the correction for sediment loading on the seafloor available measurements of sediment velocity and density indicate that a factor of 600 m s 1 of two way sediment reflection time will correct seafloor depth to yield basement depth in the absence of sediment loading this simple linear relation is derived from the results of six deep drill holes in abyssal sediments of the north and south atlantic oceans the relation predicts the sediment correction with an accuracy of about 50 m regardless of the lithology sampled down to a depth of 1 5 s of reflection time the cost wells on the u s continental shelf and empirical relations among velocity density porosity and depth provide estimates of the deeper behavior of abyssal sediments and suggest that the 600 m s 1 factor continues to provide a satisfactory sediment correction to a depth of 3 s

the geochemistry of carbonate replacement pb zn ag mineralization in the lavrion district attica greece fluid inclusion stable isotope and rare earth element studies strata bound carbonate replacement pb zn ag deposits in the lavrion district greece are spatially related to a late miocene granodiorite intrusion 7 10 ma and various sills and dikes of mafic to felsic composition the plaka granodiorite contains porphyry molybdenum mineralization and is locally associated with a ca fe skarn carbonate replacement deposits occur predominantly in marbles upper and lower marble of the basal unit kaesariani schists and along a major detachment fault that separates the basal unit from the upper unit orebodies are mainly strata bound carbonate replacement although sulfides also occur in veins the mineralogy of carbonate replacement deposits is dominated by base metal sulfides and sulfosalts of ag bi sn sb as and pb particularly at plaka and kamariza carbonates are intergrown with earlier formed sulfides and sulfosalts but are more abundant late in the paragenetic sequence with fluorite and barite fluid inclusion studies of sphalerite fluorite calcite and quartz in carbonate replacement deposits suggest that they were deposited from 132 to 365 c from co2 poor low to high salinity fluids 1 20 wt nacl equiv carbon and oxygen isotope compositions of calcite 13c 15 6 to 1 5 and 18o 9 2 to 17 3 intergrown with sulfides reflect variable exchange of the ore bearing fluid with the upper and lower marbles and proximity to the plaka granodiorite post archean australian shale paas normalized rare earth and yttrium patterns of the upper and lower marbles and calcite intergrown with sulfides show positive eu and negative ce anomalies as well as y ho ratios between 40 and 80 normalized rare earth and yttrium patterns of fluorite also have positive eu and negative ce anomalies such anomalies for both the carbonates and fluorite reflect the high ph or high f o2 conditions of the late stage hydrothermal fluids and the likely derivation of calcium from marine carbonates precursors of the upper and lower marbles the range of sulfur isotope compositions for sulfides 34s 4 9 to 5 3 with one outlier of 9 4 in carbonate replacement and vein deposits is due likely to a magmatic sulfur source with a contribution of reduced seawater sulfate sulfur isotope compositions of barite from carbonate replacement range from 34s 17 2 to 23 7 per mil and reflect miocene seawater sulfate values if a magmatic source of sulfur is assumed along with an average temperature of 250 c for the ore forming fluids as based on fluid inclusion studies sulfides in carbonate replacement deposits were deposited at values of log f o2 41 to 36 and a ph 5 8 to 9 1 however the range of sulfur isotope values does not rule out the possibility that sulfur in sulfides could have been produced by the reduction of seawater sulfate with no contribution from a magmatic source the carbonate replacement deposits resemble manto type sulfide deposits in mexico central colorado south korea nevada and northern greece

halogen and ar ar age determinations of inclusions within quartz veins from porphyry copper deposits using complementary noble gas extraction techniques abstract extension of ar ar methodology has been used to determine mineralisation ages from mica inclusions and to simultaneously evaluate the noble gas and halogen composition of inclusion fluids within irradiated quartz vein samples from five porphyry copper deposits samples have been collected from the potassic and propylitic zones of bingham canyon utah and four arizonan deposits silverbell globe miami pinto valley and ray data obtained using three noble gas extraction techniques laser ablation in vacuo crushing and stepped heating are compared with each other laser ablation provides a means for the analysis of individual fluid inclusions but is limited by blank levels and detection limits stepped heating and in vacuo crushing are bulk extraction techniques that preferentially release gases from solid and fluid inclusion phases respectively and can be used in combination to obtain accurate and meaningful ages of mineralisation ages obtained for porphyry copper deposits are as follows bingham canyon 37 1 0 5 ray 65 3 1 5 globe miami 61 7 3 4 pinto valley 63 2 8 0 and silverbell 55 8 1 8 the age of mineralisation at ray is of particular interest as it enables a reported discrepancy in k ar ages to be understood halogen data for the bingham canyon samples gives insight into the partitioning of the heavy halogens br and i between solid and liquid phases

the behavior of trace elements during the chemical evolution of the h 2 o b and f rich granite pegmatite hydrothermal system at ehrenfriedersdorf germany a sxrf study of melt and fluid inclusions detailed melt and fluid inclusion studies in quartz hosts from the variscan ehrenfriedersdorf complex revealed that ongoing fractional crystallization of the highly evolved h2o b and f rich granite magma produced a pegmatite melt which started to separate into two immiscible phases at about 720 c 100 mpa with cooling and further chemical evolution the immiscibilty field expanded two conjugate melts a peraluminous one and a peralkaline one coexisted down to temperatures of about 490 c additionally high salinity brine exsolved throughout the pegmatitic stage along with low density vapor towards lower temperatures a hydrothermal system gradually developed boiling processes occurred between 450 and 400 c increasing the salinities of hydrothermal fluids at this stage below the late hydrothermal stage is dominated by low salinity fluids using a combination of synchrotron radiation induced x ray fluorescence analysis and raman spectroscopy the concentration of trace elements mn fe zn as sb rb cs sr zr nb ta ag sn ta w rare earth elements ree and cu was determined in 52 melt and 8 fluid inclusions that are representative of distinct stages from 720 c down to 380 c homogenization temperatures and water contents of both melt and fluid inclusions are used to estimate trapping temperatures thus revealing the evolutionary stage during the process trace elements are partitioned in different proportions between the two pegmatite melts high salinity brines and exsolving vapors concentrations are strongly shifted by co ncomitant crystallization and precipitation of ore forming minerals for example pegmatite melts at the initial stage 700 c have about 1 600 ppm of sn concentrations in both melts decrease towards lower temperatures due to the crystallization of cassiterite between 650 and 550 c tin is preferentially fractionated into the peralkaline melt by a factor of 2 3 while the last pegmatite melts are low in sn 64 ppm at 500 c early hydrothermal fluids become again enriched with about 800 ppm of sn at the boiling stage a sudden drop in late hydrothermal fluids 23 ppm of sn at 370 c results from precipitation of another cassiterite generation between 400 and 370 c zinc concentrations in peraluminous melts are low some tens of parts per million and are not correlated with temperature in coexisting peralkaline melts and high t brines they are higher by a factor of 2 3 zinc continuously increases in hydrothermal fluids 3 000 ppm at 400 c where the precipitation of sphalerite starts the main removal of zn from the fluid system occurs at lower temperatures similarly melt and fluid inclusion concentrations of many other trace elements directly reflect the crystallization and precipitation history of minerals at distinctive temperatures or temperature windows

the empirical age depth relation and depth anomalies in the pacific ocean basin this paper presents a new age depth relation and a comprehensive depth anomaly map for the pacific ocean age depth and sediment thickness were averaged for each 1 1 area bathymetry was corrected for isostatic effects due to sediment and water load and for the variation of sound velocity in water seafloor existing at extreme distance from hot spot tracks is found to be anomalously deep hot spots were treated as thermal anomalies and data within 800 km of them were eliminated from further analysis an age depth equation was determined by fitting a least squares line to the remaining data the resulting depth versus age distribution confirms the linear dependence of depth on age up to 80 ma all older seafloor is within 800 km of hot spots or hot spot tracks and is shallower than predicted this flattening of the age depth distribution requires that a separate function be fit to data older than 80 ma as a result data representing the deepest seafloor older than 80 ma were selected for curve fitting and the age depth distribution was approximated by an exponential function it is impossible to distinguish between the infinite half space and cooling plate models of the lithopshere using the age depth data from the pacific ocean a depth anomaly map prepared by comparing observed depth with the depth predicted by the new age depth formula shows several newly recognized features including swells over the louisville ridge in the south pacific and in the gulf of alaska seamounts

a note on the correction of ocean floor depths for sediment loading the measured physical properties of sediments recovered in a number of deep sea drill holes in the north atlantic have been used to derive expressions for the correction to basement depths required to account for loading by sediments the average density and porosity over a given thickness of sediment show an approximate linear dependence on sediment thickness this behavior can be explained as primarily the result of compaction if the compaction of the sediments is neglected in correcting basement depths for sediment loading errors of a few hundred meters in the corrected depths can be made a sediment loading correction based on the observed variation of density with depth can give corrected depths to better than 100 m with remaining uncertainties due to variablity in sediment properties and rebound effects on the measured densities a relation between sediment thickness and vertical travel time was obtained from sonic velocity measurements on samples from drill holes sonobuoy wide angle reflection experiments and direct correlation of seismic reflectors with downhole lithology the sediment loading correction can then be expressed directly in terms of the vertical travel time measured along seismic reflection profiles the loading correction obtained here for the north atlantic may not be applicablemore in areas with different sedimentary enviroments when direct measurements of physical properties in drill holes are not available in such areas it is shown that it is preferable to assume a compaction curve for the appropriate lithology rather than to use observed seismic velocities together with a velocity density relationship less

