methana the westernmost active volcanic system of the south aegean arc greece insight from fluids geochemistry abstract an extensive geochemical survey of the fluids released by the volcanic geothermal system of methana was undertaken gases were characterized based on the chemical and isotopic helium he and carbon c analysis of 27 samples carbon dioxide soil gas concentration and fluxes were measured at 179 sampling sites throughout the peninsula forty samples of thermal and cold groundwaters were also sampled and analysed to characterize the geochemistry of the aquifers gases of hydrothermal origin gave a preliminary geothermometric estimate of about 210 c the he isotope composition indicated mantle contributions of up to 40 and the c isotope composition of co 2 indicated that it predominantly 90 originated from limestone decomposition the groundwater composition was suggestive of mixing between meteoric and hydrothermally modified sea water endmembers and water rock interaction processes limited to simple rock dissolution driven by an increased endogenous co 2 content all of the thermal manifestations and anomalous degassing areas although of limited extent were spatially correlated with the main active tectonic system of the area the total co 2 output of the volcanic system has been preliminary estimated to be less than 0 05 kg s 1 although this value is very low compared to those of other volcanic systems anomalous co 2 degassing at methana which is currently restricted to limited areas and at present is the only volcanic risk of the peninsula is a potential gas hazard that warrants further assessment in future studies

changes in the 300 mb north circumpolar vortex 1963 2001 abstract the mean monthly polar stereographic map analyses of the free university of berlin terminated at the end of 2001 this paper summarizes the changes in size of the 300 mb north circumpolar vortex and quadrants for the full period of record 1963 2001 where the size has been defined by planimetering the area poleward of contours in the jet stream core a contracted vortex has tended to be a deep vortex in winter but a shallow vortex in summer during 1963 2001 there was a statistically significant decrease in vortex size of 1 5 per decade the decrease in size of western hemisphere quadrants being twice that of eastern hemisphere quadrants a significant increase in arctic oscillation ao index accompanies the significant decrease in vortex size but since the vortex contracts appreciably in all four seasons whereas the positive trend in the ao index is mainly in winter the vortex cannot serve as a proxy for the ao index the evidence for vortex contraction at the time of the 1976 77 regime

seismicity normal faulting and the geomorphological development of the gulf of corinth greece the corinth earthquakes of february and march 1981 three major destructive earthquakes of m s 6 7 6 4 6 4 occurred in the eastern part of the gulf of corinth in february and march 1981 associated normal faulting was observed on both the north and the south sides of the gulf examination of teleseismic local seismic surface faulting and geomorpbological data suggests that the first and second of these shocks activated major north dipping normal faults these faults control the topography and bathymetry and are related to the recent uplift and subsidence of the coastline it is probable that the first earthquake occurred on a faultwhich outcrops underwater and the second on a fault which is visible on land it appears that the third shock activated an antithetic normal fault dipping southwards on the north side of the gulf and that the overall structure of the gulf of corinth graben is asymmetric the northern antithetic fault clearly demonstrates the geomorphological changes associated with developing young normal faulting in addition we suggest that observations of recent coastline movement provide a powerful tool for identifying major active fault systems and predicting their historical role in the paleogeography of an area

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

an early pliocene thermal disturbance of the main central thrust central nepal implications for himalayan tectonics since the beginning of the collision between india and asia at about 50 ma the convergence in the himalaya has largely been taken up along major thrust zones in this study samples of the lesser himalaya formations up to 10 km below the main central thrust mct and the greater himalaya sequence up to 12 km above the mct have been analyzed by the 40ar 39ar and u pb methods to investigate the thermal history of the mct the ages can be summarized as follows 1 the youngest ages from muscovites 3 1 ma biotites 3 4 ma and hornblendes 4 1 ma all come from within 1 km of the mct 2 there is a marked asymmetry of ages between the footwall and the hanging wall of the mct the maximum mica age in the hanging wall greater himalaya sequence is 13 ma whereas a muscovite 5 km below the mct in the footwall has an age spectrum with a gradient from 400 to 1400 ma 3 five k feldspars from 6 2 to 11 9 km above the mct all give minimum ages in the range 3 0 6 4 ma and 4 a 206pb 238u age on a brannerite from the greater himalayan sequence is 4 8 ma structural and petrologic observations preclude the possibility that this age distance distribution reflects faulting within the greater himalaya sequence and production of the necessary thermal energy by shear heating requires unrealistically high shear stresses infiltration of hot fluids through the mct zone appears to be the best hypothesis to explain these data simple numerical simulations which account for heat transfer by advection within the fluid flow zone and by conduction outside it indicate that the observed age distribution could have been produced by infiltration of hot fluids through the mct zone at circa 5 to 4 ma within the following range of conditions the fluids heated rocks to temperatures in the range 470 to 510 c for less than 1 million years in a region narrower than the entire mct zone the temperature of the thermal disturbance inferred from the 40ar 39ar data is consistent with petrologic data from albitic alteration assemblages in the greater himalaya sequence and the u pb age of the brannerite is similar to the youngest 40ar 39ar hornblende age this scenario hydrothermal heating culminating at about 4 ma is similar to the model of le fort 1981 for the generation of the high himalayan leucogranites in the late oligocene early miocene by dehydration of the footwall rocks of an active thrust in the younger instance we interpret that fluids derived from the footwall rocks of the main boundary thrust migrated upward through the lesser himalaya formations and were subsequently channeled along the mct producing the thermal disturbance

the influence of el nino southern oscillation events on the northern hemisphere 500 hpa circumpolar vortex the relationship between el nino the southern oscillation and their joint effect enso and northern hemisphere 500 hpa midlatitude circulation for the 1946 1994 observational record is determined seasonally standardized vortex positions at a spatial resolution of 5 longitude are correlated with an equatorial pacific sea surface temperature anomaly index and the southern oscillation index soi the 500 hpa circumpolar vortex is consistently expanded over the central pacific during and for the entire year following warm enso periods the vortex is contracted over north america concurrently with warm enso and to a lesser degree during the following season expansion contraction variability is also evident over east asia although the linkages to warm or cold enso are weak sea surface temperatures have a stronger association with the vortex than does the soi

elliptical diagnostics of stratospheric polar vortices diagnostics based on the spatial moments of isopleths of a long lived tracer or of potential vorticity are presented that enable the structure and evolution of stratospheric polar vortices to be concisely summarized and quantified the area centre aspect ratio and orientation of the equivalent ellipse of the vortex on an isentropic surface are defined using the second and lower order spatial moments of contours within the vortex edge region by examining the variations of these elliptical diagnostics with time and altitude the temporal evolution and vertical structure of the polar vortices can be quantified the usefulness of the diagnostics is assessed by examining nitrous oxide data from the geophysical fluid dynamics laboratory skyhi general circulation model the diagnostics show and quantify several differences between the arctic and antarctic vortices in the skyhi model the arctic vortex moves further off the pole is generally more elongated and has a more complicated vertical structure than the antarctic vortex with larger variations of both the vortex centre and elongation with height the elliptical diagnostics also identify the occurrence of large scale rossby wave breaking events both at the vortex edge and in the subtropics in the model

