relating wave attenuation to pancake ice thickness using field measurements and model results wave attenuation coefficients m a1 were calculated from in situ data transmitted by custom wave buoys deployed into the advancing pancake ice region of the weddell sea data cover a 12 day period as the buoy array was first compressed and then dilated under the influence of a passing low pressure system attenuation was found to vary over more than 2 orders of magnitude and to be far higher than that observed in broken floe marginal ice zones a clear linear relation between and ice thickness was demonstrated using ice thickness from a novel dynamic thermodynamic model a simple expression for in terms of wave period and ice thickness was derived for application in research and operational models the variation of was further investigated with a two layer viscous model and a linear relation was found between eddy viscosity in the sub ice boundary layer and ice thickness

new constraints on the active tectonic deformation of the aegean 1 site velocities from six separate global positioning system gps networks comprising 374 stations have been referred to a single common eurasia fixed reference frame to map the velocity distribution over the entire aegean we use the gps velocity field to identify deforming regions rigid elements and potential microplate boundaries and build upon previous work by others to initially specify rigid elements in central greece the south aegean anatolia and the sea of marmara we apply an iterative approach tentatively defining microplate boundaries determining best fit rigid rotations examining misfit patterns and revising the boundaries to achieve a better match between model and data short term seismic cycle effects are minor contaminants of the data that we remove when necessary to isolate the long term kinematics we find that present day aegean deformation is due to the relative motions of four microplates and straining in several isolated zones internal to them the rms misfit of model to data is about 2 sigma very good when compared to the typical match between coseismic fault models and gps data the simplicity of the microplate description of the deformation and its good fit to the gps data are surprising and were not anticipated by previous work which had suggested either many rigid elements or broad deforming zones that comprise much of the aegean region the isolated deforming zones are also unexpected and cannot be explained by the kinematics of the microplate motions strain rates within internally deforming zones are extensional and range from 30 to 50 nanostrain year nstrain year 10 9 year 1 to 2 orders of magnitude lower than rates observed across the major microplate boundaries lower strain rates may exist elsewhere within the microplates but are only resolved in anatolia where extension of 13 4 nstrain year is required by the data our results suggest that despite the detailed complexity of active continental deformation revealed by seismicity active faulting fault geomorphology and earthquake fault plane solutions continental tectonics at least in the aegean is to first order very similar to global plate tectonics and obeys the same simple kinematic rules although the widespread distribution of aegean seismicity and active faulting might suggest a rather spatially homogeneous seismic hazard the focusing of deformation near microplate boundaries implies the highest hazard is comparably localized

zircon u pb ages and geochemistry of granitoids in the truong son terrane vietnam tectonic and metallogenic implications abstract truong son terrane one of the most important tectonic and metallogenic terranes in indochina block is composed of many volcano plutonic complexes reported here is geochronological and geochemical data obtained from six different volcano plutonic complexes the new data reveals that the granite from the hai van complex is 438 ma in age and shows collision related geochemical characteristics whereas another five samples from five volcano plutonic complexes present consistent emplacement and crystallization ages ranging from 261 to 242 ma dien bien granodiorite phia bioc monzogranite and dong trau rhyolite display typical subduction related calc alkaline affinity e g depletion in nb ta and ti and enrichment in rb and la while monzogranite from song ma complex displays collision related shoshoniteseries and granites from bengiang queson complex are related to post collision calc alkaline series based on these observations in combination with the previous published geochronological data we propose that at least four major stages of magmatic activities occurred during the paleozoic and the early mesozoic through the truong son terrane ordovician silurian 420 470 ma late carboniferous early permian 280 300 ma late permian to mid triassic 245 270 ma and middle late triassic 200 245 ma these magmatic activities are not only attributed to the tethyan song ma ocean southwestward subduction but also related to paleo tamky phuoc son oceanic bidirectional subduction synthesized with regional metallogenic data we identified three metallogenic epochs 1 late carboniferous early permian 280 300 ma arc magmatic hydrothermal cu au fe polymetallic metallogenic system related to the tamky phuoc son ocean north dipping subduction 2 late permian middle triassic 245 280 ma arc magmatic hydrothermal cu au fe and orogenic w sn au polymetallic metallogenic system which linked to both paleo tethyan song ma ocean south dipping subduction and tamky phuoc son ocean closure 3 middle to late triassic 200 245 ma syn collisional magmatic epithermal fe au w sn and post collisional or orogenic au system

wind and wave influences on sea ice floe size and leads in the beaufort and chukchi seas during the summer fall transition 2014 sea ice floe size distribution and lead properties in the beaufort and chukchi seas are studied in the summer fall transition 2014 to examine the impact on the sea ice cover from storms and surface waves floe size distributions are analyzed from medea landsat8 and radarsat 2 imagery with a resolution span of 1 100 m landsat8 imagery is also used to identify the orientation and spacing of leads the study period centers around three large wave events during august september 2014 identified by swift buoys and wavewatch iii model data the range of floe sizes from different resolutions provides the overall distribution across a wide range of ice properties and estimated thickness all cumulative floe size distribution curves show a gradual bending toward shallower slopes for smaller floe sizes the overall slopes in the cumulative floe size distribution curves from landsat8 images are lower than while those from radarsat 2 are similar to previously reported results in the same region and seasonal period the medea floe size distributions appeared to be sensitive to the passage of storms lead orientations regardless of length correlate slightly better with the peak wave direction than with the mean wave direction their correlation with the geostrophic wind is stronger than with the surface wind the spacing between shorter leads correlates well with the local incoming surface wavelengths obtained from the model peak wave frequency the information derived shows promise for a coordinated multisensor study of storm effects in the arctic marginal ice zone

wave attenuation and wave drift in the marginal ice zone abstract surface gravity waves in a viscous rotating ocean are studied theoretically when they penetrate an area covered by highly concentrated brashlike ice the motion is described by a lagrangian formulation and the brash is modeled by a viscous newtonian fluid results for wave attenuation and wave drift are obtained in the asymptotic limit of a thin very viscous upper layer the derived damping rate compares favorably with field data from the marginal ice zone miz the drift velocity in the ocean exhibits a marked maximum in the viscous boundary layer near the ice ocean interface at the outer edge of the boundary layer it exceeds the inviscid stokes drift by a factor of 7 4 computed values for the mean viscous drag on the ice induced by the wave motion show that this effect may compete with the frictional effected of the wind in packing the ice finally it is demonstrated that the integrated horizontal mass transports in the open ocean and under the ice do not match which leads to upwelling in

in situ geochemistry and fe o isotopic composition of iron oxides from the pha lek fe deposit northwest truong son orogenic belt laos implications for ore forming processes the pha lek fe polymetallic deposit in the southwest of the truong son orogenic belt records the evolution and metallogenesis of the southeastern asia tethys debates remain on the roles the late triassic volcanism played in the formation of the iron oxides of the deposit petrographic and sem studies led to the recognition of two dominant iron oxides magnetite and hematite and three stages of mineralization pre ore syn ore and post ore stages in situ la icp ms analyses for trace elements and fe and o isotopic analyses were applied to understand the origin of the iron oxides generally iron oxide of the syn ore stage has higher total trace elements than post ore stage and magnetite has higher lithophile elements whereas hematite has higher chalocophile elements the trace element abundance in magnetite is most comparable to porphyry skarn hydrothermal magnetite and hematite is more comparable to supergene and secondary non magmatic hydrothermal chemistry all 56fe values of the iron oxide separates are above 0 and have an igneous signature and syn ore stage magnetite has relatively higher 56fe values than the post ore stage hematite all 18o values of the iron oxide separates are below 1 and plot within the non igneous field and show a similar decreasing trend from syn ore stage magnetite to post ore stage hematite we propose that the triassic volcanic activities played a limited role during the mineralization process the deposit was formed because of the late carboniferous early permian porphyry skarn related magmatic hydrothermal alteration and the mixing of non magmatic fluid and or the supergene weathering caused the wide reprecipitation of fe oxides an evolutionary mineralization model related to the low angle subduction for the deposit is also proposed

wave propagation in the marginal ice zone model predictions and comparisons with buoy and synthetic aperture radar data in this paper the ocean wave dispersion relation and viscous attenuation by a sea ice cover are studied for waves propagating into the marginal ice zone miz the derivation of the dispersion relation and the viscous attenuation by an ice sheet are discussed for waves under flexure and pack compression in the miz the flexure effect is important for short waves for a fixed wave period the changes in wavelength and group velocity as a function of ice thickness are significant in turn the exponential wave attenuation rate shows a rollover at short wave periods whereby the rapid increase in wave attenuation rate with decreasing wave period slows down or even turns into a decrease the labrador ice margin experiment limex conducted on the miz off the east coast of newfoundland canada in march 1987 provides us with aircraft synthetic aperture radar sar imagery wave buoy and ice property data on the basis of the wave number spectrum from the sar data and the concurrent wave frequency spectrum from the ocean buoy data and accelerometer data on the ice during limex 87 the dispersion relation has been estimated and compared with a model wave energy attenuation rates are estimated from sar data and the ice motion package data which were deployed at the ice edge and into the ice pack and compared with the model the model data comparisons are reasonably good for the ice conditions observed during limex 87 some previously reported data of wave attenuation in the miz are revisited for model comparison

