new global marine gravity model from cryosat 2 and jason 1 reveals buried tectonic structure gravity models are powerful tools for mapping tectonic structures especially in the deep ocean basins where the topography remains unmapped by ships or is buried by thick sediment we combined new radar altimeter measurements from satellites cryosat 2 and jason 1 with existing data to construct a global marine gravity model that is two times more accurate than previous models we found an extinct spreading ridge in the gulf of mexico a major propagating rift in the south atlantic ocean abyssal hill fabric on slow spreading ridges and thousands of previously uncharted seamounts these discoveries allow us to understand regional tectonic processes and highlight the importance of satellite derived gravity models as one of the primary tools for the investigation of remote ocean basins

late pleistocene extension and strike slip in the dead sea basin a newly discovered active small scale pull apart mor structure located in the western part of the dead sea basin shows recent basin parallel extension and strike slip faulting and offers a rare view of pull apart internal structure the mor structure is bounded by n s trending strike slip faults and cross cut by low angle e w trending normal faults the geometry of this pull apart suggests that displacement between the two stepped n s strike slip faults of the mor structure is transferred by the extension associated with the normal faults the continuing deformation in this structure is evident by the observation of at least three deformation episodes between 50 ka and present the calculated sinistral slip rate is 3 5 mm yr over the last 30 000 years this slip rate indicates that the mor structure overlies the currently most active strike slip fault within the western border of the dead sea pull apart the mor structure is an example of a small pull apart basin developed within a larger pull apart this type of hierarchy in pull apart structures is an indication for their ongoing evolution

magmatic history of red sea rifting perspective from the central saudi arabian coastal plain a newly recognized tertiary dike complex and comagmatic volcanic rocks exposed on the central saudi arabian coastal plain record early stages of magmatism related to red sea rifting intrusive and stratigraphic relationships and new potassium argon dating indicate episodic magmatism from about 30 ma to the present additional stratigraphic and radiometric evidence suggests that limited rift related magmatism began as early as about 50 ma an early phase of crustal extension in the region was accompanied by faulting and graben formation and by dike swarm intrusion the style of extension and intrusion changed at 20 ma localized volcanism and sheeted dike injection ceased and were replaced by the intrusion of thick gabbro dikes this change may mark the onset of sea floor spreading in the central red sea the dikes and volcanic rocks consist of a bimodal mafic felsic suite with transitional subalkaline to alkaline chemistry although no unique petrogenetic model can be developed for the suite the following observations and conclusions have been drawn from the available reconnaissance geochemistry 1 strontium isotopic initial ratios overlap in the range 0 7031 to 0 7047 and are not clearly related to alkalinity or silica content the bimodality and alkalinity of the suite are therefore not products of contamination by the radiogenic precambrian upper crustal granitic rocks exposed in the region 2 several of the evolved rocks rhyolites and comendite show large to extreme negative europium anomalies and heavy rare earth element hree enrichment features that cannot be explained by low pressure crystal fractionation of potential parent magmas an intriguing possibility is that hree enrichments and large negative eu anomalies of some peraluminous rhyolites and granites may result from the complete melting of garnet from middle or lower crustal rocks 3 most of the basalts are light rare earth element lree enriched consistent with derivation from fertile mantle in a continental rift setting however interaction of the mafic melts with lower continental crust cannot be ruled out a model of poly baric mantle melt derivation producing several alkaline subalkaline cycles best explains magmatism in the red sea region differences in the depths and dynamics of mantle melt extraction and transport brought about through changes in crust and mantle structure as the rift and paar developed may account for the transition from mixed alkaline subalkaline bimodal magmatism of the pre 20 ma rift basin to exclusively subalkaline tholeiitic magmatism at the red sea spreading axis and to predominantly alkali basalt volcanism inland within the arabian shield

contrasted styles of rifting in the eastern gulf of aden a combined wide angle multichannel seismic and heat flow survey continental rifts and passive continental margins show fundamental along axis segmentation patterns that have been attributed to one or a number of different processes extensional fault geometry variable stretching along strike preexisting lithospheric compositional and structural heterogeneities oblique rifting and the presence or absence of eruptive volcanic centers the length and width scales of the rift stage fault bounded basin systems change during the late evolution of the new plate boundary and the role of magmatism may increase as rifting progresses to continental rupture along obliquely spreading ridges first order mid ocean ridge geometries originate during the synrift stage indicating an intimate relationship between magma production and transform fault spacing and location the gulf of aden rift is a young ocean basin in which the earliest synrift to breakup structures are well exposed onshore and covered by thin sediment layers offshore this obliquely spreading rift is considered magma poor and has several large offset transforms that originated during late stage rifting and control the first order axial segmentation of the spreading ridge widely spaced geophysical transects of passive margins that produce only isolated 2 d images of crust and uppermost mantle structure are inadequate for evaluation of competing rift evolution models using closely spaced new geophysical and geological observations from the gulf of aden we show that rift sectors between transforms have a large internal variability over short distances 10 km the ocean continent transition oct evolves from a narrow magmatic transition to wider zones where continental mantle is probably exhumed we suggest that this small scale variability may be explained 1 by the distribution of volcanism and 2 by the along strike differences in time averaged extension rate of the oblique rift system the volcanism may be associated with 1 the long offset alula fartak fracture zone which may enhance magma production on its younger side or 2 channeled flow from the afar plume material along the newly formed oct and the spreading ridge oblique extension and or hot spot interactions may thereby have a significant control on the styles of rifting and continental breakup and on the evolution of many magma poor margins

angular velocities of nubia and somalia from continuous gps data implications on present day relative kinematics abstract this study focuses on the break up of the african tectonic plate into separate nubian and somalian blocks based on recent global positioning system gps data a new unique velocity field has been obtained by processing all available observations of permanent gps stations on africa since 1996 the quantity and distribution of the stations and the length of the time series of observations exceed that of previous studies by a considerable margin allowing one to derive a reliable estimate of the differential motion between the nubia and somalian plates which are considered as a single african block in the prevailing global tectonic plate models the estimated relative pole of rotation of somalia with respect to nubia is located at 54 8 s 37 0 e with magnitude 0 069 ma implying distinct opening in the ethiopian rift of magnitude 7 mm year and azimuth n94 e whereas in southeastern south africa this value is reduced to 2 mm year in almost the same direction this is in accordance with some of the independent geological and geophysical tectonic models of the nubia somalia plate boundary region however the spatial density of the current tracking network is still not optimal to establish the exact location of the entire somalia nubia plate boundary in particular the possible branch east of lake victoria and heading towards the mozambique channel is impossible to confirm or reject at this moment

propagating rifts and continental breakup a simple quantitative model is proposed whereby continental breakup starts with a phase of continental rifting and continues with the propagation of rifts toward locked zones these zones are deformed in the rifting process while oceanic crust is generated in the wake of the rift tip the deformed zones will cause overlaps when a continental reassembly is attempted the model accounts for the shape and distribution of magnetic quiet zones at ocean continent boundaries and for the detailed geometry of some v shaped zones of oceanic magnetic anomalies the former provide an estimate of the scale at which the hypothesis of rigid plates fails and the latter are used to measure the velocity of rift propagation illustrations are provided for present rifting in the red sea and gulf of aden and for early rifting of the south atlantic and breakup of pangea

