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

rate of outward growth of the mediterranean ridge accretionary complex abstract the position as a function time of the deformation front on the southwest flank of the mediterranean ridge accretionary complex is constrained as follows 1 a the deformation front is now active 2 b the site of core ban84 05gc was still near the abyssal plain when displaced shallow water benthic foraminifera of inferred african provenance were redeposited within an upper pliocene age unit 3 c the site of core ban84 05gc on the outer flank of the mediterranean ridge was already within the topographically rugged accretionary complex when a pliocene debris flow was emplaced 4 d dsdp site 125 had already been uplifted into a topographically elevated position when lower pliocene pelagic ooze was deposited 5 e a gypsum bearing breccia in dsdp site 125 requires that the site was either on the abyssal plain or within the tectonically active outer perimeter of the accretionary complex during the messinian salinity crisis 6 f dsdp site 377 had already been uplifted into a topographically elevated position when middle miocene age pelagic marl was deposited 7 g dsdp site 377 was still on or near the abyssal plain when early to lower middle miocene age smectite bearing turbidites of inferred african provenance were deposited and 8 h the mediterranean ridge began to grow by offscraping against a backstop formed by the alpine nappes of the hellenic arc at the time that subduction began 33 ma together these constraints define a range of potential growth curves for the mediterranean ridge with a rate of outward growth of approximately 0 5 to 2 cm yr this growth rate is faster than that inferred for most other modern accretionary prisms both as an absolute value and as a fraction of the subduction velocity an unusually thick incoming section and or an unusually weak evaporitic decollement may contribute to the rapid growth rate the inferred age of accretion does not increase linearly with distance from the deformation front rather there is an apparent acceleration of the rate of outward growth through time this observation may reflect a true acceleration of growth rate in response to the onset of back arc extension in the overriding plate aegean sea and or in response to the development of a weak basal decollement following the introduction of halite into the incoming stratigraphic section alternatively the non linearity of the age vs distance curve may indicate that shortening of the offscraped sediments continues across the breadth of the mediterranean ridge rather than being confined to the outer flank

strain distribution over the east mediterranean ridge a synthesis incorporating new sea beam data abstract we present the results of several multi narrow beam sea beam traverses of the mediterranean ridge on board r v jean charcot these results can be considered to be complementary in resolution and coverage to the previously published long range side scan sonar gloria results a characteristic of the mediterranean ridge is the presence over about half of its surface of an extensive fold system affecting the messinian and plio quaternary cover which is dissected by conjugate strike slip faults the resolution of sea beam was used to map the main characteristics of folding and faulting this analysis together with previously available data enables us to define the strain pattern over the mediterranean ridge we thus now have an overall view of the strain pattern from a marginal basin aegea through the hellenic trench and adjacent sea floor to the opposite continent the bottom of the hellenic trench is a boundary between an extensional domain to the north and a compressional one to the south the southern domain is strongly affected by the presence of the lybian promontary it is related to the formation of an accretionary ridge due to the inability of the upper 3 4 km of sediments to subduct this ridge is similar to the accretionary prism but it is much wider with respect to its height probably because of the existence of a decollement over a level of overpressure the hellenic trench then is in the situation of a fore arc basin its origin is due to the fact that the aegean continental slope is not vertical but rather has a small 4 dip as a result a sedimentary wedge symmetric but shorter than the main accretionary wedge develops over the buried portion of the slope it is characterized by landward thrusts such an origin probably applies to fore arc basins in general

permian early mesozoic tectonism and continental margin formation in israel and its implications for the history of the eastern mediterranean summary the early mesozoic tectonic reorganization of the tethys region also affected the levant area here two processes were superimposed a the pattern of long wavelength vertical motions of the arabo nubian platform changed in the late permian when israel and nearby areas began to subside b rifting occurred in this subsiding area probably in several phases late anisian and ladinian carnian norian and liassic differential movements reached 2 3 km and magmatism occurred in the liassic and perhaps also in the triassic the tectonism was strongly felt up to 50 km landward of the present coast the crust was thinned and modified under the present continental margin and in the main rifts passive margin conditions were established in late liassic times over the previously faulted area later in the jurassic a carbonate shelf was constructed along this subsiding margin its basinward edge was 1 1 5 km high which shows that the adjacent se mediterranean was already a deep sea hence this basin and its passive margin are considered to have been shaped by the early mesozoic rifting which is recognized in israel the rifting process probably signifies oblique separation of the tauride block from the levant part of gondwana