early cretaceous adakitic granites in the northern dabie complex central china implications for partial melting and delamination of thickened lower crust abstract to date few adakitic rocks have been reported in direct association with contemporary intra continental extensional structures which has cast doubt on genetic models involving partial melting of the lower crust this study presents early cretaceous 143 129 ma new sensitive high resolution ion microprobe shrimp zircon u pb ages adakitic granites which are directly associated with a contemporary metamorphic core complex i e the northern dabie complex in the dabie area these granites exhibit relatively high sr contents negligible to positive eu and sr anomalies high la yb and sr y ratios but very low yb and y contents similar to subducted oceanic crust derived adakites they are also characterized however by very low mgo or mg and ni values and nd sr isotope compositions end t 14 6 to 19 4 and 87sr 86sr i 0 7067 0 7087 similar to triassic continent derived eclogites subducted in the dabie sulu orogen additionally late granitic dikes in the adakitic intrusions exhibit low sr contents clearly negative eu and sr anomalies low la yb and sr y ratios but relatively high yb and y contents similar to 118 105 ma granites in the northern dabie complex based on composition and geochronology data of neoproterozoic amphibolites and orthogneisses triassic high to ultra high pressure metamorphic rocks and early cretaceous mafic ultramafic intrusive rocks and the constraints provided by experimental melt data for tonalites metabasaltic rocks and eclogites we suggest that the adakitic granites were most probably generated by partial melting of thickened amphibole or rutile bearing eclogitic lower crust as a consequence of triassic middle jurassic subduction and thrusting the late dikes probably originated from plagioclase bearing intermediate granulites moreover we suggest that late mesozoic delamination or foundering of thickened eclogitic lower crust is also a more plausible mechanism for the petrogenesis of early cretaceous mafic ultramafic intrusive rocks in the dabie area and probably involved partial melting of a mixed source comprising eclogitic lower crust that had delaminated or foundered into upper lithospheric or asthenospheric mantle peridotite asthenospheric upwelling in response to post collisional delamination of lithospheric mantle was likely to have provided the heat source for the cretaceous magmatism

emplacement and cooling of the dien bien phu granitic complex implications for the tectonic evolution of the dien bien phu fault truong son belt nw vietnam the dien bien phu dbp fault strikes nearly perpendicular to the general tectonic framework separating northwest vietnam into two compartments the dbp and muong lay granites are exposed respectively east and west of the fault the u pb age of 277 2 ma obtained for the muong lay granite is similar to the age of the chieng khuong complex exposed within the song ma structure east of the dbp fault these two magmatic intrusions are considered as belonging to a same tectonic structure related to the subduction of the song ma ocean under the indochina block during the indosinian orogeny the dbp fault with a total post permian dextral offset of 30 40 km shifts the song ma suture it could then be connected to the ailao shan shuanggou suture to the north the undeformed dbp granite gave a u pb age of 230 1 ma sealing the indosinian deformation on the fault the ladinian carnian activity of the fault is confirmed by the 40ar 39ar biotite age of 228 4 ma obtained from the paragneiss forming the fault zone a geodynamic model is proposed to describe the various tectonic phases recorded by on the dbp fault it associates field data stratigraphic observations and geochronology analyses u pb ar ar fission tracks following the late triassic exhumation of the granite and the end of the indosinian orogeny marked by the norian unconformity the granite was buried under jurassic and lower cretaceous sediments a strong cooling event during the early late cretaceous 100 ma is associated with the reactivation of the dbp fault and the accommodation of a southward thrusting of the song da terrane onto the truong son belt this newly recognised tectonic phase could be associated to the subduction of the paleo pacific plate under the indochina block no data are available yet to constrain the tertiary evolution of the dbp system however the tertiary deformation is likely similar to the cretaceous one

observation of wave refraction at an ice edge by synthetic aperture radar in this note the refraction of waves at the ice edge is studied by using aircraft synthetic aperture radar sar penetration of a dominant swell from open ocean into the ice cover was observed by sar during the labrador ice margin experiment limex conducted on the marginal ice zone miz off the east coast of newfoundland canada in march 1987 at an ice edge with a large curvature the dominant swell component disappeared locally in the sar imagery six subscenes of waves in the miz from the sar image have been processed revealing total reflection refraction and energy reduction of the ocean waves by the ice cover the observed variations of wave spectra from sar near the ice edge are consistent with the model prediction of wave refraction at the ice edge due to the change of wave dispersion relation in ice developed by liu and mollo christensen 1988

carboniferous triassic felsic igneous rocks and typical mineral deposits in the truong son orogenic belt se asia implications for paleo tethyan tectonic evolution and metallogeny abstract the truong son orogenic belt tsob is part of the eastern tethyan mineral deposit domain and preserves a near complete record of paleo tethyan orogeny related magmatism and mineralization by compiling and evaluating the data of plutonic and sub volcanic rocks and associated deposits on a regional scale and combining with new data of typical igneous rocks and mineral deposits we establish a unified paleo tethyan evolutionary model to help understanding the metallogeny in the tsob the geochronological data reveal the felsic magmatism and associated mineralization occurred in carboniferous triassic ca 317 202 ma with a magmatic lull at ca 270 263 ma before the lull most igneous rocks are high mg sodic metaluminous i type granitoids or volcanic equivalents with depleted hf isotopes which were derived from a juvenile crustal source with significant mantle contribution after the lull the igneous rocks ca 262 235 ma consist of metaluminous i type granitoids and abundant s type granitoids with geochemical features of low mg potassic peraluminous and enriched hf isotopes suggesting their derivation from ancient continental crust without obvious mantle contribution this magmatic lull corresponds to the tectonic transition from subduction to initial collision which reasonably accounts for the changing of petrogenetic types and magma sources of the associated igneous rocks in the tsob the slightly depleted hf isotopes of the ca 234 202 ma rocks possibly suggest another episode of tectonic transition in late triassic the distinct mineralization styles and s isotopes of ore deposits of each episode indicate that mineralization was related to the tectonic evolution and magmatism in each stage here we propose an evolutionary model for the paleo tethys orogeny in the tsob as follows 1 low angle subduction beneath the tsob during late carboniferous late permian favored the formation of juvenile crust derived adakitic rocks and high mg i type felsic rocks as well as associated porphyry cu au skarn fe cu au and epithermal au ag mineralization 2 subsequent collision during late permian middle triassic not only accounted for the generation of precambrian crust derived i type granitoids and intrusion related au ag deposits but also resulted in the formation of low mg s type rocks minor volcanic rocks and associated porphyry and or skarn sn zn pb deposits 3 possible post collisional extension during late triassic may be favorable for the formation of metaluminous high k high mg i type granitoids and volcanic rocks and carlin au porphyry and or skarn mineralization

i type plutonism in a continental back arc setting miocene granitoids and monzonites from the central aegean sea greece miocene extension in the aegean sea was accompanied by the intrusion of granitoid and monzonitic magmas at upper crustal levels with increasing distance from the trench the metaluminous to slightly peraluminous i type intrusives show a systematic regional variation in their compositions medium to high k granodiorites in the wsw high k low silica granites in the central region and high k high silica granites monzonites monzogranites and composite lamprophyric monzonitic dikes in the ene the granodioritic and low silica granitic plutons comprise similar ranges of sio2 63 5 71 6 wt and initial nd sr and o isotopic values end i 7 0 to 9 8 87sr 86sr i 0 7092 0 7115 18o 9 7 11 5 but display significant differences in their chemical compositions compared with the granodiorites the low silica granites have higher abundances of large ion lithophile light rare earth and some high field strength elements initial isotopic signatures of the high silica granites in the ene end i 9 0 to 9 6 87sr 86sr i 0 7128 0 7144 18o 10 8 12 0 are slightly more crust like than those of the low silica granites in chemical variation diagrams samples from the high silica granites continue the trends defined by those from the low silica granites it is suggested that all granitoid magmas originated by dehydration melting of metaluminous older crustal sources most probably metagreywackes u pb systematics of zircon populations in conjunction with zr sio2 systematics and zircon saturation temperatures suggest a high proportion of restitic or assimilated crustal material in these magmas monzonitic to monzogranitic rocks show chemical and isotopic characteristics end i 0 8 to 3 6 87sr 86sr i 0 7059 0 7071 18o 9 4 10 6 that are significantly different from those of the granitoids a small portion of an older crustal component in these magmas is indicated by u pb systematics of zircon populations lamprophyric dikes display chemical and isotopic signatures end i 0 5 87sr 86sr i 0 7044 18o 8 9 that are compatible with an origin from either a mantle source previously enriched by slab derived hydrous fluids melts as suggested by negative nb ta anomalies or a new k rich basaltic underplate abundant composite dikes indicate the coexistence of and mingling mixing between lamprophyric melts and monzonitic magmas

