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

210pb derived sediment accumulation and mixing rates for the washington continental slope abstract total sediment accumulation rates g yr in four canyons indenting the washington continental shelf are about twice those on the nearby open slope even though canyons comprise less than 40 of the depositional area of the entire slope this is because 210 pb derived sediment accumulation rates g cm 2 yr for astoria and quinault canyons are 3 4 times greater than those for willapa and grays canyons and intermediate open slope areas supporting the hypothesis that columbia river derived solids are preferentially transported to these two canyons quinault canyon currently appears to be accumulating solids at rates much greater than its low long term accumulation rate which is attributed to turbidity currents transporting solids down this canyon roughly every 500 years the following four different approaches all show that mixing may cause 210 pb derived sediment accumulation rates for slope and canyon sediments to be 2 3 times higher than true accumulation rates 1 comparison between accumulation rates calculated from 210 pb profiles with and without surface zones in which mixing has obviously affected 210 pb distributions 2 comparison between 210 pb derived and independently determined long term accumulation rates 3 comparison between 210 pb derived accumulation and modern columbia river discharge rates 4 comparison between two and three layer steady state one dimensional diffusion advection decay models mixing coefficients for surface sediments calculated using a one dimensional two layer vertical eddy diffusion model show large differences within the region with most in the 3 30 cm 2 yr range mixing rates are several times larger in canyon sediments from 0 2 1 1 km water depth probably due to physical reworking processes erroneously neglected mixing at depth of no more than 5 of that calculated for the surface mixed layer can cause the 2 3 fold calculated overestimation of true sediment accumulation rates and 2 4 fold calculated underestimation of true mixing coefficients

u pb single zircon ages and geochemistry of metagranitoid rocks in the cycladic blueschists evia island implications for the triassic tectonic setting of greece abstract u pb zircon geochronology geochemical and microstructural analyses were carried out to a metagranitoid suite exposed in the blueschist unit of the attic cycladic zone on evia island concordant zircons from three metagranitoid samples yielded id tims u pb single grain ages of 234 1 2 ma 232 1 ma and 214 0 7 ma which are interpreted to constrain the intrusion of the igneous protolith in late triassic times these age data in combination with previously published early middle triassic protolith ages of meta igneous rocks from other greek islands support magmatic activity in the cycladic area throughout the triassic major and trace element whole rock analyses reveal that the granitic protolith of the evia metagranitoid suite is of a type affinity implying triassic magmatism in an extensional setting along the northern gondwanan margin rather than back arc extension above a subduction zone subsequent alpine subduction and related high pressure metamorphism led to pervasive non coaxial fabrics of the evia metagranitoid which indicate top to the e se shearing this alpine deformation took place under ductile viscous conditions at temperatures close to 450 500 c and differential stresses of 65 15 10 mpa

evidence for neotethys rooted within the vardar suture zone from the voras massif northernmost greece abstract three conflicting models are currently proposed for the location and tectonic setting of the eurasian continental margin and adjacent tethys ocean in the balkan region during mesozoic early tertiary time model 1 places the eurasian margin within the rhodope zone relatively close to the moesian platform a tethyan oceanic basin was located to the south bordering a large serbo pelagonian microcontinent model 2 correlates an integral serbo pelagonian continental unit with the eurasian margin and locates the tethys further southwest model 3 envisages the pelagonian zone and the serbo macedonian zone as conjugate continental units separated by a tethyan ocean that was sutured in early tertiary time to create the vardar zone of northern greece and former yugoslavia these published alternatives are tested in this paper based on a study of the tectono stratigraphy of a completely exposed transect located in the voras mountains of northernmost greece the outcrop extends across the vardar zone from the pelagonian zone in the west to the serbo macedonian zone in the east within the voras massif six east dipping imbricate thrust sheets are recognised of these units 1 4 correlate with the regional pelagonian zone in the west and related almopias sub zone by contrast units 5 6 show a contrasting tectono stratigraphy and correlate with the paikon massif and the serbo macedonian zone to the east these units form a stack of thrust sheets with unit 1 at the base and unit 6 at the top unstacking these thrust sheets places ophiolitic units between the pelagonian zone and the serbo macedonian zone as in model 3 additional implications are first that the paikon massif cannot be seen as a window of pelagonian basement as in model 1 and secondly jurassic andesitic volcanics of the paikon massif locally preserve a gneissose continental basement ruling out a recently suggested origin as an intra oceanic arc we envisage that the almopias vardar ocean rifted in triassic time followed by seafloor spreading the almopias ocean was consumed beneath the serbo macedonian margin in jurassic time generating subduction related arc volcanism in the paikon massif and related units ophiolites were emplaced onto the pelagonian margin in the west and covered by late jurassic pre kimmeridgian conglomerates other ophiolitic rocks formed within the vardar zone ano garefi ophiolite unit 4 in latest jurassic early cretaceous time and were not deformed until early tertiary time the vardar zone finally sutured in the early tertiary creating the present imbricate thrust structure of the voras mountains