three dimensional controls on subsidence of a foreland basin associated with a thrust belt recess black warrior basin alabama and mississippi tectonic transport from different directions and convergence of separate thrust belts at structural recesses impart three dimensional variations to the pattern of foreland basin subsidence assuming approximately uniform flexural rigidity of the lithosphere subsidence is directly controlled by the geometry and density of the separate thrust loads and flexural deformations caused by the loads interfere within the recess for example the black warrior foreland basin which is located in mississippi and alabama within a recess in the appalachian ouachita orogen formed in response to two separate thrust loads 1 the ouachita accretionary prism along the southwest side of the basin and 2 thrust imbricated passive margin rocks in the appalachian thrust belt along the southeast side of the basin the subsidence history differs along two profiles each perpendicular to the appalachian and ouachita thrust fronts subsidence of the foreland basin began in middle mississippian meramecian time in response to northeast directed translation of the ouachita accretionary prism subsequently northwest directed appalachian thrusting began in middle early pennsylvanian morrowan time subsidence curves from the profile perpendicular to the ouachita prism show a clear progression of increasing subsidence rates and amounts toward the thrust front whereas curves from the profile perpendicular to the appalachian belt indicate out of plane effects from the ouachita thrust front and a later increase in subsidence toward the appalachian thrust front the major implication of this work is that the three dimensional geometry of a foreland basin within a thrust belt recess includes diachronous interfering elements

role of the tectonic facies concept in orogenic analysis and its application to tethys in the eastern mediterranean region abstract the purpose of this paper is to advocate the use of a tectonic facies concept which aids systematic and objective analysis of orogenic belts the tectonic facies concept as discussed here focuses on the recognition of discrete tectonic settings mainly those exposed at high crustal levels in orogenic belts application of the tectonic facies concept can help field geologists to relate plate scale processes to outcrop geology tectonic facies are recognised based on knowledge of the modern oceans and margins and well constrained land settings tectonic facies analogous to sedimentary facies can be identified from integrated sets of field data and related laboratory studies a number of tectonic facies models can be recognised in this way their identification aids interpretation and comparisons of orogenic belts palinspastic reconstructions require additional information particularly age kinematic and palaeomagnetic data in this paper the tectonic facies concept is tested by application to a well documented mainly high level orogenic segment tethys in the eastern mediterranean area and is found to be an effective way both of the describing and interpreting this region other methods of tectonic analysis e g recognition of tectono stratigraphic terranes may also be found useful in certain settings and can be used in conjunction with the tectonic facies concept

age variation in the source of the diapiric mud breccia along and across the axis of the mediterranean ridge accretionary complex abstract pleistocene or younger mud diapirism is recorded along the arcuated crest of the mediterranean ridge accretionary complex over a distance of more than 450 km the extruded mud supported breccia named mud breccia is poorly fossiliferous but the matrix may be dated as late aptian to albian and late burdigalian to langhian in age based on the calcareous plankton content calcareous nannofossils and planktonic foraminifera diagnostic of other ages are sparse within the two above mentioned major assemblages they indicate the presence of sediments attributable 1 to the santonian and cenomanian which occur in association with the mid cretaceous assemblages toronto unnamed and aros domes and 2 to the serravallian which occur in association with the late burdigalian langhian assemblages in the gelendzhik dome aptian albian to late cretaceous sediments are pelagic in origin and are similar to the scisti a fucoidi and scaglia rossa formations well known from continental italy mixed dolomitic clasts and crystals also occur within the matrix indicating the presence of portions of the evaporitic sequence of messinian age in four cores from the western locations single very rare plankton specimens indicative of other ages different from those mentioned above also occur within the matrix at various places they are interpreted as reworked primarily within the late burdigalian langhian sediments the age of the emplacement of the breccia should be older than the middle pleistocene as supported by the occurrence of clasts of this age in the mud breccia and is still an ongoing process at least in the napoli dome

