extracting time domain green s function estimates from ambient seismic noise 1 it has been demonstrated experimentally and theoretically that an estimate of the green s function between two seismic stations can be obtained from the time derivative of the long time average cross correlation of ambient noise between these two stations this tdgf estimate from just the noise field includes all tensor components of the green s function and these green s function estimates can be used to infer earth structure we have computed cross correlations using 1 to 30 continuous days of ambient noise recorded by over 150 broadband seismic stations located in southern california the data processing yielded thousands of cross correlation pairs for receiver separations from 4 500 km which clearly exhibit coherent broadband propagating dispersive wavetrains across frequency band 0 1 2 hz

surface wave tomography of the western united states from ambient seismic noise rayleigh and love wave phase velocity maps summary we present the results of rayleigh wave and love wave phase velocity tomography in the western united states using ambient seismic noise observed at over 250 broad band stations from the earthscope usarray transportable array and regional networks all available threecomponent time series for the 12 month span between 2005 november 1 and 2006 october 31 have been cross correlated to yield estimated empirical rayleigh and love wave green s functions the love wave signals were observed with higher average signal to noise ratio snr than rayleigh wave signals and hence cannot be fully explained by the scattering of rayleigh waves phase velocity dispersion curves for both rayleigh and love waves between 5 and 40 speriod were measured for each interstation path by applying frequency time analysis the average uncertainty and systematic bias of the measurements are estimated using a method based on analysing thousands of nearly linearly aligned station triplets we find that empirical green s functions can be estimated accurately from the negative time derivative of the symmetric component ambient noise cross correlation without explicit knowledge of the source distribution the average traveltime uncertainty is less than 1 s at periods shorter than 24 s we present rayleigh and love wave phase speed maps at periods of 8 12 16 and 20 s the maps show clear correlations with major geological structures and qualitative agreement with previous results based on rayleigh wave group speeds

seasonal variations of observed noise amplitudes at 2 18 hz in southern california we show that noise amplitudes at frequencies above 1 hz exhibit strong seasonal variations in a broad southern california region the results are based on 3 component seismic data recorded between 2002 and 2009 by 30 stations focusing on continuous 6 hr night time segments the seismograms are bandpass filtered in nine frequency bands between 2 and 18 hz squared amplitudes are median filtered to reduce the influence of earthquake signals and integrated to yield half hourly noise energy estimates the 6 hr minimum energy values are converted back to ground velocity and used as representative daily noise level amplitudes notwithstanding various trends drifts and other transient complexities a common feature of the resulting time series in both the horizontal and vertical components are annual amplitude changes at all examined frequencies and all stations the strength of amplitude variations shows no correlation with distance from the coast and some particularly clear seasonal changes are seen near topographic features in arid uninhabited areas comparison to meteorological data suggests that the main sources for the high frequency noise field are variations of temperature and wind at the surface in addition to acting directly on topographic irregularities and other surface features these sources and especially temperature changes may also generate high frequency noise by inducing multitudinous small scale failures in the shallow crust

reply to comment on tectonic rotations in extensional regimes and their paleomagnetic consequences for ocean basalts by kenneth l verosub and eldridge m moores

trace element modelling of pelite derived granites the presence or absence of a vapour phase during incongruent melt reactions of muscovite and biotite together with the composition of the protolith determines the trace element characteristics of the resulting melt provided that equilibrium melting occurs for those phases that host the tracc elements of interest for granitic melts rb sr and ba provide critical constraints on the conditions that prevailed during melting whereas ree are primarily controlled by accessory phase behaviour mass balance constraints for eutectic granites that are formed by the incongruent melting of muscovite in pelites indicate that melting in the presence of a vapour phase will result in a large melt fraction and deplete the restite in feldspar hence the melt will be characterized by low rb sr and high sr ba ratios in contrast vapour absent melting will result in a smaller melt fraction and an increase in the restitic feldspar consequently high rb sr and low sr ba ratios are predicted vapour absent melting will also enhance the negative eu anomaly in the melt granites that result from the incongruent melting of biotite in the source will be characterized by higher rb concentrations than those that result from the incongruent melting of muscovite the himalayan leucogranites provide an example of unfractionated crustally derived eutectic melts that are enriched in rb but depleted in sr and ba relative to their metasedimentary protoliths these compositions may be generated by the incongruent melting of muscovite as a low melt fraction f 0 1 from a pelitic source under vapour absent conditions

geochemistry of the granitic rocks and their minerals from serra da estrela central portugal abstract several types of hercynian peraluminous granitic rocks ranging from biotite muscovite granodiorite to muscovite granite occur in the horst of serra da estrela variation diagrams of most major and trace elements of the rocks and biotites and cr and v of muscovites show fractionation trends however nb li rb k rb li mg variation diagrams of the rocks and muscovites and also of sn cs cs k of the muscovites indicate that the muscovite granite probably originated by another mechanism least squares analysis of major elements and modelling of trace elements indicate that the coarse grained porphyritic biotite muscovite granite granite porphyry and fine to medium grained muscovite biotite granite were derived from the granodiorite magma by fractional crystallization of plagioclase quartz and biotite emplacement of granodiorite magma took place at 3 5 3 kb and 720 c granites and granite porphyry probably originated about 690 c but were completely crystallized about 520 c o2 was about 10 17 for the granodiorite and hcl hf was higher whereas log h2o hcl was lower in the granodiorite than in the other granitic rocks of the fractionated series the coarse grained porphyritic biotite muscovite granite was hydrothermally altered between 400 350 c and 260 230 c at about 1 5 1 kb the hydrothermal fluids were probably mainly meteoric in origin but some fluids released during the late stage of granite solidification might also have been involved

