paleolatitudes determined from paleomagnetic data from vertical cores most of the paleomagnetic data available from oceanic plates consist of measurements of inclination but not declination from azimuthally unoriented vertical cores similarly the basic paleomagnetic data to be analyzed from crustal blocks that have rotated by varying amounts about vertical axes are a set of paleoinclinations a new method is proposed for determining the paleocolatitude of a sampling site and the associated confidence limits paleomagnetic inclinations are first converted to paleocolatitudes and averaged to produce a mean colatitude after showing that this mean is biased we derive a paleocolatitude correction to remove the bias using a model for geomagnetic secular variation based on the latitude dependence of secular variation during the past 5 million years after testing the validity of the model by applying it to paleomagnetic data from quaternary lavas for which both inclination and declination are known we apply the method to inclination only paleomagnetic data from suiko seamount the most complete data set from a drilling site the method is then applied to paleomagnetic data from all deep sea drilling project sites for the pacific plate to obtain for each site an unbiased mean paleocolatitude and its confidence limits these paleocolatitudes and confidence limits are then used as input for a least squares analysis to obtain early and late cretaceous poles for the pacific plate and 95 confidence limits for these poles it is shown that the scatter of individual site paleocolatitudes about the best fit pole is consistent with the confidence limits at each site as determined by the new method of analysis

landslide susceptibility mapping at golestan province iran a comparison between frequency ratio dempster shafer and weights of evidence models abstract the purpose of the present study is to investigate the landslide susceptibility mapping using three statistical models such as frequency ratio dempster shafer and weights of evidence at southern part of golestan province at first landslide locations were identified from the interpretation of aerial photographs and field surveys a total of 392 landslides were mapped in gis out of which 275 70 locations were chosen for the modeling purpose and the remaining 118 30 cases were used for the model validation then layers of the landslide conditioning factors were prepared the relationship between the conditioning factors and the landslides were calculated using three models for verification the results were compared with landslides which were not used during the training of the models subsequently the roc receiver operating characteristic curves and area under the curves auc for three landslide susceptibility maps were constructed and the areas under curves were assessed for validation purpose the validation results showed that the area under the curve for frequency ratio dempster shafer and weights of evidence models are 0 8013 80 13 0 7832 78 32 and 0 7460 74 60 with prediction accuracy 0 7516 75 0 7396 73 and 0 6998 69 respectively the results revealed that frequency ratio model has higher auc than the other models in general all the three models produced reasonable accuracy the resultant maps would be useful for general land use planning

tracking the late jurassic apparent or true polar shift in u pb dated kimberlites from cratonic north america superior province of canada different versions of a composite apparent polar wander apw path of variably selected global poles assembled and averaged in north american coordinates using plate reconstructions show either a smooth progression or a large 30 gap in mean paleopoles in the late jurassic between about 160 and 145 ma in an effort to further examine this issue we sampled accessible outcrops subcrops of kimberlites associated with high precision u pb perovskite ages in the timiskaming area of ontario canada the 154 9 1 1 ma peddie kimberlite yields a stable normal polarity magnetization that is coaxial within less than 5 of the reverse polarity magnetization of the 157 5 1 2 ma triple b kimberlite the combined 156 ma triple b and peddie pole 75 5 n 189 5 e a95 2 8 lies about midway between igneous poles from north america nearest in age 169 ma moat volcanics and the 146 ma ithaca kimberlites showing that the polar motion was at a relatively steady yet rapid 1 5 myr pace a similar large rapid polar swing has been recognized in the middle to late jurassic apw path for adria africa and iran eurasia suggesting a major mass redistribution one possibility is that slab breakoff and subduction reversal along the western margin of the americas triggered an episode of true polar wander

the drift history of adria and africa from 280 ma to present jurassic true polar wander and zonal climate control on tethyan sedimentary facies article i nfo the orogenic belts surrounding the undeformed adriatic sea represent the margins of an area known as adria the african promontory we have undertaken a critical appraisal of paleomagnetic data from regions of adria considered parautochthonous relative to africa obtained either from biostratigraphically dated sed imentary rocks corrected for inclination shallowing or from igneous rocks that are regarded as free from any inclination shallowing bias paleomagnetic directions were used to calculate paleomagnetic poles for compar ison with coeval and inclination flattening free paleomagnetic poles from stable africa visual coherence of paleopoles for several time slices from the early permian to the eocene supports the construction of a com posite apparent polar wander path apwp valid for parautochthonous adria and stable africa this compos ite apwp is compared to previous apwps finding good agreement with the global apwp of kent and irving 2010 both apwps show a remarkable and rapid polar shift of 40 in the jurassic that other apwps tend to underestimate we interpret this shift to represent a major episode of true polar wander tpw from 183 ma in the early jurassic to 151 ma in the late jurassic using a simple zonal climate model the drift motion of adria attached to africa appears to be consistent with the distribution of permian cretaceous sed imentary facies on adria

anomalous late jurassic motion of the pacific plate with implications for true polar wander abstract true polar wander or tpw is the rotation of the entire mantle crust system about an equatorial axis that results in a coherent velocity contribution for all lithospheric plates one of the most recent candidate tpw events consists of a 30 rotation during late jurassic time 160 145 ma however existing paleomagnetic documentation of this event derives exclusively from continents which compose less than 50 of the earth s surface area and may not reflect motion of the entire mantle crust system additional paleopositional information from the pacific basin would significantly enhance coverage of the earth s surface and allow more rigorous testing for the occurrence of tpw we perform paleomagnetic analyses on core samples from ocean drilling program odp site 801b which were taken from the oldest available pacific crust to determine its paleolatitude during the late jurassic and early cretaceous 167 133 ma we find that the pacific plate underwent a steady southward drift of 0 49 0 74 my 1 except for an interval between kimmeridgian and tithonian time 157 147 ma during which it underwent northward motion at 1 45 0 76 my 1 1 this trajectory indicates that the plates of the pacific basin participated in the same large amplitude 30 rotation as continental lithosphere in the 160 145 ma interval such coherent motion of a large majority of the earth s surface strongly supports the occurrence of tpw suggesting that a combination of subducting slabs and rising mantle plumes was sufficient to significantly perturb the earth s inertia tensor in the late jurassic

