warming in the agulhas current system since the 1980 s 1 since the 1980 s the sea surface temperature of the agulhas current system has increased significantly the warming is due to an augmentation of its transport in response to an increase in wind stress curl in the south indian ocean at relevant latitudes this causes an increase in the fluxes of salt and heat into the atlantic ocean and in the transfer of energy from the ocean to the atmosphere therefore the changes we are witnessing in the region could have far reaching consequences on top of the regional impacts on ecosystem and climate the increase in wind stress curl is consistent with a poleward shift of westerly wind in the southern hemisphere reported by others

nd sr isotopic composition of granulites and constraints on the evolution of the lower continental crust in a statistical study of granulite facies rocks we have analysed 32 samples with ages ranging from 2 900 to 200 myr for sm nd rb and sr and 143nd 144nd and 87sr 86sr ratios the sm nd ratio is found to be constant compared with the highly variable rb sr ratio using the model age formalism we show that in many cases internal differentiation of continental crust follows external differentiation with a large time interval

magnetic susceptibility of the rock matrix related to magnetic fabric studies non ferromagnetic minerals constitute what is called the rock matrix whose susceptibility k1 is directly accessible using only high magnetic fields measurements on minerals and a wide range of rock types show that k1 is mainly due to paramagnetism and hardly exceeds 10 3 si with an anisotropy degree p less than 1 35 different methods to estimate the role of the matrix component in low field susceptibility k and its anisotropy include petrological and chemical analysis evolution of p vs k low temperature studies and comparison of k with remanent magnetizations

nd and sr isotopic variations in acidic rocks from japan significance of upper mantle heterogeneity initial nd and sr isotopic ratios have been measured for cretaceous acidic and related intermediate rocks 24 volcanic and two plutonic rocks from the inner zone of southwest japan izswj to investigate the genesis of acidic magmas the initial nd and sr isotopic ratios for these rocks show three interesting features 1 end values for acidic rocks 2 to 9 are negatively correlated with esr values 10 to 90 together with those for intermediate rocks end 3 to 8 esr 0 to 65 2 the end values for silica rich rocks 60 sio2 correlate with the longitude of the sample locality decreasing from west to east in a stepwise fashion four areas characterized by uniform end values are discriminated 3 low silica rocks 60 sio2 in a certain area have distinctly different end values from those of the high silica rocks in the same area

sm nd age of kambalda and kanowna greenstones and heterogeneity in the archaean mantle a precise sm nd age of 2 790 30 myr and an initial ratio corresponding to nd 3 4 0 6 has been determined for the kambalda sequence from the eastern yilgarn block of western australia the high initial 143nd 144nd implies a long lived light rare earth element depleted high sm nd source for the kambalda volcanics and therefore provides definitive evidence for ancient heterogeneities in the archaean mantle

nd and sr isotopic study of crustal and mantle inclusions from the sierra nevada and implications for batholith petrogenesis sm nd and rb sr systematics have been examined for eight upper mantle and lower crustal xenoliths the xenolith bearing trachyandesite and the granodiorite intruded by the trachyandesite in the sierra nevada batholith isotopic heterogeneity is shown by the xenoliths with 143 nd 144 nd ranging from 0 51169 to 0 51306 and 87 sr 86 sr ranging from 0 7031 to 0 7333 these ranges are similar to those of the plutonic rocks of the batholith this similarity suggests that the xenoliths believed to be representative of mantle and crustal reservoirs may approximate the diverse source regions from which the varied granitic rocks of the batholith were derived and that the sr nd isotopic correlation seen in granitic rocks may not be due to simple mixing of two end member components the subgranitic crust in this part of the sierra nevada apparently consists of metamorphosed sedimentary and igneous rocks which are highly variable isotopically the mantle beneath the sierra nevada is also isotopically heterogeneous both vertically and laterally

the composition and evolution of the continental crust rare earth element evidence from sedimentary rocks the composition of the present day upper crust inferred from the uniformity of sedimentary rock r e e rare earth element patterns is close to that of granodiorite a revised andesite model is used to obtain total crustal composition the lower crust is the composition remaining assuming that the upper crust one third of the total is derived from intracrustal partial melting the upper crustal r e e pattern has pronounced eu depletion eu eu 0 64 the lower crustal pattern has eu enrichment eu eu 1 17 and the total crust has no eu anomaly relative to chondritic abundances the eu depletion in the upper crust is attributed to retention of eu in plagioclase in the lower crust because plagioclase is not stable below 40 km 10 kbar the anomaly is intracrustal in origin the archaean upper crust has a different r e e pattern to that of the present day upper crust being lower in total r e e and la yb ratios and lacking an eu anomaly these data are used to infer the archaean upper crustal composition which resembles that of the present day total crust except that ni and cr contents are higher the archaean crustal composition can be modelled by a mixture of tholeiites and tonalite trondhjemites the latter have steep light r e e enriched heavy r e e depleted patterns consistent with equilibration with garnet and hence probable mantle derivation there is little reason to suppose that the archaean lower crust was different in composition from the upper crust except locally where partial melting episodes occurred the r e e evidence is consistent with isotopic and geological evidence for a low continental growth rate in the early archaean a massive increase to about 70 of the total crust between about 3000 and 2500 ma b p and a slow increase until the present day the change from archaean to post archaean r e e patterns in the upper crust is not isochronous but is reflected in the sedimentary rock r e e patterns at differing times in different continents on the basis of a model composition for the mantle 36 of the potassium 30 of uranium 15 of lanthanum and 3 of ytterbium are concentrated in the present continental crust this enrichment is related to ionic size and valency differences from common mantle cations e g mg fe pre 3 9 ga b p crusts were obliterated by meteorite bombardment no geochemical evidence exists for primordial anorthositic sialic or mafic crusts

nd and sr isotopic systematics of central australian granulites chronology of crustal development and constraints on the evolution of lower continental crust nd and sr isotopic data are reported for a granulite terrain in the proterozoic arunta block of central australia sm nd data from a wide range of rock types define a crust formation age of 2 070 125 ma and provide further evidence for voluminous crustal growth in the proterozoic an nd value of 1 5 0 8 indicates a depleted mantle source for this crustal segment and there is no evidence for a large component of significantly older sialic crust field relationships geochemistry and rb sr data for mafic and felsic granulites indicate that intracrustal differentiation and polyphase deformation were followed by granulite facies metamorphism rb depletion at 1 800 ma rb sr data for strongly retrogressed granulites define an age of 1 700 ma which is interpreted as the time of retrograde biotite growth partial melting at the presently exposed crustal level and anatexis at deeper crustal levels were broadly coeval with the retrograde metamorphism sm nd and rb sr isotopic systematics of minerals indicate that the terrain cooled slowly did not experience significant uplift until 1 000 ma and remained at temperatures above 320 c until the late palaeozoic the mineral data are consistent with geological relationships and petrological evidence for a prolonged period of isobaric cooling followed by uplift late in the metamorphic evolution of the terrain the granulite protoliths appear to have formed in a rift which closed within 280 ma of initial separation deformation and granulite facies metamorphism at 1 800 ma are interpreted to be a consequence of collision between the continental blocks which defined the rift regional retrogression and granitoid magmatism at 1 700 ma are attributed to underthrusting of the granulites by lower grade rocks in the final stages of collision subsequent events in the cooling and uplift history appear to have been controlled by the presence of long lived major faults in the crust and a prolonged history of episodic compression in the continental lithosphere the results of this study suggest that granulite terrains in general cannot be equated with lower continental crust but instead represent assemblages of mainly supracrustal rocks which in some instances have been involved in major collision events

mafic magmatic enclaves and mafic rocks associated with some granitoids of the central sierra nevada batholith california nature origin and relations with the hosts abstract the calc alkaline granitoids of the central sierra nevada batholith are associated with abundant mafic rocks these include both country rock xenoliths and mafic magmatic enclaves mme that commonly have fine grained and less commonly cumulate textures scarce composite enclaves consist of either xenoliths enclosed in mme or of mme enclosed in other mme with different grain size and texture enclaves are often enclosed in mafic aggregates and form meter size polygenic swarms mostly in the margins of normally zoned plutons enclaves may locally divert schlieren layering mafic dikes which also occur in swarms are undisturbed composite or largely hybridized in central sierra nevada with the exception of xenoliths that completely differ from the other rocks host granitoids mafic aggregates mme and some composite dikes exhibit a bulk compositional diversity and at the same time important mineralogical and geochemical including isotopic similarities mme and host granitoids display distinct major and trace element compositions however strong correlations between mme host granitoid pairs indicate interactions and parallel evolution of mme and enclosing granitoid in each pluton identical mafic mineral compositions and isotopic features are the result of these interactions and parallel evolution mafic dikes have broadly the same major and trace element compositions as the mme although variations are large between the different dikes that are at distinctly different stages of hybridization and digestion by the host granitoids the composition of the granitoids and various mafic rocks reflects three distinct stages of hybridization that occurred respectively at depth during ascent and emplacement and after emplacement the occurrence and succession of hybridization processes were tightly controlled by the physical properties of the magmas the sequential thorough or partial mixing and mingling were commonly followed by differentiation and segregation processes unusual mme that contain abundant large crystals of hornblende resulted from disruption of early cumulates at depth whereas those richer in large crystals of biotite were formed by disruption of late mafic aggregates or schlieren layerings at the level of emplacement mme and host granitoids are considered cogenetic because both are hybrid rocks that were produced by the mixing of the same two components in different proportions the felsic component was produced by partial melting of preexisting crustal materials whereas the dominant mafic component was probably derived from the upper mantle however in the lack of a clear mantle signature the origin of the mafic component remains questionable

small scale heterogeneity of phanerozoic lower crust evidence from isotopic and geochemical systematics of mid cretaceous granulite gneisses san gabriel mountains southern california an elongate belt of mid cretaceous compositionally banded gneisses and granulites is exposed in cucamonga terrane in the southeastern foothills of the san gabriel mountains of southern california banded gneisses include mafic granulites of two geochemical types type 1 rocks are similar to high al arc basalts and andesites but have higher hfse high field strength element abundances and extremely variable lile largeion lithophile element abundances while type 2 rocks are relatively low in al and similar to alkali rich mor midocean ridge or intraplate basalts intercalated with mafic granulites are paragneisses which include felsic granulites aluminous gneisses marble and calc silicate gneisses type 1 mafic granulites and calcic trondhjemitic pegmatites also oceur as cross cutting synmetamorphic dikes or small plutons small scale heterogeneity of deep continental crust is indicated by the lithologic and isotopic diversity of intercalated ortho and paragneisses exposed in cucamonga terrane geochemical and isotopic data indicate that k rb and u depletion and sm nd fractionation were associated with biotite muscovite dehydration reactions in type 1 mafic granulites and aluminous gneisses during high grade metamorphism field relations and model initial isotopic ratios imply a wide range of protolith ages ranging from early proterozoic to phanerozoic

