos tilted to the se drowning the southeastern coast to a depth of 500 600 m between 2 5 and 1 8 ma then to the nw which resulted in the re emergence of the drowned relief between 1 5 and 1 1 ma we relate the rotations of rhodos to incipient formation of the south aegean sinistral strike slip system and the foundering of the rhodos basin the previously shown absence of messinian evaporites in the deep marine rhodos basin in combination with the 3 8 ma onset of ccw rotation of rhodos constrains the onset of the formation of the south aegean strike slip system between 5 3 and 3 8 ma the formation of this strike slip system is probably related to the interplay of oblique collision between the southeastern aegean region and the northward moving african plate the westward motion of anatolia gravitational spreading of the overthickened aegean lithosphere and the recently postulated southwestward retreat of the african subducted slab along a subduction transform edge propagator fault

temporal change of the vertical crustal movement on the western coast of suruga bay central japan abstract we investigated the spatial pattern of vertical crustal movement and its temporal change in the eastern tokai region central japan on the basis of leveling measurements by the geographical survey institute of japan in order to analyze the data along the leveling route between kakegawa bm140 1 and hamaoka bm25951 we used the program baysea to see how the trend of subsidence at bm25951 relative to bm140 1 has changed since 1982 we found that the subsidence accelerated in the period of 1987 1989 and has been decelerating since then the average spatial pattern of vertical displacement in the eastern tokai region for the last 18 years is characterized by conspicuous subsidence along the western coast of suruga bay with a gradual decrease of the subsidence rate in the inland direction the spatial pattern however was noticeably different during the period when the subsidence at hamaoka relative to kakegawa was accelerated the subsidence rate at that time was larger in the northern part of the western coast of suruga bay compared to that in the southern part on the other hand it seems that subsidence on the western coast of suruga bay has been decelerating in late 1990s

pseudopaleosecular variation due to remanence anisotropy in a pyroclastic flow succession 1 in order to check the reliability of a paleosecular variation record in a sequence of pyroclastic rocks miocene sardinia we measured various types of anisotropy magnetic susceptibility ams anhysteretic remanent magnetization aarm and thermoremanent magnetization atrm the main magnetic carrier is pseudo single domain titanomagnetite no general relation appears between the degrees of ams and aarm while the degrees of aarm and atrm are almost identical measuring the aarm thus provides a fast and reliable method to correct paleomagnetic deviation in volcanic rocks once corrected for anisotropy deviation the apparent scatter of the paleomagnetic directions mostly on inclination is drastically reduced

understanding progressive arc and strike slip related rotations in curve shaped orogenic belts the case of the olevano antrodoco sibillini thrust northern apennines italy 1 we report on a paleomagnetic study of the southern sector of the olevano antrodoco sibillini oas thrust front which corresponds to the southern limb of the northern apennines italy orogenic salient a lively debate has developed regarding the oroclinal progressive arc versus non rotational nature of the oas which has been alternatively interpreted as a dextral strike slip fault dextral transpressive fault or frontal to oblique ramp that reactivated pre existing jurassic normal faults here we document the paleomagnetism integrated with biostratigraphic and structural data of 52 new sites from both the oas hanging wall and footwall on the basis of 39 retained sites we find a peculiar pattern of tectonic rotations along the oas thrust that evidences four rotational domains the thrust footwall is characterized by a southern domain that undergoes an approximately 30 counterclockwise rotation with respect to the stable foreland and an approximately non rotated domain the data from the hanging wall indicate the occurrence of a dextral strike slip component along the southern sector of the oas thrust supported by a strong clockwise rotation close to the ne sw lateral ramp which rapidly fades 1 km from the thrust front a slight but significant cw rotation observed in the remaining sites from the hanging wall confirms the progressive nature of the oas and its structural position as the southern limb of the northern apennines salient our detailed paleomagnetic study is crucial in discriminating between progressive arc and strike slip related components in the main curved orogenic front of the northern apennines

paleomagnetism magnetic anisotropy and mid cretaceous paleolatitude of the duke island alaska ultramafic complex we report paleomagnetic results from layered igneous rocks that imply substantial post mid cretaceous poleward motion of the insular superterrane western canadian cordillera and southeast alaska relative to north america the samples studied are from the stratiform zoned ultramafic body at duke island which intruded rocks of the alexander terrane at the south end of the southeastern alaska archipelago at about 110 ma thermal and alternating field demagnetization experiments show that the characteristic remanence of the ultramafic rocks has high coercivity and a narrow unblocking temperature range just below the curie temperature of magnetite this remanence is likely carried by low ti titanomagnetite exsolved within clinopyroxene and perhaps other silicate hosts the duke island intrusion exhibits a well developed gravitational layering that was deformed during initial cooling but below 540 c into folds that plunge moderately to the west southwest the characteristic remanence clearly predates this early folding and is therefore primary the fisher parameter describing the concentration of the overall mean remanence direction improves from 3 to 32 when the site mean directions are corrected by restoring the layering to estimated paleohorizontal all samples exhibit a magnetic anisotropy that is strong but nonuniform in orientation across the intrusion and we show that it has no significant or systematic effect on the site mean directions of remanence at least some of the anisotropy derives from secondary magnetite formed during partial serpentinization the mean paleomagnetic inclination 56 10 corroborates paleomagnetic results from five coeval silicic plutons of the canadian coast plutonic complex to the south and southeast and implies 3000 km 1300 km of poleward transport relative to the north american craton between mid cretaceous and middle eocene time the insular superterrane and coast plutonic complex shared a common paleolatitude history with more poleward transport than coeval inboard terranes