petrogenetic modelling of in situ fractional crystallization in the zoned loch doon pluton scotland the late caledonian loch doon granitic intrusion ranges in composition from hypersthene diorite at the margin through quartz diorite granodiorite and granite to cordierite microgranite at its core petrogenetic modelling of trace element variations and least squares analysis of major elements indicate that two distinct magmas are involved each magma controlled by crystallization of plag opx cpx bio late stage rocks related to the second magma include the cordierite microgranites and aplites which are interpreted as the final residue which crystallized rapidly after a build up and loss of volatiles analyses of whole rocks and minerals for ree s and other elements of moderate high ionic potential indicate that these elements are strongly controlled by minor phase crystallization apatite zircon sphene and allanite are dominant at intermediate compositions but other accessory minerals such as monazite and xenotime may also become important at acid compositions it is probable that within each magma the mechanisms of crystal settling and filter pressing operated the former being initially dominant and the latter becoming more important with increasing degree of fractional crystallization

mineralogy and geochemistry of coal wastes from the starzykowiec coal waste dump upper silesia poland abstract coal wastes the products of coal processing deposited on dumps can undergo processes of self heating and self ignition causing endogenic fires burning coal waste dumps are dangerous for the environment the coal dump located at the chwalowice coal mine upper silesian coal basin poland represents a long term fire which affected the organic mineral and chemical composition of a huge amount of deposited wastes collected samples were divided into groups on the basis of kind on the amount or absence of organic matter content and on the basis of mineral phase composition chemical composition of examined samples reveals heating combustion processes in altered coal wastes the organic matter present in the coal wastes changes through the following processes all causing changes in c n o and h content 1 organic matter oxidation 2 organic matter devolatilization and 3 coke formation two processes alter the mineral phases and change the chemical composition of the combusting wastes 4 mineral phase oxidation e g pyrite and marcasite oxidation to fe 2 o 3 and 5 mineral dehydration h 2 o or oh groups are released from clay minerals and micas the latter are followed by isochemical processes 6 mineral structure rebuilding while heating enantiotropic transformations of e g sio 2 and 7 metastable phase formation processes 6 and 7 can change the chemistry of deposited wastes through 8 the formation of high temperature minerals in combustion process e g mullite and 9 mineral crystallization from melt e g indialite after dump quenching some minerals can become unstable because of 10 weathering processes the behavior of trace elements is also strictly connected with the behavior of mineral phases which have undergone the burning processes most of them appear to stay unchanged moreover organic matter content does not generally influence their concentration although the combustion processes are so spontaneous that their products cannot be predicted in all details some dependence between chemical composition of the sample and its location within the dump or after burning were found

rare earth element and oxygen isotope studies of altered variscan granites the western harz germany and southern sardinia italy abstract studies on whole rock samples and mineral separates from granitoids of the harz mountains germany and southern sardinia italy have revealed postmagmatic changes of rare earth element ree concentrations and isotopic composition of oxygen the ree distribution patterns of the altered rocks do not deviate significantly from the unaltered samples but the ree patterns of the feldspars and biotites show characteristic changes some of the feldspars lost their typical positive eu anomalies whereas some of the biotites gained negative ce anomalies in the altered samples the quartz feldspar oxygen isotopic fractionation is either too low or even reversed relative to primary magmatic pairs the observed effects are discussed as the interactions of the cooling granitoids with either surface or magmatic waters it is concluded that a high temperature water rock interaction with essentially magmatic waters best explains the observed phenomena

magmatic tectonic evolution of a volcanic rifted margin abstract many north atlantic continental margins are underlain by huge volcanic edifices near the continent ocean boundary a deep crustal hole drilled on the voring plateau odp leg 104 has provided important constraints on the initial breakup history and the subsequent margin evolution by penetrating more than 900 m of igneous rocks and interbedded sediments below a post early eocene cover the rocks constitute two distinct different volcanic series the upper series comprising a seaward dipping reflector wedge consists of transitional mid oceanic tholeiitic lava flows and thin volcaniclastic sediments dacitic flows some dikes and thicker interbedded sediments constitute the lower series the margin evolved by paleocene crustal extension accompanied by uplift and pervasive intrusion of the rift zone just prior to breakup magma from shallow crustal melts produced the lower series the upper series was constructed during an intense rapidly waning subaerial volcanic surge following breakup near the paleocene eocene transition it covers both the new oceanic crust and large areas of the continental crust the dipping wedge was formed by subsidence due to loading and thermal contraction possibly amplified by tectonism when the surge abated the injection center rapidly subsided and normal oceanic crust was formed there is a direct temporal and compositional relationship between the onshore north atlantic volcanic province and the margin volcanism compared to the transverse part of the province including the iceland hotspot which has been active over 60 m y the volcanic margins reflect a 2500 km long transient segment related to continental breakup lasting only about 3 m y the volcanic surge and uplift at breakup are related to a modest regional increased temperature at the base of the lithosphere this mode of margin formation has had important paleoenvironmental implications

s type granites and their probable absence in southwestern north america criteria that have been and still are used to characterize s type granites of the lachlan fold belt lfb of southeastern australia are reviewed and comparisons are made with various peraluminous granites of southwestern north america some of which have been classified as s types on the basis of insufficient data virtually all of the vast volume of s type granites in the lfb are near surface batholithic granites that are commonly associated with s type volcanics and are not associated with regional metamorphic rocks and migmatites they are strongly peraluminous as shown by the presence of cordierite granites with primary muscovite are rare all are low in na ca and sr as a result of chemical weathering during formation of the sedimentary sources peraluminous granites of various ages in southwestern north america are distinctly different they rarely contain cordierite a mineral characteristic of lfb s types but some are highly evolved such that fe mn rich garnet has crystallized they are dominantly two mica granites indicating crystallization at higher water fugacities and greater depths than most peraluminous granites of the lfb cordierite bearing volcanics s types have not been reported sodium is generally high in the peraluminous granites of southwestern north america some of these rocks have trondhjemitic affinities the parent magmas seem more likely to have been produced by partial melting of altered basaltic rocks locally some peraluminous rocks marginal to metaluminous types may owe their compositions to high level contamination of i types these are not s type rocks no compelling evidence has been presented that any of the peraluminous granites of southwestern north america are s types