quantitative correlation of texture and magnetic anisotropy of compacted calcite muscovite aggregates abstract deformation of carbonate rocks leads to crystallographic preferred orientations cpos of calcite which in turn generates an anisotropy of magnetic susceptibility ams the use of the diamagnetic anisotropy which arises from the preferential orientation of calcite for texture characterization is usually hindered by 1 the weakness of the anisotropy and 2 overlapping contributions from paramagnetic and ferromagnetic minerals to the ams in this study the diamagnetic paramagnetic and ferromagnetic sub fabrics of synthetic calcite muscovite samples have been separated using high field torque measurements the cpo of calcite and muscovite has been determined by neutron diffraction and the magnetic sub fabrics are compared to the ams that was re calculated from the cpo the isolated diamagnetic sub fabric shows a good correlation with the calcite texture for calcite concentrations above 70 the paramagnetic sub fabric is shown to be a reliable texture parameter for muscovite even at a concentration of 5 the results demonstrate the capability of the ams method as a texture parameter in impure carbonate rocks

isotopic variation in the tuolumne intrusive suite central sierra nevada california granitoid rocks of the compositionally zoned late cretaceous toulumne intrusive suite in the central sierra nevada california have initial87sr 86sr values sri and143nd 144nd values ndi that vary from 0 7057 to 0 7067 and from 0 51239 to 0 51211 respectively the observed variation of both sri and ndi and of chemical composition in rocks of the suite cannot be due to crystal fractionation of magma solely under closed system conditons the largest variation in chemistry ndi and sri is present in the outer most equigranular units of the tuolumne intrusive suite sri varies positively with sio2 na2o k2o and rb concentrations and negatively with ndi al2o3 fe2o3 mgo feo cao mno p2o5 tio2 and sr concentrations this covariation of sri ndi and chemistry can be modeled by a process of simple mixing of basaltic and granitic magmas having weight percent sio2 of 48 0 and 73 3 respectively isotopic characteristic of the mafic magma are sri 0 7047 ndi 0 51269 and 18o 6 0 and of the felsic magma are sri 0 7068 ndi 0 51212 and 18o 8 9 the rocks sampled contain from 50 to 80 of the felsic component an aplite in the outer equigranular unit of the tuolumne intrusive suite apparently was derived by fractional crystallization of plagioclase and hornblende from magma with granudiorite composition that was a product of mixing of the magmas described above siliceous magmas derived from the lower crust having a maximum of 15 percent mantle derived mafic component are represented by the inner prophyritic units of the tuolumne intrusive suite

satellite observations of an annual cycle in the agulhas current 1 ocean models show an annual cycle in the agulhas current transport which has not yet been confirmed in analyses of in situ or satellite observations a cross stream coordinate approach is used to study the variability of the agulhas current from 18 years of along track altimetry and merged altimetry and close to 7 years of high frequency sea surface temperature sst observations while the position and width of the agulhas current s dynamical core do not display an annual cycle the geostrophic current speed at the current s core exhibits distinct seasonal variations with a stronger flow observed in austral summer the annual cycle dominates the frequency spectra of the current s core geostrophic velocities

restoration of the cretaceous uplift of the harz mountains north germany evidence for the geometry of a thick skinned thrust reverse movement on the harz northern boundary fault was responsible for the late cretaceous uplift of the harz mountains in northern germany using the known geometry of the surface position and dip of the fault and a published cross section of the base permian horizon we show that it is possible to predict the probable shape of the fault at depth down to a detachment level we use the inclined shear method with constant heave and argue that a shear angle of 30 was most likely in this case the detachment level is at a depth of ca 25 km kinematic restoration of the harz mountains using this fault geometry does not produce a flat horizon rather it results in a ca 4 km depression airy heiskanen isostatic equilibrium adjustment of the harz mountains restores the base permian horizon to the horizontal as well as raising the moho to a depth of 32 km a typical value for northern germany restoration also causes a rotation of tectonic fabrics within the harz mountains of about 11 clockwise we show that this model geometry is very good fit to the interpreted dekorp basin 9601 deep seismic profile

sm nd dating and cooling history of scourian granulites sutherland the scourian gneisses of the lewisian complex of north west scotland have been the subject of many geochronological investigations sm nd whole rock measurements suggest that the protoliths of the lewisian complex differentiated 2 92 0 05 gyr ago from an approximately chrondritic mantle1 rb sr and pb pb whole rock ages between 2 8 and 2 6 gyr reflect subsequent depletion in rb and u refs 2 3 which has generally been associated with granulite facies metamorphism zircons which are thought to have crystallized during this metamorphism have also given u pb ages of 2 66 gyr ref 4 this granulite facies metamorphism involving pressures in excess of 10 kbar and peak temperatures estimated between 820 50 c ref 5 and 1 250 c refs 6 7 affects a terrain including supracrustal rocks7 and thus implies a major tectonic event we report here the first geochronological data measured on mineral assemblages that have also provided estimates of the conditions of metamorphism such measurements are possible because the major minerals of granulite facies assemblages show an unusually favourable spread in sm nd ratios garnet especially is strongly enriched in sm ref 8 data for three garnetiferous basic gneiss assemblages suggest that closure of the sm nd system occurred significantly later than the peak of the metamorphism

oxygen isotope evidence for shallow emplacement of adirondack anorthosite oxygen isotopic analysis of wollastonites from the willsboro mine adirondack mountains new york reveals a 400 ft wide zone of 18o depletion at anorthosite contacts values of 18o vary more sharply with distance and are lower to 1 3 than any yet reported for a granulite fades terrain exchange with circulating hot meteoric water best explains these results and implies that the anorthosite was emplaced at relatively shallow depths 10 km in marked contrast to the depth of granulite fades metamorphism 23 km these 18o depletions offer the first strong evidence for shallow emplacement of anorthosite within the grenville province and suggest that regional metamorphism was a later and tectonically distinct event

characterization of the magnetic fabric of rocks abstract an inextensive system of magnetic susceptibility anisotropy factors is suggested which is sufficient in the majority of practical applications for characterizing the magnetic fabric of rocks the system involves three newly devised factors the corrected anisotropy degree the shape factor and the difference shape factor the first of these characterizes the quantity of anisotropy somewhat better than the commonly used anisotropy degree the shape factor characterizes the quality of anisotropy i e the shape of the susceptibility ellipsoid in a convenient way its definition is based on a certain analogy between the anisotropy ellipsoid and the strain ellipsoid the difference shape factor can replace the shape factor when only the differences between the principal susceptibilities are given while the mean susceptibility is unknown

isotopic and geochemical studies of nodules in kimberlite have implications for the lower continental crust lower crustal xenoliths from the calcutteroo kimberlitic pipes in south australia show a surprisingly diverse range in nd and sr isotopic compositions and rare earth element ree abundances mafic granulite and garnet clinopyroxenite xenoliths have measured end 0 values between 6 1 and 7 9 both light l ree enrichments and depletions low rb sr ratios 0 005 0 040 and relatively high 87sr 86sr ratios of from 0 70675 to 0 70919 a felsic xenolith has compositions more typical of upper crustal rocks with end 0 21 4 lree enrichments rb sr 1 47 and 87sr 86sr 0 85987 an approximate correlation also exists between sm nd versus 143nd 144nd and rb sr versus 87sr 86sr indicating major intracrustal differentiation in the lower crust at 2 400 myr this produced extremely low rb sr ratios and both relative lree enrichments low sm nd and depletions high sm nd if these results are typical then they indicate that the lower crust has higher 87sr 86sr and more positive end 0 values than previous estimates1 5 this may require revision of total crustal compositions and crust mantle evolutionary models1 5

crustal accretion in the pan african nd and sr isotope evidence from the arabian shield abstract nd and sr isotope determinations on late precambrian to early palaeozoic igneous and sedimentary rocks from the arabian shield are used to investigate the proportion of reworked older crust and the rate at which new crust was generated during the pan african event eight rb sr whole rock isochrons on igneous suites yield ages in the range 770 590 ma and initial 87 sr 86 sr ratios of 0 7038 0 7023 these data confirm that magmatism in this area was largely restricted to the period 850 550 ma and the initial ratios are sufficiently low to preclude significant contributions from a long lived upper crustal source the initial 143 nd 144 nd ratios of a variety of lithologies including several samples of possible basement are all higher than the contemporaneous values for chur e nd 1 6 to 6 9 suggesting that many were derived directly from the upper mantle and that any inferred crustal source regions for the remainder could not have separated from likely lree depleted mantle reservoirs before 1200 ma the arabian shield therefore provides an example of rapid crustal growth during the late proterozoic and contrasts with the damara intracratonic belt of namibia where nd and sr isotopes provide strong evidence for extensive reworking of older continental crust during the same period

rheology of rocksalt abstract we review progress in experimental determinations of transient and steady state flow properties and processes of natural rocksalt aggregates focusing primarily on results from avery island louisiana domal salt the steady state flow field established from constant stress and constant strain rate tests at temperatures from 50 to 200 c strain rates from 10 5 to 10 9 s 1 and differential stresses from 20 7 to 2 5 mpa has been separated into two flow regimes each fit by a power law relation at the higher stresses and strain rates this relation is e 1 6 10 4 exp 68 1 rt 10 3 5 3 for which the pre exponential constant is expressed in mpa 5 3 s 1 and the apparent activation energy is in j mol 1 creep rates predicted by equation a do not differ appreciably from those predicted previously the relatively low stress low strain rate data are very well fit by e 8 1 10 5 exp 51 6 rt 10 3 2 4 which is comparable conditions predicts creep rates higher and equivalent viscosities lower than does equation a by two orders of magnitude the change in behavior from a to b is ascribed to a change in rate limiting mechanism from cross slip of screw dislocations to the climb of edge dislocations in this dry material subgrain formation dominates microstructural development during steady state flow of salt and from determinations of average subgrain diameters in crystals from 20 different rocksalt bodies flow stress levels between 0 6 and 1 4 mpa have been estimated these values do not bear directly on arguments concerning the nature of forces initiating salt pillow growth because apparently evidence relating to the early deformational history has been overprinted at that stage fluid assisted grain boundary diffusional processes might dominate dislocation creep leading to a linear stress strain rate mechanical response considering buoyancy forces alone behavior described by equation b rather than a reduces the relief necessary to initiate pillow growth but a 1000 fold amplification is required to produce stress differences near 1 mpa that forces other than buoyancy are important is indicated by the occurrence of these same paleostress levels in bedded salts and in shallow offshore concordant intrusions differential loading generally provides the most plausible initial driving force for the growth of diapiric salt structures