porphyry and epithermal deposits in greece an overview new discoveries and mineralogical constraints on their genesis abstract greece hosts a variety of magmatic hydrothermal ore deposits prospects with porphyry and epithermal styles playing a major role in its total gold endowment these deposit types are mainly clustered in two areas the rhodope and attico cycladic massifs and formed from about 33 ma to the pleistocene as a result of back arc extension in the aegean sea metamorphic core complex formation and contemporaneous post subduction and arc magmatism in the serbo macedonian massif porphyry cu au deposits include skouries fisoka tsikara vathi and gerakario causative intrusives are oligocene to miocene granodiorites to monzonites gold and pge mineralization is associated with potassic alteration of the intrusives in the eastern rhodope massif and the ne aegean islands porphyry prospects occur at pagoni rachi konos hill myli melitena west thrace fakos sardes and kaspakas limnos island and stypsi lesvos island mineralization is associated with oligocene to miocene subvolcanics of calc alkaline to shoshonitic affinity feature of these prospects which they share in common with several porphyry au only systems is their shallow depth of emplacement the presence of potassic sodic calcic and or phyllic alteration a strong epithermal overprint their low cu content an extreme re enrichment the multistage introduction of au the presence of banded quartz veinlets and the local presence of tourmaline new discoveries of porphyry style mineralization at king arthur st philippos and aisymi increases the gold potential in west thrace high intermediate sulfidation epithermal au ag polymetallic deposits prospects overprint and or occur laterally from porphyry style mineralization where they are spatially associated with lithocaps of advanced argillic alteration high intermediate sulfidation au ag epithermal mineralization at perama hill mavrokoryfi and pefka in west thrace and at pterounda mesotopos and megala therma on lesvos island is controlled by steeply dipping extensional faults within volcanic rocks without any obvious genetic relationship to spatially related porphyry style mineralization polymetallic epithermal deposits and prospects contain critical and energy critical metals e g te se bi sb in ge and ga which may be considered as by products in the attico cycladic area porphyry mo w mineralization occurs as sheeted quartz veins and stockworks cutting a potassic to sericitic altered miocene granodiorite stock in the lavrion district bonanza grade au and or ag rich veins with epithermal affinities crosscut metamorphic rocks at lavrion and on syros tinos antiparos and anafi islands milos island is characterized by shallow submarine volcanic hosted is hs epithermal au ag te and base metal deposits antimony as ag au deposits prospects on chios samos and kos islands in the eastern aegean sea indicate the potential for carlin style mineralization in greece several factors played a role to the metal endowment of the aegean porphyry epithermal systems magma fertility in the source regions depth of emplacement of causative intrusives relative contribution of mantle versus crustal material redox state of subduction related magmas and physico chemical fluid conditions at the site of ore deposition

is there a link between faulting and magmatism in the south central aegean sea a distinct spatial relationship between surface faulting magmatic intrusions and volcanic activity exists in the aegean continental crust in this paper we provide detailed structural observations from key onshore areas as well as compilations of lineament maps and earthquake locations with focal plane solutions from offshore areas to support such a relationship although pluton emplacement was associated with low angle extensional detachments the nne to ne trending strike slip faults also played an important role in localizing the middle miocene plutonism providing ready pathways to deeper magma batches and controlling the late stage emplacement and deformation of granites in the upper crust additionally the linear arrangements of volcanic centres from the quaternary volcanoes along the active south aegean volcanic arc are controlled primarily by ne trending faults and secondarily by nw trending faults these volcanic features are located at several extensional settings which are associated with the main ne trending faults such as i in the extensional steps or relay zones between strike slip and oblique normal fault segments ii at the overlap zones between oblique normal faults associated with an extensional strike slip duplex and iii at the tip zone of a ne trending divergent dextral strike slip zone the ne trend of volcano tectonic features such as volcanic cone alignments concentration of eruptive centres hydrothermal activity and fractures indicates the significant role of tectonics in controlling fluid and magma pathways in the aegean upper crust furthermore microseismicity and focal mechanisms of earthquakes in the area confirm the activity and present kinematics of these ne trending faults

3d subduction dynamics a first order parameter of the transition from copper to gold rich deposits in the eastern mediterranean region the natural variability of geometry and dynamics of subduction zones leads to a variety of mantle and crustal processes that may influence the genesis of ore deposits in the overriding plate these complex interactions cannot be fully represented by two dimensional 2d models but require that the spatial and temporal evolution of ore deposits be examined in a detailed 3d tectonic framework we compare and discuss the geodynamic and metallogenic evolution of the eastern mediterranean subduction zone since the late cretaceous by integrating a newly compiled metallogenic database with a recent kinematic reconstruction model the resulting paleotec tonic maps identify 1 a late cretaceous cu rich metallogenic period with large deposits formed above a linear and stable subduction zone that produced large amounts of potentially fertile magmas in a narrow magmatic arc and 2 a late eocene miocene pb zn followed by au rich metallogenic period with generally smaller deposits spread over a wide back arc basin that was opened due to subduction retreat and lateral slab tearing supported by high resolution numerical modeling the proposed dynamic arc and back arc metallogenic models emphasize 1 the influence of 3d slab dynamics and associated asthenospheric flow on ore distribution in space and time and 2 the importance of exhuming metamorphic domes in extensional back arc setting to focus metal bearing fluid circulations these models differ from collision and post collision models and may be valid on the western and eastern terminations of the whole tethyan orogenic belt i e mediterranean and southeast asia where fast 3d subduction dynamics has influenced the geodynamic and metallogenic evolution of the overriding plate

topography the geoid and compensation mechanisms for the southern rocky mountains the southern rockies of colorado are anomalously high elevations greater than 2800 m topographically rough implying active uplift and underlain by significant low velocity anomalies in the upper mantle that suggest an intimate relationship between mantle geodynamic processes and the surface topography the region is in isostatic equilibrium i e near zero free air gravity anomaly however the poor correlation between the high topography and crustal thickness makes the application of simple compensation models e g pure heiskanen or pratt hayford problematic knowledge of how the current topography of the rockies is isostatically compensated could provide constraints on the relative role of sublithospheric buoyancy versus lithospheric support here we evaluate the geoid and its relationship to the topography using the geoid to elevation ratio gtr in the spatial domain and the admittance in the frequency domain to constrain the mechanism of compensation we separate the upper mantle geoid anomalies from those with deeper sources through the use of spherical harmonic filtering of the egm2008 geoid we exploit the fact that at wavelengths greater than the flexural wavelength where features are isostatically compensated the geoid topography ratio can be used to estimate the depth of compensation and the elastic thickness of the lithosphere the results presented below indicate that the main tectonic provinces of the western united states have moderate geoid topography ratios between 3 5 and 5 5 m km 3 9 for the southern rockies 4 25 for the colorado plateau and 5 2 for the northern basin and range suggesting shallow levels of isostatic compensation in terms of the elastic thickness of the lithosphere our results indicate an elastic thickness of less than 20 km these value support the notion that a major portion of the buoyancy that has driven uplift resides at depths less than 100 km and that upper mantle processes such as small scale convection may play a significant role in the buoyant uplift of the southern rockies as well as other actively uplifting areas of the western united states further support for this hypothesis is provided by high coherence for the geoid topography relationship for nearly all wavelengths between 50 and 1000 km

the evolution of impact basins cooling subsidence and thermal stress potentially important contributors to the topography and tectonics of multi ring impact basins are the thermal contraction and thermal stress that accompany the loss of heat emplaced during basin formation heat converted from impact kinetic energy and contributed from the uplift of isotherms during cavity collapse are important components in the energy budget of a newly formed basin that the subsequent cooling may have been an important factor in the tectonic evolution of the orientale basin is suggested by the deep central depression and by a surrounding region of extensive fissuring to test these concepts we develop models for the anomalous temperature distribution immediately following basin formation and we calculate the resulting elastic displacement and stress fields that then would accompany cooling of the basin region all models predict subsidence of the basin floor and a near surface stress field consistent with fissuring in addition the rates of cooling and of accumulation of thermal stress are in agreement with the inferred timing of fissure formation in orientale the sensitivity of the predicted displacements and stresses to the initial temperature field allows us to place bounds on the quantity and distribution of impact heat emplaced during basin formation in order to be consistent with the observed topography and the distribution of fissures in the orientale basin the buried heat deposited during the basin forming event was between 1032 and 1033 erg it is likely that most of this heat was concentrated within a distance of 100 200 km from the point of impact

controls on tellurium in base precious and telluride minerals in the panormos bay ag au te deposits tinos island cyclades greece tellurium bearing base metal assemblages dominate the eight stages of mineralization in quartz calcite adularia illite epithermal au ag te veins at panormos bay tinos island cyclades tellurium bearing sulfides and sulfosalts both preceded and followed the main telluride forming event stage v the complex stage v telluride assemblage was characterized by a sequence of early ag middle cu and late au bearing tellurides there is textural evidence for epitaxial growth of the tellurides phase separation of carbon dioxide would have caused h2te g to partition into a gaseous phase and resulted in ph neutralization due to rapid up vapor transport tellurium bearing vapors probably supersaturated condensed as droplets and were resorbed into the ore forming solution these mechanisms enhanced local te enrichment in the mineralizing liquid above equilibrium of te as h2te g i e log f h2te g values of 0 5 to 1 5 and resulted in epitaxial growth of stage v tellurides epitaxy in the panormos bay case can be simulated by the stranski krastanov crystal growth model for supersaturation ratios with s values of 1 and 4 we predict an overall increase of the nucleation rate of tellurium and subsequent telluride precipitation

an oligocene extrusion wedge of blueschist facies nappes on evia aegean sea greece implications for the early exhumation of high pressure rocks we show that the styra nappe of the cycladic blueschist unit on evia constitutes a wedge of high pressure rocks extruded during early stages of orogeny the nappe pile on evia was assembled during d 2 top to the ssw directed thrusting in restored oligocene coordinates which emplaced the styra and ochi nappes of the cycladic blueschist unit above the almyropotamos nappe between c 33 and 21 ma peak metamorphism of the almyropotamos nappe at c 23 ma occurred at lower metamorphic pressure showing exhumation of the styra nappe during underthrusting and burial of the almyropotamos nappe this exhumation was largely accomplished by the d 2 top to the nne displacing mt ochi normal sense shear zone normal shearing commenced at c 33 ma under peak high pressure metamorphism in the styra and ochi nappes fission track dating indicates slow cooling after d 2 in the styra nappe subsequently the former thrust contact between the almyropotamos nappe and the styra nappe was reactivated as a d 3 top to the ese extensional shear zone and this extensional phase led to the formation of a number of middle to late miocene graben our main conclusion is that there is strong evidence for an oligocene extrusion wedge accomplishing the early exhumation of the styra nappe which demonstrates the importance of extrusion wedges for the initial exhumation of the cycladic blueschist unit