paleomagnetic evidence for rotation in opposite senses of adjacent blocks in northeastern aegea and western anatolia paleomagnetic data from western anatolia and from the island of lesbos demonstrate significant counterclockwise clockwise or null rotations of coherent blocks which occurred during the neotectonic period these results suggest that the brittle carapace of the lithosphere may not everywhere follow the motion of the ductile lower part but that its movement arises from adjustment to the extensional tectonic regime

new paleomagnetic data from oligocene formations of northern aegea new paleomagnetic data obtained from volcanic and plutonic formations in thrace northern aegea show that this region has not undergone any significant rotation since the lower oligocene the mean value of the inclination is shallower than expected on the basis of a geocentered dipole field implying a large northward drift of about 1000 km although a comparison with published data from bulgaria leads to a puzzling large shortening between these two regions the measured shallow inclinations are coherent with most of other paleomagnetic studies from oligocene formations throughout the entire mediterranean area together with published results from chalkidiki peninsula our data suggest that the circum rhodopean belt was almost rectilinear and trending e w in lower oligocene time

neotectonic deformation in the western sector of tectonic escape in anatolia palaeomagnetic study of the afyon region central turkey abstract following final closure of the neotethyan ocean during the late miocene deformation in central turkey has led to crustal thickening and uplift to produce the anatolian plateau followed by westward extrusion of terranes by strike slip widespread volcanism has accompanied this latter neotectonic phase and palaeomagnetic study of the volcanism shows a coherent record of differential block rotations indicating that the anatolian region is not a plate or platelet sensu stricto but is undergoing distributed internal deformation to evaluate the scale of neotectonic rotations in the transition zone near the western limit of tectonic escape and the border of the extensional domain in central west turkey we have studied the palaeomagnetism at 82 sites in volcanic suites distributed along a 140 km lineament with north south trend and ranging in age from 18 to 8 ma comparable deflection of magnetic remanence from the present field direction is identified along the full length of the lineament a mean clockwise rotation of 12 3 4 2 is determined for this western sector of the anatolian strike slip province since similar rotations are observed in the youngest and oldest units this cumulative rotation occurred after the late miocene when interpreted together with results elsewhere in anatolia it is inferred that the rotation is later than crustal thickening and uplift of the anatolian plateau and entirely a facet of the tectonic escape inclinations are mostly 10 shallower than the predicted miocene field and are considered to reflect the presence of a persistent inclination anomaly in the mediterranean region larger rotations departing from the regional trend are also observed within the study region but are confined to the vicinity of major faults notably those bounding the afyon aksehir graben the pattern of neotectonic declinations across anatolia identifies strong anticlockwise rotation in the east near the arabian pincer with progressive reduction in the amount of rotation towards the west it becomes zero or slightly clockwise at the western extremity of the accreted terrane collage rotations also appear to become generally younger towards the south crustal deformation has therefore been distributed and the net effect of terrane extrusion to the west and south has been to expand the curvature of the tauride arc the westward radial expansion of the extruded terranes is inferred to combine with backroll on the hellenic arc to produce the contemporary extensional province in western turkey

field impressed anisotropies of magnetic susceptibility and remanence in minerals the application of alternating af or direct df magnetic fields to samples containing dispersed particles of magnetite titanomagnetite or maghemite has been found to alter significantly the measured low field susceptibility anisotropy even though the particle orientation is unchanged the acquisition of isothermal remanent magnetization irm is also strongly dependent on the previous af treatment given to the samples a method of quantifying the changes brought about by application of the fields is described the samples studied were intrinsically isotropic or only weakly anisotropic and the computed impressed susceptibility or irm ellipsoids produced by the applied fields were ellipsoids of revolution with the unique axis aligned with the applied field axis the size and shape of the field impressed ellipsoids were strongly dependent upon particle size these effects might thus form the basis of a rapid nondestructive means of estimating particle size in rocks the results also have important implications for magnetic fabric analysis and the static af demagnetization of rocks in particular to ensure that the intrinsic magnetic fabric is measured without any field impressed component of anisotropy samples should not be subjected to static af demagnetization prior to the determination of either low field susceptibility anisotropy or irm anisotropy samples should also not carry a significant remanence such as an irm acquired in a field greater than about 5 mt prior to low field susceptibility anisotropy analysis

paleomagnetism paleointensity and geochronology of miocene basalts and baked sediments from velay oriental french massif central paleomagnetic study of miocene basalts and baked sediments from velay oriental france yields a paleomagnetic pole with coordinates 84 1 n 171 2 e a95 8 6 k 29 n 11 the pole is supported by a positive reversal test and it corresponds well with the apparent polar wander path for eurasia for 10 ma paleosecular variation estimated as the angular standard deviation of the vgp distribution 14 9 6 5 3 5 is close to expected suggesting that the paleomagnetic pole represents a time averaged field moreover five new 40ar 39ar plateau ages falling between 9 20 and 13 55 ma were obtained thellier paleointensity experiments were carried out on both basalts and baked sediments almost all basalts are chemically unstable during the laboratory heatings and of the 36 preselected samples only three yield usable results in contrast the baked sediments are ideal for thellier experiments with 11 out of 13 samples giving reliable paleointensity estimates rock magnetic experiments show that the main ferromagnetic minerals in the baked sediments are fine grained magnetite and hematite with a large proportion of superparamagnetic grains in addition to the standard partial thermoremanent magnetization ptrm check used in thellier experiments to detect chemical crystalline alteration we introduce a second ptrm tail check designed to test the basic prerequisite of the method namely the equality of unblocking and blocking temperatures for the baked sediments unblocking and blocking temperatures are found to be identical which indicates that the remanence is carried by single domain grains