neogene recent extension on the eastern flank of mount olympus greece abstract the olympus massif of ne greece comprises metamorphosed and deformed triassic and cretaceous eocene carbonates considered to represent part of the passive southwestern margin of neotethys which separated the apulia plate of mainland greece from southern europe in the mesozoic ocean closure in the early tertiary led to subduction of this passive margin as a result of which the olympus carbonates were tectonically overridden in the eocene by a series of thrust sheets consisting of locally high p t blueschist metamorphosed continental margin sediments basement granitoid gneisses and ophiolitic rocks following collision uplift of the olympus carbonates by 6 8 km was accomplished by early neogene ductile and late neogene recent brittle normal faulting which exposed the carbonates in the form of a structural window through the overriding thrust stack the focus of this exhumation occurred on the eastern flank of the massif where a thick calc mylonite with down to the east sense of shear indicators and a prominent zone of nnw to nw trending brittle normal faults separate the carbonates from telescoped structurally overlying units published 40 ar 39 ar microcline ages that indicate a thermal perturbation close to the contact zone in excess of 100 150 c at 16 23 ma early miocene are taken to date the onset of ductile extension and imply long term uplift rates of 0 4 to 1 km m y degradation of pleistocene glacial features on the olympus massif and the presence on its eastern piedmont of deeply incised streams erosional terraces and fault scarps that offset the sedimentary deposits of three cycles of pleistocene glacial deposition units 1 3 testify to its continuing uplift a prominent frontal fault offsets unit 2 by 150 m and several subsidiary nw trending normal faults with a cumulative displacement of 130 m offset a paleosol developed on unit 1 kinematic indicators indicate normal dip slip movement cumulative fault displacement for unit 1 exceeds 277 m yielding a minimum uplift rate of 1 3 mm yr given the oxygen isotope stage 7 mindel riss age of 210 ka proposed for the unit 1 paleosol cumulative offset of 196 m for the paleosol developed on unit 2 yields an uplift rate of 1 6 mm yr given its proposed isotope stage 5e riss wurm age of 125 ka this estimate is supported by longitudinal valley profile data that document 200 m of stream incision since unit 2 deposition and show the offset as reflecting uplift of the olympus massif rather than subsidence of the adjacent gulf of thermaikos assuming 1 8 ma for the base of the pleistocene these rates yield a total uplift range for the quaternary of 2 3 4 1 km consistent with the present 2 6 km height of olympus above the exposed frontal fault neogene uplift of olympus was likely facilitated by extension accompanying the opening of the aegean back arc basin during the miocene as a result of the southward retreat of the hellenic subduction zone for the pliocene recent uplift was likely facilitated by extension linked to the termination of dextral motion at the western end of the north anatolian fault associated with the westward tectonic escape of anatolia