3d vsp migration by image point transform the common characteristic of the seismic methods involving downhole measurements is the difficulty of designing surveys able to image the subsurface space evenly migration schemes for these layouts are sensitive to reconstruction artifacts the defining property of the image point ip transform is its ability to accumulate amplitudes of curved reflection events appearing in time distance profiles into approximately discoidal or spherical in three dimensions vicinities in the ip domain due to the reflected wavefields collapsing into such vicinities in the ip domain the emphasizing of the reflectors consists of enhancing regions with higher amounts of accumulated amplitude true dip filtering can also easily be performed even for reflectors appearinginthetime distanceprofilesascurvedeventsduetotheirdip source offset or variable velocity field reflecting interfaces are definedassetsoflinkedpiecewiseplanar reflectorelementsrather than as collections of point diffractors true reflectors fitting this description are enhanced by the ip transform while diffraction patterns events produced by other wave types multiples and noise of any kind tend to be suppressed the inverse transformleadstofilteredversionsoftime distanceprofiles analternative to performing the inverse transform back to the original time distance representation is computing 2d 3d migrated imagesdirectlyfromthetransformedipspace althoughthe3dmigrationbyiptransformisapplicabletoanyseismicsurveygeometry we focused on procedures for enhancing prestack migrated images obtained by sparse multioffset multiazimuth vertical seismic profiling vsp surveys as typically performed for mining site characterization and mineral exploration the real data used were collected within an extensive mining seismic investigationprogramperformedincanada

seismic moment distribution summary we review possible errors in determining the size of earthquakes we propose that the size distribution can be effectively defined only for earthquake sequences not for individual earthquakes as a result of the error analysis we question the validity of many reported correlations between the 6 value and spatio temporal characteristics of tectonics and seismicity the study of the distribution of earthquake seismic moment largely avoids the influence of these errors and biases and is therefore superior to the standard analysis of the magnitude frequency law the gamma distribution is applied to describe the distribution of seismic moments of earthquake sequences this distribution which generalizes the well known gutenberg richter g r relation is characterized by two parameters we use the maximum likelihood method to determine the parameters of the gamma distribution for worldwide earthquakes in different depth ranges the empirical distribution is derived from the moment tensor catalogue compiled by the harvard group the p value for scalar seismic moment of earthquake sequences an analogue of the 6 value in the g r magnitude frequency law is close to 1 2 for all earthquakes the value predicted by a critical branching model of seismicity this result which will be improved as more seismic moment data become available provides input for modelling of seismicity based on percolation or on self organized criticality models if 3 equals 1 2 then using the critical branching model we find that most small earthquakes in available catalogues are dependent shocks i e aftershocks even among earthquakes of intermediate magnitudes the number of dependent events may exceed that of independent events

confirmation of arabia plate slow motion by new gps data in yemen 1 during the last 10 years a network of about 30 gps sites was measured in djibouti east africa additional points were also measured in yemen oman ethiopia iran and on la reunion island merged with data from the available international gps service permanent stations scattered on the different plates in the area eurasia anatolia africa arabia somalia this unique data set provides new insight on the current deformation in the africa somalia arabia triple junction area and on the arabian plate motion here we show that coherent motions of points in yemen bahrain oman and iran allow us to estimate a geodetically constrained angular velocity for the arabian plate 52 59 n 15 74 w 0 461 myr in itrf2000 this result differs significantly from earlier determinations and is based upon our vectors in yemen they provide new additional data and better geometry for angular velocity determination combined with the african and somalian motions this new angular velocity results in predicted spreading rates in the red sea and the gulf of aden which are 15 20 lower than those measured from oceanic magnetic anomalies and thus averaged over the last 3 myr with respect to eurasia the geodetic motion of arabia is also about 30 slower than predicted by nuvel 1a on the basis of the kinematic results presented here and on other evidence for a similar slower geodetic rate of the indian plate we suggest that the whole collision zone between africa arabia india on one hand and eurasia on the other hand has slowed down in the last 3 myr

global positioning system measurements of strain accumulation and slip transfer through the restraining bend along the dead sea fault system in lebanon an edited version of this paper was published in geophysical journal international by blackwell publishing blackwell publishing retains the copyright to this paper copyright 2007 see also http www blackwell synergy com doi abs 10 1111 j 1365 246x 2006 03328 x http atlas geo cornell edu deadsea publications gomez2007 gji htm

geochemistry of the late archean banting group yellowknife greenstone belt slave province canada simultaneous melting of the upper mantle and juvenile mafic crust this study investigates the geochemistry and tectonic setting of the 2 66 ga banting group the younger sequence of volcanic rocks in the yellowknife greenstone belt and its relationship to older tholeiitic volcanic rocks of the 2 72 2 70 ga kam group the banting group includes a much higher proportion of felsic volcanic and volcaniclastic rocks than the kam group but mafic to intermediate volcanic rocks are common banting basalts are tholeiitic and are melts of archean depleted upper mantle as are basalts of the kam group in contrast banting dacites and rhyolites have much lower heavy rare earth element abundances and generally have higher initial 143nd 144nd than kam felsic rocks the chemistry of the felsic rocks provides a geochemical signature to distinguish rocks of kam versus banting age where complex structures have obscured the stratigraphy whereas kam felsic rocks evolved from mafic parents by assimilation fractional crystallization processes banting felsic rocks have compositions sim

the somalia plate and the east african rift system present day kinematics summary the motion of the somalia plate relative to the nubia africa arabia and antarctica platcs is re evaluated using a new inversion method based on a monte carlo technique and a least absolute value misfit criterion a subset of the nuvel 1 data set with additional data along the levant fault and in the red sea is used the results confirm that the motion of arabia with respect to africa is significantly different from the motion relative to somalia it is further shown that the data along the sw indian ridge are compatible with a pole of relative motion between africa and somalia located close to the hypothetical diffuse triple junction between the ridge and thc east african rift the resulting africa somalia motion is then compatible with the geological structures and seismological data along the east african rift system assuming a separate somalia plate thus solves kinematic and geological problems around the afar triple junction and along the east african rift

the angular velocity of nubia relative to somalia and the location of the nubia somalia antarctica triple junction summary an ew analysis of geologically current plate motion across the southwest indian ridge swir and of the current location of the nubia antarctica somalia triple junction is presented spreading rates averaged over the past 3 2 myr are estimated from 103 well distributed nearly ridge perpendicular profiles that cross the swir all available bathymetric data are evaluated to estimate the azimuths and uncertainties of transform faults six are estimated from multibeam data and 12 from precision depth recorder pdr data if both the nubian and somalian component plates are internally rigid near the swir and if the nubia somalia boundary is narrow where it intersects the swir that intersection lies between 26 e and 32 e thus the boundary is either along the spreading ridge segment just west of the andrew bain transform fault complex abtfc or along some of the transform fault complex itself these limits are narrower than and contained within limits of 24 et o 33 e previously found by lemaux et al from an analysis of the locations of magnetic anomaly 5 the data are consistent with a narrow boundary but also consistent with a diffuse boundary as wide as 700 km the new nubia somalia pole of rotation lies 10 north of the bouvet triple junction which places it far to the southwest of southern africa the new angular velocity determined only from data along the swir indicates displacement rates of somalia relative to nubia of 3 6 0 5 mm yr 1 95 per cent confidence limits towards 176 s04 e between somalia and nubia near the swir and of 8 3 1 9 mm yr 1 95 per cent confidence limits towards 121 s59 e near afar the new nubia somalia angular velocity differs significantly from the nubia somalia angular velocity estimated from gulf of aden and red sea data this significant difference has three main alternative explanations i that the plate motion data have substantial unmodelled systematic errors ii that the nubian component plate is not a single rigid plate or iii that the somalian component plate is not a single rigid plate we tentatively prefer the third explanation given the geographical distribution of earthquakes within the african composite plate relative to the inferred location of the nubia somalia boundary along the swir

