first evidence of high pressure metamorphism in the cover series of the southern menderes massif tectonic and metamorphic implications for the evolution of sw turkey abstract the menderes massif occupies a large part of western turkey it is tectonically overlain by nappes of the izmir ankara suture zone including the bornova flysch zone on its northern flank the afyon zone on its eastern border and the lycian nappes on its southern flank the discovery of magnesiocarpholite kyanite assemblages in the mesozoic cover sequence of the southern menderes massif leads to the very first consideration that a major high pressure hp metamorphic event affected the massif during its alpine evolution estimations of minimum pressure temperature conditions about 10 12 kbar and 440 c suggest a minimum burial of 30 km for the metasedimentary rocks of the menderes massif similar to that for the eocene dilek blueschists which belong to the cycladic complex this finding of high pressure rocks within the menderes cover series as well as the recent description of low grade high pressure parageneses in the basal thrust sheets of the overlying lycian nappe complex has strong implications for the tectono metamorphic evolution of these units the characteristics of this high pressure metamorphism and the deformation features observed in the southern menderes massif allow consideration of a fast burial during alpine subduction and nappe stacking three high pressure units were piled up during the eocene collision of the sakarya continent and the tauride menderes block the lowermost unit consists of the imbricated core and cover of the menderes massif the intermediate unit is the cycladic blueschist complex dilek and samos regions and the uppermost unit is made of the lycian nappes the retrogression of high pressure parageneses from the menderes massif follows an isothermal decompression path and the associated deformation is characterized by a severe stretching oriented n s to ne sw during the high pressure event and its exhumation we propose a tectono metamorphic model in three main stages 1 the southward translation of the high pressure lycian nappes and the burial of the menderes and cycladic metasediments to a depth of at least 30 km to allow their eocene high pressure metamorphism 2 a northward continuum of deformation responsible for top to the north fabrics associated with the main menderes metamorphism peak paleocene eocene and its progressive cooling late eocene north verging folding thrusting imbrication of core and cover series and n s to ne sw intense stretching associated with the menderes high pressure metamorphism and its exhumation these top to the north to top to the northeast movements are probably related to the northward backthrusting of the lycian nappes reactivating the contact between the menderes massif and the lycian nappes as a top to the ne shear zone that allowed exhumation of the lycian high pressure rocks 3 oligo miocene n s extension during which the final exhumation of the metamorphic rocks along kilometre scale low angle detachments occurred

separate episodes of eclogite and blueschist facies metamorphism in the aegean metamorphic core complex of ios cyclades greece

40ar 39ar and oxygen isotope studies of polymetamorphism from tinos island cycladic blueschist belt greece petrological oxygen isotope and 40ar 39ar studies were used to constrain the tertiary metamorphic evolution of the lower tectonic unit of the cyclades on tinos polyphase high pressure metamorphism reached pressures in excess of 15 kbar based on measurements of the si content in potassic white mica temperatures of 450 500 c at the thermal peak of high pressure metamorphism were estimated from critical metamorphic assemblages the validity of which is confirmed by a quartz magnetite oxygen isotope temperature of 470 c some 40ar 39ar spectra of white mica give plateau ages of 44 40 ma that are considered to represent dynamic recrystallization under peak or slightly post peak high pressure metamorphic conditions early stages in the prograde high pressure evolution may be documented by older apparent ages in the high temperature steps of some spectra eclogite to epidote blueschist facies mineralogies were partially or totally replaced by retrograde greenschist facies assemblages during exhumation oxygen isotope thermometry of four quartz magnetite pairs from greenschist samples gives temperatures of 440 470 c which cannot be distinguished from those deduced for the high pressure event the exhumation and overprint is documented by decreasing ages of 32 28 ma in some greenschists and late stage blueschist rocks and ages of 30 20 ma in the lower temperature steps of the ar release patterns of blueschist micas almost flat parts of ar ar release spectra of some greenschist micas gave ages of 23 21 ma which are assumed to represent incomplete resetting caused by a renewed prograde phase of greenschist metamorphism oxygen isotope compositions of blueschist and greenschist facies minerals show no evidence for the infiltration of a 18o enriched fluid rather the compositions indicate that fluid to rock ratios were very low the isotopic compositions being primarily controlled by those of the protolith rocks we assume that the fundamental control catalysing the transformation of blueschists into greenschists and the associated resetting of their isotopic systems was the selective infiltration of metamorphic fluid a quartz magnetite sample from a contact metamorphic skarn taken near the miocene monzogranite of tinos gave an oxygen isotope temperature of 555 c and calculated water composition of 9 1 the value of 18o obtained from this water is consistent with a primary magmatic fluid but is lower than that of fluids associated with the greenschist overprint which indicates that the latter event cannot be directly related to the monozogranite intrusion

eclogite blueschist relationships as evidenced by mineral equilibria in the high pressure metabasic rocks of sifnos cycladic islands greece

thermochronology of the south cyclades shear zone ios greece effects of ductile shear in the argon partial retention zone micas and potassium feldspars from the south cyclades shear zone ios cyclades greece yield varied and complex 40ar 39ar apparent age spectra a correlation exists between 40ar 39ar apparent ages and the relative timing of different episodes of recrystallization and grain growth as indicated by fabric and microstructural analysis the 40ar 39ar apparent age spectra record the effects of variation in the degree of recrystallization and grain growth and partial to complete resetting of argon systematics in potassium bearing minerals during hercynian m0 alpine m1 and late oligocene early miocene m2 metamorphism deformation was strongly partitioned within the shear zone and this led to localized recrystallization and heterogeneous resetting of argon systematics within preexisting minerals modeling suggests the oligo miocene thermal events were of insufficient magnitude and or duration to completely reset the isotopic systematics in these samples our data lead to the concept of the argon partial retention and resetting zone prz defined as that portion of the crust where temperatures are insufficient to completely reset argon systematics within preexisting potassium bearing minerals within the prz some radiogenic argon in preexisting potassium bearing minerals will be outgassed and only partially retained tectonic exhumation of the prz involves movement on crustal scale ductile shear zones accompanied by strongly partitioned deformation and localized recrystallization recrystallization leads to resetting of argon systematics and thus will result in heterogeneous 40ar 39ar age distributions within these ductile shear zones e g in the south cyclades shear zone

isotopic dating of pre alpidic rocks from the island of ios cyclades greece the lower tectonic unit of ios provides evidence of an at least four stage metamorphic and intrusive history which well might be generalized for large parts of the internal pelagonian

kinematic characteristics of a mei yu front detected by the quikscat oceanic winds abstract based on conventional surface observations and nasa quick scatterometer quikscat data a heavy rainfall event that occurred in the taiwan mei yu season was chosen to further study the kinematic characteristics of the accompanying surface front with the help of the quikscat oceanic surface winds it was found that the location and propagation of a mei yu front over the ocean to the east of taiwan during 10 12 june 2000 are better represented by the frontal wind shift line which was located approximately on the leading edge of the baroclinic zone the mesoscale system with cyclonic circulation embedded within the frontal zone was clearly shown in the wind field and kinematic parameters horizontal divergence and vorticity as well as satellite clouds and rainfall estimations the conditional instability of the second kind cisk process was suggested to be responsible for the intensification of the mei yu front and the frontal disturbance over the ocean under the influence of island topography

metamorphic evolution of the attic cycladic metamorphic belt on naxos cyclades greece utilizing 40ar 39ar age spectrum measurements 40ar 39ar age spectrum analysis of phengite separates from naxos part of the attic cycladic metamorphic belt in greece indicates that cooling following high pressure low to medium temperature metamorphism m1 occurred about 50 ma ago phengite has 40ar gradients that suggest that part of the scatter observed in conventional k ar ages was caused by diffusion of radiogenic argon from the minerals during a younger metamorphism m2 in central naxos this metamorphism m2 has overprinted the original mineral assemblages completely and is associated with development of a thermal dome excellent 40ar 39ar plateaus at 15 0 0 1 ma 11 8 0 1 ma and 11 4 0 1 ma obtained on hornblende muscovite and biotite respectively from the migmatite zone indicate that relatively rapid cooling followed the m2 event and that no significant thermal overprinting occurred subsequent to m2 toward lower m2 metamorphic grade 40ar 39ar plateau ages of hornblendes increase to 19 8 0 1 ma concomitantly the proportion of excess 40ar in the spectra increases as well we propose that the peak of m2 metamorphism occurred beween 15 0 and 19 8 ma ago k ar ages of biotites from a granodiorite on the west coast are indistinguishable from those found in the metamorphic complex and hornblende k ar ages from the same samples are in the range 12 1 13 6 ma as the latter ages are somewhat younger than most ages obtained from the metamorphic complex intrusion of the granodiorite most likely followed the peak of the m2 metamorphism the metamorphic evolution of naxos is consistent with rapid crustal thickening during the cretaceous or early tertiary causing conditions at which supracrustal rocks experienced pressures in the range 900 1500 mpa transition to normal crustal thicknesses ended the m1 metamorphism about 50 ma ago the m2 metamorphism and granodiorite intrusion occurred during a period of heat input into the crust possibly related to the migration of the hellenic volcanic ar c in a southerly direction through the area

unroofing of active metamorphic core complexes in the d entrecasteaux islands papua new guinea metamorphic core complexes in the d9entrecasteaux islands are forming as a result of active extension at the western end of the woodlark basin spreading center high grade metamorphic rocks exist in the cores of gneissic domes including eclogites formed at minimum depths of 45 75 km i e 13 21 kbar high temperatures were maintained during uplift of basement rocks from 13 21 kbar t 730 900 c through 7 11 kbar t 570 730 c to 5 6 kbar t 730 c subsequent rapid cooling 100 c m y of the basement occurred between 1 and 2 ma on the basis of 40 ar 39 ar geochronology the core zone rocks were transected by kilometre scale amphibolite facies ductile shear zones active at depths of 25 35 km extensive intrusion of granodiorite plutons occurred and the age of granodiorite intrusions constrains late stage shear zone activity to 2 ma and younger unroofing was accomplished by faults and shear zones bounding the gneiss domes juxtaposing them against ultramafic rocks and sedimentary deposits surface uplift continues today and has led to topographic elevations of up to 2 5 km