high resolution 40ar 39ar dating of the oldest oceanic basement basalts in the western pacific basin 1 we report new 40ar 39ar ages for the oldest pacific oceanic floor at ocean drilling program site 801c in the pigafetta basin and site 1149d close to the izu bonin subduction zone in the nadezhda basin these ages were determined by applying high resolution incremental heating experiments including 15 30 heating steps to better resolve the primary argon signal from interfering alteration signatures in these low potassium ocean crust basalts combined with previous results from pringle 1992 for site 801b and 801c we arrive at a multistage history for the formation of the pigafetta ocean crust the oldest part of the pacific plate was formed at the spreading ridges at 167 4 1 4 3 4 ma n 2 2 internal absolute error offering an important calibration point on the geological reversal timescale grts since it represents the old end of the mesozoic magnetic anomalies this mid ocean ridge basalt sequence however is overlain by more tholeiites and alkali basalts that were formed 7 3 1 5 myr later around 160 1 0 6 ma n 7 2 internal error the older age group is confirmed independently by radiolarian ages ranging from late bajocian to middle bathonian 167 173 ma bartolini and larson 2001 and by profound differences in the structural characteristics of this basement section pockalny and larson 2003 thin layers comprising hydrothermal deposits separate these sequences which in addition to the difference in isotopic age show distinct major and trace element compositions this indicates that key volcanic and hydrothermal activity took place 400 600 km away from the spreading ridges on the basis of a jurassic 66 km myr half spreading rate in the pacific it remains unclear if these processes were active continuously after the initial formation of the pacific oceanic crust but all our observations seem to point to an episodic history site 1149d gives another important calibration point on the grts of 127 0 1 5 3 6 ma n 1 2 internal absolute error for anomaly m12 that is slightly younger when compared to current timescale compilations 134 2 2 1 ma gradstein et al 1995 this might suggest that the dated basalt from site 1149d does not represent the age of the ocean crust formed at its ridge axis it may also be part of the early cretaceous intraplate events that have produced dolerite sills in the pacific crust at sites 800 and 802 around 114 126 ma

scale invariance in the spatial development of landslides in the umbria region italy understanding the spatial distribution of mass movements is a major issue in the management and forecasting of landslide risk in this context the present study examines the most widespread types of landslide in the umbria region central italy that is slides and flows in order to establish if it is possible to identify a well defined structure in their spatial pattern by using the landslide inventory map available for the area and by resorting to the principles of fractal theory the scaling properties of the landslide sample were investigated the application of the box counting algorithm to the maps of landslide triggering points and landslide areas allowed for the identification of a clear scale invariant structure two distinct types of fractal behaviour were recognized separated by a scale value of 1 km and characterized by capacity dimensions of 1 35 and 1 76 in the ranges of 25 m 1 km and 1 16 km respectively the comparison between the scaling exponents obtained from a map of points and one of areas and the elaboration of the cumulative frequency distributions of landslide areas supported the interpretation of this result the higher capacity dimension describes the spatial distribution of landslides in the umbria region while the lower contains additional information about their geometries suggesting that the latter also possess scaling properties based on the finding of two different types of behaviour of landslides in space the hypothesis is discussed that the contribution of each causal factor i e predisposing and triggering factors to the occurrence of landslide events and to their spatial development could be different in the two scale ranges identified depending on its spatial variability at local and regional scale according to this hypothesis factors with high local variability i e topographic attributes would mainly affect the assortment of landslide geometries while those with high regional variability e g rainfalls and lithology would mainly affect the pattern of the landslides

late cretaceous polar wander of the pacific plate evidence of a rapid true polar wander event we reexamined the late cretaceous early tertiary apparent polar wander path for the pacific plate using 27 paleomagnetic poles from seamounts dated by 40ar 39ar geochronology the path shows little motion from 120 to 90 million years ago ma northward motion from 79 to 39 ma and two groups of poles separated by 16 to 21 degrees with indistinguishable mean ages of 84 2 ma the latter phenomenon may represent a rapid polar wander episode 3 to 10 degrees per million years whose timing is not adequately resolved with existing data similar features in other polar wander paths imply that the event was a rapid shift of the spin axis relative to the mantle true polar wander which may have been related to global changes in plate motion large igneous province eruptions and a shift in magnetic field polarity state

towards absolute plate motions constrained by lower mantle slab remnants the movement of tectonic plates before the cretaceous period is poorly understood a global mantle tomography model suggests that the longitude of oceanic subduction zones up to 300 million years ago was offset by up to 18 compared with tectonic reconstructions for the same period

closure of the mongol okhotsk ocean insights from seismic tomography and numerical modelling abstract the existence of the palaeozoic and mesozoic mongol okhotsk ocean is evident from the mongol okhotsk suture which stretches from central mongolia to the sea of okhotsk a lack of sufficient palaeomagnetic data and an otherwise diffuse suture with an abrupt termination to the west has led to difficulties in reconstructing the history geometry and closure of this ocean both the timing and style of the ocean s closure are unclear and have led to several alternative reconstructions closure timing ranges between the late jurassic 155 ma and beginning of the early cretaceous 120 ma and the proposed kinematics include contemporaneous subduction along two opposite margins subduction along only one margin or with a component of left lateral shear in the present study numerical models of mantle convection are coupled with global plate reconstructions to investigate ambiguities regarding the closure of the mongol okhotsk ocean in order to decipher the tectonic history of this enigmatic region two end member scenarios of subduction location either along the present day northern or the southern margins of the mongol okhotsk ocean are imposed as kinematic surface boundary conditions for the past 230 myrs through a comparison to seismic tomography the results indicate a preferred subduction history along the siberian margin relative northern margin of the mongol okhotsk ocean at present day the slab remnant is predicted to be located farther west than previously proposed furthermore we find that the subducting slabs in this region generate a hot dense pile at the same location and with a similar shape as the perm anomaly

testing the occurrence of late jurassic true polar wander using the la negra volcanics of northern chile abstract true polar wander tpw is the reorientation of the crust mantle system driven by the redistribution of masses in the mantle and on the earth s surface in the ideal case characterization of tpw requires paleomagnetic constraints on the motion of all major plates and independent reconstructions of relative plate positions while such complete datasets are absent for pre mesozoic tpw inferences due to the absence of oceanic plates they are available for the late jurassic 165 145 ma monster shift a 30 amplitude proposed tpw event here we perform paleomagnetic sampling and ar ar geochronology on the la negra volcanics of northern chile producing two new paleomagnetic poles with ages 165 8 1 8 ma 1 84 3 n 0 9 e 95 7 6 n 28 and 152 8 0 8 ma 84 5 n 256 4 e 95 10 8 n 18 by combining these data with other recently published results we compute a net lithospheric rotation of 25 3 7 3 1 at a mean rate of 1 21 0 35 my 1 between 170 and 145 ma with a peak rate of 1 46 0 65 my 1 between 160 and 145 ma these rates are consistent with inferences from the pacific plate implying true whole lithosphere rotation given coherent motion involving the entire lithosphere we conclude that the earth underwent rapid tpw between approximately 165 and 145 ma potentially driven by the cessation of subduction along the western north american margin

