the origin and evolution of low δ18o magma recorded by multi growth zircons in granite we for the first time reported low 18o granites within craton in bengbu uplift southeast margin of north china craton integrated ion microprobe study of 18o and u pb age on single zircon grains and zircon populations gives direct evidence for the origin and later magmatic evolution of the low 18o granites three types of zircon domains are recognized inherited magmatic core type i inherited metamorphic core mantle type ii and overgrown magmatic rim type iii type i zircons were formed in neoproterozoic and have the average 18o values of 5 3 0 6 around mantle value triassic type ii zircons have extremely low and highly heterogeneous 18o values ranging from 9 4 to 8 6 consistent with the values and variations exhibited by metamorphic zircons from dabie sulu orogen this feature argues for a triassic metamorphic origin for the 18o depletion signature of zircons from ultrahigh pressure metamorphic rocks in dabie sulu orogen jurassic type iii zircons have isotopically homogeneous 18o values of 3 3 0 5 collectively zircon populations recorded the 18o variations from source to low 18o granite the primary protolith of jurassic granites in bengbu uplift is a neoproterozoic granitic intrusion in south china block later high temperature meteoric hydrothermal alteration has lowered the whole rock 18o values in various degrees the low 18o protolith was then buried to the middle lower crust by triassic continental subduction and jurassic anatexis produced the low 18o granitic magma moreover 18o values of type iii zircons are isotopically lighter than previously reported values of magmatic garnets in jurassic granites indicating later magmatic evolution of low 18o magma toward high 18o values probably as a result of infiltration of high 18o fluid from wall rocks

abrupt change in slope causes variation in the deposit thickness of concentrated particle driven density currents abstract abrupt changes in slope occur frequently in some marine environments laterally confined laboratory experiments show that when dense surge like particulate flows travel over abrupt slope reductions their deposits may have an asymmetric bell shaped thickening near the break of slope this thickening is herein called a slope break deposit and is related to the change in kinetic energy of the flow slope break deposits are particularly pronounced under relatively high velocity flows in our experiments these are flows with high particle concentrations c 5 10 by volume silicon carbide moving down slopes steeper than 3 the experiments were designed such that currents generated by a lock exchange mechanism flowed down a slope variable slope angle onto a flat surface the bodies of the flows became thicker and slower just downstream of the slope break because the flow body slows very rapidly particles are dumped forming the slope break deposit the peak in sediment thickness of the slope break deposit is downstream of the break in slope because falling particles continue to move forward in the flow during settling the slope break deposits may be several tens of percent thicker than deposits from an equivalent flow in which no change in slope occurred the parameters of the slope break deposit correlate with slope angle change

downward particle fluxes in the guadiaro submarine canyon depositional system north western alboran sea a river flood dominated system abstract three moorings equipped with sediment traps were deployed in the north western alboran continental margin to study downward particle fluxes in the guadiaro submarine canyon depositional system this area is located close to the strait of gibraltar and is influenced by the upwelling induced by the atlantic jet and by episodic flood events from the guadiaro river sediment traps were installed in the guadiaro canyon in the guadiaro channel and in the adjacent continental slope the overall duration of the deployment was 12 months from november 1997 to october 1998 time series of downward particle fluxes major constituents organic carbon nitrogen biogenic opal calcium carbonate and lithogenics and 210pb were determined near the surface at mid depths and near the bottom total mass fluxes tmf in this area fluctuated more than two orders of magnitude and showed an important seasonal variability with higher fluxes in winter increases in tmf and lithogenics together with decreases in 210pb organic carbon and opal were recorded in all traps coinciding with river floods indicating a direct response of the system to these events and a rapid offshore transport of suspended matter affecting the entire water column the channel site received similar particle fluxes to the western open slope site indicating that this channel did not act as a preferential sediment conduit during the deployment period in the guadiaro canyon tmf were more than one order of magnitude higher 210pb concentration was lower one half and organic matter was more degraded than at the channel site during spring and summer as a consequence of receiving particles resuspended by internal waves and occasionally by trawling activities these particles were mainly retained in the canyon which works as a trap also during spring and summer the opal and organic carbon percentages increased in all traps both in magnitude and variability and peaks seem to be associated with biological blooms

oxygen isotope trends and anomalies in granitoids of the tibetan plateau abstract extreme transhimalayan oceanic mantle i type and high himalayan anatectic collision s type granitoids in the himalaya kashmir and tibet range in their original oxygen isotope composition from 6 to 7 5 and from 10 to 12 5 18osmow respectively in the sutured paleozoic and mesozoic orogen of the eastern tibetan plateau purely oceanic batholiths seem absent shalouli shan 8 10 but high himalayan values are matched in dongda shan and at luxi towards the east oceanic values are found again only on the margin of the yangtse platform the regional pattern of normal oxygen isotope data provides a background for anomalous feldspars to 1 in lhasa granite and in the active geothermal system at yangbachen recharged by 6000 m a s l meteoric water for lhasa granite oxygen isotope exchange paths and preliminary k ar dating of feldspars suggest exchange with meteoric water from over 3000 m altitude before 20 ma ago

seismic evidence of current controlled sedimentation in the alboran sea during the pliocene and quaternary palaeoceanographic implications abstract a seismic analysis of the pliocene and quaternary stratigraphy was conducted in the alboran sea westernmost mediterranean using more than 1250 profiles consisting of single and multi channel seismic records this allowed for the updating and renaming of the stratigraphic boundaries and the establishment of a new pliocene and quaternary seismic stratigraphy for the alboran sea after the relocation of the base of the quaternary from 1 8 to 2 6 ma the boundaries of the stratigraphic division are as follows the messinian m at 5 96 to 5 33 ma the intra lower pliocene p0 at ca 4 5 ma the top of the zanclean p1 at ca 3 3 ma the base of the quaternary bqd at ca 2 6 ma the top of the gelasian q0 at ca 1 8 ma the intra lower quaternary q1 at ca 1 12 ma and the top of the calabrian q2 at ca 0 7 ma additionally for the first time the seismic analysis allowed us to present and discuss the evidence of contourite features reaching the scale of the alboran basin contourite drifts plastered sheeted elongated separated and confined monticular drifts and erosive features terraces scarps moats and channels were developed under the continuous influence of mediterranean water masses light and dense after the opening of the strait of gibraltar in the latest miocene 5 46 ma there are at least two primary factors controlling the contourite features based on the seismic analysis as follows i tectonics which has governed the relocation of the main mediterranean flow pathways and their circulation patterns and ii climate which has influenced both water mass conditions interfaces and hinterland sediment sources conditioning the morpho seismic expression and growth pattern of the drifts and terrace formation dimensions the distribution of contourite features through time and space has allowed us to propose the three following main scenarios for ocean circulation since the opening of the strait of gibraltar atlantic zanclean flooding the pliocene sea with two different stages for the dense circulation and the quaternary sea with well defined and stable interfaces for the atlantic waters aw light and dense mediterranean waters

quantitative textural analyses of tobi sonar imagery along the almeria canyon almeria margin alboran sea se spain hydrocarbon exploration and the ongoing assessment of potential seismic risks are the main drivers behind the high resolution mapping of continental margins the large volume of literature devoted to turbidite systems in particular shows the importance of detailed descriptions of their characteristics and overall geomorphological variability primarily through the distribution of sediment facies these descriptions rely mainly on acoustic measurements which are notoriously difficult to interpret textural analyses quantify the second order statistics of sonar imagery detecting and quantifying details invisible to the human eye we show the potential and limitations of this approach using high resolution 6m towed ocean bottom instrument tobi sidescan sonar imagery acquired in the alboran sea south of almeria spain during the high resolution imaging of tsunamigenic structures hits 2001 programme the imagery is co registered with em 12 multibeam bathymetry topographic parametric sonar topas sub bottom profiles and localized ground truthing our study focuses on the almeria canyon a meandering channel system more than 57 km long and transporting large amounts of sediments from the coast down to the alboran trough c 1700 m deep textural analyses quantify the variations of sediment processes along the slope of the almeria canyon they agree with the results of previous studies and they can be used to provide new insights into the dynamics and evolution of the canyon

oxygen isotope trends of granitic magmatism in the great basin location of the precambrian craton boundary as reflected in zircons the 18 o values of magmas in the great basin help to decipher the tectonic assembly of north america and to determine the magmatic source and potentially the composition of the crust at depth igneous zircons from precambrian jurassic cretaceous and tertiary intrusive bodies of the northern great basin best preserve the rec ord of magmatic oxygen isotope ratios the variation of 18 o values in zircon with age reconciles previous differences in interpretation based on 18 o wr and radiogenic isotope data the new 18 o zrc data support the results of previous radiogenic isotope studies documenting the increased availability of crustal and sedimentary components to magmas in the cretaceous during the sevier orogeny and a return to a larger proportion of mantle derived components in the tertiary during basin and range extension in the great basin 18 o zrc values also vary systematically with crustal structure as determined by radiogenic isotope systematics plutons emplaced east of the 87 sr 86 sr i 0 706 isopleth have higher 18 o zrc values than plutons intruded west of the 0 706 line however analyses of 18 o values in quartz do not show the bimodal distinction across the 0 706 line owing to subsolidus alteration on the basis of 18 o zrc plutons intruding the walker lane belt are indistinguishable from other plutons emplaced west of the 0 706 line despite significant tectonic displacement and rotation of the belt the difference in 18 o values across the 0 706 line reflects the involvement of high 18 o precambrian and paleozoic sedimentary rocks of the continental margin and precambrian craton in magmas intruded east of the 0 706 line whereas magmas west of the 0 706 line are dominated by lower 18 o rocks derived from juvenile volcanic arcs crustal boundaries and discontinuities in the great basin determined by radiogenic isotope systems agree with discontinuities observed in 18 o zrc values this agreement indicates that the 0 706 line marks a geochronologic and compositional discontinuity in the basement rocks

oxygen and neodymium isotope evidence for recycling of juvenile crust in northeast china it has been long recognized from nd and sr isotopes that depleted mantle sources consist of recycled oceanic materials but difficulty was encountered in identifying this signature by means of oxygen isotopes because of significant postemplacement hydrother mal alteration zircon is expected to preserve this signature because it is resistant to high temperature hydrothermal alteration this effect is illustrated by a combined sm nd and oxygen isotope study of whole rock and mineral samples from a mesozoic a type granite at nianzishan in northeastern china the sm nd isotope results show positive nd t val ues of 10 86 to 14 27 with young nd model ages of 569 846 ma manifesting a significant input of newly mantle derived material the zircon d 18 o values of 3 12 4 19 are significantly lower than the d 18 o value of 5 3 6 0 3 for the normal mantle zircon and thus appear to require remelting of hydrothermally altered oceanic crust the combined nd o isotope studies not only provide compelling evidence for geochemical recycling of young juvenile crust by plate subduction but also demonstrate that the granitic magmas can result from partial melting of mantle derived rocks that were subjected to seawater hydrothermal alteration before magma generation disequilibrium oxygen isotope frac tionations are observed between common rock forming minerals with significantly lower d 18 o values for alkali feldspar than seawater corresponding to meteoric hydrothermal alteration after magma crystallization