palaeomagnetic evidence for clockwise rotations related to dextral shear along the southern troodos transform fault cyprus abstract the southern troodos arakapas fault represents a late cretaceous oceanic fracture zone which was locally disrupted during late cretaceous eocene palaeorotation of the troodos microplate opinions are divided as to the sense of displacement along the transform fault and the exact timing of initiation of palaeorotation palaeomagnetic studies of turonian zeolite facies lavas and sediments exposed within the transform domain have revealed considerable variations in the declination of remanent magnetisation between sites along the arakapas fault belt the western margin of the limassol forest complex and the eastern flank of the troodos ophiolite at seven sites clockwise rotation of fault blocks has occurred about steeply inclined axes one fault block at the western end of the arakapas fault belt has experienced a net anticlockwise rotation while at six other sites only simple tilting about sub horizontal axes is indicated the overall clockwise sense of block rotation and initial dyke strikes calculated at three sites are consistent with right lateral slip along the transform cross cutting relationships revealed by the analysis of one site demonstrate that these rotations took place during crustal genesis and are not a product of post spreading disruption of the fracture zone sites located further south in the eastern limassol forest complex show no relative rotation with respect to the main troodos ophiolite to the north and have experienced only simple tilting however if our results are considered in conjunction with existing palaeomagnetic data from the area it appears that the entire area lay within a complicated zone of localised and predominantly clockwise block rotations produced by dextral slip along the transform some areas were rotated by over 100 about steeply inclined axes whereas others experienced only simple tilting the whole area was later subjected to a bulk 90 anticlockwise rotation along with the troodos microplate data obtained from the umbers and radiolarites perapedhi fm exposed on the eastern flank of the limassol forest block indicate that at least 30 and possibly up to 45 of this 90 rotation took place over a maximum of 15 ma

eratosthenes seamount collisional processes in the easternmost mediterranean in relation to the plio quaternary uplift of southern cyprus important new light is shed on subduction and incipient collisional processes in the easternmost mediterranean notably the plio quaternary uplift of the troodos ophiolite from new geophysical information collected during a cruise of the r v gelendzhik in july 1993 as part of the training through research programme the data collected over the eratosthenes seamount formed part of the site survey work for leg 160 of the ocean drilling program scheduled for spring 1995 the main results are that the eratosthenes seamount is in the process of actively subsiding breaking up and being thrust beneath both cyprus to the north and the levantine basin to the south northwards thrusting appears to post date the messinian when evaporites accumulated around the lower flanks of a pre existing seamount feature comparison with the geology of southern cyprus and offshore areas suggests a causative link between northward underthrusting of the eratosthenes seamount and late pliocene mid quaternary uplift of southern cyprus focused on the centre of the troodos ophiolite

the eastern and western ends of nankai trough results of box 5 and box 7 kaiko survey abstract seabeam mapping and detailed geophysical surveying have been conducted over the eastern and western ends of the nankai trough the eastern survey covers the transition between the large izu bonin izu ogasawara ridge collision with honshu and the nankai trough subduction it includes a northeast trending basement ridge the zenisu ridge to the southeast of nankai trough as well as two large channel systems one following the trench the nankai channel and the other coming from the north the tenryu canyon the zenisu ridge is a zone of recent intra plate shortening consisting of three distinct segments with an increasing deformation from southwest to northeast we interpret this gradient of deformation as a way to absorb the kinematic discontinuity between the diffuse shortening prevailing over the izu bonin ridge and the concentrated shortening along the nankai trough the shortening axis appears to change from north south along the zenisu ridge to northwest southeast along the nankai trough and finally to east west within honshu the western survey covers the junction between the nankai and ryukyu trenches and the kyushu palau ridge which is subducted without major internal deformation the ridge appears to act as an indenter upon the margin the tip of the indenter is presently situated under the upper accretionary prism

tectonic significance of the eratosthenes seamount a continental fragment in the process of collision with a subduction zone in the eastern mediterranean ocean drilling program leg 160 abstract one of the objectives of odp leg 160 in the eastern mediterranean sea april may 1995 was concerned with the study of processes of genesis and incipient collision of an inferred crustal fragment the eratosthenes seamount with the active margin of the eurasian plate to the north represented by southern cyprus the upper part of the eratosthenes seamount i e upper several hundred metres was found to include both shallow and deep water carbonates dating back to early cretaceous time shallow water platform carbonate deposition similar to that of the onshore levant continental margin to the east i e part of the north african plate was followed by submergence to bathyal depths 1000 m in the late cretaceous to middle eocene punctuated by depositional and tectonic hiatuses tectonic uplift approximately 1 km was followed by shallow water carbonate deposition in the early miocene the platform was exposed during the messinian desiccation crisis during the early pliocene the platform subsided to bathyal depths associated with localised accumulation of limestone debris flows subsidence accelerated in the late pliocene early pleistocene reaching a present day maximum depth of ca 2500 m deformation of the eratosthenes seamount i e subsidence and high angle faulting resulted from crustal flexure induced by southward overthrusting of the cyprus active margin tectonic subsidence of the eratosthenes seamount was approximately synchronous with rapid surface uplift of the over riding plate the troodos ophiolite of southern cyprus this uplift is explained in terms of incipient collision of an eratosthenes continental fragment with a subduction trench coupled with the effects of diapiric protrusion of serpentinite located within the core of the troodos ophiolite the eratosthenes drilling thus documented a modern analogue of subduction collisional processes leading to accretion of continental fragments and carbonate platforms in orogenic belts