sm nd studies of archaean metasediments and metavolcanics from west greenland and their implications for the earth s early history metasedimentary and metavolcanic rocks from the archaean of west greenland have been examined for evidence of crustal components greater than 3 8 ga in age and for their compatibility with the presently adopted bulk earth sm nd parameters sm nd isotopic data have been obtained for the garbenschiefer metagabbro unit metasediments from the isua supracrustal belt gneisses interior to the isua belt and metasediments from the malene supracrustal belt using estimates of emplacement age t of between 3 77 and 3 67 ga for the parental volcanics to the garbenschiefer unit initial143nd 144nd ratios yield positiveendt values between 1 0 and 3 1 relative to the chur parameters for seven out of eight samples model sm nd ages for the isua gneisses and metasediments are only compatible with their estimated stratigraphic ages if their sources were ca 2end relative to chur at those times similarly model sm nd ages for the malene samples are only compatible with stratigraphic age constraints when based on a source evolution with positiveendt implications of these results for the early development of the earth s mantle are discussed

late cretaceous to recent tectonic evolution of the north german basin and the transition zone to the baltic shield southwest baltic sea abstract in this study we investigate the late cretaceous to recent tectonic evolution of the southwestern baltic sea based on a dense grid of seismic reflection profiles this area covers the baltic sea sector of the salt influenced north german basin and its transition to the salt free baltic shield across the tornquist zone the upper cretaceous to recent structural evolution is discussed by means of individual seismic sections and derived high resolution time structure maps of the main horizons i e the upper cretaceous tertiary and pleistocene the upper cretaceous and tertiary layers reveal numerous significant faults throughout the study area several of these faults propagate upwards across the unconsolidated pleistocene sediments and occasionally penetrate the surface the salt influenced north german basin reveals three major fault trends nw se n s and nne ssw several of these faults are located directly above basement sub salt faults and salt pillows the majority of these faults are trending n s to nne ssw and parallel the direction of the gluckstadt graben faults in the salt free tornquist zone we identify two major shallow fault trends which are nw se and ne sw the majority of these faults are located above basement faults following the direction of the tornquist zone we conclude that generally basement tectonics controls activation and trends of shallow faults if salt is present the ductile salt layer causes a lateral shift between the sub and supra salt faults major plate reorganisation related to the africa iberia europe convergence and the subsequent alpine orogeny caused reactivation of pre existing faults and vertical salt movement in the late cretaceous the change of stress orientation from ne sw to a nw se during neogene caused another phase of fault and salt tectonic reactivation we explain that the ice sheet loading and or present day stress field may have acted in combination causing the recent tectonics and upward extension of the faults

some additional observations on inclusions in the granitic rocks of the sierra nevada microgranular quartz diorite and diorite inclusions are widespread in central sierra nevada granitoid rocks and are almost exclusively restricted to hornblende bearing rocks most commonly felsic tonalites and mafic granodiorites strontium 87 strontium 86 values of the inclusions and host granitoids from individual plutons generally plot on single isochrons that agree closely with previously determined ages neodymium 143 neodymium 144 values of five inclusions ranged from 0 51229 to 0 51248 and yield end values that correlate closely with values of their respective hosts the nd sm and rb sr systematics indicate that most inclusions were in isotopic equilibrium with enclosing materials at the time of formation silica contents of inclusions and granitoids are contiguous but inclusions generally contain less than and granitoids more than 60 sio2 linear continuity of the femic oxide and h2o trends relative to sio2 suggests many inclusions formed as concentrations of hydrous mafic minerals variation of other major element oxides and trace elements support this inference the aforementioned data are generally inconsistent with a direct genetic link between the mafic inclusions and the mantle derived basalt however many initial sierra nevada magmas were produced by mixing of mafic mantle derived melts and felsic crustal materials resulting in isotopically varied tonalitic and granodioritic magmas most inclusions thus represent fragmented crystal accumulations of early formed near liquidus minerals generated from these previously mixed magmas

nd sr and pb isotopic characteristics of cretaceous intrusive rocks from deep levels of the sierra nevada batholith tehachapi mountains california the cretaceous gabbroic to granitic intrusive rocks of the tehachapi mountains were emplaced at depths of 25 30 km and thus afford a view of deep processes in the sierra nevada batholith they consist of the 115 ma tehachapi suite and the 100 ma bear valley suite new zircon u pb age data reveal the presence of the latter as far west as grapevine canyon the nd sr pb and o isotopic whole rock data and zircon pb inheritance patterns for the bulk of the suites suggest an origin by mixing between depleted mantle derived magmas and metasedimentary material with a substantial component of old continental material however this mixing is not evident in variations between isotopic ratios and chemical and lithologic parameters this implies that isotopic hybridization of magmas took place deeper than 30 km and that fractionation processes are likely responsible for the bulk of the chemical variation in this part of the sierra nevada batholith consideration of the isotopic data in the context of the sierra nevada batholith as a whole suggests that the well known east to west isotopic gradients in the batholith may reflect a change in the average isotopic character of the preintrusive framework rather than a change in amount of crustal component on the other hand the lack of areal gradients in sr and nd isotopic ratios in the main study area may indicate a lack of pronounced gradation at deep levels at least within the western batholith

strontium and oxygen isotopic variations in mesozoic and tertiary plutons of central idaho regional variations in initial 87sr 86sr ratios r i of mesozoic plutons in central idaho locate the edge of precambrian continental crust at the boundary between the late paleozoic mesozoic accreted terranes and precambrian sialic crust in western idaho the r i values increase abruptly but continuously from less than 0 704 in the accreted terranes to greater than 0 708 across a narrow 5 to 15 km zone characterized by elongate lens shaped highly deformed plutons and schistose metasedimentary and metavolcanic units the chemical and petrologic character of the plutons changes concomitantly from ocean arc type diorite tonalite trondhjemite units to a weakly peraluminous calcic to calcalkalic tonalite granodiorite granite suite the idaho batholith plutons in both suites yield late cretaceous ages but permian through early cretaceous bodies are confined to the accreted terranes and early tertiary intrusions are restricted to areas underlain by precambrian crust the two major terranes were juxtaposed between 75 and 130 m y ago probably between 80 and 95 m y oxygen and strontium isotopic ratios and rb and sr concentrations of the plutonic rocks document a significant upper crustal contribution to the magmas that intrude precambrian crust magmas intruding the arc terranes were derived from the upper mantle subducted oceanic lithosphere and may have been modified by anatexis of earlier island arc volcanic and sedimentary units plutons near the edge of precambrian sialic crust represent simple mixtures of the precambrian wall rocks with melts derived from the upper mantle or subducted oceanic lithosphere with r i of 0 7035 rb sr varies linearly with r i producing pseudoisochrons with apparent ages close to the age of the wall rocks measured 18o values of the wall rocks are less than those required for the assimilated end member by sr o covariation in the plutons however indicating that wall rock 18o was reduced significantly by exchange with circulating fluids metasedimentary rocks of the belt supergroup are similarly affected near the batholith documenting a systematic depletion in 18o as much as 50 km from the margin of the batholith plutons of the bitterroot lobe of the idaho batholith are remote from the accreted terranes and represent mixtures of precambrian wall rocks with melts dominated by continental lower crust r i 0 708 rather than mantle pseudoisochrons resulting from these data are actually mixing lines that yield apparent ages less than the true age of the wall rocks and meaningless ri assimilation fractional crystallization models permit only insignificant amounts of crystal fractionation during anatexis and mixing for the majority of plutons of the region

proterozoic age and cumulate origin for granulite xenoliths lesotho rare earth element ree 143nd 144nd and 87sr 86sr analyses on a range of granulite xenoliths from kimberlite pipes in lesotho demonstrate that useful whole rock ages can be obtained from such lower crustal material the characteristic positive eu anomalies relatively low ree abundances and large variation in sr contents suggest that many of the xenoliths are crystal cumulates rather than residua after partial melting they yield an sm nd whole rock age of 1 400 100 myr and are unrelated to the younger magmatic rocks of the karoo

petrology and geochemistry of granulite xenoliths from central hoggar algeria implications for the lower crust granulitic xenoliths enclosed in neogene alkali basalts from the atakor and adrar n addjer volcanic massifs in central hoggar southern algeria include mafic metaigneous and felsic metasedimentary rocks the main mineral phases of metaigneous xenoliths are plagioclase and pyroxenes whereas quartz feldspars sillimanite garnet and sapphirine occur in metasedimentary granulites the metaigneous xenoliths represent a magmatic sequence of cumulitic and non cumulitic rocks which resembles gabbroic bodies associated with anorthosites and has calc alkaline affinities similar types and distributions of granulitic xenoliths are widespread and are probably characteristic of the lower crust in general suggesting its homogeneity on a large scale but heterogencity on a local scale

late cretaceous and cenozoic intra plate compressional deformations in the alpine foreland a geodynamic model abstract the mesozoic grabens and wrench induced troughs of western and central europe developed in response to triassic early cretaceous intra plate tensional stresses which affected the arctic north atlantic and the tethys borderlands during the rifting phase preceding the opening of the respective oceans this resulted in the fragmentation of the continental crust of the alpine foreland during the late cretaceous and tertiary alpine orogeny collision related compressive stresses exerted on the foreland induced the reactivation of these fracture systems causing the inversion of mesozoic grabens and the uplifting of major basement blocks at distances up to 1300 km to the north of the present alpine deformation front the structural style of these inverted basins and basement uplifts is indicative of compressional and transpressional deformations the total amount of crustal shortening associated with these deformations is unlikely to exceed a few tens of kilometres these displacements require a coupling between the foreland and the orogen at the alpine a subduction zones and within the foreland a decoupling at intra crustal levels between the crust and mantle and or at deeper lithospheric levels the example of the alpine foreland indicates that compressive stresses inducing major deformations can be transmitted from a collisional plate boundary through continental lithosphere over distances of up to 1300 km circumstantial evidence suggests that collision related compressive stresses not large enough to give rise to significant deformations can be transmitted through continental lithosphere over even greater distances

