three dimensional splay fault geometry and implications for tsunami generation megasplay faults very long thrust faults that rise from the subduction plate boundary megathrust and intersect the sea floor at the landward edge of the accretionary prism are thought to play a role in tsunami genesis we imaged a megasplay thrust system along the nankai trough in three dimensions which allowed us to map the splay fault geometry and its lateral continuity the megasplay is continuous from the main plate interface fault upwards to the sea floor where it cuts older thrust slices of the frontal accretionary prism the thrust geometry and evidence of large scale slumping of surficial sediments show that the fault is active and that the activity has evolved toward the landward direction with time contrary to the usual seaward progression of accretionary thrusts the megasplay fault has progressively steepened substantially increasing the potential for vertical uplift of the sea floor with slip we conclude that slip on the megasplay fault most likely contributed to generating devastating historic tsunamis such as the 1944 moment magnitude 8 1 tonankai event and it is this geometry that makes this margin and others like it particularly prone to tsunami genesis

elevated pore pressure and anomalously low stress in regions of low frequency earthquakes along the nankai trough subduction megathrust 1 recent seismic reflection and ocean bottom seismometer obs studies reveal broad regions of low seismic velocity along the nankai subduction plate boundary megathrust offshore sw japan these low velocity zones lvz s extend 55 km landward from the trench corresponding to depths of 10 km below sea floor here we estimate the in situ pore pressure and stress state within these lvz s by combining p wave velocities obtained from the geophysical surveys with new well constrained empirical relations between p wave velocity porosity and effective mean stress defined by laboratory deformation tests on drill core samples of the incoming oceanic sediment we document excess pore pressures of 17 87 mpa that extend 55 km into the subduction zone indicating that trapped pore fluids support 45 91 of the overburden stress along the base of the upper plate and surrounding major fault zones the resulting effective stresses in the lvz are limited to 1 3 of the values expected for non overpressured conditions these low effective stresses should lead to a mechanically weak and predominantly aseismic plate boundary the region of lowest effective stress coincides with precisely located very low frequency earthquakes providing the first quantitative evidence linking these anomalous slip events to low stress and high pore pressure

stress induced smectite dehydration ramifications for patterns of freshening and fluid expulsion in the n barbados accretionary wedge abstract presented is new experimental evidence that smectites can partially dehydrate from 18 5 a to 15 4 a hydrates when they are subjected to effective mineral framework stresses above 1 3 0 3 mpa we show here that this process can substantially freshen saline pore fluids and impact our understanding of the hydrogeologic processes in convergent margins where smectites are abundant the general anomalous freshening of pore fluids in the n barbados accretionary wedge was previously proposed to relate to the widespread lateral expulsion of fluids derived from mineral dehydration reactions at great depth in contrast our analysis suggests that a significant part of the widespread anomalous freshening relates to stress induced smectite dehydration that occurred during the ocean drilling program odp pore water extraction process clear evidence for long distance lateral flow appears to be limited to localized chloride and isotopic anomalies developed in a 20 m thick locally mineralized region at the top of decollement horizon at site 948 our reinterpretation is consistent with the fluid flow in the decollement zone being 1 highly transient on time scales of several hundreds of years and 2 channeled laterally into heterogeneous finger like flow paths that are apparently not intersected and or sampled by drilling in most regions at the toe of the wedge the incipient stress induced dehydration of smectite may also be buffering in situ fluid pressures in the wedge maintaining the effective stresses at 1 3 mpa

pyrometamorphic processes at the magma hydrothermal system interface of active volcanoes evidence from buchite ejecta of stromboli aeolian islands italy pyrometamorphic ejecta erupted during recent paroxysmal explosions and hydrothermally altered volcanic and subvolcanic rocks from stromboli volcano aeolian islands italy were studied by combined polarizing microscopy electron microprobe scanning electron microscope x ray diffraction transmission electron microscope and whole rock inductively coupled plasma optical emission spectrometry mass spectrometry analysis the pyrometamorphic ejecta are compositionally heterogeneous at the macroand micro scale and are classified as buchites that is glass coupled with a high temperature low pressure modal mineralogy three distinct facies i e cordierite plagioclase mullite plagioclase palisade and tridymite clinopyroxene are recognized among the buchites whose bulk rock chemistry is compatible with aluminousto silica rich protoliths abundant mineral growth e g plagioclase palisades and clinopyroxene coronae occurs at the contact between the ejecta and the crystal rich host shoshonitic basalt which typically coats the pyrometamorphic blocks mineral constraints pseudoporphyritic microstructures plagioclase relict phenocrysts and major and trace element compositions strongly support the origin of the buchite ejecta as hydrothermally altered rocks from thevancori edifice a period of activity spanning 410 kyr which underwent high temperature low pressure contact metamorphism in the uppermost magmatic system of an active island arc volcano such as stromboli volcanic and subvolcanic rocks usually undergo alteration processes induced by acid sulphate hydrothermal systems the circulation of acidic fluids results in leaching of the stromboli rocks in the upper part of the volcano edifice and depending on the ph temperature and exposure time to the hydrothermal fluids production of different alteration facies the hydrothermally altered stromboli rocks show facies consistent with argillic to silicic alteration containing abundant hydrous sulphate and hydroxy sulphate minerals such as the alunite group minerals hexahydrite millosevichite pickeringite and kieserite the hydrothermally altered wall rocks heated by contact with the basaltic magma of the feeder dyke system of stromboli can easily undergo pyrometamorphic processes inducing partial melting and subsolidus crystallization of the volcanic protoliths this results in the development of buchite rocks at the magma hydrothermal system interface

effects of geometry on the seismic wavefield of alpine glaciers passive seismology allows measurement of the structure of glaciers and ice sheets however most techniques used so far in this context are based on horizontally homogeneous media where parameters vary only with depth 1 d approximations which are appropriate only for a subset of glaciers here we analyze seismic noise records from three different types of glaciers plateau valley and avalanching glacier to characterize the influence of the glacier geometry on the seismic wavefield using horizontal to vertical spectral ratios polarization analysis and modal analysis we show that the plateau glacier and the valley glacier can be seen as 1 d whereas the relatively small avalanching glacier shows 3 d effects due to its bed topography and the deep crevasses in principle the techniques proposed here might allow monitoring such crevasses and their depth and thus to constrain a key parameter of avalanching and calving glacier fronts

geochemical and isotopic zoning patterns of plagioclase megacrysts in gabbroic dykes from the gardar province south greenland implications for crystallisation processes in anorthositic magmas chemical and sr isotopic zoning patterns in plagioclase megacrysts from gabbroic dykes in the gardar province can be used to elucidate magma chamber and emplacement processes the megacrysts occur either as single crystals or assembled as anorthosite xenoliths the size of the megacrysts varies from 1 cm to 1 m they consist of a large core with variable zonation an58 39 and a relatively small 600 m normally zoned rim an62 27 the contact between core and rim is sharp and marked by a sharp increase in anorthite content which can reach 11 mol an this gap is interpreted as having formed during dyke emplacement due to a sudden pressure release some of the megacryst cores show a fairly constant composition whereas others exhibit an unusual wavy oscillatory zoning which has not been reported elsewhere to our knowledge the oscillatory zoning has wavelengths of up to 2 500 m and a maximum amplitude of 7 mol an it is interpreted as reflecting movements of the crystals in the magma reservoir the sr isotopic composition of one crystal shows a radiogenic inner core 87sr 86sr i 0 7044 and a less radiogenic outer core 87sr 86sr i 0 7039 0 7036 the lack of a significant change between outer core and rim 87sr 86sr i 0 7037 is consistent with formation of the more an rich rim due to pressure release variations in the core may be related to movements of the crystal and or magma mixing a trace element profile across a megacryst shows a small increase in sr and small decreases in ba and la contents of the recalculated melt composition across the core rim boundary whereas p ce nd and eu remain constant melt compositional changes upon emplacement are therefore considered to be of minor importance constant ratios of incompatible trace elements in the megacryst cores indicate a dominant influence of a lower crustal source on trace element budgets