gps measurements of current crustal movements along the dead sea fault 1 a network of 11 continuous gps stations was constructed in israel between 1996 and 2001 to monitor current crustal movements across the dead sea fault dsf analysis of the gps measurements with respect to the itrf2000 reference frame yields time series of daily site positions containing both secular and seasonal variations horizontal secular variations station velocities are evaluated with respect to the main tectonic element in the region the dsf we use six velocity vectors west of the dsf to define the itrf2000 pole of the sinai sub plate and rotate the velocity field for all stations into the sinai reference frame srf the velocity vectors reveal that 1 relative station movements are less than 4 mm yr 2 the nine stations located west of the dsf show no statistically significant motion with respect to the srf and 3 the two stations located in the golan heights katz and elro and a station in damascus syria udmc show 1 7 2 8 mm yr northward motion with respect to sinai indicating a left lateral motion along the dsf using locked fault models we estimate the current slip rate across the dsf as 3 3 0 4 mm yr if we exclude the northern sites elro and udmc which are located adjacent to the compressional jog of mount hermon our estimate increases to 3 7 0 4 mm yr the calculated itrf2000 sinai eurasia and nubia poles and a published pole for arabia allow us to calculate the current relative plate motion of sinai arabia and sinai nubia

seismotectonics of the sinai subplate the eastern mediterranean region summary we define the sinai subplate from a seismotectonic perspective as a distinct component in the plate tectonics of the eastern mediterranean region this is based on the tectonic characteristics of a comprehensive listing of all ml 4 recorded seismicity in the region during the 20th century on newly calculated and recalculated fault plane mechanisms of first p wave arrivals and on published solutions based on waveform inversion of broad band data the low seismicity level and scarcity of strong events in the region required a thorough search for useful data and a careful examination of the reliability of the focal solutions we gathered all available records of first p wave onsets from the iss and isc bulletins and the local seismic networks altogether we were able to calculate 48 new focal mechanisms and 33 recalculated ones of events that occurred during the years 1940 1992 with the increasing number of teleseismic and regional broad band stations in the later years we added 37 solutions based on teleseismic and regional waveform inversions of events that occurred during 1977 2001 these mechanisms enabled us to examine the seismotectonic character of the sinai subplate the strike and rake directions of the calculated mechanisms usually reflect the geometry and the large scale type of deformation observed along the boundaries of the sinai subplate the dead sea transform the cypriot arc convergent zone and the suez rift nevertheless along each of these boundaries we found anomalous solutions that attest to the complexity of the deformation processes along plate margins earthquakes along the dead sea transform exhibit mainly sinistral transtension and transpression reflecting its leaky manner and local change in the transform geometry the presence of other unexpected mechanisms near the transform however reflects the heterogeneous deformation it induces around as expected thrust mechanisms along the cypriot arc mirror its convergent nature and typical curved geometry transtension and transpressional solutions in the eastern segment of the arc reflect the sinistral shear motion between anatolia and sinai there however shear mechanisms found between cyprus and the eratosthenes seamount pose a problem regarding its collision process most intriguing of all are ml 4 thrust and shear solutions found in the gulf of suez they are associated with predominantly normal mechanisms within a rift zone and therefore constitute a unique phenomenon yet to be deciphered

evidence for motion between nubia and somalia along the southwest indian ridge the east african rift marks the northern boundary of the nubian west african and somalian east african plates and has formed by horizontal stretching due to the separation of these plates1 south of 20 s any expression of deformation or seismicity due to the relative motion of these two distinct plates vanishes although the boundary must continue until it intersects another plate boundary the nearest such boundary is that of the antarctic plate marked by the southwest indian ridge but previous analyses of plate motion data have indicated no significant difference between nubia antarctica and somalia antarctica motion2 3 here we show using a large compilation of plate motion data that nubia antarctica motion does differ from somalia antarctica motion and we determine a relative angular velocity of the two plates that has compact confidence limits our analysis places the pole of rotation near to the southern limit of african seismicity implying that the southern part of the nubian somalian plate boundary is a diffuse zone of convergence up to 2 mm yr 1 whereas up to 6 mm yr 1 of separation is accommodated across the east african rift about half the separation rate of the slowest mid ocean ridge

late cenozoic uplift along the northern dead sea transform in lebanon and syria an edited version of this paper was published in earth and planetary science letters by elsevier science elsevier science retains the copyright to this paper copyright 2006 elsevier science see also http dx doi org 10 1016 j epsl 2005 10 029 http atlas geo cornell edu deadsea publications gomez2006 epsl htm

strain transfer between disconnected propagating rifts in afar we showed before that both the aden and red sea plate boundaries are currently rifting and propagating along two distinct paths into afar through the opening of a series of disconnected propagating rifts here we use new geochronological tectonic and paleomagnetic data that we acquired mostly in the southeastern part of afar to examine the geometry kinematics and time space evolution of faulting related to strain transfer processes it appears that transfer of strain is accommodated by a bookshelf faulting mechanism wherever rifts or plate boundaries happen to overlap without being connected this mechanism implies the rotation about a vertical axis of small rigid blocks along rift parallel faults that are shown to slip with a left lateral component which is as important as their normal component of slip rates of 2 3 mm yr by contrast where rifts do not overlap either a classic transform fault maskali or an oblique transfer zone mak arrasou kinematically connects them the length of the aden red sea overlap has increased in the last 0 9 myr as the aden plate boundary propagated northward into afar as a consequence the first order blocks that we identify within the overlap did not all rotate during the same time span nor by the same amounts similarly the major faults that bound them did not necessarily initiate and grow as their neighboring faults did despite these variations in strain distribution and kinematics the overlap kept accommodating a constant amount of strain 7 to 15 of the extension amount imposed by plate driving forces which remained distributed on a limited number seven or eight of major faults each one having slipped at constant rates 3 and 2 mm yr for vertical and lateral rates respectively the fault propagation rates and the block rotation rates that we either measure or deduce are so fast 30 130 mm yr and 15 38 myr respectively that they imply that strain transfer processes are transient as has been shown to be the case for the processes of tearing rift propagation and strain jumps in afar

magmatism at continental passive margins inferred from ambient noise phase velocity in the gulf of aden non volcanic continental passive margins have traditionally been considered to be tectonically and magmatically inactive once continental breakup has occurred and seafloor spreading has commenced we use ambient noise tomography to constrain rayleigh wave phase velocity maps beneath the eastern gulf of aden eastern yemen and southern oman in the crust we image low velocities beneath the jiza qamar yemen and ashawq salalah oman basins likely caused by the presence of partial melt associated with magmatic plumbing systems beneath the rifted margin our results provide strong evidence that magma intrusion persists after breakup modifying the composition and thermal structure of the continental margin the coincidence between zones of crustal intrusion and steep gradients in lithospheric thinning as well as with transform faults suggests that magmatism post breakup may be driven by small scale convection and enhanced by edge driven flow at the juxtaposition of lithosphere of varying thickness and thermal age