the motion of crustal blocks driven by flow of the lower lithosphere and implications for slip rates of continental strike slip faults geodetic measurements in actively deforming areas of the continents reveal the pattern of deformation in the lithosphere if the dominant forces acting on crustal blocks are tractions at their bases then the long term motion of each block will be given by the average velocity of the underlying lithosphere slip rates between blocks estimated in this way from recent geodetic measurements across fault zones in the south island of new zealand and southern california are in good agreement with slip rates estimated geologically

tectonics and metallogeny of mainland southeast asia a review and contribution abstract the southeast asia region is endowed with a diversity of mineral resources notably porphyry related skarn epithermal and sediment hosted orogenic gold deposits formation of these deposits was associated with a long and complex tectonic history of gondwana supercontinent break up arc magmatism backarc basin development together with arc continent and continent continent collisions that created the present day mainland se asia this paper summarizes historical and current se asian geological research and ore deposit studies here we present a new tectonic and metallogenic model for phanerozoic mainland se asia from this model we conclude that incipient arc backarc basin magmatism is the key to the formation of many important ore deposits in the truong son and loei fold belts the two major metallogenic belts in mainland se asia in addition triassic to cenozoic arc continent and continent continent collisions have led to the formation of many sediment hosted orogenic gold deposits in the sukhothai and the sibumasu terranes oblique cretaceous to recent subduction along the andaman sunda trench was responsible for gold and copper gold molybdenum porphyry and epithermal mineralization along the kawlin wutho mt popa arc in myanmar in the north and the sumatran volcanic arc in the south we anticipate that the present emphasis on exploring for shallower level epithermal deposits will increasingly lead to exploration for deeper level porphyry and porphyry related skarn systems in the coming decades

petrogenetic interpretation of granitoid rock series using multicationic parameters abstract granitoid rock compositions from a range of tectonic environments are plotted on a multicationic diagram devised by de la roche and his coworkers this shows that there is a systematic change through an orogenic cycle which leads progressively to the ultimate development of alkaline magmas possible source materials and mechanisms of magma generation are considered from analysis of mineral compositional vectors these suggest that most granitoid series result from a two stage process first fractional crystallisation of clinopyroxene olivine and calcic plagioclase from a basic source with tholeiitic affinities produces a magma of intermediate composition this magma then undergoes periodic mixing with a felsic magma followed by in situ fractionation to generate individual intrusions within granitoid series

measurements of waves in landfast ice using inertial motion units inertial motion units imus are used to perform measurements of waves in water covered by landfast ice close to the ice edge in svalbard the effective noise level of the instruments is assessed in controlled wave tank experiments a set of measurements collected in tempelfjorden svalbard in march 2015 is presented and the ability of the sensors to operate in the field is validated several characteristics of the recorded signals including correlation between the different sensors are analyzed horizontal and vertical motions are of the same order of magnitude a clear transition in the signal properties is observed in relation with changes in incoming wave field and the development of cracks in the ice layer we show that complex physics takes place when waves propagate in landfast ice and that the use of times series containing information on the full three dimensional linear acceleration rather than spectra is required to capture the underlying phenomena

a palaeoseismological and geoarchaeological investigation of the eliki fault gulf of corinth greece abstract palaeoseismological and morphotectonic analyses enable us to define a 400 m wide actively deformed zone associated with the active eliki normal fault central greece bounded on the south by a second order fault and on the north by a composite and prominent fault scarp this scarp is further analysed by trenching based on colluvium stratigraphy displacement of distinct horizons and deposition of sedimentary layers three faulting events have been identified along four fault strands affecting unconsolidated sediments in the trench the two younger events with throws of 0 93 and 1 37 m respectively the third event with a throw of 0 44 m and the penultimate 373 bc event suggest a variable seismic history the entire alluvial plain of the kerynitis and vouraikos rivers which cross the eliki fault has subsided at a rate of 1 4 mm year resulting in the burial of the late hellenistic roman occupation horizons under 3 m of fluvial and colluvial sediments in places extension in the broader area is accommodated by the seismically active eliki and egion faults structural and palaeoseismological analysis of those two faults indicates that they accommodate 1 5 mm year or about 10 of the geodetically estimated extension of up to 13 mm year

the south china block indochina collision where when and how this study uses new field observations and existing studies to shed new light on the origin and significance of two nw se striking orogens in nw and ne vietnam we conclude that the architecture of each belt is a stack of ne directed nappes formed either under deep ductile synmetamorphic conditions or under shallow depth in the sw and ne parts respectively the song ma zone and song chay ophiolitic melange represent two ophiolitic sutures however the late permian song da and babu mafic rocks are not ophiolites but intraplate basalts related to the emeishan plume a late triassic unconformity the 225 205 ma postorogenic plutonism and the 250 230 ma syntectonic metamorphism support an early to middle triassic age for these tectonic events both nw and ne belts are due to sw directed subduction with arc magmatism ocean closure and continental collision though two contemporary s dipping subduction zones might explain the structural evolution of the two belts a single convergent system offset by the tertiary red river fault is preferred as this s directed subduction better accounts for the late permian intraplate magmatism this scenario is discussed in the general geodynamic framework of se asia

waves in frazil and pancake ice and their detection in seasat synthetic aperture radar imagery a theoretical model of waves propagating into an ice cover composed of frazil and pancake ice is developed and compared with measurements of wavelength and direction derived from synthetic aperture radar sar imagery obtained from seasat in october 1978 the theoretical model is based on the concept that ice of these types which consists of small crystals or cakes has only a mass loading effect on the water surface we derive the dispersion relation for phase and group velocities finding that there is an upper frequency limit for propagation into the ice from the reflection coefficient at the ice edge we derive the wave radiation pressure exerted on the ice showing that it will cause a slick of frazil ice backed by thicker floes to become more dense or thick with increasing penetration the implications for radar scattering enabling detection on sar are that the bragg resonant wavelength corresponds to waves above the frequency limit for propagation so that a frazil slick appears dark on an sar image when the frazil ice becomes transformed into pancake ice through slick compression or other means the raised edges of the pancakes cause the ice to appear bright despite the fact that there are no waves present at the bragg wavelength these results are applied to a seasat sar image obtained from the chukchi sea the appearance of the ice in the image corresponds to what we expect for frazil ice gradually transforming itself into pancake ice backed by thicker floes we derive directional wave number spectra outside and inside the ice cover by digital fourier analysis of image subscenes and we find that the change of wavelength and angle of refraction of the dominant wave entering the ice field are both characteristic of the dispersion relation derived theoretically mean ice thicknesses extracted from the theory correspond to thicknesses expected for such slicks the technique offers a possible means of extracting the thickness of fields of frazil and pancake ice from sar imagery this may be of considerable utility when ers 1 sar is used to study the advancing winter ice edge in the antarctic which consists of vast areas of these ice types

geodynamics of the indosinian orogeny between the south china and indochina blocks insights from latest permian triassic granitoids and numerical modeling

rollover of apparent wave attenuation in ice covered seas wave attenuation from two field experiments in the ice covered southern ocean is examined instead of monotonically increasing with shorter waves the measured apparent attenuation rate peaks at an intermediate wave period this rollover phenomenon has been postulated as the result of wind input and nonlinear energy transfer between wave frequencies using wavewatch iii we first validate the model results with available buoy data then use the model data to analyze the apparent wave attenuation with the choice of source parameterizations used in this study it is shown that rollover of the apparent attenuation exists when wind input and nonlinear transfer are present independent of the different wave attenuation models used the period of rollover increases with increasing distance between buoys furthermore the apparent attenuation for shorter waves drops with increasing separation between buoys or increasing wind input these phenomena are direct consequences of the wind input and nonlinear energy transfer which offset the damping caused by the intervening ice

a fresh look at how ocean waves and sea ice interact because of their capacity to alter floe size distribution and concentration and consequently to influence atmosphere ocean fluxes there is a compelling justification and demand to include waves in