mud volcano field seaward of the barbados accretionary complex a deep towed side scan sonar survey a 30 km2 diapiric field has been identified near 13 50 n up to 12 km seaward of the deformation front of the barbados accretionary complex using a deep towed side scan sonar with a 3 5 khz profiler we identified 31 different diapiric structures based on seismic stratigraphy we show that this field has been active for 200 000 years and that it is a transient feature triggered by the seaward propagation of the high pore fluid pressure associated with the decollement beneath the accretionary complex both basement and decollement in this area are anomalously shallow due to the presence of a n110 basement ridge the height of the diapirs above seafloor does not exceed 40 50 m and can be related to the pressure head of the mud below the decollement two types of structures are identified mud volcanoes and massively emplaced diapirs and ridges on the one hand enigmatic circular very flat mud pies and conical mounds on the other hand the second type of structures has steeper slopes and appears to be associated with very active venting as confirmed by a submersible exploration reported in a companion paper le pichon et al this issue b the venting results in the formation of a stiff carbonate crust and of large subsiding basins around the mud pies continuous active fluid expulsion through these structures indicates that an efficient piping system still connects them to the zone of anomalously high pore pressure below the protodecollement

palaeorotation of the troodos microplate cyprus the troodos ophiolite represents one of the best preserved fragments of ocean floor crust that is exposed on land as the extrusive series of the ophiolite retains a stable magnetization that is directed westward the ocean crust is considered to have rotated anticlockwise through 90 since its formation in the late cretaceous1 to determine the timing of the rotation event over 3 000 orientated samples have been collected from the ophiolite and from its in situ turonian to recent sedimentary cover here we report that pelagic chalks immediately overlying the highest extrusive lava units of the ophiolite complex give reliable magnetic vector directions indicating that at least 60 of rotation occurred before the lower eocene and that rotation was completed by the end of the lower eocene rotation cannot have occurred within a single late miocene event as reported previously2 regional geological considerations support the rotation of only a small fragment of oceanic crust that was stranded adjacent to an active continental margin in this tectonic setting the oblique consumption of oceanic crust beneath troodos crust could provide the necessary driving force for tectonic rotation

mud diapirism and subcretion in the barbados ridge accretionary complex the role of fluids in accretionary processes mud diapirism has recently been recognized in several modern accretionary wedges it provides an important means of dewatering accretionary wedges and should be regarded as an important process for producing the melanges found in both modern and ancient accretionary terranes mud diapirism affects a large area of the barbados ridge accretionary complex the distribution of the mud diapirs appears to be primarily controlled by the presence of underconsolidated terrigenous submarine fan deposits that are being accreted to the complex the frequency of diapir occurrence decreases northward as the fan becomes thinner mud diapirs are absent from the very eastern most part of the complex formed from sediments accreted at its toe with the exception of a few mud volcanoes on the ocean floor in front of the complex the initiation of diapirism appears to be spatially coincident with the onset of subcretion or underplating of sediment to the base of the complex at a ramp between two levels of decollement it is proposed that the release of mud and pore water from the subcreted sediments is a direct or indirect cause of most of the mud diapirism in the accretionary complex there is a range of diapiric form dependent on the viscosity of the mud from mud volcanoes fed by low viscosity mud to higher viscosity mud ridges the diapirs in the eastern areas of the complex are generally mud volcanoes with narrow conduits feeding a surface mound mud ridges are prominent in the western parts of the complex this is interpreted as reflecting a general westward decrease in the fluid content of the accretionary complex bottom simulating seismic reflectors formed by gas hydrate are commonly developed in the areas of mud volcano occurrences the presence of the hydrate indicates that large volumes of methane are being generated at depth in these regions the generation of methane may be contributing to zones of overpressuring in the wedge methane may also be partly responsible for driving the diapiric material to the surface to form mud volcanoes ridges in the subducting oceanic crust beneath the accretionary complex locally enhance diapirism above their crests and southern flanks faults formed later in the development of the complex are more commonly associated with diapirism than those resulting from accretion at the toe of the wedge these later faults play an important role in controlling the sites of individual mud volcanoes chains of mud volcanoes and mud ridges