post rifting relaxation in the afar region ethiopia 1 crustal accretion at divergent plate boundaries typically occurs via the periodic intrusion of dikes but their emplacement and the associated deformation are rarely observed the few existing observations at subaerial rifts show that these diking events are followed by a decadal scale period with extension rates faster than the secular divergent plate motion this transient accelerated deformation has been explained by continued subsurface magma injection or by relaxation in the viscoelastic mantle of the stress changes imparted by dike opening for the first time gps measurements were collected within a few months of a rifting event at a major plate boundary the september 2005 60 km long dike intrusion in the dabbahu segment afar ethiopia extension rates for the first 3 years greatly exceed the plate motion nubia arabia secular divergence rate even at sites located more than 60 km from the rift axis here we show that these observations are consistent with stress relaxation in a viscoelastic upper mantle with a viscosity of about 5 1018 pa s overlain by a 12 14 km thick elastic crust the alternative model of continued diking requires continuous opening well below the moho and is therefore unlikely instead magma injection in afar since june 2006 has taken the form of smaller discrete diking events tapping into a mid crustal melt reservoir under the segment center

nubia arabia eurasia plate motions and the dynamics of mediterranean and middle east tectonics summary we use geodetic and plate tectonic observations to constrain the tectonic evolution of the nubia arabia eurasia plate system two phases of slowing of nubia eurasia convergence each of which resulted in an 50 per cent decrease in the rate of convergence coincided with the initiation of nubia arabia continental rifting along the red sea and somalia arabia rifting along the gulf of aden at 24 4 ma and the initiation of oceanic rifting along the full extent of the gulf of aden at 11 2 ma in addition both the northern and southern red sea nubia arabia plate boundary underwent changes in the configuration of extension at 11 2 ma including the transfer of extension from the suez rift to the gulf of aqaba dead sea fault system in the north and from the central red sea basin bab al mandab to the afar volcanic zone in the south while nubia eurasia convergence slowed the rate of arabia eurasia convergence remained constant within the resolution of our observations and is indistinguishable from the present day global positioning system rate the timing of the initial slowing of nubia eurasia convergence 24 4 ma corresponds to the initiation of extensional tectonics in the mediterranean basin and the second phase of slowing to changes in the character of mediterranean extension reported at 11 ma these observations are consistent with the hypothesis that changes in nubia eurasia convergence and associated nubia arabia divergence are the fundamental cause of both mediterranean and middle east post late oligocene tectonics we speculate about the implications of these kinematic relationships for the dynamics of nubia arabia eurasia plate interactions and favour the interpretation that slowing of nubia eurasia convergence and the resulting tectonic changes in the mediterranean basin and middle east resulted from a decrease in slab pull from the arabia subducted lithosphere across the nubia arabia evolving plate boundary

a new kinematic approach for the danakil block using a digital elevation model representation abstract data from the literature are integrated in a regional digital elevation model dem in order to analyse the motion of the danakil block with regard to the arabian and somalian plates the application of the poles and angles of rotation taken from the literature induces a superposition of the danakil block on the arabian plate and the formation of a gap in the afar region the determination of new poles of rotation using a best fitting procedure allows one to avoid these drawbacks in all cases calculations are carried out keeping the nubian plate stationary the present approach shows that the danakil block is an independent entity and is not related to the nubian and arabian plates between the oligocene and the miocene it has been submitted to a n20 e sinistral strike slip motion anterior to the rotation itself that was started in the middle miocene this rotation is directed by a mechanical couple due to the combination of the red sea and north afar extensions

initial burst of oceanic crust accretion in the red sea due to edge driven mantle convection the 500 m y cycle whereby continents assemble in a single supercontinent and then fragment and disperse again involves the rupturing of a continent and the birth of a new ocean with the formation of passive plate margins this process is well displayed today in the red sea where arabia is separating from africa we carried out geophysical surveys and bottom rock sampling in the two red sea northernmost axial segments of initial oceanic crust accretion thetis and nereus areal variations of crustal thickness magnetic intensity and degree of melting of the subaxial upwelling mantle reveal an initial burst of active oceanic crust generation and rapid seafloor spreading below each cell occurring as soon as the lid of continental lithosphere breaks this initial pulse may be caused by edge driven subrift mantle convection triggered by a strong horizontal thermal gradient between the cold continental lithosphere and the hot ascending asthenosphere the thermal gradient weakens as the oceanic rift widens therefore the initial active pulse fades into steady more passive crustal accretion with slower spreading and along axis rift propagation

a 48 kyr long slip rate history for the jordan valley segment of the dead sea fault abstract we investigate the late quaternary active deformation along the jordan valley segment of the left lateral dead sea fault and provide new insights on the behaviour of major continental faults the 110 km long fault segment shows systematic offsets of drainage systems surveyed at three sites along its southern section the isotopic dating of six paleoclimatic events yields a precise chronology for the onset of six generations of gully incisions at 47 5 ka bp 37 5 ka bp 13 ka bp 9 ka bp 7 ka bp and 5 ka bp additionally detailed mapping and reconstructions provide cumulative displacements for 20 dated incisions along the fault trace the individual amounts of cumulative slip consistently fall into six distinct classes this yields i an average constant slip rate of 4 7 to 5 1 mm yr for the last 47 5 kyr and ii a variable slip rate ranging from 3 5 mm yr to 11 mm yr over 2 kyr to 24 kyr long intervals taking into account that the last large earthquake occurred in ad 1033 we infer 3 5 to 5 m of present day slip deficit which corresponds to a mw 7 4 earthquake along the jordan valley fault segment the timing of cumulative offsets reveals slip rate variations critical to our understanding of the slip deficit and seismic cycle along major continental faults

tectonic evolution of the fundy rift basin canada evidence of extension and shortening during passive margin development seismic and field data show that the fundy rift basin of southeastern canada experienced two distinct episodes of deformation during mesozoic time the first episode during middle triassic to early jurassic time was extensional rifting associated with nw se extension reactivated ne trending paleozoic compressional structures as normal faults forming the northwestern boundary faults of the fundy basin displacements on the low angle boundary faults locally exceeded 10 km rifting also reactivated east trending paleozoic compressional structures as oblique slip faults with normal and sinistral strike slip components forming the northern boundary faults of the fundy basin several kilometers of sediments and lava flows filled the basin during rifting the second deformational episode occurred during or after early jurassic time and probably before or during early cretaceous time inversion associated with nw se shortening occurred along all faulted margins of the fundy basin the northwestern boundary faults experienced several kilometers of reverse displacement broad anticlines developed within their hanging walls and the fundy basin acquired its synclinal form the northern boundary faults of the fundy basin became oblique slip faults with reverse and dextral strike slip components gentle synclines tight anticlines and faults with reverse separation deformed the synrift strata near the northern margin of the fundy basin neither collision nor subduction zones existed near the fundy basin during mesozoic time hence we believe that tectonic processes associated with seafloor spreading e g incipient ridge push forces continental resistance to plate motion produced the shortening in the fundy basin shortening occurred during the transition from rifting to drifting as north america separated from northern africa and or during the early stages of drifting as the seafloor spreading centers of the north atlantic propagated northward

current plate motion across the dead sea fault from three years of continuous gps monitoring 1 the dead sea fault dsf is a transform plate boundary between the arabian plate and the sinai sub plate the rate of displacement across the fault has been estimated as 1 10 mm yr in this study we present a new estimate of the current displacement across the dsf which is based on three years of continuous global positioning system measurements july 1996 to july 1999 our analysis of these data shows that relative northward velocity which is the fault parallel component on the baseline between tel aviv and katzerin golan heights and katzerin and elat is 1 4 0 3 mm yr and 1 0 0 5 mm yr respectively assuming a colored noise white noise plus flicker noise model for the daily position estimates by using a simple locked fault model we estimate that during the three year observation period the relative plate motion across the dsf was 2 6 1 1 mm yr