gps derived strain rate field within the boundary zones of the eurasian african and arabian plates we use the gps velocity field 1988 1998 for eastern mediterranean and asia minor to determine the crustal deformation strain rate field in an area bounded by 35 n and 43 n and 20 e and 48 e we calculate the normal and shear strain rate components associated with the major faults and compare these qualitatively with seismological data uncertainties in the calculation of the strain rates reach 50 nstrain yr 1 in sparsely observed parts of anatolia whereas we estimate errors 20 nstrain yr 1 in the aegean and marmara regions the largest compressional strain rate components in the eastern part of the study area occur along the greater caucasus mountain front reaching 70 nstrain yr 1 1 nstrain yr 1 0 0317 10 15 s 1 the north anatolian fault zone is the clearest feature in the shear strain rate field it is expressed as a pronounced dextral strike slip fault zone reaching rates of up to 170 nstrain yr 1 this holds true also for the izmit area where the august 17 1999 earthquake occurred central anatolia is almost strain free whereas extension prevails in western anatolia the principal axes of extension vary around the n s direction with strain rates of up to 85 nstrain yr 1 these extensional areas coincide with graben features and normal faulting earthquakes the central and southwestern aegean sea is strain free with values far below 40 nstrain yr 1 the seismic cluster around the dodekanissa islands southeastern aegean sea coincides with nw se oriented extension attaining strain rates of up to 90 nstrain yr 1 this area of extension also exhibits recent active volcanism the entire hellenic arc shows compressional strain rates perpendicular to the arc the pliny strabo troughs along the eastern segment of the arc show left lateral shear strain rates reaching 80 nstrain yr 1 significant extension is found in central greece with a nne ssw oriented maximum of 120 nstrain yr 1 centered around the gulf of corinthos the kephalonia fault zone in nw greece is a distinct dextral fault zone separating apulia from the rapidly moving aegean microplate right lateral shear strain rates reach 150 nstrain yr 1

the continuity of active fault systems in greece summary evidence from geomorphology the distribution of large earthquakes and geodetic measurements suggests that the active faulting in mainland greece and the north aegean sea is concentrated into a small number of discrete linear zones that bound relatively rigid blocks on land the zones are most clearly identified where the faulting is associated with large escarpments particularly in hard footwall rocks the zones can become indistinct and diffuse near their ends sometimes because they enter high unstable topography where landsliding obscures the fault morphology but mostly because the extension rates decrease along strike as a consequence of the relative rotation of the blocks they bound the main graben systems of chalkidiki southern thessaly and the north gulf of evia all seem to connect with the strike slip faulting in the offshore aegean and to die out in the west a configuration related to clockwise rotations in east central greece by contrast the gulf of corinth which is the fastest opening graben system in greece opens more rapidly in the west than the east both these features of the gulf of corinth are consequences of the motion of the south aegean and peloponnese as a single block late pliocene and quaternary geology and geomorphology indicate that the boundaries of the rigid blocks in central greece have changed over that time with faulting migrating into the hanging walls sometimes changing in orientation these changes are probably related to the way faulting in the seismogenic layer adapts to block rotation so as to maintain the general features of a velocity field that is controlled by larger scale effects such as buoyancy forces and the seaward migration of the subducting slab beneath crete the image of greece as a mosaic of rigid blocks whose boundaries change with time is a useful framework for seismic hazard evaluation but we emphasize that some moderate sized earthquakes do occur away from the main fault zones within the relatively rigid blocks and especially near their diffuse ends

permo triassic granitoids in the northern part of the truong son belt nw vietnam geochronology geochemistry and tectonic implications abstract the northern segment of the truong son belt of northwestern vietnam is composed of three granitoid complexes chieng khuong dien bien and song ma respectively our new la icp ms u pb dating results of magmatic zircons from five granitoid samples in the dien bien and the chieng khuong complexes reveal the existence of three age populations of magma emplacement and crystallization from 276 to 202 ma the new data show that the quartz diorite of the chieng khuong complex is dated to be 271 ma however the previously named dien bien complex exposed at different localities has various ages from 281 to 202 ma of magmatic crystallization the chieng khuong quartz diorite exhibits high mg value 60 7 and enriched sr nd isotopic features i sr 0 713822 end t 11 34 with subduction related geochemical features e g depletion in nb ta and ti and enrichment in rb and la the dien bien gabbroic diorite at muong lay is characterized by relatively depleted isotopic data i sr 0 705050 end t 0 09 and extensive depletion in nb and ta by contrast the dien bien granodiorite and quartz monzonite at dien bien are high k calc alkaline to calc alkaline with high mg values 45 5 to 54 4 and they display enriched sr nd isotopic data i sr 0 714912 to 0 716430 end t 9 58 to 8 85 and post collisional geochemical characteristics e g enrichment in total alkali lile and lree and depletion in eu sr p ti and nb under the framework of regional tectonic evolution the permo triassic magmatism along the northern truong son belt is thus grouped into an early stage from ca 280 to 250 ma and a late stage from 229 to 202 ma the early permian early triassic arc magmatism 280 270 ma and 250 245 ma which is widely distributed in the truong son belt provides reliable information on the continuous subduction of the song ma oceanic plate beneath the indochina block furthermore the magmatism of the dien bien complex at dien bien was formed during post collisional extension at ca 229 to 202 ma diachronous suturing of the eastern tethyan evolution is characterized by the differences in the ages of subduction post collisional evolution along the ailaoshan and the song ma belts

a theoretical laboratory and field study of ice coupled waves field and laboratory data of ice coupled waves propagating beneath shore fast ice are presented and compared with a theoretical model for sea ice which allows temperature variation although the laboratory data set is essentially qualitative because of scaling problems the measured wave characteristics compare favorably with those seen in the field the theory fits the field data set well both for the dispersive behavior and for the energy decay as the ice coupled waves penetrate the ice sheet moreover a maximum displacement suggested by theory is seen in field data for the first time it is proposed that this peak may be associated with the breakup of shore fast ice in exposed regions the theoretical treatment presented assumes sea ice to be thermorheologically simple an untested hypothesis which will require later experimental verification however the theory is quite general and can be used to solve a variety of sea ice mechanical problems where creep is considered important but where the loads and displacements are small enough that linearity prevails

a review of the relationships between granitoid types their origins and their geodynamic environments abstract granitoids are divided into several types according to their mineral assemblages their field and petrographical features and their chemical and isotopic characteristics this typology complements most of the recent classifications because it is not based solely on chemical and isotopic criteria but also on the field petrographical and mineralogical criteria it thus has the advantage of distinguishing the various granitoid types in the field in most cases the proposed classification shares many similarities with the twenty most used genetic classifications of granitoids both types of peraluminous granitoids are of crustal origin the tholeiitic alkaline and peralkaline granitoids are of mantle origin and both types of calc alkaline granitoids are of mixed origin and involve both crustal and mantle materials each granitoid type is generated and emplaced in a very specific tectonic setting each stage of the wilson cycle is characterised by typical associations of granitoids well typed and precisely dated granitoids can then complement structural approaches and indicate on the geodynamic environment with reference to some case studies the use of granitoids as tracers of the geodynamic evolution is also proposed and discussed

comparison of wave propagation through ice covers in calm and storm conditions motivated by a dramatic reduction in arctic sea ice cover interest in the field of wave ice interaction has accelerated over the past few years recent observations have identified that large waves 3 m have a linear attenuation rate rather than the previously assumed exponential rate that is found for small waves this suggests that waves penetrate further into the ice cover than previously expected to explore this further we tested two exponentially decaying wave models contributions from nonlinear and wind generation source terms enabled both models to reproduce the observed regime shift essentially the accumulation of nonlinear and wind energy contributions to long and thus higher amplitude waves can offset the ice damping thus reducing the apparent attenuation this study highlights the relevance of considering frequency dependence when analyzing wave attenuation in sea ice field data

a new velocity field for greece implications for the kinematics and dynamics of the aegean 1 a new set of geodetic velocities for greece and the aegean derived from 254 survey mode and continuous gps sites is used to test kinematic and dynamic models for this area of rapid continental deformation modeling the kinematics of the aegean by the rotation of a small number 3 6 of blocks produces rms misfits of 5 mm yr 1 in the southern aegean and western peloponnese indicating significant internal strain within these postulated blocks it is possible to fit the observed velocities to within 2 3 mm yr 1 rms by models that contain 10 or more blocks but many such models can be found with widely varying arrangements of blocks that fit the data equally well provided that the horizontal dimension of those blocks is not larger than 100 200 km a continuous field of velocity calculated from the gps velocities by assuming that strain rates are homogeneous on the scale of 120 km fits the observed velocities to better than 2 3 mm yr 1 rms with systematic misfits representing more localized strain confined to a region approximately 100 100 km in size around the western gulf of corinth this velocity field accounts for the major active tectonic features of greece and the aegean including the widespread north south extensional deformation and the distributed strike slip deformation in the ne aegean and western greece the t axes of earthquakes are aligned with the principal axes of elongation in the geodetic field major active normal fault systems are perpendicular to those axes and 90 of the large earthquakes in this region during the past 120 years took place within the areas in which the geodetic strain rate exceeds 30 nanostrain yr 1 these observations suggest that the faulting within the upper crust of the aegean region is driven by forces that are coherent over a scale that is significantly greater than 100 km it is likely that those forces arise primarily from differences in gravitational potential energy within the lithosphere of the region