complex rotational deformations in the serbo macedonian massif north greece structural and paleomagnetic evidence abstract structural data concerning the neotectonic deformation of the serbo macedonian massif suggest a possible counterclockwise rotation of the stress field which corresponds to a clockwise rotation of the geological structures such a rotation is confirmed by paleomagnetic data providing a new alternative interpretation of the geodynamic evolution of this area

first paleomagnetic results from neocene formations in evia skyros and the volos region and the deformation of central aegea paleomagnetic results from neogene volcanic and sedimentary formations in central aegea indicate that evia and skyros have undergone a 48 and 26 clockwise rotation respectively the volos region does not show any significant rotation in the last 3 ma the rotation of evia is about twice as large as the one measured from coeval formations in the external hellenic arc the results are interpreted in terms of a published model of distributed deformation by faulting which also provides an explanation for the significant differential rotation of evia and skyros

deflection of paleomagnetic directions due to magnetization of the underlying terrain in the summers of 1989 and 1991 we made 344 near ground level measurements of the ambient geomagnetic field above recent basalts on the island of hawaii using a three component fluxgate magnetometer we studied 12 surface features including a lava pond lava channels long tilted blocks smooth sloping surfaces two fissures and a deep u shaped road cut we observed substantial differences up to 20 between the observed and expected international geomagnetic reference field igrf magnetic field directions over these features except those composed of shelly pahoehoe and a flat horizontally thin lava pond we also observed inclinations that were systematically shallower than the igrf field by up to 5 we show that these shallower inclinations can be explained by the magnetization of the regionally sloping surface of the southern side of the island we found that all of the observed inclination deflections can be explained by simple two dimensional models which assume uniform induced and remanent magnetization parameters in the local terrain our observations imply that the inclination deflections cannot be corrected without a complete knowledge of the preexisting terrain and the remanence in the underlying flows upon which the lavas cooled since this information is rarely available it is difficult or impossible to discriminate between dispersion of paleomagnetic directions caused by the magnetic terrain effect and dispersion due to other factors such as paleosecular variation psv we therefore conclude that psv dispersion parameters cannot be accurately determined from paleomagnetic measurements on highly magnetic volcanic flows we also suggest that some of the geomagnetic excursions inferred from measurements on volcanic rocks may be at least in part due to the magnetic terrain effect it is unnecessary to invoke ad hoc mechanisms such as clastic block or crustal rotations distortion of the top crust or flow deformation to explain the large between site dispersions or inclination anomalies observed in many of the paleomagnetic data from volcanic rocks our observations also bring into question the general reliability of paleomagnetic pole positions inferred from volcanic rocks as a systematic inclination deflection due to local and regional slopes and irregular terrain such as those we observed would lead to a corresponding error in the inferred paleolatitude the magnetic terrain effects also offer alternative explanations for anomalous paleomagnetically inferred plate motions

distributed neotectonic deformation in the anatolides of turkey a palaeomagnetic analysis abstract the palaeotectonic phase of deformation in anatolia accompanied closure of the tethyan ocean and was finally completed with sealing of the bitlis suture bordering the arabian shield at 12 ma arabia has since continued to indent the collage of terranes accreted to the eurasian margin by differential northward movement relative to africa along the dead sea fault zone and counterclockwise ccw rotation accompanying the opening of the red sea this neotectonic phase of deformation has accompanied uplift of the anatolian plateau and establishment of intracontinental transforms comprising the north and east anatolian fault zones deformation has included extrusion and rotation of blocks away from the arabian syntaxis by tectonic escape we produce an updated summary of palaeomagnetic results from this region to show that deformation has been distributed so that block rotations vary systematically across anatolia ranging from strongly ccw in the zone of high strain north of the arabian indenter to near zero in central anatolia and then progressively cw in western anatolia new palaeomagnetic results from the ankara igneous district are also reported and help to constrain the east to west change from ccw to cw rotation within central anatolia the transition of tectonic regimes from compression in the east to extension in the west involves the expulsion of blocks and their rotation along arcuate strike slip faults at an acute angle to the maximum compressive stress 1 between arabia and eurasia the comparable distribution of rotations in palaeotectonic and neotectonic units indicates that the bulk of the observed palaeomagnetic rotations have been concentrated within the last plio pleistocene phase of the neotectonic era as is found in the aegean domain to the west and has involved blocks of the order of 100 km in size the weak collage of accretionary terranes sandwiched between the arabian indenter and the eurasian margin now defined by the north anatolian fault zone has evidently taken up the bulk of the strain imparted by the continuing northward motion of arabia to expand the radius of the tauride arc and the perimeter of extruded crust bordering the limit of the extensional province in western turkey the distributed character of neotectonic deformation is illustrated by equivalent polar distributions both palaeotectonic and neotectonic palaeomagnetic poles show arcuate distributions with poles to best fitting small circles focussed close to the study area differences between the distributed neotectonic deformation resolved from palaeomagnetism and the contemporary gps record reflect the contrasting time periods being evaluated the palaeomagnetic record incorporates evolving and changing tectonic regimes whereas the gps signature has no long term validity within the weak anatolian collage hence the full spectrum of techniques for resolving neotectonic deformation is relevant to unravelling deformation in such regions

