motion of the easter hot spot relative to hawaii and louisville hot spots 1 hot spots have been widely used as a fixed reference frame for plate motions however it should be expected that the underlying plumes are advected in a dynamic mantle here a simple numerical model of hot spot motion due to large scale mantle flow is applied to the easter hawaii and louisville hot spots computations are performed for a range of different buoyant plume rising speeds ages and locations mantle density and viscosity structures etc it is shown that a westward motion of the easter hot spot at several cm per year relative to hawaii and louisville hot spots is a robust result for a large range of model parameters in order to obtain an appropriate boundary condition for mantle flow near the easter hot spot and to find out on which plate to expect the easter hot spot track for a given time published isochrons were rotated to the past ridge locations in a reference frame that takes the computed motion of hawaii and louisville hot spots into account calculations that include flow in the mantle and therefore relative movement of hot spots yield a better explanation of the observed age distribution along the sala y gomez ridge than assuming hot spot fixity at the same time they predict a hot spot track on the nazca plate that is roughly similar to the shape of the nazca and sala y gomez ridges furthermore the easter hot spot was in an intraplate location on the nazca plate during the past 43 ma somewhat closer to the ridge between 43 and 26 ma than between 26 ma and now in contrast if hot spots are assumed fixed a location close to the ridge and rather on the pacific plate between 43 and 26 ma is predicted based on morphology and gravity signature it is suggested that the nazca ridge and the eastern tuamotu island plateau were created by plume material that erupted at the east pacific rise while the easter plume was located sufficiently close to enable such an interaction whereas the sala y gomez ridge was formed above the easter plume in an intraplate setting this implies that if hot spots have indeed moved as computed here during formation of the nazca ridge between 43 and 26 ma plume material erupted at the ridge several 100 km away from the plume whereas no volcanism occurred directly above the plume it also implies that any seamounts on the pacific plate east of the tuamotu plateau are unrelated to the easter plume

on the hellenic subduction zone and the geodynamic evolution of crete since the late middle miocene abstract in recent syntheses of the geodynamic evolution of the aegean area the hellenic subduction zone and in particular its initiation plays a central role two basic aspects of the recent comprehensive model put forward by le pichon angelier and co workers are a initiation of subduction along the hellenic arc is inferred to have taken place approximately 13 ma ago whereas several others have suggested approximately 5 ma and b migration of the trench system to the south southwest giving rise to an extensional regime in the back arc region which led to general subsidence and formation of the present day aegean sea new data on the structure of the upper mantle underneath the aegean area indicate that the former aspect requires modification the seismic velocity structure indicating a northward dipping slab down to a depth of at least 600 km and the depth distribution of earthquake hypocenters can not be reconciled with straightforward initiation of subduction approximately 13 ma ago estimates of about 5 ma for the time of initiation of the present subduction zone are even more difficult to reconcile assuming 400 km as an upper bound for the effect of stretching of the aegean sea and of other processes contributing to the separation of crete from the eurasian mainland we arrive at an age for the hellenic subduction zone of at least 26 ma as to aspect b geological data of crete lend strong support to the idea that on crete compressional tectonics is of much greater importance than current models imply combining geophysical and geological data we propose a modification of the tectonic evolution for the cretan segment of the hellenic arc whereas the basic process of extension caused by a migrating trench system roll back in a land locked basin remains a very useful and sound concept the tectonics of the margins of a region subject to stretching in this case crete may be more complicated than hitherto thought in our model the documented fragmentation of crete into several basins which started about 12 ma ago is not attributed to initiation of subduction but to inception of the roll back process compressional tectonics on crete is taken to be associated with deformation of the crust resulting from the overall tensional stress regime

the adjustment of mantle plumes to changes in plate motion the relative motion of hotspots and lithospheric plates implies a velocity shear in the underlying mantle causing horizontal advection of mantle plumes as they rise toward the lithosphere consequent tilting of plumes parallel to the direction of plate motion indicates that plumes must undergo a period of readjustment after the velocity vector for plate motion is altered thus the shape of bends in the surface tracks of hotspots resulting from changes in plate motion will reflect the plume adjustment laboratory experiments as well as computations using a simple theory developed in richards griffiths 1988 for the dynamics of continuous plume conduits demonstrate that the bend in the surface track has a radius of curvature approximately equal to the maximum horizontal deflection of the conduit thus the sharpness of the bend at an age of 43ma in the hawaiian emperor volcanic chain implies that the deflection of the underlying plume in that case was small 200 km this small deflection is expected for plumes carrying large buoyancy fluxes and it indicates that tilting of the conduit is unlikely to be sufficient to cause diapiric instability

imaging crustal discontinuities and the downgoing slab beneath western crete the migration of teleseismic receiver functions yields high resolution images of the crustal structure of western crete data were collected during two field campaigns in 1996 and 1997 by networks of six and 47 short period three component seismic stations respectively a total of 1288 seismograms from 97 teleseismic events were restituted to true ground displacement within a period range from 0 5 to 7 s the application of a noise adaptive deconvolution filter and a new polarization analysis technique helped to overcome problems with local coda and noise conditions the computation and migration of receiver functions results in images of local crustal structures with unprecedented spatial resolution for this region the crust under crete consists of a continental top layer of 15 20 km thickness above a 20 30 km thick subducted fossil accretionary wedge with a characteristic en echelon fault sequence the downgoing oceanic moho lies at a depth of 40 60 km and shows a topography or undulation with an amplitude of several kilometres as a consequence of slab depth and distribution of local seismicity the mediterranean ridge is interpreted as the recent accretionary wedge

upper holocene sea level changes in the west saronic gulf greece abstract along the peloponnesian coast of the saronic gulf and on the coast of aegina and poros islands submerged coastal geomorphological features related directly with submerged ancient coastal constructions indicate three distinct sea levels submerged tidal notches incised on the carbonate basement beachrocks formed in the intertidal zone and archaeological indicators such as the ancient harbour installations in kenchreai and epidaurus and on aegina island the extended coastal buildings and constructions in agios vlasis psifta and palaiokastro methana and vagionia on poros island are used to determine the age and magnitude of submersion and the extent of the upper holocene marine transgression by the correlation of geomorphological historical and archaeological indications three distinct sea levels were identified at 3 30 0 15 m 0 90 0 15 m and 0 55 0 05 m initial change in sea level occurred definitely after ad 400 100 the intermediate change is dated between ad 1586 and 1839 and the most recent change after 1839 sea transgression followed a long period of sea level stability which lasted at least 2200 years from the middle bronze age to the late roman period

effects of change in slab geometry on the mantle flow and slab fabric in southern peru the effects of complex slab geometries on the surrounding mantle flow field are still poorly understood here we combine shear wave velocity structure with rayleigh wave phase anisotropy to examine these effects in southern peru where the slab changes its geometry from steep to flat to the south where the slab subducts steeply we find trench parallel anisotropy beneath the active volcanic arc that we attribute to the mantle wedge and or upper portions of the subducting plate farther north beneath the easternmost corner of the flat slab we observe a pronounced low velocity anomaly this anomaly is caused either by the presence of volatiles and or flux melting that could result from southward directed volatile rich subslab mantle flow or by increased temperature and or decompression melting due to small scale vertical flow we also find evidence for mantle flow through the tear north of the subducting nazca ridge finally we observe anisotropy patterns associated with the fast velocity anomalies that reveal along strike variations in the slab s internal deformation the change in slab geometry from steep to flat contorts the subducting plate south of the nazca ridge causing an alteration of the slab petrofabric in contrast the torn slab to the north still preserves the primary fossilized petrofabric first established shortly after plate formation

istrian and dalmatian fishtanks as sea level markers roman age fishponds along the istrian and dalmatian coast were studied with the aim of using the data as sea level markers although the adriatic fishponds do not display the architectural features crepidines channels etc that can be observed in the tyrrhenian ones and serve as precise sea level markers their structural elements can be used to define the sea level rise fishponds at s bartolomeo and fisine in slovenja kupanja near parenzo and at katoro near umago in croatia were studied and measured the pool investigated in the island of svrsata vela on the kornati islands represents a different feature located on the northwest coast of the island adjacent to the southern part of the gulf it is a single square pool with dimensions clearly less than the istrian fishtanks similar to those associated with the tyrrhenian villae maritimae these data the altitude of archaeological markers below sea level were corrected for tide and pressure and compared with predictions derived from the selen glacio hydro isostatic model comparison with the predicted sea level allows calculation of tectonic rates that range between 0 63 and 0 89 mm year since roman times

a geometric technique for relocating hotspots and refining absolute plate motions an age independent geometric relationship is presented that links hotspots to the seamounts which they produce and so permits the use of undated seamounts to refine the motion of tectonic plates this technique has the potential to rigorously assess hotspot fixity and to locate extinct hotspots the present application of this method points to a recent change in pacific plate motion and suggests a relocation of the louisville hotspot to the hollister ridge south of the eltanin fracture zone

fault structure and deformation rates at the lastros sfaka graben crete abstract the lastros and sfaka faults have an antithetic relationship and form a ca 2 km wide graben within the ierapetra fault zone in eastern crete both faults have impressive bedrock fault scarps many metres in height which form prominent features within the landscape t lidar investigations undertaken on the lastros fault are used to accurately determine vertical displacements along a ca 1 3 km long scanned segment analyses show that previous estimations of post glacial slip rate are too high because there are many areas along strike where the scarp is exhumed by natural erosion and or anthropogenic activity in areas not affected by erosion there is mean scarp height of 9 4 m this leads to a slip rate of 0 69 0 15 mm a using 15 3 ka for scarp exhumation using empirical calculations the expected earthquake magnitudes and displacement per event are discussed based on our observations trenching investigations on the sfaka fault identify different generations of fissure fills retrodeformation analyses and 14c dating of the fill material indicate at least four events dating back to 16 055 215 cal bp with the last event having occurred soon after 6102 113 cal bp the lastros fault is likely the controlling fault in the graben and ruptures on the lastros fault will sympathetically affect the sfaka fault which merges with the lastros fault at a depth of 2 4 km the extracted dates from the sfaka fault fissure fills therefore either represent activity on the lastros fault assuming they formed coseismically or accommodation events cross sections show that the finite throw is limited to around 300 m and the derived slip rate for the lastros fault therefore indicates that both faults are relatively young having initiated 435 120 ka

two way exchange between the easter mantle plume and the easter microplate spreading axis the conventional model whereby plume volcanism forms linear age progressive volcanic chains with the youngest activity occurring nearest a spreading axis at a hotspot has been challenged for the easter seamount chain1 4 whereas early work suggested the existence of a linear melting anomaly a hotline 1 2 more recent studies3 4 have proposed a hotspot near salas y gomez island connected with the easter microplate spreading system by an 800 km long volcanically active plume channel here we use geochemical geological and geochronological data to argue that the hotspot lies close to easter island moreover new isotopic data for lavas from the seamount chain provide evidence for bidirectional flow between the spreading axis and the plume thus supporting geophysical and fluid dynamical models of mantle flow in a plume spreading axis system5 7 material balance and flux considerations show the easter plume to be weak and cool compared with those beneath larger features such as iceland hawaii and the galapagos islands