gravity waves propagating into an ice covered ocean a viscoelastic model 1 a viscoelastic model is proposed to describe the propagation of gravity waves into various types of ice cover the ice ocean system is modeled as a homogeneous viscoelastic fluid overlying an inviscid layer both layers have finite thickness the viscosity is imagined to originate from the frazil ice or ice floes much smaller than the wavelength and the elasticity from ice floes which are relatively large compared to the wavelength a compact form of the dispersion relation is obtained under proper limiting conditions this dispersion relation can be reduced to several previously established models including the mass loading model the viscous layer model and the thin elastic plate model the full dispersion relation contains several propagating wave modes under the ice cover the following two criteria are used to select the dominant wave mode 1 wave number is the closest to the open water value and 2 attenuation rate is the least among all modes the modes selected from those criteria coincide with the ones discussed in previous studies which are shown to be limiting cases in small or large elasticity regimes of the present model in the intermediate elasticity regime however it appears that there are three wave modes with similar wavelengths and attenuation rates implications of this intermediate elasticity range remain to be seen the general viscoelastic model bridges the gap among existing models it also provides a unified tool for wave ice modelers to parameterize the polar regions populated with various types of ice cover

tracking changes in crustal thickness during orogenic evolution with sr y an example from the north american cordillera global compilations indicate that the geochemistry of arc magmatism is sensitive to moho depth magmatic products are prevalent throughout the history of cordilleran orogenesis and can be employed to constrain the timing of changes in crustal thickness as well as the magnitude of those changes we investigate temporal variations in crustal thickness in the united states cordillera using sr y from intermediate continental arc magmas our results suggest that crustal thickening began during the late jurassic to early cretaceous and culminated with 55 65 km thick crust at 85 95 ma crustal thicknesses remained elevated until the mid eocene to oligocene after which time crustal thicknesses decreased to 30 40 km in the miocene the results are consistent with independent geologic constraints and suggest that sr y is a viable method for reconstructing crustal thickness through time in convergent orogenic systems

stages of late paleozoic to early mesozoic magmatism in the song ma belt nw vietnam evidence from zircon u pb geochronology and hf isotope composition the song ma zone in nw vietnam bears important tectonic implications as a potential subduction corridor between the indochina and south china blocks on the basis of u pb ages the hf isotopic characteristics of zircons and the geochemical composition of granitoids a two stage magmatic evolution process of the song ma zone at 290 260 and 245 230 ma can be proposed isotopic analyses indicate magmatic contributions from neoproterozoic oceanic island basalt proterozoic continental crust and depleted mantle or juvenile lithosphere by combining geochronological and geochemical data from the granitoid rocks we suggest that the staged magmatic processes of song ma zone may be related to a long lasting period of ocean subduction ca 290 260 ma and subsequent syn post collisional evolution ca 245 230 ma

in situ measurements of an energetic wave event in the arctic marginal ice zone r v lance serendipitously encountered an energetic wave event around 77 n 26 e on 2 may 2010 onboard gps records interpreted as the surface wave signal show the largest waves recorded in the arctic region with ice cover comparing the measurements with a spectral wave model indicated three phases of interaction 1 wave blocking by ice 2 strong attenuation of wave energy and fracturing of ice by wave forcing and 3 uninhibited propagation of the peak waves and an extension of allowed waves to higher frequencies above the peak wave properties during fracturing of ice cover indicated increased groupiness wave ice interaction presented binary behavior there was zero transmission in unbroken ice and total transmission in fractured ice the fractured ice front traveled at some fraction of the wave group speed findings do not motivate new dissipation schemes for wave models though they do indicate the need for two way wave ice coupling

the use of sar to measure ocean wave dispersion in frazil pancake icefields abstract icefields composed of frazil and pancake ice play important roles in both polar regions in winter during the early to midwinter period pancake ice is a major component of the antarctic sea ice cover while in the arctic the odden ice tongue in the greenland sea associated with deep convection is composed mainly of pancake ice the retrieval of sea ice thickness by remote sensing is in general a very difficult task in this paper the change in dispersion of ocean waves as they penetrate into pancake ice is considered so as to gain insight into its possible relationship with thickness spectral analysis of subscenes from ers 2 second european remote sensing satellite synthetic aperture radar sar images yields the wavelength and direction of the principal spectral component both outside and inside the ice cover there is a decrease of wavelength at the ice edge as well as refraction toward the normal and a loss of amplitude the analysis is complex because the true wave spectrum must be re

comparison of viscoelastic type models for ocean wave attenuation in ice covered seas continuum based models that describe the propagation of ocean waves in ice infested seas are considered where the surface ocean layer including ice floes brash ice etc is modeled by a homogeneous viscoelastic material which causes waves to attenuate as they travel through the medium three ice layer models are compared namely a viscoelastic fluid layer model currently being trialed in the spectral wave model wavewatch iii and two simpler viscoelastic thin beam models all three models are two dimensional a comparative analysis shows that one of the beam models provides similar predictions for wave attenuation and wavelength to the viscoelastic fluid model the three models are calibrated using wave attenuation data recently collected in the antarctic marginal ice zone as an example although agreement with the data is obtained with all three models several important issues related to the viscoelastic fluid model are identified that raise questions about its suitability to characterize wave attenuation in ice covered seas viscoelastic beam models appear to provide a more robust parameterization of the phenomenon being modeled but still remain questionable as a valid characterization of wave ice interactions generally

the tam ky phuoc son shear zone in central vietnam tectonic and metallogenic implications abstract the tam ky phuoc son shear zone tkpssz is one of the most pronounced crustal structures in central vietnam and juxtaposes high grade rocks of the kontum massif against lower grade rocks of the truong son fold belt an internal zone comprises highly strained rocks including ultramafic mafic tectonites bounded by mylonitic zones that straddle tens to hundreds of kilometers an external zone comprises mainly high grade metamorphic complexes southern flank and weakly metamorphosed siliciclastic and carbonate rocks with subordinate greenstone northern flank detailed structural analysis reveals that the shear zone is a multi deformed terrane d1 produced a regional high grade schistosity and mylonitization d2 generated regional northwest southeast trending fold arrays and brittle ductile shear zones d3 locally produced northeast trending folds brittle faulting occurred during d4 d5 u pb dating of zircon and monazite suggests that d1 involved metamorphism and felsic magmatism at ca 430 ma recording part of a regional collisional orogeny monazite and titanite growth at ca 250 240 ma in basement rocks is synchronous with widespread syn to post d2 magmatism between ca 260 and 245 ma suggesting a second major collisional event during the indosinian orogeny d3 may have occurred as part of or soon after this permo triassic event deformation during post collisional stages perhaps in response to extrusion wedging and oroclinal rotation of terranes led to post d3 structures d4 d5 the e w trending tkpssz is here shown to be a continuation of the n s trending po ko shear zone pksz most of the significant lode gold occurrences in central vietnam occur along this tkpssz pksz structure and are associated with and controlled by d1 ductile to ductile brittle high strain zones mineralized later stage structures support remobilization and reconcentration of ore during subsequent events at ca 240 ma re os molybdenite age the tkpssz pksz d1 structure likely represents part of a paleosuture zone marking the closure of an ancient ocean basin through terrane assembly in the early paleozoic

paleoseismicity of the 1981 corinth earthquake fault seismic contribution to extensional strain in central greece and implications for seismic hazard we present paleoseismological trenching results for the active skinos fault which ruptured the surface on the alkyonides gulf basin margin in the 1981 gulf of corinth earthquake sequence three trenches expose evidence of up to six previous events which are comparable to the 1981 deformation in terms of size and geometry vertical displacement produced by the 1981 earthquake ranged from 0 45 to 1 3 m at the bambakies fan trench sites decreasing towards the eastern fault tip east of the trenches trench 1 reveals two previous events with vertical displacements between 0 5 and 1 2 m since 390 a d trench 2 reveals five or six previous events but these are not dated trench 3 reveals four previous events since 670 a d vertical displacements associated with interpreted paleoearthquakes at the trench sites are 1 2 m the recurrence interval on the skinos fault is estimated to average 330 years however significant variation in recurrence interval is allowed by the available radiometric dates average vertical displacement rates derived from the trenches are in the range 0 7 2 5 mm yr a similar long term average vertical displacement rate of 1 2 2 3 mm yr is estimated for the lifespan of the basin bounding fault this equates to a horizontal seismic strain contribution of 2 5 mm yr from the skinos fault this local seismic strain rate overlaps within error with geodetically determined velocities across the alkyonides gulf assumed to represent uniform deep crustal strain thus seismic deformation on the basin bounding fault system may take up the major part of extension across the basin and aseismic strain is not necessitated by the data if correct this would imply that geodetically determined strain rates may be used as a proxy for potential seismic moment release in seismic hazard analyses for this region