on the shape of paleomagnetic data sets a quick and easy method to analyze the shape of paleomagnetic data sets is described and illustrated the elongation e of a set of directions of virtual geomagnetic poles vgp is defined as e k2 k3 where k2 and k3 are the second and third eigenvalues of the bingham distribution it is shown that e 3 or so indicates that the distribution is significantly elongate although the size of the sample and the paleolatitude both affect this conclusion because the azimuth of k2 gives the direction of elongation it can be used to help determine why a particular distribution is elongate it is shown that for most units from the craton both directions and vgp are nearly circular except for units magnetized at very low latitudes in general poles are more circular than directions some units formed in plate margin locations also are circular but many are highly elongate many units from the western cordillera of north america have highly elongate distributions that are compatible with origin within a shear zone others are obviously underformed internally units formed during extension are less commonly elongate but some show the probably effects of normal faulting it is hoped that shape analysis will be part of any complete paleomagnetic study in the future

a paleomagnetic and rock magnetic study of tertiary volcanics from the vogelsberg germany abstract paleomagnetic results are presented for orientated cores from 37 sites in the vogelsberg germany tertiary volcanic province the available radiometric dates indicate that the main volcanic activity occurred between 18 and 15 5 ma early miocene with intermittent mainly intrusive activity continuing into the late miocene a stable natural remanent magnetization nrm direction was obtained from most sites by stepwise alternating field af demagnetization the mean direction excluding sites with intermediate nrm directions is d 358 6 i 64 0 95 5 2 n 31 this gives a virtual geomagnetic pole vgp of 85 1 n 200 9 e which agrees well with the late tertiary apparent polar wander path apwp for eurasia a reverse normal reverse magnetostratigraphy is observed which can be correlated with chrons 5cr 5c and 5br 17 6 15 2 ma results of rock magnetic and reflected light microscopy studies indicate that titanomagnetite and its oxidation products are the main magnetic phases present the grain size and degree of deuteric oxidation varies considerably between sites with the titanomagnetites of thin vesicular lava flows tending to be more oxidized than those in thick massive bodies low temperature susceptibility measurements show a range of behaviour with some samples possessing grains which unblock below room temperature

the tectonic development of the hellenic arc and the sea of crete a synthesis abstract we use field analyses together with interpretation of aerial photographs orbital imagery and sea beam data to define more accurately the geometry of fault systems in the hellenic arc the tectonics of the area are dominated by extensional processes related to normal faulting we then use sea beam data previous oceanographic studies and extrapolation of field analyses on surrounding islands to describe the fault pattern of the cretan sea basin which is found consistent with the land fault pattern the mechanisms of the late neogene and quaternary deformation of the central and southern aegean region are analysed in terms of stress trajectories as revealed by field studies of fault populations we then examine the subsidence of the sea of crete in terms of a model of uniform stretching of the lithosphere the opening of the sea of crete was cylindrical and did not result in bending of crete this leads us to modify the southern portion of an earlier kinematic reconstruction of aegea in agreement with recent paleomagnetic results the implications of the opening of the sea of crete on the tectonic evolution of the straits to the west and east of crete are discussed finally the uplift of the outer arc is explained by underplating due to subduction

palaeomagnetic study of tertiary volcanic domains in southern turkey and neogene anticlockwise rotation of the arabian plate abstract following collision with eurasia the arabian shield indenter has continued to deform into the weak anatolian collisional collage that resulted from subduction of the neotethyan ocean differential movements have involved rotation and continuing northwards translation and have been accommodated mainly by slip along major transforms including the northward extension of the dead sea fault zone dsfz and the east anatolian fault zone eafz to aid in evaluating post collisional motions the palaeomagnetism of extensive volcanic domains at the northern margin of the stable shield in southern turkey is reported here together with the timing of emplacement as constrained by k ar study the age dating results indicate that volcanic activity occurred mainly during mid late miocene times corresponding to the final stages of suturing volcanic fields in the east of the investigated region are younger and correspond to neotectonic volcanism in brunhes and matuyama chrons thermal and alternating field demagnetization of 399 cores from 83 sites in basaltic lavas identifies 29 units of normal and 43 of reversed polarity with 11 sites having transitional or random directions volcanic fields west of the euphrates kilis gaziantep region with ages in the range 7 0 20 3 ma average 14 9 ma sd 4 3 ma have mean remanence d i 353 52 38 sites 5 3 lava fields east of the euphrates urfa region are dated 10 4 12 1 ma and yield a comparable mean remanence d i 350 50 17 sites 6 0 these collections are shown to have properly recorded palaeosecular variation with only minimal inclination shallowing and inferred anticlockwise rotations with respect to eurasia since mid miocene times are 10 9 4 3 and 14 0 5 0 respectively these contrast with clockwise rotation of 6 3 4 3 derived from late matuyama brunhes epoch volcanic rocks immediately to the north west of the arabian margin where rotational impingement of the shield indenter into fault blocks within the karasu rift at the northern extension of the dsfz interacts with left lateral motion at a rate of 0 5 cm year along this zone to produce small scale vertical axis rotations results from the volcanic suites sited on the stable shield are compared with other results from the arabian plate to conclude that it did not rotate significantly following closure of the bitlis suture until late miocene early pliocene times since when it has rotated anticlockwise at a rate of 1 0 myr this is comparable to the present day rate of rotation deduced from gps and correlates with crustal separation and sea floor spreading in the red sea it also temporally links the rotation of the arabian plate to the initiation of the intracontinental transforms north and east anatolian fault zones within anatolia and to the subsequent extrusion of blocks within this accretionary domain by tectonic escape to the west