the opening of the woodlark basin subduction of the woodlark spreading system and the evolution of northern melanesia since mid pliocene time abstract magnetic anomaly and seismological data define segments of active seafloor spreading and associated magnetic lineations trending ene in the woodlark basin the total opening rate has been approximately 6 cm yr for the last 1 m y spreading rates diminish by over 10 from east to west along the woodlark spreading system implying a pole of current opening 15 20 to the west commencement of seafloor spreading in the basin has apparently been time transgressive beginning prior to 3 5 m y in the east and at successively later times to the west earthquake focal mechanisms and geological evidence suggest that the land areas bounding the western end of the woodlark basin are undergoing tensional deformation we believe that eventually the woodlark basin plate boundary will propagate westward through the d entrecasteaux islands into the papuan peninsula hitherto unreported shallow seismicity associated with the northern margin of the ne trending section of the woodlark rise probably reflects partial decoupling of the woodlark and solomon basins possibly due to mechanical difficulties in subducting the young woodlark lithosphere analysis of the relative motions between the solomon indo australian and pacific plates shows that the woodlark spreading system has been subducted at high rates 10 cm yr beneath the solomon islands during the opening of the woodlark basin several tectonic and geological features limited to the region of interaction of the woodlark basin with the solomon trench and arc may be symptomatic of ridge subduction these features include high heat flow in the solomon trench which shoals to 4 km low levels of seismicity and only shallow hypocenters and voluminous eruptions of high k 2 o tio 2 olivine basalts and basaltic andesites extremely close to the trench axis this close association in space and time of an unusual volcanic suite with ridge subduction implies a strong dependence of the petrogenesis on the tectonic regime a combination of this study of the woodlark basin and the previous study of the bismarck basin taylor 1979 provides a reconstruction of the positions of the continents ocean basins and island chains in northern melanesia for mid pliocene time in accepting the existence of a solomon plate we can explain the trench like structure off the trobriand margin of new guinea the occurrence of late cenozoic calc alkaline volcanism along the papuan peninsula and the presence of intermediate depth seismicity beneath the north papuan peninsula the rapid changes in relative motions along or across the new ireland solomons chain over the past 3 5 m y may explain the spatial and temporal changes in igneous activity observed on these islands

overview of the late tertiary recent tectonic and palaeo environmental development of the mediterranean region the late tertiary history of the mediterranean region exemplifies processes of ocean basin closure and continental collision as determined from integrated land and marine evidence during the mesozoic early tertiary tectonic settings were dominated by evolution of neotethys this ocean generally widened eastwards with a number of oceanic strands in the eastern mediterranean area great diversity of tectonic settings and palaeo environments developed during the tertiary closure history of these oceanic basins in the eastern mediterranean region more northerly neotethyan strands were closed by the mid tertiary while oceanic crust remained in the south in the present eastern mediterranean sea area northwards subduction of the remaining southerly neotethyan strand was probably active by the early miocene different areas exhibit different stages of convergence and ocean basin closure in the east the amalgamated eurasian plate had collided with the arabian margin africa by the late miocene while oceanic crust still persisted further west steady state subduction during the late tertiary gave rise to the mediterranean ridge as a substantial mud dominated accretionary wedge in the aegean area sufficient northward subduction took place to activate arc volcanism and pervasive back arc extension short of marginal basin opening in the easternmost mediterranean only limited subduction took place associated with supra subduction zone extension e g in cyprus today steady state subduction continues only locally where vestiges of neotethys remain e g herodotus abyssal plain in the western mediterranean area suturing of the african and eurasian plates initially took place in the betic region early mid tertiary where the neotethys had existed only as a narrow connection with the central north atlantic in the central mediterranean region where the western neotethys was wider northward subduction was active apparently as early as the late cretaceous in a widely accepted interpretation an andean type magmatic arc developed along the southern margin of europe and was then rifted off in the late oligocene early miocene to form the corsica sardinia block opening the north balearic marginal basin in its wake the migrating subduction zone and microcontinent then collided diachronously with north africa related continental units north africa and apulia from late oligocene early miocene giving rise to collisional thrust belts in the northern and southern apennines and along the north african continental margin i e the maghrebian chain to the betic rif area from the early miocene onwards a separate subduction system became active related to removal of neotethyan oceanic crust to the southeast ionian sea fueling suprasubduction zone extension and opening of the tyrrhenian sea orogenic collapse is an alternative mechanism of such extension and is widely believed to have caused divergent thrusting in the betic and rif regions of the westernmost mediterranean at the same time as crustal extension and subsidence of the alboran sea