a lower crustal origin for massif type anorthosites the origin of batholith sized masses of plagioclase rich crustal rocks mainly proterozoic in age has mostly been ascribed to aluminous magmas of mantle derivation here we propose that such masses are derived by partial melting of an aluminous lower continental crust which has developed following extraction of a granitic upper crust by intra crustal melting this segregation of upper and lower crusts occurred principally in the late archaean as the lower crust was depleted in heat producing elements during the initial melting to produce granites an external source of heat is required to produce proterozoic massif type anorthosites we speculate that this heat resulted from the continental crust moving over a mantle hotspot or line plume

acoustics of marine sediment under compaction binary grain size model and viscoelastic extension of biot s theory this paper presents a model of acoustic wave propagation in unconsolidated marine sediment including compaction using a concept of a simplified sediment structure modeled as a binary grain size sphere pack compressional and shear wave velocities and attenuation follow from a combination of biot s model used as the general framework and two viscoelastic extensions resulting in complex grain and frame moduli respectively an effective grain model accounts for the viscoelasticity arising from local fluid flow in expandable clay minerals in clay bearing sediments a viscoelastic contact model describes local fluid flow at the grain contacts porosity density and the structural biot parameters permeability pore size structure factor as a function of pressure follow from the binary model so that the remaining input parameters to the acoustic model consist solely of the mass fractions and the known mechanical properties of each constituent e g carbonates sand clay and expandable clay of the

a low velocity zone with weak reflectivity along the nankai subduction zone three dimensional seismic reflection data reveal the presence of a low seismic velocity zone lvz with weak reflectivity character along the nankai accretionary prism this lvz is intercalated between an upper offscraped layer and a lower underthrusting layer in the outer accretionary wedge wide angle ocean bottom seismograph data also support the presence of the lvz which is estimated to be a maximum of 2 km thick 15 km wide and 120 km long the lvz could be an underthrust package underplated in response to the lateral growth of the nankai accretionary prism underplating of the underthrusting layer beneath the overlying offscraped layer would maintain a critical taper of the accretionary prism so that the offscraped layer can continue to grow seaward the lvz could have elevated fluid pressure leading to rigidity reduction of the entire outer accretionary wedge the rigidity lowered outer wedge containing the lvz may be more easily uplifted and thus eventually foster tsunami generation during a nankai megathrust earthquake if the fluid rich lvz supplies a significant amount of the fluid to the megasplay fault zone at depth it may affect stick slip behavior of the fault

origins of porosity and velocity variations at cascadia accretionary prism at cascadia accretionary prism log based porosities exhibit complex lateral changes in response to variations in cementation horizontal compression and fracturing porosities at the prism toe are lower than in reference sediments whereas porosities landward of the toe are slightly higher than those of reference sediments ideally a porosity velocity relationship can be used to determine two dimensional porosity structure from seismic velocities porosity is the major control on velocity at cascadia but variations in grain framework strength frame bulk modulus cause deformed and undeformed rocks to have quite different velocity porosity relationships within the prism cementation can raise velocities substantially above those for unconsolidated reference sediments of the same porosity also compression induced compaction and fracturing may affect this velocity porosity transform because these factors vary both within and between prisms velocity porosity transforms are local not universal

elevated fluid pressure and extreme mechanical weakness of a plate boundary thrust nankai trough subduction zone pore fluid pressure is a key parameter governing both the shear strength of faults and the conditions for seismic and tsunamigenic slip on subduction zone megathrusts however quantitative constraints on this parameter based on in situ data in these or any faults have proven elusive using seismic interval velocities derived from a three dimensional seismic reflection survey we compute porosity fluid pressure and effective stress at the plate interface in the nankai trough subduction zone offshore southwestern japan to 20 km down the fault dip using well constrained locally calibrated empirical relationships between velocity porosity and effective stress we show that the fault and immediately subjacent footwall are nearly undrained implying that the subduction megathrust slips under a shear stress of

two contrasting styles of interaction between basic magmas and continental crust in the british tertiary volcanic province some of the magmas that were extruded to form the 59 ma early plateau forming basalt dominated floods in the british tertiary volcanic province mixed with small amounts of sialic melt during their uprise through the continental crust while others underwent concomitant fractional crystallization and crustal assimilation magma batches of the first group originated in the uppermost asthenosphere and mostly ponded at the moho where they crystallized fractionally to form a basalt benmoreite suite the major element compositions of members of this series show that they underwent negligible further fractional crystallization between the moho and the surface nevertheless they paused long enough during their uprise to dissolve their high pressure phenocrysts and in many cases to mix with small amounts of acid melt from lower crustal granulite facies archaean lewisian leucogneisses basalts and tholeiitic andesites of the second group outcrop locally at the base of the lava piles in mull and skye their major element compositions show that they equilibrated within the upper third of the crust under conditions approximating to anhydrous 1 atm cotectic equilibria most of these lavas are in sw mull where proterozoic moine metasediments form the uppermost crust the major and trace element and isotopic compositions of the sw mull basal lavas show that they assimilated substantial amounts of moine metasediments progressively as they fractionated within the upper crust pb isotope data reveal that before their final upper crust evolution some of the sw mull basal lavas had already mixed with small amounts of lower crust acid melts

the petrogenesis of massif anorthosites a nd and sr isotopic investigation of the proterozoic of rogaland vest agder sw norway sm nd and rb sr isotopic analyses of charnockitic migmatite augen gneiss anorthosite leuconorite and two acid plutons from the rogaland and vest agder districts of southwest norway constrain their crustal residence ages origin and evolution the charnockitic migmatites which are a major component of the metamorphic basement complex represent the oldest and largest episode of accretion in which new crust was derived 1 5 1 9 ga ago from a mantle source of depleted nd isotopic composition the basement complex was intruded by a number of large anorthositic to granitic plutons during and after the sveconorwegian orogenic period samples from the ca 1050 ma old synorogenic haland anorthosite leuconorite massif exhibit substantial variation of initial nd of 2 1 to 4 4 at an anorthosite locality and 0 5 to 2 3 at a leuconorite locality but display significant variation of initial 87sr 86sr ratio only between the localities anorthosite mean 0 70369 leuconorite mean 0 70560 a model is proposed whereby the anorthosite and leuconorite were derived by major crustal contamination of and fractional crystallization from a picritic magma derived from isotopically depleted mantle two younger acid intrusions the 950 ma old lyngdal granodiorite and the 930 ma old farsund charnockite both have initial sr and nd isotope ratios consistent with massive contamination of depleted mantle derived magma by old continental crustal material

effects of diagenesis and clays on compressional velocities in rocks experimental results at ultrasonic frequencies in brine or water saturated samples cut perpendicular to bedding demonstrate that compressional velocities vary linearly with porosity and volume fraction clay in detrital silicate rocks characterized by pores with low aspect ratios p wave velocity is more sensitive to porosity than clay content obeying the empirically derived expression vp 2 4c 8 6 5 8 at 800 bars confining pressure and 400 bars pore pressure where the units of vp are kilometers per second is the volume fraction pores and c is the volume fraction clay deviations from this equation are less than 2 with the exception of the high pore aspect ratio st peter sandstone which has a compressional velocity that is 17 higher than the predicted value the equation is insensitive to the chemical compostion of the dominant clay mineral and apparently insensitive to the location of the clay grains with respect to the mineral framework e g in free pore space or in contact zones between mineral grains of lower compressibilities

clay mineral diagenesis and quartz cementation in mudstones the effects of smectite to illite reaction on rock properties abstract the late cretaceous to early tertiary sequence of the voring and more basins from the norwegian sea has been examined with respect to mineralogy based on 319 cutting samples from five wells a clear relationship between mineralogy and well log data is demonstrated a significant change with respect to velocity porosity and density occurs within the depth interval corresponding to 80 90 c at shallow depths temperatures