alternating field demagnetization of rocks and the problem of gyromagnetic remanence abstract alternating field a f demagnetization has proved to be a very reliable technique for separating the magnetization components of rock samples the method is subject to errors caused by either imperfection of the technique or by intrinsic properties of a rock recently stephenson 1 2 introduced the term gyroremanent magnetization grm for a disturbing remanent magnetization that can be acquired by magnetic material during tumbling or stationary a f demagnetization the implications for the routine a f demagnetization of anisotropic rock samples seemed to be very serious here however a method is presented on how to avoid the effect of grm on results obtained from stationary a f demagnetization

use of anisotropy to determine the origin of characteristic remanence in the siwalik red beds of northern pakistan it is often difficult or impossible to determine the origin of the characteristic remanent magnetization of red beds from the bulk remanence alone however anisotropy of remanence or susceptibility is strongly controlled by the statistical alignment of hematite grains this in turn may reflect the development of the magnetic fabric of the sediment over time so the shape of the anisotropy ellipsoid may provide clues to the origin of remanence in this work we make a study of the anisotropy of magnetic susceptibility ams in siwalik red beds of miocene age from northern pakistan comparison of the results with detailed petrographic studies and other information suggests that advanced soil development leads to the destruction of primary fabrics and often with it a coherent magnetization furthermore it should be possible to use ams fabric information to quantify the degree of pedogenesis in these miocene soils we attempted to determine the anisotropy of isothermal remanence air but found ams to be the technique of choice because of apparent changes in coercivity during air experiments we interpret the air data as resulting from metastable domains in hematite grains which change domain state during the air experiment

aegean paleomagnetic inclination anomalies is there a tectonic explanation abstract more than a decade of paleomagnetic research in the aegean area mainly by french investigators c laj c kissel and their colleagues has provided a valuable data base for the evaluation of cenozoic aegean tectonics systematic rotations are documented and have been interpreted by the original investigators in the light of the evolution of the hellenic arc however less attention has been paid to the significance of the paleomagnetic inclinations which also are anomalous twenty one out of 22 paleomagnetic studies performed to date within the general aegean region have yielded paleolatitudes that are too shallow when compared with reference curves for either africa or eurasia suggesting northward relative transport with respect to both continents sedimentary volcanic and plutonic units are involved ages range from oligocene to pliocene some of these apparent paleolatitude anomalies may merely be the result of inclination flattening in certain kinds of clastic sedimentary rocks however shallow inclinations in igneous rocks cannot be so easily dismissed the explanation for these anomalously shallow inclinations does not appear to lie with the reference curves because several other reference curves calculated in several different ways yield essentially the same result we suggest that the paleomagnetic pattern may reflect real northward displacement of crustal blocks within the aegean region measured with respect to both europe and africa the amount of displacement appears to increase systematically to the west the pattern of local block rotations noticed by earlier investigators argues that the displacement did not involve a single coherent aegean block but rather a collection of smaller blocks moving quasi independently geological consequences of northward relative displacement of the aegean block ought to include mid tertiary and or later compressional structures in the north e g rhodope and extensional structures in the leading edge of the african plate

revised and synthetic apparent polar wander paths of the african eurasian north american and indian plates and true polar wander since 200 ma we have reviewed paleomagnetic data available for the eurasian african north american and indian plates over the last 200 ma selection criteria are those generally accepted with an emphasis on evidence for lack of remagnetization accurate dating and proper structural analysis this results in 23 35 51 and 2 poles for eurasia africa north america and india respectively we believe that this limited set of higher quality data is more likely to reveal key features of apparent polar wander apw paths than averaging of larger data sets involving less stringent selection criteria we propose and describe revised apw paths but more importantly we next use relative motion models to transfer all data in a common reference frame we find good agreement between transferred data when they are averaged separately for each plate in independent 20 ma windows this is a check on consistency of paleomagnetic data kinematic models and of the geocentric dipole hypothesis transferred data from all plates are averaged in 20 ma windows to generate synthetic apw paths for all plates studied these synthetic paths are in agreement with the original revised apw paths that use only data from a single plate moreover both geographic and time resolution are improved spatial confidence intervals are of the order of 5 the synthetic paths display interesting features such as a previously ill recognized apw loop for eurasia paleomagnetic and hotspot apw are next compared and a determination of true polar wander tpw is derived we find significant tpw amounting to over 20 in the last 200 ma tpw appears to be episodic with a standstill between 180 and 110 ma there is general agreement with a previous study of livermore et al 1984 the tpw standstill appears to correlate with a time of decreasing reversal frequency ending with the cretaceous long normal superchron other periods of fast tpw would seem to correspond to increasing reversal frequency however it is suggested that the major tpw hairpin at 50 ma might correspond to the collision of india with eurasia tentative correlations with core or mantle indicators can be understood as a result of couplings between the core mantle and lithosphere we believe primarily related to episodic evolution of the d layer

magnetic anisotropy in the trenton limestone results of a new technique anisotropy of anhysteretic susceptibility a new method for determining magnetic anisotropy using anhysteric remanence susceptibility is described the magnetic fabric of a collection of trenton limestone specimens has been determined using this method as well as by conventional anisotropy of magnetic susceptibility the results demonstrate the usefulness of the new method for finding the magnetic fabric of rock units such as the trenton in which the bulk magnetic susceptibilities are low a model is proposed to explain the observed foliated and lineated fabric as a consequence of overburden compaction and regional horizontal stresses the original fabric is inferred to have been isotropic the anisotropy resides in secondary magnetite of late paleozoic age it is argued that the observed magnetic fabric must therefore be alleghenian or younger in age our method has the potential to determine paleostress directions in carbonates elsewhere provided our assumptions are correct