elemental and sr nd isotope geochemistry of microgranular enclaves from peralkaline a type granitic plutons of the emeishan large igneous province sw china abstract microgranular enclaves are common within intermediate to felsic granitic rocks that have i and s type affinity however they are rare within alkaline anorogenic granitoids of a type affinity the permian 260 ma emeishan large igneous province elip of southwest china contains two peralkaline silica saturated a type granitic plutons that host microgranular enclaves the enclaves from the baima pluton are intermediate in composition and have lower sio 2 and higher tio 2 cao and mg sio 2 57 2 to 63 0 wt tio 2 0 8 to 1 8 wt cao 1 7 to 3 3 wt mg 28 to 44 than their host sio 2 62 6 to 67 8 wt tio 2 0 5 to 1 4 wt cao 0 4 to 1 8 wt mg 15 to 31 the enclaves from the taihe pluton are more felsic sio 2 63 8 to 71 3 wt tio 2 0 3 to 0 6 wt cao 0 6 to 2 3 wt mg 8 to 22 but are still less evolved than their host sio 2 69 8 to 75 1 wt tio 2 0 2 to 0 6 wt cao 0 4 to 0 8 wt mg 3 to 12 in both cases the enclaves have very similar end t values baima end t 2 8 to 3 2 taihe end t 1 0 to 2 0 as their hosts baima end t 3 0 to 3 2 taihe end t 1 5 to 1 9 the major and trace element trends of the enclave host pairs suggest that fractional crystallization occurred and that element diffusion was likely minimal the enclaves are interpreted as entrained accumulations of early formed crystals of a silicic magma which was originally produced by fractional crystallization of a mafic magma

uncertainties in the mean ocean dynamic topography before the launch of the gravity field and steady state ocean circulation explorer goce 1 in anticipation of the future observations of the gravity mission gravity field and steady state ocean circulation explorer goce the present day accuracy of mean dynamic topography mdt is estimated from both observations and models a comparison of five observational estimates illustrates that rms differences in mdt vary from 4 2 to 10 5 cm after low pass filtering the fields with a hamming window with wavenumber n 120 corresponding to an effective resolution of 167 km rms differences in observational mdt reduce to 2 4 8 3 cm for n 15 1334 km differences in data sources geoid model in situ data are mostly visible in the small scale oceanic features while differences in processing filtering inverse modeling techniques are reflected at larger scales a comparison of seven different numerical ocean models demonstrates that model estimates differ mostly in western boundary currents and in the antarctic circumpolar current rms differences between modeled and observed mdt are at best 8 8 cm for n 120 and reduce to 6 4 cm for n 15 for models with data assimilation a minimal rms difference of 6 6 cm n 120 to 3 4 cm n 15 is obtained with respect to the observational mdts the reduction of differences between mdts with increasing filtering scales is smaller than expected while it is expected that goce will improve mdt estimates at small spatial scales improvement of mean sea surface estimates from satellite altimetry may be needed to improve mdt estimates at larger scales

intrusion of lamprophyre dyke and related deformation effects in the host rock salt a case study from the loule diapir portugal abstract a rock salt lamprophyre dyke contact zone sub vertical ne sw strike was investigated for its petrographic mechanic and physical properties by means of anisotropy of magnetic susceptibility ams and rock magnetic properties coupled with quantitative microstructural analysis and thermal mathematical modelling the quantitative microstructural analysis of halite texture and solid inclusions revealed good spatial correlation with ams and halite fabrics the fabrics of both lamprophyre and rock salt record the magmatic intrusion plastic flow and regional deformation characterized by a nw se trending steep foliation ams and microstructural analysis revealed two deformation fabrics in the rock salt 1 the deformation fabrics in rock salt on the nw side of the dyke are associated with high temperature and high fluid activity attributed to the dyke emplacement 2 on the opposite side of the dyke the emplacement related fabric is reworked by localized tectonic deformation the paleomagnetic results suggest significant rotation of the whole dyke probably during the diapir ascent and or the regional tertiary to quaternary deformation

evidence from the lamarck granodiorite for rapid late cretaceous crust formation in california strontium and neodymium isotopic data for rocks from the voluminous 90 million year old lamarck intrusive suite in the sierra nevada batholith california show little variation across a compositional range from gabbro to granite data for three different gabbro intrusions within the suite are identical within analytical error and are consistent with derivation from an enriched mantle source recognition of local involvement of enriched mantle during generation of the sierran batholith modifies estimates of crustal growth rates in the united states these data indicate that parts of the sierra nevada batholith may consist almost entirely of juvenile crust added during cretaceous magmatism

formation of the earliest continental crust inferences from the scourian complex of northwest scotland and geophysical models of the lower continental crust abstract in this paper the structure composition and pre metamorphic lithology of the scourian complex at its type locality are compared with models of the lower continental crust proposed by several authors on the basis of seismic reflection profiling and exposures in the ivrea zone and the vredefort dome it is shown that the scourian complex resembles these models in major characteristics consisting of gently dipping granulite gneisses of intermediate bulk composition formed from partly or largely supracrustal precursors in addition seismic investigations of northwest scotland indicate that granulites of the scourian type make up most of the 26 km of continental crust in the area it is therefore proposed that the scourian complex provides a representative exposure of the lower continental crust if this is so it implies that the lower crust is dominantly of supracrustal origin with normal superposition age relationships except for localized thrusting and intrusion such age relationships in turn imply that isotopic investigations sm nd and rb sr date only later additions to the early crust either intrusions or supracrustal additions not formation of entire crustal segments it is therefore proposed that older continental crust may underlie even the oldest exposed rocks that primordial crust may survive near the moho and that the earliest continental crust was formed largely by andesitic volcanism that produced a widespread possibly global layer now represented by granulites of the scourian type

microfabrics and 3d grain shape of gorleben rock salt constraints on deformation mechanisms and paleodifferential stress abstract the permian knauel and streifensalz formations z2hs1 and z2hs2 are main constituents of the gorleben salt dome northern germany and show different amounts and distributions of anhydrite the reconstruction of 3d halite grain shape ellipsoids reveals small grain size 3 4 0 6 mm and heterogeneous grain shapes in both formations the latter attributed to the polyphase deformation of the rock salt during diapirism the halite microfabrics of both formations indicate that strain induced grain boundary migration was active during deformation crystal plastic deformation of halite is further documented by lattice bending subgrain formation and minor subgrain rotation evidence for pressure solution of halite has not been found but cannot be excluded because of the small grain size the lack of lpo and the low differential stress 1 1 1 3 mpa as deduced from subgrain size piezometry anhydrite has been deformed in the brittle ductile regime by solution precipitation creep minor dislocation creep and brittle boudinage no continuous anhydrite layers are preserved and halite has acted as a sealing matrix embedding the disrupted anhydrite fragments prohibiting any potential migration pathways for fluids thus anhydrite should not have a negative effect on the barrier properties of the gorleben rock salts investigated in this study

satellite altimeter monitoring the kuroshio transport south of japan in 1993 1995 we carried out observations of the kuroshio south of japan including direct current measurements and repeated hydrographic surveys along a satellite track of the topex poseidon altimeter the velocity field of the kuroshio is determined by geostrophic calculation using the repeated hydrographic survey data referenced to velocities observed at mid and abyssal depths the volume transport of the kuroshio is estimated from this velocity field the estimated transports of the kuroshio have a high correlation with sea surface height differences across the kuroshio having this relationship and using the altimeter data we obtained a time series of the kuroshio transport over seven years at ten day intervals the kuroshio transport excluding contributions by local recirculations is estimated to be 42 106 m sec on average the correlation between sea surface height difference and transport provides a practical method of long term monitoring of the kuroshio transport using satellite altimetry

geochemistry and petrology of the jequie granulitic complex brazil an archean basement complex the jequie granulitic complex is part of the extensive high grade metamorphic terrain located within the sao francisco craton of northeastern brazil some jequie rocks appear to have been formed in the middle archean 3 1 ga from preexisting sialic crust the dominant mineral composition of these rocks is quartz microcline plagioclase hyperstene and occurs over an extensive area 2 000 km2

granites and early proterozoic crustal evolution in sweden evidence from smnd upb and o isotope systematics abstract u pb zircon and whole rock rb sr sm nd and o isotope results are reported for granitoids from three proterozoic provinces in sweden that represent different crustal environments the radiometric ages span the period 1 89 1 65 ga and record events ranging from original igneous crystallisation to late metamorphic resetting these events occurred at different times in the crustal segments the o isotope ratios identify different crustal source materials for the granitoids the sm nd results indicate that the major crustal source components common to most of the granitoids formed shortly before 1 9 ga close in time to the formation of the earliest granitoids contributions from recycled archaean basement are minimal the geographically widespread occurrence of such crustal sources indicates that the period around 2 ga was of great importance for the growth of new continental crust in sweden

microstructural evolution of deformation modified primary halite from the middle triassic rot formation at hengelo the netherlands the microstructure of halite from the subhorizontal bedded main rot evaporite member at hengelo the netherlands akzo well 382 depth interval of 420 460 m was studied by transmitted and reflected light microscopy of gamma irradiation decorated samples primary microstructures compare favourably with those found in recent ephemeral salt pans large blocky fluid inclusion poor halite grains and elongated chevrons are interpreted to have formed in the saline lake stage while void filling clear halite is interpreted to have formed during the desiccation stage of the salt pan in addition in all layers the grains are rich in deformation related substructures such as slip bands and subgrains indicating strains of a few percent the study of gamma irradiation decorated thin sections shows that the main recrystallization mechanism is grain boundary migration grain boundary migration removes primary fluid inclusions and produces clear strain free new grains differential stresses as determined by subgrain size piezometry were 0 45 0 97 mpa the deformation of the salt layers is probably related to cretaceous inversion in the area

magnetic fabrics of the morcles nappe complex abstract anisotropy of magnetic susceptibility ams measured with high fields at ambient and low temperatures 77 k has been used to separate ferromagnetic sensu lato paramagnetic and diamagnetic sub fabrics for deformed limestones located in a nappe structure from southwest switzerland the magnetic fabrics are dominantly controlled by paramagnetic and diamagnetic minerals and ferromagnetic minerals contribute significantly only at two of the eight study locations separation of the magnetic sub fabrics is possible in the root zone and overturned limb of the morcles nappe which contains a high ratio of diamagnetic matrix calcite to paramagnetic secondary phases each of the sub fabrics displays a relationship with structural cleavage and the crystallographic preferred orientation cpo of calcite in the root zone and overturned limb the maximum axis of the paramagnetic ams ellipsoid kmax lies close to the pole to cleavage with the intermediate kint and minimum kmin axes near the cleavage plane conversely the diamagnetic kmin lies close to the pole to cleavage with kmax and kint axes near the cleavage plane slight offsets in the poles to cleavage and in the principal ams directions are observed they are interpreted to be the consequence of a second phase deformation event affecting only the cpo but not the macroscopic structural elements the diamagnetic sub fabric reflects the cpo of calcite produced through recrystallization during nappe deformation iron rich calcite appears to control the paramagnetic sub fabric susceptibility ellipsoids approach oblate shapes for the diamagnetic sub fabric with the most extreme shapes reaching susceptibility differences k kmax kmin close to that of single crystal calcite whereas the paramagnetic sub fabric is represented mainly by prolate shape ellipsoids the low field ams ellipsoids show mixed oblate and prolate shapes without consistency within or between sites it is evident that when the magnetic sub fabrics of the root zone and overturned limb are separated their individual shapes and distribution of principal directions mirror the developed cpo