waveform tomography imaging of a megasplay fault system in the seismogenic nankai subduction zone abstract we apply frequency domain waveform tomography to form quantitative high resolution p wave velocity images of a megasplay fault system within the central nankai subduction zone offshore of southwest japan using controlled source ocean bottom seismometer obs data originally acquired in 2004 the waveform tomography method exploits recorded seismic waveforms beyond their first arrivals and thus achieves a much higher resolution of the order of a wavelength than that of conventional traveltime tomography methods frequency domain waveform tomography facilitates a multi scale approach to stabilize the inversion in which initial traveltime tomography results are sequentially improved on by first fitting low frequency components of the seismic records starting at 2 25 hz higher frequency components up to 8 5 hz are then introduced progressively our final waveform tomography image allows velocity anomalies as small as 700 m horizontally and 350 m vertically to be discerned and interpreted as confirmed by checkerboard modeling tests the improved explanatory power of the final images is verified by observing that synthetic waveforms calculated from the final results yield much better fit to the observed waveforms than those estimated from the original traveltime tomography image apparent lithological boundaries from waveform tomography agree well with corresponding reflections on seismic migration images providing further confidence in the validity of the results the megasplay fault is evident on the final waveform tomography image as a sharp velocity discontinuity delineating the upper surface of a velocity reduction of nearly 1 km s with respect to the regional 1d velocity trend the megasplay fault can be traced continuously throughout the entire image from a nearly horizontal section at the landward extent moving seaward through to a steeper angle penetrating the old accretionary prisms with several additional splays appearing to branch in the shallow subsurface the location of the low velocity zones imaged by our waveform tomography method coincides with two previously identified low velocity zones the image reveals a low velocity zone that is continuous from deeper to shallower portions of the subsurface suggesting that pore fluids may be transported from the inner wedge to the transition zone and to the surface through fluid conduits associated with the megasplay fault system

evidence of crustal contamination of mafic rocks associated with rapakivi rocks an example from the nordingra complex central sweden gabbro and leucogabbro are volumetrically important rocks in the nordingra rapakivi complex east central sweden plagioclase ortho and clinopyroxenes and olivine dominate the gab bro perthitic orthoclase and quartz are interstitial in relation to the major minerals the present work is based on 232 major element and a large number of trace element analyses together with 15 whole rock sm nd isotope analyses of the nordingra gabbroic rocks end t values are negative 1 1 to 3 2 the most negative values come from the gabbro most rocks are enriched in iron some extremely enriched none represent primitive mantle melts the range of mg numbers is the same in the gabbro and the leucogabbro plots of the ni content vs the mg number are scattered but there is a positive correlation between these two parameters the primary mantle normalized ratios between similar trace elements are normally strongly different from one values larger as well as smaller than one are found for the same ratio in different rocks the rare earth elements are only weakly fractionated with small eu anomalies negative for the gabbros and positive for the leucogabbros the primary magma of the nordingra gabbro anorthosite is thought to have been derived from a mildly depleted mantle source variations in the degree of partial melting of a reasonably homogeneous enriched mantle do not explain the observed chemical evolution crystal differentiation can account for some geochemical features especially the fe enrichment crustal contamination is required by other characteristics as for example the negative end t values and the irregular and sometimes high primary mantle normal ized incompatible trace element ratios al rich relic material from the formation of the rapakivi gran ite melt is another source of assimilation most probably contaminants are heterogeneous including undepleted crust represented for example by early svecofennian and archaean granitoids depleted crust restitic after rapakivi magma extraction and to some degree the associated rapakivi magma itself significant parts of this crust should be archaean in age

porosity corrections for smectite rich sediments impact on studies of compaction fluid generation and tectonic history porosity is a fundamental parameter that must be correctly determined in order to relate physical property hydrologic and chemical flux studies to natural systems traditional porosity determinations generated from physical property or seismic data can greatly overestimate the true porosity of sediments in which hydrated minerals such as smectite are abundant to produce a true porosity distribution such data must be corrected to account for the h 2 o residing in smectite interlayers which can make up to 25 of the total hydrated mineral mass such h 2 o is easily removed from the mineral by oven drying and or exposure to low humidities standard physical property measurements can be corrected provided the weight percent smectite in the sediment is known and the interlayer h 2 o content of the mineral can be estimated we illustrate the significant consequences of this correction by comparing profiles of reported and corrected porosities for smectite rich barbados abyssal plain and accretionary wedge sediments from ocean drilling program leg 110 sites 671 and 672

tectonic signatures in centimeter scale velocity porosity relationships of costa rica convergent margin sediments 1 the costa rica convergent margin investigated during ocean drilling program leg 170 offers a unique opportunity to compare the tectonic effects of rapid subduction on incoming oceanic sediments to their laterally equivalent underthrust counterparts and to terrestrially derived wedge materials elevated pressure laboratory measurements of ultrasonic compressional and shear wave velocity and porosity are used to examine the importance of tectonic lithologic and diagenetic controls on physical and elastic properties of sediments in these three key tectonic domains depositional and stress path histories of the three domains for example can be distinguished by 1 trends of in situ velocity porosity and derived measurements correspondence and 2 the mechanical response of representative materials to isotropic consolidation a compressional wave velocity porosity model critical for the application of seismic imaging to margin wide physical property and mass balance estimates is developed from the laboratory measurements and shown to be consistent with the information derived from lwd bulk density and migrated seismic reflection data this consistency of the velocity porosity model over the large range of both frequency and length measurement scales is a key result supporting the assertion that core and borehole physical property measurements can be extrapolated to larger domains finally dewatering and overpressure effects critical factors in subduction zone and fault process dynamics and increasingly common multiphase converted wave imaging targets are discussed in terms of laboratory estimated in situ compressional and shear wave velocity relationships

the loch scridain xenolithic sill complex isle of mull scotland fractional crystallization assimilation magma mixing and crustal anatexis in subvolcanic conduits

porosity formation factor and porosity velocity relationships in barbados prism ocean drilling program leg 171a collected logging while drilling lwd data to investigate the porosity and velocity structure of barbados accretionary complex porosity and velocity measurements were needed for interpretation of prism dynamics however the lwd tool string did not measure velocity and previous velocity data from barbados prism are scarce and generally of low quality furthermore most density based porosities are subject to errors associated with variations in smectite content to determine porosities more accurately we use smectite corrected density based porosities to calibrate a porosity formation factor ff transform then calculate porosities from resistivity logs we used cation exchange capacity cec measurements and lwd logs to evaluate the possibility that resistivity is affected by clay conduction the cec data warn of potential clay conduction especially in smectite rich zones but lwd data indicate that clay conduction is minor in these high porosity sediments instead tortuosity is the secondary control of ff after porosity by comparing resistivity based porosities to velocities from vertical seismic profiles we determine a porosity velocity transform applicable to barbados we then use this transform to calculate velocity logs from resistivity based porosity logs

a new velocity model for clay sand mixtu res1 none of the standard porosity velocity models e g the time average equation raymer s equations is satisfactory for interpreting well logging data over a broad depth range clays in the section are the usual source of the difficulty through the bias and scatter that they introduce into the relationship between porosity and p wave transit time because clays are composed of fine sheet like particles they normally form pores with much smaller aspect ratios than those associated with sand grains this difference in pore geometry provides the key to obtaining more consistent resistivity and sonic log interpretations a velocity model for clay sand mixtures has been developed in terms of the kuster and toksoz effective medium and gassmann theories in this model the total pore space is assumed to consist of two parts 1 pores associated with sand grains and 2 pores associated with clays including bound water the essential feature of the model is the assumption that the geometry of pores associated with sand grains is significantly different from that associated with clays because of this porosity in shales affects elastic compliance differently from porosity in sand stones the predictive power of the model is demonstrated by the agreement between its predictions and laboratory measurements and by its ability to predict sonic logs from other logs over large depth intervals where formations vary from unconsolidated to consolidated sandstones and shales