the early triassic indosinian orogeny in vietnam truong son belt and kontum massif implications for the geodynamic evolution of indochina new structural field data at various scale and 40ar 39ar geochronological results from the basement rocks in the truong son belt and kontum massif of vietnam confirm that ductile deformation and high temperature metamorphism were caused by the early triassic event of the indosinian orogeny in the range of 250 240 ma a compilation of isotopic data obtained in other countries along the sibumasu indochina boundary broadly indicates same interval of ages this tectonothermal event is interpreted as the result of a synchronous oblique collision of indochina with both sibumasu and south china inducing dextral and sinistral shearing along e w to nw se and n s fault zones respectively the collision along song ma follows the northwards subduction of indochina beneath south china and the subsequent development of the song da zone which in turn was affected by the late triassic indosinian phase of shortening within the indochina plate internal collisions occurred coevally in the early triassic as along the poko suture at the western border of the kontum massif

the ban houayxai epithermal au ag deposit in the northern lao pdr mineralization related to the early permian arc magmatism of the truong son fold belt abstract the ban houayxai au ag deposit is located in the truong son fold belt in the northern lao pdr mainland se asia the deposit is hosted within an early permian volcano sedimentary unit which is a part of a late carboniferous early permian 310 270 ma volcanic plutonic sequence of the truong son fold belt the main au ag mineralization stages i e stages 2 and 3 at ban houayxai consist of hydrothermal veins breccias associated with a carbonate quartz sulfides pyrite sphalerite galena chalcopyrite sericite chlorite electrum native silver stephanite mineral assemblage geochronological studies from la icp ms zircon u pb and adularia ar ar and k ar dating identified early permian cretaceous and eocene ages the early permian age is related to the emplacement of the mineralized volcanic arc sequence whereas the cretaceous and eocene ages represent resetting probably related to yanshanian and or himalayan orogenies a regional tectonic reconstruction indicates that the au ag epithermal deposit at ban houayxai was formed as a result of southward subduction of an oceanic crust attached to the south china terrane beneath the indochina terrane during the early permian from the metallogenic point of view the recognition of the old epithermal system at ban houayxai implies that the truong son fold belt possesses high potential for the presence of deeper magmatic related deposits such as porphyry and porphyry related skarn deposits

spectral modeling of ice induced wave decay abstractthree dissipative two viscoelastic and one viscous ice models are implemented in the spectral wave model wavewatch iii to estimate the ice induced wave attenuation rate these models are

past present and impendent hydroelastic challenges in the polar and subpolar seas current and emergent advances are examined on the topic of hydroelasticity theory applied to natural sea ice responding to the action of ocean surface waves and swell with attention focused on methods that portray sea ice more faithfully as opposed to those that oversimplify interactions with a poor imitation of reality a succession of authors have confronted and solved by various means the demanding applied mathematics associated with ocean waves i entering a vast sea ice plate ii travelling between plates of different thickness iii impinging on a pressure ridge iv affecting a single ice floe with arbitrarily specified physical and material properties and v many such features or mixtures thereof the next step is to embed simplified versions of these developments in an oceanic general circulation model for forecasting purposes while targeted on specific sea ice situations many of the reported results are equally applicable to the interaction of waves with very large floating structures such as pontoons floating airports and mobile offshore bases

llandovery lower silurian graptolites from the sepon mine truong son terrane central laos and their palaeogeographical significance abstract graptolites are described from the llandovery of the sepon mine area central laos part of the truong son terrane the palaeobiogeographical affinities of the rhuddanian graptolites are with peri gondwanan europe and arabia rather than equatorial regions such as south china and laurentia arctic canada a review of previous palaeontological research on the middle palaeozoic of the indochina terranes reveals an often contradictory picture with vertebrates suggesting close proximity of south china to the truong son terrane in the devonian and invertebrates and radiolarians providing evidence for a palaeogeographical barrier between the two graptolites from the mojiang area yunnan are typical of low latitude silurian faunas and suggest that this area simao or loei terrane was separate from the truong son terrane

ocean waves and ice sheets a complete analytical study is presented of the reflection and transmission of surface gravity waves incident on ice covered ocean the ice cover is idealized as a plate of elastic material for which flexural motions are described by the timoshenko mindlin equation a suitable non dimensionalization extracts parameters useful for the characterization of ocean wave and ice sheet interactions and for scaled laboratory studies the scattering problem is simplified using fourier transforms and the wiener hopf technique the solution is eventually written down in terms of some easily evaluated quadratures an important feature of this solution is that the physical conditions at the edge of the ice sheet are explicitly built into the analysis and power flow theorems provide verification of the results asymptotic results for large and small values of the non dimensional parameters are extracted and approximations are given for general parameter values

geodetic estimate of seismic hazard in the gulf of korinthos the recent 15 june 1995 m0 6 0 1018 n m aigion earthquake in the western gulf of korinthos has focussed attention on the seismic hazard of the region although there have been few large earthquakes in the region during this century the historical record suggests that there may have been many large earthquakes there in the interval 1750 1900 we present geodetic data that give estimates of the rate of extension of the gulf of korinthos during this century and which suggest that less than half of the elastic strain in the central and western gulf of korinthos has been released by earthquakes during this century in contrast the seismic and geodetic strains in the eastern gulf of korinthos are in agreement with each other if the discrepancy between seismic and geodetic strains in the western gulf of korinthos that has accumulated during this century is removed in earthquakes the moment release will be equivalent to several ms 6 5 earthquakes

in situ measurements and analysis of ocean waves in the antarctic marginal ice zone in situ measurements of ocean surface wave spectra evolution in the antarctic marginal ice zone are described analysis of the measurements shows significant wave heights and peak periods do not vary appreciably in approximately the first 80km of the ice covered ocean beyond this region significant wave heights attenuate and peak periods increase it is shown that attenuation rates are insensitive to amplitudes for long period waves but increase with increasing amplitude above some critical amplitude for short period waves attenuation rates of the spectral components of the wavefield are calculated it is shown that attenuation rates decrease with increasing wave period further for long period waves the decrease is shown to be proportional to the inverse of the period squared this relationship can be used to efficiently implement wave attenuation through the marginal ice zone in ocean scale wave models

tectonic evolution of high grade metamorphic terranes in central vietnam constraints from large scale monazite geochronology abstract several metamorphic complexes in southeast asia have been interpreted as precambrian basement characterized by amphibolite to granulite facies metamorphism in this paper we re evaluate the timing of this thermal event based on the large scale geochronology and compositional variation of monazites from amphibolite to granulite facies metamorphic terranes in central vietnam most of the samples in this study are from metamorphic rocks n 38 and granitoids n 11 in the kontum massif gneisses n 6 and granitoids n 5 from the hai van migmatite complex and the truong son belt located to the north of the massif were also studied two distinct thermal episodes 245 230 ma and 460 430 ma affected kontum massif gneisses while a single dominant event at 240 220 ma is recorded in the gneisses from the hai van complex and the truong son belt monazites from granitoids commonly yield an age of 240 220 ma mesoproterozoic ages 1530 1340 ma were obtained only from monazite cores that are surrounded by c 440 ma overgrowths thermobarometric results combined with concentrations of y 2 o 3 ce 2 o 3 and heavy rare earth elements in monazite and recently reported pressure temperature paths suggest that triassic ages correspond to retrograde metamorphism following decompression from high to medium pressure temperature conditions ordovician silurian ages reflect low pressure temperature metamorphism accompanied by isobaric heating during prograde metamorphism some samples were affected by both metamorphic events we conclude that high grade metamorphism observed in so called precambrian basement terranes in central vietnam occurred during both the permian triassic and the ordovician silurian while peraluminous granitoid magmatism is triassic additionally our preliminary analyses for u pb zircon age and whole rock chemistry of granitic gneisses from the truong song belt suggests the presence of the ordovician silurian volcanic arc magmatism in the region based on the pressure temperature time protolith evolutions metamorphic rocks from central vietnam provide a continuous record of subduction accretion collision tectonics between the south china and indochina blocks in the ordovician silurian the region was characterized by active continental margin tectonics followed by continental collision during the late permian to early triassic and subsequent exhumation during the late triassic the results also suggest that the timing of metamorphism and protolith formation as well as the geochemical features in other southeast asian terranes should be verified to achieve a better understanding of the precambrian to early mesozoic tectonic history in asia

wave attenuation by sea ice turbulence the dissipation of wave energy in the marginal ice zone is often attributed to wave scattering and the dissipative mechanisms associated with the ice layer in this study we present observations indicating that turbulence generated by the differential velocity between the sea ice cover and the orbital wave motion may be an important dissipative mechanism of wave energy through field measurements of under ice turbulence dissipation rates in pancake and frazil ice it is shown that turbulence induced wave attenuation coefficients are in agreement with observed wave attenuation in the marginal ice zone the results suggest that the turbulence induced attenuation rates can be parameterized by the characteristic wave properties and a coefficient the coefficient is determined by the ice layer properties

paleotethyan evolution of the indochina block as deduced from granites in northern laos abstract the paleotethyan evolution of the southeast asia has become better understood in recent years questions remain however over the role of the dien bien phu suture zone in the evolution of the indochina block and whether the song ma suture represents the boundary between the indochina block and the south china block granitoid geochronological and geochemical data obtained in northern laos provide new information vis a vis these arguments zircon u pb ages together with whole rock trace and rare earth element data from 27 granitic rocks from five complexes allow us to conclude that these granites are typical of i type indosinian volcanic arc granites however the 234 256 ma i type granites mismatch the initiation age obtained from the ductile shear zone of the dien bien phu fault thus repudiating the existence of the dien bien phu suture zone this then implies that the qamdo simao and indochina blocks were united the geochemical and geochronological data further suggest that the main crust in the indochina block formed in the late paleoproterozoic to early mesoproterozoic much later than the archean crustal formation age identified east of the song ma suture moreover the 440 404 ma and 234 256 ma i type granites suggest that the boundary between indochina and south china should be the jinsha river suture song ma suture kontum massif instead of the jinsha river suture song chay suture finally the emeishan basalt and granite complexes both form part of the south china tectonic units subducting westward under the qamdo simao and indochina blocks