slip rate on the dead sea transform fault in northern araba valley jordan the araba valley lies between the southern tip of the dead sea and the gulf of aqaba this depression blanketed with alluvial and lacustrine deposits is cut along its entire length by the dead sea fault in many places the fault is well defined by scarps and evidence for left lateral strike slip faulting is abundant the slip rate on the fault can be constrained from dated geomorphic features displaced by the fault a large fan at the mouth of wadi dahal has been displaced by about 500 m since the bulk of the fanglomerates were deposited 77 140 kyr ago as dated from cosmogenic isotope analysis 10 be in chert of pebbles collected on the fan surface and from the age of transgressive lacustrine sediments capping the fan holocene alluvial surfaces are also clearly offset by correlation with similar surfaces along the dead sea lake margin we propose a chronology for their emplacement taken together our observations suggest an average slip rate over the late pleistocene of between 2 and 6 mm yr 1 with a preferred value of 4 mm yr 1 this slip rate is shown to be consistent with other constraints on the kinematics of the arabian plate assuming a rotation rate of about 0 396 myr 1 around a pole at 31 1 n 26 7 e relative to africa

stress tensor and focal mechanisms along the dead sea fault and related structural elements based on seismological data the dead sea fault is among the largest active strike slip fault of the world this study is focused on the southern part of this fault from the sea of galilee to the gulf of aqaba as monitored mainly by the jordanian and israeli seismic networks the data of arrival times and polarities allowed relocation of earthquakes with a better azimuthal coverage and computation of focal mechanisms this last step has been realized by inverting the polarities to determine a unique stress tensor for the region and the compatible focal mechanisms inversion with different subsets of the data set based on tectonic regionalization has also been performed to evaluate the impact of each cluster of earthquakes on the global solution the population of focal mechanisms is clearly dominated by strike slip events with the notable exception of a cluster of earthquakes south of the dead sea which displays several normal focal mechanisms this last cluster forces 1 to be vertical and 2 to be horizontal a large number of fault planes however are close to the vertical inhibiting the action of the vertical component of the stress tensor and acting like under strike slip stress regime we observed a good agreement between the location of the earthquakes and the active faults based on geological data in addition there is a good agreement between the fault plane solutions and the orientation of the active faults

slip rate and locking depth from gps profiles across the southern dead sea transform 1 the dead sea transform is a major strike slip fault bounding the arabia plate and the sinai subplate on the basis of two gps campaign measurements 6 years apart at 17 sites distributed in israel and jordan complemented by israeli permanent stations we compute the present day deformation across the southern segment of the dead sea transform the wadi araba fault elastic locked fault modeling of fault parallel velocities provides a slip rate of 4 9 1 4 mm a and a best fit locking depth of 12 km this slip rate is slightly higher than previous results based only on israeli permanent gps stations data which are located west of the fault it is in good agreement with results based on offset geomorphologic and geologic features that average longer periods of time 10 ka to 1 ma projection in itrf2000 reference frame allows using our data combined with results published earlier to further study the kinematics between arabia nubia and sinai systematic combination of euler poles available in the literature in addition to our new set of data shows that a wide range of arabia sinai pole positions and angular velocities predict reasonable slip rate on the dead sea fault we highlight uncertainties of calculating such poles due to the small size of the blocks and their slow relative motion along a short and almost straight strand of the transform fault which lead to a large trade off between pole location and angular velocity

punctiform initiation of seafloor spreading in the red sea during transition from a continental to an oceanic rift transition from a continental to an oceanic rift occurs in the red sea by initial emplacement of oceanic crust in regularly spaced hot points which serve as nuclei for axial propagation into segments of oceanic crust accretion and for initiation of seafloor spreading hot points develop above upwelling mantle diapirs caused by density viscosity inversion beneath continental and oceanic rifts

structure and evolution of the eastern gulf of aden conjugate margins from seismic reflection data the gulf of aden is a young and narrow oceanic basin formed in oligo miocene time between the rifted margins of the arabian and somalian plates its mean orientation n75 e strikes obliquely 50 to the n25 e opening direction the western conjugate margins are masked by oligo miocene lavas from the afar plume this paper concerns the eastern margins where the 19 35 ma breakup structures are well exposed onshore and within the sediment starved marine shelf those passive margins about 200 km distant are non volcanic offshore during the encens sheba cruise we gathered swath bathymetry single channel seismic reflection gravity and magnetism data in order to compare the structure of the two conjugate margins and to reconstruct the evolution of the thinned continental crust from rifting to the onset of oceanic spreading between the alula fartak and socotra major fracture zones two accommodation zones trending n25 e separate the margins into three n110 e trending segments the margins are asymmetric offshore the northern margin is narrower and steeper than the southern one including the onshore domain the southern rifted margin is about twice the breadth of the northern one we relate this asymmetry to inherited jurassic cretaceous rifts the rifting obliquity also influenced the syn rift structural pattern responsible for the normal faults trending from n70 e to n110 e the n110 e fault pattern could be explained by the decrease of the influence of rift obliquity towards the central rift and or by structural inheritance the transition between the thinned continental crust and the oceanic crust is characterized by a 40 km wide zone our data suggest that its basement is made up of thinned continental crust along the southern margin and of thinned continental crust or exhumed mantle more or less intruded by magmatic rocks along the northern margin abstract from author

spatial distribution of the seismicity parameters in the red sea regions the spatial distribution of the seismicity parameters of the magnitude frequency relation has provided preliminary quantitative basis for establishing different zones of seismic activities in the southern red sea regions four zones were constructed from application of proposed models that yielded approximate b value range for each zone thus providing relative bases for preliminary classification as follows zone iii has b value 1 0 the zones were characterized through correlation to seismotectonic and some geophysical configuration in the study area narrow contour spacing among zones is observed to occur along intersections of areas of probably different seismic source zones while wider spacing occurs seemingly for a prominently dominating source of seismic activity corresponding spatial distribution of estimated maximum magnitude and expected magnitude at 90 non exceedance in 50 years was prepared likely occurrence of a major earthquake is spread over a wider area of coverage characterized by presence of rift zones structural discontinuities and dislocations in the study area broad confidence limits for the parameter values are encountered but correlation to primary tectonic structures is seen to be possible comparison of the present results to previous relevant studies indicates general agreement with regards to tectonics and related phenomena the spatial distribution of the parameters seemed to provide appropriate basis of analysis to the observed complexities of seismic occurrences in the red sea and adjacent shield areas 1998 elsevier science ltd all rights reserved