evidence of eocene high temperature high pressure metamorphism of ophiolitic rocks and granitoid intrusion related to neotethyan subduction processes dogansehir area se anatolia

facies and tectonic significance of two contrasting miocene basins in south coastal turkey several miocene basins are developed on a mosaic of deformed mesozoic carbonate platforms and ophiolitic units in the antalya region of south west turkey two of these the manavgat and kopru basins show contrasting orientations and stratigraphies the manavgat basin is orientated broadly se nw and contains a succession of shallow water reef carbonates overlain by a thick sequence of deeper water marls the upper part of the succession consists of sandstones siltstones and conglomerates mainly deposited by gravity processes the stratigraphy of the n s kopru basin can be subdivided into a western part which consists of coarse fan delta conglomerates with local patch reefs and an eastern part with thinly bedded sandy turbidites tooi marks indicate north to south flow in the north of the basin but a southeasterly direction in the area of intersection with the manavgat basin in the south east in the light of alternative regional hypotheses it is thought that early miocene basin initiation is related to coeval southeastward thrusting of the mesozoic lycian nappes flexural loading is inferred to have resulted in block faulting of the foreland and this exploited pre existing lines of structural weakness dating from early mesozoic rifting mid miocene relative sea level rise may relate to global eustacy and or regional tectonic subsidence finally late miocene renewed coarse clastic input locally very coarse and basin infilling reflect tectonic uplift to the north possibly related to continuing africa eurasia convergence in the region

quaternary uplift and sea level change at an active plate boundary cyprus a combination of northward underthrusting of the african plate and serpentinite diapirism resulted in progressive uplift of cyprus during the quaternary the uplift was associated with the development of succession of alluvial fans and marine terraces marine terraces in coastal southern cyprus are developed at 350 360 m 110 100 m 60 50 m 11 8 m and 2 3 m above present sea level the terraces display sequences of regressive deltaic carbonate and siliciclastic sub littoral to littoral and sub aerial type alluvial fans of the fanglomerate group crop out on the northern flanks of the troodos massif forming extensive dissected peneplaned terraces later uplift resulted in the formation of channel fans and river terraces proximal sheetflood conglomerates pass distally into channelized braid plain environments on the southern margin of the troodos massif the fanglomerate group comprises braided channelized and floodplain sequences which pass laterally into littoral facies provenence studies indicate that uplift and resulting erosion of cyprus was centred on the troodos massif mount olympus radiometric dates indicate that uplift was rapid in the early and mid pleistocene in the late pleistocene holocene eustatic sea level changes and anthropogenic effects dominated while the rate of uplift was reduced with local submergence of southern coastal areas

retrieving photometric properties of desert surfaces in china using the hapke model and misr data abstract the retrieval of photometric properties of desert surfaces is an important first step in the parameterization of land surface components of regional dust emission and global radiation models and in earth system modeling in this study the values of hapke s photometric parameters h b c b0 and were retrieved from the multi angle imaging spectroradiometer misr instrument at locations in china s deserts four pixels represented the typical surface characteristics of the taklimakan desert sand dunes of kumtag desert relatively smooth areas of the kumtag desert and the aeolian sandy soil of loulan in contrast to earlier studies we found that the retrieved parameter values were largely affected by the initial value to combat this problem we used a monte carlo method with physical constraints and a conformity indicator to ensure physically meaningful inversion the results showed that the angular domain of misr observations was sufficiently large to determine confidently the values of hapke s photometric parameters with the exception of the opposition effect width h retrieved values for the single scattering albedo and macroscopic roughness were consistent with qualitative observations about the structure and composition of the surface material and the nature of the dune forms respectively at loulan where the surface was smoother than other sites retrieved values exhibited the strongest backward scattering these results indicated that at the sensor scale a rough surface e g dunes does not necessarily mean more backward scattering than a smooth surface this finding has significant implications for empirical methods e g using the normalized index of backward scattered radiance minus forward scattered radiance as an indicator to indicate surface roughness which should be used carefully for analyzing surface roughness from remote sensing data future research is needed to 1 understand how surface roughness at the sub pixel scale modifies the angular characteristics of reflectance and to 2 find practical methods for rapid whole image processing for mapping the photometric parameters

formation of melanges in the indus suture zone ladakh himalaya by successive subduction related collisional and post collisional processes during late mesozoic late tertiary time

seismic refraction profiles between cyprus and israel and their interpretation summary a long seismic refraction profile was carried out between southern israel and cyprus the seismic energy was generated by 33 sea shots each of 0 8 t explosives and was recorded by land stations in israel and cyprus and by ocean bottom seismographs deployed along the profile the results showed that the continental crust of southern israel thins towards the mediterranean underneath a northward thickening sedimentary cover cyprus is underlain by a 35 km thick continental crust thinning south wards and extending to mt eratosthenes between mt eratosthenes and the israel continental shelf the crystalline crust is composed of high velocity 6 5 km s 1 material and is about 8 km thick it is covered by 12 14 km of sediments and may represent a fossil oceanic crust