nd isotopic systematics and chemistry of central australian sapphirine granulites an example of rare earth element mobility abstract lower proterozoic sapphirine bearing and associated granulites from central australia exhibit the greatest range of present day 143 nd 144 nd ratios nd o 26 5 to 112 3 yet reported for rocks believed to be cogenetic the nd isotopic data and ree abundances of these rocks demonstrate extreme fractionation of the rare earths during the formation of stratiform cu pb zn sulfide deposits with which they are closely associated field relationships petrography and chemistry of the sapphirine granulites suggest that their protoliths comprised chlorite rich rocks which were generated by hydrothermal alteration of a range of rock types prior to metamorphism calculations employing ree abundances of the sapphirine granulites and associated rocks combined with bulk solid fluid distribution coefficient data yield high fluid rock ratios consistent with a pre metamorphic hydrothermal origin for the unusual ree patterns the sm nd data for these rocks define an age of 1760 75ma which is significantly younger than the crust formation age of the terrain 2070 125ma but indistinguishable from the rb sr whole rock age for granulite facies metamorphism 1790 35ma these data are interpreted in terms of major hydrothermal fractionation of the rare earths shortly perhaps tens of millions of years before granulite facies metamorphism followed by redistribution of nd isotopes or small fractionations of the sm nd ratio during the granulite facies event and possibly also during intense retrogression which reset rb sr whole rock and u pb zircon and monazite systematics at about 1700 ma

isotopic constraints on the production rates crystallisation histories and residence times of pre caldera silicic magmas long valley california pre caldera high silica rhyolites of glass mountain california erupted episodically from 2 1 ma until the catastrophic eruption of the bishop tuff at 0 74 ma the lavas are extremely evolved with rb sr ratios between 128 to 3640 the latter being the highest recorded from a volcanic rock glass separates from pre l 2 ma lavas define two geographically controlled rb sr isoehrons lavas adjacent to the current caldera rim define an isochron age of 2 047 0 013 ma with an initial ratio of 0 7063 2 and lavas more distant from the caldera define an isochron of 1 894 0 013 ma with the same initial ratio the isochrons are consistent with the magmas forming within 26 ka which implies a minimum magma production rate of 0 75 10 3 km3 yr over this period new 4 ar 39ar ages on sanidine and biotite have established that lavas defining each isochron were erupted over a long time interval the isochron ages being up to 360 ka older than the youngest eruption age rb sr isotope data are reported for minerals from three lavas with eruption ages of 1 990 0 012 1 866 0 014 and 1 686 0 011 ma petrographically early apatite inclusions in biotite and biotite inclusions in feldspar and quartz have glass mineral rb sr ages that are indistinguishable from the relevant regional isochron sr diffusion in feldspar is slow at the magmatie temperatures inferred for glass mountain rhyolites 700 c such that over 0 5 ma the cores of large feldspars 1 ram will retain 99 9 of their original sr the cores of sanidine and plagioclase yield glass mineral ages that are up to 300 ka older than eruption ages feldspar rim ages for two samples are indistinguishable from eruption ages the rims of sanidines and plagioclases from the third sample are 110 and 280 ka older than the eruption age and 180 and 20 ka younger than the cores these mineral age data probably reflect the combination of extended periods of mineral growth and partial isotopic exchange with the host liquid during protracted residence in a magma reservoir however the ar and sr isotopic data for biotite phenocrysts are consistent with the presence of a significant component that is recycled from earlier magmatic pulses due to the extreme rb sr ratios of the rocks and minerals it is possible to very precisely resolve the time difference between the formation of different phases assuming that they crystallised from the same host magmas

petrogenesis of sierra nevada plutons inferred from the sr nd and o isotopic signatures of mafic igneous complexes in yosemite valley california mafic complexes in the central sierra nevada batholith record valuable geochemical information regarding the role mafic magmas play in arc magmatism and the generation of continental crust in the intrusive suite of yosemite valley major and trace element compositions of the hornblende bearing gabbroic rocks from the rockslides mafic complex and of the mafic dikes in the north america wall are compositionally similar to high alumina basalt of these rocks two samples have higher ni and cr abundances as well as higher end values than previously recognized for the intrusive suite plagioclase crystals in rocks from the north america wall and the rockslides have prominent calcic cores and sharply defined sodic rims a texture commonly associated with mixing of mafic and felsic magmas in situ analyses of 87sr 86sr in plagioclase show no significant isotopic difference from the cores to the rims of these grains we propose that the high 87sr 86sr 0 7067 and low end 3 4 of bulk rocks the homogeneity of 87sr 86sr in plagioclase and the high 18o values of bulk rocks 6 6 7 3 and zircon lackey et al in j petrol 49 1397 1426 2008 demonstrate that continental crust was assimilated into the sublithospheric mantle derived basaltic precursors of the mafic rocks in yosemite valley contamination 20 40 likely occurred in the lower crust as the magma differentiated to high alumina basalt prior to plagioclase and zircon crystallization as a consequence the isotopic signatures recorded by whole rocks plagioclase and zircon do not represent the composition of the underlying lithospheric mantle we conclude that the mafic and associated felsic members of the intrusive suite of yosemite valley represent 60 80 new additions to the crust and include significant quantities of recycled ancient crust

the nd and sr isotopic composition of i type microgranitoid enclaves and their host rocks from the swifts creek pluton southeast australia abstract initial nd and sr isotopic compositions have been determined for microgranitoid enclaves and their host rocks from the siluro devonian swifts creek pluton within the lachlan fold belt of southeastern australia enclaves are of quartz dioritic to tonalitic composition and their textures support an igneous origin host rocks range from tonalite to granite the isotopic data form an array in nd 87 sr 86 sr space with enclaves systematically displaced towards higher nd and lower 87 sr 86 sr values enclaves range in nd t 405 ma from 7 3 to 3 1 with a narrow range in 87 sr 86 sr from 0 70613 to 0 70718 whereas host rocks range from 9 0 to 6 4 and 0 70761 to 0 70946 in nd and 87 sr 86 sr respectively the isotopic relations rule out simple crystal liquid fractionation or restite unmixing alone as the major genetic link between enclaves and host rocks the data are also incompatible with an origin of the enclaves by crystal accumulation or liquid immiscibility instead mixing between a mafic mantle derived and a crustal derived end member to generate the host rock enclave spectrum is compatible with the data because the initial isotopic ratios of enclaves and host rocks are well within the range of crustal rocks we favour the alternative view that both enclave and host rock magmas are of crustal origin consequently we avoid extrapolations to hypothetical end members we suggest that the enclaves from the swifts creek pluton are derived by partial melting of a mafic lower crust and mixed at or near the site of magma generation with a chemically less primitive and isotopically more evolved component to generate the enclave and host rock spectrum the isotopic heterogeneities within the enclave and host rocks survived the superimposed effects of crystal liquid fractionation model ages tdm for enclaves and host rocks are almost identical averaging 1 7 and 1 6 ga respectively these model ages indicate that both the enclave and host rock protoliths were derived from a mantle reservoir during the proterozoic

applicability of magnetic fabrics in rocks associated with the emplacement of salt structures the bicorb quesa and navarres salt walls prebetics se spain abstract this work assesses the applicability of the analysis of the anisotropy of magnetic susceptibility ams to rocks associated with salt structures magnetic fabrics from 16 sites sampled on upper triassic clays keuper facies interbedded within the salt layers of the bicorb quesa and navarres salt walls prebetic zone se spain are mostly characterized by oblate magnetic ellipsoids with their magnetic foliation parallel to the bedding and magnetic lineation contained in the bedding plane but without a constant relationship with dip direction to evaluate the quality and significance of the low field ams several experiments were carried out to characterize the magnetic mineralogy of representative samples and enable separation of the contributions from paramagnetic and ferromagnetic s l minerals the comparison between the orientation of the observed magnetic lineation and that of the structural elements characterizing the internal geometry of the studied salt structures antiforms minor folds faults and shear zones and flanks indicates that the magnetic fabric is controlled by deformation processes affecting the salt walls during their growth and or evolution samples were also analyzed from sixteen sites from miocene rocks outcropping in several syn diapiric miocene half grabens related to the salt walls studied their magnetic fabric is interpreted to reflect the dominant stretching direction at the syn diapiric half grabens during and or shortly after deposition our results indicate that caution is required in interpreting magnetic lineations related to salt flow mechanics from rocks associated with salt structures

a time series of agulhas undercurrent transport abstract a 550 day record of agulhas undercurrent transport between march 2003 and august 2004 is constructed from five deep moorings placed on the continental shelf off south africa at nominally 32 s the vertical and lateral scales of the undercurrent are estimated to be 2000 m and 40 km respectively using the average of seven direct velocity sections predominantly taken in austral autumn over a 10 yr period from 1995 to 2005 peak speeds in the undercurrent are some of the greatest ever seen at depth over 90 cm s 1 at 1400 m the undercurrent has a transport of 4 2 5 2 sv 1 sv 1 106 m3 s 1 in close agreement with a previous estimate from a single current meter record during 1995 of 4 2 2 9 sv records below 1800 m within the north atlantic deep water nadw layer of the undercurrent show a higher level of coherence and less variance than those at intermediate depths on average 2 3 3 0 sv of nadw is carried northeastward within the undercurrent an amount similar to that estimated p

