assessing landslide potential using gis soil wetness modeling and topographic attributes payette river idaho this study utilizes gis modeling to determine if the location of 559 landslides in the 875 km2 catchment of the middle fork of the payette river idaho can be predicted based on topographic attributes and a wetness index generated by the dynwet model slope and elevation were significantly related to landslide occurrence at this landscape scale aspect was also retained as a variable for further analysis because despite a non significant chi square relation to landslide occurrence graphical analysis suggested a relation between aspect and mass wasting chi square analysis indicated that plan and profile curvature flow path length upslope contributing area and the dynwet based moisture index were not significantly related to landsliding a bayesian probability model based on combinations of elevation slope aspect and wetness indicates that elevation exhibits the closest relation to landsliding followed by slope but that neither aspect nor wetness index values help in prediction the bayesian probability model using elevation and slope generates a map of relative landslide risk that can be used to direct activities away from mass wasting prone areas the association between elevation and landslides is perplexing but is perhaps due to the location of logging road at specific elevations roads could not be included in the input data for analysis because they have not been adequately mapped the lack of explanation provided by the dynwet wetness index was also surprising and may be due to the 30 m digital elevation model dem and the soils data having resolutions too coarse to adequately portray local variations key to mass wasting we believe the inadequacy of data to drive the models is typical of the majority of catchment scale setting for now the ability of researchers to effectively model landscape scale landsliding is more limited by the type resolution and quality of available data than by the quality of the landslide models

preliminary model for an early transform history in central atlantic rifting dextral and sinistral shear along an arcuate intracontinental transform system parallel to the present coastlines of eastern north america and western africa is believed to have played a significant role in the decoupling of continental blocks during the extremely complex tectonic history of central atlantic rifting near pole small circle transform systems are developed as wide zones of shear during counterclockwise and clockwise rotations of africa and south america relative to north america about a pole of rotation in the sahara transform and rifting histories are combined in a model proposed for atlantic rifting that includes the following phases of rotation interacting with the linear belt of pre existing appalachian structural grain 1 late permian to middle triassic counterclockwise rotation of africa with dextral shear localizing an initial thermal arch and early sedimentation in southern appalachian grabens along a reactivated structural grain 2 dominant late triassic to early jurassic extensional reactivation in a northwest southeast direction with minor plate separation producing the main phase of graben sedimentation and a major 190 m y b p basalt sill and flow event 3 middle jurassic clockwise rotation of africa with sinistral shear resulting in the folding and faulting of graben sediments and the injection of basalt dikes 175 m y b p along a distinctive fan shaped distribution of extensional structures and 4 separation of the north american and african continents parallel to early atlantic fracture zone trends with the onset of plate accretion

thermal core mantle interactions and time averaged paleomagnetic field recent studies of historical geomagnetic secular variation and lower mantle seismic velocity suggest the earth s magnetic field is controlled by lateral variations in mantle temperature in this paper the average expected magnetic field pattern is compared with the time averaged field obtained from paleomagnetic pole positions from the last 5 m y the historical record suggests that the time averaged inclination anomalies are negative far sided in the atlantic region north of 30 s and the west pacific and positive in the south atlantic extreme north and south pacific and east pacific the pole positions give positive inclination anomalies in the south atlantic and extreme north pacific and negative anomalies elsewhere in agreement with the theory except for the east pacific this suggests that the historical record is not long enough to give an accurate picture of long term secular change in the eastern pacific but that elsewhere the time averaged field of paleomagnetism is predicted satisfactorily the preponderance of far sidedness in the paleomagnetic record is a consequence of the present distribution of temperature at the base of the mantle rather than a fundamental property of the geodynamo and it may therefore change on the long time scale of mantle convection in the historical record declinations average to negative values in the atlantic hemisphere and positive values in the pacific which if typical of longer term behavior could explain the preponderance of positive declinations for reversed polarity which are mainly in the atlantic hemisphere

the frequency and distribution of recent landslides in three montane tropical regions of puerto rico landslides are common in steep mountainous areas of puerto rico where mean annual rainfall and the frequency of intense storms are high each year landslides cause extensive damage to property and occasionally result in loss of life average population density is high 422 people km2 and is increasing this increase in population density is accompanied by growing stress on the natural environment and physical infrastructure as a result human populations are more vulnerable to landslide hazards the blanco cibuco and coamo study areas range in surface area from 276 to 350 km2 and represent the climatologic geographic and geologic conditions that typify puerto rico maps of recent landslides developed from 1 20 000 scale aerial photographs in combination with a computerized geographic information system were used to evaluate the frequency and distribution of shallow landslides in these areas several types of landslides were documented rainfall triggered debris flows shallow soil slips and slumps were most abundant hillslopes in the study area that have been anthropogenically modified exceed 12 in gradient are greater than 300 m in elevation and face the east northeast are most prone to landsliding a set of simplified matrices representing geographic conditions in the three study areas was developed and provides a basis for the estimation of the spatial controls on the frequency of landslides in puerto rico this approach is an example of an analysis of the frequency of landslides that is computationally simple and therefore may be easily transferable to other settings

intracontinental movements in western gondwanaland a palaeomagnetic test abstract early cretaceous intracontinental movements within africa and or south america to account for misfit problem in the pre drift reconstruction of western gondwana have been tested using palaeomagnetic poles from both continents each continent has been considered as comprising separate subplates according to the boundaries proposed by pindell and dewey 1982 and curie 1983 i e northern africa naf southern africa saf northern south america nsa and southern south america ssa visual and statistical distribution of late permian to jurassic poles from the african subplates indicate two distinct groups before rotating saf relative to naf while after the rotation they become indistinguishable the distribution and sparsity of data from south america limit the study in this continent as the data are statistically indistinguishable before and after rotation of ssa with respect to nsa when the test is extended to the reconstruction of western gondwana the tightest grouping of the poles occurs when an intracontinental movement is assumed within africa this suggests that the misfit between the two continents is probably due to intracontinental deformation within africa and not in south america if confirmed this may have profound implications in the kinematics of the processes related to the opening of the south and central atlantic oceans and also the origin of the west african rift system

landslide susceptibility analysis using gis and artificial neural network the purpose of this study is to develop landslide susceptibility analysis techniques using an arti cial neural network and to apply the newly developed techniques to the study area of yongin in korea landslide locations were identi ed in the study area from interpretation of aerial photographs eld survey data and a spatial database of the topography soil type and timber cover the landslide related factors slope curvature soil texture soil drainage soil effective thickness timber age and timber diameter were extracted from the spatial database using those factors landslide susceptibility was analysed by arti cial neural network methods the landslide susceptibility index was calculated by the back propagation method which is a type of arti cial neural network method and the susceptibility map was made with a geographic information system gis program the results of the landslide susceptibility analysis were veri ed using landslide location data the validation results showed satisfactory agreement between the susceptibility map and the existing data on landslide location a gis was used to ef ciently analyse the vast amount of data and an arti cial neural network to be an effective tool to maintain precision and accuracy the results can be used to reduce hazards associated with landslides and to plan land use and construction copyright 2003 john wiley sons ltd

evolution of pangea paleomagnetic constraints from the southern alps italy abstract a new early late triassic paleopole for adria has been obtained from the val sabbia sandstone in the southern alps as early permian and jurassic cretaceous paleomagnetic data from para autochthonous regions of adria such as the southern alps are consistent with african apwps 1 2 paleomagnetic data from this region can be used to bolster the west gondwana apwp in the poorly known late permian triassic time interval the southern alpine paleopoles are integrated with the west gondwana and laurussia apwps of van der voo 1 and used to generate a tectonic model for the evolution of pangea the early permian overall mean paleopole for west gondwana and adria in conjunction with the coeval laurussia paleopole support pangea b of morel and irving 3 the late permian early triassic and the middle late triassic paleopoles from adria and laurussia support pangea a 2 of van der voo and french 4 the phase of transcurrent motion between laurasia and gondwana 5 that caused the pangea b to a 2 transition occurred essentially in the permian at the end of variscan orogeny with an average relative velocity of approximately 10 cm yr finally the late triassic early jurassic paleopoles from west gondwana and laurussia agree with pangea a 1 of bullard et al 6 the widely accepted pangea configuration at the time of the jurassic breakup

evaluation of prediction capability of the artificial neural networks for mapping landslide susceptibility in the turbolo river catchment northern calabria italy abstract landslides are one of the most widespread natural hazards that cause damage to both property and life every year and therefore the spatial distribution of the landslide susceptibility is necessary for planning future developmental activities in this paper the artificial neural network ann technique is tested for developing a landslide susceptibility map in turbolo river catchment north calabria south italy landslides were mapped through air photo interpretation and field surveys by identifying both the landslide depletion zones dzs and accumulation zones azs and relevant geo environmental thematic layers pertaining to landslide predisposing factors were generated using air photo interpretation field surveys and geographic information system gis tools ten predisposing factors were related to the occurrence of landslide lithology faults land use drainage network and a series of topographic factors elevation slope aspect plan curvature topographic wetness index twi and stream power index spi in order to evaluate and validate landslide susceptibility the dzs were divided in two groups using a random partition strategy the first group training set was used to prepare the susceptibility map employing a back propagation learning algorithm in the idrisi taiga software the second group testing set was used to validate the landslide susceptibility model using the confusion matrix and the receiver operating characteristic roc curve the susceptibility map was classified into five susceptibility classes very low low moderate high and very high about 46 of the study area falls in high to very high susceptible classes and most of the dzs mapped 87 3 occur in the same classes the validation results showed satisfactory agreement between the susceptibility map and the dzs locations over 85 of the dzs of the validation set are correctly classified falling in high and very high susceptibility areas also the roc curve had shown an area under curve auc value of 0 90 which demonstrates the robustness and good reliability of the landslide susceptibility model according to these results we conclude that the map produced by the artificial neural network is reliable and the methodology applied in the study produced high performance and satisfactory results which may be useful for land planning policy