the spinel and quartz associations in high grade xenoliths from tallante s e spain and their potential use in geothermometry and barometry remarkable spinel quartz associations are observed in some xenoliths found in the basaltic rocks from tallante the main primary parageneses are quartz plagioclase sillimanite spinel garnet ilmenite graphite quartz plagioclase garnet orthopyroxene spinel ilmenite

lower crustal cumulate nodules in proterozoic dikes of the nain complex evidence for the origin of proterozoic anorthosites

pyrometamorphic aureoles of cretaceous sandstones and shales by cenozoic basic intrusions ne brazil petrograhic textural chemical and experimental approaches abstract in this paper we present the case study of thermal aureoles developed in cretaceous sedimentary rocks from the potiguar basin ne brazil nearby shallow cenozoic mafic intrusions the study integrates the field and petrologic study of the metamorphic aureole with experimental work the pyrometamorphic aureole is discontinuous and less than one hundred meters wide along the contact with the intrusions sandstones siltstones and shales were transformed into light and dark buchites the light buchite has acicular clinoenstatite and tridymite as well as microphenocrysts of sanidine sekaninaite and anorthite within a gray to brown sio2 and k2o rich and al2o3 and feo poor rhyolitic glass the dark buchite is richer in feo and al2o3 and has pyrometamorphic al magnetite hercynite and fe mullite buchites derived from shales have a cryptocrystalline to vitreous groundmass and macroscopically resemble tachylites a series of low pressure and high temperature experiments were conducted at 3 kbar and 1000 1200 c on a piston cylinder apparatus using sandstone and shale starting materials sandwiched with olivine basalt the experimental results indicated that melting occurred at approximately 1150 c followed by relatively slow cooling until approximately 1000 c and then by quenching this multidisciplinary approach suggested that the sedimentary units were submitted to very high temperatures upon contact with the intrusions and this outcome is corroborated by the mineralogy and textures observed in the natural rocks

geomechanical and ultrasonic characterization of a norwegian sea shale anisotropy of velocity in shaly overburden is known to cause significant problems for geophysical interpretation including depth conversion and fluid identification in addition mechanical and dynamic elastic shale behavior is not well understood because few tests have been performed on well preserved samples multiple stage triaxial tests were performed upon horizontal core plugs of a shale from the norwegian sea with a view to evaluating rock strength and the evolution of ultrasonic response during rock deformation in addition standard rock physical properties were characterized as well as composition the shale microfabric is seen to be strongly laminated with alternating thick clay rich laminae and thin silt rich laminae occasional microfractures are also noted parallel to these laminations the shale has low friction coefficient and cohesive strength and shows anisotropy of these parameters when the maximum principal stress is oriented parallel to and at 45 to the microfabric the orientation of the maximum principal stress parallel to the intrinsic fabric and microcracks was seen to significantly impact on velocity normal to the fabric as stress parallel to the fabric increased s wave anisotropy was significantly affected by the increasing stress anisotropy stress orientation with respect to fabric orientation was therefore found to be an important control on the degree of anisotropy of dynamic elastic properties in this shale

critical porosity a key to relating physical properties to porosity in rocks discovering accurate relations between porosity and seismic wave velocities in porous rocks has been an important topic of rock physics for decades such relations if they actually exist are critical when seismic and or sonic data are to be used to infer porosity and porosity related properties e g permeability strength saturation in situ these inferences became especially important in recent years with the rapid development of seismic and sonic methods which are applied to the characterization of heterogeneous reservoirs and recovery monitoring

velocity porosity relationships for slope apron and accreted sediments in the nankai trough seismogenic zone experiment integrated ocean drilling program expedition 315 site c0001 in this study we focused on the porosity and compressional wave velocity of marine sediments to examine the physical properties of the slope apron and the accreted sediments this approach allows us to identify characteristic variations between sediments being deposited onto the active prism and those deposited on the oceanic plate and then carried into the prism during subduction for this purpose we conducted ultrasonic compressional wave velocity measurements on the obtained core samples with pore pressure control site c0001 in the nankai trough seismogenic zone experiment transect of the integrated ocean drilling program is located in the hanging wall of the midslope megasplay thrust fault in the nankai subduction zone offshore of the kii peninsula sw japan penetrating an unconformity at 200 m depth between slope apron sediments and the underlying accreted sediments we used samples from site c0001 compressional wave velocity from laboratory measurements ranges from 1 6 to 2 0 km s at hydrostatic pore pressure conditions estimated from sample depth the compressional wave velocity porosity relationship for the slope apron sediments shows a slope almost parallel to the slope for global empirical relationships in contrast the velocity porosity relationship for the accreted sediments shows a slightly steeper slope than that of the slope apron sediments at 0 55 of porosity this higher slope in the velocity porosity relationship is found to be characteristic of the accreted sediments textural analysis was also conducted to examine the relationship between microstructural texture and acoustic properties images from micro x ray ct indicated a homogeneous and well sorted distribution of small pores both in shallow and in deeper sections other mechanisms such as lithology clay fraction and abnormal fluid pressure were found to be insufficient to explain the higher velocity for accreted sediments the higher slope in velocity porosity relationship for accreted sediments can be explained by weak cementation critical porosity or differences in loading history

hydrogeology and mechanics of subduction zone forearcs fluid flow and pore pressure at subduction zones fluid flow pore pressure and tectonic processes are tightly interconnected excess pore pressure is driven by tectonic loading and fluids released by mineral dehydration and it has profound effects on fault and earthquake mechanics through its control on effective stress the egress of these overpressured fluids which is in part governed by the presence of permeable fault zones is a primary mechanism of volatile and solute transport to the oceans recent field measurements new constraints gained from laboratory studies and numerical modeling efforts have led to a greatly improved understanding of these coupled processes here we summarize the current state of knowledge of fluid flow and pore pressure in subduction forearcs and focus on recent advances that have quantified permeability architecture fluxes the nature and timing of transience and pressure distribution thus providing new insights into the connections between fluid metamorphic mechanical and fault slip proc

river valley pluton ontario a late archean early proterozoic anorthositic intrusion in the grenville province abstract the river valley pluton is a ca 100 km2 body of anorthositic and gabbroic rocks located about 50 km northeast of sudbury ontario the pluton is situated entirely within the grenville province but its western margin is a series of imbricate thrust faults associated with the grenville front tectonic zone it is dominated by coarse leuconorite and leucogabbro with lesser anorthosite gabbro and rare ultramafics igneous textured rocks are abundant and consist of plagioclase an60 70 charged with fe ti oxide inclusions low ca pyroxene orthopyroxene and or inverted pigeonite and augite the most unfractionated rocks are minor olivine gabbros with fo70 80 a variety of deformed and recrystallized equivalents of the igneous textured rocks is also present and these are composed largely of calcic plagioclase and hornblende ten samples including both igneous and deformed lithologies give a pb pb whole rock isochron of 2560 155ma which is our best estimate of the time of primary crystallization the river valley pluton is thus the oldest anorthositic intrusive yet reported from the grenville province but is more calcic and augitic than typical massifs and lacks their characteristic fe ti oxide ore deposits the river valley body may be more akin to similar gabbro anorthosite bodies situated at the boundary between the archean superior province and huronian supracrustal belt of the southern province west of the grenville front an sm nd isochron from 3 igneous textured leucogabbros and an augite mineral separate gives 2377 68 ma implying slight disturbance of the sm nd whole rock mineral system during later metamorphism the rb sr system has been substantially disturbed giving an age of 2185 105 ma which is similar to internal pb pb isochron ages of 2165 130 ma and 2100 35 ma for two igneous textured rocks it is uncertain whether these ages correspond to a discrete event at this time or represent a partial resetting of the rb sr and pb pb systems from a younger event such as the grenvillian orogeny of ca 1 0 ga none of the isotopic systems we investigated however gives an age near 1 0 ga suggesting that neither the river valley pluton nor the immediately surrounding gneisses were strongly affected by metamorphism associated with the grenvillian orogeny initial isotopic ratios for the river valley pluton correspond to single stage model parameters of 8 06 nd 0 to 3 and isr 0 7015 to 0 7021 collectively these suggest either an enriched mantle source or crustal contamination of a mantle derived magma the crustal component involved must have been older and more radiogenic than the majority of rocks exposed at the surface in the nearby superior province