deformation and recrystallization mechanisms in actively extruding salt fountain microstructural evidence for a switch in deformation mechanisms with increased availability of meteoric water and decreased grain size qum kuh central iran microstructural study of rocksalt samples from an active salt fountain qum kuh central iran enabled to identify the relative contribution of different deformation mechanisms on extrusive salt flow the microstructural study combined reflected and transmitted light microscopy of gamma irradiated thin sections textural analysis of digitized microstructures and electron back scattered diffraction ebsd deformation microstructures record the strongly variable deformation conditions of salt flow in the diapiric system from the diapiric stem towards the distal part of the mature viscous fountain high stress deformation conditions typical for diapiric stems are recorded in the small subgrains within the porphyroclasts of all documented samples recovery and recrystallization due to divergent and decelerating flow associated with differential stress drop in the salt extrusion above the diapiric orifice is reflected by abundant growth band microstructures this study reveals also evidence for penetration of rainwater into the salt mass and documents the switch from the dominant dislocation creep into dominant solution precipitation creep from the upper part to the distal part of the fountain this deformation mechanism switch is provided by influx of meteoric water and grain size decrease likely controlled by subgrain rotation and grain boundary migration recrystallization

anisotropy of diamagnetic susceptibility in thassos marble a comparison between measured and modeled data abstract a study of shear zones within the calcite marble complex of the island of thassos greece shows that the low field anisotropy of magnetic susceptibility ams technique can be successfully applied to diamagnetic rocks for characterizing rock fabrics the strain path involves both an early pure shear stage and a simple shear overprint that is documented by a transition from triaxial neutral to uniaxial prolate shapes of ams ellipsoids the maximum susceptibility is oriented perpendicular to the rock foliation reflecting the preferred orientation of calcite c axes in the protolith as well as in the mylonites for three samples that represent different types of calcite fabrics the ams was recalculated from neutron and electron backscatter diffraction textural data a comparison of the measured and modeled data shows a good coincidence for the orientation of the principal ams axes and for the recalculated anisotropy data both measured and modeled data sets reflect the change from neutral to distinct prolate ellipsoids during progressive deformation

thermobarometric constraints on the depth of exposure and conditions of plutonism and metamorphism at deep levels of the sierra nevada batholith tehachapi mountains california we present thermodynamic estimates of pressures temperatures and volatile activities in variably deformed gabbroic to granitic cretaceous 115 100 ma batholithic and framework rocks of the tehachapi mountains southernmost sierra nevada california al contents of hornblende in granitoids imply igneous emplacement at 8 kbar in the southernmost tehachapi mountains with lower pressures 3 7 kbar to the north metamorphic pressures and temperatures for garnet bearing paragneisses and metaigneous rocks were estimated on the basis of garnet hornblende plagioclase quartz and garnet biotite plagioclase quartz thermobarometers disparate results for the metaigneous rocks from the latter system point to the difficulty of applying pelite based thermobarometers to rocks of contrasting composition and mineralogy preferred pressures cluster at 7 1 9 4 and 3 6 4 3 kbar incomplete knowledge of reaction histories however limits our interpretation of the lower pressures because they are minimum estimates the 4 kbar samples are all from a small area and if our interpretation is correct they imply a local more shallow event superimposed on crust once residing at deeper structural levels garnet hornblende and garnet biotite temperatures are less coherent likely owing to retrograde fe mg exchange and range from 570 to 790 c the majority of the rocks are igneous and affected by recrystallization and metamorphism during subsolidus cooling they are not granulites country rock paragneisses are typically migmatized at peak metamorphic conditions near that of the wet granite solidus 690 c veinlike paragenesis of garnet in the metaigneous rocks suggests formation related to the presence of a fluid phase thermodynamic estimates of volatile activities in these garnet bearing assemblages suggest variable mostly co 2 rich fluid compositions in the absence of any pervasive fluid flux the igneous rocks of the tehachapi mountains were thus intruded at depths of 30 km making them the deepest known exposed components of the cretaceous sierra nevada batholith metamorphism occurred at these great depths and perhaps locally after 15 km of uplift before 87 ma implying an uplift rate of 1 2 mm yr a minimum uplift rate is 0 6 mm yr this original uplift and possible subsequent uplift events may have been related to underthrusting of a block of rand schist from what is now the southeast with concomitant widespread ductile deformation the deduced pressure temperature and uplift history is similar to those of high pressure high temperature cretaceous batholithic rocks in salinia and the san gabriel mountains but direct correlation is not wan anted when compared with higher level intrusive rocks from analogous portions of the sierra nevada batholith to the north the tehachapi rocks reveal a deep batholith that is more heterogeneous and somewhat more mafic on average but displaying a similar level of isotopic hybridization involving mantle and crustal sources the batholith is quartz rich at these levels suggestive of a weak ductile middle crust susceptible to prolonged deformation and possible delamination

rheological behaviour of synthetic rocksalt the interplay between water dynamic recrystallization and deformation mechanisms abstract the ductile deformation of rocks in nature can be greatly enhanced by the presence of water part of the water induced weakening of rocks at depth may come from fluid assisted deformation or recrystallization mechanisms that are absent in dry rocks in this study we investigate the effect of water on the rheological behaviour of rocksalt we focus on quantification of the contribution of individual deformation and recrystallization mechanisms to deformation we also aim to calibrate a flow law that incorporates the effect of all the relevant microphysical processes and hence more accurately describes the flow of rocksalt in nature for this purpose the mechanical behaviour and microstructural evolution of synthetic rocksalt samples that are similar except for differences in water content determined using ftir analysis are investigated the samples are deformed to natural strains of 0 07 0 46 at 50 mpa confining pressure strain rates of 5 10 7 1 10 4 s 1 and temperatures of 75 240 c resulting in flow stresses of 7 22 mpa the flow stress of samples with a water content below 5 ppm dry is higher than that of samples with a water content of 9 46 ppm wet at all strains under the investigated conditions the difference in flow stress can be explained as due to the operation of only work hardening dislocation creep without dynamic recrystallization in the dry material versus combined dislocation and solution precipitation creep plus fluid assisted grain boundary migration in the wet material the results allow us to calibrate a flow law for wet rocksalt that incorporates the effects of solution precipitation creep and fluid assisted grain boundary migration the results also suggest that strain localization in natural rocksalt is more likely to be localized due to fluid infiltration and associated rheological weakening than due to progressive removal of strain hardening substructure by grain boundary migration

strain partitioning of deformation mechanisms in limestones examining the relationship of strain and anisotropy of magnetic susceptibility ams abstract in order to investigate the relationship between rock strain and anisotropy of magnetic susceptibility ams strain partitioning and ams analysis was conducted at 35 sites from two stratigraphically adjacent paleozoic limestone units in the patterson creek and wills mountain anticlines in the central appalachian orogen of west virginia in addition anisotropy of anhysteretic remanent magnetization aarm was conducted on selected samples to examine the role of preferentially oriented magnetite on the ams fabric strain is partitioned into bed normal shortening due to compaction solution strain 35 0 shortening bed parallel shortening due to tectonic solution strain 13 3 shortening calcite twinning strain 5 8 shortening and grain boundary sliding 26 7 shortening the ams fabrics in the rocks were found to be a result of a complex interaction between rock lithology deformation mechanisms and strain magnitude although all the rocks have experienced the same deformation conditions six different ams fabrics are exhibited each of the different ams fabrics is a composite fabric resulting from the overprinting of three components 1 an inherent primary depositional ams fabric that is attributed to preferentially oriented phyllosilicates in the rock matrix 2 a diagenetic and or compaction ams fabric formed during burial that is due to preferentially oriented phyllosilicates in solution structures and in the rock matrix and 3 a tectonic ams fabric that was imparted on the rocks by layer parallel shortening deformation prior to folding and is also attributed to preferentially oriented phyllosilicates in solution structures and in the rock matrix as well as twinning of ferroan calcite

deformation and recrystallization mechanisms in mylonitic shear zones in naturally deformed extrusive eocene oligocene rocksalt from eyvanekey plateau and garmsar hills central iran abstract microstructural processes in mylonitic shear zones from extrusions of eocene oligocene rocksalts from garmsar hills and eyvanekey plateau central iran are described and analyzed the halite samples were studied by transmitted light microscopy of gamma irradiated thin sections subgrain size palaeopiezometry of polished and chemically etched samples and texture measurements by electron backscatter diffraction ebsd the studied shear zones are thin using published flow laws the strain rate in the fine grained mylonites is about 10 10 l s which is in a good agreement with earlier in situ measurements on glacier salt flow rate

age and origin of anorthosites charnockites and granulites in the central virginia blue ridge nd and sr isotopic evidence rb sr isotopic data for anorthosites charnockites ferrodioritic to quartz monzonitic plutons and high grade gneisses of the blue ridge of central virginia show evidence of post emplacement metamorphism but in some cases retain grenville ages the pedlar river charnockite suite yields an isochron age of 1021 36 ma initial 87sr 86sr ratio of 0 7047 6 which agrees with published u pb zircon ages five samples of that unit which contain paleozoic mylonitic fabrics define a regression line of 683 ma interpreted as a mixing line with no age significance samples of the roseland anorthosite complex show excessive scatter on a rb sr evolution diagram probably due to paleozoic 475 m y metamorphism data from the ferrodioritic to quartz monzonitic plutons of the area yield an age of 1009 26 ma inital ratio 0 7058 4 which is in the range of the u pb zircon ages of 1000 1100 ma the stage road layered gneiss yields an age of 1147 34 ma initial ratio of 0 7047 5 sm nd data for the pedlar river charnockite suite reflect a pre grenville age of 1489 118 ma nd 6 7 1 2 data for the roseland anorthosite complex and the ferrodioritic to quartz monzonitic plutons yield grenville isochron ages of 1045 44 ma nd 1 0 0 3 and 1027 101 ma nd 1 4 1 0 respectively two roseland anorthosite samples plot far above the isochron demonstrating the effects of post emplacement disturbance of sm nd systematics while mylonitized pedlar river charnockite suite samples show no evidence of sm nd redistribution the disparity of the sm nd age and other isotopic ages for the pedlar river charnockite suite probably reflects a sm nd source age suggesting the presence of an older crust within this portion of the ca 1 ga old basement

mafic xenoliths from i and s type granitoids evidence for variations in deep crustal radioactive heat production mafic xenoliths from s type granitoids in the lachlan fold belt lfb australia have radioactive heat productions which may exceed those of the host pluton mafic xenoliths from the lfb i type granitoids contain low to moderate radioactive heat productions compared to the host plutons these lfb granitoid mafic xenoliths indicate that large variations in radioactive heat production could occur beneath the plutons in this area in the sierra nevada batholith snb california two i type granitoid groups occur these are granitoids having inherently low radioactive heat productions in the western snb and granitoids having inherently high radioactive heat productions in the eastern snb mafic xenoliths from the eastern snb granitoids contain radioactive heat productions that in some specimens exceed that found in the western snb granitoids therefore the low radioactive heat productions of the western snb granitoids can not be used to constrain heat production deep beneath the eastern snb