local seismic array observations at north evoikos central greece delineate crustal deformation between the north aegean trough and corinthiakos rift abstract in order to better constrain and define the microseismic activity at the north evoikos gulf and its surrounding area we deployed an onshore offshore seismic array consisting of 31 three component seismic digital stations the array was active from 30 june to 24 october 2003 and covered an area of 2500 km 2 we located more than 2000 seismic events ranging from 0 7 to 4 5 m l by using six stations as a minimum in order to define the foci parameters recorded seismicity delineated three major zones of deformation from south to north the eretria parnis eastern corinthiakos zone the psachna viotia zone and the northern sporades north evia bralos zone alignments of the recorded seismicity follow the tectonic trends and their orientation in the above zones the whole area accommodates the stress field between the north aegean trough and the corinthiakos gulf rate of deformation intensifies from north to south as revealed also by historical and instrumental seismicity the successive change of orientation between the two stress fields fragments the crust in relatively small units and the fault systems developed do not permit the generation of major earthquakes in the north evoikos area and its immediate vicinity this is also supported by the instrumental seismicity of the last century larger events reported in historical times are probably overestimated most seismic activity is crustal subcrustal events were recorded mainly below the lichades area and are interpreted as the consequence of the subduction of the ionian oceanic lithosphere below the hellenides the lichades volcano is the most northern end of the hellenic volcanic arc at present the highest seismic activity is associated with the psachna region of north evia that has been continuously active since 2001 considering however the development of the seismic activity during the last decade there has been a sequence of large events i e parnis in 1999 skyros in 2001 and psachna in 2001 2003 this demonstrates the fact that the tectonic deformation in all this area is intense and important for the accommodation of the stress field of the north aegean trough to that of the corinthiakos rift

seismic source parameter relations for earthquakes in greece a data set of nineteen mainly shallow moderate to large earthquakes which occurred in the aegean and the surrounding area has been used to derive empirical relations for kinematic fault parameters thus the relations between seismic momentm 0 and magnitudem s andm b and betweenm 0 andm s and fault dimensionss andl have been determined from these relations and theoretical ones it was deduced that earthquakes in the aegean and the surrounding events chiefly interplate are characterized by low average stress drop values values of ranging from 1 to 30 bar are consistent with the data it was also found that in general terms most of the data obey the geometrical similarity conditionl 2w wherel is the fault length measured along the strike andw is its width measured along the dip for strike slip faults however the conditionl 4w seems to hold

the effect of changing regional tectonics on an arc volcano methana greece abstract the peninsula of methana has the longest recorded volcanic history of any volcanic centre in the south aegean arc regional fault patterns in the arc changed during the pliocene quaternary with e w striking listric faulting increasingly important through the quaternary as recorded in well dated sedimentary basins this study investigates how the geochemistry and eruptive style of volcanic products is influenced by regional tectonics the volcanic stratigraphy of methana was refined using radiometric dating lithogeochemistry and field observations that included recording deformational structures and enclave abundance small n s striking pliocene domes and a central volcano of uncertain type phase a were eroded to produce a widespread volcaniclastic apron phase b in the early quaternary an explosive central volcano with flank eruptions of andesite developed phase c dacite domes and small andesitic stratovolcanoes formed throughout the mid and late quaternary phases d h basaltic andesite and andesite of phase c are the least evolved rocks characterised by high tio 2 rocks that have experienced important assimilation and fractional crystallisation in the crust have a high abundance of enclaves th u and alkalies na k ni and cr are abundant in phase a andesites due to crystallisation and entrainment of olivine and pyroxene whereas phase h andesites have the highest relative abundance of ba rb and sr from crystallisation and entrainment of hornblende and biotite pliocene domes of phase a were emplaced on n s striking listric faults during regional e w extension onset of ne sw faulting arguably crustal scale and strike slip in character led to the eruption of the least evolved rocks of phase c thereafter e w striking faults controlled the location of volcanism volcanism in phases f and g was particularly voluminous and was synchronous with the onset of steep normal faulting in the gulf of corinth 150 km west of methana these steep faults cross cut older lower angle listric faults it is times of changes in regional fault patterns as in phases c f and g that have the greatest influence on the eruptive style and abundance of volcanic products

active tectonics of the north and central aegean sea summary in this paper we examine the connection between the westward motion of turkey relative to europe and the extension in and around the aegean sea the principal new data available since the last attempt to synthesize the tectonics of this region by mckenzie 1978 are much improved focal mechanisms of earthquakes constrained by p and sh body wave modelling as well as by first motions these mechanisms show that the faulting in the western part of the aegean region is mostly extensional in nature on normal faults with a nw to wnw strike and with slip vectors directed nnw to nne there is evidence from palaeomagnetism that this western region rotates clockwise relative to stable europe in the central and eastern aegean and in nw turkey distributed right lateral strike slip is more prevalent on faults trending ne to ene and with slip vectors directed ne palaeomagnetic data in this eastern region is more ambiguous but consistent with very small or no rotations in the northern part and possibly anticlockwise rotations relative to europe in the south the strike slip faulting that enters the central aegean from the east appears to end abruptly in the sw against the nw trending normal faults of greece the kinematics of the deformation is controlled by three factors the westward motion of turkey relative to europe the continental collision between nw greece albania and the apulia adriatic platform in the west and the presence of the hellenic subduction zone to the south as the right lateral slip on the north anatolian fault enters the aegean region it splays out becoming distributed on several parallel faults the continental shortening in nw greece and albania does not allow the rotation of the western margin of the region to be rapid enough to accommodate this distributed e w right lateral shear and thus leads to e w shortening in the northern aegean which is compensated by n s extension as the southern aegean margin can move easily over the hellenic subduction zone the dynamics of the system once initiated is self sustaining being driven by the high topography in eastern turkey and by the roll back of the subducted slab beneath the southern aegean the geometry of the deformation resembles the behaviour of a system of broken slats attached to margins that rotate in spite of its extreme simplicity a simple model of such broken slats is able to reproduce quantitatively most of the features of the instantaneous velocity field in the aegean region including the slip vectors and nature of the faulting in the eastern and western parts the senses and approximate rates of rotation the overall extensional velocity across the aegean and the distribution of strain rates as seen in the seismicity and topography or bathymetry and using geodetic measurements as part of this study we re examined the relation between the surface faulting and the focal parameters determined seismologically for the three large 1981 gulf of corinth earthquakes and reassessed the evidence for associating particular earthquakes in the sequence with observed surface faulting an important result is that in one of the events there is a resolvable discrepancy between the slip vector measured at the surface and that determined from the seismic body waves

classification seasonality and persistence of low frequency atmospheric circulation patterns abstract orthogonally rotated principle component analysis rpca of northern hemisphere 1 month mean 700 mb heights is used to identify and describe the seasonality and persistence of the major modes of interannual variability the analysis is detailed and comprehensive in that 1 a high resolution approximately equal area 358 point grid is used for the virtually maximum possible 35 year period of record 2 a positive bias in the nmc data base in the early 1950s in the subtropics is largely eliminated for the first time and 3 homogeneous separate analyses of each month of the year are carried out detailing the mouth to month changes in the dominant circulation patterns winter results are similar to those of other recent rpca and teleconnection studies except that some less obvious patterns are identified and further detail of the better known patterns is provided two north south dipole patterns are found over the pacific ocean west pacific oscillation and east pacific pattern and over the atla

ages of deformation from k ar and 40ar 39ar dating of white micas a structural and isotopic dating study of white micas from mylonites in the ruby gap duplex off central australia shows that mylonitic deformation occurred during the paleozoic alice springs orogeny deformation of the white micas took place under greenschist facies conditions in the approximate temperature range 250 350 c two distinct populations of white mica have been found 1 porphyroclasts of original muscovite and 2 neocrystallized phengites that define the fabric associated with deformation 40ar 39ar age spectra of neocrystallized phengites yield plateau like spectra of paleozoic age in contrast 40ar 39ar age spectra of muscovite porphyroclasts exhibit proterozoic apparent ages indicating that white micas were not open to significant argon diffusion during formation of the ruby gap duplex we conclude that the ages measured on neocrystallized phengites record the cessation of ductile deformation and migration of tectonic activity toward the internal zones of the thrust system

crustal scale ductile fault systems in the arunta inlier central australia discussion discussion sur l article crustal scale ductile fault systems in the arunta inlier central australia collins w j teyssier c tectonophysics 158 1989 46 99