effects of porosity and clay content on wave velocities in sandstones the ultrasonic compressional vp and shear vs velocities and first arrival peak amplitude ap were measured as functions of differential pressure to 50 mpa and to a state of saturation on 75 different sandstone samples with porosities ranging from 2 to 30 percent and volume clay content c ranging from 0 to 50 percent respectively both vp and vs were found to correlate linearly with porosity and clay content in shaly sandstones at confining pressure of 40 mpa and pore pressure of 1 0 mpa the best least squares fits to the velocity data are vp km s 5 59 6 93 2 18c and vs km s 3 52 4 91 1 89c deviations from these equations are less than 3 percent and 5 percent for vp and vs respectively the velocities of clean sandstones are significantly higher than those predicted by the above linear fits about 7 percent for vp and 11 percent for vs which indicates that a very small amount of clay 1 or a few percent of volume fraction significantly reduces the elastic moduli of sandstones for shaly

a partisan review of proterozoic anorthosites most anorthosites of the massif type crystallized in the episode 1 7 1 2 gyr with a pronounced peak of the age distribution near 1 4 gyr they were emplaced anorogenically at depths as shallow as 7 km where the ambient temperature of country rocks was probably less than 250 c depths of emplacement may have been as great as 25 km or more in rare cases the greater depths of equilibration estimated from granulite facies metamorphism may be incorrectly interpreted as emplacement depths but in any case they are demonstrably not required or characteristic of anorthosite emplacement penetrative deformation and metamorphism of anorthosites are post emplacement accidents of the local geologic history and are not directly caused by the presence of anorthosites granitic rocks mangerite charnockite suite associated with anorthosite are in general later or contemporaneous products of crustal anatexis with chemical and isotopic signatures distinct from the anorthosites and their residua such granitic rocks should not therefore be summed with the anorthositic rocks to obtain bulk compositions the magmas that produced most anorthosites were dry as shown by high temperature mineralogy and anhydrous mineral assemblages in contact aureoles residua from their crystallization are ferrodiorites to ferrosyenites typical of closed system fractionation these residua were locally and frequently ejected into contemporaneously molten granite where they formed pillows and cooled rapidly the overall chemistry of anorthosites and residua is broadly tholeiitic and consistent with derivation from the mantle olivine bearing magmas locally ranged from leucotroctolite anorthosite to later but coexisting picrite or melatroctolite in the same pluton confirming a wide spectrum of magma types a signal feature of troctolitic and noritic magmas is their low augite content implying high content of spinel component large anorthosite complexes such as nain and harp lake consist of many plutons representing repeated injections of separate magma batches with varying chemistry the abundant true anorthosites richer in plagioclase than magmas cosaturated with a mafic phase must represent plagioclase enrichment by either mechanical or chemical processes or both the role of kinetics in nucleation and solidification of such rocks may be centrally important it is proposed that hyperfeldspathic plagioclase supersaturated liquids were generated by quasi isothermal extraction of mafic minerals from tholeiitic magma enroute to and at the site of emplacement and that such a kinetic process was uniquely permitted in an environment of aborted continental rifting anorthositic rocks may have much to say about the episodic versus continuous geochemical evolution of the earth s mantle

the origin of proterozoic massif type anorthosites evidence from interactions between crustal xenoliths and basaltic magma plagioclase rich reaction zones occur around numerous aluminous crustal xenoliths within a suite of palaeogene sub volcanic basic sheets on the isle of mull nw scotland the xenoliths consist of a glassy core containing mullite needles generated from the melting of pelitic source rocks thick plagioclase mantles grew at the interface between the aluminous liquid and the enclosing basaltic magma and provide a high level analogue for the petrogenesis of proterozoic massif type anorthosites similar interactions between mantle derived basic magmas ponded at the base of the crust and relatively al rich lower crustal lithologies would result in the precipitation of large volumes of plagioclase anorthosite massifs were then emplaced at higher crustal levels as crystal rich mushes within relatively juvenile proterozoic crust the model negates the need to crystallize large volumes of mafic minerals prior to the production of plagioclase saturated liquids and also accounts for the significant influence of crustal sources on the isotopic signatures of all members of the anorthosite suite

geochemistry of the nain massif anorthosite labrador magma diversity in five intrusions abstract the petrography and major and trace element concentrations of the anorthositic bird lake massif blm susie brook slab sbs lister massif lm port man vers run pmr and kikkertavak area kik in the nain plutonic suite nps labrador delineate the mineralogical and composition ranges of these large intrusions from these a variety of magmas and staging histories can be inferred the blm and sbs are mainly noritic anorthosites of the western region exposed along tikkoatokhakh bay tik tilting and stretching deformation distinguish sbs from blm but the two units show no mineralogical or chemical differences the kik and pmr intrusions are mainly troctolitic to noritic anorthosites of the eastern region and they contain more mafic components than the tik bodies chemically all the anorthositic rocks are high in ba sr and the ratio k rb and low in zr rb and rb sr the three plutonic bodies blm sbs and lm along tik are similar and can be clearly distinguished from kik and pmr intrusions by element concentrations and ratios diagrams of element pairs show that each intrusion or group has its own evolutionary trend and variable style indicating that they represent independent magma batches rather than fractionally related volumes of the same magma ree patterns show light ree enrichment and heavy ree depletion and strong positive eu anomalies correlated with cumulus plagioclase in chemical comparison with adjacent plutons one pmr chilled leucotroctolite after subtraction of 18 cumulus plagioclase is similar to the kiglapait magma ki one melatroctolite in kik is close to the comb layered melatroctolite of the snowflake zone in the hettasch intrusion hi and the average leucotroctolite and leuconorite in kik are similar to the leucotroctolite unit and the upper leuconorite respectively at paul island pi therefore the magmas from pmr and kik are similar to those of wellknown troctolitic bodies and their feldspar rich cumulates kik differs from pmr in having somewhat higher an and xmg values all these lines of evidence show that at least three types of magma existed in the study area sodic noritic magma accumulating plagioclase in tik troctolitic magma in kik and a magma similar to but more evolved than kik in pmr the methods used also illustrate the feasibility of characterizing magma compositions from diverse types of cumulates regional differences in modal and chemical composition occur in the nps noritic compositions with pale plagioclase are located in the western and southern regions and troctolitic compositions with darker plagioclase are located in the eastern region a reasonably accurate boundary can now be drawn between the two regions which differ in the nature of their transport from the mantle in comparison with a primitive mantle composition high ba pb k sr ti and low rb nb zr in the nain anorthositic rocks are distinctive these anomalies and the isotopic results of other investigators are consistent with mantle source enrichment followed by variable contamination during magma ponding at the base of the depleted crust