whole flow field dynamics and velocity pulsing within natural sediment laden underflows sediment laden density underflows are important agents of erosion and deposition and are especially significant in the management of human made reservoirs pollutant dispersal and sediment deposition in the world9s oceans quantification of continuous sediment laden underflows in lillooet lake british columbia shows that the underflows descend along a distinct plunge line but although the input from the source is constant adopt a distinct pulsing in their velocity structure such velocity pulsing will produce temporally and spatially varying bed shear stresses sediment erosion and or deposition and fluid mixing and represents a central property of underflows that must be incorporated into models of density current behavior

exhumation paths of high pressure low temperature metamorphic rocks from the lycian nappes and the menderes massif sw turkey a multi equilibrium approach the menderes massif and the overlying lycian nappes occupy an extensive area of sw turkey where high pressure low temperature metamorphic rocks occur precise retrograde p t paths reflecting the tectonic mechanisms responsible for the exhumation of these highpressure low temperature rocks can be constrained with multiequilibrium p testimatesrelyingonlocalequilibria whereasasimple isothermal decompression is documented for the exhumation of highpressure parageneses from the southern menderes massif various p t paths are observed in the overlying karaova formation of the lycian nappes in the uppermost levels of this unit far from the contact with the menderes massif all p t estimates depict cooling decompression paths these high pressure cooling paths are asso

weakening of rock salt by water during long term creep the rheological properties of rock salt are of fundamental importance in predicting the long term evolution of salt based radioactive waste repositories and strategic storage caverns and in modelling the formation of salt diapirs and associated oil traps1 2 the short term high stress rheology of rock salt is well known from laboratory experiments however extrapolation to appropriately low stresses fails to predict the rapid flow seen in certain natural structures furthermore experiments have failed to reproduce the recrystallized microstructure of naturally deformed salt here we report experiments indicating that the above discrepancies can be explained by taking into account the influence of trace amounts of brine trace brine is always present in natural salt but sometimes escapes during experiments our tests on dry dilated salt show more or less conventional dislocation creep behaviour but brine bearing samples show marked weakening at low strain rates this is associated with dynamic recrystallization and a change of deformation mechanism to solution transfer creep because natural rock salt always contains some brine these results cast substantial doubt on the validity of presently accepted dislocation creep laws for predicting the long term rheological behaviour of salt in nature

structure and kinematics of upper cenozoic extensional detachment on naxos and paros cyclades islands greece this paper presents a study of the ductile and brittle deformation on naxos and paros islands cyclades greece previous maps and studies of the two islands have shown that a major low angle fault zone separates surface rocks above the contact from an initially deep seated unit below showing a metamorphic evolution from high to low pressures structural analysis as well as available stratigraphical metamorphic and geochronological data taken together demonstrate that this fault zone is a major normal sense detachment zone dipping to the north rapid denudation of footwall rocks subsequent to high temperature metamorphism at an estimated rate of 1 8 9 5 mm yr attests for tectonic unroofing during regional scale top to the north ductile shearing the change from ductile to brittle behavior of the footwall rocks together with a progressive localization of high strain intensity deformations just below the hangingwall is explained by the progressive cooling of the uprisen footwall of the detachment mio pliocene clastic sediments in the hangingwall represent the infilling of half grabens opened in between major normal faults that are synthetic to the underlying ductile shear zone these sediments are as old as aquitanian 25 ma or younger than the earliest recognized evidence of ductile extension in the footwall this provides a minimum age for the onset of extension in the cyclades which appears significantly older than maximum ages reported up to now 13 5 ma structural data strongly suggest that the detachment fault was initially rather low dipping 35 an evolutionary model is proposed in which migmatite domes in the footwall correspond to the uprise of the lower ductile crust between two separating upper crustal blocks during a process of asymmetric boudinage of the crust this detachment model applies to a previously thickened continental lithosphere which then suffers thermal relaxation and weakening allowing extensional deformation to reach a climax during and subsequent to high temperature metamorphism in the cyclades crustal scale extension started after early cenozoic thrusting while the crust was still thick or less likely before late underthrusting below the present surface

sedimentation by river induced turbidity currents field measurements and interpretation turbidity currents initiated from spring runoffs of an influent river were observed in the upper region of a reservoir in hokkaido japan by measuring water temperature velocity and suspended sediment concentration their profiles offer some physical parameters for the sedimentary conditions assuming the turbidity currents to be quasi uniform the bottom sediment deposited by the turbidity currents was then collected by a portable core sampler the bottom sediment consists of more than 90 silt and clay and thus offers a hydraulically smooth bed for shear flow a plane bed as a bed configuration was formed on the reservoir bed probably because of the low shear velocity and small grain size of sediment using a graphic method with log normal probability paper the bottom sediment is divided into several overlapping log normal subpopulations grain size analysis indicates that the bottom sediment may be regarded as cohesionless criteria for complete deposition of transported grains can then be incorporated into the extended shields diagram giving the minimum shear stress to erode bottom sediment applying the new diagram to the grain size distribution of the bottom sediment it is suggested that each of the log normal subpopulations was deposited in each of four different modes of deposition i e traction saltation or intermittent suspension suspension and suspension under equilibrium the last mode may be observed under a sedimentary condition where upward flux of suspended sediment by eddy diffusion is almost equal to its depositional flux due to gravity the mean and critical grain sizes for bottom sediment and each of the corresponding subpopulations decrease consistently with an increase of fd2 log10re fd is the densimetric froude number and re is the flow reynolds number correlates inversely with shear velocity which bears a linear relationship to mean velocity these results lead to the conclusion that relatively fine suspended sediment is deposited as a result of decreasing bottom friction with a relative decrease of turbulent energy

structural analysis of basement tectonites from the aegean metamorphic core complex of ios cyclades greece abstract the island of ios in the cyclades aegean sea greece exposes high pressure metamorphic rocks that were subjected to miocene continental extension subsequent to the alpine collisional orogeny the pre alpine history of the lower plate of this aegean metamorphic core complex involves intrusion of granitoids into metasediments which subsequently underwent hercynian amphibolite facies metamorphism during the alpine orogeny d2 these rocks were overthrust by the cyclades blueschist nappe later the lower plate was tectonically exhumed during oligo miocene continental extension and associated plutonism final exhumation occurred as a result of the operation of a south directed crustal scale shear zone and low angle normal faults this study shows that the ios core complex reflects an intrinsic relationship between early thrusting and later extensional tectonism basement rocks have been exhumed from beneath the nappes that originally overrode them

the tyrrhenian apennines system structural setting and seismotectogenesis abstract the available geological geophysical and seismological data of the tyrrhenian apennines system are briefly reviewed and synthesized in a number of sketch maps integrating and comparing these data a large scale simple shear kinematic model is proposed for the tyrrhenian apennines system that is here interpreted as an oblique asymmetric passive continental margin developed during the progressive counterclockwise rotation of the adriatic foreland from the late miocene to the present in the frame of this working hypothesis the thinning and stretching of the tyrrhenian crust were accommodated by progressive eastward motion of extensional allochthonous slices bounded by low angle west dipping oblique shear zones rotating above a common detachment that penetrates into the mantle lithosphere at any given time the most external eastward moving slice is bounded by a transtensional shear zone at the top and by a transpressional one at the bottom the displacement within the hanging wall of the transtensional shear zone is accommodated by high angle normal faults and en echelon grabens the displacement within the hanging wall of the transpressional shear zone is instead accommodated by co axial en echelon sets of folds thrusts and high angle strike slip faults thus the development of the late miocene pliocene pleistocene contractional strain field of the apennines of italy might not be a consequence of complex subduction processes but subordinate to the deformation processes that lead to the progressive opening of the tyrrhenian sea the seismicity of the crustal apennines of italy is analyzed in the frame of the above history of progressive deformation and a seismotectogenetic model is outlined

magmatism as an essential driving force for formation of active metamorphic core complexes in eastern papua new guinea the d entrecasteaux islands in eastern papua new guinea are composed of a number of active metamorphic core complexes which have been intruded by granodiorite plutons during their formation the plutons do not appear to have been intruded by diapiric processes as previously suggested late relatively undeformed plutons form flat lying bodies which crosscut structural boundaries and are strongly discordant to core complex shear zones granodiorite magmatism and the development of the metamorphic core complexes have occurred in a linear zone which coincides with a zone of thick crust and rugged topography it is proposed that plutonism facilitated deformation in ductile extensional shear zones which resulted in tectonic exhumation of deep crustal rocks and formation of the metamorphic core complexes the source of the plutons is thought to be related to a linear zone of mantle upwelling beneath the islands related to the propagation of the woodlark seafloor spreading center into continental crust it is suggested that a localized heat source of this type which can provide heat and magmatic material to the crust is essential for the development of metamorphic core complexes

aegean tectonics strain localisation slab tearing and trench retreat abstract we review the geodynamic evolution of the aegean anatolia region and discuss strain localisation there over geological times from late eocene to present crustal deformation in the aegean backarc has localised progressively during slab retreat extension started with the formation of the rhodope metamorphic core complex eocene and migrated to the cyclades and the northern menderes massif oligocene and miocene accommodated by crustal scale detachments and a first series of core complexes mccs extension then localised in western turkey the corinth rift and the external hellenic arc after messinian times while the north anatolian fault penetrated the aegean sea through time the direction and style of extension have not changed significantly except in terms of localisation the contributions of progressive slab retreat and tearing basal drag extrusion tectonics and tectonic inheritance are discussed and we favour a model 1 where slab retreat is the main driving engine 2 successive slab tearing episodes are the main causes of this stepwise strain localisation and 3 the inherited heterogeneity of the crust is a major factor for localising detachments the continental crust has an inherited strong heterogeneity and crustal scale contacts such as major thrust planes act as weak zones or as zones of contrast of resistance and viscosity that can localise later deformation the dynamics of slabs at depth and the asthenospheric flow due to slab retreat also have influence strain localisation in the upper plate successive slab ruptures from the middle miocene to the late miocene have isolated a narrow strip of lithosphere still attached to the african lithosphere below crete the formation of the north anatolian fault is partly a consequence of this evolution the extrusion of anatolia and the aegean extension are partly driven from below asthenospheric flow and from above extrusion of a lid of rigid crust