earthquake clustering in the eastern mediterranean during historical times most coastal sectors which show evidence of holocene coseismic uplift in greece and the eastern mediterranean were raised during a short period called here the early byzantine tectonic paroxysm ebtp between the middle of the fourth and the middle of the sixth century a d the areas uplifted at that time include cephalonia and zante in the ionian islands lechaion and the perachora peninsula in the gulf of corinth the pelion coast of thessaly antikythira and the whole of western crete a coastal sector near alanya in southern turkey and the entire levant coast from hatay turkey to syria and the lebanon the amount of the ebtp uplift was generally between 0 5 m and 1 0 m but reached a maximum of about 9 m in southwestern crete in several areas zante pelion coast antikythira western crete alanya the ebtp uplifted shoreline is the only evidence of holocene emergence in other areas however a similar uplift occurred earlier in the holocene levant coast or more recently cephalonia evidence of preseismic subsidence prior to the ebtp uplift has been reported from thessaly antikythira and crete in both the latter islands the ebtp uplift was preceded by a series of about 10 coseismic small subsidence movements each measuring some tens of centimeters which took place in the preceding 3000 years no evidence was observed of postseismic vertical displacements

relative motion of the nazca farallon and south american plates since late cretaceous time by combining reconstructions of the south american and african plates the african and antarctic plates the antarctic and pacific plates and the pacific and nazca plates we calculated the relative positions and history of convergence of the nazca and south american plates despite variations in convergence rates along the andes periods of rapid convergence averaging more than 100 mm a between the times of anomalies 21 49 5 ma and 18 42 ma and since anomaly 7 26 ma coincide with two phases of relatively intense tectonic activity in the peruvian andes known as the late eocene incaic and mio pliocene quechua phases the periods of relatively slow convergence 50 to 55 30 mm a at the latitude of peru and less farther south between the times of anomalies 30 31 68 5 ma and 21 and between those of anomalies 13 36 ma and 7 correlate with periods during which tectonic activity was relatively quiescent thus these reconstructions provide quantitative evidence for a correlation of the intensity of tectonic activity in the overriding plate at subduction zones with variations in the convergence rate

plumes in a convecting mantle models and observations for individual hotspots the motion of hotspots and the deformation of their underlying plume conduits as calculated within models of global mantle flow are presented a new list of 44 possible hotspots with associated tracks has been compiled for all of them calculations have been performed under consideration of individual age and anomalous mass flux for three different models of plume buoyancy and mantle flow plume source depth has usually been assumed to be the top of d but an alternative source depth at the 670 km discontinuity has also been considered using models of relative plate motions and boundaries hotspot tracks on plates have been calculated and compared with age data ocean floor topography and distribution of volcanics on continents absolute plate motions have been redetermined under consideration of hotspot motion using a new least squares method for the hawaiian and yellowstone hotspots source locations and hotspot motion have been computed for a total of up to 23 different models the results show plume conduits being tilted with source regions at the d moving in the lowermost mantle flow generally toward large scale upwellings under southern africa and the south central pacific hotspot surface motion often represents the horizontal component of midmantle flow which is frequently opposite to plate motion toward ridges and away from subduction zones in particular almost all models tested predict southward motion of the hawaii and kerguelen hotspots and westward motion of the iceland hotspot for models including hotspot motion the agreement between calculated and observed hotspot tracks is frequently about as good as or better than for the fixed hotspot model but sometimes fixed hotspots give the best fit in some cases where the track ends at a subduction zone e g for the bowie hotspot results can give indications about the otherwise unknown age of the hotspot in other cases especially for the tahiti hotspot results suggest an origin shallower than d and in yet other cases particularly east africa the failure of the hotspot models used supports other evidence indicating the presence of comparatively broad upwellings rather than localized plumes

instabilities of fluid conduits in a flowing earth are plates lubricated by the asthenosphere summary a laboratory and theoretical study of the stability of conduits of buoyant fluid in a viscous shear flow has been conducted the object of the study is to explain the formation of discrete islands in island chains such as the hawaiian emperor seamount chain and to investigate a new method by which the variation of shear with depth in the mantle may be determined the conduits were made by injecting oil into a more viscous oil of greater density initially a growing chamber of lower viscosity oil formed near the injector but when the chamber got sufficiently large it rose as a buoyant spheroid behind this trailed a vertical cylindrical conduit through which fluid could continue to rise to the surface as long as the source continued if the more viscous fluid was sheared laterally the conduit was gradually rotated to a more horizontal position the diameter of the conduit increased with time due to a decreasing component of gravitational force along the axis of the conduit when the conduit was tilted to more than 60 with the vertical it began to go unstable by developing bumps which ultimately initiated a new chamber which rose to a new spot in addition if the reynolds number of the conduit was greater than approximately ten an axisymmetric wavy instability appeared in the walls of the conduit and the conduit had to be tilted less before a new chamber was initiated if shear under the pacific plate has to tilt buoyant mantle plumes to as much as 60 to form the relatively regular island chains associated with hot spots most of the shear would be found in a zone with a vertical extent of less than 200 km

crustal investigation of the hellenic subduction zone using wide aperture seismic data abstract we present the results of a wide aperture seismic onshore offshore study crete seismic experiment in the cretan region as part of the hellenic arc compressional system three seismic lines were carried out on and around the island of crete in order to investigate the crustal structure of the region up to 119 three component recording stations were deployed on each profile that observed seismic energy generated by a 48 l airgun array and eight 20 kg landshots a total of 6208 shots were fired upon completing the fieldwork the vertical components of all stations were evaluated 300 common receiver gather crg sections of the ocean bottom seismographs obs and land stations as well as 100 common source gather csg sections of the land shots and selected airgun shots were compiled and modeled in order to generate a 2d p wave velocity depth model for each profile the accuracy of the model depends on the depth and position along the profiles and does not exceed 5 for both depth and p wave velocity we identified strong lateral variations in crustal and sedimentary thickness mainly in a north south direction but also along strike east west the crust is continental and has a maximum thickness of 32 5 km below northern central crete its subdivision in an upper v p 5 8 6 3 km s locally up to 6 5 km s and a lower v p 6 4 6 9 km s part is justified by a first order discontinuity with v p velocity a contrast of up to 0 6 km s the eastern part of crete shows a significantly thinner crust of 24 to 26 km to the north the crustal thickness decreases to 15 km below the central cretan sea the prominent decrease of the moho depth north of central crete is interpreted to represent the northern end of a microcontinent that was subducted in oligocene times and later surfaced by buoyant escape stockhert et al 1999 thomson et al 1999 the p t t d history of the high pressure rocks of crete greece denudation by buoyant escape in exhumation processes normal faulting ductile flow and erosion ring u lister g willet s brandon m eds spec publ of the geol soc of london p 154 to the south and southwest of the island the continental crust gradually thins to a minimum of 17 km and at approximately 100 km off the southern coast of crete it is in contact with oceanic crust below the mediterranean ridge upper mantle velocities were determined to be 7 7 km s below the cretan sea and 8 0 km s south of crete below the continental cretan crust a 6 to 7 km thick layer with v p velocities between 6 6 and 7 1 km s was identified on each line and could be followed by reflections to a depth of 42 km it is decoupled from the overlying continental crust at central crete and is interpreted as oceanic crust presently under subduction towards the nne below the aegean sea

the mineralogy of gold and its relevance to gold recoveries processing of most gold ores other than placers involves conventional gravity separation and direct cyanidation the difficult or refractory gold ores are not amenable to direct cyanidation and these ores require detailed mineralogical investigations to assist in determining the recovery processes there are six mineralogical factors that can contribute to poorer recoveries these are 1 the nature of the gold containing minerals 2 the grain size of the gold minerals 3 the nature of the gangue minerals 4 the associated sulfide minerals 5 coatings on gold and 6 chemically bound or invisible gold

southeast pacific tectonic evolution from early oligocene to present plate tectonic reconstructions of the nazca antarctic and pacific plates are presented from late oligocene to present these reconstructions document major plate boundary reorganizations in the southeast pacific at dirons 6c 24 ma 6 o 20 ma and 5a 12 ma and a smaller reorganization at chron 3 o 5 ma during the chron 6 o reorganization it appears that a ridge propagated into crust north of the northernmost pacific antarctic ridge between the chiloe fracture zone fz of the chile ridge and agassiz fz of the pacific nazca ridge which resulted in a northward jump of the pacific antarctic nazca pac ant naz mid ocean triple junction during the chron 5a reorganization the chile ridge propagated northward from the valdivia fz system to the challenger fz through lithosphere formed roughly 5 myr earlier at the pacific nazca ridge during this reorganization a short lived microplate the friday microplate existed at the pac ant naz triple junction the pac ant naz triple junction jumped northward 500 km as a result of this reorganization from a location along the valdivia fz to a location along the challenger fz the chron 5a reorganization also included a change in spreading direction of the chile and pacific antarctic ridges the reorganization at chron 3 o initiated the formation of the juan fernandez and easter microplates along the east pacific rise the manner of plate boundary reorganization at chron 6 o and chron 5a and possibly today at the juan fernandez microplate included a sequence of rift propagation transfer of lithosphere from one plate to another microplate formation and microplate abandonment and resulted in northward migration of the pac ant naz triple junction the associated microplate differs from previously studied microplates in that there is no failed ridge

structure of axisymmetric mantle plumes results of high resolution numerical calculations of axisymmetric thermal plumes in an infinite prandtl number fluid with thermally activated viscosity are used to infer the structure of axisymmetric subsolidus thermal plumes in the earth s lower mantle we calculate the velocity and temperature distribution for axisymmetric convection above a heated disk in an incompressible fluid cylinder 2400 km in height and 1200 km in diameter initially at a uniform temperature t the lower boundary representing the plume source region near the core mantle boundary is stress free and maintained at temperature tc t the upper boundary is permeable allowing the plume to escape the cylinder we determine the sensitivity of plume structure to viscosity variations c ranging from 102 to more than 104 and temperature differences t tc t in the range 400 850 k starting plumes consist of a large leading diapir and a trailing conduit connected to the thermal boundary layer above the heated surface the leading diapir expands during ascent to about 400 km diameter at 2200 km height in steady state the plume consists of a narrow high velocity conduit imbedded within a broader thermal halo the width of both these structures is proportional to height above the heated boundary and inversely proportional to t and the viscosity ratio heat transport in the plume is nearly independent of viscosity variations a simplified boundary layer model yields a heat transfer law nu ra where nu is the plume nusselt number and ra is the rayleigh number based on t and the radius of the heated circular region feeding the plume calculated steady state plume heat transports fit this law to within a few percent we present several calculations of plumes with heat transport in the range 100 400 gw similar to the advective heat transport by the hawaiian hotspot at the top of the lower mantle plumes with large viscosity variations have high velocity conduits 50 60 km in diameter and 125 km diameter thermal halos a centerline temperature anomaly of about 500 k and a centerline velocity of about 75 cm yr 1 plumes with weak viscosity variations are approximately twice as broad and have centerline temperature anomalies less than 160 k at the same height and much smaller velocity large viscosity variations and a minimum heat transport are both

digital isochrons of the world s ocean floor we have created a digital age grid of the ocean floor with a grid node interval of 6 arc min using a self consistent set of global isochrons and associated plate reconstruction poles the age at each grid node was determined by linear interpolation between adjacent isochrons in the direction of spreading ages for ocean floor between the oldest identified magnetic anomalies and continental crust were interpolated by estimating the ages of passive continental margin segments from geological data and published plate models we have constructed an age grid with error estimates for each grid cell as a function of 1 the error of ocean floor ages identified from magnetic anomalies along ship tracks and the age of the corresponding grid cells in our age grid 2 the distance of a given grid cell to the nearest magnetic anomaly identification and 3 the gradient of the age grid i e larger errors are associated with high age gradients at fracture zones or other age discontinuities future applications of this digital grid include studies of the thermal and elastic structure of the lithosphere the heat loss of the earth ridge push forces through time asymmetry of spreading and providing constraints for seismic tomography and mantle convection models