tectonic implications of s wave anisotropy beneath se brazil summary sks shear wave splitting has been analysed for fast polarization direction and delay time at 14 broad band portable seismic stations arrayed in se brazil across the silo francisco craton the brasilia mobile belt the intracratonic parana basin the rio apa block to its west and the coastal transpressional ribeira belt splitting parameters are consistent with fossil mantle anisotropy resulting from major geological events and exhibit only coincidental correlation with absolute plate motion for the coastal ribeira belt the anisotropy while not unusually large 1 05 s parallels the local and regional fault trends at the surface consistent with anisotropy formed by regional transpressional tectonics in the region comprised of the siio francisco craton the brasilia mobile belt and the eastern margin of the parana basin fast polarization directions trend monotonously wnw ese parallel to the dominant regional faulting and consistent with their having formed during a ne sw brasiliano ca 600 ma collisional event between the silo francisco craton and the parana basin the delay time is smallest 0 6 s for station cdcb in the craton interior and largest 1 6 s for station rifb located near the north eastern edge of the parana basin and on the prominent bouguer gravity anomaly gradient inferred by lesquer et al 198 1 to mark the cryptic i e basement suture between craton and basin within the parana basin shear wave splitting is uniformly small 1 0 s indicating relatively weak mantle foliation in the horizontal plane fast polarization directions within the cratonic nucleus of the basin near the basin axis average approximately e w within the marginal regions of the basin fast polarization directions tend to be subparallel to the trend of the bordering brasiliano basement structures indicating the pervasive influence of the brasiliano accretionary events in the eastern and northern parana basin fast polarization directions are dominantly wnw ese whereas in the western basin the fast polarization direction is ne sw parallel to observed anisotropy in the rio apa block to the west minimal delay times 0 5 s are observed in the eastern parana basin above the axis of the seismic low velocity anomaly interpreted to be the fossil conduit of the parana plume head vandecar james assumpcilo 1995 while the splitting results are not definitive the regional anisotropy of the eastern parana basin may also reflect plume head spreading beneath the continental lithosphere and partial destruction of pre existing mantle fabric large shear wave splitting 1 55 s is observed for the station in the rio apa block adjoining the western margin of the parana basin the fast polarization direction ne sw is oriented parallel to that of the station in the western parana basin and almost normal to the fast polarization direction of the stations on the eastern margin of the parana basin the orientation of anisotropy in the rio apa block and western parana basin appears to be consistent with the inferred regional trends of brasiliano structures suggesting that the anisotropy may have been produced by nw se convergence and collision between the cratonic basement of the parana basin and the rio apa block

metamorphism and crustal considerations in the harts range and neighbouring regions arunta inlier central australia abstract the harts range region consists of several segments or terrains which have behaved essentially independently though some overlap of history permitting correlation is apparent some analogy with the terrane concept is envisaged the harts range terrains are 1 the strangways orogenic belt sob south of the muller thrust 2 the sob of the oonagalabi tongue 3 the sob of the entia dome together comprising a basement and 4 the harts range cover hrc all separated from each other by thrusts or faults the terrains consist of supracrustal sequences comprising metasediments and some metabasites thought to have been deposited in extensional rift depressions plus varying amounts of intrusive granitoids both granulite facies and amphibolite facies mineralogies characterise the basement terrain of the oonagalabi tongue and that south of the muller thrust the entia dome and cover terrains have only amphibolite facies mineralogy a combination of thermobarometry and petrogenetic data suggests equilibration of the sob south of the muller thrust at 700 800 c and 5 7 kbar and of the hrc in the ruby mine area at 680 780 c and 6 8 kbar some thickening of the supracrustal accumulations owing to compression is considered necessary for the development of these pressures comparison of the harts range terrains with the strangways terrain shows some similarities and some differences

thermal and structural evolution of the intracratonic arltunga nappe complex central australia the thermal and structural evolution of a paleozoic thrust system in central australia the arltunga nappe complex has been examined through field mapping petrographic microstructural and chemical analyses k ar and 40ar 39ar thermochronology and multi diffusion domain time temperature modeling of k feldspar 40ar 39ar data the arltunga nappe complex contains three distinct tectonic units bounded by regional faults and shear zones that have undergone contrasting deformational and metamorphic histories the cooling history of the three tectonic units has been constrained by k ar and 40ar 39ar isotopic age data from k feldspars micas and amphiboles results are consistent with a piggyback history of crustal imbrication spanning over 100 m y with the hottest rocks uplifted and cooled first and with imbrication acting progressively toward the foreland implications for the intracratonic paleozoic tectonics of central australia are 1 uplift within the structurally highest tectonic unit was initiated before 400 ma 2 continued piggyback imbrication footwall failure and uplift and exhumation of the crust resulted in duplexing in the lowest structural unit at approximately 325 300 ma 3 the contrast in thermal history between the tectonic units indicates that once widely separated crustal segments were juxtaposed during thrusting above a hinterland dipping megathrust resulting in 85 km of crustal shortening

contraction of the 300 mbar north circumpolar vortex during 1963 1997 and its movement into the eastern hemisphere the size of the 300 mbar north circumpolar vortex and its partition into western and eastern hemispheres and quadrants 0 90 w 90 w 180 90 e 180 and 0 90 is estimated by planimetering the area poleward of contours in the main belt of westerlies on the polar stereographic mean monthly analyses of the institute of meteorology of the free university of berlin during 1963 1997 the trend in annual vortex size is a significant 1 4 decade vortex contraction but with the trend in the western hemisphere portion of the vortex a significant 2 1 decade compared to 0 7 decade in the eastern hemisphere portion signifying a movement of the vortex farther into the eastern hemisphere thus while on average 52 of the vortex was in the eastern hemisphere during 1963 1997 this value increased by a significant 0 4 decade during the period resulting in a substantial increase in vortex eccentricity in winter and spring the vortex has moved mainly into the asian quadrant 90 e 180 whereas in summer the vortex has become elliptical with less of a decrease in size of quadrants 90 e 180 and 0 90 w and in autumn there has been a decrease in size of quadrant 90 w 180 relative to the other quadrants the standard deviation of the annual quadrant size anomalies has decreased significantly during 1963 1997 indicating a decrease in the annual displacements of the vortex center from its mean location as the eccentricity increases and the vortex contracts on the basis of a 41 station northern hemisphere radiosonde network during 1963 1997 the annual 850 300 mbar temperature increased by a significant 0 12 c decade in the northern hemisphere as a whole and by a significant 0 17 c decade in the western half and by 0 06 c decade in the eastern half of the hemisphere the resulting association of a 1 decade decrease in 300 mbar vortex size with about an 0 1 c decade increase in 850 300 mbar temperature differs by a factor of 2 from what would be expected hydrostatically a difference that would be eliminated by an 0 4 mbar decade increase in midlatitude surface pressure during 1963 1997

a detailed study of the active crustal deformation in the aegean and surrounding area abstract a detailed study of the active crustal deformation in the aegean sea and surrounding area is presented the estimation of the deformation velocities is not performed in broad seismic zones but in seismogenic sources of limited spatial extent where the seismic energy is practically released in order to describe the spatial variations of the components of the strain rate tensor the deformation analysis is based on previous work where the seismicity and the available focal mechanisms are used separately for estimating the rate and shape of the deformation respectively the calculations were performed for 63 seismogenic sources identified in the aegean sea and surrounding area which belong to eight belts with an almost uniform orientation of the stress field along the coasts of albania and northwestern greece up to leukada island the collision of the adria plate with eurasia results in a compressional velocity of about 4 mm yr in a direction n49 e almost normal to the coast line the dextral movement with almost 3 cm yr along the cephalonia transform fault with strike n45 e is expressed as an almost equal extension and compression in n s and e w direction respectively along the convex outer part of the hellenic arc a crustal shortening of 1 3 cm yr is observed in a mean direction n34 e the direction of this shortening is almost constant from the southern ionian islands zakynthos up to rodos while the shortening rate does not significantly change from the outer sources to the inner ones the aegean sea and surrounding area is characterised by an extensional deformation the direction of the maximum extension in the northern part of this area shows an anticlockwise rotation from east to west thus this extension has a nne direction in northwestern turkey n11 e a nnw direction in central and northern greece as well as along the southern aegean volcanic arc and its extension to southwestern turkey n12 w and a wnw direction in the westernmost part of this extensional area n72 w the mean value of the extensional velocities in this area is 5 mm yr the northern part of asia minor and of the aegean sea is characterised by the dextral strike slip movement of about 2 cm yr of the north anatolian fault and its continuation in the northern aegean where this movement gradually decreases to about 6 mm yr the vertical crustal upper 10 km of the crust thickening is about 2 mm yr along the convex side of the hellenic arc and the vertical crustal thinning is about 1 mm yr in the aegean sea these values were obtained from the component u 33 of the velocity tensor