the ebro continental shelf quaternary seismic stratigraphy and growth patterns abstract single channel seismic reflection profiles on the ebro shelf and upper slope between cap salou and the columbretes islands have been interpreted to outline the quarternary shelf evolution in this deltaic area three types of unconformity surfaces can be differentiated in the seismic records type 1 and 2 unconformities and toplap surfaces these surfaces are the stratigraphic expression of the difference between rate of eustatic sea level fall and subsidence on the outer shelf a type 1 unconformity forms if the rate of eustatic sea level fall is the more rapid a type 2 unconformity forms if subsidence is faster and toplap forms if subsidence and eustatic sea level fall are equal thirteen stratigraphic units can be differentiated on the basis of unconformities based on their relative location on the shelf these units are subdivided into inner and outer units the inner units occur on the inner and middle shelf and are characterized by an underlying transgressive surface while the outer units extend onto the middle to outer shelf and upper slope and show unconformities at their bases the inner units are interpreted to be stacked transgressive and highstand systems tracts bounded by a maximum flooding surface the outer units correspond to shelf deltas and shelf margin deltas that prograded southward and seaward over an unconformity in relatively stable water depths when sea level fall was compensated for by subsidence the progradation of these units ends with an episode of generalized erosion of the shelf and canyon cutting across the new shelf edge the growth pattern of the northern ebro shelf is characterized by important hiatuses condensed stratigraphic sections and units which are older than those on the southern shelf the depositional processes were mainly controlled by eustatic sea level oscillations subsidence and changes in sediment supply the subsidence during the late pleistocene was sufficient to compensate for the sea level falls and allow the development of shelf deltas and shelf margin deltas on the middle and outer shelf during low sea level stands

post calabrian sequence stratigraphy of the northwestern alboran sea southwestern mediterranean abstract the post calabrian sedimentary column of the northwestern alboran sea comprises three depositional sequences the two older depositional sequences are defined by lowstand systems tracts shelf margin deltas slope base of slope and basin deposits and the guadiaro channel levee complex in contrast the most recent depositional sequence also includes transgressive relict shelf facies and high stand the guadalmedina guadalhorce prodelta and hemipelagic facies systems tracts the stratigraphic architecture of these depositional sequences is controlled by the synchronism between high frequency sea level changes variations in sediment supply and sedimentary processes the configuration of the depositional sequences is variable and their distribution is complex as a result of the relative importance played by sea level changes and tectonism through the area the sequence boundaries are represented by polygenetic surfaces in the proximal margin and by monogenetic surfaces in the distal margin and basin each polygenetic surface results from the interaction between the sequence boundary with the lowstand erosional truncation surface and the transgressive surface both developed during the previous sea level cycle the monogenetic surfaces correspond to unconformities and their correlative conformities formed during sea level lowstands this pattern of depositional sequences developed in the margin and basin of the northwestern alboran sea shows differences with the exxon sequence stratigraphy model as traditionally applied sea level change control is essentially recognized through lowstand systems tracts and sequence boundary coincides with lowstand erosional truncation surface and transgressive surface both developed during the previous sea level cycle

constraints from zircon u pb ages o and hf isotopic compositions on the origin of neoproterozoic peraluminous granitoids from the jiangnan fold belt south china zircon textures and micro chemical compositions precisely record the origin and petrogenesis of granitoids which are crucial for evaluating crustal growth and reworking thermal and geodynamic evolution zircons in peraluminous granitoids from the three largest 820 ma complexes guibei yueyang and jiuling in the jiangnan fold belt in south china are used to constrain their sources and petrogenetic processes zircons in the guibei granitoids have complex internal structures nearly all magmatic and inherited zircons have similar ehf 6 8 to 5 6 and 18o values 8 8 11 6 and dominantly lie between ehf evolution vectors for a crust created between 1 7 and 2 1 ga suggesting that the guibei granitoids were produced by partial melting of recycled heterogeneous supracrustal material however the yueyang granitoids contain zircons with high ehf 0 5 to 9 7 and relatively low 18o values 5 9 8 4 and two stage model ages of 1 1 1 8 ga and thus may have been formed by melting of mafic rocks from the lower crust the jiuling granitoids and their enclaves contain more complex zircons with more variable ehf 7 2 to 9 7 and 18o values 7 0 10 6 and lie along the mixing trend between the above proposed infracrustal and supracrustal granitoids therefore the neoproterozoic peraluminous granitoids in the jiangnan fold belt were produced by melting and mixing of continental crust compared with extremely low 4 and negative 18o values of neoproterozoic igneous zircons formed in its northern active continental margin the high 18o peraluminous granitoids in the southeastern yangtze block are considered to have been formed by melting of hydrothermally unaltered continental crust triggered by asthenosphere upwelling in the nanhua back arc basin

insight into zircon ree oxy barometers a lattice strain model perspective abstract zircon rare earth element ree oxy barometers have been widely used to calculate magma oxygen fugacity however sometimes confusing results are obtained such as extremely reduced oxygen fugacity in hadean magmas e g fmq 8 extremely oxidized oxygen fugacity in post hadean magmas e g fmq 10 and contradictory oxygen fugacities recorded in ore related porphyry magmas nno 5 vs nno 1 to address these issues this work reviews the underlying assumption of zircon ree oxy barometers the lattice strain model by introducing a geochemical filter to identify clean inclusion free zircon and a new parameter k to constrain the d zircon whole rock deviation from the lattice strain model we systematically re evaluate the common zircon ree oxy barometers address the issues noted in hadean post hadean and ore related magmas and provide an alternate approach to using zircon ree in studies of magmatic processes

oxygen isotopes and sea level from the time that detailed oxygen isotope records derived from foraminifera living in the constant temperature environment of the abyssal ocean became available there has been a discrepancy between the ice volume record that these records imply and that derived from the altitude of dated coral terraces around the world here we re examine the data and conclude that the temperature of the abyssal ocean has been an actively varying component of the climate system

crustal assimilation during turbulent magma ascent ata new isotopic evidence from the mull tertiary lava succession n w scotland assimilation of crustal rocks with concomitant fractional crystallisation afc is a well documented phenomenon in many igneous suites but geochemical evidence from the tertiary mull lava succession suggests that in these magmas crustal contamination occurred by a distinctly different mechanism lavas from the lower half of the mull plateau group mpg can be divided into two broad sub types high 8 mgo basalts with elevated ba and k and lower mgo 8 basaltic hawaiites with lower ba and k the lower crust and most of the upper crust beneath mull is probably of lewisian age the sr nd and pb isotope compositions of local lewisian crustal samples yield the following ranges 87sr 86sr 0 71002 0 72348 143nd 144nd 0 51045 0 51058 and 206pb 204pb 14 0 14 6 ten lavas have also been analysed and yield the following ranges 87sr 86sr 0 7028 0 7042 143nd 144nd 0 51214 0 51230 and 206pb 204pb 15 1 17 9 however within this range it is predominantly the more primitive mafic compositions with elevated mg ba and k that show the lowest nd and pb and the highest sr isotope values modelling of these isotopic results in conjunction with major and trace element data show that 1 contamination by lewisian lower crustal material does occur 2 that the process involved was not one of assimilation with concomitant fractional crystallisation afc the proposed contamination process is one whereby the hottest most mgo rich magmas have assimilated acidic partial melts of lewisian lower crust during turbulent ascent ata through thin poorly connected dyke and sill like magma chambers the chemical composition of the contaminated lavas can be modelled successfully through addition of 5 acidic lewisian crust to an uncontaminated lava in contrast the more evolved magmas which probably fractionated at sub crustal levels were either not hot enough to molt significant amounts of crust or did not ascend turbulently because of their higher viscosity and so are less contaminated with crust

two contrasting late paleozoic magmatic episodes in the northwestern chinese tianshan belt nw china implication for tectonic transition from plate convergence to intra plate adjustment during accretionary orogenesis abstract late carboniferous to early permian is a critical period for the final amalgamation of the central asian orogenic belt caob however as most of the accreted terranes of the caob are unclear in tectonic nature and origin the timing and processes of their mutual amalgamation have been poorly constrained to understand assembly of the west junggar terrane with the yili block a suite of the late paleozoic magmatic rocks including ignimbrite rhyolite and granite in northwestern chinese tianshan belt were studied for their petrogenesis and tectonic implications our new results of secondary ion mass spectrometry sims zircon u pb dating reveal two separate magmatic episodes ca 300 ma volcanism ignimbrite and rhyolite and ca 288 ma plutonsim biotite granite geochemically for the ca 300 ma volcanism the ignimbrites have low sio2 65 8 71 5 wt and mg 6 13 values and exhibit arc affinity with significantly enriched in large ion lithophile elements lile and depleted in high field strength elements hfse such as nb ta and ti the whole rock end t and zircon ehf t values range from 6 9 to 7 0 and 9 9 to 14 1 respectively indicating a juvenile basaltic lower crustal origin rhyolites have slightly high sio2 72 7 74 0 wt and k2o 3 86 4 53 wt contents high zircon 18o 11 67 13 23 values and low whole rock end t 2 9 to 3 8 and zircon ehf t 2 8 to 10 0 values which may suggest sediment involvements during magma generation in contrast for the ca 288 ma plutonism the biotite granites have obviously higher sio2 74 7 75 5 wt contents and whole rock end t 7 7 to 8 8 zircon ehf t 9 8 to 12 7 and lower zircon 18o 5 99 6 84 values than those of the ca 300 ma volcanic rocks which are consistent with signatures of juvenile magma source according to our estimates of zircon saturation temperatures together with their contrasting genesis we attribute the formation of ca 300 ma high temperature 815 938 c volcanism to oceanic slab break off during assembly of the west junggar terrane with the yili block and relate the generation of ca 288 ma low temperature 723 735 c plutonism to subsequent strike slipping of north tianshan fault that facilitated introduction of water fluxes triggering hydrous partial melting of juvenile lower crust the sequential magmatic episodes in the northwestern chinese tianshan belt may provide a crucial clue to a tectonic transition from plate convergence to intra plate adjustment during the formation of the kazakhstan orocline in the late paleozoic

the oldest zircons of africa their u pb hf o isotope and trace element systematics and implications for hadean to archean crust mantle evolution abstract more than 450 detrital zircon grains from two limpopo belt quartzite samples were investigated by a combination of scanning electron imaging u pb dating 18 o lu hf isotope and trace element analyses in order to get robust information about the early earth s crust mantle evolution the detrital zircon grains have crystallization ages between 3 95 ga and 3 18 ga show hf t between 1 to 15 1 unit and 18 o vsmow mostly between 5 5 and 8 1 0 2 pristine zircon domains reveal ti in zircon temperatures between 700 and 865 c and th u of 0 3 2 3 trace elements point to zircon formation in predominately granitoid rocks metamorphic zircon rims have ages 2 65 ga hf 2 65ga 15 18 o 7 0 8 1 and th u mostly hf t age array i which starts from a chondritic uniform reservoir chur at about 4 5 ga and requires 176 lu 177 hf 0 020 indicative for mafic crust most zircon grains however plot on or above an hf t age array ii which runs parallel to array i 176 lu 177 hf 0 021 and starts from chur at 4 01 ga oxygen isotope compositions of 18 o 5 5 indicate that the magmatic host rocks of the zircons have been formed either by melting of altered mafic crust which interacted with cold water prior to granitoid formation and or that ancient sedimentary and or magmatic rocks were involved in the melting process the new u pb hf 18 o datasets together with compiled data from worldwide sources indicate a significant gap of about 5 epsilon units between arrays i and ii furthermore they illustrate that many hadean zircon analyses plot well below array i and some above chur these findings support an interpretation that the hadean earth was covered by a long lived mafic protocrust perhaps forming a partially open stagnant lid this protocrust was affected by internal reworking but also injected and overlain by ultra mafic rocks derived from chondritic and highly depleted mantle sources at

