kinematic reconstructions and magmatic evolution illuminating crustal and mantle dynamics of the eastern mediterranean region since the late cretaceous the relationship between subduction dynamics and crustal deformation in the mediterranean region has been recently studied using three dimensional 3d numerical models such models require however a detailed information concerning the past geological evolution we use stratigraphic petrologic metamorphic structural paleomagnetic and magmatic data to build new kinematic reconstructions of the eastern mediterranean region since the late cretaceous using the principle of non rigid domains the motions of the 56 deforming domains defined in this work are calculated based on published paleomagnetic rotations the directions and amounts of displacement on crustal scale shear zones and the burial and exhumation histories of the main metamorphic units extracted from these reconstructions paleotectonic maps and lithospheric scale cross sections illustrate that the present day subduction zone has been continuously retreating southward since the late cretaceous and has accreted several small continental domains in the process we find evidence for two back arc related extensional events 1 slow extension along the balkans and the pontides in the late cretaceous while the trench was long and linear and 2 faster extension in the rhodope aegean west anatolian region since the eocene oligocene rapid rotation of the hellenides between 15 and 8 ma probably indicates a slab tearing event below western anatolia that could have further accelerated this extensional kinematics spatial distribution and the geochemical signature of magmatic centers integrated in these reconstructions allow us to trace mantle related processes revealing the deep dynamics that controls both the magma genesis and the crustal deformation

crustal structure of the eastern algerian continental margin and adjacent deep basin implications for late cenozoic geodynamic evolution of the western mediterranean the karukera spur is an easternmost submerged rise of the lesser antilles fore arc in the guadeloupe archipelago culminating about 4000 m above the fore arc basin 150 km west of the deformation front the analysis of 3500 km 2d high resolution multichannel seismic reflection and multibeam bathymetric data and the study of 14 core samples allow for the first time to reconstruct its sedimentary anatomy and tectonic evolution seven seismic units us1 to us7 are evidenced organised into four major depositional sequences separated by erosional surfaces units us1 to us4 thicken to the south southeast on the spur the sedimentary deposits rest upon a deeply eroded metamorphic basement of the caribbean plate as in la desirade island sequence 1 units us1 and us2 remains unknown in its lower part because it does not outcrop its upper part comprises early miocene shallow water carbonates sequence s2 unit us3 only comprises an upper miocene transgressive systems tract deposited into basinal environment it is bounded by major erosional surfaces sb2 and sb3 sequence 3 us4 to us6 is zanclean to pleistocene it is dominantly composed of shallow water reefal deposits sequence 4 corresponds to recent deposits the karukera spur experienced three main extensional episodes with alternations between uplift and subsidence periods uplifts are responsible for emersions and erosions subsidence severely drowned shallow water deposits the first extensional episode led to the formation of horsts and grabens in the basement prior to early miocene deposits the second extensional episode occurred during upper miocene in accordance with data in surrounding islands the third tectonic episode developed since calabrian noticeable is the constant reactivation of n130 n150 n150 n180 and n40 trending faults since early miocene and the neoformation of e w trending faults since calabrian our results suggest that at the latitude of guadeloupean archipelago the lesser antilles subduction zone is an erosional margin because of the successive sweepings of the santa lucia then tiburon ridges

displacement partitioning and arc parallel extension in the aleutian volcanic island arc abstract convergence between the pacific and north american plates along the aleutian volcanic island arc is generally right oblique the obliquity increases from 0 in the east to nearly 90 in the west where the plate boundary becomes a transform fault zone preliminary results of a structural geology study of attu island the most westerly u s island in the aleutian chain and part of the near islands group shows that the deformational structures are not directly related to the relative plate convergence rate vector but to the plate boundary normal and parallel components of this vector the plate boundary sub normal component is responsible for conjugate sets of arc sub parallel thrust faults and the plate boundary parallel component resulted in arc parallel dextral strike slip faults and their conjugates however the most penetrative structures measured in outcrop are conjugate sets of strike slip faults and arc perpendicular normal faults and fractures veins and dikes which have formed by arc parallel extension this extension is most likely the result of the increase of obliquity from east to west and thus the increase of the arc parallel component of the convergence rate vector along the aleutian arc these structures require that attu island migrated westward possibly for as many as 1150 km

silurian graptolite biostratigraphy in the welsh basin silurian graptolite zones are of markedly shorter duration than those of the ordovician averaging 0 8 ma several can be sub divided and further refinement will undoubtedly follow a revision of many of the graptolite species and their stratigraphic range locally integration of palaeontological and sedimentological studies facilitates correlation a premilinary subdivision of the crispus and griestoniensis zones in central wales is made

numerical simulations of tropical cyclone ocean interaction with a high resolution coupled model the tropical cyclone ocean interaction was investigated using a high resolution tropical cyclone ocean coupled model the model design consisted of the noaa geophysical fluid dynamics laboratory tropical cyclone prediction model which was coupled with a multilayer primitive equation ocean model coupling between the hurricane and the ocean models was carried out by passing into the ocean model the wind stress heat and moisture fluxes computed in the hurricane model the new sea surface temperature sst calculated by the ocean model was then used in the tropical cyclone model a set of idealized numerical experiments were performed in which a tropical cyclone vortex was embedded in both easterly and westerly basic flows of 2 5 5 and 7 5 m s 1 with a fourth experiment run with no basic flow specified initially the profile of the tangential wind for hurricane gloria at 1200 utc 22 september 1985 was used as the initial condition of the tropical cyclone for each of the experiments the model ocean was initially horizontally homogenous and quiescent to clarify the impact of the ocean response to the hurricane s behavior analogous experiments were also carried out with the sst kept constant control cases the experiments indicated that the cooling of the sea surface induced by the tropical cyclone resulted in a significant impact on the ultimate storm intensity due to the reduction of total heat flux directed into the tropical cyclone above the regions of decreased sst the sea surface cooling produced by the tropical cyclones was found to be larger when the storms moved slower in the experiments run without an initial basic flow the maximum sst anomaly was about 5 6 c with a resulting difference in the minimum sea level pressure and maximum surface winds of 16 4 hpa and 7 m s 1 respectively in contrast in the experiments run with the 7 5 m s 1 basic flow the maximum sst anomalies ranged from about 2 6 to 3 0 c with a difference in the minimum sea level pressure and maximum surface winds of about 7 3 hpa and 2 7 m s 1 the tropical cyclone ocean coupling significantly influenced the storm track only for the case with no basic flow and the 2 5 m s 1 easterly flow in these cases the storm with the ocean interaction turned more to the north and east no basic flow or the north 2 5 m s 1 easterly flow of the experiments with constant sst in the first case the storm by 72 hours was located over 70 km to the east southeast of the control case a possible explanation for this track deviation is related to a systematic weakening of the mean tangential flow at all radii of the storm due to the interaction with the ocean and resulting alteration of the beta drift

thermochronology of the high pressure metamorphic rocks of crete greece implications for the speed of tectonic processes new fission track thermochronologic data from the high pressure p low temperature t rocks of crete greece combined with pressure temperature and stratigraphic constraints reveal that their subduction began between 36 and 29 ma metamorphism took place in western crete at peak conditions of 10 2 kbar and 400 50 c between 24 and 19 ma and rapid exhumation to 10 km and 300 c at a minimum rate of 4 km m y was completed before 19 ma constraints from the thermal history of the plate above the inferred extensional detachment reveal that tectonic unroofing contributed 85 to 90 of the overall exhumation of the high p low t rocks of crete we propose that the hellenic subduction zone has acted as a retreating plate boundary since at least the early oligocene and collision and extension during this time were driven by roll back associated with slab pull rather than by gravitational collapse as a consequence of crustal thickening the speed of subduction and exhumation of the high p low t rocks of crete within 10 m y has important implications for other orogenic belts showing that rocks can be subducted metamorphosed at high pressure and exhumed despite slow overall plate convergence within the uncertainties of many paleontologic and isotopic age data

impact of the configuration of stretching and ocean atmosphere coupling on tropical cyclone activity in the variable resolution gcm arpege this study starts by investigating the impact of the configuration of the variable resolution atmospheric grid on tropical cyclone tc activity the french atmospheric general circulation model arpege the grid of which is rotated and stretched over the north atlantic basin was used with prescribed sea surface temperatures the study clearly shows that changing the position of the stretching pole strongly modifies the representation of tc activity over the north atlantic basin a pole in the centre of the north atlantic basin provides the best representation of the tc activity for this region in a second part the variable resolution climate model arpege is coupled with the european oceanic global climate model nemo in order to study the impact of ocean atmosphere coupling on tc activity over the north atlantic basin two pre industrial runs a coupled simulation and a simulation forced by the sea surface temperatures from the coupled one are compared the results show that the coupled simulation is more active in the caribbean sea and the gulf of mexico while the forced simulation is more active over eastern florida and the eastern atlantic the difference in the distribution of tc activity is certainly linked with the location of tc genesis in the forced simulation tropical cyclogenesis is closer to the west african coast than in the coupled simulation moreover the difference in tc activity over the eastern atlantic seems to be related to two different mechanisms the difference in african easterly wave activity over the west of africa and the cooling produced in the coupled simulation by african easterly waves over the eastern atlantic finally the last part studies the impact of changing the frequency of ocean atmosphere coupling on atlantic tc activity increasing the frequency of coupling decreases the density of tc activity over the north atlantic basin however it does not modify the spatial distribution of the tc activity tc rainfalls are decreased by 8 in the high frequency coupled run