plate kinematics of the central atlantic during the oligocene and early miocene summary a new plate motions model for the northwest africa north america plate pair during the oligocene and early miocene is presented the model is accompanied by a high resolution isochronmapforthecentralatlanticregion resultingfromare examinationof423shiptracks from the ngdc data base for the area between the 15 20 fz and the azores triple junction a new digital model of fracture zones for this region and a set of 309 magnetic profiles crossing the oligocene to recent oceanic crust within the study area allowed to determine accurate finite reconstruction poles for the north america northwest africa conjugate plate pair between the early miocene chron 6 and the early oligocene chron 13 for times older than chron 7 25 ma the finite reconstruction poles were calculated using a reliable data set coming exclusively from the region south of the canary islands fz 32 n which allowed to test the rigidity of the northwest african oceanic lithosphere during the oligocene early miocene phase of atlas orogeny a comparison of theoretical magnetic isochrons with observed magnetic lineations systematically shows that anomalously high spreading rates occurred in the area north of the canary islands fz before chron 7 thereby suggesting that the formation of the atlas mountain rather than being a localized intracontinental process was logically linked to the central atlantic spreading history thus an independent moroccan plate could have existed during the oligocene early miocene time interval which included both the oceanic lithosphere north of the canary islands fz and the northern maghrebian areas of morocco algeria and tunisia in this eventuality the atlas mountain belt should be reinterpreted as a giant flower structure associated with dextral transpression

gps constraints on africa nubia and arabia plate motions summary we use continuously recording gps cgps and survey mode gps sgps observations to determine euler vectors for relative motion of the african nubian arabian and eurasian plates we present a well constrained eurasia nubia euler vector derived from 23 igs sites in europe and four cgps and three sgps sites on the nubian plate 0 95 4 8 n 21 8 4 3 e 0 06 0 005 myr 1 we see no significant 1m m yr 1 internal deformation of the nubian plate the gps nubian eurasian euler vector differs significantly from nuvel 1a 21 0 4 2 n 20 6 0 6 e 0 12 0 015 myr 1 implying more westward motion of africa relative to eurasia and slower convergence in the eastern mediterranean the arabia eurasia and arabia nubia gps euler vectors are less well determined based on only one cgps and three sgps sites on the arabian plate the preliminary arabia eurasia and arabia nubia euler vectors are 27 4 1 0 n 18 4 2 5 e 0 40 0 04 myr 1 and 30 5 1 0 n 25 7 2 3 e 0 37 0 04 myr 1 respectively the gps arabia nubia euler vector differs significantly from nuvel 1a 24 1 1 7 n 24 0 3 5 e 0 40 0 05 myr 1 but is statistically consistent at the 95 per cent confidence level with the revised euler vector reported by chu gordon based on a re evaluation of magnetic anomalies in the red sea 31 5 1 2 n 23 0 2 7 e 0 40 0 05 myr 1 the motion implied in the gulf of aqaba and on the dead sea fault dsf by the new gps nubia arabia euler vector i e ignoring possible sinai block motion and possible internal plate deformation grades from pure left lateral strike slip in the gulf and on the southern dsf with increasing compression on the central and northern dsf with relative motion increasing from 5 6 to 7 5 mm yr 1 1m m yr 1 from south to north along the northern dsf i e north of the lebanon restraining bend motion is partitioned between 6 1m m yr 1 left lateral motion parallel to the fault trace and 4 1m m yr 1 faultnormal compression relative motions on other plate boundaries including the anatolian and aegean microplates derived from the gps euler vectors agree qualitatively with the sense of motion indicated by focal mechanisms for large crustal earthquakes m 6 where data are available on fault slip rates on plate bounding faults north anatolian fault east anatolian fault dead sea fault red sea rift they are generally lower than but not significantly different from the full plate motion estimates suggesting that the majority of relative plate motion is accommodated on these structures

crustal deformation in northwestern arabia from gps measurements in syria slow slip rate along the northern dead sea fault summary new global positioning system gps measurements in nw syria provide the first direct observations of near field deformation associated with the northern dead sea fault system dsfs and demonstrate that the kinematics of the northern section of this transform plate boundary between the arabian and sinai plates deviate significantly from plate model predictions velocity estimates based on gps survey campaigns in 2000 2007 and 2008 demonstrate left lateral shear along the northern dsfs with 1 uncertainties less than 0 7 mm yr 1 these velocities are consistent with an elastic dislocation model with a slip rate of 1 8 3 3 mm yr 1 and a locking depth of 5 16 km this geodetically determined slip rate is about half of that reported farther south along the central section lebanese restraining bend and the southern section jordan valley and wadi araba of the transform and consequently requires some deformation to occur away from the transform along other geological structures the factor of two difference in slip rates along the transform is also consistent with differing estimates of total fault slip that have occurred since the mid miocene 20 25 km along the northern dsfs in nw syria versus about 45 km along the southern dsfs segment some of the strain deficit may be accommodated by north south shortening within the southwestern segment of the palmyride fold belt of central syria additionally a distinct change in velocity occurs within the sinai plate itself these new gps measurements when viewed alongside the palaeoseismic record and the modest level of present day seismicity suggest that the reported estimates of recurrence time of large earthquakes m 7 along the northern section of the dsfs may be underestimated owing to temporal clustering of such large historical earthquakes hence a revised estimate of the earthquake hazard may be needed for nw syria

transverse structures in the central part of the red sea and implications on early stages of oceanic accretion summary transverse structures in the central part of the red sea are mapped according to bathymetric seismic gravity and magnetic data five classes of structures are detected three of these are fractures intertrough zones and transform faults the remaining two are classified as transform zones and pseudo transform faults most structures can be related to ancient lineaments on land intertrough and transform zones are manifestations of unorganized seafloor spreading and their crustal structure is of an oceanic nature that might be similar to quiet magnetic zones

african stress pattern from formal inversion of focal mechanism data abstract the kinematic models and the associated orientation of extensional stress of the east african rift system have been subjected to much debate since a long time in the past decades the proposed models relied on the interpretation of the overall rift geometry geological fault slip data and the few focal mechanisms available these models generally suffer of a poor time control and an underestimation of the possible changes in the stress field and geodynamic regime with time and space in the recent years there has been a significant increase in the number of focal mechanisms available for the entire rift system and it is now possible to estimate the present day stress field in relative detail based on seismotectonic data alone we compile 347 focal mechanism data from the global harvard cmt catalogue and various other sources and grouped 332 of them in 24 distinct regions boxes on the basis of their geographical proximity kinematic homogeneity and tectonic setting for each box and for the same data set reduced stress tensors have been obtained by formal stress inversion using both the tensor program delvaux sperner 2003 and the slick method michael 1984 1987 both inversion methods show in comparable results in terms of horizontal stress axes orientations and tectonic stress regimes which stem for the robustness of the approach the obtained stress pattern reflects a complex interaction between 1st order effects as different driving forces including plate boundary forces and 2nd and 3rd order effects as gravitational potential of topography intra lithospheric processes and the influence of structural heterogeneities of the rift structures the evidence present in the stress orientations of the 2nd and 3rd order stress pattern as the variations in the horizontal stress axes along the axis of the rift are of particular interest as they were not yet captured or shown in earlier numerical models of the stress field additional sources of tectonic forces in supplement to the gravitational potential energy forces as considered in the earlier models are necessary to explain the observed patterns

recent kinematics of the tectonic plates surrounding the red sea and gulf of aden this work was funded by the miur prin prot 20125jkany the geodas ship track data used in this study can be found at ngdc http www ngdc noaa gov mgg geodas trackline html