nicolas and eel submarine fans california continental borderland nicolas and eel submarine fans occur in the san nicolas basin an outer basin of the california continental borderland that has a low sedimentation rate nicolas fan lies southeast of san nicolas island and the broad san nicolas bank the upper fan is characterized by numerous channels the midfan region may be divided into three distinct areas a central midfan and two subfans the central midfan depositional system is typical of normark s suprafan the subfans are essentially flat sandy lobes eel fan lies west of san clemente island and is fed by an erosional valley its midfan region may also be characterized as a flat sandy lobe box core data show that holocene turbidity currents have occurred on the central nicolas fan whereas the subfans and eel fan are nearly nactive the local tectonic regime influences these fans by determining slope trends creating bathymetric obstacles controlling canyon location and triggering mass movements sea level changes affect sedimentation patterns of the fans by increasing the mean grain size and the amount of sediment delivered to the fan during lowstands these changes may in turn affect the morphology of the fan the characteristics of these fans represent variations of the generalized fan models described in the literature

geochronological constraints on late archean magmatism deformation and gold quartz vein mineralization in the northwestern anialik river greenstone belt and igneous complex slave province n w t three phases of the anialik river igneous complex aric give u pb zircon ages in the range 2705 2683 ma and three units from the adjacent northwestern anialik river greenstone belt argb give ca 2678 ma ages titanite from unsheared aric rocks crystallized during localized metamorphism and deuteric alteration between 2693 and 2683 ma hydrothermal titanite in wall rocks to gold mineralized shear zones crystallized during early shear zone development 2670 1 ma and was subsequently locally altered to rutile with gold occurring within the rutile bearing assemblage unaltered second generation hydrothermal titanite overgrowing the rutile assemblage crystallized during later brittle ductile movement 2656 2 ma and provides a minimum age for gold mineralization relatively high 207pb 204pb ratios of pb in gold associated galena suggest that it was partly derived from significantly older crustal material possibly underlying the igneous complex and greenstone belt this interpretation is consisten

submarine fans and related depositional systems ii variability in reservoir architecture and wireline log character abstract the architecture and heterogeneity of deep marine clastic reservoir systems can be assessed at three scales at the macroscale lateral and vertical variations in the stacking patterns of submarine fans or fan complexes fundamentally affects the shape and scale of a reservoir and its trapping geometry at the mesoscale the distribution and type of architectural elements e g channel levees lobes sheet sands within the fan system have a major impact upon reservoir compartmentalisation and the distribution continuity and connectivity of sand shale bodies finally at the microscale the vertical and horizontal arrangement of reservoir and non reservoir facies and lithotypes defines flow units which fundamentally control fluid flow and production performance each type of submarine fan and related deep marine clastic reservoir system sand rich fans mixed sand mud ramps etc exhibits a predictable arrangement of architectural elements which form the basic building blocks of the system these features control reservoir architecture seismic expression and the geometry of sandbodies and non reservoir section a suite of reservoir architectural models is proposed for different deep marine clastic systems using unpublished and cited data from outcrop and subsurface studies these conceptual models are idealised simplifications which provide a preliminary framework for understanding broad scale reservoir archsitecture and wireline log character within contrasting types of fan and related systems the models are of value in the exploration for turbidite reservoirs by highlighting the risk on reservoir presence and distribution from an appreciation of the architectural style within appraisal and production they provide a basic framework from which an objective reservoir description can be made use of such conceptual analogue models for reservoir description will not adequately reflect the reality and individuality of a specific reservoir their use in understanding detailed reservoir complexity should therefore be approached with caution

morphology of turbidite systems within an active continental margin the palomares margin western mediterranean abstract the palomares margin an nne ssw segment of the south iberian margin located between the alboran and the algerian balearic basins is dissected by two major submarine canyon systems the gata in the south and the alias almanzora in the north new swath bathymetry side scan sonar images accompanied by 5 khz and topas subbottom profiles allow us to recognize these canyons as mediterranean examples of medium sized turbidite systems developed in a tectonically active margin the gata turbidite system is confined between residual basement seamounts and exhibits incised braided channels that feed a discrete deep sea fan which points to a dominantly coarse grained turbiditic system the alias almanzora turbidite system larger and less confined is a good example of nested turbiditic system within the canyon concentric sediment waves characterize the alias almanzora deep sea fan and the size and acoustic character of these bedforms suggest a fine grained turbidite system both canyons are deeply entrenched on a narrow continental shelf and terminate at the base of the continental slope as channels that feed deep sea fans while the alias almanzora turbidite system is the offshore continuation of seasonal rivers the gata turbidite system is exclusively formed by headward erosion along the continental slope in both cases left lateral transpressive deformation influences their location longitudinal profiles incision at the upper sections and canyon bending associated with specific fault segments

significance of bottom currents in deep sea morphodynamics an example from the alboran sea we present an interdisciplinary study of the geomorphology sedimentology and physical oceanography of the alboran sea south western mediterranean sea to evaluate the potential role of bottom currents in shaping the spanish and moroccan continental margins and adjacent basins bathymetric and seismic data have allowed the recognition of the contourite deposits including depositional plastered sheeted channel related mounded confined elongated and separated drifts erosive moats channels and furrows and mixed terraces and scarps features hydrographic data offer new insights into the distribution of the mediterranean water masses and reveal that bottom circulation of the western intermediate water wiw and the levantine intermediate water liw interact with the spanish slope and the western mediterranean deep water wmdw on the moroccan slope spanish base of slope and deep basins the integration of distinct datasets and approaches allows a proposal of a new sedimentary model for the alboran sea that details the significance of bottom current processes in shaping deep sea morphology this model considers the bottom circulation of water masses governs physiography that interface positions of water masses with contrasting densities sculpt terraces on a regional scale and that the morphologic obstacles play an essential role in the local control of processes and water mass distributions our findings demonstrate the pivotal role of bottom water circulation in seafloor shaping and sedimentary stacking patterns for continental margins establishing a new outlook for future studies of deep marine sedimentation

oxygen isotope ratios of zircon magma genesis of low δ18o granites from the british tertiary igneous province western scotland igneous zircons from granites of the british tertiary igneous province btip in western scotland preserve magmatic oxygen isotope ratios in spite of hydrothermal alteration and thus provide new evidence for the genesis of granites co2 laser and mass spectrometer based bulk 1 3 mg oxygen isotope analyses from individual plutons show remarkable homogeneity in zircon 18o regardless of zircon size and magnetism average reproducibility of 18o zrc in a single pluton is 0 2 in addition ion microprobe analysis shows that individual zircons all have the same 18o and thus bulk samples are homogeneous fourteen granite bodies from the isle of skye show extreme variability in zircon 18o values from pluton to pluton 18o zrc 0 6 5 3 vsmow all the granites record zircon 18o values less than would be in high temperature equilibrium with normal mantle 18o zrc 5 except for the beinn an dubhaich granite zircons from one intrusion in the mafic cuillins center also have low 18o 2 5 similar variability is observed in 18o amongst three intrusions on the isle of mull 18o zrc 3 4 5 9 both mull and skye are characterized by intense shallow paleohydrothermal systems and the low and variable 18o values of the magmas likely result from melting or interaction with hydrothermally altered country rock analysis of granites on the isle of arran where the percentage of low 18o country rocks is much less yields higher 18o zrc of 6 8 and 5 4 published trace element and radiogenic isotope data for btip mafic and felsic rocks have supported the hypothesis that the granites are formed primarily by differentiation from the mantle with magmas experiencing minimal crustal input dickin et al phil trans r soc london a 310 1984 755 780 however conservative estimates based on oxygen isotope compositions suggest that some of the btip granites can only be formed from normal magmas 18o wr 6 if they assimilated significant amounts of hydrothermally altered crustal material some granites require up to 40 bulk crustal input and are better explained as the result of wall rock melting by an adjacent mafic pluton whereas pb and sr suggest a general trend towards increasing input of shallow crust for the younger granites dickin et al phil trans r soc london a 310 1984 755 780 the correlation between age and 18o is less apparent suggesting that pb and sr isotopic compositions are decoupled from oxygen isotopes this would be expected of melted country rock that was hydrothermally altered in oxygen isotope ratios but not in pb and sr isotope ratios

subsurface basin analysis of fault controlled turbidite system in bradano trough southern adriatic foredeep italy subsurface data seismic lines wireline logs cores and drill cuttings from intensive hydrocarbon exploration in the pliocene pleistocene bradano trough were used in performing a three dimensional basin analysis and in reconstructing the time space evolution of the basin a middle pliocene sedimentary system characterizes the hydrocarbon bearing sands of the major gas field of the bradano trough the candela field this system includes two phases of deposition in a migrating basin the first phase of deposition caused by strong subsidence due to continental shortening was accompanied by the influx of large quantities of clastic material the outer part of the basin was filled with turbidites the inner part is characterized by olistostromes formed by gravitational sliding along the slope which progressively prograded basinward the fault controlled bottom physiography acted as a channel for turbidity currents that deposited elongate bodies between the inner slope and the compressional faults growing outward the coarser grained material deposited in the trough by currents onlapped the upthrown flanks of the faults thus providing potential hydrocarbon traps turbidity currents carrying the finer grained material flowed over the fault scarps in the meanti e other external faults were activated as the turbidity currents spilled over the former faults deposition expanded laterally continuous basin subsidence kept pace with deposition and superposed wedges accumulated to a thickness of at least 1 000 m 3 281 ft the second phase of deposition is characterized by a decreasing rate of subsidence currents filled a flat trough with tabular turbidites which accreted longitudinally the sand bodies became more muddy clayey in the distal southern part of the basin at this point the system consisted of a major fan shaped sand body upcurrent downcurrent partially overlapping lobate sand bodies with large lobe fringes migrated transversally the entire fan system was later blanketed with mud and finally with a transient carbonate platform which preceded a new cycle of subsidence

early permian a type granites from central inner mongolia north china magmatic tracer of post collisional tectonics and oceanic crustal recycling abstract a type granitoids constitute volumetrically minor but genetically important building blocks of most post archean continental landmasses on earth and their diversified genesis encapsulates key information for ascertaining critical geodynamic controls on continental crustal formation and differentiation this zircon u pb dating and geochemical study documents the early permian peralkaline granites from central inner mongolia of china eastern central asian orogenic belt caob these granites show an a type magmatic affinity with typical enrichment in alkalis ga zr nb and y depletion in sr and p and fractionated ree patterns showing strong negative eu anomalies they have meaningful initial 87 sr 86 sr ratio of 0 70594 e nd t of 4 25 to 6 05 zircon e hf t from 9 8 to 16 0 and 18 o values from 2 41 to 4 72 these elemental and isotopic characters argue for parental magmas from partial melting of a newly trapped charnockitic lower crustal protolith and their subsequent fractional crystallization with an inherent hydrothermally altered oceanic crustal heritage and possible tectonic linkage to post collisional slab breakoff this kind of a type granites could not only serve as an insightful temporal milestone for monitoring the amalgamation between various constituent terranes in the caob but also present a spatial magmatic proxy for marking the maturation stage of juvenile crustal reworking during the final phase of a large orogenic event

alboran basin southern spain part i geomorphology abstract bathymetric 3d relief and shaded relief maps created from multibeam echo sounding data image the morphology of the alboran basin a structural low along the east west trending eurasian african plates boundary topographic features in the basin are the consequence of volcanism associated with miocene rifting rift and post rift sedimentation and recent faulting resulting from the convergence of the african eurasian plates pleistiocene glacially induced regressions transgressions when the sea level dropped to about 150 m below its present level gas seeps and bottom currents recent faulting and the pleistocene transgressions regressions led to mass wasting formation of turbidity currents and canyon erosion on the basin s slopes recent fault traces at the base of the northern basin slope have also served as passageways for thermogenic methane the oxidation of which by bacteria led to the formation of carbonate mounds along the fault intercepts on the sea floor expulsion of thermogenic or biogenic gas has led to the formation of pockmarks erosion by bottom currents has resulted in the formation of moats around seamounts and erosion of the seafloor of the alboran ridge and kept the southern edge of the 36 10 n high sediment free