oscillatory sr isotopic signature in plagioclase megacrysts from the damiao anorthosite complex north china implication for petrogenesis of massif type anorthosite abstract formation of proterozoic massif type anorthosites is known to be related to polybaric process involving early high pressure crystallization of plagioclase and high al orthopyroxene megacrysts at mantle crust boundary followed by emplacement of plagioclase dominated mushes to shallow level crust therefore the plagioclase megacrysts record important information about the magmatic sources and crystallization process of anorthosites the 1 74 ga damiao complex north china comprises 90 vol anorthosites and leuconorites containing abundant plagioclase megacrysts associated with minor high al orthopyroxene megacrysts haoms the plagioclase megacrysts are generally euhedral to subhedral mostly 1 to 30 cm in diameter and some of them contain very fine lamellae of orthoclase and undefined fe ti rich minerals 1 5 m the haoms occur as subhedral grains or as angular grains with an intercumulus relationship to the plagioclase megacrysts they contain abundant thin regular lamellae of exsolved plagioclase 15 20 vol indicative of originally high al features originally 6 0 7 3 wt al2o3 based on the al in orthopyroxene geobarometry the haoms and associated plagioclase megacrysts are constrained to be crystallized together at pressures of 9 4 11 2 kbar 33 36 km indicative of their crystallization at lower crust depths or crust mantle boundary in contrast orthopyroxene grains from late differentiation phases such as oxide apatite gabbronorites do not contain plagioclase lamellae and have much lower al2o3 contents 1 5 to 1 7 wt indicating final crystallization at

origin of mantle rapakivi feldspars experimental evidence of a dissolution and diffusion controlled mechanism experiments designed to simulate the dissolution of alkali feldspar during magma mixing produced plagioclase mantles that are texturally and compositionally similar to those in some hybrid volcanic rocks in hydrous dacite melt 69 sio2 at 0 8 gpa 850 c orthoclase or93 and sanidine or30 partially dissolved and were mantled by sodic plagioclase an25 30 although plagioclase nucleated epitaxially as a thin shell on the alkali feldspar surface near the time of initial resorption plagioclase subsequently grew inward mostly in the form of parallel blades toaard the receding dissolution surface orthoclase dissolved at a rate approximately proportional to the square root of run duration indicating diffusional control plagioclase grew inward within a static boundary zone of melt that formed between the original crystal dacite interface and the dissolution surface during orthoclase dissolution this boundary zone rapidly and simultancously gained na by diffusion from dacite and lost k by diffusion into dacite ca diffused more slowly into this zone from which non feldspar species were mostly excluded plagioclase was stable where sufficient ca had diffused in that the boundary zone melt intersected the plagioclase saturation liquidus plagioclase subsequently grew toward the receding dissolution surface as the ca compositional gradient and hence the site of plagioclase saturation stepped inward crystallization of plagioclase in the form of parallel blades allowed continued diffusive exchange of melt components between the dissolution surface and the host melt bladed growth also served to maintain at blade tips proximity of plagioclase to the dissolution surface thereby apparently preserving locally a thin zone of low variance melt in natural systems mantling of alkali feldspar by plagioclase will occur in a similar manner when a p t or x are changed to induce alkali feldspar dissolution b sufficient ca is available in the host melt to drive by diffusion boundary zone melt compositions to plagioclase saturation and c temperatures are low enough to stabilize sodic plagioclase and to maintain a coherent boundary zone these reqjirements are satisfied in volcanic systems when alkali feldspar is juxtaposed during mixing with hybrid melts of dacitic composition mantled feldspars in some intrusive systems i e rapakivi granites may form by a similar dissolution and diffusion controlled mechanism textural evidence of a similar origin may be obscurred in intrusive rocks however by products of late stage magmatic and subsolidus processes

velocity and inferred porosity model of the oregon accretionary prism from multichannel seismic reflection data implications on sediment dewatering and overpressure a two dimensional model of seismic velocity derived from multichannel seismic data collected off oregon in 1989 shows that as sediments are carried from cascadia basin into the accretionary prism there are measurable changes in velocity depth profiles in the seaward most area of the basin where no thrust faults are observed there is a landward and downward increase of velocity in the sedimentary section we attribute the velocity increase in the basin to a reduction of porosity resulting from consolidation and cementation accompanied by diffusive flow of pore water driven by lateral tectonic as well as gravitational stress near the base of the slope there is an area of incipient thrusting the protothrust zone where protothrusts sole out into a protodecollement synthetic seismogram modeling of the reverse polarity reflection from the protodecollement shows a 100 m thick layer with a slightly lower velocity relative to the sediments above it above the protodecollement velocity continues to increase landward we suggest that in this area the diffusive flow of pore water out of the sediment is augmented above the protodecollement by fault focused flow below the protodecollement a reversal in velocity may be due to an increase in porosity resulting from overpressuring of pore fluid trapped by reduction of the permeability of the sediment above the protodecollement farther landward where thrusting has formed a fault bend fold velocity values are lower in the accreted section of sediments relative to the velocity at a comparable subbottom depth in the protothrust zone the decrease in velocity is a result of microfracturing of the highly consolidated sediments accompanying uplift and folding and reflects the increasing role of fracturing and faulting in the control of dewatering of the sediments

acoustic and mechanical properties of nankai accretionary prism core samples we studied undeformed sediment and accreted strata recently recovered by ocean drilling program integrated ocean drilling program odp iodp drilling in nankai trough convergent margin to unravel the changes in physical properties from initial deposition to incipient deformation we have derived acoustic vp and mechanical uniaxial poroelastic compliance compaction amplitude properties of samples from various drill sites along the muroto odp 1173 and kii transects iodp c0001 c0002 c0006 and c0007 from isotropic loading tests where confining and pore pressure were independently applied we quantified the dependence of vp on both effective peff and confining pc pressure which can be used to correct atmospheric pressure measurements of vp experimental vp obtained on core samples extrapolated to in situ conditions are slightly higher than logging derived velocities which can be attributed either to velocity dispersion or to the effect of large scale faults and weak zones on waves with longer wavelength in the high porosity 30 60 tested sediments velocities are controlled at first order by porosity and not by lithology which is in agreement with our static measurements of drained framework incompressibility much smaller than fluid incompressibility rather than framework incompressibility shear modulus is probably the second order control on vp accounting for most of the difference between actual vp and the prediction by wood s 1941 suspension model we also quantified the mechanical state of nankai samples in terms of anisotropy diagenesis and consolidation both acoustic and mechanical parameters reveal similar values in vertical and horizontal directions attesting to the very low anisotropy of the tested material when considering the porous samples of the upper shikoku basin sediments site 1173 as examples of diagenetically cemented material several mechanical and acoustic attributes appeared as reliable experimental indicators of the presence of intergrain cementation we also detected incipient cementation in samples from iodp site c0001 accretionary prism unit in terms of consolidation we distinguished two classes of material response shallow deformable samples and deep hardly deformable ones based on the amount of compaction upon application of a peff large with respect to the inferred in situ value with a transition that might be related to a critical porosity

velocity porosity relationships for water saturated siliciclastic sediments seeking a global empirical relationship between compressional wave velocity and porosity for siliciclastic sediments we have brought together an extensive suite of both new and published log and core based data we undertook a detailed statistical analysis of ocean drilling program data from amazon fan to examine variables affecting compressional velocity in shallow unconsolidated sediments we identify three dominant variables porosity shale fraction and consolidation history and present two empirically determined boundary curves one for normally consolidated sediments and a second for highly consolidated environments e g accretionary prisms these two empirical relationships predict the compressional velocity of siliciclastic sedimentary rocks with water filled pores as a function of porosity and clay content for the full range of observed porosities velocities of siliciclastic sedimentary rocks decrease rapidly with both increasing porosity and increasing clay content at fractional porosities higher than about 0 4 fluid dominates the elastic properties and velocity exhibits a subtle dependence on porosity remarkably the amazon fan data show that clay content has no direct influence on velocity at high porosities both clay content and sorting do indirectly affect velocity through their control of porosity burial affects velocity not only by compaction related porosity decrease but also by pressure induced increase of intergrain coupling because of the sensitivity of velocity to consolidation history particularly at intermediate fractional porosities of about 0 30 0 40 no single velocity porosity relationship can apply to all high porosity sediments the two proposed relationships fit the majority of published and new data they are applicable however only for normally pressured in situ conditions and water filled pores