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

abnormal seismological and magmatic processes controlled by the tearing south american flat slabs abstract the influence of flat slab subduction on the formation of intra slab earthquakes volcanic activities and mantle seismic velocity anomalies remains unclear we attempt to better understand these processes by simulating the two flat slabs in peru and chile using data orientated geodynamic models our results successfully reproduce the observed flat slabs as mainly due to two subducting aseismic ridges in contrast to the traditional view of flat slab subduction we find that these slabs are internally torn as is due to the 3d nature of the subducting buoyancy features this broken slab configuration confirmed by regional tomography naturally explains the abnormal distribution of and stress regimes associated with the intermediate depth earthquakes we further show that the slab tearing process could also better explain the formation of adakitic and ore forming magmatism the evolution of the magmatic arc and the enigmatic mantle seismic structures beneath these regions we propose that slab tearing may represent a common result of buoyancy feature subduction and that the resulting mantle processes could affect the long term geodynamic evolution of continents

can slab melting be caused by flat subduction slab melting has been suggested as a likely source of adakitic arc magmas i e andesitic and dacitic magmas strongly depleted in y and heavy rare earth elements existing numerical and petrologic models however restrict partial melting to very young 5 ma oceanic crust typically at 60 80 km depth paradoxically most of the known pliocene quaternary adakite occurrences are related to subduction of 10 45 ma lithosphere which should not be able to melt under normal subduction zone thermal gradients we propose an unusual mode of subduction known as flat subduction occurring in 10 of the world s convergent margins that can produce the temperature and pressure conditions necessary for fusion of moderately old oceanic crust of the 10 known flat subduction regions worldwide eight are linked to present or recent 6 ma occurrences of adakitic magmas observations from chile ecuador and costa rica suggest a three stage evolution 1 steep subduction produces a narrow calc alkaline arc typically 300 km from the trench above the asthenospheric wedge 2 once flat subduction begins the lower plate travels several hundred kilometers at nearly the same depth thus remaining in a pressure temperature window allowing slab melting over this broad distance and 3 once flat subduction continues for several million years the asthenospheric wedge disappears and a volcanic gap results as in modern day central chile or peru the proposed hypothesis which reconciles thermal models with geochemical observations has broad implications for the study of arc magmatism and for the thermal evolution of convergent margins

geodetic strain of greece in the interval 1892 1992 a first order triangulation of greece was carried out in the 1890s reoccupation using global positioning system receivers of 46 of the 93 original markers yielded estimates of the deformation of the region over the intervening interval broad regions have similar geodetic strain over the 100 year time span strain north of the gulf of korinthos is predominantly north south extension though with a significant east west component the central peloponnisos is relatively stable whereas the gulfs of the southern peloponnisos are all characterized by uniaxial east west extension the seismic expression of strain for the entire region calculated from the seismic moment tensors of earthquakes of m s 5 8 during the past 100 years accounts for only 20 50 of the geodetically determined strain at a scale of 50 100 km the fraction of the strain that is expressed seismically varies much more than this range in particular whereas seismic strain in the eastern gulf of korinthos over the past 100 years is commensurate with the geodetic strain there is rapid extension across the western gulf of korinthos 0 3 strain yr 1 with negligible seismic strain for the 100 year period prior to 1992 the egion earthquake of june 1995 in the western gulf of korinthos released only a small proportion 20 of the elastic strain that had accumulated in that region the observed distribution of displacements can be explained by the relative rotation of two plates with a broad accommodation zone between them but it is equally consistent with the deformation that would be expected of a sheet of fluid moving toward a low pressure boundary at the hellenic trench a simple calculation implies that if the region does behave as a fluid then its effective viscosity is 10 22 10 23 pa s such viscosities are consistent with the deformation of a lithosphere obeying a rheological law similar to that obtained for olivine in the laboratory

the geology and mineralization of the long chieng track lct subvolcanic au ag cu pb zn deposit lao pdr abstract the long chieng track deposit contains a mineral resource of 32 mt 0 77 g t au 4 9 g t ag 0 12 cu it is described here as a subvolcanic polymetallic au ag cu pb zn deposit occurring within a folded and faulted permian age volcanosedimentary formation in the truong son fold belt of north central laos the geological sequence is interpreted to have formed in a subduction related arc environment mineralization is associated with dacitic porphyritic dykes and small stocks which were intruded into a sequence of volcaniclastics carbonaceous sediments sedimentary breccias and limestones age dating by u pb geochronology of the dacitic porphyry unit yielded an intrusion age of 279 4 ma whole rock chemical analysis demonstrates that the rock suites are classified as i type calc alkaline series with elevated levels of alkali elements mineralization at lct occurs predominantly as stockwork veins which are spatially associated with the dacitic intrusions the veins may be classified into main four types including undifferentiated vnn base metals bmv massive pyrite mpy and buck buk veins all vein types are mineralized except the buk veins cross cutting and overprinting relationships indicate that the vnn and bmv veins were formed earlier than the mpy veins the dominant sets include steep nne dipping 66 010 and steep nnw dipping 70 340 veins and shallow to moderate sse dipping veins 21 172 the majority of high gold grades are hosted within the vnn veins which predominantly dip to the sse in contrast lead and zinc are dominant in the bmv veins while the highest copper grades are mainly hosted in steep nne and nnw dipping mpy veins ore minerals include pyrite galena sphalerite chalcopyrite electrum and native gold with minor arsenopyrite and molybdenite gold occurs either as electrum or native gold grains or as inclusions in pyrite five distinct alteration phases are recognized 1 quartz adularia sulfide 2 sericite quartz pyrite carbonate chlorite 3 fe carbonate 4 epidote carbonate chlorite 5 kaolin halloysite alunite phases 1 to 4 are generally progressively zoned from the deposit centre to the periphery phase 5 is associated with late steam heated hot spring alteration and weathering and oxidation the field geology relationships suggests that the depth of formation can be estimated to be approximately 1 3 km below the paleo surface the style of mineralization and geological relationships of the lct deposit are similar to those described in other deposits formed in the transitional zone between the porphyry and epithermal environments therefore we consider that sub volcanic style is the most appropriate environment to characterize the lct deposit

sea ice floes dissipate the energy of steep ocean waves a laboratory experimental model of an incident ocean wave interacting with an ice floe is used to validate the canonical solitary floe version of contemporary theoretical models of wave attenuation in the ice covered ocean amplitudes of waves transmitted by the floe are presented as functions of incident wave steepness for different incident wavelengths the model is shown to predict the transmitted amplitudes accurately for low incident steepness but to overpredict the amplitudes by an increasing amount as the incident wave becomes steeper the proportion of incident wave energy dissipated by the floe in the experiments is shown to correlate with the agreement between the theoretical model and the experimental data thus implying that wave floe interactions increasingly dissipate wave energy as the incident wave becomes steeper

continental tectonics in the aftermath of plate tectonics the success of plate tectonics required an acceptance of continental drift and thus a reinterpretation of the large scale geological history of most of the earth but the basic tenet of plate tectonics rigid body movements of large plates of lithosphere fails to apply to continental interiors where buoyant continental crust can detach from the underlying mantle to form mountain ranges and broad zones of diffuse tectonic activity

mio pliocene adakite generation related to flat subduction in southern ecuador the quimsacocha volcanic center abstract new geochemical and geochronological data on the miocene pliocene quimsacocha volcanic center qvc have led to the recognition of adakitic lavas generated by slab melting related to the flat slab subduction in southern ecuador and northern peru the qvc located in the presently inactive southern part of the ecuadorian arc was built up during three distinctive volcanic phases the first phase generated a basal edifice with mainly andesitic lava flows while the second phase is characterized by the emplacement of cryptodomes domes and related outflow breccias comprised of andesites and some dacites the last phase released rhyolitic ignimbrites associated with the formation of a large caldera which was later partly filled by dacitic rhyolitic domes geochemical data for the qvc indicate higher al2o3 tio2 na2o zr and sr contents and lower fe2o3 mgo y mree and hree abundances compared to other eruptive rocks of the plio quaternary volcanic front of ecuador such geochemical features as well as the frequent presence of an associated epithermal gold deposit are characteristic of the involvement of slab melts also known as adakites 1 2 in the generation of these magmas after a calc alkaline arc magmatism phase slab horizontalization in response to the subduction of a buoyant oceanic plateau results in increased involvement of a slab melting component in the magmas produced however pristine adakites were generated and emplaced during a relatively short period as indicated by zircon fission track ages then volcanic activity stopped and a volcanic gap formed the identification of these adakites their location and age support a model of slab melting associated with flat slab subduction m a gutscher et al geology 28 2000 535 538