mesozoic seafloor spreading between iberia europe and north america abstract a new earliest cretaceous palaeogeographic reconstruction for the iberian north american and european plates is proposed which attempts to clarify some of the outstanding reconstruction problems in the region from the time of initial opening to the time of magnetic anomaly 34 the instantaneous motion of iberia can be described by a single rotation about a pole off the southwest coast of france in contrast to many previous proposals the new reconstruction places galicia bank east of flemish cap but satisfies all the constraints imposed by palaeomagnetic studies deep sea drilling project results and magnetic anomaly and ocean continent boundary identifications

supposed permo triassic megashear between laurasia and gondwana a consensus has emerged that during the palaeozoic several landmasses progressively collided to form the supercontinent pangaea which subsequently split up in the mesozoic and tertiary to produce the present array of continents but whereas there is a high measure of agreement about the general shape of the early jurassic pangaea shortly before the initial atlantic opening three very different reconstructions of the end palaeozoic supercontinent have recently been proposed these differences which involve the relative positions of the northern and southern sectors of pangaea known respectively as laurasia and gondwana relate to the interpretation of palaeomagnetic data the three constructions are here tested with reference to geological and palaeobiogeographic data and arguments

fracture zones in the equatorial atlantic and the breakup of western pangea the early breakup of western pangea has been investigated by mapping the pattern of fracture zones and distribution of seismic reflectors within the sedimentary cover of the atlantic between the cape verde islands and the equator two distinct sets of transverse oceanic lineaments are present separated by the guinea fracture zone near lat 10 sup 0 n lineaments to the north are associated with the formation of the central atlantic in the late jurassic and early cretaceous those in the south relate to the cretaceous opening of the south atlantic the guinea fracture zone is thus the conjugate of the jurassic transform boundary under peninsular florida which linked the atlantic with the gulf of mexico the distribution of dated seismic reflectors suggests that deposition of deep water sediments was confined to the region north of the guinea transform until aptian time when the sierra leone basin began to open the latter started to widen at least 15 m y after the initiation of the cape basin off southwest africa an age difference that can be explained if a short lived plate boundary developed in either africa or south america during the early cretaceous neither the trends of the equatorial fracture zones nor the seismic stratigraphymore supports the existence of a predrift gap between west africa and brazil less

relative displacement between eurasia and north america prior to the formation of oceanic crust in the north atlantic abstract the relative positions of north america and eurasia prior to the opening of the north atlantic can be reconstructed using three independent data sets ocean floor magnetic anomalies and fracture zones the shape of the shelf line at the continental margins of north america and eurasia and the apparent polar wander paths apwps of these two continents together with geological constraints we here examine the internal consistency of these reconstructions discuss the tectonic implications of the inconsistencies and show how all three data sets can be combined to obtain a best fit reconstruction pole in our analysis we find that the combined errors of the new north american and european apwps are smaller for 290 240 ma than at earlier or later times therefore this interval was used rotation poles derived from magnetic anomalies from the north atlantic do not bring the apwps into coincidence a rotation pole located at 88 n 215 e with rotation angle 42 superimposes the two apwps and is reasonably consistent with the geology of the continental margins in the north atlantic the difference between the rotation pole based on apwps and that based on magnetic anomalies probably reflects relative motion of the two cratons between the early triassic and the late cretaceous cratonal germany moving about 800 km to the east relative to north america and norway moving about 500 km northeast relative to greenland this motion is expressed in extension in the north sea and the continental shelves on the other side of the globe in the vicinity of siberia and alaska our reconstruction places cratonal north america farther away from cratonal eurasia than do reconstructions based on north atlantic magnetic anomalies this greater separation is consistent with the presence in the late paleozoic and early mesozoic of a sea way in siberia located in the gap between eurasia and north america the magnitude of this gap is uncertain because of mesozoic deformation in alaska and siberia

the apparent polar wander path for south america during the permian triassic abstract many of the controversies that arise in global reconstructions for permian triassic time could be resolved by taking into account the large latitudinal and counter clockwise movement of gondwana during that interval of time the proper trace of the apparent polar wander curve should differentiate one position for the early permian another position for the late permian and yet another for the triassic by doing so and comparing the apparent polar wander paths apwp of south america and africa it is easy to see that both curves have the same shape therefore it is possible to arrive at a good fit between them which previous analyses were unable to achieve this new proposed permian triassic track of the apwp reveals a hook not hitherto recognized that should be accounted for in global reconstructions

on the allochthonous nature of auriferous greenstones guayana shield venezuela abstract the tectonic style of paleoproterozoic orogeny in the guayana shield has been considered by most workers to be similar to those commonly invoked for the development of archean greenstone belts in which diapirs of granitoid magma supamo complex rose and deformed 2 1 2 0 ga volcanic and sedimentary rocks of the pastora supergroup to form keel like greenstone belts in this model subsequent collision with the dominantly granulite grade imataca complex to the north deformed the greenstone belts during what is known as the trans amazonian orogeny however more recent geological mapping demonstrated that the base of the greenstone belts is marked by a major mylonitic shear zone that placed rocks of the belts atop a regional unit of quartzite that sits unconformably upon granitic gneisses and plutons of both the imataca and supamo complexes these relations were interpreted to indicate that the greenstone belts are allochthonous with respect to the imataca and supamo complexes and as the quartzite oversteps the contact between the imataca and supamo complexes juxtaposition of the two complexes predated deposition of the quartzite new u pb zircon results show that volcanic rocks of the pastora supergroup are older than the quartzite beneath them and confirm the hypothesis based entirely upon field relations that rocks of the greenstone belts were thrust upon the quartzite and its granitic and gneissic basement at least two subsequent periods of deformation refolded rocks of the region similar structural relationships are common in archean cratons of southern africa australia and the canadian shield

slope vulnerability to earthquakes at subregional scale using probabilistic techniques and geographic information systems abstract the susceptibility of slopes to failure during earthquakes is calculated in terms of critical horizontal acceleration on a subregional scale for the upper part of the serchio river basin tuscany italy according to the working scale 1 10 000 and to the availability and accuracy of the input data the infinite slope analysis was judged to be the most appropriate method but particular attention was devoted to the error evaluation due to spatial variability of the geotechnic geometric and hydrologic parameters a geologic geomorphologic and hydrologic survey of the area was therefore performed and the geotechnic parameters were collected at local administrations all the data were stored in a gis used as a tool to build the spatial and attribute data base and to prepare the input data layers for the stability analysis in order to assess the variability of geotechnic parameters a statistical analysis was performed to assign the best fitting probability distribution to cohesion angle of internal friction and unit weight of the soil as hydrogeologic data were not available for the area only surface hydrology information could be used a map of probability of spring occurrences was derived by a bayesian method the weight of evidence modelling and was used as groundwater indicator a monte carlo procedure and a first order second moment method were applied and compared as error estimators in assessing the slope susceptibility to failure the differences between the two methods are discussed and two maps showing respectively the critical horizontal acceleration and the probability of failure associated with each slope are presented together with the curve plotting the reliability index against the probability of failure

continental rifting and the implications for plate tectonic reconstructions previous plate tectonic reconstructions have tried to recreate the pre rifting pangea configuration of the continents by matching contours or lineaments that are thought to represent the continental boundaries such reconstructions have the inherent assumptions that no extension occurs within the continent during rifting that the continental boundaries are isochrons and that the continents rift without distortion this paper proposes a model for continental breakup with distortion where ocean basins are formed by propagating rifts this model challenges the assumptions made by previous reconstructions and presents a new method for representing the prerift geometry of the continents as rifts propagate through a continent the region in front of the rift extends by continental faulting and crustal thinning while the region behind the rift expands by seafloor spreading the propagating rift model implies that large amounts of continental extension up to 150 km occur and that the continental boundaries are not isochrons this extension due to rifting results in apparent overlap when the continents are returned to their original configuration because of the gradational nature of this extension the best representation of the pre rift configuration is obtained by matching the initial rifting point and having overlap increase in the direction of rift propagation the overlap is equivalent to the amount of extension that has taken place on both continental edges reconstructions based on this model are presented for the gulf of california the gulf of aden the norwegian greenland sea and the south atlantic ocean they are able to resolve the discrepancies that occur when rigid plate tectonics are applied this model has implications that can be used to predict the age and structure of the continental shelves and the location and orientation of the oldest magnetic isochrons

magnetic overprinting in southeastern australia and the thermal history of its rifted margin the magnetizations of many rock units in southeastern australia have been severely overprinted interpretation of early work was hindered by this and one of the aims of the current research is to ascertain the nature of the overprint mechanism its geological significance and its regional extent results from three igneous bodies from the sydney basin which have been studied previously in a reconnaissance fashion have provided a new insight into the reason for such widespread magnetic overprinting the hornsby breccia hb and milton monzonite mm yield similar magnetic signatures both containing discrete high and low temperature magnetizations with directions of dec 72 inc 83 95 4 and dec 13 inc 76 95 2 respectively for hb and dec 60 inc 78 95 4 and dec 348 inc 79 95 6 respectively for mm the corresponding pole positions are 29 s 166 e a95 7 and 59 s 139 e a95 4 for hb and 22 s 171 e a95 7 and 55 s 158 e a95 11 for mm the paleomagnetic direction and pole from the third body studied the mogo hill basalt mh are dec 241 inc 81 95 5 and 41 s 130 e a95 9 this pole position and the two low temperature overprint pole positions from hb and mm are consistent with ages ranging from 100 m y to approximately 70 m y when compared to the late mesozoic apparent polar wander path we relate the overprinting to uplift erosion and rapid supracrustal cooling of the southeastern margin of australia associated with initial phases of marginal rift development prior to seafloor spreading in the tasman sea the temperatures of rocks now exposed may have reached 200 c or higher before the rapid cooling blocked and stabilized the overprint magnetizations