lead 210 sediment geochronology in a changing coastal environment abstract sediment accumulation rate studies utilizing excess 210 pb and 137 cs were conducted as part of recent investigations of biogeochemical cycling at a single site in cape lookout bight a rapidly changing coastal basin on the outer banks of north carolina u s a cores three meters in length reveal a depositional history for the bight interior characterized by a gradual transition in texture from coarse grained to fine grained material over the period 1946 1979 this transition is controlled by progressive enclosure of the bight by an active northerly migrating recurved spit the textural gradation is periodically interrupted by layers of well sorted sand associated with major storm events lead 210 data indicate that the upper meter of the sediment has accumulated at a rate of 3 35 to 4 71 g cm 2 yr 1 or approximately 8 4 to 11 8 cm yr 1 at o 0 84 below 120 cm depth dilution of clay and silt by low activity sand necessitates correction of the 210 pb profile in order to establish a geochronology grain size 210 pb distribution measurements at three depths reveal that the specific activity dpm g 1 of clay is 3 2 times that of silt and 24 7 times that of sand corrections of bulk sediment excess 210 pb activities based on these measurements lead to dates for textural changes which are consistent with charted changes in basin morphology and major storm events sixteen 137 cs measurements between 33 241 cm depth reveal a peak activity at 105 115 cm and indicate a minimum sedimentation rate of approximately 2 7 g cm 2 yr 1

geochemical constraints on the provenance and depositional setting of sedimentary rocks from the islands of chios inousses and psara aegean sea greece implications for the evolution of palaeotethys the provenance and depositional setting of late palaeozoic and early mesozoic clastic sediments from the eastern aegean archipelago are examined here for the first time using whole rock geochemistry and composition of detrital chrome spinel major and trace element data for late palaeozoic and permo triassic clastic sediments from the lower and upper units of chios are compatible with an acidic to intermediate source minor input of ultra mafic detritus and recycling of older sedimentary components chondrite normalized ree profiles are uniform with light ree enrichments la n yb n c 7 7 negative eu anomalies eu eu c 0 67 and flat heavy ree patterns gd n yb n c 1 5 indicating an upper continental crustal source and or young differentiated arc material detrital chrome spinel from the clastic sediments of chios has cr number cr cr al values between 0 29 and 0 89 and mg number mg mg fe 2 values between 0 24 and 0 70 suggesting a probably mixed ultra mafic source involving ridge peridotites mid ocean ridge type fore arc peridotites and island arc basalts the metasediments from the islands of inousses and psara have similar whole rock chemical signatures to those of chios although no evidence was found for an ultra mafic source we conclude that both the late palaeozoic sediments from the lower and upper units of chios and the metasediments from inousses and psara were deposited in a continental island arc setting until at least late permian times probably at a single palaeotethyan margin they are interpreted to be allochthonous tectonically transported to their present position by late mesozoic to cenozoic orogenic processes

plutonium 241am and 137cs ratios inventories and vertical profiles in washington and oregon continental shelf sediments abstract continental shelf sediments from nine locations off washington and oregon have 239 240 pu inventories which average 8 0 2 6 mci km 2 the columbia river and seawaters advecting over the shelf supply pu which is removed to underlying sediments principally through scavenging by inorganic paniculate matter mass balance calculations argue that less than 20 percent of the advected pu need be scavenged from the water column to balance river input and total shelf sediment inventories the percentage of the pu removed through scavenging is consistent with observed participate concentrations in shelf waters and published sediment water distribution coefficients no marked separation of pu from 137 cs is observed with depth in pacific shelf sediments as has been reported in atlantic coastal sediments this interocean distinctness can be explained by differences in particle mixing and downward diffusion of cs in sediments of varying porosities the transuranic inventories and pu cs ratios in the pacific sediments do not support the hypothesis of livingston and bowen that pu is remobilized within the sediment column by complexone formation with principally organic substances excess 210 pb 239 240 pu inventory ratios in eight representative cores from the washington shelf average 100 19 even though absolute values of both inventories vary by much larger factors this reasonably constant ratio for a given water depth permits estimation of total pu inventories and prediction of sites of unusual pu accumulation from data on the more easily measured natural radionuclide