physical properties and state of the crust and upper mantle of the eastern mediterranean sea deduced from geophysical data abstract by evaluating the geophysical information available for the eastern mediterranean sea ems a crustal thickness map and some conclusions as to the nature of the crustal type were drawn it was found that the ionian abyssal plain is floored by an oceanic type of crust which is 14 km thick and covered by sediments of the order of 8 km thick the herodotus abyssal plain in the levantine sea is floored by a crust 22 km thick and covered by sediments ranging between 10 and 15 km thick the eastern mediterranean rise extending more or less continuously from the apulian plateau to rhodes and the south of the antalya basin is of a thickness ranging between 28 and 34 km the thickness of its sedimentary cover is of the order of 10 km the borders of the eastern mediterranean sea are built up of thick continental crust for example the hellenides of western greece range between 40 and 44 km thick and western turkey has a similar crustal thickness the crust of sicily also exceeds 40 km whereas the southern and eastern borders of the ems are approximately 30 32 km thick tectonically the northern border of the ems is built up of active continental margins defined by the calabrian hellenic and cyprus antalya arcs whereas the southern border represents a passive continental margin controlled mainly by subsidence and stretching to the east the dead sea megashear limits the area the deep basins of the eastern mediterranean sea are tectonically controlled by subsidence and partial stretching the mediterranean ridge or rise is still an area of dispute regarded by some authors as a subsiding continental fragment and separated from the hellenic arc by the hellenic trench whereas others consider it to be a zone of crustal shortening thickened mainly by thrusting both the western and southwestern borders of the mediterranean rise and the hellenides are controlled by compressional processes similar to those deforming the calabrian arc the stravo and pliny trenches to the east southeast border of the hellenic arc are partly affected by strike slip movements various plate tectonic models of the area have been proposed by several authors though the complexity of the deformation hardly permits reliable reconstructions the lack of reliable paleomagnetic information and the absence of linear magnetic anomalies do not favour the application of plate tectonic concepts vertical processes due to the uprising of lithothermal systems below the hellenic and calabrian arcs may also be regarded as the driving force controlling the present day deformation

vertical land movements and sea level changes along the coast of crete greece since late holocene abstract geomorphological survey along the coasts of crete revealed widespread evidence of uplifted and submerged tidal notches different phases of beachrock formation and many relics of ancient coastal constructions about 1 6 ka bp when the sea level was at 1 25 0 05 m the western tectonic block of the island uplifted by 9 15 0 20 m in its westernmost extremity and by 2 00 m approximately in its eastern boundary and tilted southeastward repeated preceding episodes of subsidence submerged the western part of the island by 1 60 m in a period of 2300 years along the western coast the younger phase of the submerged beachrocks was identified and measured at nineteen locations together with the submerged tidal notches and archaeological remains land subsidence by 1 25 0 05 m subsequent to the uplift of the western part occurred after the late venetian occupation period ad 1600 coincident with the submersion of the eastern part of the island in central and eastern crete the relative sea level change evidence from tidal notches and beachrocks revealed five distinct sea level stands at 6 55 0 55 m 3 95 0 35 m 2 70 0 15 m 1 25 0 05 m and 0 55 0 05 m the lowest sea level stand can be identified with the oldest dated tidal notch of western crete between 4200 90 b p and 3930 90 b p two subsequent sea levels can be linked with the protopalatial 1900 1700 b c or 1600 b c and neopalatial period 1600 1450 b c of the minoan civilization according to submerged prehistoric morphologies and inundated minoan constructions the change of sea level from 2 70 0 15 m to 1 25 0 05 m is placed between 1450 b c and the fourth century bc the dating of 1 25 0 05 m sea level stand was based on the measurement and interpretation of ancient coastal installations built along the coast of central and eastern crete during classical hellenistic roman byzantine and venetian periods historical sources report a relative sea level rise by 0 70 m during the ad 1604 paroxysmal event over the last 400 years the relative sea level rose by 0 55 m the uplift of the coast of western crete and the submersion in its central and eastern coast indicate that during the ad 365 paroxysmal event the island was split along a tectonic boundary identified with the neotectonic graben of spili and its northern and southern prolongation

oceanic spreading center hotspot interactions constraints from along isochron bathymetric and gravity anomalies we analyzed bathymetric and gravity anomalies along present and paleoaxes of oceanic spreading centers influenced by the iceland azores galapagos tristan and easter hotspots residual bathymetry up to 4 7 km and mantle bouguer gravity up to 340 km anomalies are maximum at on axis hotspots and decrease with increasing ridge hotspot separation distance d until becoming insignificant at d 500 km along isochron widths of bathymetric anomalies up to 2700 km depend inversely on paleo spreading rate reflecting the extent to which plume material will flow along axis before being swept away by the spreading lithosphere flux balance arguments suggest that the five hotspots feed material to ridges with comparable fluxes of 2 2 106 km3 m y assuming that the amplitudes of these geophysical anomalies reflect temperature dependent crustal thickness and mantle density variations we suggest that ridge temperature anomalies are maximum 150 225 c when plumes are ridge centered and decrease with increasing ridge hotspot distance due to cooling of the ridgeward migrating plume material

asymmetric sea floor spreading caused by ridge plume interactions crustal accretion at mid ocean ridges is generally modelled as a symmetric process regional analyses however often show either small scale asymmetries which vary rapidly between individual spreading corridors or large scale asymmetries represented by consistent excess accretion on one of the two separating plates over geological time spans1 2 3 4 5 6 in neither case is the origin of the asymmetry well understood here we present a comprehensive analysis of the asymmetry of crustal accretion over the past 83 myr based on a set of self consistent digital isochrons7 and models of absolute plate motion8 9 we find that deficits in crustal accretion occur mainly on ridge flanks overlying one or several hotspots we therefore propose that asymmetric accretion is caused by ridge propagation towards mantle plumes or minor ridge jumps sustained by asthenospheric flow10 11 between ridges and plumes quantifying the asymmetry of crustal accretion provides a complementary approach to that based on geochemical12 and other geophysical data13 14 in helping to unravel how mantle plumes and mid ocean ridges are linked through mantle convection processes

geodetic determination of the kinematics of central greece with respect to europe implications for eastern mediterranean tectonics we use a new satellite laser ranging global positioning system slr gps solution at seven sites in anatolia and aegea to obtain a better definition of the extrusion motion of the anatolian aegean block with respect to europe we show that this motion can be described in a first approximation by a counterclockwise rotation which transfers most of the motion of arabia to anatolia we combine 78 displacement vectors obtained at common points of two triangulation nets measured in central greece in 1895 and 1975 with the slr gps measurements to compute the velocity field over greece with respect to europe these measurements indicate that central greece is a zone of extension between the anatolian aegean counterclockwise rotation to the south and the northern greece clockwise rotation to the north this extension is principally localized within the gulf of corinth to the east but is distributed to the west we then extrapolate this velocity field to the whole aegea and western anatolia using recently published gps results as well as the slr results the narrow dextral north anatolian fault which limits the velocity field to the north progressively gives way to a much wider boundary zone where extension becomes dominant we show that the collision between the mediterranean ridge and africa began 3 6 ma and we describe the modifications that this collision has produced on the kinematic pattern both in aegea and on the mediterranean ridge

microseismic activity and seismotectonics of heraklion area central crete island greece abstract a seismological network of 10 portable analogue stations was installed in the area of heraklion central crete from september to december 1995 during this period more than 1000 events were recorded by at least 4 stations with magnitudes ranging from 0 5 to 4 6 and depths up to 70 km analysis of 336 well located events revealed high seismic activity in the onshore area seismicity is shallow

reconciling late neogene pacific absolute and relative plate motion changes new models of pacific absolute plate motion relative to hot spots and models of relative plate motion involving the pacific plate all agree there was a significant change in the late neogene chron 3a 5 89 ma reflecting a more northerly absolute motion than previously determined as pacific absolute plate motion became slightly more northerly left stepping transform segments came under compression some left stepping segments became microplates with clockwise rotation others show clear evidence of compressional deformation conversely right stepping transforms came under tension and many developed intratransform spreading centers or show similar evidence for transform magmatism several large left stepping transform offsets represent portions of the nazca plate protruding into the pacific and as such act as obstacles to the more northerly pacific absolute plate motion we suggest these obstructions act to enhance the generally tensile equatorial pacific stress regime caused by distant slab pull as a consequence the greater french polynesia region has experienced diffuse volcanism that increased considerably following the chron 3a plate motion change we propose that since the hawaii emperor bend time the distant pacific slab pull and the friction between the large buoyant ontong java plateau and the northern margin of the australia plate have produced episodes of increased tensile stresses in the equatorial pacific we believe these stress excursions are responsible for much of the intraplate volcanism observed in a wide triangular region from samoa to the east pacific and pacific antarctic rises

geodynamic implications of moving indian ocean hotspots abstract the reconstructed positions of many of the indian ocean intraplate volcanic features are inconsistent with the present positions of the hotspots to which they have been ascribed the discrepancy can be explained by the past motion of the hotspots themselves and in the errors introduced in an absolute plate model based on fixed hotspots previous models for the motion of hotspots in the indian ocean e g steinberger and o connell in the history and dynamics of global plate motions 2000 pp 377 398 and geophys j int 132 1998 412 434 antretter et al earth planet sci lett 203 2002 635 650 have had success in matching paleolatitudes of the kerguelen hotspot but not the marion or reunion hotspots we calculate the motion of the indian ocean hotspots using a method described in steinberger and o connell op cit employing a plate motion model revised using identification of mesozoic magnetic anomalies in the enderby basin gaina et al in the evolution and dynamics of the australian plate in press we find a motion of 7 south for the kerguelen plume similar to previous models antretter et al op cit this motion alleviates the discrepancies in the position of the kerguelen plume and its purported involvement in the formation of the ninetyeast ridge rajmahal traps bunbury basalts and assorted volcanics of the western australian margin we find a motion of 5 north and 7 south for the reunion and marion plumes respectively the motion of the reunion hotspot is consistent with paleolatitude estimates the apparent fixity of the marion hotspot torsvik et al earth planet sci lett 164 1998 221 232 is not well constrained but may be due to the combination of hotspot motion and true polar wander acting in opposing directions we present revised absolute finite rotations for the indian plate for the last 65 ma based on the motion of these hotspots which place india farther north in the past than for fixed hotspot models

time space mapping of easter chain volcanism abstract new 40ar 39ar and published k ar ages show that the locus of volcanism along the easter volcanic chain evc has shifted systematically from the nazca ridge at about 26 m y to the recently active sala y gomez island easter island region this indicates a plume rather than a hotline i e mantle roll origin for the evc the time space distribution of ages combined with published ages for the galapagos and juan fernandez volcanic chains is used to reconstruct nazca plate velocities over the past 26 m y a plume now located in the region of sala y gomez island is most compatible with these data west of the plume the evc records neither nazca nor pacific plate motions this section of the evc may be related to westward channeling of plume material to the pacific nazca spreading boundary region