relation of size and displacement of the 300 mbar north circumpolar vortex to qbo el nino and sunspot number 1963 2000 the size of the 300 mbar north circumpolar vortex and its eastern western date line and greenwich hemisphere components is estimated for the period 1963 2000 by planimetering the area poleward of 300 mbar contours in the main belt of westerlies on the mean monthly polar stereographic analyses of the institute of meteorology of the free university of berlin on the basis of the superposed epoch method there is little evidence of a relation between vortex size and phase of the qbo but significant at the 90 level or better is the tendency for the vortex to be less displaced into the eastern hemisphere in the east wind phase of the qbo for the vortex to be expanded near the time of nino 3 sea surface temperature maximum el nino but contracted 3 4 seasons after and for the vortex to be displaced farther into the date line hemisphere when there is an el nino there is also an impressive tendency for the winter vortex to be less displaced into the eastern hemisphere at the time of el nino the tendency for the vortex to be contracted near sunspot maximum and expanded near sunspot minimum is significant at only about the 80 level because of the small sample size

rate of arunta inlier evolution at the eastern margin of the entia dome central australia abstract zircon dating in the entia dome of the arunta inlier helps to temporally define the multiphase successive strangways and harts range orogenies it appears that the entire activity of both orogenies took place between 1767 2 ma and 1731 1 ma with a major shearing and thrusting event associated with plutonic activity at 1747 2 3 ma these comparatively short time spans indicated are quite sufficient for the large horizontal movements required for the intra continental basin formation and deformation that has been postulated by james and ding the earlier of these events are later than those currently proposed for equivalent stages of other middle proterozoic inliers of the north australian orogenic province which raises difficulties with detailed correlations in grouping the inliers together monazite u pb muscovite rb sr and biotite rb sr isotopic systems had not closed until 360 ma 325 ma and 308 ma respectively indicating uplift and cover removal from 20 km to

relation between 300 mb north polar vortex and equatorial sst qbo and sunspot number and the record contraction of the vortex in 1988 89 abstract the size of the 300 mb north circumpolar vortex and quadrants has been estimated between 1963 and 1989 by planimetering the area poleward of contours in the main belt of westerlies on the 300 mb mean monthly polar stereographic maps analyzed by the meteorological institute free university of berlin the annual mean vortex was most contracted in 1989 6 4 less than average size and next most contracted in 1988 4 6 less than average size there have been three extensive vortex displacements during this period the last toward the north pacific and associated with the strong el nino of 1982 83 based on 108 seasonal deviations there has been a significant correlation of 0 39 between sea surface temperature sst in the eastern equatorial pacific and vortex size three seasons later that is the vortex has tended to be contracted following el nino there has been a highly significant correlation of 0 45 between this sst and the size of quadrant 90 w 180 in the same season that is this el n

tectonic deformation and microseismicity of the saronikos gulf greece we deployed an on offshore seismic network consisting of 36 three component stand alone digital stations in the saronikos gulf and surrounding area and observed the microseismic activity from 17 august to 9 december 2001 the geometry and location of the network were designed to observe the offshore activity to connect known active faults onshore with those offshore an average of 15 events per day were recorded by a minimum of six stations the focal parameters of 739 events could be defined within the network area we located 306 events with an rms travel time residual of about 0 2 sec the epicenters in the saronikos gulf are aligned mainly along an east west trending fault with a length of nearly 30 km this fault is located north of aegina and could produce earthquakes as large as ms 6 5 it is the offshore continuation of a seismic zone located in east corinthia a second active fault was identified east of aegina trending northeast southwest it is probably linked to the northeast southwest striking zone of the salamis fili seismic region activated by the september 1999 event of athens outside the network we mapped an active area at the parnis mountain still active after the ms 5 9 event and a second one further northeast at the western coast of evia this zone is close to chalkis and the recently active psachna area the network also mapped intense activity at the northeastern coast of evia close to the city of kymi and the area of skyros which was seriously damaged by an ms 5 8 earthquake in 2001 the onshore offshore local network identified several regions of very high seismic activity not detectable by regional networks and demonstrated once more the advantage of deploying local seismic networks for mapping active deformation in very short periods of time

paleozoic deformation and isotopic disturbance in the southeastern arunta block central australia proterozoic metamorphic rocks of the arunta block central australia were thrusted southward over the northern margin of the neoproterozoic to mid paleozoic amadeus basin during the 400 300 ma alice springs orogeny the extent and nature of mid paleozoic ductile deformation in the southeastern arunta block is examined in light of available u pb 40ar39ar k ar rb sr and sm nd isotopic age data most of the proterozoic amphibolite and granulite facies rocks north of the zone of basement cover interaction were exhumed and cooled from above 500 to below 125 c as a result of mid paleozoic nappe formation this suggests that deformation early in the cooling history occurred at amphibolite facies conditions and progressed to greenschist facies conditions later in the cooling history in general shear zone rocks yield the youngest isotopic ages indicating that deformation induced recrystallization grain size reduction or localized thermal perturbations are responsible for the relatively young ages we conclude that shear zones of mid paleozoic age were active under greenschist and amphibolite facies conditions though further work is needed to differentiate whether amphibolite facies shear zones are paleozoic or proterozoic some proterozoic shear zones were uplifted passively in the mid paleozoic resulting in final closure and mixed ages in key minerals like hornblende

development of the late proterozoic to mid paleozoic intracratonic amadeus basin in central australia a key to understanding tectonic forces in plate interiors the intracratonic amadeus basin in central australia is a complex composite basin covering 17 000 km with at least nine distinct episodes of evolution between 900 and 300 ma these have been identified in neighboring central australian basins and are characterized by intervals of renewed subsidence followed by intervals of erosion and changes in basin shape several unconformities separating the tectonostratigraphic sequences represent periods of mild regional uplifts and correlate with major episodes of compressive tectonism at the evolving margin of the early australian plate in the absence of direct geological evidence for thermal events in the amadeus basin after the initial period of subsidence ended possibly at about 800 ma the correlations found between events in the amadeus basin those in the neighboring interconnected basins and tectonic events at the continental or plate margins emphasize that regional horizontal stress fields contribute significantly to primary basin forming mechanisms this suggests that stresses generated at continental or plate margins may propagate to the plate interior with the lithosphere acting as a stress guide throughout the history of the amadeus basin both periods when compressional stresses were dominant and when extensional tectonics controlled subsidence can be identified there were also transitional periods when neither compression nor extension dominated so that other processes masked the effects of weak horizontal stresses the most recent compressional thrust belt concentrated at the northern margin between 300 and 400 ma and has partly obscured the record of earlier basin shape and size

influence of the arctic circumpolar vortex on the mass balance of canadian high arctic glaciers abstract variability in july mean surface air temperatures from 1963 to 2003 accounted for 62 of the variance in the regional annual glacier mass balance signal for the canadian high arctic a regime shift to more negative regional glacier mass balance occurred between 1986 and 1987 and is linked to a coincident shift from lower to higher mean july air temperatures both the interannual changes and the regime shifts in regional glacier mass balance and july air temperatures are related to variations in the position and strength of the july circumpolar vortex in years when the july vortex is strong and its center is located in the western hemisphere positive mass balance anomalies prevail in contrast highly negative mass balance anomalies occur when the july circumpolar vortex is either weak or strong without elongation over the canadian high arctic and its center is located in the eastern hemisphere the occurrence of westerly positioned july vortices has decreased by 40 since 1987 the associat