zircon u pb dating of water rock interaction during neoproterozoic rift magmatism in south china abstract a combined study of zircon u pb dating and mineral o isotope analysis was carried out for neoproterozoic granite gabbro and gabbrodiorite from the beihuaiyang zone that marks a rifted margin between the south china block and the supercontinent rodinia the results provide precise constraints on timing of water rock interaction resulting in unusual 18 o depletion in igneous minerals cl imaging reveals that zircons mostly show clear oscillatory and or sector zoning with or without thin alteration rims no metamorphic zircon occurs in the igneous intrusives although they suffered greenschist facies metamorphism during triassic continental collision la icpms zircon u pb dating yields consistent ages of 739 8 to 754 5 ma which are interpreted as timing of magma crystallization mineral separates have highly variable 18 o values of 0 6 to 6 8 for zircon 1 2 to 12 5 for quartz and 0 3 to 8 4 for plagioclase oxygen isotope heterogeneities exist within single intrusions and between different intrusions magmatic zircons with low 18 o values and a weighted mean u pb age of 748 6 ma crystallized from low 18 o magmas that were derived from melting of hydrothermally altered low 18 o rocks both low and normal 18 o intrusives in the beihuaiyang zone are shown to form at the same time contemporaneous with the rodinia breakup thus tectonic evolution from supercontinental rift to breakup is proposed to create conditions for alternating processes of high t hydrothermal alteration and low 18 o magmatism such processes are a characteristic feature of high t water rock interaction in volcanic rift margins associated with localized water saturated melting while the occurrence of low 18 o magmas demonstrates penetration of meteoric water into the rift tectonic zone of crustal melting the existence of normal 18 o magmas indicates that their emplacement may serve as a thermal engine to drive the second stage of meteoric water rock interaction resulting in the unusual 18 o depletion in adjacent rocks the concurrent occurrence of both low and normal 18 o magmas appears to indicate highly heterogeneous high t water rock interaction during rift magmatism

low δ18o rhyolites from yellowstone magmatic evolution based on analyses of zircons and individual phenocrysts the yellowstone plateau volcanic field is one of the largest centers exchange time to form zoned zircons is between a few hundred and a few thousand years which reflects the residence time of lowo of rhyolitic magmatism on earth major caldera forming eruptions are followed by unusual lowo rhyolites new oxygen isotope magmas after formation and before eruption petrologic and geochemical data from rhyolites belonging to the 2 0 my eruptive history of yellowstone are presented with emphasis on the genesis of lowo magmas erupted after the huckleberry ridge tuff 2 0 ma 2500 km and lava creek tuff 0 6 ma

stratal architecture of western mediterranean margins as the result of the stacking of quaternary lowstand deposits below glacio eustatic fluctuation base level abstract through a comparison of high resolution seismic stratigraphy of seven western mediterranean margins similarities and differences in stratigraphic architecture were highlighted and a hierarchy of controlling factors was established the areas are northwestern alboran ebro and northern catalonia in the spanish margin rho ne in the french margin and tuscany latium and calabria in the italian tyrrhenian margin despite their different tectonic physiographic and depositional setting the seismic facies and growth pattern of the middle late pleistocene deposits are comparable the margins are in fact the result of the stacking of lowstand systems tracts of 4th order depositional sequences bounded by polygenetic unconforniities on the shelf and condensed sections on the upper slope this lowstand nature results from the high frequency 100 ka high amplitude 100 m asymmetry falling 65 of the time and stationariness between 10 and 120 m with respect to the present of the glacio eustatic sea level curve if eustasy directly controls the types of deposits making up the margins tectonism conditions their growth pattern as it is the only factor accounting for similarities and differences in the external geometry stratal pattern and distribution of the middle late pleistocene depositional sequences an evolutionary model for the quaternary growth of young passive continental margins is proposed in this model tectonics determines the degree of preservation of lowstand deposits because it conditions the accommodation space left below the erosional profile produced by each glacio eustatic cycle thus some of the sequence stratigraphy principles widely used to set up the model have been modified and adjusted to take into consideration the peculiar nature of quaternary glacio eustasy

representation of northern hemisphere winter storm tracks in climate models northern hemisphere winter storm tracks are a key element of the winter weather and climate at mid latitudes before projections of climate change are made for these regions it is necessary to be sure that climate models are able to reproduce the main features of observed storm tracks the simulated storm tracks are assessed for a variety of hadley centre models and are shown to be well modelled on the whole the atmosphere only model with the semi lagrangian dynamical core produces generally more realistic storm tracks than the model with the eulerian dynamical core provided the horizontal resolution is high enough the two models respond in different ways to changes in horizontal resolution the model with the semi lagrangian dynamical core has much reduced frequency and strength of cyclonic features at lower resolution due to reduced transient eddy kinetic energy the model with eulerian dynamical core displays much smaller changes in frequency and strength of features with changes in horizontal resolution but the location of the storm tracks as well as secondary development are sensitive to resolution coupling the atmosphere only model with semi lagrangian dynamical core to an ocean model seems to affect the storm tracks largely via errors in the tropical representation for instance a cold sst bias in the pacific and a lack of enso variability lead to large changes in the pacific storm track extratropical sst biases appear to have a more localised effect on the storm tracks

small turbidite systems in a complex tectonic setting sw mediterranean sea morphology and growth patterns abstract three small turbidite systems almeria sacratif and guadiaro each tens of kilometres long are developed in the complex morpho structural setting of the northern alboran sea and have similar primary architectural elements canyons channel levee systems lobes however comparison reveals differences in the axial gradients of their canyons depth physiographic location morphological framework and lateral and longitudinal sedimentary shifts of turbidite deposition the depositional architecture and sedimentary evolution from late pliocene to quaternary seems to be conditioned by number of submarine feeding sources canyons sea level fluctuations and local tectonic e g margin canyon channel gradients faults we group the alboran turbidite systems into two models mud sand rich submarine point source and mud sand rich multiple submarine source ramp

quaternary siliciclastic sequence stratigraphy of western mediterranean passive and tectonically active margins the role of global versus local controlling factors

ion microprobe analysis of oxygen isotope ratios in quartz from skye granite healed micro cracks fluid flow and hydrothermal exchange quartz grains in hydrothermally altered granites from the isle of skye are highly heterogeneous and not equilibrated in oxygen isotope ratio at the 20 m scale ion microprobe analysis of one grain shows a gradient of 13 over 400 m and a greater range in 18o than all quartz previously analyzed on the isle of skye other crystals from the same outcrop are homogeneous digitized cathodoluminescence images reveal patterns of magmatic zoning and brittle fracturing not otherwise detectable the ion probe analysis correlates low 18o values on a micro scale to one set of healed cracks thus quartz exchanges oxygen isotopes primarily by solution and reprecipitation along fractures in contrast to more reactive feldspar that appears to exchange from the grain boundary inward macroscopic models of isotope exchange are not realistic for these rocks the flow of hydrothermal fluids was heterogeneous anisotropic and crack controlled

the tributary valley systems of the almeria canyon alboran sea sw mediterranean sedimentary architecture three tributary valley systems of the almeria canyon dalias andarax and gata located on the almeria margin alboran sea sw mediterranean were studied using high resolution techniques including swath bathymetry and topas seismic reflection profiles a detailed morphological and seismic stratigraphy study shows that the tributary valley systems tvs are formed by two types of valleys gullies and leveed channels dalias tvs is the best developed system covering an area of more than 300 km 2 from the shelf edge off cabo de dalias to the almeria canyon 100 1500 m depth andarax tvs covers about 65 km 2 from the shelf off the andarax river mouth to the westernmost branch of the almeria canyon 40 300 m depth gata tvs covers more than 100 km 2 from the shelf edge off cabo de gata to the almeria canyon 200 650 m depth tributary valley systems can be divided into two models based on the detailed morpho seismic study the sea level controlled model and the sediment supply controlled model the sea level controlled model includes the dalias and gata tvs this model is mainly governed by sea level fluctuations and the valleys grow as a result of the activity of turbidity currents and hemipelagic sedimentation displaying a retrogressive upslope pattern the valleys development would have been favoured by glacio eustatic oscillations during the late quaternary a tentative chronostratigraphic correlation has been made relating the evolution of dalias and gata tvs with the marine isotopic stages and sea level curves tectonics and margin physiography play a secondary role in the development of this type of valley the sediment supply controlled model is applicable to the andarax tvs the growth of the valleys is controlled by the ephemeral sediment discharges from the andarax river the valleys are small scale gullies located on the shelf and slope which would grow as a result of the turbidity currents which channel the fluvial sediment supplied in form of hyperpycnal currents this model would have been developed during the last highstand of sea level once the coast line reached its present situation d 2005 elsevier b v all rights reserved

degassing in kimberlite oxygen isotope ratios in perovskites from explosive and hypabyssal kimberlites interest in the radiogenic and trace element characteristics of uncontaminated kimberlitic magma has been rekindled by recent isotope studies on groundmass perovskite which is a major sink of most of the trace elements including rare earth elements ree in kimberlite magma perovskite is also quite resistant to sub aerial weathering in situ trace element oxygen isotope ratios and conventional tims sr isotopic analyses of perovskites are presented for two kimberlites one from orapa a crater facies group i kimberlite from botswana and the other from wesselton a hypabyssal facies group i kimberlite from south africa the perovskites from orapa exhibit greater ranges in trace element abundances and 87sr 86sr ratios than those from wesselton la 7000 13 600 times primitive mantle and 87sr 86sr 0 70310 0 70541 in orapa perovskites and la 4000 7000 times primitive mantle and 87sr 86sr 0 70441 0 70558 in wesselton the 18o values from orapa perovskites have two distinct peaks around 3 6 and 0 6 which are unlikely to reflect crustal assimilation processes wesselton perovskites in contrast are clustered around 18o values of 4 perovskite in equilibrium with the mantle has lower 18o than other common upper mantle minerals olivine orthopyroxene the group of orapa perovskites with 18o clustering around 3 6 and the wesselton perovskites are interpreted to have 18o values 4 2 that reflect the 18o of uncontaminated kimberlite magma of an upper mantle origin 5 2 the negative 18o values from the second group of orapa perovskites are attributed to crystallisation of perovskite after magma degassing that depleted 18o in the residual magma abundance of magmatic carbonate in the wesselton sill together with the absence of any perovskite with very low 18o indicates a lack of significant degassing for the wesselton kimberlite

pliocene quaternary tectonic sedimentary evolution of the ne alboran sea sw mediterranean sea abstract the pliocene quaternary tectonic sedimentary evolution of the ne alboran sea is established using high resolution seismic profiles the pliocene quaternary deposits resting upon an acoustic basement with a complex morphostructure are stratigraphically made up of three seismic sequences whose facies stratal patterns and nature of boundaries result from the interaction between sea level changes tectonics and physiographic configuration during the early pliocene a generalized synsedimentary transgression with extensive tectonic activity resulted in a homogeneous sedimentation deformed by extensional tectonic activity along two main fault systems ne sw and nw se the sediment distribution was controlled by the pre existing palaeotopography during the late pliocene a generalized synsedimentary regression with a n s compressive tectonic activity favoured the development of a great variety of seismic facies related to the initiation of the almeria turbidite system and the triggering of gravity mass flow deposits the deformation of these seismic facies was mainly controlled by the transcurrent ne sw and nw se structures and their distribution was related to the point source represented by the almeria canyon during the quaternary the high frequency sea level oscillations coeval to nnw sse compressive tectonic activity resulted in the progradation of the margin the occurrence of instability phenomena and the sedimentary displacements of the almeria turbidite system an analysis of subsidence evolution shows an attenuation during the pliocene quaternary from a maximum of 342 m m y to 160 m m y for the total subsidence and from a maximum of 196 to 116 m m y for the tectonic subsidence