paleozoic tectonostratigraphic units of the northwest and central dinarides and the adjoining south tisia in the central dinarides and south tisia different paleozoic complexes occur in four geotectonic zones 1 comparatively autochthonous units located in the cores of disrupted anticlines of the external dinarides 2 allochthonous disrupted units accompanied by more predominant triassic formations in the sava nappe which is thrust onto the northeastern margin of the external dinarides 3 allochthonous disrupted units also together with triassic formations in the pannonian and durmitor nappes of the internal dinarides and 4 polymetamorphic sequences in basement of the pannonian basin and south tisia respectively this paper presents basic geological features for the main paleozoic areas included in these four zones the tectonostratigraphic units of the first two zones were related to the gondwana passive continental margin those of the third zone to the paleotethyan oceanic realm and those of tisia to the active laurussia margin geodynamic evolution of all these paleozoic complexes was related to opening and closure of the rheic and paleotethys oceans rifting processes along north gondwana started in the silurian locally in the cambrian ordovician and were followed by the late silurian devonian opening of the paleotethys subduction processes were active by the end of the devonian and at the beginning of the carboniferous along the laurussia margin they were followed during the westphalian by main variscan deformation during collision of gondwana and laurussia associated metamorphism was very low grade in the paleozoic units of the sava nappe low grade to epidote amphibolite grade within the paleozoic complexes of the pannonian and durmitor nappes in the internal dinarides and poly metamorphic with migmatites and granitoids in south tisia these processes gave rise to a pangea stage with the variscan basement disconformably overlain by late carboniferous and permian sediments

a review of deep structure and ocean continent transition in the senegal basin west africa abstract in the mauritania senegal basin gravity and magnetic data reveal long n s lineations reflecting probable extensional structures which are possibly related to opening of the atlantic along the coast where the basin is considerably thicker a large gradient in the gravity field is closely associated with an important linear magnetic high this gravity feature which dominates the whole of the area concerned reflects a crustal thinning to the west together with the existence of elongate dense intrusive bodies suggesting that it is associated with a crustal discontinuity and a change towards a crust of oceanic type the long coastal magnetic high is presumed to be an onshore segment of the magnetic lineations identified on the mauritania senegal continental margin as the landward boundary of the magnetic quiet zone a comparison of conjugate magnetic quiet zones of west africa and eastern north america shows that the west africa coastal magnetic anomaly may be closely related to the east coast magnetic anomaly which probably marks the boundary between continental and oceanic basement such correlation implies that the cape vert peninsula senegal may rest on a basement of oceanic type this appears to be consistent with geological and geophysical interpretations which suggest seaward rapid thinning of the continental crust together with major subsidence and seaward progradation

paleomagnetism and the evolution of pangea we present new apparent polar wandering apw paths for the latest carboniferous to middle jurassic of europe northern asia north america and gondwana the paths have been constructed by ordering the paleopoles into a time sequence and calculating running averages globally this statistical analysis cannot be carried back before the latest carboniferous because the paleomagnetic record becomes inadequate the polar paths have all been rotated along with the land masses from which they have been observed into the classical configuration of wegener pangea a as quantified by later workers the mean paleopoles agree in the early jurassic but disagree in the latest carboniferous permian and early triassic this result is insensitive to reasonable choices made regarding the arrangement of the continents within gondwana it is true either for results from gondwana as a whole or from africa and south america alone this disagreement in apw paths suggests but does not prove that pangea a lasted for only a short interval of time in the early to middle jurassic 190 170 m y and perhaps the latest triassic 200 m y alternatively we may say either that the paleomagnetic record is biassed by sampling inadequacies or by systematically incorrect age assignments or that the earth s field has been non dipolar we regard these explanations as less likely although they cannot be discounted the polar paths can be reconciled by rotating gondwana anticlockwise by about 35 relative to laurasia placing africa beneath europe and south america beneath eastern north america this configuration is called pangea b pangea b could be a valid reconstruction for the latest carboniferous and early permian approximately 290 260 m y pangea b provides a statistically satisfactory resolution of the paleomagnetic problem it also provides a symmetrical arrangement of the continents bordering the appalachian hercynian fold belt for the late paleozoic which pangea a does not it provides a satisfactory framework for the early evolution of the gulf of mexico and it provides an explanation of the absence of geological evidence for a tethys ocean in the paleozoic the transition between b and a cannot be accurately reconstructed from the paleomagnetic data because the resolution of the record is as yet inadequate but it presumably occurred by a 3500 km minimum dextral megashear between laurasia and gondwana during the late permian and triassic approximately 250 200 m y without the formation of ocean between them and was accompanied by lesser motions between north america and europe the sense of megashear is the same as that invoked by arthaud and matte 1977 on geological grounds but the magnitude and timing are different our interpretation favors the idea that continental drift is a continuous process not confined to jurassic and later times but extending backwards into the triassic and permian we suggest that pangea was not an immobile configuration as envisaged by wegener and most subsequent workers but that it evolved more or less continuously

evidence for late paleozoic and mesozoic non dipole fields provides an explanation for the pangea reconstruction problems abstract paleomagnetic pole positions have long been calculated with the assumption that the ancient geomagnetic field was purely that of a geocentric dipole but in recent years it has become a concern that this assumption is not always valid because of long term contributions from non dipole fields in particular octupole fields we tested for the presence of a zonal octupole field in the late carboniferous permian mesozoic and early tertiary by comparing the observed paleomagnetic paleolatitude distributions for the laurentian north america and greenland and european landmasses with those predicted from the mean paleopoles such a test is possible for a good sized continent not subsequently deformed when numerous and reliable paleomagnetic results exist from sites that cover a wide range of paleolatitudes if the field were purely dipolar coeval results should form a coherent dataset such that a regression line through the individual points in an observed versus predicted paleolatitude plot has a slope of 1 if the slopes of regression lines are systematically different from 1 0 for successive time intervals and granted that the earth s radius stayed the same then it is likely that non dipole fields can be held responsible regression line slopes standard errors for three intervals analyzed are 0 78 0 04 200 300 ma 0 93 0 11 120 200 ma and 0 82 0 06 40 120 ma as might be expected with a non dipole contribution to the total geomagnetic field paleomagnetic results from the most northerly areas of laurentia and europe i e ellesmere greenland and svalbard show clearly anomalous paleolatitudes because of the agreement between the equatorial locations determined independently by paleomagnetism and equatorial rain forest occurrences d v kent p e olsen earth planet sci lett 179 2000 311 324 we argue that long term quadrupole fields are less likely than octupole fields to be the cause of the paleolatitude discrepancies estimates of the magnitude of the octupole dipole field ratio are not very precise but center around 0 1 which could cause errors in conventional paleopole determinations using the dipole formula of 7 5 because of the antisymmetry of octupole fields a comparison of paleomagnetic poles from mid northern and mid southern hemisphere locations could thus be off by as much as 15 the well known misfit between the paleomagnetic results from the laurentia european and gondwana continents in a classical pangea a configuration could be explained by such errors due to octupole fields this explanation would negate the need to seek tectonic pangea b type solutions for the misfit these solutions have generally remained unacceptable in terms of the geology of the gondwana laurussia borderzone

deep lithospheric structure across the central african shear zone in cameroon summary teleseismic p and pkp arrival times recorded by a network of 40 seismic stations deployed along a 300 km profile across the adamawa plateau at the northern end of the volcanic line in central cameroon provide constraints on lithospheric thickness and anisotropy within the subcrustal lithosphere these data indicate a thinned lithosphere beneath the central african shear zone where seismologically defined asthenosphere upwells from a depth of about 190 km to about 120 km in a relatively narrow belt thus it has only a low amplitude effect on the observed gravity anomalies the bouguer gravity high over the garoua rift is consistent with crustal thinning beneath it an abrupt change of the lithospheric thickness beneath the northern boundary fault correlates with both the topographic relief and a distinct change of the orientation of relatively high and low velocity directions which we infer to be due to anisotropy within the subcrustal lithosphere this fault may represent an important accretionary suture zone dividing lithospheric blocks that originated in different tectonic settings and acquired different frozen in anisotropy

the 270 ma palaeolatitude of baltica and its significance for pangea models summary to better constrain baltica s position within pangea we conducted a palaeomagnetic study of permo triassicdykesfromtheoslograben asafollow uptoaninitial butratherlimited study by torsvik and colleagues in 1998 the age of these so called lunner dykes had previously been determined as 240 ma in that study but details in their analyses and new 40 ar 39 ar ages reveal that there may have been some argon loss in the initially dated dyke minerals and that a combined weighted mean age of 271 2 7 2 myr for the dykes is preferable we find two major components of magnetization in our samples one carried by an fe sulphide likely pyrrhotite and the other carried by low ti magnetite these magnetization components may be found together superposed in a given sample or they may occur apart micronmetresized crystals of ti fe oxides observed with a scanning electron microscope sem show exsolution lamellae formed upon cooling from intrusion temperatures assuming that the submicronmetre sized ti magnetite grains that carry a stable remanence are of the same generation as the observed larger grains we interpret the magnetite remanence in the dykes as of primary thermoremanent origin the sulphide remanence appears to be slightly younger as seen by the sem observations of pyrite framboids and a fe sulphide grain invading a timagnetite grain moreover the sulphide mineralization is likely of region wide hydrothermal origin the magnetizations carried by the pyrrhotite and magnetite have nearly identical