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

collision related break up of a carbonate platform eratosthenes seamount and mud volcanism on the mediterranean ridge preliminary synthesis and implications of tectonic results of odp leg 160 in the eastern mediterranean sea abstract drilling of the eratosthenes seamount south of cyprus documented incipient collision of the african and eurasian plates the oldest sediments recovered mid cretaceous shallow water limestones are overlain by upper cretaceous to lower oligocene pelagic carbonates with several hiatuses following uplift a carbonate platform was established in the miocene eratosthenes was then below eustatic sea level during the messinian desiccation crisis the platform subsided to bathyal depths during the lower pliocene associated with localized breccia deposition further subsidence occurred in late pliocene early quaternary coeval with strong surface uplift of southern cyprus subsidence and break up of eratosthenes was achieved by a combination of flexural loading and normal faulting in addition the milano and napoli mud volcanoes were drilled on the northern flank of the mediterranean ridge accretionary complex south of crete a mainly extrusive sedimentary origin is indicated multiple debris flows include clasts of sandstone and limestone of at least partly miocene age both mud volcanoes are dated as 1 ma old and have been active episodically hydrocarbon gas is associated with both mud volcanoes while methane hydrates clathrates exist locally at milano the driving force of mud volcanism is overpressuring caused by incipient plate collision messinian evaporites may have acted as a localized seal material escaped through a zone of backthrusting against rigid cretan crust to the north

thrust mechanics in highly overpressured accretionary wedges rapid tectonic loading of wet sediment in accretionary wedges is likely to cause the fluid pressure to rise until it is sufficient to cause dilatant fracturing dewatering of sediment that has been underthrust and accreted beneath the wedge can produce a large steady supply of such highly overpressured fluid dilatant fracturing will create escape routes so the fluid pressure is likely to be buffered at the value required for the transition between shear and oblique tensile dilatant fracture which is slightly in excess of the load pressure if the maximum compression is nearly horizontal this in turn buffers the strength of the wedge at the cohesive strength which is not pressure dependent and will not vary greatly throughout the wedge near the wedge front the strength is likely to be that of the cohesion on existing thrust faults in the wedge the shear resistance on the base of the wedge will also be fairly constant and related to the cohesive strength of the weak sediment layer that acts as the basal detachment these assumptions allow the application of a simple plastic continuum model which successfully predicts the observed gently convex taper of accretionary wedges they also allow the use of a mechanical model for frontal imbrication which predicts the spacing of imbricate thrusts at the front of the wedge from the strength and thickness of the imbricated layer the ramp angle and the factional resistances on the bounding faults and decollement surfaces reconstruction of thrust geometries from seismic data across the makran and other accretionary wedges allows the determination of the geometrical parameters and the thrust imbrication model allows the mechanical parameters to be calculated in terms of an assumed cohesive strength for the incoming sediment layer the calculated values are reasonable and successful forward modelling of the profile of the makran shows that the postulate of a buffered value of fluid pressure in excess of the load pressure is consistent with observation

two ship deep seismic soundings in the basins of the eastern mediterranean sea pasiphae cruise summary new results from a two ship refraction and oblique reflection deep seismic cruise are presented to discuss the nature of the crust in the ionian sirte and herodotus abyssal plains these expanding spread profiles were processed and analysed in both the x t and p domains arrival times of reflected and refracted branches are matched by ray tracing in both domains in spite of a shallow evaporitic sequence messinian evaporites deposited on top of a thick sedimentary pile responsible for velocity inversions on many profiles we obtain excellent velocity control down to moho depth pmp and pn 8 4 8 6 km s 1 arrivals are observed the three basins have a relatively thin crust 8 to 11 km overlain by a thick sedimentary cover up to 10km in the herodotus abyssal plain the moho boundary and main crustal units identified in the basins can be followed beneath the calabrian prism to the west and beneath the mediterranean ridge to the east the crustal structure is of oceanic type for both the ionian and sirte basins where typical oceanic layer 2 and 3 are recognized the thin crust of the herodotus basin may be interpreted either as oceanic or thinned continental crust about 10 km thick the top of the crust of the herodotus basin is much deeper therefore the herodotus basin is probably significantly older than the ionian basin triassic versus early cretaceous in age