rainfall induced landslide susceptibility zonation of puerto rico landslides are a major geologic hazard with estimated tens of deaths and 1 2 billion in economic losses per year in the us alone the island of puerto rico experiences one or two large events per year often triggered in steeply sloped areas by prolonged and heavy rainfall identifying areas susceptible to landslides thus has great potential value for puerto rico and would allow better management of its territory landslide susceptibility zonation lsz procedures identify areas prone to failure based on the characteristics of past events lszs are here developed based on two widely applied methodologies bivariate frequency ratio fr method and logistic regression lr method with these methodologies the correlations among eight possible landslide inducing factors over the island have been investigated in detail both methodologies indicate aspect slope elevation geological discontinuities and geology as highly significant landslide inducing factors together with land cover for the fr method and distance from road for the lr method the lr method is grounded in rigorous statistical testing and model building but did not improve results over the simpler fr method accordingly the fr method has been selected to generate a landslide susceptibility map for puerto rico the landslide susceptibility predictions were tested against previous landslide analyses and other landslide inventories this independent evaluation demonstrated that the two methods are consistent with landslide susceptibility zonation from those earlier studies and showed this analysis to have resulted in a robust and verifiable landslide susceptibility zonation map for the whole island of puerto rico

eustatic curve for the middle jurassic cretaceous based on russian platform and siberian stratigraphy zonal resolution we have used the stratigraphy of the central part of the russian platform and surrounding regions to construct a calibrated eustatic curve for the bajocian through the santonian the study area is centrally located in the large eurasian continental craton and was covered by shallow seas during much of the jurassic and cretaceous the geographic setting was a very low gradient ramp that was repeatedly flooded and exposed analysis of stratal geometry of the region suggests tectonic stability throughout most of mesozoic marine deposition the paleogeography of the region led to extremely low rates of sediment influx as a result accommodation potential was limited and is interpreted to have been determined primarily by eustatic variations the central part of the russian latform thus provides a useful frame of reference for the quantification of eustatic variations throughout the jurassic and cretaceous the biostratigraphy of the russian platform provides the basis for reliably determining age and eustatic events the mesozoic section of the central part of the russian platform is characterized by numerous hiatuses in this study we filled the sediment gaps left by unconformities in the central part of the russian platform with data from stratigraphic information from the more continuous stratigraphy of the neighboring subsiding regions such as northern siberia although these sections reflect subsidence the time scale of variations in subsidence rate is probably long relative to the duration of the stratigraphic gaps to be filled so the subsidence rate can be calculated and filtered from the stratigraphic data we thus have compiled a more complete eustatic curve than would be p ssible on the basis of russian platform stratigraphy alone relative sea level curves were generated by backstripping stratigraphic data from well and outcrop sections distributed throughout the central part of the russian platform for determining paleowater depth we developed a model specifically designed for this region based on paleoecology sedimentology geochemistry and paleogeography the curve describes a series of high frequency eustatic events superimposed on longer term trends many of the events identified from our study can be correlated to those found by haq et al 1988 and other sea level studies from other parts of the world but there are significant differences in the relative magnitudes of events because the eustatic curve resulting from this study is based on a stable reference frame the curve can be used in sedimentary basin modeling and as a tool for quantifying subsidence history from the stratigraphy of passive margins basins and other active regions

oligo miocene rotation of sardinia kar ages and paleomagnetic data of tertiary volcanics abstract conventional k ar dating was carried out on mineral separates mostly plagioclases from middle tertiary volcanics of sardinia along with paleomagnetic studies the close agreement of dates from the two methods establishes the rotation age of sardinia relative to europe within a rather short time span of 1 5 ma between 20 5 and 19 ma from correlation of our results with the geomagnetic time scale it is suggested that the rotation took place shortly after the magnetic anomaly 6

aeromagnetic constraints on the geostructural interpretation of the southern part of the sardinian rift italy abstract aeromagnetic data are interpreted to better understand the relationship between the southern part of the oligo miocene rift and the plio quaternary campidano graben on sardinia particular reference is made to the geostructural location of the campidano graben the aeromagnetic data have been interpreted by applying three different methods to the original survey data spectral analysis analytical signal and werner deconvolution the results of this study give first order estimates of the depth of the magnetic basement and position of major dykes in the study area and on the efficiency of the inversion methods used

theoretical constraints on true polar wander 1 for the present geologic epoch true polar wander tpw is relatively small but simple theoretical considerations suggest that it could have been larger in other epochs in this work we use scaling arguments to assess the qualitative behavior of tpw and a simple maxwell model to analytically describe how changes in mass anomalies translate into tpw unlike previous work we derive simple analytical estimates of tpw based on the characteristic amplitudes and timescales for changes in the moment of inertia we find estimates for both the amplitude and speed of tpw as a function of earth properties the following four main factors influence how large the maximum tpw can be the geological timescale over which the desired tpw occurs tpw the viscosity structure of the mantle which yields a weighted average viscosity the characteristic amplitude of the nonhydrostatic changes in the moment of inertia c and the added moment of inertia due to the equatorial bulge c a for the nominal values 3 1022 pa s and c c a 0 003 the maximum tpw is 61 over 100 myr and 8 over 10 myr the maximum tpw speed is only sensitive to c and c a and is 2 4 myr 1 for the nominal values tpw is shown to act as a low pass filter rapid changes in moment of inertia produce smaller and delayed tpw a consequence of this is that inertial interchange tpw does not have a different character than tpw tpw can have an important contribution to plate motions over relatively long timescales but not over shorter timescales our simple approach allows us to assess whether multiple tpw events are possible but the major uncertainty continues to be the mantle viscosity structure

late cretaceous apparent polar wander of the pacific plate evidence for a rapid shift of the pacific hotspots with respect to the spin axis paleomagnetic data from the pacific plate show that the average azimuth of the pacific plate decreased by 12 between 90 ma and 81 ma whereas trends of late cretaceous seamount chains suggest that the pacific plate moved northwestward relative to the hotspots with little change in azimuth during the same time interval this difference is used to infer a 13 4 shift of the spin axis relative to the hotspots in the pacific ocean basin this shift occurred within 5 m y of the occurrence of anomalous behavior of the paleomagnetic field recorded in anomalies 33 and 34 this coincidence in timing suggests there may be a causal link between these three phenomena