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

seasat observations of lithospheric flexure seaward of trenches lithospheric flexure seaward of deep ocean trenches is evident in seasat altimeter observations of the marine geoid in fact mechanical models of lithospheric flexure can be tested directly on the seasat altimeter data we have used a simple elastic model for the oceanic lithosphere and after least squares adjustments have recovered estimates of model parameters including outer rise or amplitude or wavelength and effective lithospheric thickness effective lithospheric thicknesses have been recovered for six regions the mariana the kuril the philippine the aleutian the izu bonin and the middle america or s these results support the proposition that effective thickness te increases with age of lithosphere in approximate accord with the relation te c age1 2 where c 4 km m y 1 2 in fact our altimetric results agree more closely with this relation than do published results based on bathymetric data the close agreement with the thickness age relation suggests that there is no longer any need to assume that significant horizontal compression acts across the kuril marianas and izu bonin trenches this thickness age relation implies that flexural strength of the oceanic lithosphere is temperature controlled

behaviour of the oceanic lithosphere at subduction zones plastic yield strength from a finite element method abstract using the finite element method to study the deflection of the oceanic lithosphere at subduction zones shows that deflection of an elastic plastic model agrees with observed bathymetry data except for 2 examples kermadec and mariana where the lithospheric behaviour remains elastic seaward of the trench seven of the cases we studied could be easily fitted and enabled us to compute an effective yield strength the average value of which is about 3 8 to 4 8 kbar and seems to be the same in every case

timing slip rate displacement and cooling history of the mykonos detachment footwall cyclades greece and implications for the opening of the aegean sea basin we constrain the slip and cooling history of the mykonos detachment footwall using thermochronometry a u pb zircon age of 13 5 0 3 ma dates intrusion of the mykonos monzogranite 40 ar 39 ar hornblende and biotite ages from the monzogranite are 12 7 0 6 ma and 10 9 0 6 ma whereas zircon and apatite fission track ages range from 13 0 8 ma to 10 7 0 8 ma and 12 5 2 2 ma to 10 5 1 8 ma u th he ages range from 13 6 0 6 ma to 9 0 0 7 ma for zircon and 11 1 0 5 ma to 8 9 0 4 ma for apatite the ages in part overlap within 2 errors and together with the long apatite fission track lengths 14 m support rapid cooling at rates 100 c ma 1 the low temperature thermochronometric ages decrease east northeastwards in the direction of hanging wall transport on the mykonos detachment age distance relationships show that the mykonos detachment slipped at an average rate of 6 0 9 2 2 4 km ma 1 causing c 30 km of offset and c 12 km of exhumation this result indicates that miocene low angle normal faulting was not important for the exhumation of the cycladic blueschist unit the opening of the aegean sea basin in the miocene was controlled by a few large magnitude low angle normal faults

the kallianos au ag te mineralization evia island greece a detachment related distal hydrothermal deposit of the attico cycladic metallogenetic massif the kallianos au ag te deposit in evia island greece comprises sixteen syntaxial veins that intersect the schists and marbles of the cycladic blueschist unit the veins are filled with quartz i and quartz ii contain two hypogene ore stages stages i and ii and are surrounded by infrequent muscovite chlorite alteration zones a magmatic origin is deduced for the kallianos au ag te mineralization based on stable s c si o and h and radiogenic pb sr and rb isotopes and fluid chemistry the veins were deposited under pressures of 220 to 145 bars and temperatures of 260 to 120 c from almost neutral h2te bearing hydrothermal fluids with a salinity of 2 2 to 15 8 wt nacl equivalent the telluride mineralization related to stage ii was deposited at 180 c and evolved from au through bi to ag bearing tellurides the vein minerals precipitated by simple cooling of almost non reactive fluids that retained their initial magmatic signature taking into account the magmatic origin of the kallianos deposit we examine two proximal areas with granodioritic and leucogranitic intrusions similar to those associated with base and precious metal mineralization at lavrion 8 3 to 7 1 ma and tinos island 15 to 13 ma as potential sources for the kallianos fluids rb sr geochronology dating of the distal kallianos au ag te veins gave an age range of 8 1 to 7 6 ma implying that an overlapping and channelized hydrothermal system was active at the northern part of the attico cycladic metallogenetic massif utilizing the cbu detachment zones as fluid pathways

gis based regionalization of a karst water system in xishan mountain area of taiyuan basin north china summary a clear description of the structural features and path of groundwater flow for a karst water system is a basis for establishing a hydrogeologic conceptual model in a basin in a case study of the karst system of xishan mountain of taiyuan basin typical of hydrogeologic systems in north china and elsewhere in the world we extracted quantitative information of hydrogeologic structure and regionalized the interior structure of the karst water system using a geographic information system gis technique the information extracted from lithofacies paleogeography geology tectonics and hydrogeology includes the isolines of the top of the regional aquiclude the projected section of both planes of a fault and plotting the regional saturated zone the passage zone and the local saturated zone in the karst water system we analyzed the distribution range of karst water aquifers of xishan mountain the permeability of the stratum the boundary characteristics and the relationship between the interior and exterior system it was essential to clarify the interactions among the karst water systems of the mountain area surface water pore water in the caenozoic unconsolidated materials and the deep karst water under the basin this research shows that the study area can be divided into two subsystems 1 lancun spring and jinci spring and 2 xiye spring subsystem 1 includes the regional saturated zone the passage zone and the local saturated zone we demonstrated that lancun spring and jinci spring belong to the same regional karst water system subsystem 2 results from the perched groundwater formed by a local impermeable bed the results show that this type of integrated analysis is a useful method to extract hydrogeologic information and can be applied to a mountain area without much investigated data in particular where carbonate formations or layered permeable rock are the most important aquifers

subduction and exhumation related structures in the cycladic blueschists insights from south evia island aegean region greece 1 detailed geological mapping structural investigation and amphibole chemistry analyses in southern evia aegean sea greece allow us to place new constraints on the internal structural architecture and tectonic evolution of the cycladic blueschists we show that the early deformation history was related to ese directed thrusting resulting in the stacking of the styra and ochi nappes which constitute the cycladic blueschist unit in evia these early thrust movements initiated just before and proceeded at peak conditions of the eocene high pressure metamorphism subsequent constrictional deformation gave rise to e w trending upright folding accomplished at the early exhumation stage the main ductile stage exhumation occurred during a single deformation phase associated with the decompression of blueschist rocks from the stability field of crossite to that of actinolite this phase was characterized by localization of ductile deformation into a series of major tens of meters thick ene directed shear zones which cut up section in their transport direction and restack the early thrust and fold sequence locally bringing the structurally lower styra nappe over the higher ochi nappe it is suggested that these zones operated as thrusts rather than normal sense shear zones as has been previously argued and were possibly formed during the oligocene ene ward extrusion of the blueschists brittle ductile ne dipping normal faulting of post early miocene age was probably responsible for the final exhumation of rocks

inelastic models of lithospheric stress 11 implications for outer rise seismicity and dynamics summary outer rise seismicity and dynamics are examined using inelastic models of lithospheric deformation which allow a more realistic characterization of stress distributions and failure behaviour we conclude that thrust and normal faulting outer rise earthquakes represent substantially different states of stress within the oceanic lithosphere specifically the normal faulting events occur in response to downward plate bending which establishes the standard bending dominated state of outer rise stress and the thrust faulting events occur in response to an elevated level of in plane compression which develops only in response to exceptional circumstances this interpretation accounts for the observation that normal faulting outer rise earthquakes occur more frequently and are more widely distributed than their thrust faulting counterparts an observation for which the simple bending model offers no explanation in addition attributing both thrust and normal faulting outer rise earthquakes to plate bending implies that both classes of events should occur within relatively close lateral proximity to one another because both are allegedly a manifestation of the same bendingdominated stress distribution whereas in reality this is not observed we propose that the tendency for thrust faulting outer rise earthquakes to exhibit greater source depths than their normal faulting counterparts an observation that is frequently cited in support of the bending interpretation of the former is merely a consequence of the fact that bending induced tension is confined to the upper lithosphere our model predicts that outer rise in plane force variations may promote thrust faulting outerrise activity prior to an underthrusting interplate subduction earthquake and normalfaulting outer rise activity following such an earthquake but that both forms of outerrise activity are unlikely to be associated with the same subduction earthquake a corollary implication of our model is that subduction earthquakes are likely to be either preceded by or followed by an absence of large outer rise earthquakes levels of in plane compression necessary to generate thrust faulting outer rise earthquakes are attributed to stress concentrations within the subducting plate that are induced by relatively localized resistance to regionally distributed plate driving forces resistance of this nature may result from either the attempted subduction of relatively buoyant i e isostatically compensated bathymetric features or the existence of strong interplate

lithospheric 3 d flexure modelling of the oceanic plate seaward of the trench using variable elastic thickness summary whendescribingthemechanicalbehaviourofthelithospheremodelledasathinplate themost important parameter corresponds to itsflexural rigidity which is commonly expressed through the effective elastic thickness te this parameter is a measure of the stiffness of the plate and defines the maximum magnitude and wavelength of those surface loads that can be supported without suffering unelastic deformation realistic 3 d models of the flexural response of the lithosphere near the trench are scarce because of the mathematical and computational complexity we present a method for determining the flexure of the lithosphere caused by the combined effect of 3 d seamount loading and bending of the lithosphere near the trench our method consists on solving numerically the flexure equations of the reissner mindlin thin plate theory including variable thickness using the finite element method with mesh adaptation the method was applied to study the flexure of the oceanic nazca lithosphere beneath the o higgins seamount group which lies 70km seaward of the chile trench the results show that an elastic thickness te of 5km under the seamounts a te of 15km far from the trench and a te of 13km near the trench can explain both the down deflection of the oceanic moho and bending of the oceanic lithosphere observed in seismic and gravity profiles in order to study the impact of high trench curvature on the morphology of the outer rise we apply the same methodology to study and model the flexure of the lithosphere in the arica bend region 14 s 23 s results indicate that the te values are overestimated if the 3 d trench curvature is not included in the modelling