volcanism on the rockall continental margin continental break up in the northern north atlantic was accompanied by massive volcanism this produced sequences of basalt flows erupted close to sea level which are imaged as seaward dipping reflectors on seismic reflection profiles they comprise the upper 4 5 km of transitional crust in both the edoras bank and hatton bank areas of the rockall continental margin detailed surveys show that the reflectors are convex upward on dip lines but are sub horizontal on strike lines they are probably produced by aerially extensive basalt flows extruded from linear fissure vents aligned parallel to the rift axis along the rockall margin two sequences of seaward dipping reflectors occur separated by an 9outer high9 near the foot of the continental margin the landward set of basalt flows are emplaced above stretched and intruded continental crust while the seaward set span the region from highly distended continental crust to fully oceanic crust the outer high is capped by basalt flows but exhibits little coherent internal reflectivity we discuss possible origins of the outer high as a residual block of thinned and intruded continental crust or as a central volcano cut by fissure vents similar to those found in the neovolcanic zones of iceland

the redskin granite evidence for thermogravitational diffusion in a precambrian granite batholith the 1000 ma old composite pikes peak batholith consists largely of medium to coarse grained biotite granite but is intruded by several smaller granite plutons two of these the tarryall mountains batholith and the redskin granite hawley 1969 hawley and wobus 1977 are here interpreted as cupolas atop the main mass of the pikes peak batholith chemical analysis for 38 elements in rocks from the redskin granite the tarryall mountains batholith and the biotite granite of the pikes peak batholith support the contention that the compositions of the smaller plutons are unlikely to have evolved from that of the main mass of the batholith by crystal fractionation it is believed that these compositions arose through liquid state fractionation processes possibly the convection aided thermogravitational model of shaw et al 1976 it is important to recognize that the chemical signature of this fractionation process can be discerned in holocrystalline rocks as well as in their glassy equivalents because the process may be instrumental in the formation of some kinds of lithophile ore deposits

on the mechanism of magma injection and plate divergence during the krafla rifting episode in ne iceland geodetic observations of horizontal and vertical point displacements in a 100 km wide network across the krafla fissure swarm of ne iceland are analyzed with simple elastic models the observed displacements accumulated from 1975 to 1980 in several events of magma injection into fissures that were widened the fissure swarm was extended and it subsided while the adjacent lithosphere contracted or was compressed accompanied by surface uplift we applied two models to fit the far field deformation an infinite horizontal pressure line source or a pipe and an infinite vertically limited vertical dyke source loaded by normal stress at the walls both embedded in an elastic half space in the far field inversion the two models cannot be distinguished but geology and the observed axial graben subsidence clearly discriminate against the pipe and for the dyke the inversion suggests that the widened dykes cut through the whole lithosphere which in the fissure swarm is only 4 6 km thick during the rifting episode the general magma level in the fissure swarm rose to near the surface by 1980 but the loading increments appear to have decreased whith time from 1975 to 1980

the eagle pass detachment southeastern arizona product of mid miocene listric normal faulting in the southern basin and range mid miocene low angle normal faulting is an integral part of the regional tectonic strain of the southern basin and range the distinguishing characteristic is the presence of detachments allochthons of moderately to steeply dipping hanging wall rocks resting in very low angle fault contact on structurally deeper generally older footwall rocks rotation of detachment strata was accomplished by imbricate listric normal faulting and coordinated tear faulting regional structural domains each thousands of kilometres in area contain detachments marked by uniform sense of detachment strata rotation the eagle pass detachment 70 km northeast of tucson arizona reveals informative structural details of parts of the system steeply southwest dipping mid miocene volcanic and sedimentary rocks several thousands of metres in thickness rest in very low angle 10 fault contact on precambrian granitic basement detachment strata were faulted into position by ne directed translation accompanied by rotation of strata to steep sw dips the detachment fault which underlies the 25 km2 detachment has the form of a large northeast trending mullion trough with relief of at least 500 m along the keel of the detachment precambrian quartz monzonite was transformed into a hydrothermally altered selvage of microbreccia the steep 80 northwest margin of the mullion trough served as a tear fault along which quartz monzonite was crushed volcanics were dragged and fanglomerate was locally sheared into flattened pebble conglomerate detachments like that at eagle pass resemble slump blocks on a grand scale they are elements of a regional system of extensional deformation which coincides with the belt of cordilleran metamorphic core complexes mid miocene detachment faulting post dates the formation of exposed mylonitic tectonites of core complex affinity but the direction of translation of the detachments is parallel to penetrative lineation in nearby and or underlying tectonite moreover in southeastern arizona examples the sense of translation of detachments matches the sense of simple shear movements disclosed by tectonite fabrics we speculate that large crustal displacements achieved during extension induced formation of tectonite produced a geometric and or dynamic condition which strongly influenced subsequent detachment faulting consequently with renewed or continued extension in mid miocene time deep upper crustal slumping was triggered and detachment rocks were translated along listric normal faults in the direction and sense of the earlier displacements which had accommodated the formation of tectonite

variscan silicic magmatism and related tin tungsten mineralization in the erzgebirge slavkovský les metallogenic province integration of geochemical mineralogical isotopic and geochronological data with geodynamic considerations suggests that the variscan granites in the erzgebirge slavkovsk les domain originated from repeated melting events and were emplaced over a period of about 40 ma 330 290 ma several lines of evidence exist supporting the idea that erzgebirge granites assigned to different types biotite granites two mica granites strongly peraluminous p rich li mica granites and slightly peraluminous p poor granites are in most cases not genetically related via continuous fractional crystallization from a common magmatic reservoir the genesis of the slavkovsky les granites however might be discussed in terms of an uninterrupted fractionation series geological models of sn w deposits based upon geochemical and structural results imply that the main ore depositional events followed immediately the emplacement and solidification processes of melt via fluid melt immiscibility breccia pipe formation and or pervasive rock fluid interactions