landslide susceptibility mapping using frequency ratio analytic hierarchy process logistic regression and artificial neural network methods at the inje area korea every year the republic of korea experiences numerous landslides resulting in property damage and casualties this study compared the abilities of frequency ratio fr analytic hierarchy process ahp logistic regression lr and artificial neural network ann models to produce landslide susceptibility index lsi maps for use in predicting possible landslide occurrence and limiting damage the areas under the relative operating characteristic roc curves for the fr ahp lr and ann lsi maps were 0 794 0 789 0 794 and 0 806 respectively thus the lsi maps developed by all the models had similar accuracy a cross tabulation analysis of landslide occurrence against non occurrence areas showed generally similar overall accuracies of 65 27 64 35 65 51 and 68 47 for the fr ahp lr and ann models respectively a correlation analysis between the models demonstrated that the lr and ann models had the highest correlation 0 829 whereas the fr and ahp models had the lowest correlation 0 619

m sequence geomagnetic polarity time scale mhtc12 that steadies global spreading rates and incorporates astrochronology constraints 1 geomagnetic polarity time scales gptss have been constructed by interpolating between dated marine magnetic anomalies assuming uniformly varying spreading rates a strategy to obtain an optimal gpts is to minimize spreading rate fluctuations in many ridge systems however this has been possible only for a few spreading centers we describe here a monte carlo sampling method that overcomes this limitation and improves gpts accuracy by incorporating information on polarity chron durations estimated from astrochronology the sampling generates a large ensemble of gptss that simultaneously agree with radiometric age constraints minimize the global variation in spreading rates and fit polarity chron durations estimated by astrochronology a key feature is the inclusion and propagation of data uncertainties which weigh how each piece of information affects the resulting time scale the average of the sampled ensemble gives a reference gpts and the variance of the ensemble measures the time scale uncertainty we apply the method to construct mhtc12 an improved version of the m sequence gpts late jurassic early cretaceous 160 120 ma this gpts minimizes the variation in spreading rates in a global data set of magnetic lineations from the western pacific north atlantic and indian ocean nw of australia and it also accounts for the duration of five polarity chrons established from astrochronology cm0r through cm3r this gpts can be updated by repeating the monte carlo sampling with additional data that may become available in the future

upwelling plumes superswells and true polar wander summary the geological evolution of the rotational axis of the earth is most likely controlled by internal mass redistribution within the mantle palaeomagnetic observations suggest that it is episodic in nature with periods of quasi standstill alternating with periods of faster wander here we investigate two models for the influence of mantle plumes that vary at different spatial wavelengths on the time variations of the rotational axis true polar wander tpw in the first model we represent an upwelling plume as a sphere whose radius varies as a function of the flux of material in the conduit and that traverses the mantle at the stokes velocity such a plume produces very little wander of the rotational axis we then study the effects of two superswells that mimic the ones observed with seismic tomography and conclude that a doming regime within the mantle involves significant polar wander some of the features of this tpw that are directly linked to the periodicity of doming are reminiscent of observed phases of slow and fast tpw with similar peak velocities

intra oceanic subduction shaped the assembly of cordilleran north america the western quarter of north america consists of accreted terranes crustal blocks added over the past 200 million years but the reason for this is unclear the widely accepted explanation posits that the oceanic farallon plate acted as a conveyor belt sweeping terranes into the continental margin while subducting under it here we show that this hypothesis which fails to explain many terrane complexities is also inconsistent with new tomographic images of lower mantle slabs and with their locations relative to plate reconstructions we offer a reinterpretation of north american palaeogeography and test it quantitatively collision events are clearly recorded by slab geometry and can be time calibrated and reconciled with plate reconstructions and surface geology the seas west of cretaceous north america must have resembled today s western pacific strung with island arcs all proto pacific plates initially subducted into almost stationary intra oceanic trenches and accumulated below as massive vertical slab walls above the slabs long lived volcanic archipelagos and subduction complexes grew crustal accretion occurred when north america overrode the archipelagos causing major episodes of cordilleran mountain building a new explanation for the origin of the accreted terranes that form the mountainous cordillera of western north america is proposed and tested stationary intra oceanic subduction deposited massive slab walls in the mantle and grew volcanic archipelagos at the surface which were overridden by and accreted to north america during cretaceous times the generally accepted account of how the geology of western north america developed involves the oceanic farallon plate acting as a conveyor belt sweeping crustal terranes onto the continental margin as it moves beneath the north american plate this model fails to explain many aspects of this accreted terrane and here karin sigloch and mitchell mihalynuk present an alternative model based on new tomographic images of lower mantle slabs and modelling of deep mantle structure in the region they propose that during the cretaceous period there were a series of island arcs west of north america beneath which proto pacific plates subducted into almost stationary trenches long lived volcanic archipelagos and subduction complexes grew above the slabs and then accreted onto north america as it overrode the archipelagos causing episodes of cordilleran mountain building

landslide susceptibility mapping using index of entropy and conditional probability models in gis safarood basin iran abstract landslide susceptibility mapping is essential for land use planning and decision making especially in the mountainous areas the main objective of this study is to produce landslide susceptibility maps at safarood basin iran using two statistical models such as an index of entropy and conditional probability and to compare the obtained results at the first stage landslide locations were identified in the study area by interpretation of aerial photographs and from field investigations of the 153 landslides identified 105 70 locations were used for the landslide susceptibility maps while the remaining 48 30 cases were used for the model validation the landslide conditioning factors such as slope degree slope aspect altitude lithology distance to faults distance to rivers distance to roads topographic wetness index twi stream power index spi slope length ls land use and plan curvature were extracted from the spatial database using these factors landslide susceptibility and weights of each factor were analyzed by index of entropy and conditional probability models finally the roc receiver operating characteristic curves for landslide susceptibility maps were drawn and the areas under the curve auc were calculated the verification results showed that the index of entropy model auc 86 08 performed slightly better than conditional probability auc 82 75 model the produced susceptibility maps can be useful for general land use planning in the safarood basin iran

rock mass characterization by fractal dimension fractal theory is used in the present study to develop a more reliable method for rock mass characterization field studies have been carried out in opencast mines of dolomite limestone fluorite sandstone and shale in coalmines fractal dimension of blasted fragments dfrag and in situ rock blocks din situ is calculated using size distribution curves according to schumann s model based on the co relation between uniaxial compressive strength ucs and dfrag it is observed that change in fractal dimension is nominal beyond the ucs value of 20 from the co relation between bieniawaski s rock mass rating rmr and din situ it is found that there is a sharp increase in fractal dimension for rmr greater than 40 co relation between rmr and dfrag din situ shows that as rmr increases dfrag din situ ratio decreases rock mass classification based on fractal geometry is suggested