kinematics of conjugate shear zones displacement partitioning and fragmentation of the upper rigid crust during denudation of high p rocks pelagonian and sub pelagonian zones greece abstract in the sub pelagonian and pelagonian zones kinematic analyses on faults and cataclastic shear zones document an overall displacement vector towards nnw and wsw ssw for attica and western macedonia respectively this tectonic episode is interpreted as being triggered by the kinematically oligocene miocene detachment of the sub pelagonian and pelagonian zones from the high p rocks during this episode the sub pelagonian and pelagonian zones were decoupled along detachment zones fragmentised by brittle mechanisms and horizontally stretched in km scale the strain record of the cataclastically deformed lithologies of the upper plates reveals a complex kinematic pattern with displacement partitioning in an overall non coaxial regime these structural processes are considered to be kinematically linked to the exhumation of the high p rocks deforming the sub pelagonian and pelagonian zones

recent widening of the tropical belt evidence from tropopause observations 1 radiosonde measurements and reanalysis data are used to examine long term changes in tropopause behavior in the subtropics tropopause heights in the subtropics exhibit a bimodal distribution with maxima in occurrence frequency above 15 km characteristic of the tropical tropopause and below 13 km typical of the extratropical tropopause both the radiosonde and reanalysis data show that the frequency of occurrence of high tropopause days in the subtropics of both hemispheres has systematically increased during the past few decades so that tropical characteristics occur more frequently in recent years this behavior is consistent with a widening of the tropical belt and the data indicate an expansion of about 5 8 latitude during 1979 2005

rates of tectonic uplift in the corinth and megara basins central greece we present evidence of the rates of late quaternary tectonic uplift that have affected parts of central greece during this period of active extension and basin formation dual lines of evidence indicate upper pleistocene to holocene uplift rates of the order of 0 3 mm yr 1 for the corinth and megara basins first u series disequilibrium ages of acropora sp corals from uplifted marine sediments are used to derive minimum average rates of vertical displacement since deposition second the geometries of cyclical transgressive sequences and of erosional terraces are consistent with the radiometric evidence and the known history of late quaternary sea level fluctuations two types of uplift are distinguished on the basis of structural relationships 1 fault block rotation about a horizontal axis tilting in response to footwall uplift on the active normal fault bounding the alkyonides gulf and 2 a more regional uplift which affects the corinth basin and peloponnesos to the south the results of u series dating are discussed in the light of initial 234u 238u activity ratios derived from the coral samples which are higher than for average marine waters 1 17 1 31 compared to 1 14 these values may be related to a variable freshwater input to the structurally confined gulf of corinth or alternatively they may reflect a previously higher global 234u 238u activity ratio in marine waters or post mortem enrichment in 234u although the mechanism of the latter is not yet understood

wavelet analysis of polar vortex variability over the twentieth century recent increases in extreme weather events in the northern hemisphere have been linked to amplified planetary waves changes in planetary wave properties are linked to changes in climate hence finding a mechanism that links the planetary wave variability under climatic forcing and midlatitude blocking events has engendered a great deal of interest in this study wavelet analysis is applied to time series of planetary wave phase speeds at high latitudes as a first step to assessing the potential for identifying these mechanisms in the observational record a circumpolar multiannual cycle increase is found but signals also demonstrate a complex westward propagation pattern with periods of intense wave variability significant correlations between wavelet power at all time scales and albedo snow cover atmospheric ozone levels and surface air temperature are demonstrated

isotopic dating in metamorphic belts isotopic dating in metamorphic rocks is concerned with the timing of processes whose operation is controlled by continually changing physical conditions of these temperature has a pervasive influence and the use of physical models to elucidate the ways in which temperature is likely to vary is briefly reviewed the central concept of closure temperature is critically discussed and quantitative estimates for biotite and hornblende are evaluated in order to illustrate the factors which control closure temperatures and limit their application in practice the possibility of dating crystallization using minerals which crystallize below their respective closure temperatures is examined taking examples involving k ar rb sr sm nd and u pb analyses the indirect dating of metamorphism via structurally dated plutons is briefly considered and the problems of interpreting both discordant u pb zircon ages and rb sr whole rock isochrons in metamorphosed granites are discussed the value of near concordant zircon ages is emphasized the extent of isotopic equilibration during metamorphism specifically of sr isotopes in metasediments is shown not to be a simple function of metamorphic grade the flow of fluids produced by metamorphic reactions appears to be crucial and there is a potential for dating metamorphism using whole rock samples where such flow can he demonstrated independently the concluding discussion briefly examines existing data for the dalradian and indicates the potential for further progress using both well established and novel approaches

kinematics and deformation of central and southwestern greece from historical triangulation data and implications for the active tectonics of the aegean abstract changes in the coordinates of 38 stations 32 of which were common to three historical triangulation surveys 1889 1905 1927 1930 and 1950 1970 in central greece were computed based on conventional adjustment techniques and the assumption of a nearly fixed baseline length some of the calculated coordinate changes are significant against the a posteriori network adjustment errors and are likely to indicate tectonic motions consistent with those deduced from geological and geophysical data and other geodetic studies comparison of the first survey network with gps data more explicitly the historical geodetic data confirm the rotational character of the deformation in the area but they show that the strain pattern is likely to have changed after 1930 between 1890 and 1930 strain was changing smoothly as if no strain discontinuities existed while the peloponnesus was under contraction from the northeast probably reflecting accommodation of strain from the arc significant left lateral shear in the gulf of corinth and n s extension in the whole of the study area were observed only after 1930 estimates of strain are consistent with those deduced from comparison of historical triangulation and gps data corrected for the scale error that exists in the terrestrial geodetic data in greece and estimates of strain from seismological data the change in the kinematic pattern after 1930 seems to be confirmed by changes in the shear strain computed directly from changes in observed angles between stations and from changes in the seismicity rates such changes although not unusual in the geological record are not easy to explain but may reflect elastic rebound effects in area with an extremely complicated tectonic fabric or hysteresis in the accommodation of e w compression from the arc by n s stretching

tectonics of the aegean block rotation side arc collision and crustal extension abstract a new tectonic model for the aegean block is outlined in an effort to explain the widespread extension observed in this region a key element in this model is the concept of side arc collision this term is used to describe the interaction of subducted oceanic lithosphere with continental lithosphere in a subduction arc in which oblique subduction occurs in the hellenic arc side arc collision is proposed for the northeast corner near rhodes the collision involves subducted african lithosphere moving to the northeast almost parallel to the arc with the continental mass of southwest turkey it affects the motion of the anatolian aegean plate complex but is not similar to continental collision since it occurs mostly at depth and involves only little if any of the shallow and rigid part of the continental lithosphere the model assumes that anatolia and the aegean are part of one plate complex which undergoes counterclockwise rotation if it were not for the side arc collision near rhodes the two blocks would exhibit similar deformation and might in effect be indistinguishable at present however free and undisturbed rotation is possible only for the anatolian block excluding western anatolia where the motion is accommodated by subduction along the cyprean arc further west the side arc collision inhibits this rotation along the subduction front still further west undisturbed subduction along the central and western parts of the hellenic arc is again possible and is well documented on the other side of the anatolian aegean plate complex relatively free motion occurs along the north anatolian fault zone including in the aegean sea the combination of this motion in the north with the local obstruction of the rotation near rhodes must create a torque and a new pattern of rotation for the western part of the plate complex thus creating a separate aegean block since however the two blocks are not separated by a plate boundary the aegean block cannot move freely according to the new torque effective motion of the aegean block relative to europe and anatolia particularly in the north is achieved through extension of the crust lithosphere thus the greatest amount of deformation extension is observed along the suture zone between the two blocks and in particular in the northeastern part of the aegean block where motion relative to anatolia must be greatest