viscosity of oceanic asthenosphere inferred from remote triggering of earthquakes a sequence of large interplate earthquakes from 1952 to 1965 along the aleutian arc and kurile kamchatka trench released accumulated stresses along nearly the entire northern portion of the pacific plate boundary the postseismic stress evolution across the northern pacific and arctic basins calculated from a viscoelastic coupling model with an asthenospheric viscosity of 5 x 10 17 pascal seconds is consistent with triggering of oceanic intraplate earthquakes temporal patterns in seismicity at remote plate boundaries and space based geodetic measurements of anomalous velocity over an area 7000 by 7000 kilometers square during the 30 year period after the sequence

influence of coal mining on regional karst groundwater system a case study in west mountain area of taiyuan city northern china karstic limestone formations in the west mountain area are important water resources for taiyuan city in shanxi province northern china which is also known for its large scale coal mining production in this study area groundwater is not only exploited for water supply purposes but also drained because of coal mining the process of coal mining changes both the quantity of the karst springs and the quality of karst groundwater system because of overexploitation and overdrainage in this paper the influence of coal mining on the groundwater is analyzed from a qualitative and quantitative perspective the hydrochemical analysis results reflect the relationship of the recharge runoff and drainage the features of the medium and water rock interactions based on a qualitative understanding of the geological deposition and characteristics of the groundwater flow system three dimensional groundwater flow models are established and applied to several scenarios to explore the quantitative influence and allow better protection of the groundwater environment and better utilization of water resources

evidence of a large upper cretaceous depocentre across the continent ocean boundary of the congo angola basin implications for palaeo drainage and potential ultra deep source rocks abstract the analysis of 2d deep seismic reflection profiles across the slope and abyssal plain of the angola oceanic basin reveals the existence of a significant and formerly unknown depocentre beneath the giant cenozoic congo deep sea fan between 7000 m and 9000 m depth deposited directly onto the aptian oceanic crust the unit which is up to 2 5 km thick and extends for more than 200 km basinwards of the continent ocean boundary is probably aged albian turonian its radial fan shaped depocentre is centred on the present day congo river outlet and contains at least 0 2 mio km 3 of sediments these observations and the results from flexural modelling indicate that 1 the location of the congo river s outlet has remained fairly stable since the late cretaceous and 2 the basal unit was indeed sourced by a palaeo congo river probably located nearby the present day one thus the atlantic sedimentary system related to the exoreism of the congo river is much older than previously thought thermal modelling indicates that the maturation history of this upper cretaceous deposits is highly influenced by the interaction between the initial high heat flow of the young oceanic crust and further increase in sediment supply due to the progradation of the overlying tertiary deep sea fan during the miocene hence despite low present day heat flow values should the unit have source rock potential its basal section may be currently generating hydrocarbons all in all the results from our models also suggest that the interplay between an initially high heat flow and the further high sediment supply in areas of major river input may be a key factor for the thermal maturation of potential source rocks deposited onto a present day cold oceanic crust

granite intrusion in a metamorphic core complex the example of the mykonos laccolith cyclades greece abstract the aegean domain is a well suited place to study the formation of metamorphic core complex mcc and to investigate the role of syn tectonic granites on their development in the northern cyclades the mykonos delos rhenia mcc is characterized by the intrusion of a kilometer scale late miocene pluton of i type granitoids within a migmatitic gneiss dome new combined ams anisotropy of magnetic susceptibility and microstructural studies on the mykonos granitoids together with recently published thermochronological data allow us to use the granitoids as strain markers the mykonos granitoids form a laccolith like intrusion with a n70 e long axis the laccolith is strongly asymmetric with an outlying root zone to the sw and a major body mainly developed to the ne the laccolith construction is due to successive pulses of more or less differentiated magma that intruded the cycladic blueschist unit the attitude of stretching markers suggests an important about 60 vertical axis local rotation phenomenon in the cycladic upper crust during the exhumation of the mykonos mcc structural data suggest a four stage evolution of the mykonos mcc i a first stage characterized by flat shearing toward the n ne and by the formation of a domal structure in migmatitic paragneisses with multi scale generation of folds with axes either perpendicular or parallel to the regional stretching as a result of the interplay between regional n20 e directed extension and ew shortening ii a second stage marked by the emplacement of the mykonos laccolith at 13 5 0 3 ma at the top of the migmatitic paragneisses iii the third stage corresponding to the development of protomylonitic foliations and lineations in the whole laccolith in high to medium temperature conditions and iv the late stage marked by an acceleration of the exhumation of the mykonos mcc this exhumation was accommodated by important rotations of upper crustal blocks during the end of the exhumation processes around 10 ma deformation localized at the top of the laccolith in semi ductile conditions and then in brittle conditions in the major detachment plane our study shows that the cycladic plutonism event had no role on the initiation of the mcc however the geometry of the mykonos intrusion supports that the magmas are sucked into the direction of regional extension and that the intrusion of magmas has caused an acceleration of the last stages of the mcc development this acceleration was marked by a very fast exhumation of the laccolith after its emplacement

thermoelastic stress how important as a cause of earthquakes in young oceanic lithosphere we present a series of exploratory models which test the hypothesis that thermoelastic stress is a significant contributor to the state of stress in young oceanic lithosphere less than 35 m y in age in support of this hypothesis is the concentration of seismicity in lithosphere younger than 15 m y where cooling rates are relatively high most near ridge earthquakes have focal depths between the moho and the depth of the 800 c isotherm thrust and strike slip events dominate the shallowest seismicity while the focal mechanisms of the deeper events are generally characterized by normal faulting to assess the importance of thermal stress in the generation of near ridge earthquakes we model the lithosphere as an elastic half space in which the response to cooling is computed using the method of thermoelastic displacement potentials a key assumption in the models is that stress is relieved on time scales generally short compared with the age of the lithosphere a further assumption in some models is that material will not contribute thermal stress until it has cooled below an elastic blocking temperature normal faulting is predicted throughout the lithosphere in thermal stress models based on simple half space cooling models in which a cooled surface layer is incorporated to simulate the effect of hydrothermal circulation on shallow thermal structure predict stresses that can match the locations of both thrust and normal faulting earthquakes near mid ocean ridges the addition of a ridge push stress to the computed thermal stress enhances the likelihood of thrust faulting in the uppermost lithosphere at ages greater than about 15 m y but probably contributes little to the stress field at younger ages though these simple models are limited by several simplifying assumptions particularly in the immediate vicinity of the ridge axis they support the hypothesis that thermoelastic stress can play a major role in the tectonics of young oceanic lithosphere

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

strength and rheology of the western u s cordillera effective elastic thickness te depends primarily on temperature composition and state of stress of the lithosphere in this paper we examine high resolution spectral estimates of te and their relationships to regional heat flow age of the lithosphere seismic properties stress orientations and earthquake focal depths of the western u s cordillera the relationship of te to heat flow indicates that ductile flow accommodates long term 106 to 108 years isostatic response at different levels of the crust and upper mantle depending principally on age and by implication bulk composition of the lithosphere isostatic response is primarily controlled by the upper mantle in archean lithosphere of the middle rocky mountains whereas te depends on lower crustal flow in early proterozoic lithosphere of the colorado plateau the yellowstone snake river plain volcanic field and significantly extended regions in the basin range and northern rocky mountains are associated with latest proterozoic aged lithosphere and indicate middle to upper crustal control of long term te we also show that azimuthal variations of te reflect deviatoric stress in the lithosphere te is found empirically to approximate the 95th percentile focal depth of background seismicity the latter relationship is inconsistent with brittle ductile control of focal depth indicating that another rheological transition e g from stick slip to stable sliding frictional behavior is responsible tectonic and structural relationships expand upon the hypothesis that the geographic distribution of tectonic features depends fundamentally on spatial variations in strength of the lithosphere moreover we find a spatial correlation of the intermountain seismic belt to a marked transition in te implying that forces responsible for this active seismic zone are derived from local buoyancy anomalies rather than from current day plate boundary interactions

a new multilayered model for intraplate stress induced differential subsidence of faulted lithosphere applied to rifted basins in plane horizontal stresses acting on predeformed lithosphere induce differential flexural vertical motions a high precision record of these motions can be found in the sedimentary record of rifted basins originally it was proposed that rifted basins experience flank uplift and basin center subsidence in response to a compressive change of in plane stress which agrees well with observed differential motions subsequently published models predicted that the vertical motions may be opposite because of the flexural state of the lithosphere induced by necking during extension however the total flexural and permanent geometry of the lithosphere underlying the rifted basin is the controlling parameter for the in plane stress caused vertical motions the largest part of this preexisting geometry is caused by faulting in the uppermost brittle part of the crust and ductile deformation in the underlying parts of the lithosphere we present a new multilayered model for stress induced differential subsidence taking into account the technically induced preexisting geometry of the lithosphere including faults in the upper crust as continental lithosphere may exhibit flexural decoupling due to a weak lower crustal layer the new multilayer in plane stress model discriminates the geometries of the separate competent layers at a basin wide scale the new model predicts that a compressive change of in plane force results in basin center subsidence and flank uplift confirming the original hypothesis compared to all previous models the new model requires a lower horizontal stress level change to explain observed differential vertical motions