stratigraphy and correlation of the region surrounding the irdp drill hole 1978 reydarfjordur eastern iceland the 1 9 km thick sequence intersected by the irdp 1978 drill hole at reydarfjordur eastern iceland is correlated with the westward dipping exposed volcanic pile on the basis of extensive field mapping and paleomagnetic studies the base of the landward extension of sea floor magnetic anomaly 5 epoch 9 can be located at the top of the grjota olivine tholeiite formation intersected at about 1 5 km in the core and exposed at sea level about 9 km east of the drill site other exposed marker formations can also be identified in the core the drill site is located within a relatively dense dyke swarm 10 crustal dilation previously interpreted as the feeder of the overlying volcanic formations field observations including vertically discontinuous dykes and the lack of lava feeder relationships suggest that the dykes were intruded by lateral injection from the south and are considerably younger than and thus could not have fed the exposed lava pile in the vicinity of the drill site it is proposed that about 10 3 m y ago roughly coinciding with the lower boundary of anomaly 5 the reydarfjordur volcanic center ceased to be active and volcanic activity shifted about 20 km to the west where the breiddalur and thingmuli volcanic centers later developed the exposed stratigraphic succession between thingmuli and reydarfjordur volcanic centers is composed of lavas deposited in flank areas relatively removed from a paleovolcanic zone which now probably lies buried to the west of the irdp drill site the lowest 450 m of the core may represent lavas related to activity in the reydarfjordur volcanic center 13 5 km to the east

fault controlled lithospheric detachment of the volcanic southern south atlantic rift we present structural models of two exemplary conjugate seismic lines of the southernmost south atlantic margins to examine their initial evolution especially the seaward dipping reflectors sdrs modeling illustrates the different structure and inclination angles of the sdrs which therefore require different subsidence histories since typical symmetrical subsidence models are not applicable we suggest a model with a westward dipping detachment fault that offsets the sdrs on the south american margin and we speculate on passively subsided sdrs on the south african margin we propose a simple shear rifting mechanism to explain the initial break up of the south atlantic

geochemistry of the cornubian tin province the exposed crust of the cornubian massif in s w england has been systematically sampled and the rocks analysed for a wide range of major and trace elements geochemically this region is highly anomalous with three elements boron lithium tin occurring at levels several times higher than the average for other parts of the continental crust the greatest degree of enrichment is found in the rocks of the cornubian granite batholith but it is also present in rocks pre dating the formation of the batholith the mineral deposits of cornubia derive their trace elements from different sources b and sn from the granite and cu and s from the country rocks

cenozoic and mesozoic structure of the eastern basin and range province utah from cocorp seismic reflection data cocorp seismic reflection data collected from the eastern basin and range in west central utah provide information on cenozoic extensional tectonics mesozoic thrusting and their interrelationships those data show a series of remarkably continuous low angle reflectors that extend more than 120 km perpendicular to strike and can be traced as deep as 15 20 km over that distance none of these events are significantly cut by any high angle normal faults a major detachment beneath the sevier desert can be traced from a surface zone of normal faulting to a depth of 12 15 km with a regional apparent westward dip of 12 tentative correlation of upper and lower plate events suggests 30 60 km of extensional displacement on this detachment whether this structure is a reactivated mesozoic thrust is uncertain west steepening splays off the end of the detachment reach depths of 20 km and may represent a major mesozoic ramp or zones of distributed ductile shearing during extension some events are interpreted to be mesozoic thrusts of which at least one beneath the house range has been reactivated during the cenozoic the snake range decollement dips gently east and has a sense of cenozoic displacement opposite to that of other cenozoic detachments farther east deep events are most numerous beneath the east side of the sevier desert where they occur to depths of 30 km at the top of or perhaps partly within the anomalously low velocity upper mantle

petrology and li be b geochemistry of muscovite biotite granite and associated pegmatite near yellowknife canada prosperous granite rb sr 2520 25 ma occurs as several plutons 1 380 km2 outcrop area in a thick succession of metamorphosed greywacke mudstone of the yellowknife supergroup the average mineral content of the sparrow pluton in vol is quartz 32 plagioclase 31 k feldspar 24 muscovite 9 biotite 3 and apatite 1 average trace element concentrations in ppm are li 140 be 4 b 28 zn 47 rb 250 sr 76 zr 75 and ba 360 the central portion of the pluton is slightly richer in k sr and ba than the margin li is concentrated in mica li in biotite li in muscovite 4 7 and be and b in muscovite and plagioclase countless pegmatite dikes occur in the sparrow pluton and in schist hornfels to the east the outer limit is marked by the cordierite isograd 9 km from the granite contact dikes vary greatly in size 1 km to a few cm in length in mineral content quartz albite k feldspar muscovite tourmaline beryl spodumene in major element composition especially the na k ratio and in trace element content li 18 5000 ppm be 5 260 ppm b 20 150 ppm compared with prosperous granite the pegmatite bodies are richer in p and rb and poorer in ti fe mg zr and ba dikes rich in tourmaline beryl and spodumene occur in overlapping zones situated progressively farther from the centre of the sparrow pluton the composition of tourmaline is related to host rock the highest concentrations of fe and zn occur in crystals from pegmetite and the highest concentrations of mg and v occur in crystals from tourmalinized schist while those from granite and quartz veins occupy on intermediate position complex compositional zoning is present in some tourmaline crystals in pegmatite estimates of temperature 500 600 c and pressure 2 4 kb of granite emplacement based on the distribution of andalusite and sillimanite in the contact rocks suggest that the final stage of granite emplacement occurred at sub solidus conditions a vaportransport model is proposed to explain the widespread distribution of the pegmatite dikes and their extreme compositional variability some of the pegmatite constituents including li be and b were possibly derived from yellowknife graywacke and mudstone