sedimentology of seismo turbidites off the cascadia and northern california active tectonic continental margins northwest pacific ocean abstract holocene turbidites from turbidite channel systems along the active tectonic continental margins of the cascadia subduction zone offshore vancouver island to mendocino triple junction and the northern san andreas transform fault the triple junction to san francisco bay have been analyzed for sedimentologic features related to their seismic origin centimeter thick silt sand beds turbidite base capped by mud layers turbidite tail and interbedded with hemipelagic silty clay intervals with high biogenic content have been characterized by visual core descriptions grain size analysis x ray radiographs and physical properties along the northern california margin in upstream single tributary canyons and channels most turbidites are uni pulsed classic fining up whereas downstream below multiple tributary canyon and channel confluences most deposits are stacked turbidites because each set of stacked turbidites has no hemipelagic sediment between each turbidite unit and each unit has a distinct mineralogy from a different tributary canyon we interpret that a stacked turbidite is deposited by several coeval turbidity currents fed by multiple tributary canyons and channels with synchronous triggering from a single san andreas fault earthquake the cascadia margin is characterized by individual multi pulsed turbidites that contain multiple coarse grained sub units without hemipelagic sediment between pulses because the number and character of multiple coarse grained pulses for each correlative multi pulsed turbidite is almost always constant both upstream and downstream in different channel systems for 600 km along the margin we interpret that the earthquake shaking or aftershock signature is usually preserved for the much stronger cascadia 9 mw compared to weaker california 8 mw earthquakes which result in upstream uni pulsed turbidites and downstream stacked turbidites consequently both the strongest 9 mw great earthquakes and downstream confluences cause multi pulsed and stacked turbidites that are typical for seismo turbidites generated by a single great earthquake along both margins earthquake triggering and multi pulsed or stacked turbidites become an alternative explanation for amalgamated turbidite beds in active tectonic margins and show that multiple grain size pulses and reverse grading are not unique criteria for hyperpycnites thalweg levee turbidites or mini basin margin turbidites the analyses of the turbidites along the cascadia and northern california margins reveal common sedimentologic characteristics of turbidites triggered by great earthquakes that can be used to distinguish seismo turbidites in other active tectonic margins around the world

white mica 40ar 39ar age spectra and the timing of multiple episodes of high p metamorphic mineral growth in the cycladic eclogite blueschist belt syros aegean sea greece research support providedby arc discovery projects dp0877274 anddp1201035 54 forster ackno wledges the support ofan australian research council arc australianresearch fellowship

radar analysis of a tamex frontal system abstract during the taiwan area mesoscale experiment tamex three doppler radars complemented enhanced surface and upper air observations the focus of the experiment was to better understand the interaction of the terrain with precipitation systems in the production of the important heavy rainfall the intensive operational period iop number 8 extended from 1400 ist local standard time 7 june 1987 until 0800 lst 9 june 1987 during this time a mesoscale convective system mcs formed in the straits of taiwan and moved inland it was interrogated by many observing instruments including three doppler radars over a 6 h period during this time the front moved through the radar network the front was shallow and the precipitation widespread both ahead of and behind the front the front was only 1 6 km deep over a distance of 100 km using velocity azimuth display vad data a portion of the frontogenetic function was computed during the times the front was in the vicinity of the radar the increas

evolution of the blueschist and greenschist facies rocks of sifnos cyclades greece the metamorphism on the island of sifnos is characterized by the eocene development of a coherent highpressure blueschist terrane and an early miocene greenschist facies overprint this study documents the metamorphic evolution of the blueschist assemblages still preserved in the northern parts of the island and their subsequent transformation into greenschists in the central and southern parts the oxygen isotope geothermometry is based on calibrations for quartz pyroxenes and magnetite matthews et al 1983a augmented by revised calibrations for the minerals muscovite qz mu 1 55 106 t 2 epidote qz ep 1 56 1 92 ps 106 t 2 and rutile qz ru 4 54 106 t 2 oxygen isotope analyses of minerals from the blueschist unit of northern sifnos give consistent fractionations which are independent of rock type an average temperature of 455 c was obtained although the scatter in temperatures deduced from the various geothermometers suggests that equilibration occurs under slightly changing physicochemical conditions analyses of minerals and whole rocks shows that pervasive equilibration in the presence of a common metamorphic fluid has not occurred the minerals and whole rocks of the greenschists of central sifnos are systematically enriched in 18o relative to the blueschist assemblages chemical data indicate that the greenschist overprint was accompanied by a metasomatic enrichment of ca2 and co2 the petrologic isotopic and chemical evidence favour a metamorphism governed by the infiltration of 18o co2 enriched aqueous solutions it is reasonable to assume that this is connected with the miocene magmatic activity observed throughout the cyclades the marbles separating the blueschist from the greenschist unit probably acted as barriers to fluid infiltration into the blueschists and were responsible for their preservation the pressure of the blueschist metamorphism is estimated at 14 2 kbar corresponding to a depth of ca 50 km the structural style and stratigraphy of sifnos are suggestive of the subduction of a continental margin sequence it is clear that the considerable tectonic depression may be associated with continental collision and underthrusting

strain and flow in the metamorphic core complex of ios island cyclades greece we have analysed strain and flow kinematics in the footwall of the south cyclades shear zone scsz an important tectonic boundary within the attic cycladic crystalline complex exposed on ios island cyclades aegean sea coarse grained augen gneisses in the basement unit flooring the scsz and forming a metamorphic core complex are excellently suited to measure finite strain using the fry method and estimate the vorticity number wk of flow with the blocked object method the results show that oligo miocene exhumation of the basement unit during extension brought approximately 70 n s crustal stretching and up to 40 subvertical shortening in a plane strain environment k 0 99 linear down section strain decrease constrains a zone of contact deformation of the scsz of about 1 5 km thick kinematic vorticity number estimates suggest little deviation from pure shear wk 0 26 finite strain and wk are not correlated indicating that the ios basement and the overlying cover units were stretched compatibly while the scsz is a localized zone of high strain net displacement however may be restricted to about ten kilometres this has important repercussions on large scale tectonic models for extension in the aegean

low angle faults above and below a blueschist belt tinos island cyclades greece new observations from the island of tinos greece allow a better definition of the structural position of the alpine eocene blueschist belt exposed in the islands of the aegean sea these blueschists over a significant part of the aegean sea are delimited from below by a low angle thrust fault while from above they are delimited by a low angle normal type fault which omits a substantial crustal interval both underlying and overlying rocks were not affected by the high metamorphism the rapid uplift and exhumation of the high rocks was therefore mainly the result of fault movements rather than erosion and whole crust uplifting the low angle normal fault apparently had a major role in the uplift of the blueschists

40ar 39ar dating of white micas from an alpine high pressure metamorphic belt on naxos greece the resetting of the argon isotopic system overprinting of white micas from high pressure low to medium temperature m1 metamorphic assemblages in pelitic schists on naxos during subsequent thermal dome m2 metamorphism ranges from minor in the southeast of the island to complete recrystallization in the amphibolite facies rocks near the migmatites in the centre of the dome the original m1 minerals are phengites si4 6 7 7 0 and the overprinting minerals are muscovites si4 6 0 6 45 40ar 39ar step heating analyses of white mica separates from rocks in the area where phengite and muscovite occur together yield complex age spectra characterized by low apparent ages in the first and the last stages of gas release and high apparent ages in between these upward convex age spectra are shown to be caused by mixing of two generations of micas each of which has a different age spectrum and argon release pattern seemingly good plateaus in some age spectra from white micas of the area must be interpreted as providing meaningless intermediate ages further the upward convex age spectra have been used to trace the isotopic signature of phengites toward increasing m2 metamorphic grade and suggest that as long as phengites can be observed in the rocks upward convex age spectra occur on naxos crystallization of muscovite at the expense of phengite appears to be the main mechanism of resetting argon isotopic ages in white micas however there is also good evidence for argon loss by volume diffusion from phengites simple diffusion calculations suggest that the m2 metamorphism was caused by a shortlived heat source

flow structure of turbidity currents a two dimensional numerical model is used to describe the flow structure of turbidity currents in a vertical plane to test the accuracy of the model it is applied to historical flows in bute inlet and the grand banks flow the two dimensional spatial and temporal distributions of velocity and sediment concentration and non dimensionalized vertical profiles of velocity turbulent kinetic energy and sediment concentration are discussed for several simple computational currents the flows show a clear interaction between velocity turbulence and sediment distribution the results of the numerical tests show that flows with fine grained sediment have low vertical and high horizontal gradients of velocity and sediment concentration show little increase in flow thickness and decelerate slowly steadiness and uniformity in these flows are comparable for velocity and concentration in contrast flows with coarse grained sediment have high vertical and low horizontal velocity gradients and high horizontal concentration gradients these flows grow considerably in thickness and decelerate rapidly steadiness and uniformity in flows with coarse grained sediment are different for velocity and concentration the results show the influence of spatial and temporal flow structure on flow duration and sediment transport

the mechanism of veining and retrograde alteration of alpine eclogites the introduction of externally derived fluids into rocks of the zermatt saas zone of the swiss alps gave rise to the simultaneous formation of shear and hydraulic fractures these fractures are now filled with albite rich assemblages and surrounded by alteration halos up to c 2 m wide the alteration assemblages are zoned and an examination of reactions in p t ah2o space implies that the parageneses developed by the hydration of fluid absent eclogites a mechanical analysis of the veins after sibson 1981 shows that pfluid pload must have been at least 0 96 fluid migration into the country rocks must have been driven by excess hydraulic head either derived from the vertical extent of the veins or due to their connection to a deeper external reservoir possibly tapped along thrust surface s diffusive and capillary transport were insignificant the fluids may have been derived from underlying metasediments that were dehydrating during the quasi isothermal uplift of this part of the alps or they may have originated during the prograde mesoalpine metamorphism documented in the area