active deformation of a segment of arc the strait of kythira hellenic arc greece abstract a field analysis of late cenozoic faults has been carried out in the southwest hellenic arc on the islands of kythira and antikythira as well as on both sides of the strait in southeast peloponnisos and western crete the previously unknown geological structure of antikythira is briefly described together with accurate bathymetric data obtained using a multi beam echo sounder on submarine fault scarps the results of studies on land lead to a new interpretation of the neotectonic deformation of this segment of the hellenic arc the submersion of the strait is a consequence of extension related to normal faulting the extension rate being faster than in adjacent segments of the arc the direction of extension related to late pliocene quaternary normal faulting is determined from on land information the existence of oblique en echelon normal faults indicates that dextral deformation plays a role within the kythira strait in connection with the opening of the adjacent cretan sea triggered by subduction beneath the hellenic arc the whole pattern of fault systems in southeast peloponnisos as inferred from teledetection and field studies is consistent with the clockwise rotation that has been independently proposed and verified by palaeomagnetic studies the kythira strait thus provides an example of a complex transform extensional deformation and rotation between two major segments of external arc

an evaluation of criteria to deduce the sense of movement in sheared rocks some of the most useful criteria for the deduction of the sense of shear are summarized for use in areas where unequivocal field evidence is lacking apparently conflicting evidence from rotated pressure shadow regions around porphyroclasts and porphyroblasts is clarified the use of quartz crystallographic fabric asymmetry to deduce the shear sense in the bulk rock should be treated with caution and used only together with detailed microstructural observations

first palaeomagnetic results from the cycladic massif greece and their implications for miocene extension directions and tectonic models in the aegean abstract the aegean region is characterised by major fault bound blocks with markedly contrasting structural trends recent models account for these variations either through differential block rotation or through a process of radial extension the cycladic massif in the back arc region to the hellenic trench represents a critical area where apparently divergent extension directions are observed this contribution provides the first palaeomagnetic results from this area magnetic remanence and ams data are presented for middle miocene granodiorites on the islands of mykonos and naxos these rocks are exposed in the footwalls of major extensional detachments within the metamorphic core complexes that characterise the cycladic massif a clear correlation between the orientation of an l s fabric developed within the intrusions and the magnetic fabric data is observed demonstrating the presence of a normal magnetic fabric of extensional origin the mean extension directions inferred from the orientations of the maximum axes of the magnetic susceptibility ellipsoids are markedly divergent at 064 mykonos and 351 naxos northeasterly in situ magnetic remanences are observed on mykonos whereas those on naxos are directed to the nnw neither direction corresponds to the appropriate palaeomagnetic reference direction for the miocene standard palaeomagnetic tilt corrections cannot be applied at these sites because of the lack of palaeohorizontal markers deviations of in situ remanences away from the reference direction are potentially due to rotation around any one of an infinite number of net tectonic rotation axes each of these may be arbitrarily decomposed into components of tilting and vertical axis rotation geologically realistic solutions which restore the in situ magnetisations back to the reference direction may be found by consideration of regional structural trends assuming that tilting is controlled by the major block bounding faults these solutions indicate significant components of differential vertical axis rotations across the cyclades mykonos is bound by nw se trending regional faults and is shown to have rotated clockwise by ca 22 in contrast naxos is bound by ene wsw trending structures and has rotated anticlockwise by ca 33 the apparent divergence of extension directions inferred from both the magnetic anisotropy and structural data is resolved by correcting the mean ams data for subsequent rotation using the rotation solutions derived from the magnetic remanence data the data imply that the primary middle miocene extension direction in the cycladic massif was nearly uniform along a nne ssw azimuth we consider that the uniform extension direction and opposing senses of block rotation determined for this portion of the cycladic massif are most consistent with a recent model describing deformation within the aegean in terms of a system of broken fault bounded slats within this scenario mykonos occupies a position on a clockwise rotating slat which continues northwest at least as far as evvia a major ene wsw trending fault between the islands previously identified on shallow seismic sections separates this domain from an anticlockwise rotating slat which includes naxos

adjustment of a drainage network to capture induced base level change an example from the sorbas basin se spain abstract quaternary catchments in the south of the sorbas basin se spain have been affected by two regionally significant river captures the river captures were triggered by changes in regional gradients associated with sustained quaternary uplift in the region of 160 m ma 1 the first capture occurred in the early pleistocene and re routed 15 of the original sorbas basin drainage into the carboneras basin to the south the second occurred in the late pleistocene and re routed 73 of the original sorbas basin drainage to the east this latter capture had dramatic consequences for base level in the sorbas basin master drainage local base level was lowered by 90 m at the capture site 50 m at 7 km upstream and 25 m at 13 km upstream of the site the base level change instigated a complex re organisation of the drainage networks in systems tributary to the master drainage over the ensuing period some 100 ka after the capture drainage systems closer to the capture site experienced a tenfold increase in incision rates over most of their network those located some 13 km upstream of the capture site experienced a fivefold increase in incision although in this instance the changes do not appear to have propagated to the headwater regions of the drainage nets the sensitivity of individual catchments was largely governed by geological controls structure and lithology the detailed network evolution in the most sensitive areas can be traced by reconstructing former drainage pathways using abandoned drainage cols and the alignment and degree of incision of the drainage networks three main stages of evolution can be identified which record the progressive spread of base level changes from the master drainage these are stage 1 pre capture original south to north consequent drainage stage 2 early stage post capture aggressive subsequent southwest to northeast and east west drainage developed along structural lineaments first in the east of the area stage 2a and later in the west of the area stage 2b and stage 3 late stage post capture obsequent drainage developing on the topography of the stage 2 drainage all stages of the network evolution are associated with drainage re routing as a function of river capture at a variety of scales the results highlight the complex response of the fluvial system and the very different geomorphological histories of adjacent catchments emphasising the need for regional approaches for examining long term changes in fluvial systems

constraints on the kinematics of post orogenic extension imposed by stretching lineations in the aegean region abstract new kinematic data from shear zones of tertiary age in the metamorphosed basement of the aegean region in combination with published kinematic lithological and palaeomagnetic data have enabled us to determine a detailed kinematic evolution of the region during post orogenic extension in the aegean three distinct stages are recognised firstly extension of both the western and eastern aegean started in the late oligocene early miocene 36 25 ma ago initially in an 023 direction stage two started shortly after this with the division of the aegean crust into the west aegean block a coupled assemblage of small blocks bound on its northwestern and southeastern margins by the scutari pec line and mid cycladic lineament fracture zones respectively between 25 ma and 3 ma the west aegean block underwent 30 clockwise rotation whilst the eastern aegean underwent on average 19 anticlockwise rotation rotation of the west aegean block as a semi coherent block was aided by the relative coolness of the block compared to the warmer eastern aegean region as the crust thinned and rotated the nw se trending faults which characterise the west aegean block were cross cut by e w trending faults in the latest miocene pliocene the thermal front migrated westwards into the west aegean block and the mid cycladic lineament ceased activity the final kinematic stage marked the start of the subdivision of the west aegean block into two portions in the pliocene the southeastern portion nw cycladic area coupled with the sw cycladic area to form a central aegean block that started to translate southwest the northern and western portion rotated a further 10 15 clockwise whilst the southeastern rim rotated anticlockwise these data demonstrate that aegean post orogenic extension is not dominated by a single block rotation or radial spreading event but is characterised by the sequential formation and reformation of lithospheric scale blocks that have developed in response to large scale partitioning of rotational strain

late cenozoic uplift of mountain ranges and global climate change chicken or egg the high altitudes of most mountain ranges have commonly been ascribed to late cenozoic uplift without reference to when crustal thickening and other tectonic processes occurred deep incision and recent denudation of these mountain ranges abundant late cenozoic coarse sediment near them and palaeobotanical evidence for warmer climates where high mountain climates today are relatively cold have traditionally been interpreted as evidence for recent uplift an alternative cause of these phenomena is late cenozoic global climate change towards lower temperatures increased alpine glaciation a stormier climate and perturbations to humidity vegetative cover and precipitation

aegean crustal thickness inferred from gravity inversion geodynamical implications since oligo miocene times the aegean domain has undergone regional extension due to the southward retreat of the hellenic subduction zone boundary conditions have been more recently modified by the westward extrusion of anatolia a new map of the aegean crustal thickness inferred from gravity inversion is proposed here to better constrain the variations in space and time of crustal thinning that has accumulated since oligo miocene times moho topography is obtained by inversion of satellite marine gravity data data are first corrected for terrain anomalies and deep mantle effects african subducting slab they are then filtered between 50 and 300 km to avoid short wavelength intracrustal effects results are consistent with previous 2d geophysical studies seismic refraction receiver functions and show that an overall regional isostatic compensation of the crust holds for the aegean area with a mean crustal thickness of 25 km three different provinces north aegean cyclades and cretan sea can be identified thinner crust is observed both in the north aegean region ne sw trending of thinning with crustal thickness lower than 24 km and in the cretan sea crustal thickness of 22 23 km between these two regions the cyclades are marked by a rather flat moho at 25 km a two stage model of the aegean extension could well explain the observed crustal thickness variation from oligocene to middle miocene gravitational collapse of the hellenides due to the southward retreat of the african slab reduced the aegean continental crust from 50 km by reference to continental greece and anatolia to a mean value of 25 km at the scale of the whole aegean from upper miocene to present the westward extrusion of anatolia modified the extension and the associated crustal thinning in the north aegean domain during this second episode crustal thinning related to the southward retreat of the african slab tends to localize in the cretan sea the cyclades likely behave as a rigid block translated toward the south west without significant deformation in agreement with the gps velocity field and the lack of major earthquakes d 2004 elsevier b v all rights reserved