the role of manganese in the paragenesis of magmatic garnet an example from the old woman piute range california a reply strongly peraluminous plutons of the old woman piute range southeastern california display the differentiation sequence muscovite biotite granite rightarrow muscovite garnet biotite granite rightarrow garnet muscovite granite rightarrow garnet muscovite aplite and pegmatite the garnets show no evidence of reaction but biotites in garnet bearing rocks are rimmed by muscovite metamorphic assemblages in the country rocks suggest pressures of emplacement less than 4 5 kb the plutons become relatively enriched in manganese with differentiation whole rock ratios of molar mn fe mg increase from 0 01 in least felsic garnet free rocks to 0 3 in most felsic garnet rich rocks mno concentrations show a corresponding rise in biotites 0 4 to 1 8 wt and less clearly in garnets 9 to 25 the differentiation sequence textural relations and mineral and whole rock compositions suggest that garnet paragenesis was controlled by the reaction biotite mn rich liquid rightarrow garnet

s type granitoids and an i s line in the peninsular ranges batholith southern california peraluminous to metaluminous s type granitoids occur in the central and eastern parts of the peninsular ranges batholith southern california as highly deformed plutons and anatectic migmatites within metapelitic prebatholithic wallrocks of upper amphibolite fades the granitoids overlap in age with and have undergone a structural history similar to that of the early cretaceous i type granitoids that occur mainly to the west initial 87 sr 86 sr ratios greater than 0 7079 and 18 o greater than 11 8 indicate a significant metasedimentary component in the source rocks of the s type granitoids an i s line that defines the westernmost extent of these rocks lies close to gravity age isotopic and prebatholithic wallrock contrasts within the batholith and together these features probably mark a fundamental change in the mesozoic crust if the western part of the batholith represents an upper jurassic and lower cretaceous accreted tectonostratigraphic terrane then the zone that contains these features may represent a terrane boundary we propose that the s type granitoids and associated migmatites developed at midcrustal levels as a result of collision and crustal thickening and rose as diapirs some dragging an envelope of migmatite and wallrock with them the zone of intense metamorphism and deformation that now forms the axis of the batholith has been uplifted relative to the western part of the batholith possibly as a consequence of unloading

detachment faulting and the evolution of passive continental margins major detachment faults play a key role in the lithospheric extension process in the basin and range province and may also be important in other continental extension terranes such detachment faulting leads to an inherent asymmetry of extensional structure and of uplift subsidence patterns detachment models developed for the formation of metamorphic core complexes can also be applied to the formation of passive continental margins we therefore suggest the existence of upper plate and lower plate passive margins these give rise to a complementary asymmetry of opposing margins after continental breakup transfer faults offset marginal features and allow margins to switch from upper plate to lower plate characteristics along strike

the formation and fate of large oceanic igneous provinces abstract large igneous provinces are conspicuous features of late phanerozoic geology and include continental flood basal rifted continental margin volcanic sequences and oceanic plateaus the latter are formed in an environment which typically recycles back into the mantle on a time scale of 200 m y but because comparisons have recently been made between oceanic plateaus and precambrian greenstone belt sequences new questions arise about their formation their fate and their preservation here we review some critical aspects of three oceanic plateaus ontong java kerguelen and the caribbean colombian abducted plateau and comment on their make up and the factors governing their preservation with particular relevance to ancient terranes many large igneous provinces can be linked to mantle plumes where plumes ascend beneath spreading ridges their energy is transformed into a large melt volume producing over thickened plateau crust where the spreading rate is low in relation to magma supply the plateau may become subaerial e g iceland but with fast spreading the plateau remains submarine thicker lithosphere may result in plume incubation before magma extrusion and there are many intermediate situations where plumes could readily break through thin lithosphere oceanic or continental because magma supply exceeds extension rate plateaus may be characterised by thick sequences of flows and sills rather than the sheeted dykes typical of phanerozoic ophiolites precambrian greenstones could represent imbricated oceanic plateaus or plumes penetrating thin continental lithosphere the initial high temperature and the buoyant nature of the depleted refractory keel of plateaus contributes to their preservation relative to normal oceanic crust when they collide with active margins they choke the subduction zone causing subduction flip or backstep and the development of extensive talc alkaline arc volcanism on top of the plateau sequences however after x 100 m y they are potentially negatively buoyant so if fluids become available to promote tmnsfotmation of the deeper zones to eclogite they may be able to spontaneously subduct

balanced cross section construction from seismic sections in areas of extensional tectonics abstract the application of the technique of balanced section construction initially developed for areas of compressional folding and faulting is reviewed with reference to extensional tectonics a number of examples are discussed where these techniques have been successfully applied in the north sea the interpretation of geoseismic sections is considered to be greatly assisted by careful application of geometrical balance and a consideration of strain even in areas of low crustal extensions the nature of seismic sections however places limitations on the validity of balancing which must be borne in mind with such interpretations and wherever possible the balancing of a geoseismic section should be confirmed by complete depth conversion the rapid testing of the integrity of the geoseismic section by attempting to balance the section at the interpretational phase can eliminate many problems as well as allowing the fullest use to be made of the geophysical information