phase relations of epidote blueschists phase diagrams have been computed for minerals in the system ncmash using the optimised thermodynamic data base of berman 1988 augmented by data on glaucophane and pumpellyite to illustrate the relationships between rocks containing epidote and sodic amphibole and those containing assemblages characteristic of neighbouring metamorphic facies the stoichiometries of stable bounding equilibria yield a simple list of mineral parageneses that serves to define an epidote blueschist facies and surrounding metamorphic facies the calculations suggest that when iron free the pairs zoisite glaucophane and clinozoisite glaucophane do not possess a stability field the natural fe bearing paragenesis of epidote sodic amphibole occupies a closed field in the pt diagram whose size increases dramatically as the ratio fe3 al in the minerals is increased where garnet is involved in bounding reactions such as with respect to eclogite and garnet bearing albite epidote amphibolite the epidote blueschist field decreases in size as the ratio fe2 mg is increased the classic blueschist to greenschist transition reaction is best developed in rocks with large fe3 and fe2 contents and is possibly metastable in mgal rich rocks in the latter a wedge of albite epidote actinolite barroisite amphibolite separates the epidote blueschist from the greenschits paragenesis field a first occurrence of garnet divides the epidote blueschist field into a lower temperature garnet free zone and a higher temperature garnet bearing zone although the temperatures calculated for this garnet isograd seem high the locations of all the facies boundaries are influenced by h2o activity however even minor amounts of co2 in the fluid phase x co2 0 005 render the epidote sodic amphibole paragenesis metastable so that facies boundaries cannot be shifted by varying the co2 content of the fluid phase below 600 c no mutual boundaries exist between the amphibolite facies and the epidote blueschist and eclogite facies respectively the calculated low pressure limit for the eclogite paragenesis pyralspite omphacite jd 50 quartz typical metabasite compositions is 12 to 14 kbars with h2o activity 0 9 or 1 5 to 2 kbar lower for jd 30

the tectonic significance of a porphyroblastic blueschist facies overprint during alpine orogenesis sifnos aegean sea greece the macargon program has been used to model published 40ar39ar apparent age spectra for white micas from the island of sifnos cyclades greece these micas formed during a period of porphyroblastic mineral growth m2 in the epidote blueschist facies at 460 c and 50 c m y and since m2 is followed by d3 we infer that these are the cooling rates during d3 modelling experiments for micas from the greenschist domain gsd structurally underneath the ebd suggest that the gsd cooled rapidly but at 32 ma one tectonic model that might explain the rapidity of cooling rates inferred for the ebd model supposes that ambient temperatures were at 500 c when m2 took place but thereafter the high pressure rocks were thrust to the north and rapidly cooled as the result of their juxtaposition against cooler shallower levels of the crust

single grain argon laser probe dating of phengites from the blueschist to greenschist transition on sifnos cyclades greece measurements of 40ar 39ar age spectra on single white mica crystals of tertiary age is a new means of obtaining detailed geochronological information of alpine blueschists internal consistency of the data set as well as excellent agreement with previous conventional k ar results demonstrates that this new technique can be used with confidence to obtain information on the thermal evolution of young metamorphic belts

observation and simulation of floodwater intrusion and sedimentation in the shichikashuku reservoir wash load sedimentation during flood events is studied through comprehensive field measurements at the shichikashuku reservoir japan and numerical simulation field data during a flooding event caused by a typhoon in 1996 are used to set the boundary conditions for the model and to verify the simulation in the field experiments continuous monitoring of inflow turbidity is shown to be an effective and reliable means of estimating sediment influx in the simulations the proposed model is shown to provide an accurate reproduction of floodwater currents and sedimentation in the reservoir the model achieves good accuracy and resolution by adopting an orthogonal curvilinear grid to discretize the reservoir and by solving the flow field using a three dimensional standard k e turbulence model the simulation reproduces the observed velocity turbidity and distribution of sedimentation well demonstrating the potential utility of such models in the management of reservoir water quality and sedimentation

reaction pathways during the progressive deformation of a blueschist metabasite the role of chemical disequilibrium and restricted range equilibrium there are discrete masses of un deformed metabasite within the blueschist series of the island of syros greece around the margins of these masses are zonal sequences through rocks showing intracrystalline deformation but without a geometric fabric to rocks with discrete and anastomosing shear zones and finally to penetratively foliated rocks with isolated relics of the original undeformed texture textural relics suggest that this spatial sequence is at least qualitatively also a temporal sequence this progressive shear zone deformation took place concurrently with a glaucophane epidote to eclogite reaction the reaction pathways in the rocks that underwent the shear zone deformation can be compared with those in rocks of a similar composition that suffered a longer deformation history and show no relics of an undeformed parent although the final assemblages are in both cases the same the pathways are different these differences are in part related to reactions promoted by the change from local to bulk equilibrium on the onset of deformation in the rocks they are also related to the crystallization and later breakdown during the sequence of progressive equilibration of a metastable phase in this case an impure glaucophane

ductile extrusion of the higher himalayan crystalline in bhutan evidence from quartz microfabrics quartz textures measured from deformed quartz tectonites within the lesser himalaya and higher himalaya crystalline of bhutan show similar patterns orientation and distribution of the quartz crystallographic axes were used to confirm the regional shear sense the asymmetry of c axis and a axis patterns consistently indicates top to the south shearing the obliquity of the texture and the inferred finite strain plane strain to moderately constrictional suggest the strain regime had a combination of rotational and irrotational strain path in most of the samples from the bhutan himalaya the inferred deformation mechanisms suggest moderate to high temperature conditions of deformation that produced the observed crystallographic preferred orientation much higher temperature of deformation is indicated in the quartz veins from a leucogranite the observed ductile deformation is pervasively developed in the rocks throughout the investigated area the intensity of deformation increases only slightly in the vicinity of the main central thrust simultaneous southward shearing within a large part of the higher himalaya crystalline near and above the main central thrust and normal faulting across the south tibetan detachment is explained by the tectonically induced extrusion of a ductily deforming wedge the process of extrusive flow suggested here can be approximated quantitatively by channel flow models that have been used to describe subduction zone processes channel flow accounts for some observed phenomena in the himalayan orogen such as inverted metamorphic sequences near the main central thrust not related to an inversion of isotherms and the syntectonic emplacement of leucogranites into the extruding wedge locally leading to an inversion of isotherms due to heat advection

sedimentary features of seismoturbidites triggered by the 1983 and older historical earthquakes in the eastern margin of the japan sea abstract both mass failure deposits and turbidites are widely distributed in the epicentral area of the 1983 earthquake mw 7 9 in the eastern margin of the japan sea this basin is semi enclosed with no active conduits for the entrance of coarse detrital sediments seismic reflection surveys and sediment cores reveal that mass failure deposits which are distributed on the continental slopes merge into turbidites in the basin plain hence the mass wasting process is a major transportation process in this region one gravity core gh93 816 was recovered from the southeastern margin of the japan basin close to the epicentral area of the 1983 japan sea earthquake sedimentological results show that five turbidite beds are intercalated in the top 68 cm of the column occurrence of the b tm tephra at the depth of 68 71 cm indicates that these turbidite beds were developed during the last 1000 years the high 137cs concentration in the top 20 cm of the core implies that the uppermost turbidite bed was deposited after 1954 based on these age limits for the top and the bottom of the studied interval we estimate the recurrence intervals of turbidites as 160 330 years we suggest that these turbidites were generated by submarine slides which were triggered by the 1983 and older historical earthquakes in this region these seismoturbidites are characterized by amalgamated beds irregular structure sequences grain size breaks fluctuations abrupt changes in composition within bed and variable composition among beds from these features we infer that deposition resulted from a series of turbidity currents associated with multiple or line sources for example multiple shallow slides that were regionally initiated by the same earthquake the sedimentary features described herein may be useful as criteria for identifying modern seismoturbidites in other settings as well as seismoturbidites in the geologic record however further study is needed for the distinction of this type of turbidites from other types e g tempestites reflected turbidites

a subtropical oceanic mesoscale convective vortex observed during sowmex timrex abstractthis study examines a subtropical oceanic mesoscale convective vortex mcv that occurred from 1800 utc 4 june to 1200 utc 6 june 2008 during intensive observing period iop 6 of the southwest monsoon experiment sowmex and the terrain influenced monsoon rainfall experiment timrex a dissipating mesoscale convective system reorganized within a nearly barotropic vorticity strip which formed as a southwesterly low level jet developed to the south of subsiding easterly flow over the southern taiwan strait a cyclonic circulation was revealed on the northern edge of the mesoscale rainband with a horizontal scale of 200 km an inner subvortex on a scale of 25 30 km with maximum shear vorticity of 3 10 3 s 1 was embedded in the stronger convection the vortex relative southerly flow helped create local potential instability favorable for downshear convection enhancement strong low level convergence suggests that stretching occurred within the mcv higher e air associated with significant pot

inside the head and tail of a turbulent gravity current gravity currents are an important buoyancy driven flow in environmental geophysical and industrial settings turbulence and mixing is commonplace in these flows but is typically overlooked in theoretical models and predictions sher woods j fluid mech vol 784 2015 pp 130 162 have quantified the velocity and density structure in turbulent gravity currents by combining high quality experimental data with new theory their insights are set to stimulate significant advances in the area

the timing of partial melting barrovian metamorphism and granite intrusion in the naxos metamorphic core complex cyclades aegean sea greece abstract the relationship between partial melting and granite intrusion in a classic barrovian metamorphic terrane has been assessed thirteen samples were dated by shrimp u pb zircon geochronology from the island of naxos greece one of the aegean metamorphic core complexes the effect of partial melting during peak barrovian metamorphism on naxos is recorded by fine

tectonic juxtaposition of blueschists and greenschists in sifnos island aegean sea implications for the structure of the cycladic blueschist belt abstract in the cyclades kilometre thick high pressure rock sequences displaying blueschist and eclogite facies mineral assemblages overlie a rock sequence which was thoroughly overprinted in the greenschist and amphibolite facies during its exhumation both rock sequences subducted and metamorphosed at high pressures in eocene times have been considered by previous workers to have been exhumed as a coherent rock unit in contrast it is suggested here that the preserved high pressure rock sequences were exhumed more rapidly and prior to the underlying greenschists significant metamorphic structural and geochronological discontinuities exist across the blueschist greenschist contact and field evidence suggests that the high pressure metamorphic rocks in sifnos are tectonically juxtaposed above the greenschists these two rock sequences were juxtaposed by a low angle fault subsequent to the oligocene miocene greenschist facies overprint published geochronological data and petrological criteria are used to show that the high pressure sequence cooled below 350 c when the rocks now immediately underlying it suffered a greenschist facies overprint at temperatures of ca 450 c the section inferred to absorb this temperature difference is now missing and it is suggested that it has been cut out by the low angle fault