landslide susceptibility assessment in the izmir west anatolia turkey city center and its near vicinity by the logistic regression method a landslide susceptibility assessment for izmir city western turkey which is the third biggest city of turkey was performed by a logistic regression method a database of landslide characteristics was prepared using detailed field surveys the major landslides in the study area are generally observed in the field dominated by weathered volcanics and 39 63 of the total landslide area is in this unit the parameters of lithology slope gradient slope aspect distance to drainage distance to roads and distance to fault lines were used as variables in the logistic regression analysis the effect of each parameter on landslide occurrence was assessed from the corresponding coefficients that appear in the logistic regression function on the basis of the obtained coefficients lithology plays the most important role in determining landslide occurrence and distribution slope gradient has a more significant effect than the other geomorphological parameters such as slope aspect and distance to drainage using a predicted map of probability the study area was classified into five categories of landslide susceptibility very low low moderate high and very high whereas 49 65 of the total study area has very low susceptibility very high susceptibility zones make up 11 69 of the area

tectonic evolution of the northern pacific plate and pacific farallon izanagi triple junction in the late jurassic and early cretaceous m21 m10 abstract magnetic lineations in the northwestern pacific near the shatsky plateau were interpreted to trace the tectonic history of the northern pacific plate from the time of anomalies m21 to m10 at m22 time the pacific farallon izanagi p f i triple junction was located southwest of the plateau and migrating north northwest with respect to the pacific plate shortly thereafter the stress field acting on the three plates changed significantly and the pacific lzanagi ridge reacted by pivoting 24 clockwise from m21 to m19 time several ridge propagation events occurred while the ridge adjusted to the new spreading regime to the east of the m22 location of the junction it appears that this reorganization triggered a series of at least three ridge jumps along the pacific farallon ridge the geometry of magnetic isochron m21 suggests that several triple junctions existed simultaneously during the reorganization bordering one or more microplates differences in the spreading rate of the japanese magnetic lineations north of the plateau imply that one microplate which we call the shatsky microplate existed until about m15 m13 time it was probably captured by either the farallon or the izanagi plate and subsequently destroyed by subduction after m15 the p f i triple junction was reformed on seafloor that is now beneath the shatsky plateau the junction drifted generally northeast either in a ridge ridge ridge or in a ridge fault fault configuration perhaps alternating between the two from m11 m10 time the stress field on the three plates changed again and the pacific farallon ridge southeast of the plateau reoriented 15 clockwise at this time the p f i junction assumed a ridge ridge ridge geometry at the northeast end of the plateau

role of ocean continent contrast and continental keels on plate motion net rotation of lithosphere and the geoid three dimensional spherical shell models of mantle convection have been formulated to investigate the effects of ocean continent contrast i e different viscosity for continental and oceanic lithospheres and continental keels on plate motion net rotation of lithosphere i e degree 1 toroidal plate motion and the geoid the models include relatively realistic plate rheology i e strong plate interiors and weak plate margins and continental keel structure based on seismic models the mantle flow in the models is driven by slab buoyancy the models demonstrate that the ocean continent contrast and continental keels have minor effects on the long wavelength geoid for degrees 2 5 however continental keels overriding subducted slabs for example in north america can produce large negative gravity anomalies at a regional scale this may have important implications to interpreting the gravity anomalies in north america our models show that when plates bounded by weak plate margins have the same thickness neither weak plate margins nor the ocean continent contrast efficiently excite net rotation of lithosphere although they excite toroidal motion at higher harmonic degrees however plate thickness variations like continental keels excite the net rotation in spite of their ability to excite the net rotation continental keels as thick as 300 km cannot provide the necessary coupling to the deep mantle to produce the observed net rotation of lithosphere and slow continental motion if there is a weak asthenosphere underlying them if the thermomechanic structure of north american continental upper mantle derived from seismic and heat flow studies is representative our models suggest that the temperature and pressure dependent mantle rheology may not produce sufficiently high viscosity below continental keels that is needed to explain the observed plate motion our study hints the necessity to include more realistic treatment of plate boundaries in future studies to assess possible effects of plate plate coupling on plate motion

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 jurassic early cretaceous closure of the mongol okhotsk ocean demonstrated by new mesozoic palaeomagnetic results from the trans baikal area se siberia summary we present new palaeomagnetic results from the transba ikal area se siberia from the mongol okhotsk suture zone the boundary between the amuria and siberia blocks in order to better constrain the time of closure of the mongol okhotsk ocean in the mesozoic we col lected 532 rock samples at 68 sites in six localities of basalts trachy basalts and andesites from both sides of the mongol okhotsk suture at unda river j 3 51 7 n 117 4 e kremljevka peak k1 51 8 n 117 5 e and torey lakes k 1 50 1 n 115 9 e on the southern side of the suture and at monostoy river j 1 51 1 n 106 8 e ingoda river k 1 51 2 n 112 2 e and bichura town k 1 50 6 n 107 6 e on the northern side progressive thermal demagnetization enabled us to resolve low ltc and high htc temperature components of magnetization at most sites jurassic palaeopoles computed from the htcs show a large discrepancy with respect to the apparent polar wander path of eurasia which we interpret in terms of 1700 2700 km of post late jurassic northward movement of amuria with respect to siberia although ge ological data suggest a middle jurassic closure of the mongol okhotsk ocean in the west trans baikal region our data give evidence of a large remaining palaeolatitude difference between the amuria and siberia blocks in contrast early cretaceous sites cluster remarkably well along a small circle which is centred on the average site location this implies the absence of post early cretaceous northward motion of amuria relative to siberia and demonstrates the pre early cretaceous closure of the mongol okhotsk ocean finally we interpret the very large tectonic rotations about local vertical axes evidenced by the small circle distribution of poles as arising both from collision processes and from left lateral shear movement along the suture zone due to the eastward extrusion of amuria under the effect of the collision of india into asia

time dependent subduction dynamics driven by the instability of stagnant slabs in the transition zone abstract seismic tomographic images indicate that subducted slabs are commonly deflected within the transition zone and that accumulated slab material may be subject to localized flux into the lower mantle these observations are consistent with numerical models of mantle flow in which slab flux through phase transition at 660 km depth is impeded by the combination of rheological contrast and thermodynamic effects we use a suite of 2d numerical experiments to explore the impact of slab avalanches on plate boundary dynamics the experiments are initiated at the onset of the avalanche and two distinct classes of model geometry are considered in the first the stagnant deflected slab within the transition zone is connected to subduction at the surface of the model domain in this case we find that the location of the avalanche relative to the trench governs whether the slab dip steepens or shallows in response to the instability at 660 km depth these experiments show a relatively modest impact on plate dynamics at the surface in the second class of models the stagnant slab material is not connected to the shallow subduction and the former is interpreted as a remnant of either a relic subduction event or an accumulation of material from a distant zone of convergence in this case the impact on plate boundary dynamics is more profound for example when the avalanche is positioned under or forward of the island arc it drives a significant retreat of the trench in contrast an avalanche that initiates under the back arc leads to a thrusting of the island arc over the retro plate and a reversal in the polarity of subduction we test the influence of various boundary conditions on the evolution of these models and consider several different rheological parameterizations for the lithosphere and mantle the models are intended as general templates for the impact of slab avalanches however we discuss the potential connection of these results to various zones of convergence along the western pacific margin