isolated carbonate platforms of the mediterranean and their seismic expression searching for a paradigm abstract isolated carbonate platforms icps are spectacular features of mediterranean geology there has been a resurgence of interest in the resource potential of icps in the region following recent exploration success in this play in the eastern mediterranean these features have developed in the context of the geologic evolution of the mediterranean region over the last 250 million years their depositional architecture and seismic expression can be very different from that of isolated platforms developed elsewhere and at different times particularly the tertiary platforms of southeast asia that have formed the basis of much of the industry literature on the seismic characteristics of icps important differences arise from the fact that mediterranean icps developed on microcontinents in an active tectonic environment featuring both extension and compression from the range of carbonate factories that have characterized their development and from the prolonged nature of exposure that they have period

ion microprobe analysis of 18o 16o in authigenic and detrital quartz in the st peter sandstone michigan basin and wisconsin arch usa contrasting diagenetic histories abstract the oxygen isotopic compositions of authigenic quartz cements in sandstones provide a monitor of the temperatures compositions and origins of pore occluding fluids during diagenesis but quartz overgrowths are too fine grained to be amenable to conventional isotopic analysis we have used a cameca ims 4f ion microprobe to determine oxygen isotopic variations in authigenic and detrital quartz in four samples of the ordovician st peter sandstone from the michigan basin and wisconsin arch midwestern usa ion microprobe isotopic analyses have been successfully accomplished with an internal precision of 1 1 and a spatial resolution of 20 30 m at low mass resolution using a high voltage offset technique repeated analyses of the quartz standard demonstrate a reproducibility of close to 1 1 sd in good agreement with that expected from counting statistics the four ion probe samples were chosen as representative of thirteen samples that were mechanically and chemically disaggregated sieved and analysed as a function of sieve size by conventional bulk mineral techniques conventional and ion microprobe analyses are mutually consistent supporting the accuracy of the ion microprobe analyses within sample isotopic variations of up to 13 and micro scale isotopic variations of at least 4 over a distance of 100 m have been measured within quartz overgrowths in a sandstone from the wisconsin arch overgrowths are uniformly higher in 18o than detrital grains and gradients of up to 25 exist across a few microns 18o enriched quartz overgrowths in sandstones from the wisconsin arch show complex cl zonation and reflect one of two possible processes 1 low temperature quartz precipitation during mixing of meteoric waters with upwelling basinal fluids 2 higher temperature quartz precipitation during episodic gravity driven upwelling of warm basinal fluids of comparable isotopic composition to michigan basin fluids from the illinois basin related to evolution of mississippi valley type pb zn ore forming fluids quartz overgrowths in michigan basin sandstones which derived their silica locally by pressure solution are thought to have precipitated continuously over a range of temperatures from hot basinal fluids of restricted isotopic composition and circulation detrital quartz shows significant intea grain and intergrain isotopic variation 5 13 but no significant inter sample variation consistent with a uniform source of granitoid and metamorphic quartz in space and time

geological evidence for mud diapirism on the mediterranean ridge accretionary complex abstract a mud breccia has been repeatedly cored from four mud diapir fields located on the crest of the mediterranean ridge this breccia is composed of subrounded clasts supported by a clay rich matrix and ranges in age from cretaceous to early miocene sedimentological analysis allows identification of a primitive intrusive and a reworked mud breccia the latter being formed by mud extrusion and gravitational reworking of the former homogeneous mud sorted by grain size which occurs at the top of the diapirs has been interpreted as a lake deposit based on composition and carbon isotopic ratios gases present within the diapiric material suggest a partial thermogenic origin and gas escape structures have been identified in the mud breccia and host sediments carbonate crusts occurring in the host sediments are not related to bacterial oxidation of methane and consequent authigenic calcite precipitation their carbon and oxygen isotopic ratios reveal that they are characteristic of early deep sea lithification in the mediterranean sea the presence of a marker bed composed of mn nodules and bacterial colonies the mud lake deposits showing lower carbonate content than primitive mud breccia and the gas escape structures suggest the presence of active fluid vents in the vicinity of the diapiric structures evidence of active mud diapirism can be found from about 300 000 yrs b p to the present