the strain field in northwestern greece and the ionian islands results inferred from gps measurements abstract recent crustal movements detected by the analysis of repeated satellite geodetic measurements reflect the ongoing geodynamic processes in the alpine mediterranean area superimposed on the large scale counterclockwise rotation of the african plate complex dynamic processes are affecting the lithospheric fragments between the african and eurasian plates key features to better understand the driving forces and associated seismic activity in the africa eurasia collision zone are the calabrian and hellenic arcs in this paper geodynamic investigations along the west hellenic arc are discussed they are based on two epochs 1989 and 1993 of satellite geodetic measurements carried out using the us global positioning system gps the results are presented in terms of relative displacements and strain rates within the time span of 4 years southwestern greece has moved to the southwest relative to southeastern italy by an average of 120 mm increasing from 80 mm at lefkada in the center of the ionian islands to 160 mm at the peloponnesus the maximum strain rate is 0 18 strain a located in the vicinity of lefkada where anomalously high earthquake activity is observed the data provide strong evidence for dextral strike slip motion on the order of 25 mm a along the kephalonia fault zone kfz the deformation field of the kfz is interpreted as a transition zone between the kinematics of the apulian platform and the west hellenic fold and thrust belts

the active submarine nw termination of the south aegean active volcanic arc the submarine pausanias volcanic field abstract methana peninsula shows the longest recorded volcanic history at the western end of the south aegean active volcanic arc including volcanic products from the upper pliocene to recent times the volcanic rocks comprise widespread dacite domes and andesite lava flows from several small volcanic centers and are only imprecisely dated in this paper the integrated analysis of swath bathymetry side scan sonar data and high resolution seismic reflection profiles correlated with core samples has allowed detailed mapping characterization and precise chronological identification of the pausanias submarine volcanic field activity offshore northern methana six volcanic cones or domes are recognized typically 1 3 km in diameter some elongated ne sw and some with a small central crater on their flanks the acoustically reflective volcanic rocks pass laterally into incoherent transparent seismic facies interpreted as volcaniclastic deposits possibly including hyaloclastites that interfinger with the regional basin sediments a sea bottom hummocky field is interpreted as volcanic avalanche and appears to be the submarine continuation of the volcaniclastic apron of northern methana peninsula a robust chronostratigraphic framework has been established based on the recognition of shoreline progradational units and their connection with quaternary eustatic sea level cycles relative dating of the different phases of submarine volcanic activity during the upper quaternary has been achieved by correlating the imaged volcaniclastic flows interlayered within the chronostratigraphically dated sediments dating by stratigraphic position relative to 2d imaged eustatic sea level clinoform wedges appears to be more precise than radiometric methods on land three main submarine volcanic events ve are recognized ve3 at 450 ka a less precisely dated interval at 200 130 ka ve2 and ve1 at 14 ka based on chronostratigraphic constraints subsidence rates of 0 16 0 008 m ka in between marine isotopic stages 6 and 12 and 0 19 0 009 m ka in between marine isotopic stages 12 and 16 were estimated for the marine basin north of methana the morphological similarity to the onshore volcanoes of methana peninsula implies that magmatic constructive processes were dominant regardless of whether in air or in water the upper quaternary submarine volcanic rocks of methana differ from those known from stratovolcanoes elsewhere in the mediterranean e g kos nisyros stromboli and in other volcanic arcs e g montserrat st vincent in the submarine development of domes or small cones the paucity of volcano flank failure deposits and the lack of explosive events pausanias volcanic products date the onset of ne sw faulting as well as the following tectonic phase of e w striking faults possibly related to basin inversion caused by a major rifting phase that also affected most of the south aegean arc and the adjacent gulfs of corinth and argolikos

quaternary evolution of the corinth rift and its implications for the late cenozoic evolution of the aegean summary we present geological and morphological observations at different scales to constrain rates of faulting and the distribution of deformation in the seismically active aegean region we focus first on the 130 km long corinth rift an asymmetric graben where a flight of terraces of marine origin are uplifted we show that the edges of the terraces lie in the footwall of the normal fault bounding the corinth rift and correspond to sea level highstands of laic pleistocene age using a detailed analysis of aerial and spot imagery supported by field observations we have mapped 10 terrace platforms and strandlines ranging in elevation from 10 to 400 m over distances of 2 to 20 km from the fault the elevation of the terraces inner edges was estimated at 172 sites with an error of 5m this data set contains a precise description of the uplift and flexure of 10 different palaeohorizontal lines with respect to the present sea level to date the deformation we correlate the corinth terraces with late pleistocene oxygen isotope stages of high sea level stands and with global sea level fluctuations using a thick elastic plate model consistent with our current understanding of the earthquake cycle and a boundary element technique we reproduce the geometry of the shorelines to constrain both mechanical parameters and the slip on the fault we show that the seismogenic layer behaves over the long term as if its elastic modulus were reduced by a factor of about 1000 all the terraces are fitted for fault slip increasing in proportion to terrace age and the component of regional uplift is found to be less than 0 3 mm yr 1 the best fits give a slip rate of 11 3 mm yr 1 on the main rift bounding fault over the last 350 kyr other geological and morphologic information allows us to estimate the total age of the main fault 1 ma and to examine the mechanical evolution of the corinth rift the minimum observed sediment thickness in the gulf places an extreme check on the results of the modelling and a lower bound on slip rate of 6 7 mm yr 1 40 per cent less than estimated with modelling even this slip rate is nearly 10 times higher than for comparable features in most of the aegean and elsewhere in the world at a larger scale the spacing and asymmetry of the rift systems in the aegean suggest strain localization in the upper mantle with slow extension starting 15 myr ago or earlier the more recent 1 myr rapid phase of rifting in corinth partly reactivated this earlier phase of extension the younger faulting in corinth appears to result from its present location in the inhomogeneous stress field process zone of the south westward propagating tip of the southern branch of the north anatolian fault we extend these relations to propose a mechanical model for the late cenozoic evolution of the aegean as the arabia europe collision progressed in eastern turkey it caused anatolia to move to the west and the north anatolian fault to propagate into the aegean where the early slow extension started to be modified about 5 ma ago the process of propagation dramatically increased the activity of some but not all of the earlier rifts the model we present is compatible with tectonic observations as well as with the seismicity the palaeomagnetic rotations and the displacement field now observed with gps and slr

metamorphic events in the eastern arunta inlier part 1 metamorphic petrology abstract in the entia dome of the eastern arunta inlier kyanite facies metamorphism is recorded over a substantial area at least 160 km 2 and thus contrasts with the regionally extensive belts of high temperature low pressure andalusite sillimanite facies metamorphism documented elsewhere in the arunta inlier this amphibolite facies event appears to postdate regional granulite facies metamorphism evidence for which is almost totally obliterated in the entia dome prograde kyanite occurs in meta basites in comparatively rare associations involving hornblende staurolite and anorthite and in other rocks in association with gedrite and hornblende or garnet and biotite these kyanite bearing assemblages equilibrated at intermediate temperatures 570 710 c at peak pressures of 7 kbar and are overprinted by lower pressure assemblages including hornblende gedrite cordierite and sillimanite while this sequence of reactions may be simply interpreted in terms of a single clockwise orogenic cycle textural evidence and the available mineral isotopic data suggest a more complex history involving multiple heating and cooling episodes during the mesoproterozoic and possibly the palaeozoic the occurrence of regional retrogressive kyanite facies assemblages in the eastern arunta inlier provides evidence that the widely held perception that proterozoic crustal evolution in australia involved a distinct ensialic orogenic style characterised by high geothermal gradients etheridge et al 1987 loosveld and etheridge 1990 sandiford and powell 1991 is not universally true rather petrological evidence presented here with isotopic constraints described by foden et al 1995 suggests that the harts range region has experienced substantial crustal reworking at elevated temperatures during both the proterozoic and palaeozoic under thermal regimes more familiar to modern continental collision zones