fault plane solutions of microearthquakes and small events in the hellenic arc abstract the hellenic arc is the most active seismic region of the transition zone between the african and eurasian plates in this rapidly deforming region the physical state of the crust and upper mantle may vary laterally and vertically however a detailed 3d model of the region is lacking the reliable determination of fault plane solutions is crucial if such a model is to be produced on this basis fault plane solutions have been determined from recent microearthquakes and small events to assess their reliability for use in tectonic interpretation a search algorithm on first motion data and amplitude ratios and also a waveform matching scheme were employed on data from our temporal network operated on the western part of the island of crete there a network of 47 three component digital stations with an aperture of 60 km and an average station spacing of 5 km was operated in 1997 the majority of the shallow microearthquakes under crete for which fault plane solutions were determined have a near horizontal t axis oriented essentially e w differences between well determined fault plane solutions from the search algorithm and the waveform matching technique were significant strike up to 45 dip up to 10 and slip up to 50 second data of small events within the hellenic subduction zone were obtained from recently installed broadband stations at local and regional distances and inverted for a deviatoric seismic moment tensor available solutions from other sources such as the harvard group emsc or sed show drastic differences in part owing to still limited azimuthal station coverage the resulting fault plane solutions of small events have generally not been well constrained the observed large variation of fault plane solutions for micoearthquakes and small events poses a caveat to tectonic interpretation in case of using data from a few stations only

geophysics of the pitman fracture zone and pacific antarctic plate motions during the cenozoic multibeam bathymetry and magnetometer data from the pitman fracture zone fz permit construction of a plate motion history for the south pacific over the past 65 million years reconstructions show that motion between the antarctic and bellingshausen plates was smaller than previously hypothesized and ended earlier at chron c27 61 million years ago the fixed hot spot hypothesis and published paleomagnetic data require additional motion elsewhere during the early tertiary either between east antarctica and west antarctica or between the north and south pacific a plate reorganization at chron c27 initiated the pitman fz and may have been responsible for the other right stepping fracture zones along the ridge an abrupt 8 clockwise rotation in the abyssal hill fabric along the pitman flowline near the young end of chron c3a 5 9 million years ago dates the major change in pacific antarctic relative motion in the late neogene

structure and dynamics of sheared mantle plumes 1 an extensive series of laboratory experiments is used to investigate the behavior of sheared thermal plumes the plumes are generated by heating a small circular plate on the base of a cylindrical tank filled with viscous fluid and then sheared by rotating a horizontal lid at the fluid surface the motion of passive tracers in the plumes is visualized by the release of several dye streams on the hot plate we systematically examine the dependence of the convective flow on four dimensionless numbers a velocity ratio a rayleigh number the viscosity ratio and an aspect ratio we identify and delineate two transitions in the convective behavior from a regime where the plume can spread upstream against the shear to a regime where the entire plume is advected downstream and from a regime of negligible cross stream circulation to a regime with significant cross stream circulation and thermal entrainment our analysis of the steady profiles of the plumes shows that they initially rise with a constant vertical rise velocity this rise velocity depends on the buoyancy flux and ambient viscosity but is almost independent of the centerline plume viscosity which suggests that most of the thermal plume has a viscosity that is much closer to the ambient viscosity than the centerline viscosity as the plumes approach the lid they decelerate as the viscous drag on them steadily increases the lateral spreading of the plumes under the lid is found to be well described by similarity solutions derived for the spreading of compositional plumes on a rigid surface if the effective viscosity of the thermal plumes is taken to be the ambient viscosity rather than the centerline viscosity a similar theoretical model is found to roughly predict the upstream spreading of thermal plumes at low shear but it breaks down at moderate to high shear where the entire plumes are advected downstream when our results are applied to the earth we find that mantle plumes are mostly divided into only two flow regimes in the upper mantle plumes under slow moving plates experience upstream flow and negligible cross stream circulation while plumes under faster moving plates including all pacific plumes experience significant cross stream circulation and are advected downstream we also demonstrate that geochemical heterogeneities in a plume s source region will result in an azimuthally zoned plume and in an asymmetric geographical distribution of geochemical heterogeneities in the erupted hot spot basalts as is seen in the hawaiian galapagos marquesas and tahiti society island chains for individual mantle plumes we determine their diameter and vertical rise velocity as well as the extent of upstream spreading and the rate of lateral spreading under the lithosphere

deflection of plumes by mantle shear flow experimental results and a simple theory summary linear hotspot tracks indicate relative motion between some hotspot sources and the overlying lithosphere in order to better understand the effects of plate motions and mantle convection on mantle plumes and associated hotspots we consider the path of a continuous plume of buoyant material in a shear flow laboratory experiments show that steady plumes bent over by a linear velocity profile follow parabolic trajectories plume trajectories are also shown to evolve quadratically in time toward a new steady shape after a change in the ambient flow a remarkably simple description of plume dynamics provides good agreement with the experimental data the plume trajectory is determined by the combination of horizontal advection by mantle flow and vertical rise according to a modified stokes law these results are applied to some idealised examples which demonstrate effects of depth dependent mantle viscosity and return flow at least some mantle plumes are likely to be sufficiently robust that they remain close to vertical and therefore stable

the 8 5 magnitude ad365 earthquake in crete coastal uplift topography changes archaeological and historical signature abstract an up to 9 m uplift of western crete a cluster of coastal uplifts in the east mediterranean radiocarbon dated approximately 1500 bp as well as historical and archaeological data are evidence for major although poorly documented seismic destruction on a nearly mediterranean scale in the 4th to 5th c ad including the destruction of the nile delta in egypt by a tsunami in ad365 these data represent parts of a puzzle for historians archaeologists geologists and seismologists detailed analysis of geological historical and archaeological data including precise numismatic evidence permits recognition of a major earthquake in crete responsible for coastal uplift at ad365 elastic dislocation analysis of coastal uplift data reveals that this earthquake was associated with a reverse fault offshore of southwestern crete that its minimum magnitude was 8 5 and that this model is consistent with the available seismological and large scale tectonic data despite its magnitude this earthquake cannot have produced the necessary short period high energy waves which are necessary to explain the seismic damage which occurred circa ad365 in a very broad region from sicily to cyprus and libya hence the ad365 earthquake sequence included at least two other major events with epicentres close to cyprus and sicily although significant changes in the coastal morphology widespread destruction and a high human death toll occurred the ad365 crete earthquake was not responsible for any major cultural change it occurred during the transition from the roman to the christian period characterized by vast luxurious villas and modest dwellings on crete respectively

hydrothermal processes and ore forming fluids in the le bourneix gold deposit central france the le bourneix gold deposit in the french massif central occurs within a shear zone in gneisses of the limousin hercynian basement gold bearing quartz lenses formed during extension phases after cataclasis of initially barren quartz postdating mylonites bouchot et al 1989 the economic mineralization arsenopyrite gold pyrite galena and pb sulfosalts hosted by microsaccharoidal quartz formed after crystallization of arsenopyrite and pyrite synchronous with white milky quartz a later paragenesis associated with hyaline quartz comprises ag rich gold sphalerite galena tetrahedrite and sulfosalts arsenopyrites have a range of compositions with a mean as content equivalent to an equilibrium temperature with pyrite of about 400 degrees or 30 degrees c hydrothermal alterations synchronous with ore deposition resulted in a phengite chlorite association and then a propylitic chlorite carbonate assemblage from fluid inclusion studies it appears that the general evolution of the ore fluids is 1 circulation under high pressure 2 kbars at 400 degrees or 50 degrees c of a low salinity solution with minor volatile contents 2 mixing of this solution with a co 2 rich vapor induced by a drop in pressure down to 0 6 kbars producing a heterogeneous fluid at 320 degrees c and 3 circulation of volatile free aqueous solutions at decreasing temperature 300 degrees 120 degrees c and salinity most of the economic ore probably formed at the transition from 1 to 2 lead isotope data suggest a local source for metals with mixing of poorly radiogenic lead from the basement orthogneiss with radiogenic lead from a supracrustal source

postnappe stacking extension and exhumation of high pressure low temperature rocks in the island of crete greece the island of crete consists largely of nappes of contrasting lithologies and metamorphism that were stacked southward during an oligocene early miocene n s compression with the lower nappes undergoing a high pressure low temperature hp lt metamorphism this was followed by a n s miocene crustal extension that caused thinning of the nappes and uplift of the hp lt metamorphic rocks ductile conditions took place in the lower nappes associated with a retrograde greenschist metamorphism while semiductile to brittle conditions took place in the upper nappes a major normal detachment fault separates the lower and the upper nappes the quartz texture analyses and the symmetry of structures indicate bulk coaxial deformation while the results of strain analysis suggest both constrictional and flattening strains a younger ne sw compression affected both the thinned nappe pile and the late miocene pliocene sedimentary basins finally a pliocene ne sw extension led to further uplift and exhumation of the hp lt metamorphic rocks this cyclic tectonometamorphic process of alternate compression and extension took place during the migration of the hellenic orogenic belt toward the most external units including successive tectonic events

fish tanks of eastern crete greece as indicators of the roman sea level abstract the ancient fish tanks and fish traps of crete are relics of the roman domination of the island they were usually constructed near the major urban centers of that period the direct relationship of their various functional characteristics with past sea levels and the relatively accurate determination of their construction dates establish them as sensitive indicators of sea level change through space and time the fish tanks presented in detail in this study namely those of matala chersonissos mochlos and sitia and the fish trap in the gulf of zakros have all been reported recorded and or interpreted in regard to their operation by previous researchers in the absence of a comprehensive interdisciplinary approach to the issue uneven methodologies inaccurate data and wrong measurements have led to erroneous conclusions about sea level during their operation and about the size and direction of vertical tectonic movements in eastern crete during the upper holocene the present study is based on a new underwater survey in the course of which the architectural and functional features of the ancient constructions were reexamined precisely their depth from modern sea level was measured and their relationship with coastal landforms indicative of a past sea levels was investigated a review of their manner of operation and their modern submerged position allowed the definition of a roman mean sea level 1 24 m 0 09 m below the present one the submersion of the central and eastern parts of crete included in the same tectonic block with a total length of at least 150 km at an average tectonic rate of 0 65 mm year during the last 1900 100 years occurred as is shown by historical evidence during a paroxysmal tectonic event probably related to the strong earthquake of 1604

incipient continental collision and plate boundary curvature late pliocene holocene transtensional hellenic forearc crete greece u ring t c brachert write in their recent paper ten veen kleinspehn 2003 proposed that the western messara graben of central crete underwent transtensional deformation since about 3 4 ma transtension is supposed to be dominantly resolved along 070 striking sinistral faults and that the 070 striking faults have strike slip normal slip ratios of 10 100 1 ten veen kleinspehn 2003 then use their results from the western messara graben to propose that sinistral transtension should represent tectonic escape of central and eastern crete during incipient collision of the libyan passive margin the interpretation of the kinematic data on which ten veen kleinspehn 2003 base their tectonic model is in contrast to earlier studies which have attributed the young i e pliocene to recent kinematics of crete largely to radial extension angelier et al 1982 fassoulas 2001 ring et al 2001 ten veen kleinspehn 2003 p 167 argued that onshore structural assemblages is critical to deciphering forearc kinematics and therefore we present our kinematic data from onshore faults in the western and central messara graben and compare our data together with the fault slip data of fassoulas 2001 from the heraklion graben and microseismicity data hatzfeld et al 1993 delibasis et al 1999 with the fault slip data of ten veen kleinspehn 2003 fig 9 for discussing the kinematics of the young faults we believe that fault slip data directly reflect the kinematics of the faults from which they were collected and therefore allow testing the proposition often veen kleinspehn that sinistral transtension is supposed to be mainly resolved at the 070 striking faults the latter of which are known to be an integral part of the youngest set of faults on crete fassoulas 2001 and are in part seismically active delibasis et al 1999 in general