tectonics of slow spreading mid ocean ridges and consequences of a variable depth to the brittle ductile transition geophysical evidence especially microearthquakes that extend into the upper mantle beneath the inner floor of the mid atlantic and gorda ridges indicates that the axial magma chamber episodically freezes beneath slow spreading ridges freezing of the axial magma chamber will result in a variable thermal structure that has important tectonic consequences most importantly large near axis faults will intersect as the brittle ductile transition deepens causing some of the faults to become locked the topographic effect of fault locking will be a variation in the width of the inner floor from narrow 10 km when a magma chamber is absent the deep microearthquakes also imply that faults at slow spreading ridges extend into the upper mantle the nature of these faults at depth is unknown but the following hypotheses are presented 1 the faults may be planar and pass downward into aseismic ductile shear zones and 2 the faults may sole into a flat detachment fault defining a sharp boundary between brittle faulting and homogeneous ductile flow such low angle normal faults are common in continental extensional domains large scale tilting 50 70 is probably common at slow spreading ridges and implies either listric faulting or rotation of planar faults and fault blocks similar to toppling dominoes calculations of temperatures at the brittle ductile transition are made assuming olivine and diabase rheologies for the mantle and crust respectively the temperature is approximately 800 c when the transition is at 8 km depth and approximately 600 when the transition is at 2 km depth the strength of the lithosphere varies dramatically with the rise and fall of the brittle ductile transition as magma chambers form and subsequently freeze strong lateral temperature gradients will be present when a magma chamber is formed resulting in localization of faulting within thin weak crust above the chamber when the magma chamber freezes lateral temperature gradients will be small and the strength of the lithosphere will be similar over a wide area this results in active faulting occurring over a width of as much as 60 km some ophiolites possibly provide insights to the tectonic processes at slow spreading ridges the entire crustal section of the josephine ophiolite was tilted by approximately 50 prior to deposition of overlying pelagic sediments this tilting probably took place by faulting suggesting that oceanic faults extended into the upper mantle possible oceanic faults have been identified in the josephine ophiolite but their oceanic origin cannot be established beyond doubt

the localised distribution of u and other incompatible elements in spilitic pillow lavas the fission track technique was used not only to determine the u distribution but indirectly to locate the host minerals of other incompatible elements such as p ti y zr and nb in spilitic pillow lavas from sw england the majority of u was introduced early in the alteration process probably due to interaction with sea water at a later stage in the process these elements some previously considered to be relatively immobile during low grade alteration were mobilised and subsequently redeposited in stable secondary phases the hydrothermal fluid responsible for mobility was rich in co2 and h2o carbonate complexes were the most likely mobile species

extracting seismic attenuation coefficients from cross correlations of ambient noise at linear triplets of stations s u m m a r y we develop and apply an algorithm for deriving interstation seismic attenuation from crosscorrelations of ambient noise recorded by linear arrays theoretical results on amplitude decay due to attenuation are used to form a linear least square inversion for interstation qr values of rayleigh surface waves propagating along linear arrays having three or more stations the noise wave field is assumed stationary within each day and the interstation distances should be greater than the employed wavelength the inversion uses differences of logarithmic amplitude decay curves measured at different stations from cross correlation functions within a given frequency band the background attenuation between noise sources and receivers is effectively cancelled with this method the site amplification factors are assumed constant or following similar patterns in the frequency band of interest the inversion scheme is validated with synthetic tests using ambient noise generated by ray theory based calculations with heterogeneous attenuation and homogenous velocity structure the interstation attenuation and phase velocity dispersion curves are inverted from cross correlations of the synthetic data the method is then applied to triplets of stations from the regional southern california seismic network crossing themojave section of the san andreas fault and a dense linear array crossing the southern san jacinto fault zone bootstrap technique is used to derive empirical mean and confidence interval for the obtained inverse q values the results for the regional stations yield qr values around 25 for a frequency band 0 2 0 36 hz the results for the san jacinto fault zone array give qr values of about 6 30 for frequencies in the range 15 25 hz

the lack of equipartitioning in global body wave coda correlation of the coda of large earthquakes can be used to retrieve body waves at teleseismic distances this retrieval depends on waves propagating with equal energy in all directions equipartitioning we carry out a beamforming analysis of body waves at periods of 10 and 40 s recorded at usarray and show that the late coda up to 10 h after the okhotsk earthquake is dominated by waves propagating in the great circle direction late coda waves are not equipartitioned this implies for seismic interferometry that teleseismic body waves can only be extracted from the coda when the earthquake and the receivers are located on a great circle this happens automatically when the employed stations are antipodal or when the autocorrelation of waves is used the use of long period ambient seismic noise relies on the distribution of sources because scattering only marginally randomizes directions this provides insight into recent observations of core phases extracted from seismic interferometry

seismic tomography of the southern california plate boundary region from noise based rayleigh and love waves we use cross correlations of ambient seismic noise between pairs of 158 broadband and short period sensors to investigate velocity structure over the top 5 10 km of the crust in the southern california plate boundary region around the san jacinto fault zone sjfz from the 9 component correlation tensors associated with all station pairs we derive dispersion curves of rayleigh and love wave group velocities the dispersion results are inverted first for rayleigh and love waves group velocity maps on a 1 5 1 5 km2 grid that includes portions of the sjfz the san andreas fault saf and the elsinore fault we then invert these maps to 3d shear wave velocities in the top 7 km of the crust the distributions of the rayleigh and love group velocities exhibit 2 azimuthal anisotropy with fast directions parallel to the main faults and rotations in complex areas the reconstructed 3d shear velocity model reveals complex shallow structures correlated with the main geological units and strong velocity contrasts across various fault sections along with low velocity damage zones and basins the sjfz is marked by a clear velocity contrast with higher v s values on the ne block for the section se of the san jacinto basin and a reversed contrast across the section between the san jacinto basin and the saf velocity contrasts are also observed along the southern parts on the saf and the elsinore fault with a faster southwest block in both cases the region around the salton trough is associated with a significant low velocity zone strong velocity reductions following flower shape with depth are observed extensively around both the sjfz and the saf and are especially prominent in areas of geometrical complexity in particular the area between the sjfz and the saf is associated with an extensive low velocity zone correlated with diffuse seismicity at depth and a similar pattern including correlation with deep diffuse seismicity is observed on a smaller scale in the trifurcation area of the sjfz these results augment local earthquake tomography images that have low resolution in the top few km of the crust and provide important constraints for studies concerned with behavior of earthquake ruptures generation of rock damage and seismic shaking hazard in the region