resolution of ferrimagnetic and paramagnetic anisotropies in rocks using combined low field and high field measurements summary a method of separation of ferrimagnetic and paramagnetic components of magnetic anisotropy from the total anisotropy is developed from the anisotropy measurement of a specimen in a low field susceptibility anisotropy and from measurement in two high fields stronger than the saturation field of the ferrimagnetic fraction present the following anisotropy components can be calculated susceptibility anisotropy field independent of the paramagnetic fraction low field susceptibility anisotropy of the ferrimagnetic fraction and high field anisotropy of the ferrimagnetic fraction errors possibly arising from imperfect saturation of the ferrimagnetic fraction in the field practically available are analysed

variability and coherence of the agulhas undercurrent in a high resolution ocean general circulation model abstract the agulhas current system has been analyzed in a nested high resolution ocean model and compared to observations the model shows good performance in the western boundary current structure and the transports off the south african coast this includes the simulation of the northward flowing agulhas undercurrent it is demonstrated that fluctuations of the agulhas current and undercurrent around 50 70 days are due to natal pulses and mozambique eddies propagating downstream a sensitivity experiment that excludes those upstream perturbations significantly reduces the variability as well as the mean transport of the undercurrent although the model simulates undercurrents in the mozambique channel and east of madagascar there is no direct connection between those and the agulhas undercurrent virtual float releases demonstrate that topography is effectively blocking the flow toward the north

the finne fault zone central germany structural analysis of a partially inverted extensional fault zone by balanced cross sections the finne fault zone located in central germany to the southwest of the harz mountains was studied by means of detailed map analysis investigations of fault displacement and balanced cross sections for the most strongly deformed area in the center of the fault zone ca 50 of total fault zone length the system of the finne fault zone shows a nearly 100 km long straight flexure that symbolizes the morphological and geological northeastern border of the thuringian basin in the central part which should be surveyed here the fault zone corresponds to a distinctive narrow band of highly deformed triassic sedimentary rocks the northwestern and especially the southeastern parts of the research area are developed as several parallel branch faults in the southeastern elongation of the fault zone which is not part of our survey the sedimentary cover is missing here it is possible to gain insight to the fact that the basement is also involved to the kinematics of the fault zone based on our results we propose a subdivision of the fault zone into four sectors from the northwest to the southeast we interpret the structure of these sectors to reflect 1 a compressional flexure 2 an overthrust graben and 3 a partially inverted and folded half graben in the extreme southeast 4 the fault zone is characterized by an anticline with some strike slip movement parallel to the fold axis this segmentation is caused by a thrust fault system whose strike direction deviates slightly from that of the earlier formed graben system the structural configuration can be explained by a two phase deformation in which the contractional strain exceeded the preceding extensional deformation in the investigated area the horizontal shortening attains a maximum of ca 1 km the present study confirms many earlier hypotheses presents new results on the deformation history of the fault zone and attempts to evaluate the deformation in a regional geological context the results of earlier studies were refined and revised using modern methods and a unified structural and kinematic model of the finne fault zone was created

smnd isotopic systematics of enderby land granulites and evidence for the redistribution of sm and nd during metamorphism measurements of143nd 144nd and147sm 144nd are reported for whole rocks and mineral separates from granulites of the napier complex at fyfe hills charnockites leuconorites and gabbros yield a whole rock smnd isochron age of3060 160m y and an initial143nd 144nd ratio of0 50776 10 nd 3060m y 2 0 1 8 the negative nd value and the presence of geologically induced dispersion in the data suggest that the isochron age does not represent the time of primary crystallization of the complex but instead indicates a time of later redistribution of sm and nd and partial re equilibration of143nd 144nd ratios this probably occurred during the upper granulite facies metamorphism which has also been dated at 3100m y by rbsr and upb zircon studies 1 coexisting clinopyroxene apatite and total rock fractions in two adjacent samples define an approximately linear array corresponding to an age of 2300 300 m y this array indicates that redistribution of sm and nd and re equilibration of143nd 144nd ratios occurred on an intermineral scale during the upper amphibolite to lower granulite facies metamorphism at 2450m y due to the resetting of the smnd system on both whole rock and mineral scales the primary crystallization age of the igneous protolith is not well constrained by the present data although it is clearly3100m y if it is assumed that the complex was derived initially from a depleted mantle reservoir nd t 2 evolution of the negative nd value of 2 0 with the observed sm nd ratios requires a prehistory of 380m y this implies a primary age of 3480m y however substantially older primary ages can be inferred if the source reservoirs had nd t 2 and or substantial reductions in the sm nd ratio occurred in whole rocks during the granulite facies metamorphism at 3100 m y such an inferred reduction in the sm nd ratio may have been the result of preferential loss of sm relative to nd or introduction of a low sm nd fluid with nd 0 during granulite facies metamorphism

u pb zircon strontium and oxygen isotopic and geochronological study of the southernmost sierra nevada batholith california the southernmost sierra nevada offers a view into the deep levels of the mesozoic batholithic belt which constitutes much of the range to the north and represents one of the major tectonic features of western north america the main crystalline rocks of the study area are 1 the intrusive suite of bear valley a middle cretaceous tonalite batholith complex with coeval gabbroic intrusives and 2 the gneiss complex of the tehachapi mountains which consists of early cretaceous orthogneiss and subordinate paragneiss with local domains having granulite facies metamorphic assemblages the orthogneisses are dominantly tonalitic in composition with significant layers of granodioritic to granitic and lesser dioritic to gabbroic gneiss quartz rich and psammitic metasedimentary rocks with subordinate marble constitute the main framework assemblage into which the plutonic rocks were emplaced field relations demonstrate assimilation of metasedimentary material into the orthogneiss and tonalite batholith magmas and magma mixing between mafic tonalitic and granitic materials significant domains of both homogenization and inhomogenization are recognized isotopically within the mixed rocks u pb zircon studies have resolved two major igneous suites and a third suite of postdeformational intrusives all lying between 90 and 120 ma the first suite gneiss complex of the tehachapi mountains was emplaced at 115 ma and exhibits penetrative high temperature deformation developed at or near solidus conditions a number of discordance patterns along with the physical properties of the zircon suggest minor inheritance of proterozoic zircon and limited open system behavior in response to a major 100 ma plutonic event the 100 3 ma intrusive suite of bear valley crosscuts the older suite but also exhibits significant synplutonic deformation mainly concordant zircon ages indicate the igneous crystallization age but some discordances occur due to inheritance or entrainment of proterozoic zircon the high temperature deformation fabrics in these suites and within the metasedimentary framework rocks were crosscut by the granodiorite of claraville 90 ma and pegmatite dikes 95 ma the granodiorite of claraville shows strong inheritance of proterozoic zircon and high initial 87 sr 86 sr and 18 o zircon populations from paragneiss and quartzite samples are dominated by proterozoic detrital grains strontium and oxygen isotopic data on the zircon geochronology sample suite suggest simple twocomponent mixing of mantle derived gabbroic to tonalitic magmas with partial to complete melt products from the metasedimentary framework rocks sedimentary admixtures for some granitic rocks may be as high as 45 but for the tonalitic batholithic complex are no higher than about 15 modeled values of 10 20 metasediment are typical for the orthogneisses initial 87 sr 86 sr correlates directly with 18 o and generally correlates inversely with sr content some subtle complexities in the sr and o isotopic data suggest the involvement of a third cryptic component such a component could be early phanerozoic ensimatic accretionary terranes that were structurally beneath the observed metasedimentary sequence or altered oceanic crust and sediments introduced into the mantle magma source area by subduction one of the initial aims of this study was to seek out remnants of proterozoic sialic crystalline rocks within the gneiss complex of the tehachapi mountains no such remnants were found and our studies strongly suggest that sialic components within this link of the mesozoic batholithic belt were introduced into mantle derived magraatic systems by anatexis of continent derived sedimentary rocks

sea surface slope as a proxy for agulhas current strength the linear relation between the strength of the agulhas current at nominal latitude 34 s and the gradient in sea level height anomaly across the current is investigated in a 1 10 resolution regional numerical ocean model our results show that the strength of the current can be estimated with reasonable accuracy using altimeter data once it has been calibrated using in situ transport measurements three years of transport measurements provide a calibration with worst case correlation r 0 78 in that case the errors in proxy transport have a standard deviation of 9 8 sv compared to a 20 2 sv standard deviation of the transport time series itself from these results we conclude that the design of the agulhas current timeseries act experiment a three year deployment of moorings across the agulhas current and along a topex jason altimeter ground track will likely produce a good quality multi decadal time series of agulhas current strength

early silurian granitic rocks and associated enclaves as evidence of rapid cooling in a cognate magma system the case of the xuehuading panshanchong pluton south china block

evaluating magnetic lineations ams in deformed rocks magnetic lineation in rocks is given by a cluster of the principal axes of maximum susceptibility kmax of the anisotropy of magnetic susceptibility ams tensor in deformed rocks magnetic lineations are generally considered to be the result of either bedding and cleavage intersection or they parallel the tectonic extension direction in high strain zones our ams determinations based on a variety of samples that were taken from mudstones slates and schists from the pyrenees and appalachians show that strain is not the only factor controlling the development of magnetic lineation we find that the development and extent to which the magnetic lineation parallels the tectonic extension direction depends on both the original ams tensor which in turn depends on the lithology and the deformation intensity rocks having a weak pre deformational fabric will develop magnetic lineations that more readily will track the tectonic extension

chemical and isotopic systematics of the caledonian intrusions of scotland and northern england a guide to magma source region and magma crust interaction chemical and 0 sr nd and pb isotope relations for the british caledonian granitoids exhibit systematic variations that are attributed to derivation from both mantle and crustal sources the older more than ca 470 ma pre and syn tectonic granites were the product of local anatectic melting of late proterozoic metasedimentary upper crust 6180 i 8 to 14 87sr 86sr 0 710 206pb 204pb w 18 1 19 2 during the peak thermal conditions of the grampian orogeny the younger less than ca 440 ma post tectonic granitoids have a complex origin which in individual cases involved at least four different source regions i the upper mantle or subducted oceanic crust 6180 5 7 to 7 0 o 87sr 86sr w 0 7035 0 7040 206pb 204pb 17 9 to 18 1 and ii lower palaeozoic geosynclinal sedimentary upper crust 6180 11 to 14 o 87sr 6sr w 0 705 0 711 206pb 204pb 18 4 within the paratectonic caledonides in the scottish midland valley and southern uplands and in northern england or iii middle proterozoic mafic to intermediate granulitic lower crust 6180 w 8 to 10 o 87sr 86sr w 0 705 0 707 206pb 20pb 16 5 17 0 and iv middle to late proterozoic metasedimentary upper crust 6180 8 to 14 87sr 86sr 0 710 206pb 207pb w 18 1 19 2 in the scottish highlands mantle derived magmas or their direct derivatives were likely involved in the development of all of the younger granitoids either as end member components or as the source for a substantial part of the heat required for crustal melting and assimilation although the lower palaeozoic was a time during which a large amount of igneous material was introduced into the upper crust in britain it was not a major crust forming period because the caledonian granitoids are dominated by recycled continental crust