geometry and kinematics of convergent conjugate vein array systems abstract conjugate arrays of quartz veins in the neranleigh fernvale turbidite beds at norries head eastern australia occur in configurations in which the trends of the veins in a principal section converge towards the acute bisector of the conjugate arrays a convergent configuration such a configuration is common in vein arrays and has been attributed to initiation of the veins as antithetic shear fractures based on geometric arguments the morphology of the veins in this study indicates that the veins are hosted by extension fractures which formed by en echelon breakdown of faults previous models of extension fracture arrays emphasise that all fractures lie parallel to the bisector of conjugate arrays and that arrays develop after initiation of extension fractures and concurrent with fracture propagation sigmoidal vein shapes have been attributed to concurrent shear strain and fracture propagation an alternative model is proposed for the geometry of conjugate arrays formed by en echelon breakdown of faults the conjugate angle between parent faults is established before the en echelon extension fractures are formed the fracture array angle depends on the local displacement of the parent fault thus there is no necessity for the fractures in different arrays to be parallel if the fracture array angle is greater than half the conjugate angle between parent faults a convergent configuration of fractures is produced the kinematics of opening of veins in this study involved bending of rock bridges between fractures producing a gradation from planar to sigmoidal shapes in serial sections without evidence of concurrent fracture propagation

heavy minerals as a guide to turbidite provenance in the lower palaeozoic southern welsh basin a pilot study a pilot study has demonstrated that heavy mineral analysis is a useful guide to the provenance of silurian turbidites in the southern welsh basin the results confirm the sedimentological evidence for two distinct source areas of coarse clastic detritus one lying to the south and the other to the east they also provide mineralogical criteria by which the two source areas may be distinguished the southern area provided material with relatively low mineral diversity and is characteristic in having low rutile zircon ratios whereas the eastern source provided more diverse assemblages generally with high rutile zircon ratios the southern source shows variations in terms of apatite tourmaline ratio with the older aberystwyth grits group tending to contain relatively low apatite compared with the younger cwmystwyth grits group rhuddnant and pysgotwr grits formations there is evidence for polycyclic material and volcanic detritus in both southerly and easterly derived samples however easterly sourced sandstones apparently tapped a more lithologically diverse terrain

the tertiary geodynamical evolution of the aegean arc a paleomagnetic reconstruction abstract the paleomagnetic results obtained in the last 5 6 years from tertiary formations in the aegean domain indicate that the lower miocene arc was almost rectilinear with an e w trend and that its curvature has been acquired tectonically in two major phases during the middle miocene a first phase of deformation is characterized by rotations occurring at the two terminations of the arc clockwise in the west epirus anticlockwise in the east southeastern anatolia a second phase of rotation occurring in the last 5 ma about a pole situated in the southern adriatic sea has affected only the northwestern part the data also indicate that the antalya basin has not been involved in the geodynamical evolution of the arc so that the bey daglari represent its easternmost unit a more complex rotational pattern is observed in the internal zones the large rotations measured in evia 48 and skyros 26 probably occurred in the last 5 ma and result from rotation of fault bounded blocks in a shear zone connecting the north aegean trough to the external arc in the izmir region in the karaburun peninsula of western anatolia and in the island of lesbos significant counterclockwise clockwise or null rotations of coherent blocks have taken place during the neotectonic extensional regime furthermore the values of the inclination obtained from both sedimentary and volcanic oligo miocene formations are systematically shallower than expected on the basis of a geocentered dipole field this suggests that the entire studied area has undergone a northward drift of over 1000 km since the middle miocene

linking microcracks and mineral zoning of detachment exhumed granites to their tectonomagmatic history evidence from the salihli and turgutlu plutons in western turkey menderes massif abstract the menderes massif western turkey is a metamorphic core complex that displays linked syntectonic plutonism and detachment faulting fabrics in s type peraluminous granites salihli and turgutlu in the detachment alasehir footwall change from isotropic to protomylonitic to mylonitic towards the structure samples from the isotropic and protomylonitic zones were imaged in transmitted light cathodoluminescence cl backscattered bse and secondary electrons se and show that these rocks contain abundant microcracks and that plagioclase grains have zoning consistent with magma mixing the granites contain fluid inclusion planes fips myrmekite replacing plagioclase and the removal of blue luminescence in k feldspar along microcracks and grain boundaries calcite and hydrous minerals commonly fill microcracks the samples record features that formed due to 1 magma crystallization and ductile deformation fips mineral zoning 2 changes in p and or t impingement and stress induced microcracks in protomylonitic rocks and 3 differences in intrinsic mineral properties radial cleavage blunted and deflected microcracks overprinted microcracks indicate exhumation during pulses the middle miocene ages of these granites reported elsewhere are similar to those from large scale extensional structures in greece s cycladic massif the menderes and cycladic core complexes may have developed simultaneously due to the widespread intrusion of subduction related granitoids

tertiary extension of continental crust and uplift of psiloritis metamorphic core complex in the central part of the hellenic arc crete greece kinematic analysis of the deformation in central crete suggests that the structural evolution and exhumation of the high pressure low temperature hp lt rocks outcropping at the mount psiloritis metamorphic core complex are associated with a regional miocene north south extension and thinning of the continental crust this tectonic regime developed under bulk coaxial strain conditions with ductile deformation in the lower and brittle deformation in the upper crust and followed on the decompressional path a north south compression associated with a hp lt metamorphism in the lower crust this compressional event took place during oligocene early miocene and led to overthickening of the accretionary wedge in the hellenic arc an east west directed compression accompanied in the final stages the miocene north south extension of the continental crust

generation of african easterly wave disturbances relationship to the african easterly jet abstract the relationship between african easterly waves and the background climatology in which they form is studied using a regional climate model the surface and lateral boundary conditions in the model are manipulated to modify the background climatology especially the african easterly jet and the itcz and the behavior of the waves in these different settings is evaluated three climate simulations are presented with monthly mean lateral and surface boundary conditions one has a strong jet and a strong itcz the second has a strong jet and a weak itcz and the third has a weak jet and a strong itcz in these simulations the presence of wave activity is more closely associated with the concentration of the itcz than the strength of the african easterly jet in particular the simulation with a strong jet accompanied by a weak itcz does not produce significant wave activity but a weak jet with a strong itcz has realistic wave disturbances both the charney stern and the fjortoft necessary conditi

detachments in high pressure mountain belts tethyan examples abstract using the case examples of the phyllite quartzite nappe of crete the bundnerschiefer nappe of the engadine window in the alps and the infraophiolitic units of the saih hatat window in the oman mountains we describe the tectono metamorphic signature of large scale extensional detachments in high pressure belts in these three cases retrograde p t paths were accompanied by the formation of large scale extensional shear zones that contributed to the exhumation and extreme thinning of the metamorphic pile the direction of transport along later detachments was parallel to the direction of convergence detachments being first localized within or near the brittle ductile transition zone below the major shear zone or between the shear zones in oman the deformation regime was more coaxial and involved a significant component of vertical shortening metamorphic data mostly derived from the petrology of metapelites show that domains characterized by coaxial strain have nearly isothermal decompression paths type ii while those immediately below the detachments were subjected to more efficient cooling during exhumation type i the detachments thus affect both the deformation history and the p t evolution of the lower plate the existence of the two types of cooling paths is a good test of the extensional nature of a tectonic contact

impact of resolution and downscaling technique in simulating recent atlantic tropical cylone activity using the global environmental multiscale gem model we investigate the impact of increasing model resolution from 2 to 0 3 on atlantic tropical cyclone activity there is a clear improvement in the realism of atlantic storms with increased resolution in part linked to a better representation of african easterly waves the geographical distribution of a genesis potential index composed of large scales fields known to impact cyclone formation coincides closely in the model with areas of high cyclogenesis the geographical distribution of this index also improves with resolution we then compare two techniques for achieving local high resolution over the tropical atlantic a limited area model driven at the boundaries by the global 2 gem simulation and a global variable resolution model gvar the limited area domain and high resolution part of the gvar model coincide geographically allowing a direct comparison between these two downscaling options these integrations are further compared with a set of limited area simulations employing the same domain and resolution but driven at the boundaries by reanalysis the limited area model driven by reanalysis produces the most realistic atlantic tropical cyclone variability the gvar simulation is clearly more accurate than the limited area version driven by gem global degradation in the simulated interannual variability is partly linked to the models failure to accurately reproduce the impact of atmospheric teleconnections from the equatorial pacific and sahel on atlantic cyclogenesis through the use of a smaller limited area grid driven by gem global 2 we show that an accurate representation of african easterly waves is crucial for simulating atlantic tropical cyclone variability

post early messinian counterclockwise rotations on crete implications for late miocene to recent kinematics of the southern hellenic arc most geodynamical models for the kinematics of the central mediterranean recognise that major tectonic rotations must have played an important role during the neogene the hellenic arc is believed to have been subjected to clockwise rotations in the west and counterclockwise rotations in the east while the southern part crete shows no rotations kissel and laj 1988 many qualitative and quantitative models are based on the idea that crete did not rotate we present new palaeomagnetic data which show that post early messinian counterclockwise rotations have occurred on crete the amount of counterclockwise rotation generally varies between 10o and 20o but in central crete much larger rotations up to40o counterclockwise were found only a few sections did not show any rotation the anisotropy of magnetic susceptibility ams shows lineations which are consistently wnw ese throughout crete indicating post rotational wnw ese extension or nne sse compression the observed counterclockwise rotations are consistent with the results of tectonic modelling by ten veen and meijer 1998 the latter study compares the late middle miocene to recent kinematics with modelled intra plate stresses for various possible distributions of plate boundary forces observations reveal that motion along left lateral and right lateral faults occurred during the pliocene the model analysis shows these motions to be consistent with transform resistance along the eastern segment of the overriding margin the counterclockwise block rotations observed by us are probably a consequence of displacements along the left lateral and right lateral faults and could reflect a similar tectonic regime that involved transform resistance 1998 elsevier science b v all rights reserved