geodetic constraints on present day motion of the arabian plate implications for red sea and gulf of aden rifting 1 five years of continuously recording gps observations in the kingdom of saudi arabia together with new continuous and survey mode gps observations broadly distributed across the arabian peninsula provide the basis for substantially improved estimates of present day motion and internal deformation of the arabian plate we derive the following relative geodetic euler vectors latitude n longitude e rate myr counterclockwise for arabia nubia 31 7 0 2 24 6 0 3 0 37 0 01 arabia somalia 22 0 0 5 26 2 0 5 0 40 0 01 arabia india 18 0 3 8 87 6 3 3 0 07 0 01 arabia sinai 35 7 0 8 17 1 5 0 0 15 0 04 and arabia eurasia 27 5 0 1 17 6 0 3 0 404 0 004 we use these euler vectors to estimate present day stability of the arabian plate the rate and direction of extension across the red sea and gulf of aden and slip rates along the southern dead sea fault south of the lebanon restraining bend 4 5 4 7 0 2 mm yr left lateral 0 8 1 1 0 3 mm yr extension and the owens fracture zone 3 2 2 5 0 5 mm yr right lateral increasing from north to south 1 2 mm yr extension on a broad scale the arabian plate has no resolvable internal deformation weighted root mean square of residual motions for arabia equals 0 6 mm yr although there is marginally significant evidence for n s shortening in the palmyride mountains syria at 1 5 mm yr we show that present day arabia plate motion with respect to eurasia is consistent within uncertainties i e 10 with plate tectonic estimates since the early miocene when arabia separated from nubia we estimate the time of red sea and gulf of aden rifting from present day arabia motion plate tectonic evidence for a 70 increase in arabia nubia relative motion at 13 ma and the width of the red sea and gulf of aden and find that rifting initiated roughly simultaneously 2 2 myr along the strike of the red sea from the gulf of suez to the afar triple junction as well as along the west gulf of aden at 24 2 2 ma based on the present kinematics we hypothesize that the negative buoyancy of the subducted ocean lithosphere beneath the makran and the zagros fold thrust belt is the principle driver of arabia eurasia convergence and that resisting forces associated with arabia eurasia continental collision have had little impact on plate motion

the rotation of arabia and the levant fault system abstract we establish the kinematics of the rotation of arabia with respect to africa and show that the rotation rate of africa increased by a factor of about four in late serravallian time about 12 13 ma ago we discuss evidence that oceanic accretion started simultaneously in the gulf of aden and in the red sea at this time it is also at this time that the levant and anatolian fault systems were initiated our initial reconstruction of the red sea rift in late oligocene early miocene time approximately superposes the present shore lines which coincide with the mid point of the zones of rapid crustal thinning the future continental slopes the amount of extension during the early phase of continental rifting is obtained by assuming that the total volume of continental crust is conserved during extension and by checking these estimates through closure around the sinai triple junction in the late miocene the southern evant fault zone was a zone of distributed shear deformation through counterclockwise block rotation extending soul h ward within the northernmost red sea since the early pliocene the shear motion has been localized within the gulf of aqaba changing the tectonic pattern in the northern red sea

contractional salt tectonic system in the south dezful embayment zagros abstract the dezful embayment in zagros has traditionally been interpreted as a typical fold belt with multiple detachment levels including a lower detachment at the basement cover interface and an upper detachment along the miocene gachsaran halite bearing evaporites this paper constrains diapiric processes in the gachsaran detachment coeval with regional shortening that resulted in complex and hitherto unstudied salt structures and flanking synclinal minibasins in this paper well tied seismic interpretation is integrated with field and remote sensing mapping cross section construction and stepwise tectono sedimentary restoration the results indicate that after the deposition of mishan lower aghajari pre kinematic overburden sediments detachment folding initiated above the gachsaran evaporites during late tortonian times as a result of regional shortening the salt cored anticlines later actively pierced their roof to subsequently rise as passive diapirs and evolve into salt walls synclinal minibasins developed due to salt evacuation into flanking walls during the deposition of the lahbari mb in messinian pliocene remarkable sedimentary thickening and lateral shifts in minibasin depocenter towards the salt walls accompanied by overturned collars and hook halokinetic sequences are diagnostics of near surface syndepositional passive growth of diapirs during this stage from pliocene to recent the major episode of regional shortening has squeezed these precursor salt walls to form thrust welds in conclusion the well exposed structures of south dezful show an early shortening stage then a transition to a combination of shortening and passive diapirism and final thrusting along diapirs this evolution model may be more common in other salt influenced fold thrust belts than is currently recognized

current plate motions across the red sea summary a new objective method is used to estimate precisely 64 rates of seafloor spreading since chron 2a 3 2 ma from all the red sea magnetic profiles available from 15 9 to 26 n the fastest spreading rate 16 mm yr 1 occurs near 18 n whereas the slowest rate 10 mm yr 1 occurs at 25 5 n and is consistent with the rate predicted from arabia nubia data to the south the standard deviation of the spreading rates is 0 8 mm yr 1 much smaller than the median standard deviation of 4 mm yr 1 previously assigned to spreading rates in the global plate motion model nuvel 1 demets et al 1990 the fit to the spreading rates as well as the locations of earthquakes in and near the red sea indicate that spreading south of approximately 17 7 n is less than the full rate of spreading between the arabian and nubian plates the red sea spreading centre is instead usefully interpreted as the boundary between the arabian plate and a danakil microplate that includes the subaerial danakil block and a larger oceanic portion of lithosphere despite the absence of reliable azimuths of transform faults in the red sea all components of the angular velocity of arabia relative to nubia are usefully constrained from just the 45 relevant spreading rates the new compact 95 per cent confidence region of the angular velocity excludes prior estimates based on only four and two spreading rates by chase 1978 and jestin et al 1994 respectively 19 spreading rates in the southern red sea are used to estimate the angular velocity between the danakil microplate and arabia an approach based on singular value decomposition shows that without slip vectors only two of the three components of the angular velocity of the danakil microplate relative to arabia or nubia are usefully constrained but that all three components are usefully constrained if one earthquake slip vector is included

global positioning system constraints on plate kinematics and dynamics in the eastern mediterranean and caucasus we present and interpret global positioning system gps measurements of crustal motions for the period 1988 1997 at 189 sites extending east west from the caucasus mountains to the adriatic sea and north south from the southern edge of the eurasian plate to the northern edge of the african plate sites on the northern arabian platform move 18 2 mm yr at n25 5 w relative to eurasia less than the nuvel 1a circuit closure rate 25 1 mm yr at n21 7 w preliminary motion estimates 1994 1997 for stations located in egypt on the northeastern part of africa show northward motion at 5 6 2 mm yr also slower than nuvel ia estimates 10 1 mm yr at n2 4 e eastern turkey is characterized by distributed deformation while central turkey is characterized by coherent plate motion internal deformation of 2 mm yr involving westward displacement and counterclockwise rotation of the anatolian plate the anatolian plate is de coupled from eurasia along the right lateral strike slip north anatolian fault naf we derive a best fitting euler vector for anatolia eurasia motion of 30 7 0 8 n 32 6 0 4 e 1 2 0 1 myr the euler vector gives an upper bound for naf slip rate of 24 1 mm yr we determine a preliminary gps arabia anatolia euler vector of 32 9 1 2 n 40 3 1 1 e 0 8 0 2 myr and an upper bound on left lateral slip on the east anatolian fault eaf of 9 1 mm yr the central and southern aegean is characterized by coherent motion internal deformation of 2 mm yr toward the sw at 30 1 mm yr relative to eurasia stations in the se aegean deviate significantly from the overall motion of the southern aegean showing increasing velocities toward the trench and reaching 10 1 mm yr relative to the southern aegean as a whole