new cocorp profiling in the southeastern united states part ii brunswick and east coast magnetic anomalies opening of the north central atlantic ocean new cocorp profiles on the coastal plain of georgia and northern florida support the hypothesis that the brunswick anomaly marks a late paleozoic suture they do not support the alternate view that this anomaly is caused by a mesozoic rift basin the trend of the brunswick anomaly relative to the appalachian gravity gradient indicates that in westernmost georgia and adjacent alabama african basement suwannee terrane is in proximity to autochthonous north american basement grenville farther east one or more paleozoic accreted terranes intervene between the north american and african sides of the orogen offshore the brunswick anomaly closely parallels the east coast magnetic anomaly this relationship implies that the east coast magnetic anomaly marks not only the present continental oceanic crustal transition but also the northward continuation of the late paleozoic suture between north america and africa transitional crust beneath the carolina trough baltimore canyon trough and correlative parts of the african atlantic margin is thus likely to have formed within a preexisting suture zone the dramatic change in character of the u s atlantic margin southward from the carolina trough to the blake plateau probably reflects the fact that two different types of prerift crust are juxtaposed in this region

plate motions and the geomagnetic field i quaternary and late tertiary summary we have tested the hypothesis that the apparent increase in the northward offset of the axial dipole i e the ratio g gy with age for the last 25 ma wilson mcelhinny is due to the failure to correct for plate motions spherical harmonic analyses were performed on two types of data palaeomagnetic poles from continents islands and seamounts and magnetic inclinations from deep sea cores after returning the sampling sites to their predrift locations in fixed hotspots coordinates the results show that the quadrupole term g maintained a value of about 0 05 gy throughout the last 35 ma and that the axial octupole had a small value of about 0 02 gy for the last 5 ma sea core inclinations analysed separately gave essentially the same results as continental palaeopoles for the last few million years independent data sets for the past 2 ma and for the period 2 6 ma gave nearly identical solutions showing that the persistence of the axial terms is not a phenomenon of the more densely sampled quaternary field alone nor is it an artifice of predominantly northward motion of the plates returning all 0 5 ma data to a 5 ma reconstruction failed to eliminate the quadrupole the non zonal coefficients for the 0 5 ma field are typically an order of magnitude less than the zonal terms with the exception of h and are probably insignificant suggesting that longitudinal drift is generally effective in averaging out these components the present distribution of data is inadequate to determine coefficients of third and higher degree prior to 5 ma but there is evidence that g may have changed little during the last 35 ma in addition there has been very little relative motion between the palaeomagnetic dipole axis as defined by the first degree terms and the axis of the hotspots reference frame

landslide hazard evaluation a review of current techniques and their application in a multi scale study central italy in recent years growing population and expansion of settlements and life lines over hazardous areas have largely increased the impact of natural disasters both in industrialized and developing countries third world countries have difficulty meeting the high costs of controlling natural hazards through major engineering works and rational land use planning industrialized societies are increasingly reluctant to invest money in structural measures that can reduce natural risks hence the new issue is to implement warning systems and land utilization regulations aimed at minimizing the loss of lives and property without investing in long term costly projects of ground stabilization government and research institutions worldwide have long attempted to assess landslide hazard and risks and to portray its spatial distribution in maps several different methods for assessing landslide hazard were proposed or implemented the reliability of these maps and the criteria behind these hazard evaluations are ill formalized or poorly documented geomorphological information remains largely descriptive and subjective it is hence somewhat unsuitable to engineers policy makers or developers when planning land resources and mitigating the effects of geological hazards in the umbria and marche regions of central italy attempts at testing the proficiency and limitations of multivariate statistical techniques and of different methodologies for dividing the territory into suitable areas for landslide hazard assessment have been completed or are in progress at various scales these experiments showed that despite the operational and conceptual limitations landslide hazard assessment may indeed constitute a suitable cost effective aid to land use planning within this framework engineering geomorphology may play a renewed role in assessing areas at high landslide hazard and helping mitigate the associated risk

triassic magmatism of the dinarides in yugoslavia abstract the triassic magmatism of the dinarides had a polyphase character it took place during a period of about 50 ma during the initial stages of the mesozoic wilson cycle their earliest phases might have been connected with rifting processes and the subsequent ones preceeded directly the opening of the dinaridic part of the tethys and the formation of a spreading ridge the triassic magmatism is represented by basic and more commonly by intermediate and acid plutonic and volcanic rocks with calc alkaline affinity the triassic magmatic rock association can be correlated on major element evidence with calc alkaline rocks of recent convergent plate margins however field relationships and the data on immobile trace elements indicate that lavas poured out over triassic sediments on a carbonate platform which was underlain by rocks of the continental crust the basic diversity of the triassic magmatism of the dinarides was influenced by partial melting other processes crystallization contamination and others must have played a secondary role

nature and origin of the volcanic ash beds near the permian triassic boundary in south china new data and their geological implications permian triassic boundary ptb volcanic ash beds are widely distributed in south china and were proposed to have a connection with the ptb mass extinction and the assemblage of pangea however their source and tectonic affinity have been highly debated we present zircon u pb ages trace element and hf isotopic data on three new found ptb volcanic ash beds in the western hubei area south china laser ablation inductively coupled plasma mass spectrometry u pb dating of zircons yields ages of 252 2 3 6 ma 251 6 4 9 ma and 250 4 2 4 ma for these three volcanic ash beds zircons of age c 240 270 ma zircons have negative t values 18 17 to 3 91 and mesoproterozoic palaeoproterozoic two stage hf model ages t 1 33 2 23 ga integrated with other ptb ash beds in south china zircon trace element signatures and hf isotopes indicate that they were likely sourced from intermediate to felsic volcanic centres along the simao indochina convergent continental margin the qinling convergent continental margin might be another possible source but needs further investigation our data support the model that strong convergent margin volcanism took place around south china during late permian early triassic time especially in the simao indochina active continental margin and possibly the qinling active continental margin these volcanisms overlap temporally with the ptb biocrisis triggered by the siberian large igneous province in addition our data argue that the south china craton and the simao indochina block had not been amalgamated with the main body of pangea by late permian early triassic time

landslide hazard zonation using analytical hierarchy process along national highway 3 in mid himalayas of himachal pradesh india landslide zonation studies emphasize on preparation of landslide hazard zonation maps considering major instability factors contributing to occurrence of landslides this paper deals with geographic information system based landslide hazard zonation in mid himalayas of himachal pradesh from mandi to kullu by considering nine relevant instability factors to develop the hazard zonation map analytical hierarchy process was applied to assign relative weightages over all ranges of instability factors of the slopes in study area to generate landslide hazard zonation map layers in geographic information system were created corresponding to each instability factor an inventory of existing major landslides in the study area was prepared and combined with the landslide hazard zonation map for validation purpose the validation of the model was made using area under curve technique and reveals good agreement between the produced hazard map and previous landslide inventory with prediction accuracy of 79 08 the landslide hazard zonation map was classified by natural break classifier into very low hazard low hazard moderate hazard high hazard and very high landslide hazard classes in geographic information system depending upon the frequency of occurrence of landslides in each class the resultant hazard zonation map shows that 14 30 of the area lies in very high hazard zone followed by 15 97 in high hazard zone the proposed model provides the best fit classification using hierarchical approach for the causative factors of landslides having complex structure the developed hazard zonation map is useful for landslide preparedness land use planning and social economic and sustainable development of the region

the modern geoid and ancient plate boundaries abstract the non hydrostatic geoid is dominated by three large anomalies an area of high gravity potential in the equatorial pacific another stretching from greenland through africa to the southwest indian ocean and a semi continuous low region passing from hudson s bay through siberia to india and on to antarctica none of these three high amplitude greater than 60 m and long wavelength anomalies corresponds to present day plate boundaries however if the modern geoid is plotted over the positions of continents and plate boundaries at 125 ma b p reconstructed relative to hotspots a strong correlation emerges the modern geoidal low corresponds in position to the areas of subduction surrounding the pacific 125 ma ago the geoidal high now centered on africa is entirely contained within ancient pangaea and the equatorial pacific high overlies the location of the spreading centers preserved in the magnetic anomalies of the central pacific the most plausible cause of the large geoidal undulations is lower mantle convection only weakly coupled to plate motions the correspondence between modern geoid and ancient plate boundaries implies either that the coupling was much more intimate in the past or that there is a lag of at least 100 ma in response of the lower mantle to upper mantle conditions

appalachian carboniferous dextral strike slip faults an example from brookneal virginia the northern appalachian dextral fault system of late paleozoic age is also present in the central and southern appalachians an example of a dextral strike slip fault is the 4 km wide brookneal shear zone in the southwest virginia piedmont the shear zone is in part superimposed on the melrose granite where an s c mylonite was produced by dynamic recrystallization of all constituent minerals the arvonia metasedimentary and charlotte belt metavolcanic rocks contain spaced dextral shear bands at a consistent 24 3 to the shear zone boundary a minimum displacement estimate of 17 km was obtained from rotated foliation measurements in the melrose granite the age of movement on the brookneal shear zone has been constrained by isotopic dating to between 324 and 300 ma other faults in the southern appalachians including the nutbush creek and modoc zones show similar ages and relative offsets possible plate tectonic models that could account for the late paleozoic dextral fault system throughout the appalachians include 1 tectonic escape resulting from the collision of a plate with north america to the north of the canadian appalachians 2 postcollision interplate readjustments involving counterclockwise rotation of africa relative to north america and 3 oblique convergence of eastern north america with an oceanic plate moving west