the relationship between k ar mineral ages mica grainsizes and movement on the moine thrust zone nw highlands scotland muscovite and biotite separated from moine schists close to the moine thrust zone yield a range of k ar ages incompatible with the simple cooling regime previously proposed for the caledonides of northern scotland differences of only 1 ma between muscovite and biotite of the same grainsize contrast with differences of 12 13 ma between the 125 200 m and 250 500 m grainsize fractions this is contrary to the normally accepted dominance of mica type over grainsize effects dynamic recrystallization of the micas during early deformation associated with the moine thrust zone is thought to play a role as important as temperature in determining the k ar ages the conclusions drawn have important implications for the use of uplift and cooling rates derived from the absolute k ar closure temperatures of micas close to thrust zones although the k ar ages from micas with diameters greater than 200 m are not reproducible the data can be used to show that deformation associated with thrusting commenced between c 443 ma and c 435 ma and that the thrust zone was active until at least 422 ma ago

effects of progressive mylonitization on ar retention in biotites from the santa rosa mylonite zone california and thermochronologic implications the santa rosa mylonite zone developed predominantly from a granodiorite protolith in the eastern margin of the peninsular ranges batholith a wide variation in k ar biotite dates within the zone is shown to reflect the times of cooling through closure temperatures whose variability is chiefly a result of deformation induced reduction in grain size we suggest that such variation generally may be exploited to place constraints on the timing of deformation episodes previous workers have shown that deformation in the santa rosa mylonite zone involved the formation of mylonites and an imbricate series of low angle faults which divide the area into structural units field work petrographic studies and tem analysis of deformation mechanisms in biotite show that the granodiorite mylonite the lowermost structural unit formed below the granodiorite solidus the granodiorite mylonite varies from protomylonite to ultramylonite with regions of high strain distributed heterogeneously within the zone previously reported biotite and hornblende k ar dates from the granodiorite protolith below 82 89 ma and the asbestos mountain granodiorite above 61 68 ma the mylonite zone indicate dramatically dissimilar thermal histories for the lowermost and uppermost structural units other workers fission track dates on sphene zircon and apatite from the granodiorite mylonite and the asbestos mountain granodiorite suggest thermal homogenization and rapid cooling to 100 c by ca 60 ma within and adjacent to the mylonite zone k ar dates on 5 samples of biotite from variably deformed granodiorite range from 62 76 ma dates are not correlated with structural depth but clearly decrease with degree of deformation and concomitant grain size reduction 40ar 39ar incremental heating analyses of biotite from the granodiorite protolith reveals no evidence of excess argon and produces a relatively flat age spectrum 40ar 39ar incremental heating analysis of biotite from the granodiorite mylonite discloses discordance consistent with 39ar recoil loss k analysis of samples allowing k ar dates to be calculated is therefore recommended as an adjunct to 40ar 39ar step heating analysis in rocks that have experienced similar deformation during mylonitization biotite grain size reduction through intracrystalline cataclasis results in estimated grain dimensions as small as 0 05 m locally within porphyroclasts as large as 1 mm because biotite compositions are relatively uniform fe fe mg mn ti alvi 0 47 0 52 and show no systematic variation with grain size compositional dependence of activation energy and diffusivity can be eliminated as sources of variation in ar retention ar closure temperatures calculated with appropriate diffusion parameters for the observed grain sizes are in the range 220 280 c and define a cooling curve consistent with a thermal history intermediate between those of the granodiorite protolith below and the asbestos mountain granodiorite above the mylonite zone changes in the slope of the cooling curve indicate that the main deformation episode initiated at or above ca 330 c 80 ma above the closure temperature for thermally activated diffusion of argon in biotite and continued to a minimum of ca 220 260 c 62 ma

historical coastal evolution of the ancient harbor of aegina in relation to the upper holocene relative sea level changes in the saronic gulf greece abstract the extensive ancient harbor installations today submerged on the seafront of kolona in aegina are associated with the great trading and maritime development of the island from the middle bronze age to the middle classical period based on geomorphological and archeological indications three distinct relative sea levels can be defined at depths of 3 17 0 05 m 0 97 0 05 m and 0 52 0 05 m the dating of the sea level changes based on archeological evidence and historical sources shows that the initial sea level change in aegina occurred certainly after ad 170 and most likely after ad 250 the intermediate change is dated between ad 1586 and ad 1839 and the most recent change occurred between 1839 and 1999 a transgression followed a long period of sea level stability that lasted at least 2200 years from the middle bronze age ca 3900 yr bp to the late roman period ca 1700 yr bp according to the paleogeographical reconstruction of the coast the ancient harbor installations stretch along 1600 m of coastline the north harbor is bounded by the north breakwater the riprap on the once wide sandy coast the detached west breakwater and the uplift morphology of the west end of kolona hill on the south coast the harbor installations comprise the fortified closed harbor with the shipsheds the commercial harbor which is entirely destroyed by the modern port the anchorage area that is bounded by the west breakwater and built of cone shaped piles of stones the tops of which once projected above the sea level and the south curved breakwater at its southernmost boundary

structural evolution of the harts range area and its implication for the development of the arunta block central australia abstract a division of the high grade metamorphics of the arunta block in the harts range area into two main groups on the basis of lithology structure metamorphism and igneous activity is suggested as a result of detailed mapping the lower group is regarded as a basement terrain and comprises major layered felsic or granitic gneiss minor amphibolite and mafic granulite while the structurally overlying group is regarded as a cover sequence irindina supracrustal assemblage and comprises predominantly metasediments pelitic and semi pelitic gneiss calc silicate and quartzite and amphibolite anorthosite and ultramafic rock of the harts range meta igneous complex the cover sequence might have been deposited in an aulacogen or adjacent to a continental margin which developed by rifting of a pre existing basement the two groups both show early major ductile tectonothermal stages with four major fold generations and a later discrete shear event in the basement and two major fold generations and a later series of stacked nappes developing in the cover the basement s early orogenic evolution with associated granulite facies metamorphism is typical of intensely reworked early precambrian terrains and developed spatially and or temporally separated from the cover cover deformation closely resembles continental margin cordillera type overthrusting and thus thin skinned tectonics associated with large scale crustal shortening during the later harts range remobilization the basement and cover were juxtaposed by displacement on a fundamental crustal dislocation recumbent contraction fault mylonites repeatedly developed along the dislocation which was also isoclinally folded intruded by a major megacrystic granitoid bruna gneiss sheet and repeatedly rejuvenated the history of development of the dislocation is documented and described as a process of underthrusting of basement beneath cover which led to the final termination of the orogenic activity

seismicity and associated strain of central greece between 1890 and 1988 summary we examined the seismicity of central greece between 1890 and 1988 using macroseismic and instrumental data to ask two questions 1 does the seismicity of this period reveal all the major tectonic structures that are known to be active and 2 what are the likely strains associated with the seismicity over this period many known active structures have been effectively aseismic for the last hundred years and even the inclusion of all known large events earlier than 1890 reveals no activity associated with the ne coast of evia gulf of argos or graben ne of mt parnassos it is clear that even 100 years data are inadequate for either a reasonable assessment of seismic risk or for a confident estimation of maximum magnitude however we are aware of no earthquakes in central greece during the last 200 yr that were larger than ms 7 0 it is probable that the maximum magnitude is restricted by the maximum length of fault segments which appears to be around 15 20 km the earthquakes of ms 5 8 during 1890 1988 can account for a n s displacement of around 45 70 cm with maximum and minimum estimates a factor of two greater and smaller than this across part of a 1890 1900 triangulation network in central greece that was resurveyed in 1988 the contribution of smaller events may increase this displacement by about 50 per cent this cumulative seismic displacement is similar to that estimated from the geodetic work about 100 cm but a detailed comparison of the two sets of observations will be reported elsewhere a re evaluation of all the important earthquakes of 1890 1988 in central greece is presented in the appendix which summarizes information of use to both earth scientists and engineers