true polar wander as a mechanism for second order sea level variations long term wander of the rotation pole can be a significant contributor to second order time scales of 100 million years sea level variations numerical predictions based on realistic viscoelastic earth models and paleomagnetically constrained polar motion yield global scale differential sea level trends that can be as large as 200 meters from the results presented here it is argued that the well documented second order cretaceous tertiary sea level cycle should be reinterpreted as some combination of a eustatic and a regionally varying rotational signal

remote sensing and gis based landslide susceptibility mapping using frequency ratio and analytical hierarchy methods in rize province ne turkey the northeast part of turkey is prone to landslides because of the climatic conditions as well as geologic and geomorphologic characteristics of the region especially frequent landslides in the rize province often result in significant damage to people and property therefore in order to mitigate the damage from landslides and help the planners in selecting suitable locations for implementing development projects especially in large areas it is necessary to scientifically assess susceptible areas in this study the frequency ratio method and the analytical hierarchy process ahp were used to produce susceptibility maps especially ahp gives best results because of allowing better structuring of various components including both objective and subjective aspects and comparing them by a logical and thorough method which involves a matrix based pairwise comparison of the contribution of different factors for landslide for this purpose lithology slope angle slope aspect land cover distance to stream drainage density and distance to road were considered as landslide causal factors for the study area the processing of multi geodata sets was carried out in a raster gis environment lithology was derived from the geological database and additional field studies slope angle slope aspect distance to stream distance to road and drainage density were invented from digital elevation models land cover was produced from remote sensing imagery in the end of study the results of the analysis were verified using actual landslide location data the validation results showed satisfactory agreement between the susceptibility map and the existing data on landslide locations

landslide susceptibility assessment what are the effects of mapping unit and mapping method landslide susceptibility assessment forms the basis of any hazard mapping which is one of the essential parts of quantitative risk mapping for the same study area different susceptibility maps can be achieved depending on the type of susceptibility mapping methods mapping unit and scale although there are various methods of obtaining susceptibility maps the efficiency and performance of each method should be evaluated in this study the effect of mapping unit and susceptibility mapping method on landslide susceptibility assessment is investigated when analyzing the effect of susceptibility mapping method logistic regression lr which is widely used in landslide susceptibility mapping and spatial regression sr which have not been used for landslide susceptibility mapping are selected the susceptibility maps with logistic and spatial regression models are obtained using two different mapping units namely slope unit based and grid based mapping units the procedure for investigation of effect of mapping unit on different susceptibility mapping methods is applied to kumluca watershed in bartin province of western black sea region turkey 18 factor maps are prepared for landslide susceptibility assessment in the study region geographic information systems and remote sensing techniques are used to create the landslide factor maps to obtain susceptibility maps and to compare the results the relative operating characteristics roc curve is used to compare the predictive abilities of each model and mapping unit and also the accuracy is evaluated depending on the observations made during field surveys by analyzing the area under the roc curve for grid based and slope unit based mapping units it can be concluded that sr model provide better predictive performance 0 774 in grids and 0 898 in slope units as compared to the lr model 0 744 in grids and 0 820 in slope units this result is also supported by the accuracy analysis for both mapping units the sr model provides more accurate result 0 55 for grids and 0 57 for slope units than the lr model 0 50 for grids and 0 48 for slopes the main reason for this better performance is that the spatial correlations between the mapping units are incorporated into the model in sr while this fact is not considered in lr model

cenozoic global plate motions cenozoic global plate motions relative to the hot spots are investigated and compared to plate motions in a mean lithosphere reference frame plate motions were analyzed over six time intervals divided by ages 10 25 43 48 and 56 ma chosen as much as possible to coincide with key plate reorganizations alternative motion circuits and rotational parameters were considered and evaluated with paleomagnetic data from the pacific and north american plates the circuit found to be in best agreement with the paleomagnetic data is one in which the hot spots in the atlantic region are assumed to be fixed relative to the hot spots in the pacific region throughout the cenozoic the hot spot and mean lithosphere reference frames have been in continual slow relative motion the rate of motion is nonuniform however most of the motion having occurred during the middle cenozoic the net cenozoic rotation of the lithosphere relative to the hot spots is described by a right handed rotation of 7 about a euler pole at 46 s 87 e which yields a 5 displacement of the north poles of the two reference frames this motion is small enough that inferences drawn about plate speeds in one reference frame should be valid in the other analysis of the global motions resulting from our preferred model showed that many characteristics of current plate motions have persisted throughout the cenozoic plate speeds correlate with latitude plates moving faster near the equator than near the poles throughout the cenozoic as at present continental plates except for the indian plate moved slower than oceanic plates throughout the cenozoic even the structure of the velocity fields as revealed in a contour of root mean square velocities in equatorial bands persists throughout the cenozoic the migration of the paleomagnetic axis over time is also compared to the hot spot and mean lithosphere reference frames the paleomagnetic axis has shifted 5 10 relative to the hot spot frame and a lesser amount relative to the mean lithosphere frame

fast mapping of magnetic basement depth structure and nature using aeromagnetic and gravity data combined methods and their application in the paris basin assessment of deep buried basin basement relationships using geophysical data is a challenge for the energy and mining industries as well as for geothermal or co2 storage purposes in deep environments few methods can provide geological information magnetic and gravity data remain among the most informative and cost effective methods here in order to derive fast first order information on the basement basin interface we propose a combination of existing and original approaches devoted to potential field data analysis namely we investigate the geometry i e depth and structure and the nature of a deep buried basement through a case study sw of the paris basin joint processing of new high resolution magnetic data and up to date gravity data provides an updated overview of the deep basin first the main structures of the magnetic basement are highlighted using euler deconvolution and are interpreted in a structural sketch map the new high resolution aeromagnetic map actually offers a continuous view of regional basement structures and reveals poorly known and complex deformation at the junction between major domains of the variscan collision belt second werner deconvolution and an ad hoc post processing analysis allow the extraction of a set of magnetic sources at or close to the basin basement interface interpolation of these sources together with the magnetic structural sketch provides a werner magnetic basement map displaying realistic 3d patterns and basement depths consistent with data available in deep petroleum boreholes the last step of processing was designed as a way to quickly combine gravity and magnetic information and to simply visualize first order petrophysical patterns of the basement lithology this is achieved through unsupervised classification of suitably selected gravity and magnetic maps and as compared to previous work provides a realistic and updated overview of the cartographic distribution of density magnetization of basement rocks altogether the three steps of processing proposed in this paper quickly provide relevant information on a deep buried basement in terms of structure geometry and nature through petrophysics notwithstanding limitations of the proposed procedure are raised in the case of the paris basin for instance this study does not provide proper information on pre mesozoic basins some of which have been sampled in deep boreholes