deciphering shallow paleomagnetic inclinations 2 implications from late cretaceous strata overlapping the insular intermontane superterrane boundary in the southern canadian cordillera 1 significant discrepancies exist between paleomagnetic and geologic estimates of the timing and magnitude of terrane displacement in the southern canadian cordillera lithostratigraphic palynological geochronologic geochemical and structural data to which we add paleomagnetic data demonstrate that upper cretaceous strata in churn creek are laterally equivalent facies of the silverquick powell creek spc succession these rocks therefore comprise a single overlap sequence linking the insular and intermontane superterranes by late albian cenomanian time 95 ma contradicting previous assertions based solely on paleomagnetic interpretation that major 2000 km latitudinal displacement separated the two regions the churn creek succession retains primary magnetic remanence as demonstrated by positive fold conglomerate and contact tests the sediments do not hold the anisotropy signature of compaction shallowed inclinations the mean inclination of all spc sites from both mount tatlow and churn creek is 55 6 2 3 n 36 sites corresponding to a paleolatitude of 36 1 2 4 this reflects northward translation of the composite insular intermontane superterrane of 3050 450 km between 85 and 50 ma the silverquick powell creek succession at churn creek unconformably overlies the northern end of the spences bridge group a late early cretaceous volcanic arc assemblage on the intermontane superterrane paleomagnetic data in the companion paper place it 1050 450 km south of its current position between 100 and 105 ma integration of these new data sets require that the insular and intermontane superterranes formed a single enormous crustal block that underwent complex episodic south north translation between circa 105 and 50 ma the timing rate and vectors of translation are problematic in terms of geologic constraints along the continental margin

reconstructions of east asian blocks in pangea preface abstract pangea is the youngest supercontinent in earth s history forming about 300 250 ma ago as supported by large amounts of geological paleomagnetic and paleontonlogical data there is little debate on the positions of major continental blocks in pangea however controversy has long surrounded the relations of east asian blocks with pangea most pangea reconstructions assume that the east asian blocks were not the components of pangea but separated from pangea by the paleo tethys ocean these reconstructions were mainly based on geological and paleomagnetic data before the 1990 s but did not fully consider recent data especially for major orogenic belts that formed through the subduction and closure of the proto tethys paleo asian and paleo tethys oceans in east asia to determine where when and how these oceans were closed and whether or not the east asian blocks were added to pangea the national natural science foundation of china nsfc set up a nsfc major program entitled reconstructions of east asian continental blocks in pangea which started in 2012 and was completed in 2016 in the past five years the researchers of this project carried out extensive field based geological and paleomagnetic investigations on the east asian blocks and their intervening mountain belts and produced large amounts of data and competing interpretations which provide constraints on the paleogeographic evolution of the east asian blocks from the breakup of rodinia to the assembly of pangea this forms the justification for organizing this special issue in which we collected ten papers that timely summarize these new data and interpretations and present new models for the reconstructions of the east asian continental blocks in pangea

is the brunswick magnetic anomaly really the alleghanian suture the southeastern margin of the united states presents a complex picture of accreted paleozoic terranes and a rift related mesozoic overlap assemblage buried by a thick veneer of coastal plain sediments basement terranes have been defined on the basis of drilling and geophysical data their relationship to each other and to plate tectonics is in debate the brunswick magnetic anomaly in georgia has been cited as the location of the late paleozoic suture between north america and a continental fragment with african affinities known from the northern florida subcrop this paper poses a new plate model for this region based upon the following assumptions 1 that deep well tests furnish a reasonable data set for the discrimination of various basement rock types across the region and 2 that the brunswick anomaly is the outboard limit of the north american piedmont avalon terrane we propose that the area between the northwest limit of african rocks and the trace of the brunswick anomaly is a region of crustal overlap as african related rocks were overthrust to the northwest the original irregular outline of the north american continental margin and the landward extensions of oceanic fracture zones are intimately related to the kinematics of suspect terranes in the appalachian orogen the implications of the model suggest that differential shortening during collision and differential extension during subsequent rifting accommodate movements on repeatedly activated transforms

paleomagnetic results from saudi arabia and the permo triassic pangea configuration the pangea configuration for the interval of late carboniferous to early jurassic is still debated was it similar to the well known wegenerian pangea or did gondwanaland move with respect to laurussia along a major right lateral lineament of several thousand kilometres during the triassic as suggested by irving we try here to answer this important question with the paleomagnetic study of well dated permo triassic sediments from a borehole in saudi arabia sediments of the same age have also been sampled at the surface but proved to be remagnetized probably by a strong desert alteration the paleomagnetic study of the bore hole core yielded a high temperature component magnetization thought to be of primary origin carried either by magnetite late permian limestones or hematite early triassic red shales with antipodal normal and reversed inclinations its co latitude and pole directions compare well with those from a selection of south american african madagascar and moroccan poles a new reliable pole west gondwana with a mean age of 244 11 m y is derived 53 4 n 259 4 e a95 3 6 in west african coordinates and its comparison with the laurussian poles of same age window strongly suggests a pangea in which the northern part of south america was facing the east of north america pangea b of irving at the permo triassic boundary a large right lateral strike slip movement of some 3500 km during the triassic is thus required to reconstruct pangea to its jurassic pre atlantic opening position

a method for producing digital probabilistic seismic landslide hazard maps abstract the 1994 northridge california earthquake is the first earthquake for which we have all of the data sets needed to conduct a rigorous regional analysis of seismic slope instability these data sets include 1 a comprehensive inventory of triggered landslides 2 about 200 strong motion records of the mainshock 3 1 24 000 scale geologic mapping of the region 4 extensive data on engineering properties of geologic units and 5 high resolution digital elevation models of the topography all of these data sets have been digitized and rasterized at 10 m grid spacing using arc info gis software on a unix computer combining these data sets in a dynamic model based on newmark s permanent deformation sliding block analysis yields estimates of coseismic landslide displacement in each grid cell from the northridge earthquake the modeled displacements are then compared with the digital inventory of landslides triggered by the northridge earthquake to construct a probability curve relating predicted displacement to probability of failure this probability function can be applied to predict and map the spatial variability in failure probability in any ground shaking conditions of interest we anticipate that this mapping procedure will be used to construct seismic landslide hazard maps that will assist in emergency preparedness planning and in making rational decisions regarding development and construction in areas susceptible to seismic slope failure

the geomagnetic field in permo triassic time summary a least squares fit of the 500 fathom or 1000 metre contour of the principal continental masses has been constructed which may approximate to the arrangement of the continents in permo triassic time reliable permotriassic palaeomagnetic data have been plotted on this reassembly mean pole positions for the larger fragments have been calculated and grand mean poles for permian and triassic time have been estimated to a first approximation results are consistent with a geocentric dipole field but small systematic departures have been detected these may be attributed to superimposed multipole components coaxial with a dipole field although other explanations such as anomalies originating in the crust cannot be completely excluded tests for the existence of multipole components are suggested the effect of such components on the accuracy of continental reassemblies based on palaeomagnetism is briefly noted

palaeomagnetism of the early permian mount leyshon intrusive complex and tuckers igneous complex north queensland australia summary this study provides reliable precisely defined and well dated early permian 286 6 ma palaeomagnetic poles for australia from the mount leyshon intrusive complex mlic and the tuckers igneous complex tic both complexes are associated with prominent negative magnetic anomalies indicating the presence of rocks carrying stable remanence of reverse polarity with a koenigsberger ratio greater than unity the characteristic remanence carried by the intrusive phases and by locally remagnetized contact metamorphosed host rocks is always of reverse polarity consistent with acquisition during the permo carboniferous kiaman reverse superchron the corresponding palaeopoles confirm that australia occupied high latitudes in the early permian the pole positions are mlic lat 43 2 s long 137 3 e dp 6 0 dm 6 4 q 6 tic lat 47 5 s long 143 0 e dp 6 0 dm 6 6 q 6 permian palaeomagnetic overprinting is detectable at considerable distances from the mlic 2 3 km well beyond the zone of visible alteration the primary nature of the early permian palaeomagnetic signature is established by full baked contact aureole tests at both localities other new data from australia are consistent with the poles reported here comparison of the australian african and south american apparent polar wander paths apwp suggests that mean permian and triassic poles from west gondwana particularly from south america are biased by remagnetization in the jurassic cretaceous and that the late palaeozoic mesozoic apwp for gondwana is best defined by australian data the australian apwp exhibits substantial movement through the mesozoic provided only that the time averaged palaeofield was zonal the early triassic palaeomagnetic data from australia provide an important palaeogeographic constraint that the south geographic pole was within or very close to se australia around 240 ma the new early permian poles are apparently more consistent with pangaea b type reconstructions of gondwana and laurussia than with the pangaea a2 configuration this may be partly an artefact of reconstruction problems within gondwana as systematic differences between approximately coeval apparently reliable permo carboniferous poles from africa south america and australia are evident in standard gondwana reconstructions these discordances require a tighter fit of the southern continents suggesting that some attenuation of continental margins not accounted for in the reconstructions has occurred during breakup of gondwana or that the fit between east and west gondwana needs to be substantially modified if stretching of continental margins during breakup of supercontinents is a general phenomenon it may help to ameliorate but not solve the long standing controversy regarding pangaea reconstructions although alternative pangaea reconstructions such as pangaea b may reconcile poles from laurussia with australian poles in the late carboniferous early permian no plausible reconstruction can bring the early triassic poles into agreement this suggests that persistent departures from a pure dipole field may have been present in the early triassic lesser but still significant non dipole effects may also have been present during the late carboniferous and permian and may help resolve the pangaea a versus b controversy without requiring substantial attenuation of continental margins or intracontinental deformation we suggest that the most parsimonious interpretation of the palaeomagnetic and geological information is that laurussia and gondwana remained in a pangaea a2 type configuration through the permian and triassic discordance between the apwps for these two supercontinents is attributable mainly to persistent non dipole components of the geomagnetic field which were most important in the early triassic