core complex related extension of the aegean lithosphere initiated at the eocene oligocene transition 1 core complex related stretching of the aegean lithosphere was accommodated in part by the south cyclades shear zone scsz which outcrops on the islands of ios and thera aegean sea greece this paper reports new microstructurally focused 40ar 39ar geochronology that suggests the scsz initiated just before the time of the eocene oligocene transition at 35 ma therefore it is not only miocene extension that led to the tethyan metamorphic core complexes exposed in the cycladic archipelago it is shown here that pervasive top to the south directed ductile shear took place in the scsz for 5 ma during the early oligocene followed by initiation of overprinting north sense shear zones at the time of the oligocene miocene transition at 25 ma this means that modern core complex related extension in the aegean started much earlier than has been previously recognized and that stretching of the aegean lithosphere took place in a distinctly episodic fashion not in a manner that can be described as continuous or progressive the data also mean that the complementary shear sense geometry of the scsz and the north cyclades shear zone ncsz cannot be interpreted as crustal scale boudinage initiated during crustal extension in miocene time since the opposing sense shear zones operated at distinctly different times the paper illustrates the difficulties involved in systematically determining the age of deformation fabrics using 40ar 39ar geochronology and provides a case study that shows the value of carefully designed step heating experiments on microstructurally controlled samples in samples such as these from complex metamorphic tectonites laser fusion or step heating experiments with relatively few steps would have led to erroneous conclusions

inverse grading resulting from coarse sediment transport lag inverse grading in turbidites is conventionally ascribed to dispersive pressure caused by mutual collisions among grains within a traction carpet or grain flow the shearing traction carpet is supposed to become stratified with particle size increasing upward freezing of this traction carpet yields an inversely graded layer an alternative mechanism proposed here emerges from the fact that coarse sediment fractions are transported more slowly than fine fractions in a turbidity current a sufficiently heterogeneous mix of sediment sizes should undergo streamwise size segregation as the coarsest fractions lag behind if deposition begins before the coarsest fraction that will reach a particular station has arrived the lower part of the resulting deposit should be inversely graded a similar mechanism may produce inversely graded intervals in pyroclastic flow deposits because the head of a turbidity current typically travels only about 0 83 as fast as flow velocity in the body a short distance behind the head the coarsest grains able to keep up with the front of the flow are those having transport velocity v sed nearly equal 0 83 u body if coarser size fractions are available they will arrive later than the head permitting the development of inverse grading the proposed mechanism will not operate when the coarsest size fraction travels as fast as or faster than the head of the flow or when onset of deposition is delayed until after the coarsest size fraction has arrived assuming a logarithmic velocity profile below the maximum velocity streamline transport velocity can be calculated for particular sizes of suspended sediment and expressed as a fraction of flow velocity an upper limit for flow strength shear velocity can then be derived from the fall velocity of the coarsest grains at the base of an inversely graded interval u 4 w init where deposition of an inversely graded turbidite began immediately after passage of the head of the current u nearly equal 4 w init

case study of an unusually heavy rain event over eastern taiwan during the mei yu season abstract a heavy rain event during the mei yu season was observed over eastern taiwan on 28 may 2001 under a potentially unstable environment with high cape and copious moisture this event with an unusually high daily rainfall maximum of 307 mm was observed in the ilan area over northeastern taiwan the retrogression of a mei yu front over the nearby ocean collocated with a short wave trough provided favorable large scale conditions for the production of localized heavy rainfall latent heating was suggested to be responsible for the retrogression and the development of the mei yu front over the nearby ocean to the east of taiwan in addition to the large scale forcings the local circulations and local topography modulated the rainfall distribution over the ilan area during the daytime hours the strengthened onshore wind component due to the intensified mei yu frontal circulation and orographic lifting provided enhanced rising motion over the windward slopes of the mountain to produce the significan

in situ measurements of velocity structure within turbidity currents 1 turbidity currents are thought to be the main mechanism to move 500 000 m3 of sediments annually from the head of the monterey submarine canyon to the deep sea fan indirect evidence has shown frequent occurrences of such turbidity currents in the canyon but the dynamic properties of the turbidity currents such as maximum speed duration and dimensions are still unknown here we present the first ever in situ measurements of velocity profiles of four turbidity currents whose maximum along canyon velocity reached 190 cm s two turbidity currents coincided with storms that produced the highest swells and the biggest stream flows during the year long deployment

neogene lateral extension during convergence in the central alps evidence from interrelated faulting and backfolding around the simplonpass switzerland abstract the simplon fault zone occurs at the western end of the lepontine metamorphic dome in the central alps and represents a major low angle 25 dip normal fault associated with wsw ene directed lateral extension movement began in the early miocene and continued until at least 3 ma accumulating a total vertical throw of around 10 km corresponding to 24 km displacement parallel to the fault this displacement is partitioned between a broad zone of ductile mylonites in the footwall and a more discrete cataclastic detachment fault the simplon line in the central region simplon village to zwischbergen some 3 km of the total vertical displacement is accommodated by the discrete cataclastic zone due to the higher exposed structural level the importance of the cataclastic component increases towards the northwest in the northern steep belt around the simplonpass retrograde greenschist facies mylonite formation and younger cataclastic faulting associated with lateral extension occurred contemporaneously with sse vergent large scale backfolding representing nnw sse shortening and crustal thickening the combined effect was an overall shortening across the orogen accommodated by an extension parallel to the orogen allowing lateral escape of continental material normal faulting and the resultant lateral escape was not just superficial it extended to depths of at least 15 km and probably to depths exceeding 25 km the overall geometry and kinematics of the simplon fault zone and in particular the interplay between folding and faulting is very similar to that described from the metamorphic core complexes and detachment faults of the cordillera of the southwestern usa within the central alps extension was associated with rapid exhumation of the lepontine metamorphic dome as evidenced by very rapid cooling rates determined from mineral ages in the footwall similar to the cenozoic tectonics of the himalayas and tibet orogen parallel extension in the mountain belt may have been promoted by an overall reduction in the horizontal compressive stress in this direction more limited extension of the same age and orientation is known from a large area of the european foreland greater extension in the mountain belt compared with the foreland was accommodated by major strike slip transfer fault systems and was linked to coeval overthrusting of the lowlands towards the southwest in the external southwestern alps of haute provence france coeval folding and orogen parallel extension such as at the simplonpass were developed in a dextral transpressive regime due to oblique wnw ese convergence across the alps during the neogene

several distinct tectono metamorphic slices in the cycladic eclogite blueschist belt greece several relatively thin tectono metamorphic slices have been recognized in the cycladic eclogite blueschist belt through detailed studies on ios sifnos syros and tinos a sequence of distinct metamorphic mineral growth events has been documented these re cur in each tectonic slice although individual slices are dominated by different events to constrain the timing of these processes the method of asymptotes and limits has been used to reanalyze published 40 ar 39 ar apparent age spectra this reanalysis supports the concept that there were separate and quite distinct high pressure metamorphic mineral growth events and allows poten tial constraints as to the timing of some of these events to be developed m1b eclogite facies metamorphism is estimated to have occurred at some time in the period 53 49 ma the m1c blueschist facies metamorphic event at some time in the period 44 38 ma and the m1d transitional blueschist facies metamorphic event is esti mated to have occurred at some time in the period 35 30 ma a kinematic model is proposed to explain the geometry of a thinly sliced tectono metamorphic stra tigraphy as observed and the reason as to why indi vidual tectonic slices in this tectono metamorphic stratigraphy should display distinctive patterns of fab rics and micro structures as well as characteristic tem perature time curves as inferred by 40 ar 39 ar geochronology

scaling analysis of multipulsed turbidity current evolution with application to turbidite interpretation deposits of submarine turbidity currents turbidites commonly exhibit upward fining grain size profiles reflecting deposition under waning flow conditions however more complex grading patterns such as multiple cycles of inverse to normal grading are also seen and interpreted as recording deposition under cycles of waxing and waning flow such flows are termed multipulsed turbidity currents and their deposits pulsed or multipulsed turbidites pulsing may arise at flow initiation or following downstream flow combination prior work has shown that individual pulses within multipulsed flows are advected forward and merge such that complex longitudinal velocity profiles eventually become monotonically varying although transition length scales in natural settings could not be predicted here we detail the first high frequency spatial vertical streamwise and temporal measurements of flow velocity and density distribution in multipulsed gravity current experiments the data support both a process explanation of pulse merging and a phase space analysis of transition length scales in prototype systems the point of merging corresponds to the transition in any deposit from multipulsed to normally graded turbidites the scaling analysis is limited to quasi horizontal natural settings in which multipulsed flows are generated by sequences of relatively short sediment failures 10 km sequences of breaches or where pulsing arises from combination at confluences of single pulsed flows such flows may be responsible for the pulsing signatures seen in some distal turbidites 100 km from source

tectonic history of subduction zones inferred from retrograde blueschist p t paths many phanerozoic convergent plate junctions are marked by discontinuous blueschist belts reflecting relatively high pressure p prograde trajectories common blueschist paragneisses such as those of the western alps exhibit widespread overprinting by greenschist and or epidote amphibolite facies assemblages for this type of high p belt retrograde metamorphism involved fairly rapid nearly isothermal decompression some terranes underwent continued heating during early stages of pressure release uplift probably occurred as a consequence of the entrance of an island arc oceanic plateau or segment of continental crust into the subduction zone collision resulting in marked deceleration or cessation of underflow and buoyant approximately adiabatic rise of the stranded recrystallized subduction complex other high p belts such as the franciscan of western california preserve metamorphic aragonite and lack a low p overprint retrogression approximately retraced the prograde p t temperature path or for early formed high grade blocks occurred at even higher p t ratios parts of this type of metamorphic belt evidently migrated slowly back up the subduction zone in response to isostatic forces during continued plate descent and refrigeration upward motion took place as tectonically imbricated slices as laminar return flow in melange zones and perhaps partly a lateral spreading extension of the underplated accretionary prism retrograde p t trajectories of high pmore belts therefore provide important constraints on the tectonic evolution of convergent plate junctions less