fine grained sediment deposition on mussel beds in the oosterschelde the netherlands determined from echosoundings radio isotopes and biodeposition field experiments sedimentation rates of 5 20 cm year 1 were calculated from 137 cs 134 cs activity profiles and echosoundings in a mussel cultivation area in the western part of the oosterschelde sedimentation rates based on 210 pb activity profiles are far too low mainly due to the deposition of aged sediment i e sediment eroded elsewhere inside the basin and not fully enriched with 210 pb at the moment of deposition also specific adsorption to the finest sediment components mixing winnowing and mobilization of the caesium have affected the lead and caesium profiles field experiments on mussel plots showed that mussels deposit 5 10 cm of fine grained sediment during the summer this biodeposition about equals the settling from flocculation in the water column micro fabric microscope studies revealed that pellets do not dominate the sediments indicating that some of the pellets are broken down or resuspended

thrust faults and extensional detachment faults in cretan tectono stratigraphy implications for middle miocene extension abstract the revised tectono stratigraphy of crete and especially of the phyllites quartzites complex demonstrated the distinction of the probable paleozoic low medium grade metamorphic rocks of the arna unit from the underlying permo triassic phyllites and associated carbonate sediments trypali facies of western crete unit as well as the overlying permo triassic phyllites and associated sediments of the tyros ravdoucha beds at the base of the tripolis unit the pre existing mixture of the above tectono stratigaphic units in a single complex created a number of misinterpretations as far as stratigraphy metamorphism and interpretation of low angle faults as thrusts or detachments especially in cases where the inferred tectonic contact concerns the transition between the tyros beds and the base of the tripolis carbonate platform there is no structural omission and therefore the contact represents a minor disharmonic sliding surface and not a detachment based on the revised tectono stratigraphic analysis the determination of the structural omission for each tectonic contact was possible and several detachments were described for the first time footwall rocks of the detachments comprised several tectonic units usually from the lower nappes and hanging wall rocks comprised several tectonic units usually from the upper nappes the detachment may separate not only metamorphosed units in the footwall mani western crete arna from non metamorphosed units in the hanging wall tripolis pindos and higher nappes but also all other possible combinations from the cretan nappe pile extension in crete started in the middle late miocene with the formation of extensional detachment faults the reported extensional structures of oligocene to early miocene age do not correspond to crustal extension of crete but to localized shear zones related to nappe stacking and the exhumation of metamorphic rocks extensional detachments in crete form a tectonic horst through two oppositely dipping e w trending zones one dipping north related to the opening of the cretan basin and the other dipping south related to the formation of the messara supra detachment basin the deformation history of units within crete can be summarized as i compressional deformation producing arc parallel east west trending south directed thrust faults in oligocene to early miocene time ii extensional deformation along arc parallel east west trending detachment faults in middle miocene time with hanging wall motion to the north and south and iii late miocene quaternary transtensional deformation along high angle normal and oblique normal faults that disrupt the older arc parallel structures

sedimentary processes in the inner new york bight evidence from excess210pb and239 240pu abstract particle reactive radionuclides were determined in sediments from the inner new york bight to trace transport and storage of fine grained sediments and associated reactive materials seven sediment cores 20 50 cm in length were analyzed for water content loss on ignition loi and excess 210 pb three of these were also analyzed for 239 240 pu excepting some depth horizons in a core from a dredge spoil dumpsite every sample analyzed contained excess 210 pb variations in the concentration of excess 210 pb with depth in the sediment at all stations correlated strongly with loi which apparently traces that fraction of the sediment which is active in removing reactive elements from the water column in the cores analyzed for 239 240 pu every sample contained finite pu and pu concentrations correlated strongly with excess 210 pb the radionuclide distributions may be simply viewed as products of steady state sediment accumulation or of mixing geochemically reasonable accumulation rates are very high 0 5 2 6 g cm 2 y and could probably only be sustained by offshore transport of dumped materials at the other extreme the relationships between excess 210 pb and loi are compatible with rapid mixing of a 210 pb carrier phase traced by loi into the pre existing substrate with little or no actual accumulation other non steady state processes such as sediment gravity flow could also explain the observed distributions measured sediment inventories dpm cm 2 of excess 210 pb and pu at these stations are greatly in excess of those supportable by direct atmospheric deposition lateral supply is required incorporation of sedimentary fines into the sand substrate could make the inner new york bight an important repository of reactive materials