paleomagnetic evidence for an inverse rotation history of western anatolia during the exhumation of menderes core complex abstract within the aegean extensional system the izmir balikesir transfer zone ibtz is a crucial element in the late cenozoic evolution of western anatolia since it accommodates the differential deformation between the cycladic and the menderes metamorphic core complexes here we determine the rotational history of western anatolia using new paleomagnetic data from 87 sites in miocene volcano sedimentary rocks to better understand the role of the ibtz our results reveal two discrete and opposite major rotational phases during the miocene the first phase is derived from early miocene volcanic sedimentary and granitic rocks and is controlled by detachment and strike slip faults it is characterized by an average net 23 6 clockwise cw rotation within the ibtz since the early miocene our new data from the menderes part on the other hand show an average 23 10 counter clockwise ccw rotation the data from the cycladic part show no significant net rotation since the early miocene the second phase is derived from middle late miocene volcanic and sedimentary rocks and is controlled by high angle normal and strike slip faults the rotations from this phase show a very consistent pattern of 22 11 ccw within the ibtz while now the menderes part shows an average cw rotation of 25 14 our paleomagnetic results hence document a major change and inversion of rotation between the early and late miocene the ibtz region experienced a large 45 cw rotation while during the same time interval the menderes part outside the zone experienced a similar 48 ccw rotation after that the ibtz became narrower and the sense of rotation inverted to ccw 23 10 since the late miocene while in the menderes part it inverted to cw 25 14 since the late miocene our new results do therefore fit the hypotheses of two stage extension scenario rather than a one single phase of extension we also conclude that the observed rotations are not directly related to major detachment faulting but to the change in extensional regime of western anatolia the focal mechanism solutions of recent seismic events corroborate that the ibtz is still active and transfers west anatolian extensional strain into the south aegean sea

neotectonic deformation in the transition zone between the dead sea transform and the east anatolian fault zone southern turkey a palaeomagnetic study of the karasu rift volcanism in southern turkey ongoing differential impingement of arabia into the weak anatolian collisional collage resulting from subduction of the neotethyan ocean has produced one of the most complex crustal interactions along the alpine himalayan orogen several major transforms with disputed motions including the northward extension of the dead sea fault zone dsfz meet in this region to evaluate neotectonic motion on the amanos and east hatay fault zones considered to be northward extensions of the dsfz the palaeomagnetism of volcanic fields in the karasu rift between these faults has been studied remanence carriers are low ti magnetites and all except 5 of 51 basalt lavas have normal polarity morphological polarity and k ar evidence show that rift formation occurred largely during the brunhes chron with volcanism concentrated at 0 66 0 35 ma and a subsidiary episode at 0 25 0 05 forty four units of normal polarity yield a mean of d i 8 8 54 7 with inclination identical to the present day field and declination rotated clockwise by 8 8 4 0 within the 15 km wide hassa sector of the karasu rift the volcanic activity is concentrated between the amanos and east hatay faults both with left lateral motions which have rotated blocks bounded by nw se cross faults in a clockwise sense as the arabian block has moved northwestwards an average lava age of 0 5 ma yields a minimum cumulative slip rate on the system bounding faults of 0 46 cm year according with the rate deduced from the africa arabia euler vector and reduced rates of slip on the southern extension of the dsfz during plio quaternary times estimates deduced from offsets of dated lavas flows and morphological features on the amanos fault zone tectonophysics 344 2002 207 are lower 0 09 0 18 cm year probably because they are limited to surface fault breaks and do not embrace the seismogenic crust results of this study suggest that most strike slip on the dsfz is taken up by the amanos east hatay afrin fault array in southern turkey comparable estimates of quaternary slip rate are identified on other faults meeting at an unstable fff junction dsfz east anatolian fault zone karatas fault zone a deceleration in slip rate across the dsfz and its northward continuation during plio quaternary times correlates with reorganization of the tectonic regime during the last 1 3 ma including tectonic escape within anatolia establishment of the north and east anatolian fault zones bounding the anatolian collage in mid late pliocene times a contemporaneous transition from transpression to transtension and concentration of all basaltic magmatism in this region within the last 1 ma

the palaeomagnetism of lesbos ne aegean and the eastern mediterranean inclination anomaly summary palaeomagnetic results for 44 sites in 16 22 ma volcanic rocks from lesbos ne aegean yield a mean pole at 81 8 n 178 1 e k 9 0 a95 7 6 the mean direction for these sites d 4 3 i 48 5 k 10 8 95 6 9 is 5 9 6 1 shallower than the reference direction for miocene lesbos calculated from besse courtillot 1991 combining these new data with previous work yields a mean inclination that is 5 6 4 7 too shallow experimental problems magnetic anisotropy the magnetic terrain effect geomagnetic anomalies and problems with the reference path all seem unable to account for this observation shallow inclinations are a common feature of the aegean region 17 of 18 palaeomagnetic studies on cenozoic igneous rocks have returned an inclination that is shallower than expected northward motion of the aegean block by 500 km with respect to northern europe would account for this observation