the gibraltar arc seismogenic zone part 2 constraints on a shallow east dipping fault plane source for the 1755 lisbon earthquake provided by tsunami modeling and seismic intensity the great lisbon earthquake has the largest documented felt area of any shallow earthquake and an estimated magnitude of 8 5 9 0 the associated tsunami ravaged the coast of sw portugal and the gulf of cadiz with run up heights reported to have reached 5 15 m while several source regions offshore sw portugal have been proposed e g gorringe bank marquis de pombal fault no single source appears to be able to account for the great seismic moment as well as all the historical tsunami amplitude and travel time observations a shallow east dipping fault plane beneath the gulf of cadiz associated with active subduction beneath gibraltar represents a candidate source for the lisbon earthquake of 1755 here we consider the fault parameters implied by this hypothesis with respect to total slip seismic moment and recurrence interval to test the viability of this source the geometry of the seismogenic zone is obtained from deep crustal studies and can be represented by an east dipping fault plane with mean dimensions of 180 km n s 210 km e w for 10 m of co seismic slip an mw 8 64 event results and for 20 m of slip an mw 8 8 earthquake is generated thus for convergence rates of about 1 cm yr an event of this magnitude could occur every 1000 2000 years available kinematic and sedimentological data are in general agreement with such a recurrence interval tsunami wave form modeling indicates a subduction source in the gulf of cadiz can partly satisfy the historical observations with respect to wave amplitudes and arrival times though discrepancies remain for some stations a macroseismic analysis is performed using site effect functions calculated from isoseismals observed during instrumentally recorded strong earthquakes in the region m7 9 1969 and m6 8 1964 the resulting synthetic isoseismals for the 1755 event suggest a subduction source possibly in combination with an additional source at the nw corner of the gulf of cadiz can satisfactorily explain the historically observed seismic intensities further studies are needed to sample the turbidites in the adjacent abyssal plains to better document the source region and more precisely calibrate the chronology of great earthquakes in this region

new discoveries in dynamics of an m8 earthquake phenomena and their implications from the 2003 tokachi oki earthquake using a long term monitoring cabled observatory at the 2003 tokachi oki earthquake of m8 seafloor phenomena such as a generation process of tsunami seafloor uplifts turbidity current etc were observed using a cabled observatory installed on the seafloor the turbidity current was observed as a benthic storm caused presumably by the mainshock the seafloor uplifts were observed at the mainshock and continuously after the mainshock the uplifts were 0 35 0 37 and 0 12 m for epicentral distances of 25 5 31 4 and 81 7 km respectively after the mainshock a continuous uplift of the seafloor is observed at all three pressure gauge locations indicating that there was a change in the state of friction on the plate boundary interface by the mainshock in this paper we first show what was observed using the cabled observatory installed right above the focal area of the earthquake and then we discuss to summarize these phenomena associated with the earthquake its possible causes and future directions in long term monitoring of seismogenic processes

rupture extent of the 1938 alaskan earthquake as inferred from tsunami waveforms using tsunami waveforms we estimate the source parameters of the 10 november 1938 alaskan earthquake the earthquake ruptured a 300 kin long segment of the alaskan arc which corresponds to the aftershock area the seismic moment is approximately 20x102o nm or mw 8 2 and the moment release was concentrated in the eastern end of the aftershock zone the tsunami and seismic evidence strongly suggest that the 1938 earthquake did not rupture into the shumagin islands gap

sediment gravity flows triggered by remotely generated earthquake waves recent great earthquakes and tsunamis around the world have heightened awareness of the inevitability of similar events occurring within the cascadia subduction zone of the pacific northwest we analyzed seafloor temperature pressure and seismic signals and of video stills of sediment enveloped instruments recorded during the 2011 2015 cascadia initiative experiment and seafloor morphology our results led us to suggest that thick accretionary prism sediments amplified and extended seismic wave durations from the april 11 2012 mw8 6 indian ocean earthquake located more than 13 500 km away these waves triggered a sequence of small slope failures on the cascadia margin that led to sediment gravity flows culminating in turbidity currents previous studies have related the triggering of sediment laden gravity flows and turbidite deposition to local earthquakes but this is the first study in which the originating seismic event is extremely distant 10 000 km the possibility of remotely triggered slope failures that generate sediment laden gravity flows should be considered in inferences of recurrence intervals of past great cascadia earthquakes from turbidite sequences future similar studies may provide new understanding of submarine slope failures and turbidity currents and the hazards they pose to seafloor infrastructure and tsunami generation in regions both with and without local earthquakes

powerful unconfined turbidity current captured by cabled observatory on the fraser river delta slope british columbia canada turbidity currents are one of the main sediment transport processes on earth yet are notoriously difficult to monitor directly this article presents the first direct and high bandwidth observation of a turbidity current using a cabled sea floor observatory on 5 june 2012 a platform on ocean networks canada located in 107 m of water on the fraser river delta slope was displaced downslope and severed from its data cable the platform weighed ca 1000 kg in water the event took place during high river discharge high tides and rapid sediment accumulation on adjacent upslope areas of the sea floor data recorded as it tumbled downslope allow a reconstruction of the flow which is inferred to have been an unconfined turbidity current lines of evidence indicate that the flow came in as a bed hugging wedge and built up to between 1 m and 4 m in height as the head passed through comparison with laboratory data suggest that the flow was initially supercritical while the adjacent slope offset to the north clearly exhibits change over an annual resurvey period the bathymetry directly at the event location show no resolvable change over a period from seven months before the event to one month after sediment cores collected after the event were pervasively biototurbated and they contain no obvious deposit connected with this event the remarkable aspects of this research follow the flow was powerful enough to carry a 1 tonne platform and sever a heavily armoured cable the current occurred on the unchannelized open slope this powerful event failed to cause discernible seabed elevation change the flow was triggered by tidal conditions the event was detected by a purpose designed cabled observatory thus providing high bandwidth data and also alerting researchers in real time to mount follow on investigations

the three metamorphic belts of the hellenides a review and a kinematic interpretation summary new results obtained in the three metamorphic belts of the hellenides suggest that each belt has a different structure geotectonic setting and evolution the external metamorphic belt of peloponnesus crete has probably resulted from nappe movement in the vicinity of an evolving island arc system the blueschists occurring within this external belt are allochthonous and have been transported with other nappes over the external carbonate platform of the pre apulian plattenkalk ionian tripolitza almyropotamos units this implies that there was only one true blueschist domain initiated in the cycladic area during early eocene the kinematic interpretation is based on the distinction of a and b structures and on the nature of the shear zones between the different domains especially that between the metamorphic hellenides below and the non metamorphic hellenides above the existence of the probably lower palaeozoic meta sedimentary sequence of kastoria in the northern pelagonian zone indicates that the overlying ophiolite bearing almopias unit has been derived from within the hercynian domain the kastoria sedimentary sequence the ophiolites of vertiskos and the carbonate platform of pangeon are considered to be most likely elements of a probable hercynian orogeny

thermochronologic constraints on the tectonic evolution of active metamorphic core complexes d entrecasteaux islands papua new guinea metamorphic core complexes in the d entrecasteaux islands papua new guinea formed as the result of active extension at the western end of the propagating woodlark basin spreading center domes of high grade metamorphic rocks i e amphibolites eclogites and migmatites intruded by large granodiorite bodies comprise the lower plate of the d entrecasteaux metamorphic core complexes the domes are transected by kilometer scale shear zones a thermochronologic study of the d entrecasteaux islands utilizing k ar 40ar 39ar and fission track techniques has documented the unroofing history of these active metamorphic core complexes gneisses in the cores of the domes cooled rapidly 100 c m y as indicated by hornblende and biotite 40ar 39ar apparent ages of 2 7 to 3 0 ma and 1 6 to 1 7 ma respectively and apatite fission track ages of 0 4 to 0 9 ma 40ar 39ar apparent ages on white mica biotite and potassium feldspar and fission track ages on apatites from shear zone gneisses indicate extremely rapid cooling in some cases 500 c m y and suggest shear zones were active from 4 0 to 3 5 ma and 1 9 to 1 4 ma in general 40ar 39ar mineral ages for retrogressed core zone gneisses shear zone gneisses and granodiorites are 2 0 to 3 0 ma amphiboles 1 5 to 1 7 ma muscovites and 1 4 to 1 8 ma biotites and 1 0 to 2 0 ma k feldspars apatite fission track ages from core zone gneisses shear zone gneisses and granodiorites range from 0 4 to 1 0 ma thermochronologic results indicate that emplacement of granodiorites closely coincided with retrogression of the metamorphic basement and movement on the outer shear zones bounding the gneiss domes the granodiorite bodies associated with the d entrecasteaux islands domes represent syn kinematically emplaced granitoids intruded into an area of active continental extension