the effect of geological anisotropies on the detectability of seismic electric signals abstract the detectability of seismic electric signals was examined in relation to the geological anisotropies both at the large scale of geotectonics and neotectonics and at the smaller scale of electric stations the distribution of the detected seismic events in the cases of the ioannina and assiros stations showed a strong dependence upon the geotectonic zonation and especially upon the ophiolite suture zones of north pindos and almopia axios vardar the major neotectonic transcurrent faults did not show an important effect keratea station and especially point a on a granitic dyke showed an extraordinary detectability independant of the geotectonic zonation attributed to the local anisotropy and to its connecton with batholiths at depth within the aegean paleo volcanic arc of upper miocene age

temperature time history of subducted continental crust mount olympos region greece in the mt olympos region of northeastern greece continental margin strata and basement rocks were subducted and metamorphosed under blueschist facies conditions and thrust over carbonate platform strata during alpine orogenesis subsequent exposure of the subducted basement rocks by normal faulting has allowed an integrated study of the timing of metamorphism its relationship to deformation and the thermal history of the subducted terrane alpine low grade metamorphic assemblages occur at four structural levels three thrust sheets composed of paleozoic granitic basement and mesozoic metasedimentary cover were thrust over mesozoic carbonate rocks and eocene flysch thrusting and metamorphism occurred first in the highest thrust sheets and progressed downward as units were imbricated from ne to sw 40ar 39ar spectra from hornblende white mica and biotite samples indicate that the upper two units preserve evidence of four distinct thermal events 1 293 302 ma crystallization of granites with cooling from 550 c to 20 km extension in the olympos region was synchronous with extension in the mesohellenic trough and the aegean back arc and concurrent with westward progressing shortening in the external hellenides

palaeozoic early tertiary tethyan evolution of melanges rift and passive margin units in the karaburun peninsula western turkey and chios island greece

the metamorphism and migmatization of the xanthe echinos metamorphic complex central rhodope greece the xanthe echinos metamorphic complex in the central hellenic rhodope records early tertiary convergent tectonics on the eurasian continental margin of neotethys it consists principally of layered gneiss and migmatite with minor amphibolite and calc silicate rocks three metamorphic events are recognised a high pressure eclogite event cretaceous medium pressure barrovian type metamorphism eocene and later low pressure greenschist facies metamorphism petrographic composition and electron microprobe analysis of minerals in forty four samples of gneiss and migmatite shows that the eocene barrovian event is characterized by replacement of clinopyroxene by pargasitic hornblende in clinopyroxene garnet and clinopyroxene edenitic hornblende assemblages the compositional variation and textures of the amphiboles suggest initial growth of edenitic hornblende zoned to hornblende and development of syn to late tectonic pargasitic hornblende under higher temperature conditions associated with migmatization the textures zoning and paragenetic relationships of sodic calcic amphiboles are consistent with uplift accompanied by synmetamorphic deformation partial melting in the migmatites involved plagioclase k feldspar quartz the solidification products of the produced melt are present in the form of quartz monzonitic leucosome layers and is also represented in syntectonic plutons metamorphic pressures of 7 5 8 5 kbar att 600 c were estimated from garnet clinopyroxene pairs in gneisses adjacent to the migmatites amphibole plagioclase thermometry of migmatite samples yielded temperatures of 728 746 c at p 8 5 kbar the activity of h2o was probably less than 1 0 in the partially melted rocks the geothermobarometric results indicate an increase of the geothermal gradient during uplift probably related to intrusion of basic magma into the crust and or changes in geothermal gradient associated with crustal thickening