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

a review of possible eustatic isostatic and tectonic contributions in eight late holocene relative sea level histories from the mediterranean area abstract this paper consists of a comparison between eight late holocene sea level histories investigated by the author in different mediterranean areas and sea level predictions in the same areas made by global isostatic models the areas include three regions that are generally considered as tectonically relatively stable 1 the southern coast of france 2 sardinia and 3 the southern coasts of tunisia where late holocene evidence may be either of submergence or of emergence also considered are 4 a subsidence region in the northern adriatic and actively uplifting areas 5 in calabria and 6 in nisyros island greece lastly case studies in areas affected by repeated coseismic vertical displacements include 7 western crete and antikythira island in the hellenic arc and 8 the levant coasts of turkey syria and the lebanon in each case the question of whether the evidence available may or may not be consistent with gradual isostatic or eustatic displacements has been explored it appears that in non tectonic areas the hydro isostatic effects have been overestimated sardinia or underestimated southern tunisia by the same models in the northern adriatic the closest mediterranean area to the former scandinavian ice sheet glacio eustatic effects are suspected to be almost absent our analysis failed to quantify isostatic effects in areas of rapid tectonic uplift calabria and nisyros but rejected predictions of significant isostatic subsidence in the hellenic arc and on the levant coast finally several data from tectonic and non tectonic areas are consistent with nearly stable global eustasy since 6000 bp thus challenging the assertion of significant additional melting of antarctica after the complete melting of the former northern hemisphere ice caps

new insights on the subsidence of lipari island aeolian islands southern italy from the submerged roman age pier at marina lunga abstract lipari island belongs to the aeolian archipelago located in the southern tyrrhenian sea italy which is one of the most active volcanic areas of the mediterranean basin although this region has been settled since prehistory only during roman times were coastal installations built in these islands in this study we present and discuss data on the relative sea level change estimated from a submerged pier of roman age dated 2100 100 bp this structure about 140 60 m is located along the coast of marina lunga corresponding to the present location of the main harbor of lipari island this pier which was accidentally discovered in 2008 during preliminary excavations for the construction of a new pier is a valuable indicator of relative sea level changes and vertical land movements its top surface is presently located at 9 1 0 05 m while the foundations at the outer end of the pier are at 11 6 0 05 m above a shoreline placed at 13 0 0 05 m we studied this site through direct archaeological investigations and ultra high resolution multibeam bathymetry the current submergence of this pier can be explained by the cumulative effect of the relative sea level changes caused by the regional glacio hydro isostatic signal active since the end of the last glacial maximum and the local volcano tectonic land subsidence from our investigations a relative sea level change at 12 3 0 7 m with a subsidence rate at 5 79 0 01 mm y 1 and an average value of volcano tectonic contribution at 5 17 0 01 m y 1 for the last 2100 100 years bp is estimated from comparison against the latest predicted sea level model for the southern tyrrhenian sea these rates of relative sea level change led to the disuse of the harbor after around the fourth century ad in agreement with archaeological interpretations our results provide new insights on the recent evolution of this active volcanic area

sea level in roman time in the central mediterranean and implications for recent change instrumental records indicate that ocean volumes during the 20th century have increased so as to raise eustatic sea level by f1 2 mm year and the few available records suggest that this is higher than for the previous century geological data indicate that ocean volumes have increased since the main phase of deglaciation about 7000 years ago but whether this continued into the recent past remains unclear yet this is important for establishing whether the recent rise is associated with global warming or is part of a longer duration non anthropogenic signal here we present results for sea level change in the central mediterranean basin for the roman period using new archaeological evidence these data provide a precise measure of local sea level of 1 35f0 07 m at 2000 years ago part of this change is the result of ongoing glacio hydro isostatic adjustment of the crust subsequent to the last deglaciation when corrected for this using geologically constrained model predictions the change in eustatic sea level since the roman period is 0 13f0 09 m a comparison with tide gauge records from nearby locations and with geologically constrained model predictions of the glacio isostatic contributions establishes that the onset of modern sea level rise occurred in recent time at f100f53 years before present d 2004 elsevier b v all rights reserved

on the dynamics of long lived plume conduits in the convecting mantle abstract long lived plumes responsible for mantle hotspots and associated chains of volcanism will be deflected from the vertical as they penetrate through a mantle which is overturning on much larger length scales in response to surface cooling recent experiments have shown that plume inclination leads to entrainment of surrounding material as a result of coupling between conduction of heat and laminar stirring we develop an analysis for entrainment and its effects on the structure and dynamics of continuing steady conduits in a mantle undergoing horizontal shear it is found that the stirring of surrounding mantle with plume source material can result in major modifications of the diameter temperature and mass flux in plumes this model is a departure from the axisymmetric vertical pipe models of plumes and predicts that the temperature in a defected plume will decrease with height thus reducing the plume temperature in the upper mantle while allowing a sizeable temperature difference at the source the cooling of plume conduits after they are deflected by plate motion can lead to a lower maximum temperature and lower mgo contents of basalts along some linear hotspot tracks compared with picrites from their associated flood basalt provinces the effects of entrainment depend primarily on the buoyancy or heat flux carried by the plume with greater cooling for smaller fluxes strong continuing plumes such as hawaii easter island macdonald tahiti and reunion are predicted to produce picrites having mgo contents comparable to the picrites found in continental flood basalt provinces weak plumes such as crozet bouvet and juan de fuca will give only cooler melts through entrainment long lived plumes can sample the whole depth of the mantle from the source to the surface and stirring within the plume leads to compositional zonation which may contribute to compositional heterogeneity in hotspot melts we also predict that plumes originating at the core mantle boundary and having buoyancy fluxes less than about3 103 n s 1 will not give surface hotspots in good agreement with the lower limit of hotspot buoyancy fluxes inferred from seafloor topography

the excess temperature of plumes rising from the core mantle boundary we study the rise of conduit type thermal plumes from the core mantle boundary cmb in a simplified numerical model viscosity is a strong function of temperature and pressure assuming that all plumes start with the same excess temperature at the cmb we find that their temperature in the upper mantle is controlled by the plume flux and is insensitive to variations in viscosity or other material parameters or to the kind of flow law newtonian or non linear the reduction of excess temperature with height is stronger for weaker plumes plumes with a buoyancy flux of less than 1000 kg s should have cooled so much that they would not melt beneath old lithosphere the existence of such hot spots possibly indicates that not all plumes rise from the cmb

on the rise of strongly tilted mantle plume tails abstract the rise of an initially horizontal buoyant cylinder of fluid through a denser fluid at low reynolds number is used to look at the ascent of strongly tilted mantle plumes through the mantle such ascents are characterized by 1 the growth of instabilities and 2 the development of a thermal wake downstream three dimensional numerical experiments were carried out to examine these features an hybrid particle in cell finite element method was used to look at the rise of non diffusing cylinders and a standard finite element method was used to look at the diffusing case first the experiments show that the timescale of the fastest growing instability vary with the rayleigh number and the viscosity ratio in particular the growth rate decreases as the rayleigh number decreases in agreement with our analysis of the laboratory experiments of kerr et al 2008 second the experiments show that the length of the thermal wake increases with the rayleigh number but the change in viscosity has almost no influence on the wake length applied to strongly tilted mantle plumes we conclude that such plumes cannot be unstable given the plume timescales we also discuss the application of this conclusion to weakly tilted plumes besides this study allows to predict that mantle plumes are unlikely to have developed a significant thermal wake by the time they reach the surface finally the resolution that is required to allow for the growth of mantle plume tails by combined diffusion and thermal entrainment is shown to represent a challenge for the large scale mantle convection simulations

the prina complex in eastern crete and its relationship to possible miocene strike slip tectonics abstract the basal neogene formations in the ierapetra region eastern crete are strongly influenced by a late serravallian tectonic phase which resulted in the breakup of pre existing palaeogeographic patterns important vertical movements caused the southward emplacement of neogene sediments together with parts of the underlying pre neogene nappe pile the resulting chaotic association of exotic blocks and sediments known as the prina complex has the properties of a sedimentary melange it can be traced for more than 15 km from north to south in the north a relatively coherent accumulation of large slide masses overlies deformed neogene coarse clastics and pre neogene rocks distally it comprises a poorly stratified sequence of breccias and intermixed finer grained sediments which locally contains olistostromes and debris flows and interfingers to the south with submarine fan deposits the intricate relation of faulting and gravity sliding in a rapidly subsiding basin can be explained by generation in a strike slip setting it is suggested that the ierapetra basin and its offshore extension the south cretan trough were initiated by sinistral movements along a ne sw oriented fault zone implications of this model for the geodynamic evolution of the south aegean area are discussed

late miocene to recent tectonic evolution of crete greece geological observations and model analysis abstract using a numerical model we focus on the late middle miocene to recent kinematic evolution of the cretan segment of the hellenic arc geological observations of crete are given a quantitative interpretation in terms of tectonic mechanisms controlling the evolution of the active arc boundary this was achieved by calculating intra plate stress fields for various possible distributions of forces and comparing the models with observations the models address specific questions concerning important changes in the observed horizontal stress patterns we deal with the question of what caused extension to initiate modelling results of the collapse of an earlier formed topography and extensional forces acting on the plate boundary are compared with a newly reconstructed tectonostratigraphy of crete our results suggest that arc normal pull is the dominant force that generates the late miocene extension in the cretan segment of the overriding plate although arc normal pull in combination with intra plate spreading forces cannot be excluded the observed transform motions in the pliny and strabo trenches led us to incorporate experiments with additional resistance on the eastern levantine segment of the hellenic arc the models performed with a transform resistance along the trenches are in agreement with the cretan deformation for the pliocene to recent period the stress fields for the short duration compressional periods around the middle late miocene and the miocene pliocene boundary are modelled by assuming resistive instead of tensional forces acting at the overriding margin

the environs of elaia s ancient open harbour a reconstruction based on microfaunal evidence during hellenistic and roman times elaia the harbour city of ancient pergamum was an important place of trading and traffic intense mercantile and military activities are documented by literary sources and archaeological evidences geomagnetic and geoelectric investigations detected building structures close to the ancient coastline which are interpreted as ship sheds the aim of this study was to reconstruct the coastal evolution particularly with regard to harbour related facilities for that purpose a 10 m long sediment core was drilled in the area of the ancient open harbour immediately in front of the supposed ship sheds it was studied with the tools of micropalaeontology geophysics sedimentology and geochemistry to improve the reconstruction of the palaeoenvironmental conditions reference samples of modern environments of the area were analysed as indicated by marine ostracod and foraminifer taxa the sediment core shows from bottom to top that the initially fully marine conditions changed to a more restricted fauna indicative for a more sheltered bay with brackish waters this layer dates to hellenistic times it can however be shown that the siltation process had produced a lagoon system already several hundred years bc the elaia embayment was first used as a natural harbour it was equipped with breakwaters in the hellenistic period the progressive siltation caused the abandonment of the harbour in late roman times