morphostructure growth patterns and tectonic control of the rhone and nile deep sea fans a comparison the rhone and the nile rivers shape the sediment distribution of the ligurian and the levantine basins in the mediterranean sea respectively both rivers cut huge canyons in their bed rock during the messinian desiccation of the mediterranean and the subsequent early pliocene marine transgression reached far inland both in france and in egypt the sediment supply of both rivers was affected by climatic variations during the pleistocene but whereas glacial periods were associated with reduced water flow in the rhone they can be correlated with enhanced flow of the nile the sediment distribution and accumulation patterns of both rivers built large deltas on their continental shelves during high sea level stands during lowstands both rivers flowed as far as the shelf e ge and transported their sedimentary load through the continental slopes directly to their deep sea fans the patterns of sediment distribution and accumulation in the marine basins of the ligurian and the levantine seas were affected also by pliocene quaternary tectonic activity and halokinetic offsets that led to sediment instability the present hydrographic and sedimentological regimes of both rivers do not represent their natural potential due to artificial interference the principal economic significance of the deep sea fan accumulation process is the transportation of medium and coarse grained sediments into the deep marine basin considering the effect of these sediments on stratal permeabilities and hydrocarbon potential the presented comparative overview emphasizes recent and subrecent sedimentological aspects that are critical to petroleum exploration in active and extinct deep sea depositional environments

empirical calibration of oxygen isotope fractionation in zircon new empirical calibrations for the fractionation of oxygen isotopes among zircon almandine rich garnet titanite and quartz are combined with experimental values for quartz grossular the resulting a coefficients k2 are zrc alm grs ttn qtz 2 64 2 71 3 03 3 66 zrc 0 07 0 39 1 02 alm 0 32 0 95 grs 0 63 full size table table options view in workspace download as csv for the relation 1000 ln y x ay x 106 t2 the fractionation of oxygen isotopes between zircon and coexisting minerals can provide otherwise unavailable evidence of magmatic processes including crystallization remelting and assimilation fractional crystallization

2 7 ga plume associated vhms mineralization in the eastern goldfields superterrane yilgarn craton insights from the low temperature and shallow water ag zn au nimbus deposit economic volcanic hosted massive sulfide vhms deposits of the archaean yilgarn craton of western australia are restricted to zones of juvenile crust as revealed through regional nd pb and hf isotopic variations and the geochemistry of felsic volcanic rocks interpreted as archaean paleo rift zones one of these runs n s through the eastern goldfields superterrane broadly coincident with the kurnalpi terrane and is associated with the high grade ca 2690 ma teutonic bore jaguar and bentley deposits plus sub economic vhms mineralization further south to date only small historic cu occurrences e g anaconda and barren pyritic lenses have been recognized in the older 2 7 ga plume dominated lower stratigraphy of the eastern goldfields superterrane the nimbus ag zn au deposit 12 1 mt at 52 g t ag 0 9 zn and 0 2 g t au is located approximately 10 km east of kalgoorlie near the margin of the kurnalpi terrane its origin has been contentious for a number of years with previous models favouring seafloor sub seafloor vhms mineralization or a high sulfidation fault hosted system we present a detailed account of the deposit its host stratigraphy and associated hydrothermal alteration plus two new shrimp u pb zircon ages pb isotope galena and o isotope zircon constraints compared to other vhms occurrences in the yilgarn craton the nimbus deposit is unusual in terms of its tectono stratigraphic position the geochemistry of its host sequence i e fi affinity felsic volcanic rocks ocean plateau like low th basalts mineralogy e g abundance of ag sb pb as bearing sulfosalts high hg low cu and quartz carbonate sericite dominated alteration assemblages classification of nimbus as a shallow water and low temperature vhms deposit with epithermal characteristics i e a hybrid bimodal felsic deposit is consistent with its position near the margin of the kurnalpi paleo rift zone and radiogenic 238u 204pb values the recognition that the nimbus deposit is associated with c 2705 ma plume magmatism opens new areas for vhms exploration in the eastern goldfields superterrane over a strike length exceeding 500 km

oxygen isotope compositions and magmatic epidote from two contrasting metaluminous granitoids ne brazil oxygen isotope compositions of mineral separates were determined from two metaluminous granitoids emas and sao rafael plutons from northeastern brazil the i type emas pluton has high 18o wr values 11 5 11 8 whereas the sao rafael pluton has low 18o wr values 7 5 8 1 but sr and nd are characteristics of s type granitoids measured mineral mineral fractionations suggest continuous sub solidus inter mineral isotope exchange among all minerals except zircon there is a large and consistent quartz epidote fractionation that gives apparent temperatures that are much lower than anticipated closure temperatures for epidote oxygen isotope fractionation between natural zircon and magmatic epidote is opposite to that predicted from theoretical determinations as 18o epidote 18o zircon an empirical calibration based on these results would suggests a closure t for oxygen in epidote of 500 c and qtz epi 5 19 at 500 c

sedimentary evolution of the pliocene and pleistocene ebro margin northeastern spain abstract the pliocene and pleistocene deposits of the spanish ebro margin overlie a regional unconformity and contain a major disconformity these unconformities named reflector m and reflector g mark the bases of two seismic sequences except for close to the upper boundary where a few small channel deposits are recognized the lower sequence lacks channels the upper sequence contains nine channel levee complexes as well as base of slope aprons that represent the proximal part of the valencia turbidite system diverse geometries and variations in seismic units distinguish shelf slope base of slope and basin floor facies four events characterize the late miocene to pleistocene evolution of the ebro margin a formation of a paleodrainage system and an extensive erosion to depositional surface during the latest miocene messinian b deposition of hemipelagic units during the early pliocene c development of canyons during the late pliocene to early pleistocene and d deposition of slope wedges channel levee complexes and base of slope aprons alternating with hemipelagic deposition during the pleistocene sea level fluctuations influenced the evolution of the sedimentary sequences of the ebro margin but the major control was the sediment supply from the ebro river

crustal contamination and the granite problem in the british tertiary volcanic province isotopic studies on the british tertiary volcanic province have shown that the granites contain both mantle derived and crustal components while basic rocks display pronounced crustal contamination in order to study contamination mechanisms in greater detail isotopic and chemical variations in skye plateau lavas and cuillins complex intrusive units were examined as a function of time in both cases degrees of crustal contamination generally fall with time which it is argued reflects the progressive melting and sweating out9 of lewisian acid gneissic sheets from the more refractory intermediate basement during repeated intrusion and contamination of sheet like magma reservoirs long lived developing magma chambers do not fit the data well skye granites had basic precursors that suffered similar types of contamination in the lower crust but tended to form longer lived developing magma chambers in the upper crust nevertheless skye granites display similar crustal pb contents to associated basic intrusions and are argued not to be the products of crustal anatexis but the differentiates of preshal mhor basic magmas contaminated by ca 10 with large degree partial melts of lewisian acid gneisses

highly differentiated juvenile crust derived magmas linked with the xilekuduke porphyry mo cu deposit in east junggar nw china abstract the east junggar region links the kazakhstan junggar plate with the siberian craton along the western part of the central asian orogenic belt among the major ore deposits in this region the xilekuduke molybdenite deposit is a unique example of mo dominated porphyry molybdenum and copper mineralization here occur as disseminated sulfides or veinlets mainly in granite porphyry and monzogranite with a prominent alteration from an inner potassic through sericitic to an outer propylitic zone zircon la icp ms u pb ages indicate that the granite porphyry and monzogranite were emplaced at 326 4 2 ma and 328 2 1 8 ma respectively both rocks show enrichment in light rare earth elements lree and rb k sr hf zr but depletion in nb ta ti and p suggesting magma generation in a post collisional setting a relatively high oxidation state is inferred from zircon ce values and oxygen fugacity of parental magma the ore hosted intrusions also show high differentiation index di indicating a highly oxidized parental magma and prolonged differentiation process the range of zircon ehf t values 11 5 to 17 young zircon hf model ages and consistent but slightly low zircon 18o values 4 84 to 5 20 together with the range of mg 35 53 suggest derivation of the parental magma through partial melting of juvenile crust with minor contribution from mantle components and sediments we propose that melting of juvenile oceanic components at depth with high degree of differentiation played a significant role in generating the mo mineralization in xilekuduke deposit within a post collisional setting in the east junggar domain

the rapid heating defocused beam technique a co2 laser based method for highly precise and accurate determination of δ18o values of quartz abstract we describe a laser fluorination technique specifically for quartz that allows both high accuracy and high precision determination of oxygen isotope ratios regardless of grain size the rapid heating defocused beam technique rhd utilizes a defocused 32 w co 2 laser at full power which delivers 17 w 20 w mm 2 to the sample to quickly react quartz in contrast other recent laser fluorination studies use a tightly focused laser beam and slow heating i e sharp and kirschner 1995 fouillac and girard 1996 kirschner and sharp 1997 and find laser analysis of fine grained quartz to be inaccurate three quartz standards nbs 28 qz bra and qz cwru were analyzed using the rhd technique at the university of wisconsin to test for grain size effects rhd analyses show no correlation between grain size and 18 o values and are in excellent agreement with 18 o values obtained using conventional fluorination techniques additional analyses of the same quartz standards performed at university of wisconsin using slow heating and a focused beam yield 18 o values that are both less precise and significantly up to 0 8 lower than the accepted values attempts to use the rhd technique with a 20 w co 2 laser which delivers 8 w 10 w mm 2 to the sample at brgm were unsuccessful probably due to insufficient power density of the defocused beam we conclude that the rhd technique yields excellent accuracy and precision but that power densities of 15 20 w mm 2 may be necessary across a large part of the sample surface we recommend the use of lasers with at least 30 w of power

zircon u pb age and o isotope evidence for neoproterozoic low 18o magmatism during supercontinental rifting in south china implications for the snowball earth event identification of neoproterozoic low 18 o igneous rocks is a key to demonstrate that high t water rock interaction and low 18 o magmatism in rift tectonic zones can serve as an efficient interface to transport heat and material from the earth s interior to exterior at the onset of the snowball earth event low 18 o values of 10 9 to 4 4 permil characteristic of meteoric origin were observed on an areal extent over 30 000 km2 for mid neoproterozoic metaigneous zircons from the ultrahigh pressure eclogite facies metamorphic belt of triassic ages along the dabie sulu orogenic belt china although the zircon o isotope system could be reset to acquire its low 18 o values by exchange with matrix minerals during wet eclogite facies metamorphism the abnormal 18 o depletion is confirmed by occurrence of neoproterozoic low 18 o zircons in low grade metaigneous rocks in the same belt cathodoluminscence imaging of zircons from low grade metagranitoid and metavolcanic rocks shows preservation of the internal structures of oscillatory zoning typical of magmatic origin hornblende from two granites of low 18 o zircons gave ar ar plateau ages of 747 6 and 776 12 ma ruling out that phanerozoic metamorphism effected mineral o isotope values two groups of u pb ages were measured at 756 5 ma and 782 5 ma respectively for the low 18 o zircons this indicates that low 18 o zircons crystallized during two episodes of low 18 o magmatism in response to tectonic evolution from supercontinental rifting at 780 ma to breakup at 750 ma the second episode of low 18 o magmatism is contemporaneous with the continental kaigas iceage a plate rift model is advanced to account for the tectonic connection between the low 18 o magmatism the continental glaciation and the supercontinental rifting during the cryogenian period high t meteoric water rock interaction occurred prior to low 18 o magmatism in rift tectonic zones and caldera collapse was responsible for melting of hydrothermally altered low 18 o rocks during rifting of the south china block from the rodinia supercontinent