investigation of the 1867 lesbos ne aegean earthquake fault pattern based on soil gas geochemical data abstract in this work the soil gas method is being used to compare geochemical data with the geological and structural information on lesbos island ne aegean in particular in the aghia paraskevi kalloni region the epicentral area of an earthquake in 1867 the island belongs to an seismically active zone part of the right lateral and normal fault systems of north anatolia and north and central aegean field observations aerial photo interpretation and microearthquake distribution show two main fault systems trending ne sw to nne ssw and nw se the strongest known destructive earthquake hit the island in 1867 with its epicentral area in the central part of lesbos estimated intensity ix x for the most central and eastern part of the island and vi vii for the rest the soil gas sampling was performed in august 1996 in the aghia paraskevi area by this soil gas survey an attempt was made for the recognition of active faults using the soil gases as fault tracers high values of all the investigated gases he 222rn co2 and ch4 characterize the central and southern sector of the area the soil gas anomalous concentrations are probably linked to the very active extensional tectonic structures that cause the characteristic seismicity of lesbos especially those of 222rn and co2 after statistical processing of the data and the use of contour and dot maps of each investigated gas an important accordance was found between the interpreted linear gas anomalies and the observed faults which possibly generated the 1867 shock

trm deviations in anisotropic assemblages of multidomain magnetite anisotropic assemblages of multidomain magnetite particles develop an anisotropy of magnetic susceptibility ams which in turn induces deviations of thermo remanent magnetization trm from the field direction from the theories of multidomain trm acquisition it is shown that the trm anisotropy tensor has its eigenvalue ratios ti related to the principal weak field susceptibility ratios pi by the order of magnitude ti p2i this relation has been experimentally verified on two sets of highly anisotropic rock samples the exponent has been determined to be 1 94 in the samples from a peruvian gabbro and 1 81 in those from the granite of flamanville nw france accounting for experimental difficulties in determining the trm anisotropy tensors these exponents are judged to agree well with the expected one it is therefore stressed that ams measurements provide a good means of evaluating the magnetic field direction from deviated trm directions providing magnetic carriers are mainly multidomain magnetites

paleomagnetic implications on the evolution of the tethys belt from the atlantic ocean to the pamirs since the triassic abstract we first re examined the apparent polar wander curves for stable eurasia and africa since the triassic these curves were then combined together with curves of north and south america according to the kinematics of the atlantic ocean and a synthetic polar wander curve was given then most of the paleomagnetic results from the tethys mobile belt from the atlantic to the pamirs were analysed several groups of plates microplates and blocks can be seen first relatively stable regions like maghreb and sicily which have not moved much then we have a group formed by iberia sardinia italy and to a lesser extent corsica and the western and central alps for these blocks movements are anticlockwise rotations chiefly driven by the anticlockwise rotation of africa but they are sometimes stronger to the east a major change takes place the north of the aegean sea and the ionian zone are clockwise rotated and these rotations are recent oligocene miocene for the first part pliocene to the present for the second part a major problem arises in turkey caucasus and iran paleomagnetic results indicate a position far to the south of eurasia and at the same time geological evidence is in favour of a position close to eurasia we discuss these discrepancies

map view restoration of aegean west anatolian accretion and extension since the eocene 1 the aegean region greece western turkey is one of the best studied continental extensional provinces here we provide the first detailed kinematic restoration of the aegean region since 35 ma the region consists of stacked upper crustal slices nappes that reflect a complex paleogeography these were decoupled from the subducting african adriatic lithospheric slab especially since 25 ma extensional detachments cut the nappe stack and exhumed its metamorphosed portions in metamorphic core complexes we reconstruct up to 400 km of trench perpendicular ne sw extension in two stages from 25 to 15 ma the aegean forearc rotated clockwise relative to the moesian platform around euler poles in northern greece accommodated by extensional detachments in the north and an inferred transfer fault se of the menderes massif the majority of extension occurred after 15 ma up to 290 km by opposite rotations of the western and eastern parts of the region simultaneously the aegean region underwent up to 650 km of post 25 ma trench parallel extension leading to dramatic crustal thinning on crete we restore a detachment configuration with the mid cycladic lineament representing a detachment that accommodated trench parallel extension in the central aegean region finally we demonstrate that the sakarya zone and cretaceous ophiolites of turkey cannot be traced far into the aegean region and are likely bounded by a pre 35 ma n s fault zone this fault became reactivated since 25 ma as an extensional detachment located west of lesbos island the paleogeographic units south of the izmir ankara sava suture however can be correlated from greece to turkey

did a large departure from the geocentric axial dipole hypothesis occur during the eocene evidence from the magnetic polar wander path of eurasia abstract low paleolatitudes are very frequent in eocene to oligocene formations particularly in the tethyan mobile belt these anomalies and their possible sources are discussed they are neither due to unreliable results nor to inclination errors in sedimentary rocks neither can large tectonic movements explain these discrepancies the most probable causes having been rejected therefore the best explanation consists in an alternative magnetic pole position for eurasia located at 69 n 215 e it is proposed that the mean magnetic field of the earth was dipolar but that its axis has swung from one stable position to another during the middle tertiary and was therefore sometimes different from the rotation axis

on the probability of selecting a sample with inclination less than the true mean from a circular distribution paleomagnetic and tectonic implications abstract the method of fisher if used properly will yield an unbiased estimate of inclination and hence of paleolatitude however paleomagnetic data bases for essentially all continents contain significant numbers of studies that consist of very few sites and or have sampled very small areas and or stratigraphic intervals such studies probably do not include the full range of variation of the geomagnetic field and hence may not provide an acceptable estimate of mean inclination and paleolatitude if so the value of inclination obtained is more likely to be too shallow than too steep leading to an estimate of paleolatitude that is too low even studies that properly average the non axial dipole elements of the geomagnetic field to near zero are slightly more likely than not to produce an estimate of mean inclination that is lower than the true inclination important tectonic conclusions have been drawn and continue to be drawn from paleomagnetic data bases for most of the earth s orogenic belts all of these contain multiple examples of inadequate sampling a potential bias of paleolatitudes toward the equator thus exists because of the nature of distributions on the surface of a sphere it is important to determine by how much estimates of inclination may be biased toward the horizontal a simple and straightforward method to determine the probability of drawing a sample for which i i o is described the method is illustrated using the fisher distribution but will work for any circular distribution it is shown that a bias toward shallow inclinations is consistently present but that it is trivial except for highly scattered data sets or rock units originally magnetized at very high paleolatitudes