velocity porosity relationships in smectite rich sediments shikoku basin japan 1 at the nankai trough japan smectite rich sediments of the shikoku basin are both underthrust beneath and frontally accreted to the outer accretionary wedge to understand the changes that occur in the physical properties of sediments as they are underthrust or incorporated into the accretionary wedge it is necessary to characterize those physical properties outboard of the deformation front one key relationship to constrain is between the compressional wave velocity vp and porosity in order to estimate pore fluid pressure and determine the strength of fault rocks at depth here we investigate how the type of clay minerals and proportions of the different clays may affect the velocity porosity relationship with particular emphasis on the abundance of hydrous smectitic clays using data from iodp sites c0011 and c0012 in the shikoku basin we demonstrate that when the core based porosity is corrected for the abundance of smectite the resultant velocity porosity relationship does not fit previously established transforms therefore we propose a new empirical relationship for the smectite rich sediments of the shikoku basin and caution against the indiscriminate use of global and or pre existing models in smectite rich formations

rare earth element geochemistry and strontium isotopic composition of a massif type anorthositic charnockitic body the hidra massif rogaland sw norway abstract the hidra massif rogaland complex sw norway mainly consists of plagioclase cumulates anorthosites and leuconorites which grade progressively into a fine grained 200 m locally porphyritic jotunitic rock towards the contact with the granulite facies gneisses the massif is cross cut by thin 10 cm up to 1 m charnockitic dykes the petrographical and geochemical evolution of the hidra massif can be explained by fractional crystallization of a jotunitic parental magma major and trace element constraints indicate that mafic phases are underabundant in the exposed levels of the massif most likely as a result of plagioclase flotation in the early stages of solidification partitioning into the cumulate minerals mainly plagioclase and orthopyroxene governs the trace element contents of the leuconoritic adcumulates however the trace element geochemistry of the apparently early formed anorthositic orthocumulates largely depends upon the amount of a trapped intercumulus liquid on the basis of trace element abundances high ree rb th u negative eu anomalies the silicic charnockitic dykes can be considered as the residual liquid of the anorthositic fractionation trend the higher initial 87 sr 86 sr ratios 0 7086 0 0006 vs 0 7055 0 0004 for the plagioclase cumulates and jotunites point to contamination of the charnockitic liquids by surrounding gneissic material

a deep strong reflector in the nankai accretionary wedge from multichannel seismic data implications for underplating and interseismic shear stress release 1 we present the results of structural and stratigraphic interpretations for the multichannel seismic profiles to reveal the structure of the nankai accretionary wedge off shikoku island on the basis of reflection characteristics we identify three major seismic units that correspond to a unit consisting of both oligocene miocene accretionary prism and the sedimentary cover unit a a unit of underthrust miocene pliocene hemipelagic sediments unit b and a unit of subducting pre miocene oceanic crustal rocks unit c according to relative strength of the topmost reflector of unit b the nankai accretionary wedge can be divided into three different structural zones along the cross strike direction apparent decollement reflector zone low amplitude reflector lar zone and deep strong reflector dsr zone despite the velocity uncertainty involved in the depth conversion and therefore thickness estimation error the decollement step down and the possible duplex structures in the lar and dsr zones support that the landward thickness variation of unit b is caused by the structural thickening such as the underplating process structural features and reverse polarity suggest that the dsr as an upper interface of the underplated layer unit b corresponds to a shear plane or a fault zone with high pore fluid pressures we found that most of the dsr was observed in a region which has not suffered from the 1946 coseismic dislocation even though it was locked during the interseismic period the dsr as a shear plane or a fault zone constrains a regional variety of the coseismic dislocation around the updip limit of the nankai seismogenic zone considering all of the dsr characteristics we propose a hypothesis for the dsr s development and role the dsr may play an important role as a possible releaser of the shear stress energy stored at the plate boundary around the updip limit of the nankai seismogenic zone a good correlation between the theoretical vertical displacement and seafloor topographic feature support the possible slip along the dsr as a shear plane

experimental mechanical compaction of clay mineral aggregates changes in physical properties of mudstones during burial dry and brine saturated clay aggregates ranging from pure smectite to pure kaolinite were compacted in the laboratory experiments were conducted by increasing vertical effective stress up to 50 mpa to study the changes in physical properties of mudstones during burial the results suggest that the physical properties porosity density acoustic velocity etc of mudstones vary greatly with increasing effective stress clay mineralogy and fluid content kaolinite aggregates are much more compressible than those composed of smectite brine saturated clay mixtures are much more compressible than dry clay mixtures brine may soften and lubricate the clay matrix compared to dry clays resulting in higher compressibility in the brine saturated state the lesser degree of compaction of dry smectite compared to dry kaolinite aggregates can be explained by the differences in grain size as kaolinitic clays have much larger grains than smectitic clays the extremely fine grained nature of smectite implies that the imposed vertical stress is distributed over a very large number of grain contacts so that the force per contact area is very low in smectite compared to that in coarse grained kaolinite at 20 mpa effective stress corresponding to about 2 km burial depth with hydrostatic pore pressure brine saturated pure kaolinite compacted to 20 porosity while pure smectite retained 41 porosity brinesaturated clay mixtures show higher vp and lower vs than dry clay mixtures a pronounced difference in vs was observed among the brinesaturated clay mixtures the lowest vs as a function of vertical effective stress was found for pure smectite for a given porosity value smectitic clays have higher velocities and elastic moduli than the kaolinitic clays the vp vs ratio is significantly higher in smectite than in kaolinite aggregates treating mudstones as a uniform class of rocks introduces significant errors in estimates of physical properties which are strongly affected by the clay mineralogy grain size the amount of other minerals present and fluid content our results have implications for well log interpretation and mudstone and shale property determinations from seismic data at shallow burial depth o 2k m 801c above depths where significant chemical compaction takes place r 2007 elsevier ltd all rights reserved

relationships among compressional wave attenuation porosity clay content and permeability in sandstones anelastic attenuation is the process by which rocks convert compressional waves into heat and thereby modify the amplitude and phase of the waves understanding the causes of compressional wave attenuation is important in the acquisition processing and interpretation of high resolution seismic data and in deducing the physical properties of rocks from seismic data we have measured the attenuation coefficients of compressional waves in 42 sandstones at a confining pressure of 40 mpa equivalent to a depth of burial of about 1 5 km in a frequency range from 0 5 to 1 5 mhz the compressional wave measurements were made using a pulse echo method in which the sample 5 cm diameter 1 8 cm to 3 5 cm long was sandwiched between perspex lucite buffer rods inside the high pressure rig the attenuation of the sample was estimated from the logarithmic spectral ratio of the signals corrected for beam spreading reflected from the top and base of the sample the results show that for these samples compressio

compressional wave velocity and attenuation at ultrasonic and sonic frequencies in near surface sedimentary rocks laboratory ultrasonic measurements of compressional wave velocity and attenuation were made as a function of effective pressure on samples of limestone sandstone and siltstone taken from a shallow borehole test site the results indicate that the sandstones are pervaded by grain contact microcracks which dramatically affect their compressional wave attenuations clean sandstone shows a compressional wave quality factor q sub p of 24 2 at 5 mpa effective pressure close to the estimated in situ burial pressure and a q sub p of 83 29 at 60 mpa the q sub p of limestones and siltstones at the site show negligible and small increases with pressure in the laboratory respectively the strong pressure dependence of q sub p in clean sandstone was used to infer the presence of in situ microcracks sediment velocities measured in the laboratory at about 1 mhz were compared with those from the full waveform sonic log at about 10 khz implies that they must also be highly attenuating over a significant part of the frequency range 10 khz to 1 mhz to account for the magnitude of the observed velocity dispersion assuming the laboratory q sub p values measured at 5 mpa remain constant down to 10 khzmore predicts the observed dispersion quite well furthermore the sonic log velocities of sandstones limestones and siltstones after normalizing each lithology for porosity and clay content were found to reflect the same pressure depth trends observed in the laboratory the results provide evidence for the existence of in situ microcracks in near surface sediments less