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

210pb derived sediment accumulation and mixing rates for the greater puget sound region abstract recent sediment accumulation rates of 46 1200 mg cm2 yr are calculated from excess 210pb activity profiles in 44 sediment cores from 27 sites in the greater puget sound region rates calculated for nine stations in the deeper waters of central puget sound average 480 mg cm2 yr and are greatest between seattle and tacoma near the southern end of this region the standard error of this mean is 113 mg cm 2 yr magnitudes and geographic trends of 210pb derived accumulation rates agree with limited data on sediment inputs and transport paths their accuracy is further supported by several independent approaches including comparison with particle fluxes collected in year long series of sediment trap deployments at two sites accumulation rates are calculated assuming no mixing beneath surface mixed layers of 2 22 cm sediment mixing coefficients in these surface layers average at least 43 cm2 yr four times greater than those reported in open washington coast sediments the difference is attributed to the greater benthic biomass in puget sound sediments particle residence times in surface mixed layers vary from 1 5 to 68 years and introduce corresponding uncertainties in ages of horizons beneath the mixed layers for most of this region these residence times will cause a 20 30 year time lag in achieving an equivalent response of surface sediment chemical concentrations to changes in concentrations in freshly depositing particles for constituents whose stability and phase associations resemble those of 210pb these time lags limit the ability of sediment chemistry monitoring programs to recognize recent changes in composition and fluxes of chemicals to sediments recent fluxes calculated from the product of surface sediment chemical concentration and accumulation rates will be inaccurate for chemicals if their input concentrations have changed in the last 20 30 years

alpine high pressure metamorphism at the almyropotamos window southern evia greece the alpine orogenic belt of the hellenides has been strongly reworked by ductile and brittle extensional tectonics extensional structures have affected the central aegean region and obliterated much of the original orogenic architecture since at least early miocene times in the area of almyropotamos on the island of evia flanking the western part of the aegean a unique remnant compressional nappe stack involving tertiary metamorphic rocks has been preserved this nappe sequence comprises a high pressure rock unit on top of a lower grade unit the upper unit south evia blueschist belt is thought to be the westward continuation of the cycladic blueschist belt metamor phosed at high pressure conditions during late cretaceous eocene times the underlying unit the almyropotamos unit is a continental margin sequence covered by a flysch and containing lutetian nummulites indicating that this unit accumulated sediments until at least late eocene times in the present study we analyse the petrology of the almyropotamos nappe stack and define the p t conditions of each of the different rock units exposed there the presence of glaucophane law sonite rimmed by epidote and jadeite 70 mol suggest that peak p t conditions in the south evia blueschist belt reached approximately 10 12 kbar and 350 450 c unlike previous studies which estimated that the underlying almyropotamos unit reached only greenschist facies conditions glau cophane relics and si rich phengites were found by us in this unit these indicate that high pressure metamorphism and crustal thickening in this part of the aegean lasted until at least the late eocene or early oligocene we note that in this respect the architecture of southern evia resembles that of north ern greece olympos ossa our structural data indicate that rock units in the almyropotamos area record different folding phases with the south evia blueschist belt having a more complex fold his tory than the underlying almyropotamos unit the entire nappe stack shares large scale folds which are e w trending and locally overturned to the south and which may represent at present coordi nates n s contraction and nappe transport

the pelagonian zone in greece a polyphase deformed fragment of the cimmerian continent and its role in the geotectonic evolution of the eastern mediterranean data from macedonia greece correlated with those reported from the pontides turkey indicate that the pelagonian zone of the hellenides represents a fragment of the cimmerian continent which separated the paleo tethys and neo tethys oceans a permo triassic age is suggested for separation of the paleozoic continent and initial rifting in the two oceanic basins as the pelagonian zone represented the northwestern european end of the cimmerian continent the paleo tethys and the northern branch of neo tethys would have been very close to each other on either side of this zone thus both oceans at their european end closed within a short time of each other in the late jurassic early cretaceous the sequential development of the two oceans outlines a model for the geotectonic evolution of the internal hellenides in which a correlation of thrusting and folding phases is also given