a method for the separation of paramagnetic ferrimagnetic and haematite magnetic subfabrics using high field torque magnetometry summary in this study the contribution of the paramagnetic ferrimagnetic and haematite components to the magnetic anisotropy is separated by means of high field torque magnetometry torque measurements at different fields which are high enough to saturate the ferrimagnetic minerals however still low enough that the torque resulting from the haematite is linear with field allow for the separation of the three magnetic anisotropy components the method has been applied to haematite single crystals in which no paramagnetic or ferrimagnetic components have been found contribute to the torque signal the mean direction of the poles to the crystallographic basal plane in the haematite single crystals is subparallel to the minimum susceptibility direction measured in low field the separation analysis has also been applied to highly deformed red beds from the lower glarus nappe complex switzerland no ferrimagnetic phases are present in the rocks and therefore they cannot contribute to the anisotropy of magnetic susceptibility the magnetic fabric arises from a paramagnetic subfabric carried by the phyllosilicate minerals and haematite in which the basal planes of both phases are in the cleavage plane the measured magnetic lineation seen in low field anisotropy of magnetic susceptibility appears to be an apparent lineation that arises from a weak girdling of haematite and the paramagnetic minerals conforming the rock

o sr isotopic variations in miocene granitoids from the aegean evidence for an origin by combined assimilation and fractional crystallization sr o and d h isotopic compositions have been analyzed in miocene metaluminous to slightly peraluminous i type granitoids of the central aegean individual plutonic complexes display significant variations in their 18o and initial87sr 86sr compositions d and 18o compositions of minerals and whole rocks are mostly in the magmatic range some samples from naxos and mykonos delos show low d and 18o values characteristic of meteoric water hydrothermal interaction but as a whole the changes in 18o and sr isotopic compositions as a result of hydrothermal alteration were slight even in instances where marked alteration is petrographically observable consequently the bulk rock variations of 18o from 8 1 to 12 0 and of87sr 86sr from 0 70438 to 0 71450 may be regarded as primary and indicative of the conditions of their evolution heterogeneous isotopic compositions observed in the individual plutons of serifos ikaria samos and kos may be caused by the multiple intrusion of chemically and isotopically distinct magma pulses with high viscosities and relatively rapid consolidation in most cases preventing complete homogenization the granitoids of serifos ikaria and kos display weak correlations between the initial87sr 86sr and 18o and 1 sr the granitoid province shows a positive correlation between87sr 86sr and 18o and a non linear relationship between87sr 86sr and 1 sr whereby 1 sr increases more rapidly than the isotopic ratio as the degree of fractionation of the rocks increases it is argued that assimilation of older continental material by mantle derived arc magmas with combined fractionation afc is the most plausible model to explain the chemical and isotopic characteristics of the granitoids and the geological situation in which rock types trend from granodiorites in the south west near the inferred oligocene miocene suture to granites in the center and monzonites in the north east of the province

the geochemical characteristics of granitoids in contrasting arcs and comments on magma sources geochemical variations in modern subduction related igneous suites with respect to arc maturity in time and space are illustrated using data for both volcanic suites basalt andesite and dacite and intrusive granitoid suites diorite tonalite granodiorite and granite from circum pacific arcs using trace element data we suggest that two groups of processes control the natural variation in the parental magmas of both suites a subduction zone enrichment of lithospheric mantle locally coupled with crustal assimilation allied with fractional crystallization afc in zones of thickened crust all of which yield magmas with enhanced concentrations of the large ion lithophile lil elements k rb th u lrees etc b with increasing distance from the active trench contributions from within plate sub continental lithosphere producing mantle derived magmas with enhanced levels of high field strength hfs elements among which nb ta hf and y are particularly distinctive thus even for the evolved granitoids of intrusive arc series ratios of hfs lil elements not significantly affected by crystal fractionation such as ta nb k rb la may throw some light on the origin of mafic intermediate precursor magmas in terms of these elements we suggest the following groupings for interpreting the tectonic associations of granitoid suites 1 primitive calcic arc granitoids with low lil and hfs element abundances 2 normal calc alkaline continental arc granitoids with enhanced lil element abundances and low hfs lil ratios 3 mature alkali calcic arc granitoids with high levels of lil and hfs elements and higher hfs lil ratios 4 back arc anorogenic alkaline granitoids with the highest levels of hfs elements

the origin of tectonic fabrics in undeformed clays the early stages of deformation in extensional sedimentary basins 1 an integrated approach was used to detect tectonic effects in apparently undeformed fine grained clay sediments filling extensional basins in southern italy results from low and high field anisotropy of magnetic susceptibility and mineral fabric deduced by neutron texture analysis show penetrative deformation on a grain scale the well defined tectonic magnetic lineation is parallel to the stretching direction and located at the intersection of the basal planes of phyllosilicates forming grain scale folds and crenulations this spatial configuration reflects basin scale deformation processes and suggests the existence of a nearly uniaxial stress field during the incipient extensional phases the integrated approach of magnetic and mineral fabric investigations is a valid tool to detect grain scale and regional deformation pattern in weakly deformed extensional basins where macroscopic evidence of deformation is not visible

geochemical evolution of the minto block a 2 7 ga continental magmatic arc built on the superior proto craton abstract a 400 km long by 100 km wide geological transect across the minto block of northeastern superior province reveals five plutonic suites and minor amphibolite to granulite grade supracrustal remnants the oldest regionally significant plutonic rocks include 3 0 0 1 ga foliated to gneissic tonalite characterized by high na k ratios high al contents light ree enrichment and initial gend 1 8 the leaf river plutonic suite is the most widespread with crystallization ages of about 2725 5 ma across the transect the suite comprises massive to foliated pyroxene and hornblende bearing granodiorite tonalite granite diorite and minor gabbro pyroxenite and syn plutonic mafic dykes the rocks are i type calc alkaline have variable na k ratios moderate to high ba and sr contents and ree patterns with variable light ree enrichment depletion of heavy rees with increasing silica and neutral negative or positive eu anomalies initial nd values for the suite range from 0 5 to 1 3 mean 0 4 and initial 87 sr 86 sr ratios isr are 0 7020 the diatexite plutonic suite 2713 ma occurs within a 150 km wide zone and consists of orthopyroxene garnet granodiorite containing 25 50 inclusions of granulite grade mafic supracrustal and tonalitic inclusions the variable major and trace element chemistry of the suite with generally high ni and cr contents reflects heterogeneous source materials and the presence of non liquid components initial nd values are from 0 1 to 1 7 monzogranite and orthopyroxene granite dykes plugs and plutonic masses both 2690 ma comprise the last important plutonic suites both biotite monzogranite and orthopyroxene granite are light ree enriched but the former have negative eu anomalies and the latter positive initial nd values range from 0 7 to 3 2 for monzogranite isr 0 7016 to 0 7067 and 0 7 to 0 2 for orthopyroxene granite isr 0 701 to 0 702 the initial nd and isr values of the 2 7 ga plutonic suites are lower and higher respectively than estimatesf of the contemporaneous depleted mantle suggesting significant and wide scale reworking of older tight ree enriched high rb sr lithosphere early tonalite orthogneiss from goudalie domain may be derived by partial melting of mafic crust at high pressures the lithological and geochemical diversity of the 2725 ma leaf river plutonic suite indicate a range of parental magma compositions and petrogenetic processes but fractional crystallization of mantle derived basaltic melts which had assimilated small amounts of significantly older lower crust may have been the dominant mechanism crustal inclusion charged granodioritic diatexite 2713 ma was probably derived by partial melting of heterogeneous lower crustal materials under relatively dry conditions late biotite monzogranite was generated by partial melting of older sialic crust and orthopyroxene granite by deeper melting or fractional crystallization of more juvenile source materials with garnet as a residual mineral we infer from the presence of coeval mafic dykes in all plutonic suites that heat for melting was ultimately derived from intrusion of basaltic magmas at depth the 2 7 ga magmatism in the minto block occurred during a period of active production and accretion of juvenile oceanic terranes in the southern superior province the northwest directed subduction regime inferred from the southern superior province arc terranes may also have been responsible for the magmatism that acted on 3 ga lithosphere in the northern superior province melting within the mantle wedge beneath the proto cratonic lithosphere and in the lower crust occurred within a tectonic setting similar to that of modem continental magmatic arcs

a nd isotope investigation of sediments related to crustal development in the british isles the times of original fractionation of the sm and nd component of clastic sediments from a mantle source crustal residence age have been estimated from sm nd model ages calculated relative to a depleted mantle evolution in this way the provenance and evolution of selected precambrian and phanerozoic sediments and metasediments from the british isles have been examined whereas some archaean and early proterozoic sediments have sm nd model ages that are close to their stratigraphic age the phanerozoic sediments analysed have model ages as much as 2 0 ga in excess of their stratigraphic age a more detailed study of lower palaeozoic sediments deposited on the northern margin of the iapetus ocean provides evidence for a marked change of provenance in the ordovician after the deposition of the dalradian supergroup a component with comparatively high143nd 144nd and sm nd ratio presumably basaltic is present in the sediments throughout the accretionary prism crustal residence age estimates average about 1 5 ga for both these lower palaeozoic sediments and modern pelagic clays and collectively fail to provide any evidence for significant continental growth during the phanerozoic

eastern indian 3800 million year old crust and early mantle differentiation samarium neodymium data for nine granitic and tonalite gneisses occurring as remnants within the singhbhum granite batholith in eastern india define an isochron of age 3775 89 x 10 6 years with an initial 143 nd 144 nd ratio of 0 50798 0 00007 this age contrasts with the rubidium strontium age of 3200 x 10 6 years for the same suite of rocks on the basis of the new samarium neodynium data field data and petrologic data a scheme of evolution is proposed for the archean crust in eastern india the isotopic data provide evidence that parts of the earth s mantle were already differentiated with respect to the chondritic samarium neodymium ratio 3800 x l0 6 years ago