compositional changes of minerals associated with dynamic recrystallizatin the rate of compositional and isotopic exchange between minerals may be enhanced significantly if the rock is deformed simultaneously the enhanced exchange rate may result from a reduction in grain size shorter distance for volume diffusion dissolution and growth of grains by diffusion creep pressure solution or the movement of high angle grain boundaries through strained grains during recrystallization in the dislocation creep regime the migration of high angle grain boundaries provides high diffusivity paths for the rapid exchange of components during recrystallization the operation of the latter process has been demonstrated by deforming aggregates consisting of two plagioclases an1 and an79 at 900 c 1 gpa confining pressure and a strain rate of 2x10 6s 1 the polygonal recrystallized grains were analyzed using an analytical transmission electron microscope and have a variable but often intermediate composition at the conditions of these experiments the volume interdiffusion rate of nasi caal is too slow to produce any observable chemical change and microstructural chemical relations indicate that the contribution from diffusion creep was insignificant except for initially fine grained 2 10 m aggregates these results indicate that strain induced recrystallization can be an effective mechanism for enhancing the kinetics of metamorphic reactions and for resetting the isotope systematics of minerals such as feldspars pyroxenes and amphiboles

the arctic oscillation signature in the wintertime geopotential height and temperature fields the leading empirical orthogonal function of the wintertime sea level pressure field is more strongly coupled to surface air temperature fluctuations over the eurasian continent than the north atlantic oscillation nao it resembles the nao in many respects but its primary center of action covers more of the arctic giving it a more zonally symmetric appearance coupled to strong fluctuations at the 50 hpa level on the intraseasonal interannual and interdecadal time scales this arctic oscillation ao can be interpreted as the surface signature of modulations in the strength of the polar vortex aloft it is proposed that the zonally asymmetric surface air temperature and mid tropospheric circulation anomalies observed in association with the ao may be secondary baroclinic features induced by the land sea contrasts the same modal structure is mirrored in the pronounced trends in winter and springtime surface air temperature sea level pressure and 50 hpa height over the past 30 years parts of eurasia have warmed by as much as several k sea level pressure over parts of the arctic has fallen by 4 hpa and the core of the lower stratospheric polar vortex has cooled by several k these trends can be interpreted as the development of a systematic bias in one of the atmosphere s dominant naturally occurring modes of variability

northern hemisphere circumpolar vortex trends and climate change implications 1 trends in the northern hemisphere circumpolar vortex at 700 500 and 300 hpa are examined to assess the relationship between circulation variability and air temperature a vortex climatology is developed for the period 1949 2000 at each pressure level three geopotential height contours are used to quantify the size and position of the vortex at 5 longitude resolution within and both north and south of the primary hemispheric baroclinic zone this combination of spatial specificity and the long temporal record makes this the most comprehensive vortex climatology to date the overall and seasonal vortex time series for the northern hemisphere are created for northern middle and southern contours at each of the three levels in the atmosphere from the beginning of the record until 1970 the vortex exhibits a statistically significant expansion but the vortex has been contracting significantly since then at all levels the pre 1970 expansion and subsequent contraction is strongest in the lower latitudes and weakest in the higher latitudes the trends are also stronger in the upper troposphere than in the lower troposphere spatial examination of the vortex indicates that the pre 1970 expansion and post 1970 contraction were driven primarily by expansion contraction over asia europe and north america with little change over the northern hemisphere oceans although significant climate change debate focuses on the discrepancy between positive trends in surface air temperature and little or no trends in microwave sounding unit msu satellite temperatures contraction of the circumpolar vortex at every level of the atmosphere implies that the atmosphere is warming at depth since 1970 comparisons with the msu temperature history indicate that the northern hemisphere circulation as a whole as represented by the circumpolar vortex accounts for almost two thirds of the interannual variability in midlatitude msu temperature indicating that vortex size and position are coupled strongly to atmospheric temperature and could be a good indicator of climate change on a latitude by latitude and level by level basis the lower latitudes are associated most strongly with msu temperature in the midtroposphere while the middle and higher latitudes are more closely associated with msu temperature in the upper troposphere the vortex trends are also similar to observed surface warming trends

caterpillar tectonics in the harts range area a kinship between two sequential proterozoic extension collision orogenic belts within the eastern arunta inlier of central australia abstract we propose that in the harts range area of the arunta inlier of central australia a basement and cover relationship previously described by us represents a thick complexly deformed contact zone between an early middle proterozoic fold belt the strangways orogenic belt sob and a younger middle proterozoic orogenic belt the harts range orogenic belt both of which contain their own supracrustal sequences rocks of the sob were deposited and possibly metamorphosed to a maximum grade of granulite facies at 1800 ma during an early phase of crustal extension they were subsequently intruded by a significant proportion of acidic magmas at 1767 ma and compressed to form a distinctively nne ssw trending orogenic belt a wnw ese trending shallowly north dipping zone of intense and repeated deformation termed the harts range detachment zone hrdz formed initially during a period of nne ssw crustal extension as a major low angle normal shear detachment zone within and crosses at a high angle to the trend of the basement rocks of the sob the hrdz has been intermittently active as a zone of crustal weakness since its initiation the first extensional movement on this zone began the formation of the harts range mobile belt hrmb which displays many of the characteristics of modern tectonic zones activated by plate movement a supracrustal cover sequence the harts range cover hrc formed in the major geosynclinal basin which developed on the subsiding upper plate of the hrdz continued crustal extension juxtaposed the cover sequence which was then metamorphosed to a maximum grade of amphibolite facies and granulite facies basement of the hrdz before a fundamental change in movement sense led to crustal contraction and a collision related thrusting phase the hrmb which includes the hrdz and the hrc was then internally deformed over a relatively very short time span 15 20 ma before voluminous granitic magma intruded mainly along the hrdz during the harts range orogeny hro the intrusion of this major granitoid at 1747 ma precisely fixes the time scale of evolution for the earlier phases of the hro the hro is documented in detail as a peculiar orogenic style of crustal contraction which was largely taken up by reverse sense discrete thrusting and shearing on faults and shear zones associated with the hrdz displacement on the hrdz was a stick slip process with repeated punctuation of thrust slip movement by pinning at points located progressively to the south each period of cessation of thrust slip movement was followed by folding of discrete thrusts of captured basement lobes within the hrdz and of the overlying supracrustal sequence the individual discrete movement phases and folding episodes are each named and described as is a model of this unusual type of proterozoic tectonic activity

displacements of the north circumpolar vortex during el nino 1963 83 abstract during the pronounced 1982 83 el nino the 300 mb north circumpolar vortex was displaced further toward japan from its mean seasonal locations than observed since the beginning of the vortex record in 1963 however during the strong 1972 73 el nino the vortex was displaced toward the 180th meridian and during the weaker 1965 66 el nino toward the eastern pacific so that vortex displacements are not indicated to have been the same for different el nino episodes based on the full 21 year record the vortex has tended to be displaced toward 90 w when sea surface temperature sst in the region 0 10 s 180 80 w was above average but toward the 180th meridian when the magnitude of sst deviation from average is considered

greek tectonics and seismicity abstract the validity of existing tectonic models for the area of greece is examined in the light of the new recalculated parameters for earthquakes of the region makropoulos and burton 1981 relocated hypocentral positions are extracted from the catalogue to form radial and vertical distance depth cross sections centred on a reference point near the mid point of the aegean volcanic arc and these are used to form a three dimensional topography of the base of earthquake occurrence below 60 km isodepth maps are extracted from this topography as both three and two dimensional map presentations these maps reveal several significant features of deep seated tectonic processes in the region isodepths exceeding 150 km are seen in the northwest aegean and these are more closely linked to the sporadhes and gulf of thermaicos rather than the north aegean trough the 150 km isodepths are also seen in the northeast aegean straddling the dardanelles in the northeastern part of the peloponnesus gulf of saronikos and eastern gulf of corinth in the southern peloponnesus towards crete and extending from north of kos to south of rodos the largest extent of deepest activity is seen south of rodos and this continues towards southwest of turkey the subduction zone of the hellenic arc is clear but smooth benioff zones are not the norm and these data show that structural complexity is more readily observed it is concluded that none of the proposed tectonic models completely explain the observed activity over the whole area and rather than propose yet another model places where further work is still particularly necessary are identified