tropical and extratropical responses of the north atlantic atmospheric circulation to a sustained weakening of the moc abstract the tropospheric response to a forced shutdown of the north atlantic ocean s meridional overturning circulation moc is investigated in a coupled ocean atmosphere gcm the third climate configuration of the met office unified model hadcm3 the strength of the boreal winter north atlantic storm track is significantly increased and penetrates much farther into western europe the changes in the storm track are shown to be consistent with the changes in near surface baroclinicity which can be linked to changes in surface temperature gradients near regions of sea ice formation and in the open ocean changes in the sst of the tropical atlantic are linked to a strengthening of the subtropical jet to the north which combined with the enhanced storm track leads to a pronounced split in the jet structure over europe eof analysis and stationary box indices methods are used to analyze changes to the north atlantic oscillation nao there is no consistent signal of a change in the variability of th

archaean fluid assisted crustal cannibalism recorded by low δ 18 o and negative e hf t isotopic signatures of west greenland granite zircon the role of fluids during archaean intra crustal magmatism has been investigated via integrated shrimp u pb 18o and la mc icpms 176hf isotopic zircon analysis six rock samples studied are all from the nuuk region southern west greenland including two 3 69 ga granitic and trondhjemitic gneisses a 3 64 ga granitic augen gneiss a 2 82 ga granodioritic ikkattoq gneiss a migmatite with late neoarchaean neosome and a homogeneous granite of the 2 56 ga qorqut granite complex qgc all zircon grains were thoroughly imaged to facilitate analysis of magmatic growth domains within the zircon analysed there is no evidence for metamictization initial ehf zircon values n 63 are largely sub chondritic indicating the granitic host magmas were generated by the remelting of older un radiogenic crustal components zircon from some granite samples displays more than one 207pb 206pb age and correlated with 176hf 177hf compositions can trace multiple phases of remelting or recrystallization during the archaean model ages calculated using lu hf arrays for each sample indicate that the crustal parental rocks to the granites granodiorites and trondhjemites segregated from a chondrite like reservoir at an earlier time during the archaean corresponding to known formation periods of more primitive tonalite trondhjemite granodiorite ttg gneisses zircon from the 3 69 ga granite the migmatite and qgc granite contains eoarchaean cores with chondritic 176hf 177hf and mantle like 18o compositions the age and geochemical signatures from these inherited components are identical to those of surrounding tonalitic gneisses further suggesting genesis of these granites by remelting of broadly tonalitic protoliths zircon oxygen isotopic compositions n 62 over nine age populations six igneous and three inherited have weighted mean or mean 18o values ranging from 5 8 0 6 to 3 7 0 5 the 3 64 ga granitic augen gneiss sample displays the highest 18o with a mildly supra mantle composition of 5 8 0 6 inherited eoarchaean ttg derived zircon shows mantle like values igneous zircon from all other samples spanning more than a billion years of archaean time record low 18o sub mantle compositions these are the first low 18o signatures reported from archaean zircon and represent low 18o magmas formed by the remelting and metamorphism of older crustal rocks following high temperature hydrothermal alteration by meteoric water meteoric fluid ingress coupled with crustal extension associated high heat flow and intra crustal melting are a viable mechanism for the production of the low 18o granites granodiorites and trondhjemites reported here both high and low 18o magmas may have been generated in extensional environments and are distinct in composition from phanerozoic i type granitic plutonic systems which are typified by increasing 18o during intra crustal reworking this suggests that archaean magmatic processes studied here were subtly different from those operating on the modern earth and involved extensional tectonic regimes and the predominance of remelting of hydrothermally altered crystalline basement

role of internal waves in the generation of nepheloid layers on the northwestern alboran slope implications for continental margin shaping 1 the role of internal waves in the sediment dynamics of the northwestern alboran continental slope was investigated in a selected area around the guadiaro submarine canyon nepheloid layer distribution was identified using closely spaced ctd transmissometer profiles collected during two hydrographic surveys a well defined pattern of suspended sediment distribution consisting of surface intermediate and near bottom nepheloid layers was found intermediate and bottom nepheloid layers were always observed within the canyon and on the adjacent continental slope spanning mainly from 200 to 500 m depth in addition a current meter with a turbidimeter was deployed in the lower section of the guadiaro canyon at 600 m depth 25 meters above the seafloor time series analysis indicated that the currents temperature and turbidity within the canyon fluctuate mainly at semidiurnal tidal frequencies suggesting the presence of semidiurnal internal tides affecting the near bottom suspended sediment concentration along the canyon axis high resolution bathymetry from the study area was used to evaluate the internal wave reflection conditions at semidiurnal tidal frequency for the entire continental slope region critical slope conditions were reached on the upper continental slope and along the canyon axis coinciding with the region in which nepheloid layers were observed this region also coincides with a zone of erosion on the upper continental slope of the study area previously identified by hernandez molina 1993 these results indicate that the generation of intermediate and bottom nepheloid layers as well as the erosion and shaping of the northwestern alboran continental slope may result from the interaction of internal waves and the seafloor morphology

shrimp u pb and cameca 1280 oxygen isotope results from ancient detrital zircons in the caozhuang quartzite eastern hebei north china craton evidence for crustal reworking 3 8 ga ago the caozhuang quartzite located in eastern hebei province in the eastern part of the north china craton has long been known to contain the oldest detrital zircon population in china a suite of 30 zircons with preliminary ages 3 7 ga were selected for detailed shrimp u pb and cameca 1280 oxygen isotope analyses shrimp u pb dating reveals that ages range from 3860 to 3135 ma the former being the oldest 207 pb 206 pb zircon age so far obtained from the north china craton values of 18 o range from 5 4 to 7 5 permil similar to archean igneous zircons worldwide but the average value for the 30 zircons is 6 6 permil which is 0 3 permil higher than suite averages for detrital zircons from the jack hills and beartooth mountains and nearly 1 permil higher than magmatic zircons from igneous rocks of the superior province and barberton these elevated values of 18 o suggest reworking of a significant amount of juvenile crust older than 3 8 ga that underwent a low temperature supracrustal history and was distributed throughout the source region in northeast china

seismostratigraphy and tectonic architecture of the carboneras fault offshore based on multiscale seismic imaging implications for the neogene evolution of the ne alboran sea in the se iberian margin which hosts the convergent boundary between the european and african plates quaternary faulting activity is dominated by a large left lateral strike slip system referred to as the eastern betic shear zone this active fault system runs along more than 450 km and it is characterised by low to moderate magnitude shallow earthquakes although large historical events have also occurred the carboneras fault is the longest structure of the eastern betic shear zone and its southern termination extends further into the alboran sea previously acquired high resolution data i e swath bathymetry tobi sidescan sonar and sub bottom profiler show that the offshore carboneras fault is a ne sw trending upwarped zone of deformation with a length of 90 km long and a width of 0 5 to 2 km which shows geomorphic features typically found in subaerial strike slip faults such as deflected drainage pressure ridges and en echelon folds however the neotectonic depth architecture and neogene evolution of carboneras fault offshore are still poorly known in this work we present a multiscale seismic imaging of the carboneras fault i e topas high resolution multichannel seismic reflection and deep penetration multichannel seismic reflection carried out during three successive marine cruises from 2006 to 2010 the new dataset allowed us to define a total of seven seismostratigraphic units from tortonian to late quaternary above the basement to characterise the tectonic architecture and structural segmentation of the carboneras fault and to estimate its maximum seismic potential we finally discuss the role of the basement in the present day tectonic evolution of the carboneras fault and explore the northern and southern terminations of the fault and how the strain is transferred to nearby structures

geochemical evolution of the tertiary mull volcano western scotland the early tertiary mull volcano western scotland is one of the most dissected and best exposed igneous complexes of the north atlantic province the new and published geochemical data enable us to chart the magmatic evolution of the mull volcano from the oldest lavas through the intrusive rocks of three overlapping igneous centres to the youngest dykes in this study we identify four successive magma types within the remnant volcano the earliest type the mull plateau group comprises mildly alkaline basaltic rocks with steep chondrite normalized rare earth element ree patterns this type is succeeded within the lava succession and dyke swarm by the coire gorm magma type with essentially flat chondrite normalized ree patterns a third magma type represented within the lava and dykes the central mull tholeiites is more depleted in incompatible trace elements than the preceding types and has flat to lree depleted chondrite normalized patterns the major intrusions and cone sheets of mull centre 1 and early centre 2 belong to this magma type midway through the igneous activity associated with centre 2 the magma type changed to become more alkalic and more enriched in incompatible trace elements this magma type the late mull type is found to persist through the cone sheets and major intrusions of centre 3 to the youngest dykes these changes in magma composition were related to variations in the mantle source and depth of partial melting beneath mull and or differences in the efficiency of melt pooling before ascent through the lithosphere with the exception of the early staffa magma sub type part of the mull plateau group the location of magma chambers in which the bulk of contamination occurred changed with time from deep lower crustal lewisian gneiss to shallow upper crustal moine schist intermediate members of the plateau group and the late mull magma type are enriched in fe ti and p relative to the central mull tholeiites we attribute this difference to the more alkalic nature of these suites lower fo2 and the formation of fe3 p complexes in the magma the intermediate rocks were important in magma mixing processes with two types of mixing identified on mull 1 cryptic mixing between basalts and low fe intermediate magmas typified by lavas and early basic cone sheets of the central mull tholeiite magma type 2 observable mingling between rhyolitic magmas and high fe intermediate magmas of the late mull type shown by the mixed magma bodies of the glen more and loch ba ring dykes the main factor in determining which type of mixing occurred appears to have been the density contrast between the various magmas it may safely be maintained that mull includes the most complicated igneous centre as yet accorded detailed examination anywhere in the world bailey et al 1924 memoir of the geological survey of great britain scotland hmso edinburgh 1924

sea valleys and related depositional systems in the gulf of lion and ebro continental margins 1 four main types of sea valleys submarine canyons gullies channels of turbidite systems and a mid ocean channel have been characterized in the ebro and the gulf of lion distal margins in the catalan sea together with three main types of depositional bodies pyrenean canyon deep sedimentary body pcdsb apron deposits and channel levee complexes related to the development of these sea valleys erosion and deposition mainly during the quaternary have formed the majority of these sea valleys although some structurally controlled sea valleys also exist as an example a messinian entrenchment has been confirmed in the petit rhone canyon the evolution of the drainage patterns is established from the detailed analysis of the sedimentary structure this analysis revea s the presence of buried sedimentary bodies and older drainage systems differing from those observed in the bathymetric charts specific factors determine the evolutionary differences between both margins including the absence or presence of underlying evaporitic messinian layers and the regional geodynamic evolution during and after the alpine orogeny we propose a dual evolutionary model from the end of the miocene to the quaternary