u pb dating and tectonic implication of ophiolite and metabasite from the song ma suture zone northern vietnam the song ma suture zone including the classical song ma suture and the nam co antiform between indochina and south china blocks in northern vietnam is a crucial area for understanding the tectonic evolution of southeast asia to explore their natures and evolutionary history this paper reports new petrological studies and sims zircon u pb age data for the song ma ophiolites metabasites and fine grained quartzite the song ma ophiolites consist mainly of peridotite fo90 91 en92 basalt and gabbro and experienced greenschist to lower amphibolite facies ocean floor metamorphism lenses of rodingite and altered pyroxenite in serpentinites formed during alternation of peridotite we identified two types of zircon in the altered pyroxenite i uniform metamorphic 70 vol and ii zircon having inherited magmatic cores and metamorphic rims 30 vol all u pb analyses of both zircon types yield an upper intercept age of 340 29 ma that we interpret as the protolith age type i zircon and type ii metamorphic rims together yield a mean 206pb 238u age of 280 2 ma with rodingite forming broadly coevally at 283 to 282 ma metabasalt plagioclase amphibole schist has a morb type geochemical affinity magmatic zircon from a plagioclase amphibole schist yields a protolith age of 315 4 ma high pressure eclogite garnet phengite quartz schist and garnet hornblende rock are distributed in the northwestern nam co antiform zircon crystals from both eclogite and garnet hornblende rock have low th u ratios of 0 01 to 0 07 and 0 02 to 0 06 and yield metamorphic ages of 231 8 ma and 228 3 ma respectively the ages of detrital zircon grains from fine grained banded quartzite from the nam co antiform range from paleozoic to proterozoic with a peak at 1 7 to 1 8 ga all available data indicate a three stage tectonic evolution 1 340 to 280 ma the paleotethys that separated the indochina and south china blocks was characterized by oceanic crust formation at 340 to 315 ma and ocean floor metamorphism at 283 to 280 ma 2

aerial observations of floe size distribution in the marginal ice zone of summer prydz bay 1 on the basis of aerial photographs of sea ice floes in the marginal ice zone miz of prydz bay acquired from december 2004 to february 2005 during the 21st chinese national antarctic research expedition image processing techniques are employed to extract some geometric parameters of floes from two merged transects covering the whole miz variations of these parameters with the distance into the miz are then obtained different parameters of floe size namely area perimeter and mean caliper diameter mcd follow three similar stages of increasing flat and increasing again with distance from the open ocean floe shape parameters roundness and the ratio of perimeter to mcd however have less significant variations than that of floe size then to modify the deviation of the cumulative floe size distribution from the ideal power law an upper truncated power law function and a weibull function are used and four calculated parameters of the above functions are found to be important descriptors of the evolution of floe size distribution in the miz among them lr of the upper truncated power law function indicates the upper limit of floe size and roughly equals the maximum floe size in each square sample area l0 in the weibull distribution shows an increasing proportion of larger floes in squares farther from the open ocean and roughly equals the mean floe size d in the upper truncated power law function is closely associated with the degree of confinement during ice breakup its decrease with the distance into miz indicates the weakening of confinement conditions on floes owing to wave attenuation the of the weibull distribution characterizes the degree of homogeneity in a data set it also decreases with distance into miz implying that floe size distributes increase in range finally a statistical test on floe size is performed to divide the whole miz into three distinct zones made up of floes of quite different characteristics this zonal structure of floe size also agrees well with the trends of floe shape and floe size distribution and is believed to be a straightforward result of wave ice interaction in the miz

geochemistry of au bearing pyrite from the sepon mineral district laos dpr southeast asia implications for ore genesis abstract the sepon gold copper district occurs along the truong son foldbelt in a 10 km 40 km east trending corridor in southern laos this study has investigated the nature of gold in pyrite and ore forming fluid characteristics using laser ablation inductively coupled plasma mass spectrometry la icp ms and proton induced x ray emission pixe techniques gold is present as invisible gold au 1 and as nanoparticles of gold au0 in both sedimentary rock hosted gold and skarn cu au deposits gold is present in an early syngenetic pyrite generation pyrite 2b with concentrations to 0 5 ppm post sedimentation processes included formation of quartz veins which host pyrite 3b with concentrations to 1 8 ppm au the highest concentrations of gold were found in the rims of hydrothermal vein hosted pyrite 4a and in skarn related pyrite suggesting gold concentration at a later stage during the ore forming processes and not during sedimentation as rhyodacite porphyry is proximal to calcareous shale and dolomite that host ores it is plausible that the emplacement of rhyodacite porphyry introduced significant amount of hydrothermal fluids that circulated through fractures and favoured high grade to 293 ppm au in pyrite 4a and pyrite skn2 gold is preferentially concentrated in as rich zones and in areas that underwent brittle deformation as evidenced by fracture fill coarse grained pyrite 4a indicating a structural control to ore formation the predominance of se bi and te in pyrite skn1 and the elevated concentrations of bi cu se sn and mo in pyrite skn2 raise the possibility of derivation from a magmatic source the presence of primary hematite associated with the skarn suggests prevailing oxidising fluid conditions during au mineralisation in pyrite skn2 there is a striking chemical similarity between pyrite 4a core and py skn1 and rimmed zones of pyrite 4a and pyrite skn2 which indicates possibility of two types of hydrothermal fluids the as rich fluids with elevated concentrations of au se sb tl and cu recorded in pyrite 4a rims and pyrite skn2 the as poor fluids with elevated concentrations of ni and pb yielded in pyrite 4a cores and pyrite skn1 the chemistry of pyrite has also shown that both ore forming fluids are undersaturated in au similar to au bearing pyrite in the carlin type deposits nevada usa

gps constraints on continental deformation in the africa arabia eurasia continental collision zone and implications for the dynamics of plate interactions 1 the gps derived velocity field 1988 2005 for the zone of interaction of the arabian african nubian somalian and eurasian plates indicates counterclockwise rotation of a broad area of the earth s surface including the arabian plate adjacent parts of the zagros and central iran turkey and the aegean peloponnesus relative to eurasia at rates in the range of 20 30 mm yr this relatively rapid motion occurs within the framework of the slow moving 5 mm yr relative motions eurasian nubian and somalian plates the circulatory pattern of motion increases in rate toward the hellenic trench system we develop an elastic block model to constrain present day plate motions relative euler vectors regional deformation within the interplate zone and slip rates for major faults substantial areas of continental lithosphere within the region of plate interaction show coherent motion with internal deformations below 1 2 mm yr including central and eastern anatolia turkey the southwestern aegean peloponnesus the lesser caucasus and central iran geodetic slip rates for major block bounding structures are mostly comparable to geologic rates estimated for the most recent geological period 3 5 myr we find that the convergence of arabia with eurasia is accommodated in large part by lateral transport within the interior part of the collision zone and lithospheric shortening along the caucasus and zagros mountain belts around the periphery of the collision zone in addition we find that the principal boundary between the westerly moving anatolian plate and arabia east anatolian fault is presently characterized by pure left lateral strike slip with no fault normal convergence this implies that extrusion is not presently inducing westward motion of anatolia on the basis of the observed kinematics we hypothesize that deformation in the africa arabia eurasia collision zone is driven in large part by rollback of the subducting african lithosphere beneath the hellenic and cyprus trenches aided by slab pull on the southeastern side of the subducting arabian plate along the makran subduction zone we further suggest that the separation of arabia from africa is a response to plate motions induced by active subduction

sar imaging of wave dispersion in antarctic pancake ice and its use in measuring ice thickness 1 a synthetic aperture radar sar image of the advancing winter marginal ice zone miz in the antarctic composed of frazil pancake ice has been analysed in a new way in order to test the predictions of a recently developed theory of wave dispersion in pancake ice which treats the ice as a viscous layer in the image obtained in april 2000 the structure of the wave spectrum in the miz and its change from the open water spectrum are consistent with a pancake layer 24 cm thick intensive in situ measurements of the pancake ice in the miz 280 km w of the image location were made from fs polarstern during a period covering the satellite imaging and also yielded a mean ice thickness of 24 cm we conclude that this technique gives realistic results for ice thickness whereas earlier work based on a different dispersion theory mass loading tended to over estimate thickness after further validation it is therefore possible that the sar wave technique can become an accepted method for monitoring ice thickness in pancake icefields