sediment transport part iii bed forms and alluvial roughness a method is presented that makes the classification of bed forms the prediction of the bed form dimensions and the effective hydraulic roughness of the bed forms feasible the proposed relationships are based on the analysis of reliable flume and field data a verification analysis using about 1 500 alternative reliable flume and field data shows good results in predicting the hydraulic roughness friction factor for field conditions the proposed method yields considerably better results than previously proposed methods which are reviewed here the proposed method has also been used to predict the flow depth and the total bed material load

development of concepts concerning the genesis and emplacement of tethyan ophiolites in the eastern mediterranean and oman regions this article uses evidence mainly from the eastern mediterranean and oman to help understand the origin and emplacement of ophiolites field studies in these regions emphasize the diversity of ophiolite related sedimentary and tectonic processes topics to be discussed here include the sedimentary covers of ophiolites their metamorphic soles related melanges and emplaced continental margin slope rise units modes of ophiolite emplacement will also be considered and tectonic reconstructions that have a direct bearing on the origin and emplacement of ophiolites the writer argues that there is compelling evidence that many ophiolites formed by spreading above intraoceanic subduction zones evidence from their intact sedimentary covers however indicates that such subduction was only incipient in most cases as directly associated volcanic arcs or back arc basins are rare metamorphic soles record fragments of oceanic lithosphere derived from settings ranging from open ocean to continental slope rise settings underlying melanges record the subduction of most of the ocean lithosphere formed at spreading ridges continental margin units beneath ophiolites demonstrate that these ophiolites were formed in ocean basins that were mainly initiated by continental rifting in the eastern mediterranean and oman regions ophiolite emplacement was commonly achieved by trench margin collision although strike slip transpression and large scale accretion along subducting margins played a role in some cases taking account of the mesozoic palaeotectonic setting of the eastern mediterranean region it is widely believed that ophiolites of two main ages mid jurassic and late cretaceous were formed in several small oceanic basins separated by rifted microcontinents the history of tethys in pre mesozoic time remains more open to question lastly giant subduction related ophiolites as in oman cyprus or the balkans may not be forming anywhere in the world ocean today but may instead relate to rare events in earth history when regional to global plate boundaries were drastically reorganised

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

complex basin evolution in the gokova gulf region implications on the late cenozoic tectonics of southwest turkey southwestern turkey experienced a transition from crustal shortening to extension during late cenozoic and evidence of this was recorded in four distinct basin types in the mugla gokova gulf region during the oligocene early miocene the upper slices of the southerly moving lycian nappes turned into north dipping normal faults due to the acceleration of gravity the kale tavas basin developed as a piggyback basin along the fault plane on hanging wall blocks of these normal faults during middle miocene a shift had occurred from local extension to n s compression transpression during which sediments in the eskihisar tinaz basins were deposited in pull apart regions of the menderes massif cover units where nappe slices were already eroded during the late miocene pliocene a hiatus occurred from previous compressional transpressional tectonism along intermountain basins and yatagan basin fills were deposited on menderes massif lycian nappes and on top of oligo miocene sediments plio quaternary marked the activation of n s extension and the development of the e w trending mugla gokova grabens co genetic equivalents of which are common throughout western anatolia thus the tectonic evolution of the western anotolia during late cenozoic was shifting from compressional to extensional with a relaxation period suggesting a non uniform evolution

orogenic evolution of the hellenides new aspects this progress report is based on investigations of the tectonometamorphic development of crystalline complexes and is restricted to a few key problems of the hellenides these results reveal the mechanisms of intracratonic tectonics remobilization of continental crust and intracrustal detachment throughout the evolution of the hellenides