use of fuzzy relations to produce landslide susceptibility map of a landslide prone area west black sea region turkey abstract preparation of landslide susceptibility maps is important for engineering geologists and geomorphologists however due to complex nature of landslides producing a reliable susceptibility map is not easy for this reason many procedures have been used to produce such maps in this study a new attempt is tried to produce landslide susceptibility map of a part of west black sea region of turkey to obtain the fuzzy relations for producing the susceptibility map a landslide inventory database is compiled by both field surveys and airphoto studies a total of 266 landslides are identified in the study area and dominant mode of failure is rotational slide while the other mode of failures are soil flow and shallow translational slide the landslide inventory and the parameter maps are analyzed together using a computer program fullsa developed in this study the computer program utilizes the fuzzy relations and produces the landslide susceptibility map automatically according to this map 9 6 of the study area is classified as very high susceptibility 10 3 as high susceptibility 8 9 as moderate susceptibility 27 5 as low susceptibility and 43 8 as very low susceptibility or nonsusceptible areas the prediction performance of the susceptibility map is checked by considering actual landslides in the study area for this purpose strength of the relation rij and the root mean square error rmse values are calculated as 0 867 and 0 284 respectively these values show that the produced landslide susceptibility map in the present study has a sufficient reliability it is believed that the approach employed in this study mainly prevents the subjectivity sourced from the parameter selection and provides a support to improve the landslide susceptibility mapping studies

late palaeozoic to early mesozoic evolution of pangaea several possible configurations of the pangaea supercontinent have been suggested for the interval from late carboniferous to early triassic here we re examine the palaeomagnetic basis for these models emphasizing the trends of the paths of apparent polar wander for the individual components of the supercontinent rather than simply averaging poles of presumed similar age two of the alternatives pangaea b and c may result from averaging poles of dissimilar age along common polar wander paths giving rise to spurious tectonic displacements the most likely model appears to be the formation in late devonian time of a modified pangaea a2 followed by evolution to the traditional configuration a during the triassic

isotopic composition of strontium and neodymium in potassic rocks of the little murun complex aldan shield siberia abstract this paper presents the first data on the isotopic composition of nd and sr in ultrapotassic rocks of the little murun complex aldan shield siberia the samples analysed include a sr ba carbonatite and rocks belonging to the biotite pyroxenite shonkinite series the latter are representative of rocks termed lamproites by previous investigators of the complex the rocks have isotopic compositions that indicate derivation from ancient sources that have higher rb sr and lower sm nd ratios than those of bulk earth the samples define an array on a sr nd correlation diagram suggesting that the isotopic composition of sr and nd in the rocks is a mixture of two components a dominant one derived from an ancient lithospheric mantle source that has been isolated from convecting mantle and a minor component of asthenospheric origin we do not consider that any of the samples analysed are lamproites although our isotopic data suggest that conditions in the lithospheric mantle in this region are suitable for the generation of lamproites the potassic rocks from the aldan shield have isotopic compositions that are similar to those of potassic rocks in the wyoming craton it is proposed that the geochemical evolution of the two shields was broadly similar

the gulf of aden structure and evolution of a young ocean basin and continental margin new marine geophysical data are used to describe the structure and history of the gulf of aden magnetic anomaly data shows seafloor spreading magnetic anomalies of sheba ridge from the axial anomaly to anomaly 5 10 m y b p between the owen fracture zone and 45 sup 0 e and to anomaly 2 3 m y b p or anomaly 3 4 m y b p west of 45 sup 0 e the data does not support the two episodes of seafloor spreading recently proposed landward of the seafloor spreading magnetic anomalies is a magnetic quiet zone of uncorrelatable anomalies the magnetic quiet zone boundary is also a structural boundary effectively marking the edge of sheba ridge with deeper basement lacking a significant topographic gradient found on the landward side a magnetic quiet zone is found not only where sheba ridge splits continental lithosphere but also on east sheba ridge where the ridge splits the old oceanic lithosphre of the owen and somali basins there the position occupied by the continental margin within the gulf is marked by nonmagnetic ridge complexes that stretch from the continents to the owen fracture zone the magnetic quiet zone boundary is not an isochron in either the gulf of aden ormore the red sea suggesting that significant horizontal motions can occur prior to the initiation of seafloor spreading the offset on the dead sea rift is used to estimate that from 80 to 160 km of opening amounting to between 65 and 200 extension of the initial rift valley occurred in the gulf of aden and red sea prior to the establishment of a mid ocean ridge it is suggested that the development of a new ocean basin occurs in two stages the first involves diffuse extension over an area perhaps 10 km wide in a rift valley environment without an organized spreading center this is followed by concentration of the extension at a single axis and the beginning of true seafloor spreading less

support for an a type pangea reconstruction from high fidelity late permian and early to middle triassic paleomagnetic data from argentina 1 a major disparity is observed between the late paleozoic early mesozoic apparent polar wander paths apwps of laurussia and gondwana when the landmasses are re assembled in a conventional a type pangea this discrepancy has endured from the earliest paleomagnetic reconstructions of the supercontinent and has prompted discussions of non dipole paleomagnetic fields and alternative paleogeographic models here we report on a joint paleomagnetic geochronologic study of late permian and early to middle triassic volcanic and volcaniclastic rocks from argentina which demonstrates support for an a type model without requiring modification to the geocentric axial dipole hypothesis new shrimp u pb and 40ar 39ar isotopic dating has reinforced the inferred age of the sequences which we estimate at 264 ma upper choiyoi group and 245 ma puesto viejo group field stability tests demonstrate that the volcanic rocks are carrying early primary magnetizations which yield paleopoles 73 7 s 315 6 e a95 4 1 n 40 upper choiyoi and 76 7 s 312 4 e a95 7 3 n 14 puesto viejo a comprehensive magnetic fabric analysis is used to evaluate structural restorations and to correct for magnetization anisotropy the paleomagnetic results derived from volcaniclastic rocks are interpreted to be affected by inclination shallowing and corrections are discussed a comparison of these new results with the existing permian triassic paleomagnetic data from gondwana suggests the presence of widespread bias in the latter we contend that such bias can explain the observed apwp disparity at least for late permian middle triassic time and that alternative paleogeographic reconstructions or non dipole paleomagnetic fields do not need to be invoked to resolve the discrepancy

verification of landslide susceptibility mapping a case study a methodology is proposed for mapping susceptibility to landsliding and validating the results heavy rains in late 1996 and early 1997 led to a large number of landslids in the rute sector cordoba southern spain where landslide susceptibility mapping had previously been carried out using a matrix method developed with a geographical information system gis analysis of the distribution of the new landslides or reactivated earlier ones enabled the methodology to be validated by calculating association coefficients and determining the closeness of the match between subsequent field evidence and the previously defined susceptibility levels from the data obtained it can be concluded that the susceptibility mapping effectively explained the spatial distribution of landslides thus providing valuable information on stability conditions over a widespread area copyright 1999 john wiley sons ltd

florida a jurassic transform plate boundary magnetic gravity seismic and deep drill hole data integrated with plate tectonic reconstructions substantiate the existence of a transform plate boundary across southern florida during the jurassic on the basis of this integrated suite of data the pre cretaceous florida bahamas region can be divided into the pre jurassic north american plate jurassic marginal rift basins and a broad jurassic transform zone including stranded blocks of pre mesozoic continental crust major tectonic units include the suwannee basin in northern florida containing paleozoic sedimentary rocks a central florida basement complex of paleozoic age crystalline rock the west florida platform composed of stranded blocks of continental crust the south georgia rift containing triassic sedimentary rocks which overlie block faulted suwannee basin sedimentary rocks the late triassic jurassic age apalachicola rift basin and the jurassic age south florida bahamas and blake plateau marginal rift basins the major tectonic units are bounded by basement hinge zones and fracture zones fz the basement hinge zone represents the block faulted edge of the north american plate separating paleozoic and older crustal rocks from jurassic rifted crust beneath the marginal basins fracture zones separate mesozoic marginal sedimentary basins and include the blake spur fz jacksonville fz bahamas fz and cuba fz bounding the blake plateau bahamas south florida and southeastern gulf of mexico basins the bahamas fz is the most important of all these features because its northwest extension coincides with the gulf basin marginal fault zone forming the southern edge of the north american plate during the jurassic the limited space between the north american and the south american african plates requires that the jurassic transform zone connecting the central atlantic and the gulf of mexico spreading systems was located between the bahamas and cuba fz s in the region of southern florida our plate reconstructions combined with chronostratigraphic and lithostratigraphic information for the gulf of mexico southern florida and the bahamas indicate that the gulf was sealed off from the atlantic waters until callovian time by an elevated florida bahamas region restricted influx of waters started in callovian as a plate reorganization and increased plate separation between north america and south america africa produced waterways into the gulf of mexico from the pacific and possibly from the atlantic

the secular variation of earth s magnetic field models of the magnetic field at the core mantle boundary at selected epochs from 1715 0 to 1980 0 reveal novel features in the field at the core these suggest that the flow of core fluid is coupled to the mantle and that magnetic diffusion is significant

late palaeozoic mesozoic geomagnetic reversal paths and core mantle boundary summary an analysis of transitional virtual geomagnetic poles vgps from the late permain early triassic through to the late jurassic early cretaceous shows them to be located in preferred areas which coincide with present day zones of fast seismic velocity at the core mantle boundary cmb as has been observed for late cainozoic transitional vgp paths it is therefore suggested that the similar geometries of late palaeozoic mesozoic and late cainozoic polarity transitions have been impressed by sources of the cmb which have persisted through the mesozoic and tertiary to the present