implications for timing of andean uplift from thermal resetting of radiation damaged zircon in the cordillera huayhuash northern peru abstract the cordillera huayhuash is a north south oriented range along the drainage divide of the northern peruvian andes the range has high topography with peaks in excess of 5500 m and the second highest peak in peru nevados yerupaja 6617 m bedrock is dominated by folded mesozoic miogeoclinal rocks unconformably overlain by mid tertiary volcanics intruded by late tertiary granitic rocks and silicic dikes zircon fission track zft and u th he zhe dating of zircons along a west east transect elucidates the thermal evolution of exhumed and uplifted rocks the stability of fission tracks in zircons is a function of single grain radiation damage in samples with grain to grain variability in radiation damage resetting results in variable resetting and multiple age populations low retentive zircons lrzs which have a partly disordered crystalline structure have significant radiation damage and a low temperature of annealing ca 180 200 c high retentive zircons hrzs which are nearly cry

seismicity of the sunda strait evidence for crustal extension and volcanological implications the sunda strait is located in the transitional zone between two different modes of subduction the java frontal subduction and the sumatra oblique subduction this setting implies that the sunda strait region is a key to the understanding of the geodynamic processes involved in order to study the shallow seismicity a microearthquake survey was carried out in that region twelve stations accurately located by the aim of satellite positionning recorded about 300 local events in the summer 1984 from this set 174 shallow earthquakes have been precisely located the results of this study reveal that the crustal earthquakes in the sunda strait area occurs in three main areas 1 beneath the krakatau complex where earthquakes are generated by double couples and are of tectonic origin 2 inside a graben in the western part of the strait and 3 in a more diffused zone to the south of sumatra the individual and composite focal mechanisms from the events inside the strait show an extensional regime a stress tensor which have been deduced from the individual focal mechanisms of earthquakes of the krakatau group shows that the tensional axis is oriented n130oe this study confirms that the sunda strait is in an extensional tectonic regime as a result of the northwestward movement of the sumatra sliver plate along the semangko fault zone

active simultaneous uplift and margin normal extension in a forearc high crete greece abstract the island of crete occupies a forearc high in the central hellenic subduction zone and is characterized by sustained exhumation surface uplift and extension the processes governing orogenesis and topographic development here remain poorly understood dramatic topographic relief 2 6 km astride the southern coastline of crete is associated with large margin parallel faults responsible for deep bathymetric depressions known as the hellenic troughs these structures have been interpreted as both active and inactive with either contractional strike slip or extensional movement histories distinguishing between these different structural styles and kinematic histories here allows us to explore more general models for improving our global understanding of the tectonic and geodynamic processes of syn convergent extension we present new observations from the south central coastline of crete that clarifies the role of these faults in the late cenozoic evolution of the central hellenic margin and the processes controlling quaternary surface uplift pleistocene marine terraces are used in conjunction with optically stimulated luminesce dating and correlation to the quaternary eustatic curve to document coastal uplift and identify active faults two south dipping normal faults are observed which extend offshore offset these marine terrace deposits and indicate active n s margin normal extension further marine terraces preserved in the footwall and hanging wall of both faults demonstrate that regional net uplift of crete is occurring despite active extension field mapping and geometric reconstructions of an active onshore normal fault reveal that the subaqueous range front fault of south central crete is synthetic to the south dipping normal faults on shore these findings are inconsistent with models of active horizontal shortening in the upper crust of the hellenic forearc rather they are consistent with topographic growth of the forearc in a viscous orogenic wedge where crustal thickening and uplift are a result of basal underplating of material that is accompanied by extension in the upper portions of the wedge within this framework a new conceptual model is presented for the late cenozoic vertical tectonics of the hellenic forearc

the subduction plate interface rock record and mechanical coupling from long to short timescales abstract short and long term processes at or close to the subduction plate interface e g mineral transformations fluid release seismicity and more generally deformation might be more closely related than previously thought increasing evidence from the fossil rock record suggests that some episodes of their long geological evolution match or are close to timescales of the seismic cycle this contribution uses rocks recovered episodically from subduction zones together with insights from thermomechanical modelling to provide a new dynamic vision of the nature structure and properties of the plate interface and to bridge the gap between the mechanical behavior of active subduction zones e g coupling inferred from geophysical monitoring and fossil ones e g coupling required to detach and recover subducted slab fragments based on critical observations and an exhaustive compilation of worldwide subducted oceanic units for which the presence near the plate interface rock types pressure temperature t p gradients thickness and timing of detachment can be assessed the present study demonstrates how long term mechanical coupling exerts a key control on detachment from the slab and potential rock recovery critical assessment of rock t p characteristics indicates that these fragments can indeed be used as natural probes and provide reliable information on subduction interface dynamics down to 2 8 gpa rock clusters are identified at depths of 30 55 60 and 80 km with some differences between rock types data also reveal a first order evolution with subduction cooling in the first 5 myr which is interpreted as reflecting a systematic trend from strong to weak mechanical coupling after which subduction is lubricated and mostly inhibits rock recovery this contribution places bounds on the plate interface constitution regular thickness

geomorphic tectonic control of sediment discharge to the ocean the importance of small mountainous rivers analysis of data from 280 rivers discharging to the ocean indicates that sediment loads yields are a log linear function of basin area and maximum elevation of the river basin other factors controlling sediment discharge e g climate runoff appear to have secondary importance a notable exception is the influence of human activity climate and geology on the rivers draining southern asia and oceania sediment fluxes from small mountainous rivers many of which discharge directly onto active margins e g western south and north america and most high standing oceanic islands have been greatly underestimated in previous global sediment budgets perhaps by as much as a factor of three in contrast sediment fluxes to the ocean from large rivers nearly all of which discharge onto passive margins or marginal seas have been overestimated as some of the sediment load is subaerially sequestered in subsiding deltas before the proliferation of dam construction in the latter half of this century rivers

slip vectors and stretching of the sumatran fore arc slip vectors from thrust earthquakes at the java trench southwest of sumatra demonstrate that the sumatran fore arc is not a single rigid plate that is translated to the northwest by oblique plate convergence instead they indicate arc parallel stretching of the fore arc at a uniform strain rate of 3 4 x 10 8 yr the northwestward motion of the fore arc relative to the upper plate southeast asia increases from near zero at the sunda strait to 45 60 mm yr in northwest sumatra and should result in variable slip rates on the sumatran fault

oblique plate convergence slip vectors and forearc deformation slip vectors from thrust earthquakes at subduction zones where convergence is oblique to the trench often point between the directions of relative plate convergence and normal to the trench axis suggesting that oblique convergence is taken up by partial decoupling decoupling means that a component of arc parallel motion of the leading edge of the upper plate results in less oblique thrusting at the trench partial decoupling is modeled by partitioning of oblique convergence into slip on thrust and strike slip faults that are parallel to the trench and to each other and starting with a force equilibrium condition a relationship between the obliquity and the earthquake slip vector orientation is derived assuming that either fault slips when shear stress on it reaches a yield stress oblique slip parallel to the plate vector should occur on the thrust fault when obliquity is smaller than a critical angle for obliquity at or greater than this angle the stress on the strike slip fault is large enough to start it slipping and when both faults are active the arc parallel motion of the forearc deflects the slip vector back toward the trench normal if we assume that continued slip on either fault occurs at constant stress but the two faults can be at different stresses the slip vector will maintain a constant angle relative to the trench normal even when obliquity is larger than the critical angle this limiting angle of the slip vector called max measured relative to the trench normal is simply the arcsine of the ratio of the shear forces resisting slip on the strike slip and thrust faults a consequence is that when the obliquity exceeds max the slip vectors on the thrust fault are sensitive only to the thrust fault orientation and contain no information about the convergence direction between the plates slip vectors at the java trench southwest of sumatra show the relationship clearly with max 20 5 while slip vectors at the aleutian trench show the relationship less clearly with max 25 to 45 the greater angle at the aleutian trench suggests that the upper plate is stronger in the aleutian arc relative to the thrust fault than in the sumatran arc consistent with the sumatran arc being continental and having a well developed strike slip fault while the aleutian arc is oceanic and without a clear transcurrent fault slip vectors at the philippine trench which like sumatra has a large strike slip fault inboard of it tend to stay within 25 of the trench normal when obliquity is as large as 50 if obliquity exceeds max and continues to increase along a subduction zone the rate of motion of the forearc relative to the upper plate will vary with obliquity in which case the forearc sliver should extend or contract parallel to the arc from the geometry of modern island arcs arc parallel extension should be the more common and has been hypothesized for both sumatra and the aleutians on the basis of earthquake slip vectors and for these and other arcs from geological observations from estimates of max and the arc parallel gradients in obliquity arc parallel strain rates are estimated to be 1 to 3 10 8 yr for the sumatran forearc 2 to 6 10 8 yr for the aleutian forearc and 0 3 to 3 10 8 yr for the philippine forearc oblique convergence and subsequent arc parallel extension if accompanied by crustal thinning may provide an important yet little appreciated mechanism for bringing high grade metamorphic rocks to the surface of subduction complexes