the effect of sediment mixing on pb 210 accumulation rates for the washington continental shelf abstract nine cores from the washington continental shelf were examined by radiochemical techniques in order to evaluate the effect of mixing on the calculation of sediment accumulation rates from pb 210 profiles th 234 profiles indicate mixing coefficients of 140 cm 2 yr 1 for the seabed offshore from the columbia river and 47 cm 2 yr 1 for the seabed of the mid shelf silt deposit 75 km north of the columbia river these large mixing coefficients demonstrate that particles can penetrate to the base of the intensely mixed surface layer 10 cm within one year after emplacement at the seabed surface observed depths of cs 137 penetration within the seabed are compared with depths predicted from the surface mixed layer thickness and the pb 210 accumulation rate the observed and predicted depths agree well at all but one station at this station a combination of th 234 co 60 pb 210 and cs 137 profiles suggests that active mixing occurs below the intensely mixed surface layer the agreement of pb 210 and cs 137 data at the other stations however indicates a general absence of deep mixing on the washington shelf thus the apparent accumulation rates calculated from pb 210 profiles below the intensely mixed surface layer on the washington shelf generally reflect the true rates of sediment accumulation

erosion problems in alexandroupolis coastline north eastern greece this paper deals with the coastal erosion processes and the related problems around the city of alexandroupolis ne aegean sea n greece the area is very fast developing as the city is an important port and a summer resort center in se balkans and will become soon a transportation and energy center as well the coastline under study exhibits an east west orientation and has a length of more than 50 km the spatial distribution and the characteristics of the changes in the shoreline were studied by comparing old and new air photographs and topographic maps as well as through repeated series of field observations and local measurements regarding the erosion process from these studies it was concluded that the greater stretch of the western part of the coast under consideration is of moderate to high relief with a considerable participation of coastal cliffs it consists of conglomerates of varying granulometry and consistency and is under moderate to severe erosion process the erosion phenomena in the western part of the coast may be attributed primarily to strong s sw winds blowing in the area and to trapping of sediments by alexandroupolis port breakwaters the port stops or and diverts the sediments to the open sea and to the east to west longshore sea current prevailing in the area the eastern stretch of the coast is a plain area formed by sandy silty sediments being a part of the river evros delta it is under deposition and accretes seawards the majority of the coasts under consideration are classified as coasts of high wave energy potential hard structures as shore protection measures have been constructed in some places but they were proved in rather short time period ineffective and suffered extensive failures thus it is argued that for a long term cost effective tackling of the various erosion problems on any stretch priority must be given to soft engineering measures although certain hard measures carefully selected and locally implemented can contribute to forming a rational combination of protection mitigation measures besides the development pressures in the coastal zone have to be confronted in a sustainable way through new integrated coast management regulations

back arc extension and denudation of mediterranean eclogites eclogite facies rocks exposed in mediterranean back arcs are delimited from above by low angle normal faults and detachments nevertheless our work demonstrates that these extensional structures associated with back arc extension played only a limited role in removing the overburden from above the eclogites extension in mediterranean back arcs began in the late oligocene or early miocene but the pressure temperature time p t t paths of eclogite facies rocks exposed in these areas indicate that a major part of the overburden several tens of kilometers has been removed from above these rocks prior to the oligo miocene we show that the time period bracketed between the peak of eclogite metamorphism eocene in the central aegean probably upper cretaceous in corsica and the betics and the onset of back arc extension in the oligo miocene was characterized by thrust faulting in the central aegean corsica and the betics eclogite bearing units were partly unroofed and then overthrusted lower pressure units we emphasize that with one exception tinos island greece the entire inventory of extensional contacts operated subsequently to the overthrusting of the eclogites above the lower grade sequences thus mediterranean back arc extension lags behind a major part of the denudation process and is superposed on orogenic wedges that contain eclogite facies rocks at relatively shallow structural levels we emphasize that the mode of occurrence of eclogites in mediterranean back arc regions involves a continuum of in situ crustal accretion below the eclogites widespread p t paths that show cooling or isothermal decompression and lower grade rocks at the bottom of the structural pile thus instead of reflecting whole crust back arc extension the tectonic style associated with the denudation of mediterranean eclogites better fits an active accretionary wedge setting this is similar to the mode of occurrence of eclogite facies rocks in mountain belts such as the western alps where decompression was synorogenic and back arc extension played no role

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