origin sedimentary processes and depositional evolution of the agadir turbidite system central eastern atlantic the oligocene to recent agadir turbidite system occurs in the agadir basin abutting against the continental margin off south morocco central eastern atlantic this system is part of the submarine drainage system linking back to the anti and high atlas mountains through the agadir canyon and its sedimentary evolution is shown to comprise lateral shifts of canyon channel overbank and lobe deposits governed by local topography draped palaeorelief seamounts and a contourite ridge and channel avulsions in addition the turbidite system shows an overall retrogradational stacking migrating about 60 km upslope this probably reflects a decrease in gradient on the continental margin gradual basin filling and or a progressive decrease in energy and load of the sediment gravity flows that fed the system the latter change in sediment flux could result from the interplay between the progressive denudation of the source areas together with the climatic change which led to the present arid desertic conditions in the hinterland the seismic features observed with new ultra high resolution seismic tools allow the recognition of the present day sedimentary activity within the agadir turbidite system and this is related among other factors to the active seismicity of the area

geomorphology of the iberian continental margin abstract the submarine features and processes around the iberian peninsula are the result of a complex and diverse geological and oceanographical setting this paper presents an overview of the seafloor geomorphology of the iberian continental margin and the adjacent abyssal plains the study covers an area of approximately 2 3 million km 2 including a 50 to 400 km wide band adjacent to the coastline the main morphological characteristics of the seafloor features on the iberian continental shelf continental slope continental rise and the surrounding abyssal plains are described individual seafloor features existing on the iberian margin have been classified into three main groups according to their origin tectonic and or volcanic depositional and erosional major depositional and erosional features around the iberian margin developed in late pleistocene holocene times and have been controlled by tectonic movements and eustatic fluctuations the distribution of the geomorphological features is discussed in relation to their genetic processes and the evolution of the margin the prevalence of one or several specific processes in certain areas reflects the dominant morphotectonic and oceanographic controlling factors sedimentary processes and the resulting depositional products are dominant on the valencia catalan margin and in the northern part of the balearic promontory strong tectonic control is observed in the geomorphology of the betic and the gulf of cadiz margins the role of bottom currents is especially evident throughout the iberian margin the galicia portuguese and cantabrian margins show a predominance of erosional features and tectonically controlled linear features related to faults

empirical determination of oxygen isotope fractionation factors for titanite with respect to zircon and quartz abstract measurements of oxygen isotope fractionations between coexisting igneous titanite ttn and zircon zrc have been used to formulate a self consistent empirical calibration of equilibrium oxygen isotope partitioning 1000 ln zrc ttn 1 02 10 6 t 2 this calibration is based on the average measured zrc igneous ttn 1 2 0 3 n 27 rocks and a closure temperature of titanite to oxygen diffusion of approximately 650 c the average measured fractionation between zircon and metamorphic titanite is 2 1 0 4 n 5 rocks these results show that zrc ttn can be used to distinguish igneous vs metamorphic or hydrothermal titanite the new zircon titanite fractionation has been combined with published experimental and empirical data to provide a new quartz titanite fractionation curve 1000 ln qtz ttn 3 57 10 6 t 2 this new calibration is consistent with qtz igneous ttn data from coexisting mineral pairs in granitic rocks modeling diffusional exchange of oxygen during cooling in a typical granitic rock using the new calibration results in the same qtz igneous ttn as measured 4 5 0 43 n 25 rocks both measured zrc igneous ttn and qtz igneous ttn differ from fractionations calculated using the semiempirical increment method the consistency of empirical zrc igneous ttn in a range of geologic environments allows the calculation of a more accurate fractionation factor for titanite

constraining the post emplacement evolution of the hebridean igneous province hip using low temperature thermochronology how long has the hip been cool abstract the thermal history of the hebridean igneous province has been determined through the application of low temperature thermochronology to the four central complexes in the province the zircon u th he age 59 4 3 3 ma 1 n 18 and the ages from each complex 60 7 2 3 ma for skye 58 0 0 4 ma for mull 55 9 3 2 ma for ardnamurchan 55 6 2 7 ma for rum are indistinguishable from the crystallization ages apatite fission track ages 61 2 57 2 ma mean of 59 3 3 4 ma from the major plutonic units also overlap crystallization ages implying that on a regional scale the hebridean igneous province cooled rapidly to near surface temperatures immediately after emplacement however apatite fission track ages and track lengths and apatite u th he ages from some small volume intrusions in the skye and rum central complexes identify localized mid eocene 45 47 ma cooling forward and inverse modelling suggests a discrete heating cooling event at c 47 ma which may have been caused by structurally controlled localized advection of heat above shallow emplacement this is the first suggestion of eocene magmatism in the hebridean igneous province

sources and evolution of arc magmas inferred from coupled o and hf isotope systematics of plutonic zircons from the cretaceous separation point suite new zealand abstract coupled o and hf isotopic compositions of zircons from early cretaceous 113 124 ma granitoids of the separation point suite sps new zealand obtained by cathodoluminescence imaging guided micro beam methods sims la icpms are used as a record of evolving magma compositions in a prominent mesozoic arc system eight representative sps samples from individual plutons in the nelson and fiordland regions yield magmatic zircons with initial hf isotope ratios expressed in e hf ranging from 4 to 11 nelson and 5 to 12 fiordland respectively initial hf isotope ratios of zircons are extremely heterogeneous within individual samples with the vast majority of values distinctly less radiogenic than depleted mantle at 120 ma e hf 16 o isotope ratios are likewise variable with 18 o zircon smow values of 2 8 nelson and 0 7 fiordland the within rock variability in both zircon hf and o isotope ratios is testimony to open system processes that operated during magma evolution and zircon crystallisation average 18 o zircon for cores and rims allow constraints to be placed on the o isotopic composition of magmas from which zircon precipitated 18 o magma 4 8 elevated 18 o magma 6 5 require involvement of 18 o enriched supracrustal material weathered continental crust or low t seawater hydrothermally altered oceanic crust while 18 o magma 18 o depleted crustal component whole rock sr isotope nb ta and nd pb systematics are inconsistent with 18 o depleted slab melts 18 o 0 6 as a source component for sps magmas instead low 18 o values suggest incorporation of high t meteoric hydrothermally altered country rocks similar to those of the largs terrane presently exposed in northern fiordland in diagrams of sio 2 versus inferred 18 o magma the most primitive sps samples from the nelson and fiordland regions plot close to the expected composition for primitive arc magmas more evolved granitoids however show strongly divergent trends of o isotope composition as a function of sio 2 suggestive of assimilation coupled to fractional crystallisation afc in contrasting crustal environments emplacement level contamination by local crust is supported by age distributions of inherited zircons which indicate a predominance of palaeozoic and mesozoic zircons in nelson and fiordland granitoids respectively

experiments on hydraulic jumps in turbidity currents near a canyon fan transition the point at which a submarine canyon debouches on its associated abyssal fan is generally characterized by a drop in channel slope turbidity currents of the kind responsible for the genesis of the canyon and fan should display an internal hydraulic jump near the slope transition no direct field observations of any such jump appear however to have been made experiments on the nature of the jump and the resulting sedimentary deposits indicate that the thickness of the deposits just downstream of the jump tends to increase as the ratio of bed shear velocity immediately behind the jump to particle fall velocity decreases

zircon oxygen isotopic constraint on the sources of late mesozoic a type granites in eastern china abstract a type granites are usually derived from partial melting of the lower crust and or the upper mantle within extensional settings but their exact sources for specific plutons are required to unravel a systematic laser fluorination analysis of oxygen isotopes was carried out for five well documented late mesozoic a type granites in eastern china zircon from 41 samples was separated and 109 aliquots of fresh zircon were analyzed along with whole rock powder and quartz from the same samples hydrothermally altered whole rock samples show scattered 18 o values of 2 3 to 7 4 with a total variation up to 9 7 in contrast zircon 18 o values vary only from 3 1 to 5 4 with a range of 2 3 most available zircon 18 o values of a type granites are lower than normal mantle zircon values of 5 3 0 6 2sd and high temperature equilibrium fractionations are well preserved between quartz and zircon in most cases the above lines of evidence suggest that the low 18 o zircons in a type granites were crystallized from low 18 o magmas because low 18 o magmas cannot be derived entirely from the mantle reworking and or recycling of crustal igneous rocks are involved for their petrogenesis the low 18 o zircons in this study thus offer evidence for a dominantly crustal origin of the late mesozoic a type granites in eastern china

petrogenesis of the igneous mucajai amg complex northern amazonian craton geochemical u pb geochronological and nd hf o isotopic constraints abstract the ca 1525 ma igneous mucajai anorthosite monzonite granite amg complex in northern brazil is a rare manifestation of mesoproterozoic intraplate magmatism in the northern amazonian craton the complex comprises a two phase rapakivi granite batholith with subordinate quartz fayalite monzonites and syenites and the closely associated repartimento anorthosite zircon u pb id tims geochronology reveals that the anorthosite 1526 2 ma monzonite 1526 2 ma and the main phase biotite hornblende granite 1527 2 ma of the complex intruded the paleoproterozoic 1 94 ga country rocks simultaneously at 1526 ma and that the more evolved biotite granite is marginally younger at 1519 2 ma intraplate magmatism in the mucajai region was relatively short lived and lasted 12 million years 1529 1517 ma at maximum the nd whole rock id tims e nd from 1 9 to 2 8 hf zircon lam icp ms e hf from 2 0 to 3 1 and o zircon sims 18 o from 6 1 to 7 0 isotopic compositions of the studied rocks are fairly uniform but still reveal a small degree of isotopic heterogeneity in the paleoproterozoic crust enclosing the complex the small isotopic differences observed in the two types of rapakivi granites biotite hornblende granite and biotite granite may result either from an isotopically heterogeneous lower crustal source or more likely from contamination of the granitic magma derived from a lower crustal source during prolonged residence at upper crustal levels

a cryptic record of magma mixing in diorites revealed by high precision sims oxygen isotope analysis of zircons high precision in situ ion microprobe sims oxygen isotope analysis of zircons from two diorite intrusions associated with the late caledonian lochnagar pluton in scotland has revealed large differences in the degree of heterogeneity in zircon 18o between the diorites zircon crystals from the cul nan gad diorite cng show a unimodal distribution of oxygen isotope values 18o 6 0 0 6 2 and no or only minor grain scale variation those from the allt darrarie diorite ad1 show a large range in 18o and an apparent bimodal distribution with modes of 6 6 0 4 and 7 3 0 4 variations of up to 1 2 occur between and within grains both an increase and decrease in 18o with zircon growth has been observed the 18o composition of growing zircon can only change if open system processes affect the magma composition i e if material of contrasting 18o composition is added to the magma the variability in ad1 is interpreted to represent a cryptic record of magma mixing a deep crustal hot zone is a likely site for generation of the dioritic magmas which developed by mixing of residual melts and crustal partial melts or by melting of mafic lower crustal rocks the overall small number of zircons with mantle like 18o values 5 3 0 6 2 in the lochnagar diorites is largely the product of crustal differentiation rather than crustal growth the 18o of quartz from the cng and ad1 diorites shows only minor variation cng 10 9 0 5 2 ad1 11 7 0 6 2 within single populations with no evidence of mixing quartz zircon isotopic disequilibrium is consistent with later crystallisation of quartz from late magmatic fluids and in case of the ad1 diorite after the inferred magma mixing from a homogenised higher 18o melt high precision sims oxygen isotope analysis of zircon provides a new approach to identifying and resolving previously undetected early stage magma mixing and constraining the compositions and origins of the component magmas a combination of zircon quartz and whole rock data has proven to be a powerful tool in reconstructing the petrogenetic evolution of diorite from early crystallisation to late alteration