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

seismicity of the hellenic subduction zone in the area of western and central crete observed by temporary local seismic networks temporary local seismic networks were installed in western crete in central crete and on the island gavdos south of western crete respectively in order to image shallow seismically active zones of the hellenic subduction zone more than 4000 events in the magnitude range between 0 5 and 4 8 were detected and localized the resulting three dimensional hypocenter distribution allows the localization of seismically active zones in the area of western and central crete from the mediterranean ridge to the cretan sea furthermore a three dimensional structural model of the studied region was compiled based on results of wide angle seismics surface wave analysis and receiver function studies the comparison of the hypocenter distribution and the structure has allowed intraplate and interplate seismicity to be distinguished high interplate seismicity along the interface between the subducting african lithosphere and the aegean lithosphere was found south of western crete where the interface is located at about 20 to 40 km depth an offset between the southern border of the aegean lithosphere and the southern border of active interplate seismicity is observed in the area of crete the offset varies laterally along the hellenic arc between about 50 and 70 km a southwards dipping zone of high seismicity within the aegean lithosphere is found south of central crete in the region of the ptolemy trench it reaches from the interface between the plates at about 30 km depth towards the surface in comparison the aegean lithosphere south of western crete is seismically much less active including the region of the ionian trench intraplate seismicity within the aegean plate beneath crete and north of crete is confined to the upper about 20 km between 20 and 40 km depth beneath crete the aegean lithosphere appears to be seismically inactive in western crete the southern and western borders of this aseismic zone correlate strongly with the coastline of crete

miocene high pressure metamorphism in the cyclades and crete aegean sea greece evidence for large magnitude displacement on the cretan detachment the cyclades in the backarc region of the present hellenic subduction zone are known for widespread late cretaceous to eocene high pressure metamorphism in the cycladic blueschist unit we report 40 ar 39 ar and rb sr phengite ages of 24 21 ma for high pressure metamorphism 8 10 kbar 350 400 c in the lowest tectonic unit in the cyclades the basal unit which structurally underlies the cycladic blueschist unit the basal unit is correlated with the tripolitza unit of the external hellenides in the forearc region of the hellenic subduction zone the tripolitza unit is unmetamorphosed on crete where it is separated from the underlying high pressure 8 10 kbar 300 400 c plattenkalk and phyllite quartzite units by the extensional cretan detachment the age for high pressure metamorphism in the latter units is similar to our age for the basal unit in the cyclades because pressure temperature conditions in the plattenkalk and phyllite quartzite units on crete and the basal unit in the cyclades are also similar they must have been in close proximity in the early miocene hellenic subduction zone a palinspastic reconstruction suggests a subsequent displacement of 100 km on the cretan detachment this is one of the greatest displacement magnitudes ever reported from detachment faults because of this large offset the cretan detachment was an efficient agent for exhuming high pressure rocks

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

to be or not to be that is the question the cretan extensional detachment greece we present new structural data from the contact zone between the high pressure phyllite quartzite unit pq and the overlying non high pressure tripolitza unit in east central crete for testing pro

thermobarometric data from a fossil zircon partial annealing zone in high pressure low temperature rocks of eastern and central crete greece abstract a fossil partial annealing zone of fission tracks in zircon is described from high pressure low temperature hp lt rocks of the phyllite quartzite unit pq on the island of crete greece correlation of regional trends in fission track age populations with independent thermobarometric and microstructural data and with new experimental annealing results allows a calibration of this low temperature thermochronological method to a degree hitherto not available from other field examples the zircon fission track ft ages of samples from the pq across crete range from original detrital signature through reduced to completely reset the annealing is the result of a single heating period related to the hp lt metamorphism with near peak temperatures lasting for only a few million years some time between 24 1 and 20 1 ma in eastern crete where rocks have experienced temperatures of 300 50 c and pressures of 0 8 0 3 gpa zircon ft ages range from 414 24 to 145 10 ma ages above 300 ma occur mostly near the east coast of the island in rocks which have not been heated to above ca 280 c and probably represent a pre variscan source track lengths are already indicative of a substantial annealing at this temperature most of the zircon ft ages from eastern crete scatter within error around the stratigraphic age samples with apparent zircon ft ages significantly younger than the depositional age are only observed in areas where temperatures exceeded ca 320 c towards the west a sudden decrease to very young ages ranging from 17 2 to 18 1 ma reflects a complete resetting at ca 350 c short tracks however are still observed throughout the central and western part of the island ages are consistently below 22 ma thermobarometric data for this area indicate maximum temperatures of 400 50 c and pressures of 1 0 3 gpa only samples from western crete which have been exposed to 400 50 c show exclusively long tracks consequently the high temperature limit of the zircon partial annealing zone zpaz appears to be between 350 and 400 c a significant influence of elevated confining pressure on the stability of fission tracks in zircon is ruled out by the results of annealing experiments at 0 5 gpa and at different temperatures which fit the curves previously obtained by other authors at ambient pressure

denudation vertical crustal movements and sedimentary basin infill denudation and vertical crustal movements are linked through the isostatic equation for conservation of lithospheric mass recent empirical results from a wide range of sources are presented on the rates of these processes denudation alone can cause non tectonic isostatic surface uplift of the right magnitude predicted by theory a case is made following ahnert for a single linear relationship although with much scatter between denudation rate and mean drainage basin relief for large basins some recent determinations of denudational time constants have neglected to include tectonic and isostatic terms which oppose the reduction of relief by denudation application of diffusional transport models to determine the rate of sediment deposition are severely limited by inherent one dimensionality and neglect of suspended and washload contributions basin infill sequences may be used to determine past sediment transfer coefficients from a hinterland but problems arise in the apportionment of the various hinterland fluxes that occur in real world three dimensional basins sediment yields in smaller half graben and growth fold basins must reflect the magnitude of drainage basins and the complex local controls upon sediment yields examples are given from extensional basins in the western usa and greece the length of tectonic relief produced in tilt blocks and growth folds will control the area of drainage basin developed through the fractal form of hack s law and hence the magnitude of deposition in sedimentary basins adjoining tectonic uplands

miocene detachment in crete and exhumation p t t paths of high pressure metamorphic rocks a major problem posed by the geology of crete is the horizontal contact of an upper unit without miocene metamorphism onto a metamorphosed lower one with early miocene high pressure low temperature hp lt parageneses this very sharp contact is roughly parallel to the major oligo miocene thrust planes which were reactivated as a large scale detachment which allowed exhumation of high pressure units we describe the extensional deformation and the metamorphic evolution of the lower plate most first order deformation features relate to the retrogression from high pressure to low pressure conditions a n s pervasive stretching is observed everywhere often associated with a top to the north sense of shear the extreme variation of thickness of the phyllite quartzite nappe upper part of the lower plate is probably the result of large scale boudinage similar to the one seen in large outcrops the most important observation is the systematic occurrence of fresh carpholite immediately below the base of the tripolitza nappe except in northwestern crete where a late extensional shear zone is present deeper in the nappe pile carpholite is systematically retrograded this observation reveals a drastically different pt history for the upper part of the phyllite quartzite nappe it also suggests that the late extensional shear zone found along the northern side of crete cuts inside the metamorphic structure and brings the nonmetamorphosed tripolitza nappe directly in contact with the deeper parts of the phyllite quartzite nappe pt t paths suggest a fast temperature decrease in the top of the phyllite quartzite during retrogression and hence during the top to the north shear the deeper part of the phyllite quartzite nappe shows a low temperature regime throughout but its pt path includes an isothermal decompression in the first stage we produce a tentative map of domains having experienced similar pt trajectories during decompression the overall cool regime is related to the continuous underthrusting of cola continental units during exhumation isothermal decompression observed in the core of the phyllite quartzite nappe implies fast exhumation during extension and the faster cooling of the upper part is related to a continuous displacement toward the north of a cooler unit during exhumation single grain 39ar 40ar ages obtained on phengites 15 25 ma in various structural sites are in good agreement with these conclusions and with the geological context suggesting that underthrusting of cold units at the front the accretionnary complex occurred contemporaneously with unroofing below a north dipping detachment near the top of the wedge the age of this detachment is bracketed between the end of the high pressure event 20 ma and the deposition of the breccia early to middle miocene in the neogene basins

positioning the titanite fission track partial annealing zone abstract as part of the ktb kontinentale tiefbohrung programme in germany titanite sphene fission track data were acquired for samples to a depth of 9000 m where the host rock temperature is 265 c at this depth age and confined track length information suggest that the partial annealing zone for the fission tracks in titanite was not reached by reconstructing the thermal history and backstacking of an uplifted partial annealing zone it is suggested that the in situ partial annealing zone is likely to be found in the region 265 310 c this value is more precise than previous estimates of the titanite partial annealing zone and it is also higher than previous estimates microprobe analysis indicates that the chemical composition of the titanites is rather homogeneous throughout the whole drilled section

a key extensional metamorphic complex reviewed and restored the menderes massif of western turkey article i nfo this paper provides a review of the structure and metamorphism of the menderes massif in western turkey and subsequently a map view restoration of its neogene unroofing history exhumation of this massif among the largest continental extensional provinces in the world is generally considered to have occurred along extensional detachments with a ne sw stretching direction restoration of the early miocene history however shows that these extensional detachments can only explain part of the exhumation history of the menderes massif and that ne sw stretching can only be held accountable for half or less of the

rapid exhumation of high pressure metamorphic rocks in kythera peloponnese greece revealed by apatite u th he thermochronology abstractapatite u th he and apatite fission track cooling ages from high pressure hp metamorphic rocks in the south aegean forearc along the kythera strait kythera and southeastern peloponnese suggest rapid exhumation during middle to late miocene times hp rocks from the kythera strait exhibit two perpendicular extensional structures samples with arc normal or arc parallel extensional fabrics yielded apatite u th he cooling ages of 8 10 ma the more precise u th he ages are consistent with previously reported apatite and zircon fission track ages obtained from the same rock units the less precise but still accurate fission track data provided a reference for u th he dating on relatively young uranium poor apatites the combined data therefore precisely and accurately constrain the exhumation history of hp rocks and indicate that localized arc parallel extension in the kythera strait was active for an 5 m yr interval during the regional arc expansion