the importance of site selection sediment supply and hydrodynamics a case study of submarine paleoseismology on the northern cascadia margin washington usa abstract the washington continental margin presents both a classic test of submarine paleoseismology and an opportunity to explore advancement of the field through analysis of sediment dispersal in a heterogeneous system new and archive core bathymetric backscatter and seismic reflection data from the washington cascadia margin show that during high stand conditions the northernmost canyons barkley nitinat juan de fuca jdf and to some extent quillayute are relict systems with little holocene recharge the remaining canyons quinault grays guide and willapa are recharged to a varying degrees by northward transport of columbia river derived sediment all systems are nonetheless active conduits for turbidity currents during the holocene which are weaker and more restricted than their pleistocene counterparts sedimentologic and ct analysis supported by radiocarbon ages micropaleontology and the mazama ash datum show that the holocene sedimentary sequence consists of a series of sand to mud turbidites in the active portions of all systems interbedded with hemipelagic sediment however the pleistocene astoria and nitinat fans are largely inactive in the holocene with turbidity current activity limited to the proximal parts of the main channels within active systems the turbidite record is modulated by local landsliding and growth of active folds and faults in the relict systems the turbidite record begins in the middle canyon reaches as opposed to the actively recharged systems which have a turbidite record in the more proximal canyon reaches deposits in the relict systems increase in thickness and modal grain size downstream suggesting multiple sources and or entrainment of material along the canyon walls hydrodynamic models using monte carlo model searches for best fitting flow parameters show the most likely pathways by which holocene and pleistocene currents flowed through the complex accretionary wedge to the abyssal plain model results supported by heavy mineral distributions show that the northern canyon systems barkley nitinat jdf quillayute are independent of the southern systems quinault guide grays willapa during the holocene supporting the classic confluence test balancing of sediment volumes required suggests sediment supplied to the slope canyons and abyssal channels in turbidity current events is 2 5 times greater than that supplied by recharge to the canyon heads by external sources this implies a process that is independent of recharge that scavenges the plentiful relict and hemipelagic sediment supply on the continental slope lithostratigraphic correlation and age models suggest similar sequences were deposited in most systems independently and likely synchronously the correlated turbidite sequence suggests deposition of 23 holocene and 16 post mazama turbidites in most parts of the canyon systems with only modest variation mostly attributable to evidence of bypassing and erosion the best candidate for triggering of these sequences remains great earthquakes and the sequence correlates well to onshore and other offshore paleoseismologic evidence the new data including new cores in northern oregon suggest revisions to segmented rupture boundaries several partial ruptures segment b likely extended further north to juan de fuca canyon one event was resolved into two and one washington only event was added most segment c ruptures were found to extend further northward to the latitude of astoria canyon mean recurrence times are therefore revised to 434 years for the washington coast and 340 years for the central and northern oregon coast conditional probabilities in the next 50 years also are revised to 10 17 for the washington coast and 16 22 for the central and northern oregon coast in cascadia sumatra and other locales globally core siting spatial sample density high resolution analysis of core and regional geophysics and understanding of flow dynamics are critical to capturing a paleoseismic record sedimentary records vary across turbidity current systems of varying sediment supply physiography and sediment sources variations in the record will reflect these factors yet may still present a consistent paleoseismic history this analysis highlights the importance of a thorough understanding of flow paths hydrodynamics and the interplay of sedimentation and local tectonics when testing for evidence of earthquakes in the sedimentary record of active margins

seismotectonic zoning in east central italy deduced from an analysis of the neogene to present deformations and related stress fields this paper concerns the space time evolution of the late miocene to present contractional and extensional deformations within east central italy with an analysis of the pattern and orientation of the related stress field an insight into the cover basement relations and a discussion of the seismotectonic implications the pattern and orientation of the deformation and stress fields have remained unchanged since late miocene time and have been always characterized by the coexistence and parallelism in contiguous areas in a given time of shortening to the east and elongation to the west with time during a multistage deformation history both the contraction and the extension fields have moved eastward basement involved tectonics with a west dipping multiple detachment system would have allowed the progressive eastward shift of crustal slices corresponding at the surface to well defined tectonic domains with consequent crustal thinning in the tuscan zone and crustal thickening beneath the apennine mountain chain by comparing macroseismic epicenters hypocenters and focal mechanisms with crustal structure and independently known active faults it appears evident that the pattern frequency and distribution of the crustal seismicity are tectonically controlled and that a contraction extension pair is active also at the present time in fact along the adriatic coastline contractional deformation prevails with involvement of pleistocene layers whereas beneath the apennine range extensional deformation prevails both t axes in the inner domain and p axes in the outer domain are oriented southwest northeast or west south west east northeast and this coaxiality reflects the situation depicted by the geologic stress field on this basis we have produced a seismotectonic zoning of east central italy with three distinct domains intramountain seismic zone isz foothills seismic zone fsz and coastal seismic zone csz a plausible explanation for the genesis of the active seismic deformations of east central italy is that the locally intense extensional upper crustal seismicity of the intramountain seismic zone is confined to the hanging wall of a major west dipping active extensional discontinuity whereas the less frequent contractional seismic activity of the coastal seismic zone is within the hanging wall of an outer major active west dipping contractional discontinuity an area of overlap between these two zones is represented by the foothills seismic zone where superposed epicentral patterns from different surfaces of weakness at different depths are the predictable result of the asymmetry of the deformation

coaxial flattening at deep levels of orogenic belts evidence from blueschists and eclogites on syros and sifnos cyclades greece this work presents new structural data from a high pressure low temperature hp lt metamorphic terrane exposed on the islands of syros and sifnos cyclades greece the structure and the metamorphism of a relatively coherent hp lt rock section were studied in order to elucidate how strain was accommodated at deep crustal levels during the formation and exhumation of hp lt rocks at least three deformation phases associated with eclogite and blueschist facies conditions p 8 15 kbar t 400 550 degreesc were recognised the earliest deformation fabric s1 preserved as inclusion trails within garnet porphyroblasts is aligned to define a sub vertical schistosity at present orientation which is frequently orthogonal to the flat matrix schistosity s2 and may indicate that deep crustal thickening involved upright folding the currently dominant fabric in the hp rock section s2 is usually moderately dipping and locally contains nw trending glaucophane lineations symmetric pressure shadows and eclogitic boudins the symmetric structures associated with this fabric seem to indicate coaxial vertical thinning although the existence of non coaxial structures out of the study area cannot be excluded glaucophane bearing shear bands s3 with top to nw sense of shearing locally crosscut the earlier structures the latest recognised fabric d4 is scarce and often absent within the hp rocks it is associated with top to ne kinematic criteria that formed at greenschist facies conditions p 4 7 kbar t 400 450 degreesc based on these observations it is suggested that partitioning of strain occurred at different crustal levels and at different times deep crustal deformation was governed by thickening via upright folding followed by coaxial vertical thinning whereas non coaxial shearing occurred when the rocks were already exhumed to relatively shallow crustal levels the earliest fabrics d1 to d3 pertain to alpine orogenesis and possibly to syn orogenic extension whereas the latest correspond to whole crust back are extension c 2002 elsevier science ltd all rights reserved

uplift and exhumation of high pressure metamorphic terrains the example of the cycladic blueschist belt aegean sea the cycladic blueschists emerged from a depth of more than 50 km during the tertiary these rocks are now covered only by a thin fraction of the synmetamorphic overburden upper plate remnants of the upper plate include low p crystalline rocks and sediments which have been juxtaposed onto the lower plate blueschists in several stages since the early miocene the low angle contacts operated as normal faults which removed the overburden from above the cycladic blueschists detailed investigations on tinos island indicate that the fractured blocks of the upper plate lying above a low angle normal fault did not rotate this shows that the faults initiated as rather gently dipping fractures similar structures were also reported from other blueschist terrains kinematic analysis of such flat lying faults implies that the synmetamorphic overburden should be mostly located several hundred kilometers away from the present exposure of the blueschists considering that the cycladic blueschist belt exposes successively shallower units in the west and that rocks of the upper plate have an anatolian nature we suggest that these blueschists were dragged from beneath turkey we recognize that the blueschist unit has undergone further thrusting in the final stage of the exhumation as have its counterparts elsewhere in the hellenides the emergence of the blueschists in the tertiary was concomitant with continental collision and thrusting in the hellenides the operation of low angle normal faults with large extensional displacements occurred within this context of collision tectonics this extension occurred parallel to the strike of the convergent orogen

turbidity events observed in situ along the congo submarine channel abstract as part of the multidisciplinary programme biozaire devoted to studying deep sea benthic ecosystems in the gulf of guinea particulate input and its relationship with near bottom hydrodynamics were monitored using long term moorings from 2000 to early 2005 particular attention was given to material input through the congo ex zaire submarine channel that extends 760 km from the congo river mouth to the abyssal plain 5100 m near 6 s due to its direct connection to the congo river the congo canyon and channel system are characterised by particularly active recent sediment transport during this first in situ long term monitoring along the channel an energetic turbidity event was observed in january 2004 at three locations along the channel from 3420 to 4790 m in depth this event tilted and displaced the moorings installed at 3420 m site zr and 4070 m site zd and resulted in high sediment deposition at all three mooring sites the event moved at an average velocity of 3 5 m s 1 along the numerous channel meanders between 3420 and 4070 m then at 0 7 m s 1 between 4070 m and the end of the channel at 4790 m the particle cloud rose above the top of the valley at 4070 m site zd but not at 3420 m site zr where the channel was too deep lastly the mooring line broke at site zd in october 2004 probably due to a strong event like that of 2001 previously described by khripounoff et al khripounoff a vangriesheim a babonneau n crassous p denniellou b savoye b 2003 direct observation of intense turbidity activity in the zaire submarine valley at 4000 m water depth marine geology 194 151 158 between these strong events several peaks of high turbidity and particle flux occurred but without noticeable current increases these events were probably due to local sliding of sediment accumulated on the walls or terraces on the side of the channel the area near 4000 m depth and the lobe appear to be the main depocentres of particulate input rich in organic matter derived from the congo river