depositional architecture provenance and tectonic eustatic modulation of miocene submarine fans in the shikoku basin results from nankai trough seismogenic zone experiment seismostratigraphy coring and logging while drilling during integrated ocean drilling program expeditions 319 322 and 333 sites c0011 c0012 show three miocene submarine fans in the ne shikoku basin with broadly coeval deposits at ocean drilling program site 1177 and deep sea drilling project site 297 nw shikoku basin the sediment dispersal patterns have major implications for paleogeographies at that time the oldest finer grained kyushu fan has sheet like geometry quartz rich flows were fed mostly from an ancestral landmass in the east china sea during prolonged hemipelagic mud deposition at c0011 c0012 similar to 12 2 to 9 1 ma sand supply continued at sites 1177 and 297 sand delivery to much of the shikoku basin halted during a phase of sinistral strike slip to oblique plate motion after which the daiichi zenisu fan similar to 9 1 to 8 0 ma was fed by submarine channels the youngest fan daini zenisu similar to 8 0 to 7 6 ma has sheet like geometry with thick bedded coarse grained pumiceous sandstones the pumice fragments were fed from a mixed provenance that included the collision zone of the izu bonin and honshu arcs the shift from channelized to sheet like flows was favored by renewal of relatively rapid northward subduction which accentuated the trench as a bathymetric depression increased sand supply appears to correlate with long term eustatic lowstands of sea level the stratigraphic position and 3 d geometry of the sandbodies have important implications for subduction related processes including the potential for focused fluid flow and fluid overpressures above and below the plate boundary fault in sheet like sands pathways for fluid flow have greater horizontal permeability compared with those in channel sands

velocity anisotropy in shales a petrophysical study using ultrasonic velocity and anisotropy measurements on a variety of shales with different clay and kerogen content clay mineralogy and porosity at a wide range of effective pressure we find that elastic anisotropy of shales increases substantially with compaction the effect is attributed to both porosity reduction and smectite to illite transformation with diagenesis a means of kerogen content mapping using velocity versus porosity crossplot for shales is shown matrix anisotropy of shales dramatically increases with kerogen reaching the maximum values of about 0 4 at total organic carbon toc 15 20 a strong chemical softening effect was found in shales containing even minor amounts of swelling smectite clay when saturated with aqueous solution this effect results in a significant p wave anisotropy reduction as compared to dry and oil saturated shales since mature black shales are normally oil wet this effect can only have a local significance restricted to the wellbore wall accurate measurements of phase velocities including velocities at a 45 direction to the bedding plane allow us to immediately calculate elastic stiffnesses and anisotropic parameters intrinsic high pressure properties of shales display an e 0 relation introduction of the bedding parallel microcracks in overpressured shales results in a decrease when fully fluid saturated and a increase when partially gas saturated with a characteristic effect on the shape of the p wave velocity surface at small angles of incidence filtering the contribution of the intrinsic anisotropy of shales it is possible to estimate the pore fluid phase microcrack density and aspect ratio parameters using seismic anisotropy measurements

complex interaction of aluminous metasedimentary xenoliths and siliceous magma an example from mt amiata central italy aluminous silica deficient metasedimentary xenoliths in siliceous lavas of mt amiata have preserved composite zoning patterns indicative for complex processes of magma rock interaction petrographic observations and small scale mineralogical and chemical differences between up to five distinct zones including the core and envelope of lava provide evidence that quartz poor muscovite biotite schists are considered to be the most likely parent rocks and it is believed that release of volatiles from decomposing micas played a significant role in the high temperature metamorphic evolution of the xenoliths and their interaction with the magma the conditions favourable for assimilation were enhanced by injection of mafic magma into the magma chamber although this concurrent operation of magma mixing precludes a quantitative estimate of contamination from the wall rocks which was probably of minor importance the present example indicates that dry acid magma may potentially become more mafic by interaction with partially melted hydrous rocks

monzonorites from rogaland southwest norway a series of rocks coeval but not comagmatic with massif type anorthosites duchesne j c wilmart e demaiffe d and hertogen j 1989 monzonorites from rogaland southwest norway a series of rocks coeval but not comagmatic with massif type anorthosites precambrian res 45 111 128 monzonorites members of the anorthositic suite of rocks are usually considered as residual after the formation of massif type anorthosites in rogaland s w norway they occur as large dykes intrusions and chilled margins to differentiated massifs emplaced during and soon after the main anorthosite massifs in granulite facies conditions ti p and fe are enriched in monzonorites and steadily decrease towards quartz mangerites the feo feo mgo ratios varying slightly during alkali enrichment bowen trend trace element spidergrams show deep troughs in rb th nb ta sr zr hf and ti the ree slightly decrease in the evolution with la yb s ratios about 9 and neutral to positive eu anomalies several occurrences however show highly contrasted trace element features sr isotope ratios st show a wide interval of variation 0 704 0 710 between the various dykes and intrusions without any correlation with the elements indicative of crustal contamination in the tellnes main dyke evolution towards acidic rocks occurs without contamination and variation in isr fractional crystallization with subtraction of apatite bearing noritic cumulates can account for the major and trace element evolution from monzonorite to quartz mangerite but is unable to explain the large differences between occurrences it is concluded that monzonorites cannot be comagmatic though coeval with massif type anorthosites they result from the crystallization of distinct magma batches possibly formed through partial melting of basic to intermediate rocks in the lower crust

sr nd and pb isotopes in proterozoic intrusives astride the grenville front in labrador implications for crustal contamination and basement mapping abstract we report sr nd and pb isotopic compositions of mid proterozoic anorthosites and related rocks 1 45 1 65 ga and of younger olivine diabase dikes 1 4 ga from two complexes on either side of the grenville front in labrador anorthositic or diabasic samples from the mealy mountains grenville province and harp lake nain churchill provinces complexes have very similar major minor and trace element compositions but distinctly different isotopic signatures all mealy mountains samples have isr 0 7025 0 7033 end 0 6 to 5 6 and pb isotopic compositions consistent with derivation from a mantle source depleted with respect to nd sm and rb sr pb isotopic compositions for the mealy mountains samples are slightly more radiogenic than model mantle compositions all harp lake samples have isr 0 7032 0 7066 end 0 3 to 4 4 and variable but generally unradiogenic 207pb 204pb and 206pb 204pb compared to model mantle suggesting mixing between a mantle derived component and a u depleted crustal contaminant crustal contaminants are probably a variety of archean high grade quartzofeldspathic gneisses with low u pb ratios and include a component that must be isotopically similar to the early archean 3 6 ga uivak gneisses of labrador or the amitsoq gneisses of west greenland this would imply that the ancient gneiss complex of coastal labrador and greenland is larger than indicated by present surface exposure and may extend in the subsurface as far west as the labrador trough if harp lake and mealy mountains samples were subjected to the same degree of contamination as suggested by their chemical similarities then the mealy contaminants must be much younger probably early or middle proterozoic in age the labrador segment of the grenville front therefore appears to coincide with the southern margin of the archean north atlantic craton and may represent a pre mid proterozoic suture

compressional velocity and porosity in sand clay mixtures laboratory measurements of porosity and compressional velocity were conducted on unconsolidated brine saturated clean ottawa sand pure kaolinite and their mixtures at various confining pressures a peak in p velocity versus clay content in unconsolidated sand clay mixtures at 40 percent clay by weight was found the peak in velocity is 20 30 percent higher than for either pure clay or clean sand a minimum in porosity versus clay content at 20 40 percent clay by weight is also observed such behavior is explained using a micro geometrical model for mixtures of sand and clay in which two classes of sediments are considered 1 sands and shaley sands in which clay is dispersed in the pore space of load bearing sand and thus reduces porosity and increases the elastic moduli of the pore filling material and 2 shales and sandy shales in which sand grains are dispersed in a clay matrix for these sediments the model reproduces the extrema in velocity and porosity and accounts for much of the scatter in