uplift related retrogression history of aragonite marbles in western crete greece in the low grade high pressure 400 c 10 kbar metamorphic phyllite quartzite unit of western crete widespread occurrences of aragonite marbles have been discovered recently a sedimentary precursor is proved by relic structures bedding fossils partial or complete transformation of aragonite into calcite is ubiquitous compositional and microstructural features reflect the metamorphic history 1 the high pressure stage is documented by aragonite that is chemically characterized by incorporation of variable amounts of sr and the lack of mg the most sr rich aragonite has about 9 wt sro xsrarag 0 09 a compositional zoning observed in some aragonite crystals may be due to the prograde divariant calcite aragonite transformation in the system caco3 srco3 because the parent rocks probably were sr poor calcite limestones one can speculate that strontium has been supplied from an external source under high pressure conditions 2 during uplift calcite replacing aragonite did not equilibrate with unreplaced aragonite disequilibrium is indicated by highly variable compositions of calcite crystals that show topotactic relations to the host aragonite the calcite compositions range from that of the host aragonite sr rich and mg free to mg bearing and sr poor 3 calcite that recrystallized during retrogression is generally sr poor mean value ofxsr 0 005 mg bearing xmg 0 010 and chemically homogeneous because practically no sr remains in the calcite an interaction with a fluid phase is indicated in fine grained calcite marbles rich in solid organic matter microstructural features indicative of former aragonite may be present 4 the last stage of retrogression is documented by the appearance of radiating aragonite in veins and nodules this aragonite which shows neither deformation nor retrogression was probably formed metastably in a near surface environment

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

rotational deformation during palaeogene thrusting and basin closure in eastern central greece palaeomagnetic evidence from mesozoic carbonates summary palaeomagnetic studies in greece have concentrated upon neogene sequences with mesozoic rocks of mainland greece receiving little attention the neogene data base is now sufficiently extensive however to allow meaningful interpretation of older units this paper presents new palaeomagnetic data from mesozoic and tertiary sequences of eastern central greece which document a pre neogene phase cf rotational deformation mesozoic carbonates have been sampled within the classic pelagonian zone in the argolis peninsula beotia and evvia pelagonian sequences record the development drowning and subsequent re establishment of a carbonate platform separating two strands of the neotethys ocean the pindos and vardar basins most platformal facies are tdo weakly magnetized for palaeomagnetic analysis however pelagic horizons consisting of pink condensed limestones have been deposited periodically in response to platform subsidence these middle late triassic jurassic and upper cretaceous sequences yield high quality palaeomagnetic data which reveal a consistent clockwise rotation of about 94 the constancy of rotation angle deduced from the mesozoic rocks suggests that the total tertiary rotation is uniform throughout the area studied this implies that observed variations in declination within the neogene sequences result from sampling of rocks of different ages deposited during a period of rapid overall rotation removal of the largest neogene rotation 45 from the mesozoic data set reveals a pre middle miocene post late cretaceous clockwise rotation of the southern pelagonian zone of 50 the major tectonic event during this time period was the closure of the pindos ocean during the eocene a large carbonate platform within the pindos basin now preserved in the parnassos zone presented a major obstacle to the advancing pelagonian nappes during sw directed thrusting present coordinates impingement of the nappes on to the parnassos platform resulted in pinning and subsequent clockwise rotation of thrust units around the south eastern margin of the platform the southernmost tip of the pelagonian zone southern argolis was detached along a pre existing line of weakness along the present migdhalitsa graben and experienced a different rotation history additional palaeomagnetic data from the pindos nappes in the eastern peloponnesos also provide evidence for significant rotation of thrust sheets during eocene basin closure the pindos sequences formed by pelagic sedimentation within the pindos ocean an overall anti clockwise rotation with respect to the underlying gavrovo tripolitza autochthon is implied by the data this probably reflects oblique emplacement of the pindos thrust sheets on to the adjacent platform variations in rotation angle probably result from variations in footwall topography

raman spectroscopic carbonaceous material thermometry of low grade metamorphic rocks calibration and application to tectonic exhumation in crete greece we present new raman spectra data of carbonaceous material cm to extend the range of the raman spectra of cm thermometer rscm to temperatures as low as 100 8c previous work has demonstrated that raman spectroscopy is an excellent tool to describe the degree of graphitization of cm a process that is independent of pressure but strongly dependent on metamorphic temperature a linear relationship between temperature and the raman parameter r2 derived from the area of the defect band relative to the ordered graphite band forms the basis of a previous thermometer because r2 shows little variability in low temperature samples 330 8c serves as a lower limit on the existing thermometer herein we present raman spectra from a suite of low temperature 100 to 300 8c samples from the olympics mountains and describe other aspects of the raman spectra of cm that vary over this range in particular the raman parameter r1 the ratio of heights of the disordered peak to ordered peak varies regularly between 100 and 350 8c these data together with published results from higher temperature rocks are used to calibrate a modified rscm thermometer applicable from 100 to 700 8c application to low grade metasediments in the otago region in the south island of new zealand gives temperatures consistent with previous estimates demonstrating the reliability of the modified rscm thermometer we apply the modified rscm thermometer to 53 samples from crete to evaluate the role of the cretan detachment fault in exhuming miocene high pressure low temperature metamorphic rocks exposed there the metamorphic rocks below the detachment the plattenkalk and phyllite quartzite units give metamorphic temperatures that range from 250 to 400 8c consistent with previous petrologic estimates we also demonstrate that the tripolitza unit which lies directly above the detachment gives an average metamorphic temperature of about 260 8c the modest break in metamorphic temperature in central crete indicates that the cretan detachment accounts for only 5 to 7 km of exhumation of the underlying hp lt metamorphic rocks which were initially accreted at 35 km we argue that the bulk of the exhumation 28 km out of 35 km total occurred by pervasive brittle stretching and erosion of structural units above the detachment d 2005 elsevier b v all rights reserved

extension and exhumation of the hp lt rocks in the hellenic forearc ridge localized intensive ductile and ductile brittle extension of along the arc orientation is prominent in phyllite quartzite unit pqu rocks in kythera and the adjacent southeastern peloponnese but declines in prominence to the north and to the south along the cretan peloponnese ridge using zircon and apatite fission track dating we find that this structural characteristic is correlated with the youngest zircon fission track cooling ages of 14 to 9 ma and with the highest pressure temperature condition recorded in the metamorphic rocks below the structural detachment the cooling ages of the high pressure phyllite quartzite unit pqu rocks along the hellenic forearc ridge show that exhumation migrated from both crete and from the peloponnese to the area with the youngest ages in kythera and the southeastern peloponnese starting in the early miocene and continuing to the present trench rollback and slab retreat expanded the hellenic arc and this bending of the arc from an initial more rectilinear geometry increased areas of oblique convergence and we suggest this localized the subsequent arc parallel extension and local enhanced exhumation of hp rocks the zircon fit exhumation ages from the arc parallel stretching episode restrict the ductile part of this episode in exposed rocks to between about 14 and 9 ma apatite ft ages suggest brittle along arc extension continued to about 7 ma this episode is proposed to be the result of a temporary higher rate of rollback and slab retreat younger normal faults including those which define the margins of the present hellenic arc show return to arc normal extension

middle miocene graben development in crete and its possible relation to large scale detachment faults in the southern aegean the linkage between the development of south facing cretan graben and large scale detachment faulting in the southern aegean is unknown widespread serravallian deposits in the ierapetra graben of crete supply constraints to middle miocene graben development in the southern aegean the ierapetra graben and by inference the cretan graben in general were hitherto believed to have formed as a result of sinistral transpression during n s shortening we argue that the formation of the cretan graben is due to n s extension the south dipping n s extending kritsa normal fault served as the master fault controlling graben development in the ierapetra graben the kritsa normal fault is either an antithetic fault related to the top n cretan detachment or a synthetic fault associated with the top s ios detachment the overall geometry and timing relationships lead us to favour a connection with the ios detachment which in turn implies a large scale displacement on the ios detachment

arc parallel extension and fluid flow in an ancient accretionary wedge the san juan islands washington structural analysis of the lopez structural complex a major late cretaceous terrane bounding fault zone in the san juan thrust system reveals a sequence of events that provides insight into accretionary wedge mechanics and regional tectonics after formation of regional ductile flattening and shear related fabrics the area was crosscut by brittle structures including 1 southwest vergent thrusts 2 extension veins and normal faults related to northwest southeast extension and 3 conjugate strike slip structures that record northwest southeast extension and northeast southwest shortening aragonite bearing veins are associated with thrust and normal faults but only rarely with strike slip faults high pressure low temperature hp lt minerals constrain the conditions for brittle deformation to 20 km and