origin of a barite sulfide ore deposit in the mykonos intrusion cyclades trace element isotopic fluid inclusion and raman spectroscopy evidence abstract the polymetallic mykonos vein system in the cyclades greece consists of 15 tension gashes filled with barite quartz pyrite sphalerite chalcopyrite and galena in ca 13 5 ma i type mykonos monzogranite zones of silica and chlorite muscovite alteration are associated with the veins and overprint pervasive silicification phyllic and argillic alteration that affected large parts of the monzogranite the mineralization cements breccias and consists of an early barite silica pyrite sphalerite chalcopyrite assemblage followed by later argentiferous galena a combination of fluid inclusion and stable isotope data suggests that the barite and associated mineralization were deposited from fluids containing 2 to 17 wt nacl equivalent at temperatures of 225 to 370 c under a hydrostatic pressure of 100 bars the mineralizing fluids boiled and were saturated in h 2 s and so 2 calculated 18 o h2o and d h2o initial 87 sr 86 sr isotope compositions and the trace and rees elements contents are consistent with a model in which the mineralizing fluids were derived during alteration of the mykonos intrusion and subsequently mixed with miocene seawater heterogeneities in the calculated 34 s so4 2 and 34 s h2s compositions of the ore fluids indicate two distinct sources for sulfur namely of magmatic and seawater origin and precipitation due to reduction of the so 4 2 during fluid mixing the physicochemical conditions of the fluids were ph 5 0 to 6 2 log f s2 13 8 to 12 5 log f o2 31 9 to 30 9 log f h2s g 1 9 to 1 7 log f te2 7 9 and log so 4 2 aq h 2 s aq 2 6 to 5 5 we propose that retrograde mesothermal hydrothermal alteration of the mykonos monzogranite released barium and silica from the alkali feldspars barite was precipitated due to mixing of so 4 2 rich miocene seawater with the ascending ba rich magmatic fluid venting upwards in the pluton

the lavrion pb zn fe cu ag detachment related district attica greece structural control on hydrothermal flow and element transfer deposition abstract the impact of lithological heterogeneities on deformation fluid flow and ore deposition is discussed based on the example of the lavrion low angle detachment partly accommodating gravitational collapse of the hellenides orogenic belt in greece the lavrion peninsula is characterised by a multiphase pb zn fe cu ag ore system with a probable pre concentration before subduction followed by progressive remobilisation and deposition coeval with the development of a low angle ductile to brittle shear zone the mylonitic marble below the detachment shear zone is composed of white layers of pure marble alternating with blue layers containing impurities sio2 al2o3 carbonaceous material ductile mylonitic deformation is more pervasive in the less competent impure blue marble we propose that localised deformation in the impure marble is associated with fluid circulation and dolomitisation which in turn causes an increase in competence of these layers mineralised cataclastic zones crosscutting the mylonitic fabric are preferentially localised in the more competent dolomitic layers oxygen and carbon isotopic signatures of marble invaded by carbonate replacement deposits during ductile to ductile brittle deformation are consistent with decarbonation coeval with the invasion of magmatic fluids mineralised cataclastic zones reflecting brittle deformation evolve from low 13c to low 18o signatures interpreted as local interaction with carbonaceous material that trends toward the contribution of a surface derived fluid these features indicate that the lavrion area records a complex deposition history influenced by the evolution of fluid reservoirs induced by the thermal and mechanical evolution of the marble nappe stack ore remobilisation and deposition associated with the activity of the low angle detachment is i firstly related to the intrusion of the plaka granodiorite leading to porphyry type and carbonate replacement mineralisation during ductile brittle deformation and ii then marked by progressive penetration of surface derived fluids guided by strain localisation in the more competent levels leading to epithermal mineralisation associated with brittle deformation

constraints on yield strength in the oceanic lithosphere derived from observations of flexure summary the wavelength and amplitude of outer rises seaward of sub duction zones and arches surrounding islands and seamounts are used to parameterize flexure profiles in terms of the moment and curvature at the first zero crossing the data show the clear age dependence in the mechanical thickness of the lithosphere up to 60 100myr saturation of moment at large curvature is interpreted in terms of a depth dependent yield strength for the lithosphere using relations adopted from laboratory experiments of rock deformation a comparison of theoretical curves with observed moments indicates that old oceanic lithosphere has no long term strength below about 40 km depth with no difference between 100 and 165 myr old crust moderate axial loading forces 200 mpa can explain most variations in the moment curvature observations except in the case of the kuril trench which appears anomalous given the age of the crust regional tension causes greater variability in moment as compared to regional compression because of the greater slope in the brittle failure envelope under tension the observations point to a lithosphere weaker than the prediction from experimental deformation of rocks of the possible weakening mechanisms elevated pore fluid pressure on faults does not predict the correct age dependence and is incompatible with earthquake focal mechanisms our favoured explanation is that the activation energy q appropriate for ductile flow at geological strain rates is lower than the values derived from laboratory extrapolations of dry olivine data taken at high temperatures if recent oceanic geotherms are reliable q in the lower lithosphere must be lower than 100kcal mol 1 the method used here is most appropriate for trench profiles with curvatures greater than 10 7m 1 for lower curvatures such as along seamount profiles small errors in the curvature estimate cause large changes in rheological parameters

a reassessment of outer rise seismicity and its implications for the mechanics of oceanic lithosphere we use body waveform modelling to constrain the source parameters of earthquakes occurring globally in oceanic lithosphere beneath the subduction zone outer rise and outer trench slope these data are then used to map the stress state in the lithosphere of the downgoing plate as it bends into the subduction zone our results provide new constraints on the faulting of oceanic lithosphere at the outer rise which is important for understanding the transmission of plate driving forces through the subduction system in all cases shallow normal faulting earthquakes are observed at the top of the plate and are separated in depth from any deeper thrust faulting earthquakes no temporal variation associated with large thrust faulting earthquakes on the subduction interface is seen in the depth extent of each type of faulting at the outer rise the transition depth from trench normal extension to compression is found to vary in agreement with models in which deformation is driven by the combination of in plane stresses and bending stresses resulting principally from slab pull combining the seismologically derived constraints on the thickness of the elastic core of the plate with estimates of the plate curvature we place upper bounds on the strength of the lithosphere at the outer rise which is required to be 300 mpa for a constant yield stress model or governed by an effective coefficient of friction of 0 3

a frequency domain approach to groundwater recharge estimation in karst this paper presents an alternative method for determining the values of parameters of a groundwater recharge model the phreatic zone of a karst aquifer is considered as the linear and time invariant filter that transforms the input signal of groundwater recharge rates into the output signal of spring discharges similarities between transfer functions of total rainfall rates and transfer functions of groundwater recharge rates are the basis for developing the parametric periodogram depending on parameters of a groundwater recharge model the values of parameters are estimated by minimizing the differences between the parametric periodogram and a periodogram of spring discharges the approximate whittle log likelihood function is the criterion for determining the optimal values of the parameters by using this frequency domain approach groundwater balance calculations are avoided so the method can be applied on unexplored karst aquifers when groundwater balance cannot be achieved without extensive geologic and hydrogeologic investigations the results of the applications on two springs located in the dinaric karst area in croatia are discussed

timing of tectonic emplacement of the ophiolites and terrane paleogeography in the hellenides the timing of tectonic emplacement of the ophiolites is analyzed in the four oceanic terranes of the hellenides h2 h4 h6 h8 the criteria for this analysis are based on a the post emplacement sedimentary cover or intrusive rocks b the syn emplacement tectonostratigraphic formations and c the youngest rocks involved in the structure of the autochthon and the allochthon unit in each case the timing becomes younger towards the more external tectonic units of the hellenides with i late eocene oligocene age in the external ophiolite belt of the pindos cyclades oceanic terrane h2 ii late jurassic early cretaceous age in the internal ophiolite belt of the vardar axios oceanic terrane h4 iii post liassic pre late jurassic age in the ophiolites of lesvos circum rhodope oceanic terrane h6 and iv pre late jurassic age in the ophiolites of volvi eastern rhodope terrane h8 an ophiolite obduction model can be applied with the ophiolitic nappes always emplaced on top of pre alpine continental terranes with mesozoic shallow water carbonate platforms the geometry of the continental terranes drifting during the mesozoic within the tethys ocean controls the number and dimensions of the tethyan oceanic basins where a continental terrane dies out the two adjacent oceanic basins merge into one larger basin this seems to be the case of the pelagonian terrane h3 which is terminated north of skopje where the pindos oceanic basin h2 merges with the vardar axios oceanic basin h4

lithospheric bending at subduction zones based on depth soundings and satellite gravity a global study of trench flexure was performed by simultaneously modeling 117 bathymetric profiles original depth soundings and satellite derived gravity profiles a thin elastic plate flexure model was fit to each bathymetry gravity profile by minimization of the l norm the six model parameters were regional depth regional gravity trench axis location flexural wavelength flexural amplitude and lithospheric density a regional tilt parameter was not required after correcting for age related trend using a new high resolution age map estimates of the density parameter confirm that most outer rises are uncompensated we find that flexural wavelength is not an accurate estimate of plate thickness because of the high curvatures observed at a majority of trenches as in previous studies we find that the gravity data favor a longer wavelength flexure than the bathymetry data a joint topography gravity modeling scheme and fit criteria are used to limit acceptable parameter values to models for which topography and gravity yield consistent results even after the elastic thicknesses are converted to mechanical thicknesses using the yield strength envelope model residual scatter obscures the systematic increase of mechanical thickness with age perhaps this reflects the combination of uncertainties inherent in estimating flexural wavelength such as extreme inelastic bending and accumulated thermoelastic stress the bending moment needed to support the trench and outer rise topography increases by a factor of 10 as lithospheric age increases from 20 to 150 ma this reflects the increase in saturation bending moment that the lithosphere can maintain using a stiff dry olivine rheology we find that the lithosphere of the gdh1 thermal model stein and stein 1992 is too hot and thin to maintain the observed bending moments moreover the regional depth seaward of the oldest trenches 150 ma exceeds the gdh1 model depths by about 400 m