gps evidence for northward motion of the sinai block implications for e mediterranean tectonics gps survey sites in the sinai peninsula show northerly motion relative to africa nubia at 1 4f0 8 mm yr north and 0 4f0 8 mm yr west continuous igs gps sites in israel west of the dead sea fault show a similar northerly sense of motion relative to nubia 2 4f0 6 mm yr north and 0 04f0 7 mm yr east suggesting that the entire sinai block south of lebanon is characterized by northward translation relative to the nubian plate we develop an elastic block model constrained by the gps results that is consistent with the regional tectonics and allows us to estimate slip rates for sinai bounding faults including the gulf of aqaba southern dead sea fault system 4 4f0 3 mm yr left lateral the gulf of suez 1 9f0 3 mm yr left lateral and 1 5f0 4 mm yr extension and the cyprus arc predominantly convergence at 8 9f0 4 mm yr along the western segment and 6 0f0 4 mm yr left lateral strike slip along the eastern segment these observations imply that the sinai peninsula and levant region comprise a separate sub plate sandwiched between the arabian and nubian plates d 2005 elsevier b v all rights reserved

toward a minimum change model for recent plate motions calibrating seafloor spreading rates for outward displacement summary we use seafloor spreading distances derived from reconstructions of more than 7000 crossings of young magnetic anomalies along seven plate boundaries to study outward displacement a source of systematic bias in estimates of seafloor spreading rates which is caused by a combination of processes that shift magnetic polarity transition zones away from their idealized locations linear regressions of 81 independent sequences of seafloor opening distances as a function of their magnetic reversal ages for anomalies younger than c3n 1 4 19 ma yield 75 positively valued intercepts for zero seafloor age confirming the ubiquitous outward shift of magnetic reversals reported by previous authors grouping these data into 29 locally consistent clusters yields better constrained zero age intercepts that are uniformly positive and average 2 2 0 3 km globally these values which are 1 3 km at most locations and are significantly larger 3 5 km along the well surveyed reykjanes and carlsberg ridges agree well with published magnetic polarity zone transition widths which are estimated directly from nearbottom seafloor magnetic measurements significant variations in outward displacement along the southeast indian ridge are strongly correlated with changes in axial morphology and axial depth however a similar correlation is not observed along other ridges forward magnetic anomaly modelling suggests that variations in outward displacement can be explained by differences in the magnetic source layers that are assumed to characterize different spreading centres if not corrected for outward displacement the implied systematic upward biases in seafloor spreading rates which are averaged over the width of anomaly 1 the youngest reversal that is used for plate reconstructions range from 6 mm yr 1 along the reykjanes ridge where outward displacement is 4 5 km to 3 mm yr 1 along ridges where outward displacement approximates the global average of 2 km

the uncertainties of finite rotations in plate tectonics incomplete knowledge of the pattern of magnetic lineations and fossil transform faults represented by sea floor spreading data on two plates generated by the same spreading center leads to uncertainties in a reconstruction of the past relative configuration of the plates a reconstruction may be represented by the finite rotation that describes one configuration relative to another in this paper a method of reconstruction is provided that reflects the uncertainties in the data the method minimizes a weighted least squares measure of fit as a function of the rotation parameters for a given rotation the measure of fit represents the sum of squares of the weighted distances of fixed and rotated data points representing corresponding former plate margin segments from a common plate margin the common margin is estimated from the locations of both fixed and rotated data points the estimated margin consists of a set of great circle arcs it is shown how the method of reconstruction may be utilized to obtain an uncertainty region for the pole and angle of rotation that characterize the finite rotation these techniques are then used to study the uncertainties of reconstructions in the south pacific for the times of anomalies 13 and 18 the best fit reconstructions and the uncertainty region for the anomaly 18 pole are in good agreement with previous work however the uncertainties in the anomaly 13 pole were substantially underestimated by previous investigators

shear controlled evolution of the red sea pull apart model abstract results of seismic and other geophysical investigations suggest that strike slip processes controlled the break up of the arabian plate from africa and initiated the red sea rift early oceanisation was facilitated by nucleation of pull apart basins and massive intrusives the evolution of the red sea has gone through different stages it was a zone of structural weakness already during the pan african orogeny approximately 600 ma a major reactivation however that gradually led to the present day configuration was initiated during the late oligocene with intense magmatic activity and the development of a continental rift wrench faulting played a key role in the early evolution of the red sea as it shaped most of its western flank as a sharp plate boundary and resulted in the generation and rapid oceanisation of linearly arranged pull apart basins spatial distribution of these basins reflects the geometry of the strike slip zone which was controlled by pre existing fault systems like the najd shear system the central african fault zone or the onib hamisana and baraka suture zones strike slip motion along the latter zones of weakness influenced mainly the egyptian and sudanese coastal areas arabia was therefore separated from africa by oceanisation in those regions where pull apart basins developed they were still connected in the in between segments by stretched continental crust with arabia as the moving and africa as the stable plate the eastern red sea flank was formed by pure shear through stretching thinning and diffuse extension as a consequence the eastern and western flanks of the red sea are asymmetrical the acceleration of the movement of arabia in early middle miocene could no longer be accommodated by the opening in the gulf of suez and consequently the dead sea strike slip fault developed approximately 14 ma ago since plate motion was still oblique to the major structural trends the pull apart evolution on the western flank continued and the oceanisation was accentuated while in the north the eastern flank developed en echelon fractures of aqaba orientation seafloor spreading commenced 5 ma ago at parts of the central and southern red sea this final stage is also responsible for the bathymetry with maximum depth values of 3000 m in the seafloor spread areas and a much shallower basin in the north the metalliferous red sea deeps are either associated with this infant mid ocean ridge or with the en echelon fractures in the north

faulting and block rotation in the afar triangle east africa the danakil crank arm model several domains of contrasted extensional deformation have been identified in the southern afar triangle east africa from fault patterns analyzed with panchromatic stereoscopic spot systeme probatoire d9observation de la terre images stretching directions and statistical orientation and offset variations of faults fit with the danakii crank arm model of sichler a 10 sinistral rotation of the danakil block explains the fault geometry and dextral block rotation in the southern part of the afar triangle as well as the oblique extension in the tadjoura gulf analogue modeling supports this interpretation

provenance evolution of oligocene pliocene foreland deposits in the dezful embayment to constrain central zagros exhumation history this paper presents a detailed provenance analysis of the 6 5 km thick oligocene pliocene foreland succession in the north dezful embayment in zagros iran using petrography geochemistry and palaeoflow analysis we determined three provenance shifts during the exhumation of the zagros orogen above the ahwaz sandstones sourced from the arabian craton a sharp decrease in sio2 al2o3 zr sc th sc th co and th cr within the gachsaran fm and the appearance of first cycle sands derived from metamorphic and volcanic rocks at the base of the aghajari fm characterize the onset of exhumation rising topography and denudation of the zagros orogenic system during the latest oligocene and constitute the first shift the second shift in the middle aghajari fm is marked by a distinct increase in radiolarian cherts and compatible incompatible elements indicating the exhumation of neotethyan radiolarite ophiolite allochthonous slices in the high zagros zone during the tortonian c 9 ma large quantities of carbonate clasts derived from the nearby growing izeh zone anticlines characterize the messinian c 7 ma bakhtyari conglomerates marking the third shift in conclusion a detailed hands on provenance analysis of the clastic sedimentary sequences in the north dezful embayment enabled us to determine catchment areas and shifts hitherto unstudied thus contributing to the exhumation history of the central zagros orogenic system supplementary material details of the petrography and geochemistry results are available at https doi org 10 6084 m9 figshare c 4905558