sea level change during the holocene in sardinia and in the northeastern adriatic central mediterranean sea from archaeological and geomorphological data abstract we provide new data on relative sea level change from the late holocene for two locations in the central mediterranean sardinia and ne adriatico they are based on precise measures of submerged archaeological and tide notch markers that are good indicators of past sea level elevation twelve submerged archaeological sites were studied six aged between 2 5 and 1 6 ka bp located along the sardinia coast and a further six dated 2 0 ka bp located along the ne adriatic coast italy slovenia and croatia for sardinia we also use beach rock and core data that can be related to holocene sea level the elevations of selected significant archaeological markers were measured with respect to the present sea level applying corrections for tide and atmospheric pressure values at the time of surveys the interpretation of the functional heights related to sea level at the time of their construction provides data on the relative changes between land and sea these data are compared with predictions derived from a new glacio hydro isostatic model associated with the last glacial cycle sardinia is tectonically relatively stable and we use the sea level data from this island to calibrate our models for eustatic and glacio hydro isostatic change the results are consistent with those from another tectonically stable site the versilia plain of italy the northeast adriatic italy slovenia and croatia is an area of subsidence and we use the calibrated model results to separate out the isostatic from the tectonic contributions this indicates that the adriatic coast from the gulf of trieste to the southern end of istria has tectonically subsided by 1 5 m since roman times

conditions of formation of gold bearing arsenopyrite a comparison of synthetic crystals with samples from le châtelet gold deposit creuse france in order to understand the formation mechanisms of gold bearing arsenopyrites hydrothermal experiments have been performed needle shaped gold rich up to 1 7 wt as compared to 1 6 wt in some natural occurrences zoned arsenopyrites were obtained at 400 c and 500 c under 1 and 2 kbar ph2o comparisons with natural needle like gold rich arsenopyrite from the le ch telet deposit creuse france revealed analogous zoning of as s ratio with similar gold content and zonations fluid inclusion studies carried out in the host quartz of the latter indicate high formation temperatures and variable redox conditions compared with the neighbouring villeranges gold deposit where arsenopyrite was formed at about 200 c with gold being mainly trapped within its structure it appears that temperature is not likely to be the major factor for such an incorporation alternatively it is suggested that non equilibrium rapid crystallization may induce gold trapping under an extended range of t p fo2 conditions the practical importance of the needle like habit of arsenopyrite in areas where geochemical gold anomalies are known without visible gold being detected is emphasized

conduit diameter and buoyant rising speed of mantle plumes implications for the motion of hot spots and shape of plume conduits 1 mantle plumes are expected to be affected by large scale flow in the earth s mantle related to plate motions subducted slabs and possibly large scale upwellings motion of plume conduits will depend on both large scale flow and buoyant rising speed of the conduit through the mantle here we present a model of depth dependent plume conduit temperature viscosity radius and buoyant rising speed and use it to compute plume and hot spot motion results support a temperature anomaly of about 500 k at the plume base in this case sublithospheric temperature anomaly is about 150 k for the iceland plume transition zone anomaly is between 150 and 200 k for iceland about 250 k for samoa and about 300 k for hawaii thermal plume radii are about 100 km in the upper mantle increasing to about 200 km in the lower mantle beneath the lithosphere viscosity in the vicinity of plumes is substantially reduced compared to the underlying mantle and fast moving plates deflect plumes by 200 km or less corresponding to a plume conduit buoyant rise time of about 3 myr between 400 and 100 km depth where most of the shear flow due to plate motions occurs during 100 myr plume conduits rise buoyantly from about 1500 2000 km depth in many cases computed hot spot motion agrees with previous computations south southeastward motion of the hawaiian hot spot during the past 100 myr louisville hot spot motion in a similar direction but at slower speed during the past 50 myr and westward motion of the easter hot spot relative to hawaii and louisville however the previously computed substantial southward motion of the kerguelen hot spot is not confirmed if plume sources in the lowermost mantle are assumed to move with large scale flow they are predicted to be displaced toward the two large scale upwellings beneath africa and the pacific relative to hot spot surface locations for fixed sources predicted tilts of the lower part of conduits tend to be opposite to that

a simple global model of plate dynamics and mantle convection cooling and thickening of lithospheric plates with age and subduction result in large scale horizontal density contrasts tending to drive plate motions and mantle flow we quantify the driving forces associated with these density contrasts to determine if they can drive the observed plate motions first two dimensional models are computed to evaluate the effects of assumed rheologies and boundary conditions we are unable to obtain platelike behavior in viscous models with traction free boundary conditions the piecewise uniform velocities distinctive of plate motion can be imposed as boundary conditions and the dynamic consistency of the models evaluated by determining if the net force on each vanishes if the lithosphere has a newtonian viscous rheology the net force on any plate is a strong function of the effective grid spacing used leading to ambiguities in interpretation incorporating a rigid plastic lithosphere which fails at a critical yield stress into the otherwise viscous model removes these ambiguities the model is extended to the actual three dimensional spherical plate geometry the observed velocities of rigid plastic plates are matched to the solution of the viscous stokes equation at the lithosphere asthenosphere boundary body forces from the seismically observed slabs from the thickening of the lithosphere obtained from the actual lithospheric ages and from the differences in structure between continents and oceans are included interior density contrasts such as those resulting from upwellings from a hot bottom boundary layer are assumed to occur on a scale small compared to plate dimensions and are not included the driving forces from the density contrasts within the plates are calculated and compared to resisting forces resulting from viscous drag computed from the three dimensional global return flow and resistance to deformation at converging boundaries the rms residual torque is 30 of the driving torque the density contrasts within the plates themselves can reasonably account for plate motions body forces from convection in the interior may provide only a small net force on the plates at converging boundaries the lithosphere has a yield stress of 100 bars drag at the base of the plates is 5 bars and resists plate motion the net driving forces from subducting slabs and collisional resistance are localized and approximately balance driving forces from lithospheric thickening are distributed over the areas of the plates as is viscous drag the approximate balance of these two forces predicts plate velocities uncorrelated with plate area as observed the model represents a specific case of boundary layer convection the dynamical results are consistent with either upper mantle or mantle wide convection

evidence of active subsidence at basiluzzo island aeolian islands southern italy inferred from a roman age wharf abstract the aeolian arc southern tyrrhenian sea italy is one of the most active volcanic areas of the mediterranean basin affected by volcanic hydrothermal and seismic activity ancient populations settled this region since historical times building coastal installations which currently are valuable archaeological indicators of relative sea level changes and vertical land movements in this study we show and discuss data on the relative sea level change estimated from a submerged wharf of roman age dated between 50 b c and 50 a d located at basiluzzo island this structure has been studied through marine surveys and archaeological interpretations and is presently located at a corrected depth of 4 10 0 2 m we explain this submergence by a cumulative effect of the relative sea level change caused by the regional glacio hydro isostatic signal active since the end of the last glacial maximum and the local volcano tectonic land subsidence finally a total subsidence rate of 2 05 0 1 mm yr 1 with a volcano tectonic contribution of 1 43 0 1 mm yr 1 for the last 2 ka bp is inferred from the comparison against the latest predicted sea level curve for the southern tyrrhenian sea suggesting new evaluations of the volcano tectonic hazard for this area of the aeolian islands

closing the gap between regional and global travel time tomography recent global travel time tomography studies by zhou 1996 and van der hilst et al 1997 have been performed with cell parameterizations of the order of those frequently used in regional tomography studies i e with cell sizes of 1 2 these new global models constitute a considerable improvement over previous results that were obtained with rather coarse parameterizations 5 cells the inferred structures are however of larger scale than is usually obtained in regional models and it is not clear where and if individual cells are actually resolved this study aims at resolving lateral heterogeneity on scales as small as 0 6 in the upper mantle and 1 2 3 in the lower mantle this allows for the adequate mapping of expected small scale structures induced by for example lithosphere subduction deep mantle upwellings and mid ocean ridges there are three major contributions that allow for this advancement first we employ an irregular grid of nonoverlapping cells adapted to the heterogeneous sampling of the earth s mantle by seismic waves spakman and bijwaard 1998 second we exploit the global data set of engdahl et al 1998 which is a reprocessed version of the global data set of the international seismological centre their reprocessing included hypocenter redetermination and phase reidentification finally we combine all data used p pp and pwp phases into nearly 5 million ray bundles with a limited spatial extent such that averaging over large mantle volumes is prevented while the signal to noise ratio is improved in the approximate solution of the huge inverse problem we obtain a variance reduction of 57 1 synthetic sensitivity tests indicate horizontal resolution on the scale of the smallest cells 0 6 or 1 2 in the shallow parts of subduction zones decreasing to approximately 2 3 resolution in well sampled regions in the lower mantle vertical resolution can be worse up to several hundreds of kilometers in subduction zones with rays predominantly pointing along dip important features of the solution are as follows 100 200 km thick high velocity slabs beneath all major subduction zones sometimes flattening in the transition zone and sometimes directly penetrating into the lower mantle large high velocity anomalies in the lower mantle that have been attributed to subduction of the tethys ocean and the farallon plate and low velocity anomalies continuing across the 660 km discontinuity to hotspots at the surface under iceland east africa the canary islands yellowstone and the society islands our findings corroborate that the 660 km boundary may resist but not prevent present day large scale mass transfer from upper to lower mantle or vice versa this observation confirms the results of previous global mantle studies that employed coarser parameterizations

a palaeogeographic reconstruction of the seafront of the ancient city of delos in relation to upper holocene sea level changes in the central cyclades abstract palaeogeographical reconstruction of the seafront of the ancient city of delos is based on the recording and study of all available indicators of sea level change contemporary submerged beachrock formations and presently submerged areas of ancient human activity including ancient coastal constructions indicate the phases vertical direction extent and time frame of the changes the sea level along the coasts of delos has risen by a total of 2 15 m since the end of the hellenistic period this change occurred during two successive distinct phases of submersion initially by 1 35 m and then by another 0 80 m the sea s transgression into the ancient coastal zone by a width of at least 30 m radically altered parts of its geomorphology and resulted in the submersion of the ancient sea defences

temporal variation of the hawaiian plume flux abstract the magnitude of the hawaiian swell which surrounds the hawaiian volcanic chain does not decline monotonically and smoothly with distance along the chain the observed undulations are interpreted here as reflecting past variations in the buoyancy flux of the hawaiian plume rather than the monotonic thermal decline of the swell with age as has been inferred previously this interpretation is supported by seismic evidence that indicates there has been little thinning of the lithosphere which it is shown further implies that the time scale for thermal subsidence will be very long the largest change in flux was an increase in the plume flux by more than a factor of two about 25 30 myr ago the size of the volcanic edifices shows a broad correlation with the variations in the swell supporting this interpretation

a detailed analysis of microearthquakes in western crete from digital three component seismograms summary seismological data collected during the summer of 1988 are presented and analysed to discuss the microearthquake deformation in western crete greece the experiment consisted in a dense network of 34 stations 5 km interstation spacing among them 13 three component digital stations the seismicity is essentially localized between 0 and 15 km and suggests a deformation of crete decoupled from the subducting plate which shows a very low seismicity the fault plane solutions are constrained by combining the information from p wave polarities with that from horizontal directions of s wave polarizations using the probabilistic approach developed by zollo bernard 1991 among the 16 fault plane solutions calculated there are essentially two families normal faulting on planes oriented ns and strike slip faulting both have a horizontal se to ne oriented tension axis the mean direction of the t axis confirms the e w extension of this part of the hellenic arc where observations at larger scale are available active and holocene fault scarps and fault plane solution of one teleseismic event observations of elliptical polarizations of s waves at two stations suggest the presence of a shallow low velocity anisotropic layer assuming a model of vertical cracks this anisotropy would imply that the cracks be oriented n145 170 this direction of aligned cracks is consistent with the regional e w oriented extension as determined by the fault plane solutions