analytical solutions for 3 d flexural deformation of semi infinite elastic plates summary the theory of elastic plate flexure has played a prominent role in isostatic studies and investigations of lithospheric deformation caused by vertical tectonism simple analytical asymmetrical solutions exist when the boundaries of the plate are far removed from the area where the load is applied when deformation is driven by end loads i e bending moments and shear forces the problem is usually simplified to yield a 2 d solution that approximates a cross section of the 3 d solution we present analytical green s functions for the point force response of semi infinite elastic plates resting on an inviscid substratum and being acted upon by constant in plane forces and arbitrary end loads this solution may be used to study deformation and stresses caused by loads close to a free geological boundary e g a trench or weak fracture zone we also present green s functions for the case when two semi infinite plates of different rigidities are mechanically coupled and subject to a point load this solution may be useful when studying deformation near mechanically strong fracture zones or at ocean continent transitions the analytical solutions provide simple alternatives to and calibration of complex numerical finite element or finite difference solutions and furthermore give additional physical insight into the geological process to be examined the analytical methods are used to demonstrate the different stress patterns that may arise near weak and strong geological boundaries we also illustrate how the observed scatter in 2 d determinations of elastic thickness at subduction zones may partly have its origin in 3 d effects

the accuracy of some lithospheric bending parameters summary a procedure is described for iterative least squares inference of bending parameters from lithospheric deflection profiles the method is applied to several bathymetric profiles seaward of subduction zones and used to study the accuracy with which these parameters and related ones such as plate thickness and moment curvature relations can be determined the presence of typical bathymetric undulations particularly at wavelengths of the order of the flexural wavelength and greater prevents the inference of effective elastic thickness from single profile data to better than 12 km 2 mixing of elastic and inelastic model estimates of effective thickness further increases scatter it is found that the sensitivity of inferred bending moments on the outer trench wall to typical uncertainties of regional bathymetric slope is substantial and inferred estimates of inelastic behaviour need to be interpreted with caution

an iterative spectral solution method for thin elastic plate flexure with variable rigidity s u m m a r y thin plate flexure theory provides an accurate model for the response of the lithosphere to vertical loads on horizontal length scales ranging from tens to hundreds of kilometres examples include flexure at seamounts fracture zones sedimentary basins and subduction zones when applying this theory to real world situations most studies assume a locally uniform plate thickness to enable simple fourier transform solutions however in cases where the amplitude of the flexure is prominent such as subduction zones or there are rapid variations in seafloor age such as fracture zones these models are inadequate here we present a computationally efficient algorithm for solving the thin plate flexure equation for non uniform plate thickness and arbitrary vertical load the iterative scheme takes advantage of the 2 d fast fourier transform to perform calculations in both the spatial and spectral domains resulting in an accurate and computationally efficient solution we illustrate the accuracy of the method through comparisons with known analytic solutions finally we present results from three simple models demonstrating the differences in trench outer rise flexure when 2 d variations in plate rigidity and applied bending moment are taken into account although we focus our analysis on ocean trench flexure the method is applicable to other 2 d flexure problems having spatial rigidity variations such as seamount loading of a thermally eroded lithosphere or flexure across the continental oceanic crust boundary

the effective elastic lithosphere under the cook austral and society islands abstract we have determined the elastic thicknesste of the oceanic lithosphere along two volcanic chains of the south central pacific cook austral and society islands we used a three dimensional spatial method to model the lithospheric flexure assuming a continuous elastic plate the model was constrained by geoid height data from the seasat satellite along the cook austral chain the elastic thickness increases westward from 2 4 km at mcdonald hot spot to 14 km at rarotonga at mcdonald seamount however the data are better explained by a local compensation model the observed trend shows an increase ofte with age of plate at loading time however the elastic layer under the cook austral appears systematically thinner by several kilometers than expected for normal seafloor suggesting that substantial thermal thinning has taken place in this region considering the apparent thermal age of the plate instead of crustal age improves noticeably the results along the society chainte varies from 20 km under tahiti to 13 km under maupiti which is located 500 km westward when plotting together the society and cook australte results versus age of load we notice that within the first five million years after loading te decreases significantly while tending rapidly to an equilibrium value this may be interpreted as the effect of initial stress relaxation which occurs just after loading inside the lower lithosphere and suggests that the presently measured elastic thickness under the very young tahiti load 0 8 ma is not yet the equilibrium thickness

an integrated zircon geochronological and geochemical investigation into the miocene plutonic evolution of the cyclades aegean sea greece part 1 geochronology we use 369 individual u pb zircon ages from 14 granitoid samples collected on five islands in the cyclades in the aegean sea greece for constraining the crystallisation history of i and s type plutons above the retreating hellenic subduction zone miocene magmatism in the cyclades extended over a time span from 17 to 11 ma the ages for s type granites are systematically 2 million years older than those for i type granites considering plutons individually the zircon data define age spectra ranging from simple and unimodal to complex and multimodal seven of the 14 investigated samples yield more than one distinct zircon crystallisation age with one i type granodiorite sample from mykonos island representing the most complex case with three resolvable age peaks two samples from s type granites on ikaria appear to have crystallised zircon over 2 3 million years whereas for the majority of individual samples with multiple zircon age populations the calculated ages deviate by 1 1 5 million years we interpret our age data to reflect a protracted history involving initial partial melting at deeper lithospheric levels followed by crystallisation and cooling at shallower crustal levels our study corroborates published research arguing that pluton construction is due to incremental emplacement of multiple magma pulses over a few million years assuming that multiple age peaks of our 14 samples can indeed serve to quantify time spans for magmatic emplacement our data suggest that aegean plutons were constructed over a few million years our tectonic interpretation of the u pb ages is that the s type granites resulted from partial melting and migmatisation of the lower crust possibly starting at 23 ma the i type granites and associated mafic melts are interpreted to reflect the magmatic arc stage in the cyclades starting at 15 ma

extensional faulting on tinos island aegean sea greece how many detachments zircon and apatite fission track zft and aft and u th he 40ar 39ar hornblende and u pb zircon ages from the granites of tinos island in the aegean sea greece suggest together with published zft data that there are three extensional detachments on tinos the tinos granites crosscut the tinos detachment cooling of the granites was controlled by the livadi detachment which occurs structurally above the tinos detachment our u pb zircon age is 14 6 0 2 ma and two 40ar 39ar hornblende ages are 14 4 0 4 and 13 7 0 4 ma zft and aft ages go from 14 4 1 2 to 12 2 1 0 ma and 12 8 2 4 to 11 9 2 0 ma u th he ages are from 10 4 0 2 to 9 9 0 2 ma zircon and 11 9 0 5 to 10 0 0 3 ma apatite all ages decrease northeastward in the direction of hanging wall transport on the livadi detachment and age distance relationships yield a slip rate of 2 6 3 3 1 0 km ma 1 this rate is smaller than a published slip rate of 6 5 km ma 1 for the vari detachment which is another detachment structurally above the tinos detachment because of the different rates and because published zft ages from the footwall of the vari detachment are 10 ma we propose that the vari detachment has to be distinguished from the older livadi detachment we discuss various models of how the extensional detachments may have evolved and prefer a scenario in which the vari detachment cut down into the footwall of the livadi detachment successively exhuming deeper structural units the thermochronologic ages demonstrate the importance of quantitative data for constraining localization processes during extensional deformation

stress and relaxation time in the viscoelastic lithosphere inferred from the outer topographic rise the deformation of a thin viscoelastic plate is usually analyzed by use of an equation that is derived with an artificial assumption of the poisson s ratio equal to 1 2 it is shown in this paper that a simple treatment applicable to an arbitrary value of poisson s ratio is possible by introducing a new variable that represents the pressure gradient between the top and bottom of the plate in this treatment a one dimensional stationary deformation of moving plate is given by a simple analytic equation this equation is used to analyze the bathymetry of the outer topographic rise seaward of the deep sea trenches the analysis reveals that the lithosphere in the western pacific trenches is subject to an extensional horizontal force of 100 mpa or greater the horizontal force may be much less or even compressive in the eastern pacific trenches to prevent horizontal force and bending stress from being extraordinarily large the maxwell relaxation time of the plate must be 1 m y or shorter and the effective viscosity must be 1024 pa s or less

trench motion slab geometry and viscous stresses in subduction systems summary a semi analytic 3 d model for subduction within a newtonian viscous upper mantle provides a dynamically consistent means of computing viscous stress trench motion and slab geometry in subduction systems although negative slab buoyancy provides the basic driving force for subduction slabs that extend from the surface to the base of the upper mantle are oversupported by viscous stresses in the shallow 100 150 km mantle and undersupported by viscous stresses at greater depth in the upper mantle these deeper parts of the subduction system act as an engine for subduction while shallower parts act as a brake on trench motion trench migration rates and slab geometry reflect a competition between these two effects during steady state subduction trench migration rates vary approximately linearly with slab buoyancy and model rates of trench motion are in good agreement with the range of observed rates for a two layer upper mantle viscosity of 2 10 20 pa s above 300 km and 5 10 20 pa s below steady state slab dip increases as slab density decreases especially for very low density slabs which dip significantly more steeply than high density slabs the horizontal velocity at the top of the lower mantle measured relative to the foreland has a very large effect on trench migration rates rivalling or even exceeding that of slab buoyancy slab width parallel to the trench also has a significant effect on trench migration rates due to the viscous pressure of toroidal flow around the slab the stiffness of the subducting lithosphere does not exert a significant effect on trench migration rates or slab geometries for rigidities compatible with oceanic lithosphere very stiff slabs with elastic plate thicknesses more that 40 km or viscosities in the range of 10 25 10 26 pa s subduct significantly more slowly than weak slabs with trench migration rates in the range of half to a third that of weak slabs large unexpected effects on trench migration rates and slab geometry are exerted by the structure and density of the frontal prism and overriding plate indicating that local geology can exert important constraints on slab dynamics during non steady state subduction rates of trench migration respond rapidly as variably buoyant lithosphere penetrates into the asthenosphere in the absence of other driving forces for convergence trench migration rates can change by a factor of two or more in as little as 2 3 myr for example from 35 to 70 mm yr 1 when an oceanic piece of slab follows a continental one into the subduction system subduction of variable buoyancy lithosphere is accompanied by changes in slab dip with depth and through time