the evolution of middle america and the gulf of mexico caribbean sea region during mesozoic time a plate tectonic model for the evolution of middle america and the gulf of mexico caribbean sea region is presented the model which is based upon the existence of the mojave sonora megashear incorporates into the triassic pangea reconstruction three microplates between north and south america thus avoiding the overlap of the bullard fit these plates are the yaqui bounded on the north by the mojave sonora megashear the east and west maya plates bounded on the north by the mexican volcanic zone and on the south by a predecessor of the motagua fault zone and the chortis plate parts of guatemala and honduras during late jurassic time as north america split away from europe africa and south america shear with left lateral sense of displacement occurred along the transform faults that bounded the micro plates if 800 km of left lateral displacement along the mojave sonora megashear 300 km along the mexican volcanic belt and 1 300 km along a proto motagua megashear are restored and if yucatan and cuba are rotated to fit against northern south america then 1 a curvilinear belt of late paleozoic rocks that show lithologic as well as paleontologic similarities extends across the reconstruction and links outcrops in texas eastern mexico nuclear central america and colombia 2 a mediterranean like sea is delineated that was a precursor of most of the present gulf of mexico 3 correlation is implied between the distinctive quartzose san cayetano formation of cuba and the caracas and juan griego groups of venezuela geometric constraints suggest that probably shear initially occurred along the mexican volcanic zone near the end of the middle jurassic subsequently probably about 160 m y ago displacements that total 800 km began along the mojave sonora megashear contemporaneously yucatan and fragments of pre cretaceous rocks that compose parts of central and western cuba migrated northward toward their present positions rotation of yucatan was facilitated by considerable displacement along the proto motagua zone and along a zone that is probably coincident with the modern salina cruz fault accumulation of widespread major salt units of late jurassic callovian to early oxfordian age in the gulf basin probably occurred contemporaneously with the arrival of these blocks at their present positions clastic units that interfinger with some of the youngest salt units and rim the gulf of mexico have not recorded major recognized translations since their accumulation clockwise rotation of south america and the chortis plate occurred during early cretaceous time this movement which was manifested by subduction of jurassic ocean floor against the previously rifted precursor of the island of cuba and under parts of hispaniola and puerto rico is recorded by circum caribbean orogeny abrupt changes in the relative motions between north and south america during late cretaceous time may have resulted in extension and outpourings of basalt upon the jurassic rocks of the ocean floor of the venezuelan basin west of beata ridge sea floor spreading formed the colombian basin related subduction occurred as the chortis plate including part of central america the nicaraguan rise and southeastern cuba was sutured against the maya east plate along the present motagua fault and cayman trench our model is constrained by published geologic data the relative positions of north and south america from atlantic sea floor magnetic anomalies and the requirement that the major transform faults be compatible with the poles of rotation for the appropriate relative motions between north and south america paleomagnetic data from middle america are sparse but do not conflict with the predicted motions of some of the microplates especially chortis

a revised fit of south america and south central africa abstract a new set of parameters for the total plate tectonic reconstruction of south america and south central africa is presented euler pole 46 75 n 32 65 w rotation angle 56 40 this fit is constrained by at least three pre drift tectonic features crossing from one continent to the other 1 the geophysically defined eastern and western boundaries of the submarine jurassic outeniqua basin south africa and the falkland plateau basin 2 the late precambrian transcurrent fault and mylonite belts of pernambuco brazil and foumban west africa and 3 the triassic northern tectonic front of the cape fold belt and the major morphological feature on the falkland plateau with which it is closely lined up isotopic ages of falkland plateau gneisses correspond to cape pluton and cape fold belt ages suggesting their palaeoposition was within the realm of the cape fold belt in addition the bathymetrically and geophysically defined northeastern apex of the falkland plateau fits into the re entrant angle defined on the south african margin by the steep southeast facing sheared agulhas margin and the southern face of the tugela cone simultaneously known precambrian outcrops in northeastern brazil and in the gulf of benin area of west africa are juxtaposed rather than overlapped reconstructions producing a closer fit of these cratonic areas are considered untenable

landslide susceptibility mapping using geological data a dem from aster images and an artificial neural network ann an efficient and accurate method of generating landslide susceptibility maps is very important to mitigate the loss of properties and lives caused by this type of geological hazard this study focuses on the development of an accurate and efficient method of data integration processing and generation of a landslide susceptibility map using an ann and data from aster images the method contains two major phases the first phase is the data integration and analysis and the second is the artificial neural network training and mapping the data integration and analysis phase involve gis based statistical analysis relating landslide occurrence to geological and dem digital elevation model derived geomorphological parameters the parameters include slope aspect elevation geology density of geological boundaries and distance to the boundaries this phase determines the geological and geomorphological factors that are significantly correlated with landslide occurrence the second phase further relates the landslide susceptibility index to the important geological and geomorphological parameters identified in the first phase through ann training the trained ann is then used to generate a landslide susceptibility map landslide data from the 2004 niigata earthquake and a dem derived from aster images were used the area provided enough landslide data to check the efficiency and accuracy of the developed method based on the initial results of the experiment the developed method is more than 90 accurate in determining the probability of landslide occurrence in a particular area

syntectonic remagnetization in the southern methow block resolving large displacements in the southern canadian cordillera 1 the upper cretaceous ventura member of the goat wall unit in the southern methow block of southern british columbia and northern washington state holds a syntectonic magnetization eight new sites from manning park in british columbia give a mean direction of d 27 5 i 60 1 k 304 7 95 3 2 after optimal partial tilt correction of five groups of bedded sites from farther south in the basin reported by bazard et al 1990 four have a syntectonic remanence with a direction similar to what we observe the exception is one group which has optimal concentration of remanence directions on 100 untilting and an abherent direction which must be rejected combining the accepted sites the optimal differential syntilting direction is d 11 8 i 61 5 k 39 3 95 3 4 n 47 giving a mean pole of 79 8 n 359 2 e k 19 5 and a95 4 8 the age of the remagnetization is constrained to be between 88 and 80 ma compared to cratonic north america this result indicates that the southern methow block was displaced from the south by 1800 500 km meaning it lay south of the sierra nevada subduction zone but well north of other paleomagnetically constrained cretaceous rock units from the insular superterrane including correlative strata of the mount tatlow area in the northern methow block among several possibilities to reconcile this discrepancy the most plausible has the whole methow block translated coherently but with the southern methow block strata remagnetized during transit

oroclinal bending and evidence against the pangea megashear the cantabria asturias arc northern spain the cantabria asturias arc of southwestern europe is a highly curved variscan belt that formed along the ancient plate boundary between gondwana and laurussia during the assembly of pangea new paleomagnetic data from 59 sites in the southern limb of the arc were combined with previously published data from 109 sites to determine the evolution of the arc a previously unrecognized postrotation magnetization is found in the southern limb refuting earlier models of arc formation that concluded secondary rotation of only 50 of present day arc curvature the new data show that the arc underwent true 100 oroclinal bending of an originally linear belt in a two stage tectonic history this history represents two regional compression phases 1 east west in the late carboniferous pennsylvanian and 2 north south in the permian both in present day coordinates the north south compression phase coincides with the northward movement of gondwana and its final collision with laurussia this tectonic scenario argues against an indentor scenario and does not support a 3500 km dextral megashear proposed in earlier reconstructions

new cocorp profiling in the southeastern united states part i late paleozoic suture and mesozoic rift basin new cocorp profiling in the southeastern united states has revealed a broad zone of dipping reflections that extends downward through the crust beneath the coastal plain in western georgia the zone is over 50 km wide and most of the reflections dip moderately steeply toward the south regional considerations suggest that this feature marks the late paleozoic suture between north america and africa where crossed by the cocorp survey the suture occurs beneath the north flank of the triassic early jurassic south georgia basin the main depocenter of the south georgia basin occurs about 90 km to the south and is formed by a large half graben containing more than 5 km of rift basin fill farther south the paleozoic suwannee basin sequence beneath northern florida is poorly imaged on the cocorp profiles however weak reflections suggest that these strata including basal felsic volcanics may have an aggregate thickness of about 6 km in north central florida at the northwest end of the cocorp traverse a prominent horizon imaged in the upper crust beneath the inner piedmont probably marks the southern appalachian detachment the detachment appears to be cut off by the towaliga fault implying that the towaliga fault is in part a down to the north normal fault intermittent moho reflections occur at 11 12 s two way time along the length of the cocorp survey indicating that the crust in the region has a roughly uniform thickness of about 33 36 km assuming an average crustal velocity of 6 km s

plate motions and the geomagnetic field ii jurassic to tertiary summary the analysis of the time averaged geomagnetic field is extended back to 200ma palaeomagnetic poles from the major plates have been carefully selected from recent compilations of reliable results for each region these were returned with their corresponding sampling sites to their locations at the estimated dates of magnetization in a fixed hotspots framework the corrected results were then grouped into 20ma windows at intervals of 10ma representing the past 100ma and 40ma windows at 30ma intervals for the more sparse 100 200ma data global means and fisher statistics were calculated for each window having included the axial quadrupole in the calculation the value of this coefficient which gave the maximum value for the fisher precision parameter tightest grouping of poles was taken as representative of each interval the results indicate that a small axial quadrupole of the same sign as the axial dipole may have persisted throughout the cenozoic this is equivalent to a northward offset axial dipole field far sided effect during the late cretaceous this component appears to have changed sign with respect to the dipole negative values seem to have obtained throughout the cretaceous long normal polarity interval corresponding to a southward offset dipole near sided effect the data distribution is inadequate for the resolution of the quadrupole at earlier times and zero values cannot be discounted little relative motion is implied between the hotspots and the geomagnetic axis for the past 90 ma the global mean polar path curving around the predicted fixed hotspots pole at a distance of typically 5 latitude with little sign of rapid tertiary polar wander as implied by studies of pacific data alone between 100 and 200 ma however there is a clear difference between the two reference frames amounting to 17 19 in the jurassic this may reflect motion of the mantle relative to the geomagnetic axis but may also include errors due to inaccurate determination of hotspot tracks and inter hotspot motion