low grade retrogression of a high temperature metamorphic core complex naxos cyclades greece retrogressive deformation and metamorphism are often reported from the main low angle shear zones and detachments of metamorphic core complexes but their importance is not sufficiently emphasized for the footwall interior in order to contribute to a better understanding of exhumation related retrogression processes within and at the top of metamorphic core complexes an integrated detailed microstructural textural 40 ar 39 ar geochronological and thermobarometric study on the naxos metamorphic core complex within the aegean sea is presented that provides a new perspective on low grade retrogression during exhumation through shallow ductile levels we found variable retrogressive deformation within the naxos metamorphic core complex which even pervasively affected significant portions of the migmatite grade metamorphic core and remnant high pressure areas of the metamorphic core complex where retrogression led to pervasive formation of new fabrics within greenschist facies metamorphic conditions during brittle ductile transition within a continuum of retrogression 40 ar 39 ar white mica dating allowed us to deduce three retrogressive ages at 16 52 0 39 ma within the naxos metamorphic core complex 12 6 0 28 ma moutsounas detachment shear zone on the eastern boundary of the metamorphic core complex and 10 43 0 44 ma to 8 40 0 76 ma last ductile activity along the naxos paros shear zone to the north of the metamorphic core complex a further stage of retrogression at 12 11 ma occurred along distinct low angle normal faults within the middle miocene naxos granite retrogressive microstructures low temperature calcite fabrics in marbles and chloritization in metapelites at temperatures of 350 130 c in the metamorphic core complex core resulted mainly from late stage e w shortening and folding late stage flow of hydrous fluids resulted in resetting of fabrics and enhancement of ductile deformation the middle late miocene retrogression events are also reflected by a similarly aged tectonic collapse basin in the hanging wall unit above the detachment the wide temporal range of retrogression within the naxos metamorphic core complex coincides in age with retrogressive deformation within other metamorphic core complexes of the aegean sea we interpret the long temporal range of retrogression to reflect outward southwestward retreat of the subduction and sequential activation of major detachment zones

oblique subduction and collision forearc tectonics of the kuril arc the tectonics of the southwestern kuril arc are a result of the oblique subduction of the pacific plate at the kuril trench in association with forearc sliver migration caused by the oblique subduction collision tectonics occur at the leading margin of the sliver and tensional tectonics take place at the tapering margin as a result of the collision a deep crustal section of island arc is observed at the leading margin of the forearc sliver tectonics of the kuril arc related to oblique subduction are different from those of the western sunda arc where backarc spreading occurs at the leading margin this difference is due to margin morphology of the oblique subduction zone

the crust of the western mediterranean ridge from deep seismic data and gravity modelling summary we present a crustal cross section of the western mediterranean ridge from the african margin to the aegean sea constrained by the morphology of the ridge new seismic reflection and refraction results obtained during a two ship cruise performed in december 1988 pasiphae cruise the distribution of seismicity and gravity modelling morphologically the western mediterranean ridge can be divided into three main units from the sirte abyssal plain to the hellenic trench a broad outer unit a narrow central unit and an inner unit the seismic front orgeaward extent of the interplate seismicity between the african lithosphere and the cretan arc is located 50 km seaward of the hellenic trench seismicity is thus distributed widely over the innermost unit of the ridge suggesting that brittle material is present at shallow depth beneath the inner portion of the mediterranean ridge the refraction results of the pasiphae cruise show that the crust in the ionian basin and beneath the outer and central units of the western mediterranean ridge is oceanic and that the moho discontinuity progressively deepens towards the hellenic arc in agreement with the accretionary prism model high velocity material occurs at shallow depth beneath the innermost unit of the ridge gravity modelling also indicates a significant increase in density beneath the inner unit we consequently interpret the inner unit of the ridge as the backstop of the western mediterranean ridge prism possibly composed of peloponnesus thrust sheets

the origin of summit basins of the aleutian ridge implications for block rotation of an arc massif it is proposed that many summit basins along the aleutian arc form from the clockwise rotation of blocks of the arc massif summit basins are arc parallel grabens or half grabens formed within the arc massif and are commonly located near or along the axis of late cenozoic volcanism geomorphically the aleutian arc appears to consist of contiguous rhombic blocks of varying size tens to hundreds of kilometers in length the boundaries between adjacent blocks are delineated by fault controlled canyons that cut the southern slope of the arc transverse to its regional trend evidence that these blocks have rotated clockwise is provided by the triangular shaped summit basins bordering the blocks to the north oblique physiographic trends offsets in the summit platform and broad deflections in the southern slope of the arc we present a model for block rotation that involves translation of blocks parallel to an arc it is suggested that block rotation which appears to have accelerated in late cenozoic time is linked to 1 a shift in the euler pole for the pacific plate 2 the consequential start up of late cenozoic volcanism 3 improved interplate coupling instigated by sediment flooding of the aleutian trench and 4 westward subduction of northeast striking segments of the inactive kula pacific ridge

satellite observations of modulation of surface winds by typhoon induced upper ocean cooling 1 two remote sensing data sets the tropical rainfall measurement mission sea surface temperature sst and the nasa quikscat ocean surface wind vectors are analysed to study ocean atmosphere interactions in cold sst regions formed in the trail of two typhoon events anomalously cold sst patches up to 6 c below the surrounding warm tropical ocean sst are found along the trail of typhoon tracks as cold deep waters are entrained up to the mixed layer due to typhoon forcing in both typhoon events significant and systematic weakening of surface wind speed is found over cold sst patches relative to surface wind speed in surrounding regions the wind speed anomalies disappear as the patches recover to the level of the surrounding sst the results are consistent with the mechanism proposed by wallace et al that surface winds are modulated by sst via stability as wind within the well mixed boundary layer moves over the cold patch boundary layer stability increases vertical mixing is suppressed and the vertical wind shear increases reduction in surface wind speed is caused in particular our result shows that this mechanism can act on relatively small spatial 100 km and short 1 day time scales

surface uplift uplift of rocks and exhumation of rocks uplift of the surface of mountain belts requires forces that are comparable in magnitude to those associated with plate motion and therefore determination of rates of surface uplift could provide important information on the dynamics of mountain ranges rates of uplift of the surfaces of mountain ranges have not however been quantified sufficiently well that they provide useful constraints on those processes many reports off surface uplift in mountain ranges are based on mistaking exhumation of rocks or uplift of rocks for surface uplift and provide no information whatsoever on the rates of surface uplift

the mediterranean ridge backstop and the hellenic nappes the core of the mediterranean ridge backstop consists of a pile of hellenic nappes that migrated outward from the aegean continent within the adjacent mediterranean basins during late middle miocene about 15 ma and the present mediterranean ridge has developed since that time by accretion of a new wedge the arguments we use are 1 a similarity in thickness seismic velocity and structure between the backstop and the hellenic nappes in southern peloponnesus 2 the geometry of the westward limit of the backstop that is the one expected from the amount of relative displacement of the nappes on land 3 an agreement between the estimated ages of the present accretionary wedge and the period of activity of two major faults connecting the backstop to the adjacent aegean continent the seaward limit of the backstop is situated about 170 km southwest of western crete where the displacement of the nappes is maximal and it is close to the margin near the ionian islands where their displacement is small we assume that the hellenic subduction zone migrated southwestward relative to eurasia during middle miocene and that the corresponding gravity collapse of the aegean continent was maximum at this time because the westward extrusion of anatolia had not yet started

map view restoration of aegean west anatolian accretion and extension since the eocene 1 the aegean region greece western turkey is one of the best studied continental extensional provinces here we provide the first detailed kinematic restoration of the aegean region since 35 ma the region consists of stacked upper crustal slices nappes that reflect a complex paleogeography these were decoupled from the subducting african adriatic lithospheric slab especially since 25 ma extensional detachments cut the nappe stack and exhumed its metamorphosed portions in metamorphic core complexes we reconstruct up to 400 km of trench perpendicular ne sw extension in two stages from 25 to 15 ma the aegean forearc rotated clockwise relative to the moesian platform around euler poles in northern greece accommodated by extensional detachments in the north and an inferred transfer fault se of the menderes massif the majority of extension occurred after 15 ma up to 290 km by opposite rotations of the western and eastern parts of the region simultaneously the aegean region underwent up to 650 km of post 25 ma trench parallel extension leading to dramatic crustal thinning on crete we restore a detachment configuration with the mid cycladic lineament representing a detachment that accommodated trench parallel extension in the central aegean region finally we demonstrate that the sakarya zone and cretaceous ophiolites of turkey cannot be traced far into the aegean region and are likely bounded by a pre 35 ma n s fault zone this fault became reactivated since 25 ma as an extensional detachment located west of lesbos island the paleogeographic units south of the izmir ankara sava suture however can be correlated from greece to turkey

kinematic evolution of the tethys belt from the atlantic ocean to the pamirs since the triassic abstract we present an updated series of kinematic reconstructions of the major plates around the tethys from the atlantic ocean to the pamirs between the early jurassic and the present this set is used elsewhere as a basis for paleogeographic maps of the entire region the problems related to the positions of the continents in the lower triassic are also discussed no direct analyses of magnetic anomalies and fracture zones in the atlantic have been made rather all available poles and rotations have been tested in order to eliminate or minimize possible kinematic errors the reconstructions are shown for nine key geological periods which correspond to well recognized magnetic anomalies except for the jurassic cretaceous boundary and the cretaceous tertiary boundary which correspond to interpolated positions paleolatitudes have been drawn using the study of westphal et al 1986 an attempt has been made to take into account the displacements caused by formation of the continental margins and basins by stretching the resulting relative vector of motions along the northern boundary of the tethys shows a significant change 80 m y ago left lateral motion with compression dominates before whereas right lateral motion with compression dominates after to the east rates of motion vary by a factor of three with time and four maxima can be clearly related to tectonic events in the late jurassic late cretaceous eocene and post middle miocene to the west north of apulia on the contrary the motion rate has not changed significantly since the early cretaceous and is close to 1 cm yr as an average these rather complex adjustments in rates and directions of relative motion are produced in great part through a complex migration of the africa eurasia pole of rotation and seem to be mostly governed by the tectonics of the tethys plate boundary