age dependence of oceanic intraplate seismicity and implications for lithospheric evolution we have determined depths for 16 oceanic intraplate earthquakes using body wave modeling a data set composed of these and 11 other well constrained depths shows that the maximum depth of seismicity deepens with increasing lithospheric age and appears to be bounded by a 700 800 c isotherm the maximum depth to which intraplate earthquakes occur is approximately equal to the flexural elastic thickness but much less than the seismic thickness from surface wave dispersion the maximum faulting depth is consistent with the predictions of rapid weakening at high temperatures for dry olivine rheologies determined by experimental rock mechanics oceanic intraplate earthquakes can occur at greater depths and temperatures than has previously been reported for continental crustal events presumably because oceanic lithosphere is stronger at high temperatures both the number of earthquakes and the cumulative seismic moment decrease with lithospheric age the cause of this trend is unclear possibilities include nonrandom location of preexisting weak zones with respect to the age provinces fault strengthening with age or a decrease in the stress level a decrease in intraplate stress with age is opposite that expected from ridge push stresses which increase with age but may result either from thermoelastic stresses which are greatest in young lithosphere or near ridge stress concentrations due to local heterogeneities in the spreading process

geostatistical and geochemical analysis of surface water leakage into groundwater on a regional scale a case study in the liulin karst system northwestern china abstract the liulin karst system is typical of hydrogeological systems in northern china with a group of springs as the dominant way of regional groundwater discharge surface water leakage into groundwater has been observed in six sections of the rivers in the study area to extract hydrogeological information from hydrochemical data 29 water samples were collected from the system on a trilinear diagram most of the groundwater samples are clustered around the surface waters indicating the effect of leakage on their chemistry r mode factor analysis was made on seven variables na ca mg so 4 cl hco 3 and no 3 of the samples and three principal factors were obtained the f 1 factor is composed of ca mg and so 4 the f 2 of hco 3 and no 3 and the f 3 of na and cl these factors are then used as regionalized variables in ordinary kriging for unbiased estimates of the spatial variations of their scores considering regional hydrogeological conditions the hydrogeological implications of the spatial distribution of the factor scores as related to the effects of the surface leakage are discussed to evaluate the geochemical processes the geochemical modeling code netpath was employed the modeling results show that mixing commonly occurs in the system and dolomite dissolution is more important than calcite dissolution dedolomitization calcite precipitation and dolomite dissolution driven by anhydrite dissolution is locally important in the western flank of the system where the surface water leakage has the least effect

identification of dissolved sulfate sources and the role of sulfuric acid in carbonate weathering using δ13cdic and δ34s in karst area northern china karst groundwater is one of the most important water resources for agriculture and industry in fenyang city of shanxi province northern china in the last few decades excessive exploitation of groundwater and other human activities have caused serious environmental problems in this area hence it is essential to identify the resources of pollutants that deteriorate the water quality in the area a total of 16 water samples were collected to assess the hydrochemical characteristics from wells and springs in bare karst area northern fenyang and covered karst region south of the city the chemical composition of groundwater was characterized by a dominance of ca2 mg2 hco3 and so42 which accounted for more than 85 of the total ion concentrations indicating that limestone dissolution by weathering controls water chemical composition so42 in the groundwater showed high positive significant correlation with hco3 and 13cdic showing that carbonate dissolution by sulfuric acid has important contribution to groundwater chemical composition and 13cdic value the relationship between 34s and 1 so42 revealed that the sources of so42 are different in various types of groundwater in the bare karst area so42 in springs mainly came from atmospheric precipitation while in the shallow wells it mainly came from human activities in the covered karst region so42 in quaternary pores water was mainly from anthropogenic inputs while in the deep wells it was mainly from gypsum dissolution in gypsum mine water so42 was mainly from gypsum dissolution comparing with the bare karst area human activities have significantly changed the chemical composition of groundwater in the covered karst region therefore more control policies and measures should be formulated and applied to protect the covered karst region in the future

on the reliability of lithospheric constraints derived from models of outer rise flexure summary we evaluate the common practice of utilizing elastic models of outer rise flexure to constrain lithospheric parameters such as mechanical thickness and ambient in plane force we numerically compute synthetic flexural profiles consistent with empirically determined constraints on lithospheric rheology and representative trench type boundary conditions and misfit minimization is utilized to determine the analytical solution to elastic plate flexure that most closely resembles each synthetic profile we then determine if it is possible to use the best fitting elastic solutions to recover the lithospheric mechanical thickness and level of in plane force that were assumed during the numerical computation of the synthetic profiles this methodology is analogous to the common practice of estimating lithospheric parameters by modelling bathymetric profiles with analytical descriptions of elastic plate flexure our results unequivocally indicate that in plane force cannot be reliably constrained in this manner such an approach does not even allow the qualitative nature of in plane force to be distinguished i e compressional versus tensional although in principle elastic plate models may provide reliable constraints on the mechanical thickness of oceanic lithosphere in practice uncertainties associated with bathymetric noise and the level of in plane force may in some instances render such constraints unreliable

reappraising elastic thickness variation at oceanic trenches we reassess the variation of elastic thickness as a function of lithospheric plate age using a global database of bathymetric and free air gravity profiles which are perpendicular to oceanic trenches as in many previous studies our starting point is the well known floating elastic plate model in order to remove the influence of short wavelength features not associated with lithospheric bending adjacent profiles from 10 myr bins have been stacked together to construct average profiles with standard deviations each average profile was then inverted in a two stage procedure first singular value decomposition was used to determine two unknown flexural parameters together with a regional slope and offset for any given elastic thickness this procedure was repeated for a range of elastic thicknesses second residual misfit was plotted as a function of elastic thickness and the global minimum was identified this two stage procedure makes no prior assumptions about magnitude of the load size of the bending moment or whether the elastic plate is broken continuous we obtained excellent fits between theory and observation for both bathymetric and gravity profiles from lithosphere with an age range of 0 150 ma the shape of the residual misfit function indicates the degree of confidence we have in our elastic thickness estimates the lower limit of elastic thickness is usually well determined but upper limits are often poorly constrained inverse modeling was carried out using a range of profile lengths 250 300 500 and 700 km in general our estimates show no consistent increase of elastic thickness as a function of plate age this surprising result is consistent with recent reassessments of elastic thickness beneath seamounts and implies either that elastic thickness is independent of plate age or that elastic thickness cannot be measured with sufficient accuracy to reveal such a relationship modeling of short free air gravity profiles 250 300 km does tentatively suggest that elastic thickness increases linearly from 5 to 10 km between 0 and 20 ma and from 10 to 15 km between 20 and 150 ma this variation roughly matches the depth to the 200 c isotherm which corresponds to an homologous temperature of 0 4 for wet peridotite unfortunately for longer profile lengths there is no temporal dependence and elastic thicknesses vary considerably for all plate ages bathymetric profile modeling yields similar results although uncertainties are larger

footwall mineralization during late miocene extension along the west cycladic detachment system lavrion greece the west cycladic detachment system wcds has been mapped from the western cycladic islands to lavrion mainland greece where several top to ssw low angle normal faults at different structural levels are observed near the detachment horizon hydrothermal fluid flow originating from miocene intrusions lead to high temperature carbonate strata bound pb ag zn ore deposits zircon u th he cooling ages from the mineralized footwall are 7 1 0 6 to 7 9 0 6 ma carbon and o isotope analyses of the carbonate host indicate high water to rock ratios during brittle deformation induced metasomatism and that this interaction unrelated to proximity of the intrusions plays the dominant role in the mineralization the late miocene geology of lavrion is strikingly similar to serifos island on the se termination of the wcds both characterized by strong localization of detachment faulting and the interaction of brittle deformation with the injection of fluids related to granitoid intrusions

lithospheric rheology and flexure at artemis chasma venus artemis chasma is an arcuate 2000 km diameter zone of convergence and lithospheric underthrusting on venus inelastic flexure modeling of the topography at artemis combined with observations of trench tectonics allow us to document local temperature gradients below 4 k km 1 and an immense compressive in plane force at the trench lithospheric rheology on venus may be stronger than would be predicted from conventional extrapolations of rock mechanics experiments in particular the brittle surface strength must reach a few tens of megapascals to satisfy the observed lack of flexurally induced surface faulting elastic plate bending models provide an adequate estimate of the bending moment at artemis but they fail to constrain or even recognize the in plane force the inelastic analysis implies an in plane force of the order of 1 1014 n m 1 a potential driving force is thermal thinning of regionally thick lithosphre in the highlands to the north the low heat flux at artemis which is a comparatively young structure is compatible with the notion that venus has experienced a prolonged period of cooling in the last several hundred million years the inference of such exceptionally low thermal gradients embraces three end member possibilities 1 the surface age is 600 ma 2 the lithospheric thermal age is greater than the surface age and or 3 the upper mantle temperature is anomalously low 1550 k

physicochemical controls on bismuth mineralization an example from moutoulas serifos island cyclades greece the 11 6 to 9 5 ma serifos pluton intruded schists and marbles of the cycladic blueschist unit causing thermal metamorphism the development of magnetite ca exo and endo skarns and the formation of low temperature vein and carbonate replacement ores potentially the most important ores occur in the moutoulas prospect where the mineralization in retrograde skarn and quartz veins culminated with the deposition of native bismuth a combination of fluid inclusion microthermometry and isotope geothermometry suggests that the moutoulas mineralization formed at a hydrostatic pressure of 100 bars from moderate to low temperature 190 250 c and low salinity 1 3 5 6 wt nacl equivalent fluids the calculated 34 s h 2 s compositions are consistent with the ore fluids having been derived from the serifos pluton bismuth mineralization is interpreted to have occurred as a result of wall rock interaction and mixing of a bi bearing ore fluid with meteoric waters native bismuth and bismuthinite deposited at 200 c near neutral ph 6 5 low f s 2 f o 2