statistical analysis of landslide susceptibility at yongin korea the aim of this study is to evaluate the susceptibility of landslides at yongin korea using a geographic information system gis landslide locations were identified in the yongin area from interpretation of aerial photographs field surveys and maps of the topography soil type timber cover and geology these data were collected and constructed into a spatial database using gis the factors that influence landslide occurrence such as slope aspect and curvature of topography were calculated from the topographic database texture material drainage and effective soil thickness were extracted from the soil database and type age diameter and density of timber were extracted from the forest database lithology was extracted from the geological database and land use was classified from the landsat tm satellite image landslide susceptibility was analyzed using the landslide occurrence factors by probability and logistic regression methods the results of the analysis were verified using the landslide location data the validation results showed satisfactory agreement between the susceptibility map and the existing data on landslide location the gis was used to analyze the vast amount of data efficiently and statistical programs were used to maintain specificity and accuracy the results can be used to reduce associated hazards and to plan land use and construction

truncation of the appalachian piedmont beneath the coastal plain of alabama evidence from new magnetic data a new aeromagnetic survey of a part of southern alabama reveals that magnetic signatures of the appalachian piedmont are truncated by a major magnetic lineament beneath the gulf coastal plain mylonitic rocks have been recovered from a drillhole along this lineament which is probably a fault zone of late paleozoic and or triassic jurassic age we suggest that this fault zone may initially have been the alleghanian convergent suture between the north american craton and accreted terranes to the southeast the zone may have been locally reactivated as part of an extensive buried triassic jurassic graben system

discontinuity controlled probabilistic slope failure risk maps of the altindag settlement region in turkey the evaluation of potential rock slope problems using stereographic projection techniques known as kinematic analysis is one of the most important parts of a slope stability investigation to be carried out in jointed rock media in conventional stereoprojection techniques for the assessment of possible rock slope failures the peak orientations of joints together with the slope geometry and the friction angle of the weakness planes are used other possible joint orientations which may be encountered in the rock media are ignored although they belong to the group of joint peak orientations in this study nearly vertical jointed andesites cropped out at the altindag settlement region in ankara were studied in order to evaluate the relevance of this ignored discontinuity orientation data on slope stability as a result probabilistic risk maps for planar toppling and wedge failures were produced using the kinematic rules and digital elevation model of the study area the comparison of the distribution of the actual failures in the area and the probabilistic risk maps prepared for the study area revealed that all of the identified failures are found to be located in the higher risk zones on the probabilistic risk maps

geoid pangea and convection abstract we show that the present geoid has a simple low order configuration with an axis of symmetry in the equatorial plane we show further that it is a tennis ball pattern with an equatorial high belt and a polar low one which is clearly controlled by the rotation of the earth finally we show that the outline of pangea between at least 200 ma and 125 ma ago lay along a great circle passing through the paleo poles of rotation thus it also had an axis of symmetry in the equatorial plane this hemispheric super continent configuration ended in middle cretaceous time during a major geologic catastrophe which was accompanied by high rates of spreading hotspot outbreaks and high sea level stands we interpret this evidence in terms of separate steady state lower mantle convection responsible for the present geoid weakly coupled to the upper mantle one this weak coupling leads to the hemispheric continent configuration which ends when excessive heating of the upper mantle due to the insulating continental cap leads to continent dispersal the complete cycle from one supercontinent to the next might be of the order of 400 ma

paleomagnetism of permian sedimentary rocks from tanzania and the permian paleogeography of pangea abstract we report new paleomagnetic results from karoo permian rocks in tanzania k1 and k3 redbeds and k5 siltstones and limestones from the songwe kiwira basin ndeke redbeds from the mikumi basin and group viii redbeds from the nyakatitu basin were sampled and thermally demagnetized palynologic data and lithologic correlations suggest that the k1 redbeds are lower permian and that the k3 ndeke and group viii redbeds as well as the k5 siltstones and limestones are upper permian stable magnetic directions were obtained from the k3 ndeke and group viii redbeds yielding an upper permain pole at 26 n 267 e characteristic remanence directions were also obtained from the k5 siltstones and limestones however because these directions define a pole 66 n 269 e that is very close to the upper cretaceous pole for africa and significantly different from the upper permian redbed poles these rocks may have been remagnetized the k1 redbeds did not yield stable results using our new results together with published permian poles for africa and the other gondwanan continents we revise the mean lower and upper permian poles for africa west gondwana and gondwana and investigate whether or not these revised poles can discriminate between the various pangea reconstructions proposed for the permian with any greater certainty than previous unrevised mean poles when compared to the mean lower and upper permian poles for laurussia we find that our revised west gondwanan and gondwanan poles do not necessarily provide stronger support for any particular pangea reconstruction than the previous poles therefore even though this study improves the paleomagnetic data base for gondwana for the permian it is not clear that the combination of our results with other paleomagnetic data from the gondwanan continents yields significant new insights about the permian configuration of pangea as suggested previously strong non dipole fields during the permian may provide an explanation for why it is not easy to discriminate with certainty between the various permain pangea reconstructions even with new paleomagnetic results

pangea in permian to jurassic time the apparent polar wander paths apwps for the northern and southern continents have been redetermined using revised time scales and data when plotted on the conventional pangea pangea a the paths are distinct but essentially linear and parallel from late carboniferous to late permian time both paths then undergo a sharp change in direction and converge so as to overlap in early to middle jurassic time if the permo triassic magnetic field was an axial dipole then paleomagnetic data show that pangea was mobile during most and possibly all of the mid triassic to mid jurassic interval because of the uncertainties in pole ages and positions and errors in measurements the new apwps are consistent with a range of pangeas in particular the data are compatible with two paleomagnetic pangeas a2 and a new class of pangea here named the d pangeas these resemble morel and irving s 1981 pangea b and the c pangeas of smith et al 1981 unlike the a2 pangeas the b c and d pangeas all require large 2000 km relative motion between the northern and southern continents geological data require the transition from an earlier pangea to pangea a to take place along a transform zone here named the pangea transform zone or ptz the ptz is considered to be technically analogous to the great glen fault of scotland four types of possible ptz are examined passing through either the western or eastern end of the brunswick magnetic anomaly of eastern north america or north and south of iberia the geological data suggest that those pangeas that require large displacements on ptzs that pass east of the brunswick magnetic anomaly are improbable b and c pangeas are snapshots giving precise paleomagnetic reconstructions d pangeas fit long stretches of the apwps as well as possible a2 pangeas fit the apwps moderately well but also require the geological displacement to be smaller the differences in displacement between the d and a2 pangeas reflect geometrical relationships between euler poles ptz curvature and the apwps the general geological evidence suggests that d pangeas are less probable than a2 pangeas but that they cannot be rejected transition from a2 to a is most likely to have occurred via a sequence of rotations about different poles rather than a single rotation in detail the conventional pangea requires modification africa must be broken into at least two fragments along the benue trough and its northern continuation northwest africa then fits more tightly into northern south america which modifies the apwps and reduces the gap between them by including the effects of continental extension and using detailed geological data the gap can be reduced to one in which the a63 circles touch or overlap non dipole fields or an expanding earth need not be invoked to explain the mismatch of the apwps on the conventional pangea the finite rotation required for the older pangea to pangea a is very close to van der voo and french s 1974 single rotation for a2 to a but is actually the sum of three smaller rotations that reflect the modification to pangea a continental extension and the postulated ptz displacement of the possible ptzs a ptz parallel to the west african continental magnetic anomaly with a displacement of about 170 km gives a better fit of this anomaly to the east coast magnetic anomaly of north america further refinements to pangea a2 will depend on a better knowledge of stretching factors on the passive continental margins of the modified pangea a and incorporation of rotations due to major faults such as the south atlas fault in morocco

constrains on the origin and history of the eastern mediterranean basin abstract the basin formed along the northern passive margin of gondwanaland as a relict of the mesozoic neotethys in early mesozoic time though direct information from the basin itself is meagre the geology of its passive margins and the regional framework of the tethys evolution constrain the formation and history of the basin the eastern mediterranean and its passive margins are interpreted to have formed as a result of several faulting and continental breakup phases from early permian to middle jurassic times before pangaea s complete disintegration this led to the detachment of the eratosthenes and tauride blocks from the margins of the levant and herodotus basins respectively the latter merged in the northeast with the cyprus basin that extended along arabia s northern margin the main rifting probably occurred in the triassic leading to seafloor spreading in the herodotus and cyprus basins while along the levant margin important rifting also occurred in the jurassic during the initial rifting stages extension perpendicular to the levant margin was important but subsequently the tauride block drifted mainly northward the existence of the passive margins and slopes of the eastern mediterranean is documented at least from the end of the middle jurassic until then the basin was probably narrow 200 300 km but during the main phase of the africa laurasia separation it grew to twice its present width or more this scenario depends critically on the interpretation that the tauride block was originally located next to northeastern africa on the western side of the eratosthenes block plate convergence and consumption of the northern portion of the basin have taken place since mid cretaceous times but the active convergent boundary on its northern side formed only in the neogene by modification of earlier structures some intra plate deformation also took place especially in the neogene but it hardly changed the original configuration of the remaining portion of the basin