pleistocene deglaciation and the earth s rotation a new analysis summary this paper is concerned with an analysis of the effect of the pleistocene glacial cycle upon the earth s rotation we demonstrate that two important geophysical observables may be explained as aspects of the rotational response to surface mass loading by ice sheets these are the astronomically observed non tidal component of the acceleration of planetary rotation and the secular drift of the rotation pole relative to the surface geography which is evident in the ils pole path the former observation is shown to provide an unambiguous constraint upon the viscosity of the planetary mantle and requires a depth dependence of this parameter which is the same as that which has previously been inferred in studies of the relative sea level variations and free air gravity anomalies associated with post glacial rebound the observed secular drift of the pole cannot provide an independent estimate of the viscosity of the mantle because it depends jointly upon mantle viscosity and lithospheric thickness with the viscosity profile fixed by the rebound data the observed speed of polar wander suggests a continental lithospheric thickness which is in excess of that appropriate for old ocean basins but nevertheless in accord with independent constraints

new paleomagnetic pole for the upper jurassic chon aike formation of southern argentina south america testing the tectonic stability of patagonia with respect to south america and implications to middle jurassic early cretaceous true polar wander abstract a paleomagnetic pole and a new ar ar date of 156 08 0 05 ma are reported for the chon aike formation an extensive plateau of ignimbrites outcropping in the deseado massif southern patagonia argentina the geographic coordinates and statistical parameters for the paleomagnetic pole validated by a reversal test are lat 84 3 s long 191 3 e a95 8 6 k 13 3 n 23 this pole shows a complete coherence with late jurassic and early to mid cretaceous poles of south america obtained exclusively from igneous rocks avoiding any potential inclination shallowing it is suggested that a southern patagonia was an integral part of south america in the late jurassic b any reported vertical axis tectonic rotations must pre date the late jurassic in this region c according to updated paleomagnetic data from igneous rocks south america had very limited latitudinal drift between about 160 and 140 ma and therefore d its apparent polar wander apw path when compared with global apparent polar wander paths does not support a large global shift or true polar wander tpw between 160 and 140 ma

revised pacific m anomaly geomagnetic polarity timescale summary the current m anomaly geomagnetic polarity timescale gpts is mainly based on the hawaiian magnetic lineations in the pacific ocean m anomaly gpts studies to date have relied on a small number of magnetic profiles a situation that is not ideal because any one profile contains an uncertain amount of geologic noise that perturbs the magnetic field signal compiling a polarity sequence from a larger array of magnetic profiles is desirable to provide greater consistency and repeatability we present a new compilation of the m anomaly gpts constructed from polarity models derived from magnetic profiles crossing the three lineation sets hawaiian japanese and phoenix in the western pacific polarity reversal boundary locations were estimated with a combination of inverse and forward modelling of the magnetic profiles separate gpts were established for each of the three pacific lineation sets to allow examination of variability among the different lineation sets and these were also combined to give a composite timescale owing to a paucity of reliable direct dates of the m anomalies on ocean crust the composite model was time calibrated with only two ages one at each end of the sequence these two dates are 125 0 ma for the base of m0r and 155 7 ma for the base of m26r relative polarity block widths from the three lineation sets are similar indicating a consistent pacific wide spreading regime the new gpts model shows slightly different spacings of polarity blocks as compared with previous gpts with less variation in block width it appears that the greater polarity chron irregularity in older models is mostly an artifact of modelling a small number of magnetic profiles the greater averaging of polarity chron boundaries in our model gives a gpts that is statistically more robust than prior gpts models and a superior foundation for late jurassic early cretaceous geomagnetic and chronologic studies

assessment of fractal dimension and geometrical characteristics of the landslides identified in north of tehran iran the aim of the presented study is to assess the fractal dimension d and the geometrical characteristics length and width of the landslides identified in north of tehran iran at first the landslide locations 528 landslides were identified by interpretation of aerial photographs satellite images and field surveys and then to calculate the fractal dimension d we used the computer programming named as fracek in the next step geometrical characteristics of each landslide such as length l and width w were calculated by arcgis software the landslide polygons were digitized from the mentioned landslide inventory map and rotated based on movement direction the fractal dimension for all landslides varied between 1 665 and 1 968 subsequently the relationship between the length width ratios and theirs fractal d values for 528 landslides was calculated the results showed that correlation coefficients r which are different regression models such as exponential linear logarithmic polynomial and power between d and l w ratio are relatively high respectively 0 75 0 75 0 76 0 78 and 0 75 it can be concluded that the fractal dimension values and geometry characteristics of landslides would be useful indices for the management of hazardous areas susceptible slopes land use planning and landslide hazard mitigation

global plate motion frames toward a unified model 1 plate tectonics constitutes our primary framework for understanding how the earth works over geological timescales high resolution mapping of relative plate motions based on marine geophysical data has followed the discovery of geomagnetic reversals mid ocean ridges transform faults and seafloor spreading cementing the plate tectonic paradigm however so called absolute plate motions describing how the fragments of the outer shell of the earth have moved relative to a reference system such as the earth s mantle are still poorly understood accurate absolute plate motion models are essential surface boundary conditions for mantle convection models as well as for understanding past ocean circulation and climate as continent ocean distributions change with time a fundamental problem with deciphering absolute plate motions is that the earth s rotation axis and the averaged magnetic dipole axis are not necessarily fixed to the mantle reference system absolute plate motion models based on volcanic hot spot tracks are largely confined to the last 130 ma and ideally would require knowledge about the motions within the convecting mantle in contrast models based on paleomagnetic data reflect plate motion relative to the magnetic dipole axis for most of earth s history but cannot provide paleolongitudes because of the axial symmetry of the earth s magnetic dipole field we analyze four different reference frames paleomagnetic african fixed hot spot african moving hot spot and global moving hot spot discuss their uncertainties and develop a unifying approach for connecting a hot spot track system and a paleomagnetic absolute plate reference system into a hybrid model for the time period from the assembly of pangea 320 ma to the present for the last 100 ma we use a moving hot spot reference frame that takes mantle convection into account and we connect this to a pre 100 ma global paleomagnetic frame adjusted 5 in longitude to smooth the reference frame transition using plate driving force arguments and the mapping of reconstructed large igneous provinces to core mantle boundary topography we argue that continental paleolongitudes can be constrained with reasonable confidence