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

toroidal poloidal partitioning of plate motions since 120 ma changes in plate motions and plate configurations during the cenozoic and mesozoic have been investigated extensively but most geodynamical models have concentrated on present day plate motions we have investigated the recent evolution of plate tectonics by examining the history of toroidal poloidal partitioning of plate motions taking into account estimated errors our results suggest a significant increase in the ratio of toroidal to poloidal motions postdating the hawaiian emperor h e bend at 43 ma corresponding to an overall decrease in global plate motions these changes may reflect greater mantle plume activity in the mesozoic but a causal mechanism is not obvious in general observed cenozoic and mesozoic plate motions do not appear to be random which implies that they are correlated we also find perhaps three significant changes in net rotation of the lithosphere with respect to hotspots since 120 ma

upper holocene sea level changes paleogeographic evolution and its impact on coastal archaeological sites and monuments the paper presents the evolution of the geographic environment imposed by sea level changes in selected sites of the aegean sea region during the upper holocene the changes are due mainly to paroxysmic phases of the actual neotectonic evolution and to differential in time and space block movements and emerged or submerged coasts the reconstitution of these coasts is presented and in some cases natural harbor morphology is revealed the use and evolution of these sites is discussed other sites concern coastal or inland ancient settlements or constructions affected by submersion by the sea by the rise of the groundwater table or by uplift movements a general discussion on engineering measures to be applied for protection of the antiquities affected by these geographic changes closes the presentation

late pleistocene and holocene sea level change in greece and south western turkey a separation of eustatic isostatic and tectonic contributions summary sea level change during late pleistocene and holocene times is a combination of eustatic isostatic and tectonic contributions in the central mediterranean sea region of greece and western turkey the isostatic components are important due to the changing gravitational potential of the earth the readjustment of the crust upon the removal of the large ice sheets and the addition of the meltwater into the oceans including the mediterranean changes in relative sea level due to these glacio hydro isostatic adjustments have reached amplitudes of 1 mm yr 1 during the last few thousand years a model for the isostatic contribution to sea level change including the movement of shorelines due to the combined eustatic isostatic changes is developed based on earth model and ice sheet parameters estimated from sea level observations from other areas comparisons of this model with observations of sea level change permit rates of vertical movement to be estimated for late holocene time allowance for the isostatic factors makes a significant difference to these rates the plains of argolis lakonia messinia and navarine in the southern peloponnese for example appear to be tectonically stable on time scales of a few thousand years and longer consistent with the position of the last interglacial shoreline close to the present day sea level the observations here of a rising sea level are largely the consequence of the glacio hydro isostasy and not of a long term tectonic process crete as a whole is subject to tectonic uplift but at variable rates and forms part of an arcuate zone of uplift extending from rhodes and karpathos in the east to kithera in the west at rates that locally exceed 4 mm yr 1 the southern shore of the gulf of corinthos is also subject to uplift at rates approaching 1 5 mm yr 1 these isostatically corrected estimates for the past few thousand years are in agreement with longer term estimates based on the position of the last interglacial shoreline only on the perachora peninsula do the tectonic rates over these two time intervals appear to be in disagreement with the late holocene rates being much higher than the long term rates

the dynamics of plume ridge interaction 2 off ridge plumes a variety of geophysical and geochemical evidence indicates that ascending mantle plumes can interact with ocean ridges located up to 1400 km away i investigate the dynamics of this interaction using a simple model in which a point source with volume flux q analogous to a plume stem releases buoyant fluid into a viscous corner flow driven by the divergence of rigid surface plates with thickness kx u 1 2 where u is the half spreading rate the point source is located at a distance xp from the ridge and ridge migration is neglected the buoyant fluid forms a thin sublithospheric layer whose thickness s x y satisfies a nonlinear advection diffusion equation describing the balance of advection by the corner flow buoyancy driven self spreading flow toward the ridge along the sloping base of the lithosphere and continuous accretion into the lithosphere numerical solutions of this equation yield scaling laws for the lateral extent w waist width of plume material along the ridge the fraction r of the plume flux that crosses the ridge and the maximum value of xp beyond which interaction ceases the sloping base of the lithosphere has only a minor few tens of percent influence on these quantities which are determined principally by the balance of advection and self spreading an extension of the model to include plume induced lithospheric thinning shows that this process increases the waist width by an amount of order 10 finally the model provides a new explanation for the observation that plumes interact primarily with ridges that are migrating away from them rather than toward them

the geometry of the wadati benioff zone and lithospheric kinematics in the hellenic arc abstract accurate locations of 961 shallow and intermediate depth earthquakes which occurred between 1956 and 1995 in the hellenic arc 34 39 n 19 28 e are used to define the plate boundaries in this area reliable fault plane solutions for 77 shallow and intermediate depth earthquakes are also used in order to define the interaction between the different plates in the arc an ocean continent type of interaction occurs on a curved surface which is defined by the shallow branch 20 100 km of the wadati benioff zone the intersection of this zone with the earth s surface is a curve which follows the convex outer side of the sedimentary arc western peloponnese west of cythera south coast of crete east coast of rhodes and dips at low angle 30 to the aegean sea coupling between the subducted oceanic crust and the overriding of the aegean lithospheric plate takes place on this surface the deep branch 100 180 km of the wadati benioff zone is dipping freely without coupling at a high angle 45 beneath the south aegean trough and the volcanic arc the high shallow seismicity h 20 km which is observed in the southwestern convex outer side of the arc ionian sea is attributed to the fast southwestward motion of the aegean plate location of strong deep earthquakes h 100 km in the fore arc area of the southwestern part of the hellenic arc west of cythera indicates that oceanic crust is destroyed in this part of the hellenic trench due to roll back of the descending lithospheric slab

earthquake mechanisms in the hellenic trench near crete summary in the hellenic trench south of crete convergence between the southern aegean sea and africa occurs at a rate of at least 60 mm yr 1 previously published first motion fault plane solutions show a variety of different fault orientations and types but are not well constrained furthermore the lack of reliable focal depths for these earthquakes has obscured any simple pattern of deformation that might exist nonetheless the mechanisms of these earthquakes have strongly influenced views of the tectonics in the hellenic trench we have improved estimates of the fault parameters and focal depths for 14 of these earthquakes using long period p and sh waveforms the earthquake mechanisms fall into four groups a normal faults with a n s strike in the over riding material above the subduction zone b low angle thrusts with an e w strike at a depth of about 40 km c high angle reverse faults with the same strike but shallower focal depths than b d events within the suducting lithosphere with approximately e w p axes the thrusting in groups b and c is probably the mechanism by which the sediments of the mediterranean sea underplate and uplift crete these events have slip vectors in the direction 025 12 which represents the convergence direction between crete and africa along the sw facing boundary of the hellenic trench one of the events in group d occurred beneath the mediterranean ridge and involved high angle reverse faulting with a wnw ese p axis almost perpendicular to the direction of shortening deduced from folds at the surface the mediterranean sea floor in this region appears to be in a state of e w compression for reasons that are not clear

effect of thermal diffusion on the stability of strongly tilted mantle plume tails 1 the effect of thermal diffusion on the stability of strongly tilted mantle plume tails is explored by investigating experimentally and numerically the gravitational instability of a rising horizontal cylindrical region of buoyant viscous fluid at large viscosity ratios we find that the instability is unaffected by diffusion when the rayleigh number ra is greater than about 300 when ra is less than 300 diffusion significantly increases the time for instability as the rising fluid region needs to grow substantially by entrainment before it becomes unstable when ra is less than about 140 and the rise height available h is less than about 40 times the cylinder radius the rising region of fluid is unable to grow sufficiently and instability is prevented when our results are applied to the earth we predict that thermal diffusion will stabilize plume tails in both the upper and lower mantle we also predict that some of the buoyancy flux in mantle plumes is lost during ascent to form downstream thermal wakes in any larger scale mantle flow

origin and geochemical evolution of the madeira tore rise eastern north atlantic the madeira tore rise located 700 km off the nw african coast forms a prominent ridge in the east atlantic the age and origin of the rise are controversial this study presents major and trace element sr nd pb hf isotope and 40ar 39ar age determinations from volcanic rocks dredged from different sites along the rise in addition isotopic compositions of rock samples from great meteor seamount in the central atlantic are presented the new radiometric and paleontologically constrained ages identify two major episodes of volcanism the first is the base of the rise circa 80 to 95 ma and the second is seamounts on the rise 0 5 16 ma it is proposed that interaction of the canary hot spot with the mid atlantic spreading center formed the deep basement of the madeira tore rise and the j anomaly ridge west of the atlantic spreading center in the mid cretaceous age and geochemical data and plate tectonic reconstructions suggest however that the recovered late cretaceous volcanic rocks represent late stage volcanism from the time when the madeira tore rise was still close to the canary hot spot long after moving away from the influence of the canary hot spot the madeira tore rise was overprinted by late cenozoic volcanism miocene to pleistocene volcanism at the northern end of the rise can be best explained by decompression mantle melting beneath extensional sectors of the azores gibraltar fracture zone african eurasian plate boundary the geochemical compositions of these volcanic rocks suggest that the magmas were variably contaminated by enriched material within or derived by melting of enriched material underplated at the base of the lithosphere possibly originating from the cretaceous canary plume alternatively these late cenozoic volcanic rocks may have derived from decompression melting of enriched pyroxenitic eclogitic material in the upper mantle isotopically more depleted pliocene to pleistocene volcanism at the southern end of the madeira tore rise may be related to the nearby madeira hot spot

invisible gold in ore and mineral concentrates from the hillgrove gold antimony deposits nsw australia vein hosted mesothermal stibnite gold mineralisation at the hillgrove au sb mine in northeastern new south wales has a halo of veinlet and disseminated auriferous arsenopyrite and arsenian pyrite in metasedimentary and granitic host rocks about 50 55 of the gold produced at hillgrove occurs invisibly in arsenopyrite and pyrite gold losses of 20 into tailings are due to this mineral chemical factor from pixe probe analyses it has been found that arsenopyrite contains 255 1500 ppm au and pyrite 24 223 ppm au with au contents of each mineral correlating moderately with as content arsenopyrite and pyrite also contain anomalous values of cu ag and sb whereas paragenetically later stibnite contains little invisible gold but minor fe as ag cu and pb the precipitation of invisible gold in arsenopyrite and pyrite by a possible fe au 3 as s 3 substitution mechanism may have been facilitated by rapid non equilibrium conditions involving pressure decreases and wall rock reaction sulphidation carbonatisation as a prelude to the main stage of stibnite and gold deposition

dynamics of orogenic wedges and the uplift of high pressure metamorphic rocks subduction accretion complexes can be approximated as wedge shaped continua with a rigid buttress behind and a subducting litho spheric slab beneath thick wedges undergoing prograde metamorphism have a negligible long term yield strength and are likely to exhibit a complex nonlinear viscous rheology such a wedge will tend to deform internally until it reaches a stable configuration in which the gravitational forces generated by the wedge geometry balance the traction exerted on its underside by the subducting slab accretion of material at the wedge front will lengthen the wedge and cause it to shorten internally to regain the stable geometry this shortening will be expressed as late out of sequence thrusting backthrusting and folding conversely underplating of sediment or crustal slices will thicken the wedge which may need to extend internally to regain stability extension will cause listric normal faults that may merge downward into zones of ductile extension continued underplating at depth and compensating extension above provides a mechanism for bringing high p low t metamorphic rocks to upper levels in the rear of the wedge where they are commonly observed many major tectonic boundaries in convergent orogens such as the coast range thrust in the franciscan complex major nappe contacts in the alps and the contact between the nevado filabride and higher betic nappe complexes in the betic cordillera show abrupt increases in metamorphic grade downward across them this is consistent with their origin or reactivation as uplift related extensional structures