low δ18o magma isle of skye scotland evidence from zircons abstract zircons in tertiary granitic rocks from the isle of skye scotland were resistant to measurable oxygen isotope exchange during intense hydrothermal activity in the subvolcanic environment five granite bodies from the western red hills complex were investigated four have 18o zrc 4 1 0 2 o vsmow while the fifth which intruded before major cauldron subsidence is 2 lower zircons from lewisian gneiss are visually and isotopically distinct indicating that zircons in the granite are not xenocrysts from the lewisian basement analysis of different magnetic and size fractions of zircon shows no significant correlation to 18o supporting the conclusion that these values represent the true magmatic compositions and that the western red hills granites intruded as low 18o magmas with a whole rock 18o 6 0 quartz separates from four granites are close to the calculated magmatic values in 18o but in the fifth values are 5 lower indicating variable exchange of quartz with low 18o heated meteoric waters these results might be explained by magmatic interaction with hydrothermally altered crust early in the evolution of the granites before crystallization of zircon followed by interaction with later hydrothermal fluids alternatively independent evidence for low 18o mafic magmatism in nw scotland suggests the presence of large quantities of low 18o subducted ocean crust in the subcontinental lithosphere that could contaminate or be the source of low 18o mantle derived melts

neoarchean recycling of 18o enriched supracrustal materials into the lower crust zircon record from the north china craton abstract oxygen isotope analyses were carried out using sims technique cameca 1280 on zircons from well studied lower crust xenoliths xenocrysts from the north china craton ncc the results show that magmatic zircons with archean paleoproterozoic 207 pb 206 pb ages have an extremely large variation in 18 o values that range from less than normal mantle value 4 74 0 28 2 to 18 o enriched supracrustal value 8 88 0 40 2 and differ in localities of the ncc 18 o qindao from 5 27 0 45 to 8 88 0 40 18 o hannuoba from 6 78 0 23 to 7 69 0 41 18 o xiuyan from 4 74 0 28 to 6 57 0 39 such a variation demonstrates that the neoarchean lower crust beneath the ncc was highly heterogeneous in oxygen isotope compositions even in an individual region the fact that the predominant zircons have high 18 o values suggests that the recycling of 18 o enriched supracrustal materials into the neoarchean lower crust indeed happened during zircon crystallization some zircons with core rim texture have nearly identical 18 o both in core and its rim on the other hand others have a distinctive oxygen isotope ratio between the core and its rim possessing slightly higher 18 o in the rim than its core or vice versa such an oxygen isotope feature in zoned zircons suggests a complicated evolutional history of ancient lower crust in the ncc this study provides convincing evidence that a large amounts of the supracrustal materials have been recycled into the neoarchean lower crust beneath the ncc a process resulting in the highly heterogeneity in oxygen isotopes

oxygen isotope evidence for magmatic variability and multiple alteration events in the proterozoic st francois mountains missouri abstract the st francois mountains contain at least two mesoproterozoic caldera complexes the butler hill and the taum sauk calderas each with diameters greater than 20 km igneous zircons from intrusive and extrusive units within the calderas have a range of 18o zircon from 5 8 to 8 2 v smow these zircons are similar to other proterozoic zircons from igneous rocks around the world and suggest a magma source from partial melting of older crust with variable mantle component there is no significant difference in the magmatic oxygen isotope ratios between the taum sauk and butler hill calderas values of 18o quartz zircon 2 1 2 4 indicating that most quartz from samples in the two calderas still preserves near magmatic oxygen isotope ratios the average 18o quartz from the two calderas is 8 6 2 6 in contrast felsic volcanic units within the taum sauk caldera exposed at johnson shut ins suggest interaction with water at low temperature resulting in 18o quartz as high as 16 7 quartz phenocrysts within a single sample from johnson shut ins range from 8 7 up to 16 7 the isotope heterogeneity coupled with evidence of healed microcracks in cathodoluminescence images suggests low temperature hydrothermal alteration affected the volcanics during or shortly after eruption after caldera collapse the hydrothermally altered rocks were partially re melted and incorporated into the magma chamber as evidenced by the slight increase in 18o zircon of the resurgent dome intrusions in contrast the butler hill caldera preserves evidence of high temperature hydrothermally altered country rock assimilated into the stono mountain granitic ring intrusion based on low 18o quartz values and visible zoning in cl the two calderas experienced different alteration histories suggesting the lack of any homogenizing regional fluid influx

oxygen isotope ratios of archean plutonic zircons from granite greenstone belts of the superior province indicator of magmatic source zircons commonly preserve primary magmatic oxygen isotope ratios even through high grade metamorphic events unlike quartz which more readily loses its primary 18o value by subsolidus exchange intrusive bodies from the superior province canada have an average 18o zircon of 5 8 0 6 n 59 rocks those from granite greenstone belts have an average 18o zrc 5 8 0 6 n 55 in contrast to those from metasedimentary belts that average 18o zrc 6 7 0 2 n 4 the 18o zircon values from granite greenstone belts indicate a maximum allowable input of 14 supracrustal high 18o material into archean magmas of the superior province relative to mantle 18o values igneous bodies of the superior province have been separated into two groups based on geochemistry unenriched plutons and sanukitoids magmatic oxygen isotope ratios inferred from these zircons indicate up to a subtle but significant division of 1 between the two geochemical sets of rocks this distinction is apparent only in the 18o zrc and not in more commonly analyzed less refractory minerals such as quartz and feldspar oxygen isotope data correlate with geochemical modeling of sanukitoids the average 18o zrc for sanukitoids is 6 4 0 2 in comparison to 5 5 0 4 for unenriched plutons there is almost no overlap in values the elevation of sanukitoid 18o zrc indicates input from a high 18o source such as fluids from the subducting oceanic crust melts of subducted sediments or continental crust all of the plutons analyzed in this study have been dated by u pb zircon techniques and the combination of u pb ages and 18o zrc indicates little variability of 18o versus age during archean plutonism in the superior province therefore recycling of sediments and other high 18o sources was not a dominant process during crustal growth from 3003 to 2670 ma in the superior province

proterozoic onset of crustal reworking and collisional tectonics reappraisal of the zircon oxygen isotope record a global u pb and 18o zircon database shows temporal changes in the magmatic record related to changes in the degree of crustal reworking the 18o composition of bulk sediment remains relatively constant through geologic time with a mean value of 14 9 in contrast the 18o values in magmatic zircons vary from relatively low values averaging 6 in the archean to increasingly higher and scattered values defining a series of peaks and troughs in post archean data the degree of crustal reworking increases at times of supercontinent assembly therefore we attribute the pattern of post archean 18o values recorded by magmatic zircons to a significant increase in the incorporation of high 18o sediment in response to enhanced crustal thickening and reworking associated with the onset of collisional tectonics especially during formation of supercontinents

seafloor characterization and backscatter variability of the almeria margin alboran sea sw mediterranean based on high resolution acoustic data abstract an acoustic study of the almeria margin eastern alboran sea sw mediterranean was carried out by means of an integrated dataset comprising deep towed tobi sidescan sonar swath bathymetry topas high resolution seismics and sediment gravity cores the almeria margin is a complex system dominated by volcanic and tectonic features shaped by recent sedimentary processes in which a regional hemipelagic sedimentation is intercalated by sporadic gravitative events the aim of this work is twofold the first objective is to recognize the sedimentary and tectonic features that shape the almeria margin the main morpho sedimentary and morpho structural elements observed are the almeria canyon channel turbidite system the dalias tributary valley system landslides active faults and folds and volcanic banks the second aim is to explore and quantify the surface and subsurface seafloor parameters that characterize the backscatter of the study area sedimentary geomorphological and biological elements that play a role in the acoustic signature of the almeria margin were detected nevertheless it should be noted that seafloor acoustic backscatter is also affected by geometrical and instrumental factors despite the wide variability of the environments studied a low average acoustic backscatter reflects a diffused draping of hemipelagic sedimentation in the area higher backscatter values were observed at the top of some volcanic banks along the almeria canyon and in the shallower sector of the dalias tributary valley system the influence of subseafloor properties in the acoustic signature of the area was revealed by backscatter grain size correlations which were carried out for different depth intervals in sediment cores collected in the almeria turbidite system a poor relationship was found between backscatter and superficial silty sediments of the area whereas a higher correlation resulted in the upper 50 cm the presence of subsurface turbidites in the cores associated with the higher backscatter values suggests volume interface scattering of these sandy layers as a controlling factor of the acoustic signature obtained in the almeria margin on the other hand in rough settings such as the ones observed in the dalias tributary valley system topographic relief of up to 1 1 5 m strongly interacted with the tobi acoustic pulse this suggests that large scale roughness is an additional parameter that characterizes the acoustic strength of the area extremely high reflective patches distributed along some of the volcanic banks chella and pollux banks for depths ranging from 230 to 470 m coincide with areas where carbonate cold water coral mounds develop in the tobi images coral facies reach the maximum value of acoustic backscatter which is probably related to the rough morphology of coral ecosystems the position of coral mounds in the banks suggests that the occurrence of strong bottom currents and reduced sedimentary inputs are environmental factors that favour their settling and development in the almeria margin

hydrothermal alteration of oxygen isotope ratios in quartz phenocrysts kidd creek mine ontario magmatic values are preserved in zircon zircons from rhyolites hosting the kidd creek volcanogenic massive sulfide deposit preserve magmatic oxygen isotope ratios 18 o 5 4 0 3 n 11 that are indistinguishable from average values of other plutonic and volcanic rocks of the superior province oxygen isotope ratios of petrographically pristine primary quartz phenocrysts however are greatly elevated in 18 o and heterogeneous 18 o 14 2 to 16 1 such phenocrysts are not a good monitor of magmatic processes the presence of healed microcracks in quartz phenocrysts as seen in cathodoluminescence images and the variability of quartz oxygen isotope ratios suggest that recrystallization is the process of 18 o elevation in contrast to the variability of quartz the 18 o zircon values do not vary regardless of the degree of magnetic susceptibility the 18 o values of zircon are interpreted to reflect the primitive magmatic oxygen consistent with the rhyolite geochemistry for magmas derived by partial melting of a tholeiitic source our data show that the 18 o values of quartz and whole rock at kidd creek are a good monitor of hydrothermal exchange and are 5 higher than the magmatic value that is preserved in zircon due to its refractory nature

low 18o scourie dike magmas from the lewisian complex northwestern scotland the scourie dike swarm of the lewisian complex northwestern scotland comprises a dominant suite of quartz tholeiites and lesser volumes of norites olivine gabbros and bronzite picrites that were emplaced at depths of 14km in two episodes at 2 0 and 2 4 ga unaltered quartz tholeiite dikes have low and homogeneous whole rock 18 o values 2 04 0 14 relative to standard mean ocean water and concordant mineral 18 o values plagioclase 3 1 to 4 1 clinopyroxene 1 5 to 1 9 magnetite 0 3 to 0 6 the dikes intrude granulite facies gneisses that have heterogeneous 18 o whole rock values 5 8 to 9 7 and show no evidence of 18 o depletion low 18 o intrusive igneous rocks are generally believed to have exchanged with high temperature meteoric or oceanic fluids after emplacement the heterogeneous high 18 o values of the country rocks suggest that the lewisian complex has not been pervasively infiltrated by such fluids it is also unlikely that fluids were channeled along the dikes because 1 the gneisses immediately adjacent to the dikes have unaltered mineralogies and stable isotope ratios 2 the dikes preserve unaltered igneous textures and mineralogies 3 the dike minerals do not show open system oxygen isotope resetting and 4 surface derived fluids generally do not penetrate to the depths at which the dikes were intruded it is more likely that these dikes were emplaced as primary low 18 o magmas derived from the subcontinental lithosphere the geochemistry of the scourie dikes suggests that they have not assimilated large volumes of continental crust and the best explanation of the data is that the dikes were derived from a low 18 o mantle source that possibly contained the remains of subducted hydrothermally altered oceanic crust