slope failure dynamics and impacts from seafloor and shallow sub seafloor geophysical data case studies from the costa project holocene and slightly pre holocene submarine landslide are found both in high latitude glacial dominated margins and in lower latitude river dominated margins this paper constitutes a major assessment on some of the best studied submarine instabilities in the world we review and update from original data and literature reports the current state of knowledge of storegga traenadjupet and finneidfjord slides from the mid norwegian margin afen slide from the faeroe shetland channel big 95 slide and central adriatic deformation belt cadeb from continental slope and inner continental shelf settings off the ebro and po rivers in the mediterranean sea canary slide west of the westernmost youngest canary islands and gebra slide off the northern tip of the antarctic peninsula in the southern hemisphere i e those studied in the continental slope stability costa project the investigated slides range in size from the gigantic 90 000 km2 and almost 3000 km3 storegga slide to the tiny 1 km2 and 0 001 km3 finneidfjord slide not only do individual submarine landslides rarely involve processes precisely fitting with pre established categories mostly based on subaerial research but also they display complex mechanical behaviors within the elastic and plastic fields individual events can involve simultaneous or successive vertical to translational movements including block detachment block gliding debris flow mud flow and turbidity currents the need for an in depth revision of the classification criteria and eventually for a new classification system based on the new imaging capabilities provided by modern techniques is more than obvious we suggest a new system which for the moment is restricted to debris flows and debris avalanches volume calculation methods are critically reviewed and the relations between some key geomorphic parameters are established for the selected slides the assumed volume missing from scar areas does not necessarily match the actual volume of sediment remobilised by an individual event since in situ sediment can be remoulded and eventually incorporated during the slide downslope journey cadeb a shore parallel prodelta detached from its source is the exception to the good correlation found between across slope width and alongslope length with slide area height drop measured from the headwall upper rim to its foot correlates with the debris deposit maximum thickness unless the slide moves into restricted areas which prevent farther forward expansion of the deposit such as gebra and big 95 in such cases over thickened deposits are found a particularly loose and fluid behavior can be deduced for slides showing an over thinned character such as the canary slide that traveled 600 km scar areas and slip planes have been investigated with particular emphasis although slide headwalls might present locally steep gradients up to 23 for storegga slide the slope gradients of both the failed segment margins and the main slip planes are very low max 2 and usually around 1 and less an exception is the finneidfjord slide 20 5 that occurred in 1996 because of a combination of climatic and anthropogenic factors leading to excess pore pressure and failure mechanically distinct low permeable clayey weak layers often correspond to slip planes beyond the slide headwall since not only formation of these weak layers but also sedimentation rates are climatically controlled we can state that slide pre conditioning is climatically driven too run out distances reflect the degree of disintegration of the failed mass of sediment the total volume of initially failed material and transport mechanisms including hydroplanning commonly specific run outs could be attributed to distinct elements such as cohesive blocks and looser matrix as nicely illustrated by the big 95 slide total run outs usually correspond to matrix run outs since the coarser elements tend to rest at shorter distances outrunner blocks are finally a very common feature proving the ability of those elements to glide over long distances with independence of the rest of the failed mass in addition to pre conditioning factors related to geological setting and sedimentation conditions a final trigger is required for submarine landslides to take place which is most often assumed to be an earthquake in high latitude margins earthquake magnitude intensification because of post glacial isostatic rebound has likely played a major role in triggering landslides although it cannot be totally ruled out there is little proof at least amongst the costa slides that gas hydrate destabilisation or other processes linked to the presence of shallow gas have acted as final triggers

dynamics and deposition of sediment bearing multi pulsed flows and geological implication copyright 2019 sepm society for sedimentary geology previous studies on dilute multi pulsed subaqueous saline flows have demonstrated that pulses will inevitably advect forwards to merge with the flow front on the assumption that pulse merging occurs in natural scale turbidity currents it was suggested that multi pulsed turbidites that display vertical cycles of coarsening and fining would transition laterally to single pulsed normally graded turbidites beyond the point of pulse merging in this study experiments of dilute single and multi pulsed sediment bearing flows turbidity currents are conducted to test the linkages between downstream flow evolution and associated deposit structure experimental data confirm that pulse merging occurs in laboratory scale turbidity currents however only a weak correspondence was seen between longitudinal variations in the internal flow dynamics and the vertical structure of deposits multi pulsed deposits were documented but transitioned to single pulsed deposits before the pulse merging point this early transition is attributed to rapid sedimentation related depletion of the coarser grained suspended fraction in the laboratory setting whose absence may have prevented the distal development of multi pulsed deposits this factor complicates estimation of the transition point in natural scale turbidite systems

near synchronous and delayed initiation of long run out submarine sediment flows from a record breaking river flood offshore taiwan subsea fiber optic telecommunication cables can break under fast sediment flows that travel 100s of kilometers through the deep ocean in response to earthquakes and submarine landslides similar flows are inferred to form from major river floods whose sediment laden waters plunge and travel along the seabed however the complex initiation of flood related flows and their hazard potential have not been observed until now here we use cable fault data from the gaoping canyon manila trench off taiwan to show that a major river flood formed during typhoon morakot 2009 generated two long run out destructive sediment flows one during peak flood and the other 3 days later the latter flow was more damaging with speeds and run out similar to that of landslide triggered turbidity currents formed in the same catchment if the second flow was due to remobilized canyon sediment it occurred during low earthquake mw 2 0 activity suggesting other triggering mechanisms

pulse propagation in turbidity currents submarine turbidity currents are a key mechanism in the transportation of clastic sediments to deep seas such currents may initiate with a complex longitudinal flow structure comprising flow pulses for example by being sourced from retrogressive sea floor slope failures or acquire such structure during run out for example following flow combination downstream of confluences a key question is how far along channel pathway complex flow structure is preserved within turbidity currents as they run out and thus if flow initiation mechanism and proximity to source may be inferred from the vertical structure of their deposits to address this question physical modelling of saline flows has been conducted to investigate the dynamics of single pulsed versus multi pulsed density driven currents the data suggest that under most circumstances individual pulses within a multi pulsed flow must merge therefore initiation signatures will only be preserved in deposits upstream of the merging point and may be distorted approaching it downstream of the merging point all initiation signals will be lost this new understanding of merging phenomenon within multi pulsed gravity currents broadens our ability to interpret multi pulsed turbidites

event driven sediment flux in hueneme and mugu submarine canyons southern california vertical sediment fluxes and their dominant controlling processes in hueneme and mugu submarine canyons off south central california were assessed using data from sediment traps and current meters on two moorings that were deployed for 6 months during the winter of 2007 the maxima of total particulate flux which reached as high as 300 g m 2 day in hueneme canyon were recorded during winter storm events when high waves and river floods often coincided during these winter storms wave induced resuspension of shelf sediment was a major source for the elevated sediment fluxes canyon rim morphology rather than physical proximity to an adjacent river mouth appeared to control the magnitude of sediment fluxes in these two submarine canyon systems episodic turbidity currents and internal bores enhanced sediment fluxes particularly in the lower sediment traps positioned 30 m above the canyon floor lower excess 210 pb activities measured in the sediment samples collected during periods of peak total particulate flux further substantiate that reworked shelf rather than newly introduced river borne sediments supply most of the material entering these canyons during storms published by elsevier b v

exhumation of high pressure rocks a review of concepts and processes the exhumation of high pressure metamorphic rocks requires either the removal of the overburden that caused the high pressures or the transport of the metamorphic rocks through the overburden exhumation cannot be achieved simply by thrusting or strike slip faulting it may be caused by erosion of shortened and thickened crust but this is unlikely to be the only mechanism for exhuming rocks from depths greater than about 20 km one or more of the following additional mechanisms may be involved 1 corner flow of low viscosity material trapped between the upper and lower plates in a subduction zone can cause upward flow of deeply buried rock and may explain some occurrences of high pressure tectonic blocks in melange this process does not however appear to be adequate to explain the exhumation of regional high pressure terrains 2 buoyancy forces acting directly on metamorphic rock bodies may cause them to rise relative to more dense surroundings this is likely to be the most important mechanism of exhumation of crustal rocks subducted into the mantle but cannot explain the emplacement of coherent tracts of high density metamorphic rock into shallow crustal levels some high pressure blocks emplaced at shallow levels in accretionary terrains may have been entrained in diapiric intrusions of low density mud or serpentinite 3 extension driven by the forces associated with contrasts in surface elevation may explain the exhumation and structural setting of many high pressure terrains extension may occur in the upper part of an accretionary wedge thickened by underplating or it may affect the whole lithosphere in a region of intracontinental convergence if surface elevation has been increased by the removal of a lithospheric root in the second case extension may be accompanied by magmatism and an evolution towards higher temperature during decompression of the metamorphic terrain

can turbidites be used to reconstruct a paleoearthquake record for the central sumatran margin turbidite paleoseismology aims to use submarine gravity flow deposits turbidites as proxies for large earthquakes a critical assumption being that large earthquakes generate turbidity currents synchronously over a wide area we test whether all large earthquakes generate synchronous turbidites and if not investigate where large earthquakes fail to do this the sumatran margin has a well characterized earthquake record spanning the past 200 yr including the large magnitude earthquakes in 2004 mw 9 1 and 2005 mw 8 7 sediment cores collected from the central sumatran margin in 2009 reveal that surprisingly few turbidites were emplaced in the past 100 150 yr and those that were deposited are not widespread importantly slope basin deposits preserve no evidence of turbidites that correlate with the earthquakes in 2004 and 2005 although recent flow deposits are seen in the trench adjacent slope basins and adjacent pairs of slope basin and trench sites commonly have different sedimentary records and cannot be correlated these core sites from the central sumatran margin do not support the assumption that all large earthquakes generate the widespread synchronous turbidites necessary for reconstructing an accurate paleoearthquake record

a geologic reconnaissance of the cycladic blueschist belt greece the cycladic blueschist belt consists of two distinctive segments separated by a broad zone of superposed granitic and high temperature metamorphic rocks the northern segment contains early metamorphic fold axes and parallel glaucophane lineations that trend 060 with a progressive increase in metamorphism toward the southeast the southern segment contains similar fold axes and glaucophane lineations that trend 010 with an apparent increase in metamorphism toward the northwest radiometric dating of metamorphic minerals from both segments give apparent ages of about 40 to 80 m y these data suggest the existence of late mesozoic or early cenozoic subduction zones in the aegean region that subsequently collided

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

the geology of the polymetamorphic complex of ios cyclades greece and its significance for the cycladic massif the geological structure of the island of ios cyclades greece is a dome consisting of an augengneiss core and a mantle of garnet mica schists that together form the basement which is overthrust by a marble schist series this series is mainly made up of meta volcanics and metamorphosed sediments presumably mesozoic in age it is a tectonically composed pile of marbles alternating with glaucophane schists actinolite schists and chlorite schists petrological relations and isotope dating indicate the polymetamorphic character of ios two alpine metamorphic phases m1 and m2 and relicts of a high grade metamorphic or magmatic phase mo that only affected the basement are demonstrated radiometric ages obtained for the basement confirm the interpretation that the mo phase is pre alpine the m1 and m2 were dated at 43 ma and 25 ma respectively the p t conditions of metamorphism are estimated as 9 11 kb and 350 to 400 c for the m1 phase and 5 7 kb and 380 420 c for the m2 phase the metamorphic history of the cyclades is discussed and it is suggested that pre alpine basement occurs also on sikinos and naxos