radiation damage and uranium concentration in zircon as assessed by raman spectroscopy and neutron irradiation radiation damage of natural and synthetic zircon grains is evaluated by raman spectroscopy to understand annealing and stability of fission tracks analyses focus on a suite of 338 paleozoic detrital zircon grains from metamorphosed strata in the hellenic forearc that were variably annealed by a miocene thermal event as well as a suite of 97 synthetic zircon grains the raman wavenumber shift of v 3 si0 4 reveals that radiation damage and damage distribution in this suite mainly depends on uranium concentration in zircon with similar uranium concentration the raman wavenumber shift allows for the determination of radiation damage in different crystals which is a function of effective accumulation time nine detrital zircons grains with moderate radiation damage were stepwise annealed at 1000 and 1400 c which resulted in progressive removal of radiation damage revealed in an increase of 3 si0 4 peak positions for a partly reset sample that was brought to temperatures of 350 c in a geologic setting hellenic forearc we use the raman measurements and uranium determination to estimate a zircon damage discrimination factor z rdd which is our attempt to estimate only radiation damage in single grains by accounting for affects of the uranium atom in the raman wavenumber this discrimination allows for a separation of zircon fission track zft ages of single ages based on grains that have a low track retention high damage fully reset grain thus refining the age determination of cooling in a rock that shows variable resetting

extension and exhumation of the hellenic forearc ridge in kythera abstract detailed mapping and new structural observations on kythera demonstrate that there is a major detachment fault here termed the potamos detachment fault pdf exposed on the northern part of the island and bordering the domed structure of a metamorphic core complex the detachment forms the contact of contrasting metamorphic and nonmetamorphic units and both ductile and brittle structures are found related to its extensional development the earliest potamos mylonites as well as some other early ductile structures near the mapped detachment fault indicate initiation of the pdf under ne trending extension in mid to late miocene time later ductile ductile brittle and some brittle structures in the metamorphic unit near the detachment indicate in contrast a significant nw se extension along the forearc ridge the younger brittle structures indicate return to ne sw extension late miocene pliocene strata cover the detachment unconformably and are affected only by the late faults trench r

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

asymmetrical pull aparts and foliation fish as kinematic indicators abstract from field observations asymmetrical boudins pinch and swell structures and ellipsoidal volumes of oblique foliation segments in anisotropic rocks lacking competent layers are potentially useful kinematic indicators in shear zones they are derived by the modification of initially symmetrical pull aparts and or layering by superposed layer parallel shearing the response of boudins to such shear is a synthetic flow of those corner volumes lying within the extensional quadrants of the kinematic framework of the deformation into the inter boudin gaps type 1 asymmetrical pull aparts the response of pinch and swell structure is a back rotation of the swells to form type 2 asymmetrical pull aparts discrete extensional shears in the pinches may be either absent type 2a or present type 2b analogues of types 2a and 2b asymmetrical pull aparts occur in anisotropic materials with no compositionally distinct competent members where ellipsoidal volumes contain back rotated foliation segments foliation fish the field based kinematic interpretation was successfully tested by laboratory experiment wherein initially symmetrical trains of pre formed competent internally anisotropic boudins and pinch and swell structures were deformed in bulk simple shear a mechanical model is presented in terms of two material properties of the inclusions competence viscosity and internal rheological anisotropy in an attempt to account for the observed flow in the experiments and the deduced flow and kinematic significance of the natural examples in the presence of angular corners and associated geometrical stress concentrations competence viscosity controls the response to shear in the boudins in the absence of angular corners internal anisotropy controls the response to shear in the pinch and swell structures and in the foliation fish

factors affecting the kinematic interpretation of asymmetric boudinage in shear zones abstract based on work along a major mylonite zone in the northern appalachians and scale model studies a new mechanism for the origin of asymmetric boudins in shear zones is proposed along the honey hill fault in southern connecticut granitic sills intruded into calc silicate gneisses and schists were oblique to the boundaries of the mylonite zone and experienced the following sequence in the production of sigmoidal boudins 1 as the calc silicate schists experienced mylonitization and flow the more competent coarse grained granitic sills deformed by extensional fracturing and quartz veining 2 continued extension of granitic sills was accommodated by normal shear on early formed quartz veins 3 continuing extension of sills and ductile modification of the corners of boudins resulted in granitic fish with tails which stream from the top of the boudin in the down dip direction and from the bottom in the up dip direction based on a variety of kinematic indicators the sense of asymmetry of the tails is identical to that expected for recrystallization tails on sheared augen structure models composed of silicone putty and plasticine were created to investigate the effect of pre shearing geometry on boudin evolution and were deformed in a simple shear device the models reproduce the kinematics deduced from field relations and suggest that one of the primary factors in controlling the amount of extension is the angle which early veins make with the shear zone boundary varying the angular relationships in the models suggests that other pre shearing geometric factors may affect the geometry of boudins formed in this way boudins formed through this mechanism appear very similar to hanmer s type ii asymmetric boudins because the pre shearing geometry can exert a control on boudin asymmetry caution should be used when attempting to deduce shear sense or shear strain values from asymmetric boudinage

true and apparent geometric variability of en echelon vein arrays abstract the wide range of vein array angles reported for en echelon vein arrays can be attributed to both true and apparent geometric effects a survey of published figures supports a continuum of orientations rather than distinct populations related to different fracture mechanisms the results of the survey indicate a modal veinarray angle of less than 45 which indicates area increase as described by a displacement vector oriented outward from the array a stereometric analysis of the effects of exposure plane orientation on the apparent vein array angle is developed examples of vein arrays from the nambucca slate belt of eastern australia exposed on two differently oriented surfaces are shown these examples include non profile exposures with apparent vein array angles which are 1 less than 2 greater than 3 approximately equal to and 4 of opposite shear sense to the true vein array angle

the impact of finer resolution air sea coupling on the intraseasonal oscillation of the indian monsoon abstracta newly assembled atmosphere ocean coupled model called hadkpp is described and then used to determine the effects of subdaily air sea coupling and fine near surface ocean vertical resolution on the representation of the northern hemisphere summer intraseasonal oscillation hadkpp comprises the hadley centre atmospheric model coupled to the k profile parameterization ocean boundary layer model four 30 member ensembles were performed that vary in ocean vertical resolution between 1 and 10 m and in coupling frequency between 3 and 24 h the 10 m 24 h ensemble exhibited roughly 60 of the observed 30 50 day variability in sea surface temperatures and rainfall and very weak northward propagation enhancing only the vertical resolution or only the coupling frequency produced modest improvements in variability and just a standing intraseasonal oscillation only the 1 m 3 h configuration generated organized northward propagating convection similar to observations subdaily surface forcing produced s

palaeozoic palaeomagnetic studies in the welsh basin recent advances in the last two years new palaeomagnetic data fro m wale s have resulted i n radical revision of the ordovician palaeogeography of eastern avalonia part of the southern margin of the iapetus ocean combined with palaeozoic palaeomagnetic data from laurentia and gondwana these data suggest that eastern avalonia was a peri gondwanide high latitude continental fragment during at least part of ordovician time with a palaeolatitude of about 62 s and 51 s in arenig and llanvirn time respectively this implies a latitudinal width of the early ordovician iapetus ocean between eastern avalonia and laurentia of at least 30 geological evidence for the proximity of eastern avalonia and laurentia suggests that the intervening iapetus ocean closed during silurian time from late llandovery to early ludlow recent palaeolatitude data from the iapetus bordering continents are consistent wit h closure b y middle to late silurian time new pre acadian early devonian palaeomagnetic data from the old red sandstone places the welsh basin at about 17 s consistent with a palaeogeography in which laurentia baltica avalonia armorica and possibly gondwana wer e part o f a singl e supercontinent pervasiv e lat e carboniferous early permia n remagnetization affect s the welsh basin the remagnetization i s probably associated with fluids emanating from th e variscan thrust front w e do not observe remagnetization associate d with acadian orogen y and the remagnetizations which have been studied in more detail in north america appear to be a unique feature of the variscan hercynian alleghenian orogeny

metamorphic core complexes of cordilleran type in the cyclades aegean sea greece the islands of ios and naxos in the cycladic archipelago greece contain elongate domes over which a pervasive north to north northeast stretching lineation is warped these islands may be metamorphic core complexes of cordilleran type involving middle crustal rocks drawn upward and outward from underneath the sedimentary basins now 100 km to the south from ca 25 ma onward during uplift the crystalline rocks now exposed on the islands were deformed noncoaxially in the deeper levels of a major shallow dipping ductile shear zone this shear zone may have connected with low angle normal faults in its upper levels because it is probable that its later history involved the metamorphic complexes being dragged out from under a stretching and fracturing upper plate composed mainly of unmetamorphosed sedimentary and ophiolite suite rocks this model can be extended to explain the exhumation of the high pressure low temperature metamorphic rocks on crete which with the cyclades forms a distended paired metamorphic belt separated by an active sedimentary basin

extensional tectonics in mt parnon peloponnesus greece peloponnesus in the south western part of the aegean is formed by a heterogeneous pile of alpine thrust sheets that was reworked by normal faulting from upper miocene to recent times upper miocene lower pliocene extension in mt parnon was accommodated by several mappable brittle detachment faults that exhibit a top to the ne ene sense of shear the hanging wall of the detachments comprises a number of highly tilted fault blocks containing abundant evidence of intense internal deformation by normal faulting and layer parallel shearing contemporaneous with faulting these fault blocks are remnants of a cohesive extensional block that slipped to the ne ene and broke up along high angle normal faults that sole into or are cut by the detachments the largest part of this block is located at the eastern edge of the metamorphic core forming the hanging wall of east parnon high angle normal fault that excised part of the aforementioned detachments the lowermost metamorphic unit of the nappe pile does not seem to be affected by the previous extensional episode upper plate reconstruction shows that various units of the nappe pile were affected by high angle normal faults that linked to detachment faults in the weaker layers since the middle upper pliocene further exhumation of the metamorphic rocks has resulted in the formation of high angle normal faults overprinting neogene extensional structures and cut the entire nappe pile this new fault system tilted the earlier extensional structures and produced a ne sw coaxial deformation of mt parnon