the geological signature of a slab tear below the aegean in this paper we explore the geology of the aegean region in the miocene to identify the geological signature of a first order slab tear observed in all tomographic models from 15 to 8 ma the tear is associated spatially and timely with a fast clockwise rotation of the external hellenides alkaline volcanism high temperature metamorphic domes with a predominance of north dipping detachments and south westward migration of granitoid intrusions these features suggest a warmer geodynamic environment during the rotation and the impact of a hot mantle flow associated with the tear the 8 ma duration between the first high temperature metamorphic domes in the centre of the archipelago and the beginning of the fast rotation may correspond to the time needed for the slab to bend stretch and finally tear

an explanation for the age independence of oceanic elastic thickness estimates from flexural profiles at subduction zones and implications for continental rheology most properties of oceanic lithosphere are widely observed to be dependent on the age of the plate such as water depth heat flow and seismogenic thickness however estimates of the effective elastic thickness of oceanic lithosphere based on the deflection of the plate as it enters a subduction zone show little correlation with the age of the incoming lithosphere this paradox requires reconciliation if we are to gain a full understanding of the structure rheology and behaviour of oceanic lithosphere here we show that the permanent deformation of the plate due to outer rise faulting combined with uncertainties in the yield stress of the lithosphere the in plane forces transmitted through subduction zones and the levels of noise in bathymetric and gravity data prevents simple elastic plate modelling from accurately capturing the underlying rheological structure of the incoming plate the age independent estimates of effective elastic thickness obtained by purely elastic plate modelling are therefore not likely to represent the true rheology of the plate and hence are not expected to correspond to the plate age similar effects may apply to estimates of elastic thickness from continental forelands with implications for our understanding of continental rheology

lithospheric flexure and thermal anomalies plots of effective elastic thickness te of the oceanic lithosphere as a function of age when elastically deformed show a general increase in te with the square root of age although there is much scatter some of the scatter can be eliminated by correcting for the effect of finite yield strength in rocks which makes te for more sharply bent plates underestimate the true depth tm to the rheological boundary at the base of the high strength mechanical lithosphere after converting effective values te to true thicknesses tm it appears that the mechanical lithosphere is always thinner beneath islands and seamounts compared to lithosphere of similar age flexed at subduction zones from several other lines of evidence such as depth anomalies seamount subsidence and heat flow data it has been suggested that the thermal structure in plates subjected to hot spot type volcanism is reset to values appropriate for much younger lithosphere the reduction in mechanical plate thickness beneath hot spot volcanoes is also consistent with this concept of thermal rejuvenation since the strength of rocks decreases exponentially with rising temperature this dependence implies that variations in mechanical plate thickness can be used to map temperature anomalies in the lithosphere since the mechanical plate thickness depends principally upon the temperature at one depth specifically the depth at which the temperature reaches 550 600 c depending on strain rate flexural data are particularly sensitive indicators of the vertical structure of lithospheric reheating compared to quantities dependent on depth integrals of temperature such as swell height and subsidence the thermal rejuvenation hypothesis predicts that the flexural profile should mimic viscoelastic relaxation in the first 10 ma after loading if initially reheating is confined to depths close to and below the 550 c isotherm the flexural data combined with depth anomaly information for hawaii point to extremely rapid reheating localized in the lower lithosphere rejuvenation in the society islands on the other hand is compatible with slower methods of heat injection involving the entire lithospheric column

intrusion related gold deposits in the tanami and kurundi kurinelli goldfields northern territory australia constraints from la icpms analysis of fluid inclusions abstract gold deposits in the tanami and kurundi kurinelli goldfields of the northern territory australia have geological and geochemical characteristics that distinguish them from the typical vein hosted orogenic gold deposits that occur in other parts of australia this study used cathodoluminescence cl and laser ablation inductively coupled plasma mass spectrometry la icpms analyses of fluid inclusions to investigate the source of mineralising fluids from both the highly mineralised tanami goldfield and weakly mineralised kurundi kurinelli goldfields in northern australia cathodoluminescence showed three generations of quartz in fractured and mineralised veins from the groundrush deposit in the tanami goldfield but the remaining deposits had uniform dark cl images the la icpms trace element data indicate an evolution from b as enriched magmatic fluid to a highly sr ba enriched fluid which results from interaction with sedimentary rocks the fluids from both regions have chlorinity normalised zn and pb concentrations at the magmatic end of the metamorphic magmatic mixing trend for these elements this is in agreement with previous studies showing that gold mineralisation is coeval with magmatism in the tanami region the relatively high salinity of the fluids in both the tanami and kurundi kurinelli goldfields and their trace element contents indicates that the deposits in both regions are intrusion related gold deposits the higher gold endowment of the tanami region may result from the multiple gold mineralisation events in this region whereas fluid flow associated with mineralisation in the kurundi kurinelli goldfields appears to be of limited extent

the relationship between plate curvature and elastic plate thickness a study of the peru chile trench the age of the nazca plate where it enters the peru and northern chile trenches varies from 30 ma in the north to 45 ma in the south as its dip beneath the south american continent steepens from 13 to 30 if the elastic thickness te of oceanic lithosphere depends only on its age and therefore thermal state we would expect that te determined from fitting the flexure of the lithosphere over the outer rise as revealed in the depth geoid and gravity anomalies would increase from the peru trench in the north to the northern chile trench further south we find that the opposite is true the lithosphere appears suffer outboard of the peru trench than it does offshore chile to explain deflections of the lithosphere seaward of peru the isotherm controlling the elastic ductile transition must be near 800 c providing the thermal structure of the plate is that predicted by the standard thermal plate model because the decrease in plate stiffness to the south is correlated with an increase of plate curvature over the outer rise and outer trench wall we interpret our result in terms of inelastic yielding of the oceanic lithosphere when bent to high strains the magnitude of the reduction in strength however suggests that the standard oceanic yield strength envelope underestimates the amount of failure for lithosphere bent to high strains unless the stress field off northern chile is characterized by 100 mpa level tension the more highly bent segment of subducting lithosphere at this trench also dips at a steeper angle at greater depth beneath the continent but detailed analysis of plate geometry does not support a relationship between slab dip as determined by earthquake hypocenters and elastic behavior over the outer rise

the genesis of epithermal au ag te mineralization panormos bay tinos island cyclades greece the panormos bay au ag te vein system tinos island greece which is hosted in mesozoic marbles comprises 30 subparallel steeply dipping quartz veins that extend for at least 500 m in places gold telluride mineralization occurs in hydraulic breccias and alteration halos which are the products of co 2 effervescence of the ore fluid and wall rock interaction respectively seventy ore and gangue minerals have been identified zones of chlorite talc and muscovite albite tourmaline alteration up to 50 cm wide are associated with precious metal bearing milky and clear quartz veins the au ag te mineralization is developed in stage v of eight hydrothermal stages stage v consists of three substages early middle and late that are characterized by ag cu and au bearing tellurides respectively hessite sylvanite altaite native tellurium stutzite cuprian cervelleite and an unnamed cu bearing precious metal sulfotelluride ag au cu 9 te 2 s 3 characterize the early substage whereas melonite rickardite vulcanite weissite and native tellurium are present in the middle substage the late substage contains rickardite kostovite krennerite petzite and calaverite unexploited au ag te mineralization at panormos bay is though to be genetically related to a fluorine and boron bearing per aluminous leucogranite tinos leucogranite a combination of fluid inclusion microthermometry and sylvanite geothermometry suggests that the hydrothermal mineralization was deposited under hydrostatic pressures at a minimum depth of 1 km from moderate temperature 155 320 c low to moderate salinity 0 2 13 2 wt nacl equiv effervescing co 2 bearing fluids that contained appreciable amounts of cacl 2 and mgcl 2 calculated isotope compositions of 18 o 3 3 to 5 1 per mil and d of 73 to 62 per mil for waters in equilibrium with muscovite quartz and talc are consistent with the ore fluids being derived from the tinos leucogranite 18 o 4 2 and d 71 and their subsequent mixing with a more dilute low temperature miocenic meteoric hydrothermal fluid calculated 13 c fluid 2 0 to 0 3 and 34 s h 2 s 10 5 to 0 8 compositions of the ore fluids indicate an igneous source of carbon and sulfur which were highly exchanged with a metasedimentary source physicochemical conditions of the ore fluids were t 300 to 200 c ph 4 6 to 6 5 f s 2 10 10 9 to 10 15 f o 2 10 31 5 to 10 41 f te 2 10 7 7 to 10 10 7 f co 2 10 0 2 to 10 0 8 and f h 2 s 10 1 7 to 10 1 8

the silicon isotope composition of granites because weathering results in preferential incorporation of the lighter si isotopes into clay minerals the si in magmas derived from meta sedimentary lithologies enriched in such phases should also be isotopically light relative to melts derived from igneous sources with the advent of new high precision techniques it should therefore be possible to resolve such differences hence si isotopes have to potential to distinguish between and characterise different magmatic source regions to explore this here we report the si isotopic compositions of a suite of phanerozoic i s and a type granites and mineral separates as well as samples of associated country rock the whole rock data fall between 30si 0 40 and 0 11 0 04 95 s e this range is more limited than that defined by previous low precision measurements of granites but is significantly broader than that displayed by more recent high precision measurements of high si extrusive igneous rocks as predicted s type granites are on average isotopically lighter than i and a type samples and negative correlations with alumina saturation index asi values and initial 87sr 86sr provide evidence that si isotope variations in granites can be explained by variable incorporation of an enriched sedimentary component however the relatively small isotopic perturbations and apparent degree of overlap between granite affinities suggest that si isotopes are not as sensitive to sedimentary input relative to more established proxies such as for example o isotopes the average si isotope value of all granites analysed in this study is 30si 0 23 0 15 2 s d which is entirely consistent with a recently published estimate for the continental crust based on an andesitic bulk composition and the well defined relationship between si isotopes and magmatic fractionation

the lavrion pb zn ag rich vein and breccia detachment related deposits greece involvement of evaporated seawater and meteoric fluids during postorogenic exhumation