crustal drift in iceland summary there are indications that tertiary and post tertiary volcanism in iceland has been confined to the present main belt of active volcanism the geological structure of the tertiary lava piles in the east and west of iceland and results of geophysical studies may be explained by invoking an appreciable amount of crustal drift since the beginning of the tertiary the rocks in the extreme east and west of the island may have been carried apart by 400 km or more the crustal drift is believed to result mainly from crustal extension through the injection of dykes the structure of iceland and possibly that of other flood basalt areas is believed to be closely related to the world wide rift system

hybridization between felsic and mafic magmas in calc alkaline granitoids a case study in northern sardinia italy abstract two examples of felsic mafic association resulting from a magma mingling mechanism have been studied in carboniferous calc alkaline granitoids from sardinia using mineralogical and geochemical techniques 1 the centimetric to decimetric magmatic mafic enclaves from the reversely zoned tonalitic santa restituta pluton this type of enclave which is common in calc alkaline granitoids represents blobs of mafic magma incorporated into a silicic host magma 2 the osidda mafic complex about one kilometre in diameter enclosed in the benettuti granodiorite this study intends to compare these two types of felsic mafic association in order 1 to clarify the nature of the interaction processes which occurred between the two magmatic components 2 to test the influence of the degree of fragmentation of the mafic component into the felsic matrix on the intensity of such processes the santa restituta enclaves sre and the osidda mafic complex omc exhibit the same general mineral assemblage plagioclase biotite hornblende quartz this assemblage is similar to that of the corresponding host granitoids however the sre and the omc are characterized by a greater abundance of biotite and hornblende the mineralogical study reveals the presence of two types of crystals the first type corresponds to minerals typical of the mafic or the felsic component in the mafic magma they are represented by remnants of an rich plagioclase by hornblende clots presumably pyroxene relicts and by orthopyroxene observed only in one facies of the omc these crystals represent remnants of phenocrysts present in the mafic component prior to the mingling event in the felsic component the first type of crystals is represented by quartz ocelli which are sometimes incorporated in the mafic magma as xenocrysts surrounded by a reaction rim of biotite and hornblende the second type comprises minerals which are found indiscriminantly in both magmatic components and which formed during the mingling event mingling minerals they include plagioclase an52 35 biotite hornblende quartz mineralogical data indicate that thermal equilibrium occurred between the mafic magma and the felsic matrix that equilibration was reached in the sre is shown by the compositional similarity of the mingling minerals of the enclaves and their host rocks however due to a lesser degree of fragmentation thermal equilibration was not reached in the omc geochemical data however do reveal close relationships between the two magmas which appear therefore to have both been hybridized by mutual chemical interaction a chemical comparison between the sre and the omc shows that in both cases the same qualitative interaction mechanisms operated between the host granitoids and either a voluminous mafic body osidda or a highly fragmented mafic component santa restituta enclaves however the intensity of hybridization is minor in the omc as compared with the sre it is suggested that hybridization of the host granitoids involves 1 mass to mass mixing due to disaggregation and dispersal of the mafic magma in the host granitoid resulting from mechanical stirring during the pluton s genesis from the initial meeting of the two magmas to the pluton s final emplacement 2 loss of certain elements si k rb ba li zr p nb ree which migrated towards the mafic magma through diffusion due to compositional gradients fluid transfer as a consequence the composition of the host granitoids is linked to that of their magmatic enclaves the enclaves with the lowest feo tot mgo ratios are enclosed in the least felsic granitoids and vice versa hybridization of the mafic component involves 1 mechanical transfer of crystals quartz from the host granitoid 2 enrichment in numerous elements migrating from the felsic component this is expressed mineralogically by the crystallization of numerous anhedral phases such as quartz sio2 biotite k rb h2o hornblende h2o apatite p and zircon zr 3 loss of ca and sr by the mafic component the nature of the processes of chemical migration are discussed the importance of the continuous renewal of the contact surface between the two components is emphasized the original compositions of the interacting mafic and granitic components become therefore highly modified this phenomenon can probably be generalized to apply to calc alkaline granitoids as a whole which are in fact characterized by the common occurrence of magma mingling

anelastic earth structure from the coherency of the ambient seismic field 1 cross correlation of the ambient seismic field is now routinely used to measure seismic wave travel times however relatively little attention has been paid to other information that could be extracted from these signals in this paper we demonstrate the relationship between the spatial coherency of the ambient field and the elastodynamic green s function in both time and frequency domains through measurement of the frequency domain coherency as a function of distance we sequentially recover phase velocities and attenuation coefficients from these measurements we generate 1 d shear wave velocity and attenuation models for southern california the ambient field measurements of attenuation and the exceptional path coverage that results from the many possible interstation measurements allow us to extend q estimates over a range of frequencies that has previously been difficult to analyze using earthquake data measurements from paths that cross major sedimentary basins show both lower wave speeds and lower quality factors than other paths as expected our results indicate that there is a wealth of information available in the spatial coherency of the ambient seismic field

accretionary volcanic processes and the crystal structure of iceland abstract the geology of the quaternary axial zones in iceland is dominated by the occurrence of well defined volcanic centres such as krafla 65 40 n 16 40 w marked by the occurrence of a caldera overlying a high level magma chamber the lateral injection of magma from the chamber during active volcanism and crustal extension results in the emplacement of a dyke swarm occasional fissure eruptions and associated normal faulting comparable relations are observable in the older tertiary sections of the lava pile where well defined swarms of basic dykes are focused on tertiary volcanic centres some of which have high level plutonic complexes the gently dipping tertiary lava sequences are characterised by a dip at sea level which is notably greater than the dip of the lavas at higher elevations the features of both the quaternary and tertiary areas are interpreted in terms of a model for crustal generation at the axial zone involving fissure volcanism dyke emplacement and listric faulting rotation of successive lavas along the curved fault surfaces produces the changes in the dips of the flows with elevation observed in the tertiary areas and a broad synclinal structure centred about the spreading axis the hypothesis that listric faulting is important in relation to crustal growth in iceland links that extensional regime with continental rift environments where listric faulting has been recognised as the dominant structural element