rise and deflection of mantle plume tails 1 experimental observations by kerr and meriaux 2004 of the deflection of thermal plume tails by an imposed background shear are reanalyzed using a corrected velocity profile the deflected plumes are found to be accurately described by a constant vertical rise velocity equation 14 that depends primarily on the plume buoyancy flux and the ambient viscosity our results can be used to further improve the predictions of numerical models of the shearing of plume tails in the earth s mantle

the p v t x f o2 evolution of h2o co2 ch4 bearing fluid in a wolframite vein reconstruction from fluid inclusion studies aqueous carbonaceous and later pure aqueous fluid inclusions in quartz from a ferberite fe 95mn 05 wo4 vein within the low grade metamorphic aureole of the borne granite french massif central have been studied by microthermometry and raman spectrometry the bulk v x properties of the aqueous carbonaceous inclusions have been derived using the equation of state of heyenet al 1982 for the low temperature co2 ch4 system a p t path has been proposed for their trapping using the equations of state of jacobs and kerrick 1981a for the h2o co2 ch4 system two main episodes were reconstructed for the history of the aqueous carbonaceous fluid 1 primary h2o co2 ch4 vapourrich inclusions in quartz indicated the early circulation of a low density fluid 65 mole h2o 34 mole co2 1 mole ch4 and traces of n2 d 0 35 gcm 3 at around 550 50 c and 700 100 bar fluid cooled approximately isobarically to 450 400 c and was progressively diluted by h2o with a concomitant increase in density the fo2 of the h2oco2 ch4 fluid estimated from the equilibrium co2 2h2o ch4 2o2 first ranged from 10 22 to 10 27 bar close to the q f m buffer within analytical errors these values were consistent with the presence of graphite in equilibrium with the fluid 2 a drop in pco2 and therefore a drop in fo2 was recorded by the secondary liquid rich inclusions in quartz the inclusions formed at and below 400 c were composed of h2o and ch4 only and fo2 at that stage was below that fixed by the graphite fluid equilibrium this second episode in the fluid rock system could be explained by the drop of temperature below the blocking temperature of the graphite fluid equilibrium according to this interpretation the blocking of the graphite fluid equilibrium occurred at t 370 c and probably at 400 c on account of the pressure correction mass spectrometric data show that ferberite contains h2o co2 and ch4 in fluid inclusions which lie in the gap of the v x properties of the aqueouscarbonaceous fluid in quartz deposition of ferberite probably occurred at around 400 c the previously inferred blocking temperature resulting from either the drop in pco2 the drop fo2 and or the related ph increase it is concluded that the existence of a blocking temperature for the graphite fluid chemical equilibrium may be a critical factor for maintaining a stable fluid pressure gradient in geothermal systems occurring under greenschist facies conditions in graphite bearing rocks

origin of the louisville ridge and its relationship to the eltanin fracture zone system we have combined shipboard and seasat altimeter derived data in an intergrated geological and geophysical study of the louisville ridge a 3500 km long seamount chain extending from the tonga trench to the eltanin fracture zone a break in the smooth trend of the ridge at latitude 37 5 s has been recognized in both bathymetric and altimetric data the 40ar 39ar dating of rocks dredged either side of the break suggest that it is analogous to the bend in the hawaiian emperor seamount chain although the general trend of the ridge can be fit by small circles about pacific absolute motion poles determined from other seamount chains the new bathymetric and age data allow us to refine pacific absolute motion poles the continuity in smooth trend of the ridge and the eltanin fracture zone suggests some relationship between them however a major offset developed on this transform between 60 and 80 ma prior to the oldest dated rocks from the ridge although magmatism was more or less continuous on the ridge during 28 60 ma it probably occurred on crust with little or no offset thus magmatism appears to have been little influenced by the developing fracture zone by 28 ma the distance between the magmatic source and the fracture zone had decreased sufficiently for a portion of the ridge to have been emplaced on crust with an offset after about 12 ma however volcanic activity on the louisville ridge apparently waned despite a possible influence on the magmatism of the fracture zone

notches in the northern adriatic sea genesis and development abstract the genesis and development of the submerged notch occurring along the northern adriatic limestone coasts surveyed at depth ranging between 0 35 and 2 8 m and amplitude consistent with the local tide is discussed using new and published data on its elevation and data on limestone lowering rates collected using a micro erosion meter and a traversing micro erosion meter coastal limestone lowering rates in the northern adriatic range between 0 008 and 1 170 mm y and they are about eight times higher than inland limestone lowering rates data support the hypothesis that notch is presently carving even if no present day notch has been surveyed in the area the lack of a modern notch and the presently submerged notch position could be related to 1 a rapid still acting tectonic downdrop or 2 an increase in weathering erosion rates causing by different environmental conditions e g during the so called medieval warm period marked by more aggressive weathering both chemically biologically and or mechanically than present conditions due to an increase in rainfall or variations in the acidity of seawater pros and cons of these hypotheses are discussed in the paper

tectonic history and new isochron chart of the south pacific we have developed an internally consistent isochron chart and a tectonic history of the south pacific using a combination of new satellite altimeter data and shipboard magnetic and bathymetric data highly accurate vertical deflection profiles 1 2 rad derived from 22 repeat cycles of geosat altimetry reveal subtle lineations in the gravity field associated with the south pacific fracture zones these fracture zone lineations are correlated with sparse shipboard bathymetric identifications of fracture zones and thus can be used to determine paleospreading directions in uncharted areas the high density of geosat altimeter profiles reveals previously unknown details in paleospreading directions on all of the major plates magnetic anomaly identifications and magnetic lineation interpretations from published sources were combined with these fracture zone lineations to produce a tectonic fabric map the tectonic fabric was then used to derive new poles of rotation for 12 selected times in the late cretaceous and cenozoic from our reconstructions we estimated the former location of the spreading centers in order to derive a new set of isochrons interpreted unes of equal age on the ocean floor we believe that the use of new geosat altimeter data in combination with a multi plate reconstruction has led to an improvement in our understanding of south pacific tectonics

paleomagnetic evidence for motion of the hawaiian hotspot during formation of the emperor seamounts the bend in the hawaiian emperor chain is the best example of a change in plate motion recorded in a fixed hotspot frame of reference alternatively the bend might record primarily differences in motion of the hawaiian hotspot relative to the pacific lithosphere new paleomagnetic data from the emperor chain support the latter view althouth the rate of motion is difficult to constrain because of uncertainties posed by true polar wander and limited sampling of the chain the best available paleomagnetic data suggest pacific hotspots may have moved at rates comparable to those of lithospheric plates 30 mm yr 1 in late cretaceous to early tertiary times 81 43 ma if correct this requires a major change in how we view mantle dynamics and the history of plate motions in the early to mid cretaceous 128 95 ma hotspots in the atlantic moved at similar rates these episodes during which groups of hotspots appear to move rapidly are separated by times of much slower motion such as the past 5 m y

crustal block movements from holocene shorelines crete and antikythira greece abstract marks of several shorelines left by sea level stands during the last 4000 yrs occur along the coasts of the islands of crete and antikythira in this area recent movements of the earth s crust were identified by using a systematic survey based on multidisciplinary analyses strengthened by 60 radiometric datings between 4000 and 1700 yr b p a block of lithosphere a about 150 km long fig 10 which included antikythira and the levka mountains in crete underwent a series of ten rapid subsidences from 10 to 25 cm each time without noticeable tilting these movements ended about 1 530 40 yr b p a further block of lithosphere b approximately 200 km long was then uplifted about 10 m and inclined northeastwards in a single event block b includes block a and extends 50 km further eastwards beyond the ida mountains as far as the iraklion sedimentary basin the tectonic movements were preceded by vertically reversed displacements of short duration on at least three occasions if the a block subsidences can be ascribed to gravitational forces then the b block uplift suggests a cause that originated at depth crustal consumption and elastic rebound to the east of the ierapetra graben the sitian peninsula appears to belong to a block of lithosphere c affected by a northeast tilting and separated by an active fault from the crustal block of khrisi koufonisi

a 3 d density velocity model between the cretan sea and libya abstract a 3 d density model for the cretan and libyan seas and crete was developed by gravity modelling constrained by five 2 d seismic lines velocity values of these cross sections were used to obtain the initial densities using the nafe drake and birch empirical functions for the sediments the crust and the upper mantle the crust outside the cretan arc is 18 to 24 km thick including 10 to 14 km thick sediments the crust below central crete at its thickest section has values between 32 and 34 km consisting of continental crust of the aegean microplate which is thickened by the subducted oceanic plate below the cretan arc the oceanic lithosphere is decoupled from the continental along a nw se striking front between eastern crete and the island of kythera south of peloponnese it plunges steeply below the southern aegean sea and is probably associated with the present volcanic activity of the southern aegean sea in agreement with published seismological observations of intermediate seismicity low density and velocity upper mantle below the cretan sea with 3 25 103 kg m3 and vp velocity of compressional waves around 7 7 km s which are also in agreement with observed high heat flow density values point out at the mobilization of the upper mantle material here outside the hellenic arc the upper mantle density and velocity are 3 32 103 kg m3 and vp 8 0 km s respectively the crust below the cretan sea is thin continental of 15 to 20 km thickness including 3 to 4 km of sediments thick accumulations of sediments located to the ssw and sse of crete are separated by a block of continental crust extended for more than 100 km south of central crete these deep sedimentary basins are located on the oceanic crust backstopped by the continental crust of the aegean microplate the stretched continental margin of africa north of cyrenaica and the abruptly terminated continental aegean microplate south of crete are separated by oceanic lithosphere of only 60 to 80 km width at their closest proximity to the east and west the areas are floored by oceanic lithosphere which rapidly widens towards the herodotus abyssal plain and the deep ionian basin of the central mediterranean sea crustal shortening between the continental margins of the aegean microplate and cyrenaica of north africa influence the deformation of the sediments of the mediterranean ridge that has been divided in an internal and external zone the continental margin of cyrenaica extends for more than 80 km to the north of the african coast in form of a huge ramp while that of the aegean microplate is abruptly truncated by very steep fractures towards the mediterranean ridge changes in the deformation style of the sediments express differences of the tectonic processes that control them that is subduction to the northeast and crustal subsidence to the south of crete strike slip movement between crete and libya is required by seismological observations

archaeological indicators for sea level change and coastal neotectonic deformation the submerged roman fish tanks of the gulf of matala crete greece abstract due to the direct relationship between their function and ancient sea levels roman fish tanks and fish traps are excellent indicators for sea level changes through time for this study eleven submerged systems of fish tanks were investigated along the rocky southern coast of the gulf of matala crete seven of them are still in a good state of preservation and thus underwent detailed survey and documentation the measurements of their recent submersion the determination of the way they operated as well as their correlation with coastal landforms indicative of an older sea level permit the identification of a mean roman sea level at the sw coast of central crete 1 25 m below the present one according to historical evidence the submersion of the sw coasts of the central part of crete must have been occurred between 1415 and 1865 during a paroxysmal tectonic event and is probably related with the strong earthquake of 1604