geomagnetic secular variation and the statistics of palaeomagnetic directions in this study we examine the role of palaeosecular variation psv in the use of statistics for palaeomagnetic studies and we provide new reliability criteria for palaeomagnetic poles or directions we first conclude that fisher statistics should not be applied to average palaeomagnetic directions but to virtual geomagnetic pole vgp distributions instead secondly we strongly advocate that typical properties of geomagnetic field behaviour are taken into account in the assessment of palaeomagnetic data sets the latitude dependent properties e s k provide useful guidelines for the reliability of a palaeomagnetic data set a reliable assessment of these properties depends on the sufficient number of palaeomagnetic samples being taken therefore as an additional instrument of assessing data sets we provide a n dependent a95 envelope bounded by an upper limit a95max and a lower limit a95min that helps to ascertain whether or not a distribution has sufficiently well sampled psv and therefore geomagnetic field behaviour applying these criteria is indispensable for studies of geomagnetic behaviour or for studies aiming at using tk03 gad for inclination error correction through the elongation inclination e i method for palaeomagnetic studies aimed at geological reconstructions they form helpful guidelines and increase the confidence in the rocks having faithfully recorded the field an analysis of published eastern mediterranean data shows that the vast majority of studies do not conform to the van der voo criteria in particular with respect to n and a95 we have provided criteria that are on the one hand more lenient lower n may still provide relevant information and on the other hand more strict for high n the criterion of a95 16 should be adapted to a requirement of lower a95 e g a95 80

palaeomagnetism and magnetic properties of the cappadocian ignimbrite succession central turkey and neogene tectonics of the anatolian collage abstract the cappadocian ignimbrite succession of central southern anatolia comprises at least nine major and two minor calc alkaline rhyolitic sheets emplaced at 1 2 ma intervals between 11 2 and 1 1 ma it records the last phase of neotethyan subduction during final emplacement of the tauride orogen in southern turkey this study reports magnetostratigraphy and describes associated rock magnetic properties remanence resides in ti poor titanomagnetites haematisation is locally produced by post emplacement oxidation but does not contribute significantly to the palaeomagnetic signature although secondary processes within the ignimbrite sheets have produced composite isothermal remanent magnetisation spectra and variable intensities of magnetisation weak anisotropy of magnetic susceptibility describes tensors with maximum axes close to bedding and minimum axes perpendicular to this plane directions of kmax with weak imbrication mostly suggest flow away from centres of eruption located by gravity and remote sensing older ignimbrites upper and lower goreme akdag zelve from the cardak centre are all of normal polarity later ignimbrites partly erupted from the derinkuyu centre comprise the sarimaden r cemilkoy r tahar r kizilkaya r incesu n and valibaba sofular r ignimbrites the overall reversed group mean is d i 174 51 n 10 units r 9 84 95 6 6 k 55 and all magnetisation directions from the upper goreme 9 0 ma onwards are rotated anticlockwise with respect to eurasian and african palaeofields this sense of rotation characterises most of central anatolia and averages 9 5 in this sector the rotation rate from 8 to 1 ma bp was 1 25 ma but it appears to have accelerated during the latter part of the quaternary to about an order higher than rates determined from gps rotation has resulted from extrusion of fault blocks during tectonic escape of the anatolian collage to the southwest and followed crustal thickening as the afro arabia plate has continued to impinge differentially into eurasia cenozoic magnetic inclinations are systematically shallower across anatolia than inclinations expected from the geocentric dipole model and the apparent polar wander of bordering major plates only part of this difference 400 km can be accommodated by northward movement and crustal thickening in central anatolia since mid miocene times shallow inclinations observed in the aegean region extend into turkey they are observed in young volcanics and appear to reflect a regional geomagnetic anomaly the pattern of neotectonic declinations across anatolia shows rotations that are strongly anticlockwise rotated in the east near the arabian pincer but diminish towards the west to become zero or slightly clockwise at the western extremity of the collage rotations also seem to become generally younger towards the south crustal deformation has therefore been distributed and the net effect of terrane extrusion to the west and south has been to expand the curvature of the tauride arc and by inference the cyprus arc

paleomagnetism of middle tertiary volcanic rocks from the western cascade series northern california the western cascade series wcs is a 3 5 km thick crudely homoclinal east dipping calcalkaline volcanic sequence of mid oligocene to early miocene age that crops out near the southern tip of the cascade range in northern california the mean direction of remanent magnetization in the wcs is d 4 9 i 57 6 n 53 k 14 4 95 5 3 when compared to a reference direction for the north american craton the wcs direction indicates that the southern cascade range has rotated 14 0 9 0 since the wcs accumulated a difference in mean direction between the lower and upper halves of the wcs suggests that much of this rotation occurred during the late oligocene six other paleomagnetic studies of rock units of an age roughly comparable to the wcs also are available from western oregon northwestern california and southwestern washington all show statistically significant clockwise rotation inclinations of all but one are concordant comparison of directions indicates that the pacific northwest did not rotate as a rigid body but neither did it behave as a collection of small independently rotating domains the amount of rotation found throughout the area increases to the west or northwest suggesting a driving force for rotation operating at the continental margin