landslide susceptibility mapping for ayvalik western turkey and its vicinity by multicriteria decision analysis this paper presents the results of geographical information system gis based landslide susceptibility mapping in ayvalik western turkey using multi criteria decision analysis the methodology followed in the study includes data production standardization and analysis stages a landslide inventory of the study area was compiled from aerial photographs satellite image interpretations and detailed field surveys in total 45 landslides were recorded and mapped the areal extent of the landslides is 1 75 km2 the identified landslides are mostly shallow seated and generally exhibit progressive character they are mainly classified as rotational planar and toppling failures in all 51 45 and 4 of the landslides mapped are rotational planar and toppling types respectively morphological geological and land use data were produced using existing topographical and relevant thematic maps in a gis framework the considered landslide conditioning parameters were slope gradient slope aspect lithology weathering state of the rocks stream power index topographical wetness index distance from drainage lineament density and land cover and vegetation density these landslide parameters were standardized in a common data scale by fuzzy membership functions then the degree to which each parameter contributed to landslides was determined using the analytical hierarchy process method and the weight values of these parameters were calculated the weight values obtained were assigned to the corresponding parameters and then the weighted parameters were combined to produce a landslide susceptibility map the results obtained from the susceptibility map were evaluated with the landslide location data to assess the reliability of the map based on the findings obtained in this study it was found that 5 19 of the total area was prone to landsliding due to the existence of highly and completely weathered lithologic units and due to the adverse effects of topography and improper land use

plate motions crustal and lithospheric mobility and paleomagnetism prospective viewpoint the shift in viewpoint from a static to a mobilistic solid earth as brought about by paleomagnetism opened many new directions of research that continue to be exciting today and hold prospects for an exciting future here five topics of current research on earth s mobilistic surface are reviewed and their future directions discussed first dividing earth s solid surface into two domains 1 nearly rigid plate interiors and 2 plate boundaries some of them very wide leads to a review and discussion of the kinematics of wide plate boundaries many more adjustable parameters will be needed to describe the complex kinematics of plate boundaries which cover 15 of earth surface than the few dozen parameters needed to describe the kinematics of plate interiors which cover 85 of earth s surface second the question of the degree of rigidity of plate interiors is discussed the integral of the velocity gradient across plates interiors is at least a few hundredths or tenths of millimeters per year and in several well determined cases less than 2 or 3 mm yr future investigations will no doubt be aimed at narrowing these limits and to expanding the area of earth s surface over which limits are known third space geodetic data mainly from very long baseline inter ferometry satellite laser ranging and the global positioning system have demonstrated a remarkable similarity of velocities of stable plate interiors averaged over a few to a dozen years with plate velocities averaged over a few million years already however significant differences of a few millimeters per year are emerging and the tectonic and dynamic significance of these differences need to be evaluated fourth despite more than two decades of investigation the question of how fast hotspots move relative to one another is still a contentious issue one group of researchers maintains that maximum speeds are 3 mm yr whereas another maintains that speeds are 10 20 mm yr or more the differences cannot be reconciled until the uncertainties in plate reconstructions relative to hotspots are systematically and properly incorporated into analyses of hotspot motion fifth paleomagnetists have estimated true polar wander over the past 200 myr by equating it with the apparent polar wander of hotspots however the possible motion among hotspots and the neglect of the uncertainties in reconstructions relative to the hotspots have left these analyses unconvincing further progress requires the incorporation of these uncertainties a possible exception is the apparent polar wander of the hotspots over the past 10 20 myr or less which requires only small adjustments for plate motion and has presumably smaller uncertainties due to plate reconstructions the cause of this apparently significant geologically recent shift of the pole is poorly understood compared with the rate and direction of the secular shift of the pole observed this century from the international latitude service and for 1976 to 1994 from space geodetic data the paleomagnetically observed shift is unlikely to be due to the removal of northern hemisphere midlatitude ice sheets which is the commonly accepted explanation for the shift observed over the past century i speculate instead that the apparently rapid uplift of the tibetan plateau sometime during the past 10 20 myr is at least partly responsible for the geologically recent shift of the pole finally i conclude that the theory of plate tectonics has provided a framework that leads naturally to further quantification of the kinematics and deformation of earth s solid surface chiefly because of the key assumption of the rigidity of plate interiors which permits specific predictions to be made this revolution in quantification still has far to go and holds exciting prospects for future tectonic studies

paleointensity results from the jurassic new constraints from submarine basaltic glasses of odp site 801c 1 tholeiite of the oldest oceanic crust was drilled during odp legs 129 and 185 at hole 801c in the western pacific fresh appearing submarine basaltic glass sbg was recovered from the tholeiites 167 ma which has been shown to be nearly ideal for determining absolute paleointensity paleointensities of the younger off axis alkalic basalts 160 ma overlying the tholeiites had been studied earlier here we report results from the older tholeiitic on axis sequence we subjected a total of 73 specimens from 17 cooling units to absolute paleointensity experiments of these 30 specimens and six cooling unit averages met our strictest reliability criteria yielding an average of 11 9 3 9 t the bulk of evidence suggests a paleolatitude of the site of 14 s with an uncertainty of 10 this translates the intensity to a value for the virtual axial dipole moment of 28 zam2 slightly lower than values determined from the plagioclase crystals in the three cooling units of the younger alkalic basalts overlying the tholeiites tarduno cottrell 2005 our value is low when compared to the long term median value of the field of 42 zam2 our results and those of the published literature therefore support the contention of a low magnetic field strength in the jurassic average of 28 14 zam2 n 138 individual estimates as initially suggested by prevot et al 1990 our interpretation of the body of available data argue for low field strengths for the entire jurassic extending into the early cretaceous

pacific microplate and the pangea supercontinent in the early to middle jurassic new biostratigraphic data based on radiolarians recovered from deep within the oceanic crustal section of ocean drilling program hole 801c in the western pacific along with existing radiometric information date this oceanic crust as late bajocian early bathonian 170 165 ma the overlying basal sediments at hole 801c are essentially identical in age middle bathonian 164 162 ma to the basal sediments at deep sea drilling program hole 534a in the central atlantic we estimate the time of formation of the pacific plate as 175 170 ma and the time of initial separation of the pangea supercontinent in the central atlantic as 190 180 ma we also identify a time of extensive subduction zone magmatism 175 159 ma at the eastern and western edges of pangea we suggest that the initial plate separation of pangea increased subduction rates at its outer margins and altered the plate boundaries in the pacific superocean leading to formation of the pacific plate

late cretaceous true polar wander not so fast using recalculated paleopoles from seamount anomaly modeling sam sager and koppers 1 1 proposed an episode of rapid late cretaceous true polar wander tpw a critical review of the data used however suggests that sager and koppers have underestimated the effects that errors and data