biotite chloritization process in hydrothermally altered granites abstract chloritization of biotite in a hydrothermal environment was studied in two granitic rocks of the massif central france four types of transformation were observed 1 mg chlorite growth upon 001 biotite planes in contact with quartz 2 biotite pseudomorphosed by a corrensite residual biotite assemblage 3 corrensite residual biotite pseudomorphosed by a ferromagnesian chlorite and 4 biotite pseudomorphosed by chlorite these transformations induce an expansion of the site of the ferromagnesian minerals which can be observed by the corrosion of neighbouring minerals and fracturation of the rock around the new chlorites open fractures or chloritic veinlets if al is considered as a strictly inert component the reaction biotite chlorite produces a decrease of the ferromagnesian mineral volume of 13 ferry 1979 this is not in agreement with petrographic observations of the rocks studied here therefore writing of a chloritization reaction must take into account a volume increase in this case al does not behave as an inert component but as a mobile one at the scale of the microsystem biotite neighbouring crystals albitization of plagioclase which occurs simultaneously with the chloritization process is the al furnisher in addition fe and mg must be brought into the microsystem during the transformation of biotite into chlorite this explains why the mg mg fe ratio is not the same between biotite chlorite growths and chlorite pseudomorphs because the bulk rock composition is enriched in these components the hydrothermal fluids must contain fe and mg before they flow into the rock chloritization in propylitized granites is not an isochemical process

death valley bright spot a midcrustal magma body in the southern great basin california a previously unrecognized midcrustal magma body may have been detected by cocorp deep seismic reflection profiles in the death valley region of the southern great basin high amplitude relatively broad band reflections at 6 s 15 km are attributed to partially molten material within a subhorizontal intrusion this bright spot extends laterally at least 15 km beneath central death valley a moderately dipping normal fault can be traced from the inferred magma chamber upward to a 690 000 yr old basaltic cinder cone the fault zone is inferred to have been a magma conduit during the formation of the cinder cone vertical variations in crustal reflection character suggest that the death valley magma body may have been emplaced along a zone of decoupling that separates a faulted brittle upper crust from a more ductile and or intruded lower crust the death valley bright spot is similar to reflections recorded by cocorp in 1977 in the rio grande rift where both geophysical and geodetic evidence support the inference of a tabular magma chamber at 20 km depth

the variation of cesium and 37 other elements in the sardinian granite batholith and the significance of cesium for granite petrogenesis a suite of granites from the hercynian batholith of sardinia italy was analysed for cesium and 37 other major and trace elements factor analysis was used to identify inter element associations in this set of data cesium is shown to be closely associated with tin lithium and rubidium and less closely with beryllium and thallium but it shows no correlation with any of the major elements the role of crystal fractionation magma mixing and the process of partial melting in the magmatic source region are examined as possible controls of cs distribution the pattern of element associations revealed by factor analysis eliminates crystal fractionation and magma mixing as the main cause of magmatic variation the variation in cs is considered to be primary in origin i e it originated in the magmatic source region the relationship between cs and other elements was mainly determined by the relative proportions of mica and feldspar entering the melt during anatexis

on the retrieval of attenuation and site amplifications from ambient noise on linear arrays further numerical simulations s u m m a r y while it is clear that ambient noise correlations contain information on seismic attenuation retrieval of that information requires disentangling the influences of site amplification factors and anisotropic noise intensity recent work has argued that recognition that ambient noise intensity is governed by a radiative transfer equation will facilitate that retrieval this sufficiently constrains the noise field to permit amplitudes of noise correlation waveforms to be fit to models of spatially varying attenuation noise intensity and site amplification factors numerical simulations for the case of a uniformly spaced linear array of receivers homogeneous attenuation and wave speed and mild directionality to the noise field were shown earlier to be consistent with the assertion here the numerical simulations are extended to a broader class of systems accurate retrieval is demonstrated using a priori error estimates and weighted least squares fitting attenuations and site factors are retrieved in systems with spatially varying attenuation highly directional noise intensities irregular line arrays and poor signal to noise ratios examination of a variety of systems illustrates some of the range of applicability and limits of the approach

quantifying the effects of nondiffuse noise on ballistic and coda wave amplitude from variances of seismic noise interferometry in southern california we develop a new approach based on the variance of noise cross correlation to characterize the noise source and wave propagation under the influence of a non diffuse noise field based on the rando

surface deformation in volcanic rift zones abstract the principal conduits for magma transport within rift zones of basaltic volcanoes are steeply dipping dikes some of which feed fissure eruptions elastic displacements accompanying a single dike emplacement elevate the flanks of the rift relative to a central depression concomitant normal faulting may transform the depression into a graben thus accentuating the topographic features of the rift if eruption occurs the characteristic ridge trough ridge displacement profile changes to a single ridge centered at the fissure and the erupted lava alters the local topography a well developed rift zone owes its structure and topography to the integrated effects of many magmatic rifting events to investigate this process we compute the elastic displacements and stresses in a homogeneous two dimensional half space driven by a pressurized crack that may breach the surface a derivative graphical method permits one to estimate the three geometric parameters of the dike height inclination and depth to center and the mechanical parameter driving pressure rock stiffness from a smoothly varying displacement profile direct comparison of measured and theoretical profiles may be used to estimate these parameters even if inelastic deformation notably normal faulting creates discontinuities in the profile geological structures open cracks normal faults buckles and thrust faults form because of stresses induced by dike emplacement and fissure eruption theoretical stress states associated with dilation of a pressurized crack are used to interpret the distribution and orientation of these structures and their role in rift formation