diffusion obstacles and opportunities in petrochronology many of the approaches in petrochronology are rooted in the assumption of equilibrium diffusion is an expression of disequilibrium the movement of mass in response to chemical potential gradients and isotopes in response to isotopic gradients it is extremely important that we be aware of how the effects of diffusion can place obstacles across our path towards petrochronologic enlightenment conversely the effects of diffusion also provide opportunities for understanding rates processes and conditions experienced by rocks the enormity of the field does not permit us to provide a comprehensive review of either the mathematics of diffusion or quantitative data that have been obtained relevant to the interpretation of diffusive processes in rocks and minerals many resources cover these topics including rimg volume 72 diffusion in minerals and melts zhang and cherniak 2010 and several textbooks crank 1975 glicksman 2000 particularly relevant to the discussion of petrochronology are summaries of the theory and controls on diffusion brady and cherniak 2010 zhang 2010 as well as diffusion rates in feldspar cherniak 2010a accessory minerals cherniak 2010b garnet ganguly 2010 mica pyroxene and amphibole cherniak and dimanov 2010 and melts zhang and ni 2010 zhang et al 2010 rather than duplicate that material our goal is to explore the obstacles and opportunities presented by the effects of diffusion as they inform the rates of petrologic processes to achieve this goal we emphasize key principles and illustrative examples quantitative interpretation of the effects of diffusion assumes predictability of numerous factors that may affect chemical or isotopic transport including temperature initial and boundary conditions water and oxygen fugacities activities of other components multiple mechanisms of diffusion and crystal chemistry coupling of the substitution of elements into different crystallographic sites additionally the extraction of meaningful ages durations of events and temperatures requires

diffusion closure temperature and age of a mineral with arbitrary extent of diffusion theoretical formulation and applications the commonly used expression of the closure temperature tc of a diffusing species in a mineral as derived by m h dodson contrib mineral petrol 40 1973 259 264 is applicable only to systems which have undergone sufficient diffusion so that even the composition at the center of individual grains is significantly removed from that established at the onset of cooling we have extended dodson s formulation to include cases with arbitrarily small amount of diffusion and applied it to calculate tc and age profiles which would develop in single crystals of different geometries these results permit evaluation of the extent of resetting of mineral age and of ion exchange geothermometers during cooling the measured age profile of a mineral can also be used to constrain its cooling rate these applications have been illustrated for the cases of garnet biotite fe mg exchange geothermometer and the cooling age and closure temperatures of the sm nd and lu hf decay systems in garnet

a window into the lower crust trace element systematics and the occurrence of inclusions intergrowths in granulite facies rutile abstract rutile occurs as an accessory mineral in many high temperature metamorphic assemblages and has the potential to identify and investigate uht metamorphic terranes whilst the use of zr in rutile geothermometry to identify ultrahigh temperature terranes is appealing its application to granulites can be difficult owing to diffusional resetting of zr concentrations during cooling and decompression in order to provide constraints on p t conditions and trace element systematics during ultrahigh temperature metamorphism metamorphic rutile in granulites from the archean napier complex and the palaeozoic rauer group antarctica have been investigated for trace element composition and mineral inclusions intergrowths textural observations and zr in rutile temperatures show that unlike the large proportion of rutiles grains in the matrix rutile grains that are shielded by phases with low zr diffusivities e g orthopyroxene and or are in chemical isolation from zircon have the potential to retain zr concentrations that correspond to ultrahigh temperatures principal component analysis reveals that v cr nb mo ta and w are significantly enriched in rutile from archean and proterozoic ultrahigh temperature terranes high concentrations of elements such as cr and v indicate a spinel rich source demonstrating the effect of protolith bulk chemical composition on rutile trace element signatures rutile is shown to contain inclusions and intergrowths of aluminium silicate quartz corundum and feldspar including the first reported occurrence of prograde kyanite which provides direct evidence that the napier complex experienced a typical clockwise p t evolution

forced folding and fracturing induced by differential compaction during post depositional inflation of sandbodies insights from numerical modelling abstract three series of numerical models based on the discrete element method were constructed to simulate forced folding and fracturing triggered by postdepositional inflation of fluidised sandbody the models consist of numerous particles that have relatively low to high interparticle bonds to represent overburden sediments with a relatively low to high cohesion and cohesionless frictionless particles to represent fluidised sands the modelling results show that normal faults were produced due to the upward inflation of sand domes and the resulting flexed overburden when the cohesion of the host sediments is low opening voids were created as a result of strata collapse when the intrusion related normal faults terminated within the host sediments as blind faults conical fractures that are aligned along sandbody margins were produced which consist of closed lower segments with a reverse displacement and opening middle upper segments with a minor to zero shear component forced folds were generated in most models with a moderate to high cohesion resulting in differential compaction in the overlying sediments that can account for the formation of fold related fractures which are either shear hybrid or pure tensile depending on their structural positions the amplitude of forced folds is closely associated with both cohesion and thickness of sediments in the overburden whilst fold wavelength is mainly controlled by sediment cohesion based on the modelling results three types of preferential sites for the storage of injected sands were suggested which are believed to be instructive for subsurface sandbody detection and prediction this study demonstrates that differential compaction induced by sand inflation can play an important role in overburden folding and fracturing

the transformation of sediment into rock insights from iodp site u1352 canterbury basin new zealand abstract at integrated ocean drilling program iodp expedition 317 site u1352 east of the south island new zealand we continuously cored a 1927 m thick holocene to eocene section where we can uniquely document downhole changes in induration and lithification in siliciclastic to calcareous fine grained sediment using a wide range of petrological physical property and geochemical data sets porosity decreases from around 50 at the surface to 5 10 at the base of the deepest hole with a corresponding increase in density from 2 to 2 5 g cm 3 there are progressive bulk mineral changes with depth including an increase in carbonate and decrease in quartz and clay content grain compaction is first seen in thin section at 347 m below sea floor and intensifies downhole pressure solution chemical compaction begins at 380 m and is common below 1440 m with stylolite development below 1600 m and sediment injection features below 1680 m porewater geochemistry and petrographic observations document two active zones of cementation one shallow eogenetic down to 50 m as evidenced by micritic nodules and pore water geochemistry driven by methane oxidation by sulfate and another burial related cementation zone mesogenetic starting at 300 m a transitional zone occurs between 50 and 300 m our results quantify downhole diagenetic changes and verify depth estimates for these processes inferred from outcrop studies and provide an actualistic example of cementation and compaction trends in a slope setting

experimental studies of the fluidization of layered sediments and the formation of fluid escape structures experiments demonstrate that fluid escape structures can be produced as a result of unstable fluidization behaviour where a lower base layer of granular material is inhibited from fluidizing by the presence of an overlying non fluidizing top layer before the base layer can fluidize the weight of the overlying material must be balanced and this is accomplished by base layer material pressing against the bottom surface of the confining top layer forming a static layer this static layer allows the top layer to lift away from the base layer which is then free to fluidize a water filled crack forms below the static layer and as this grows instability causes the static layer and top layer to bend and conical voids to form below the antiformal sections rupture occurs at the apex of the water void allowing the underlying water and fluidizing material to burst out through the top layer the fluidized base layer material then flows through the rupture until all of this material except that in the static layer is deposited above the previously overlying layer and a stable fluidization system results the top layer material is bent upwards around the rupture and the resulting pillar type escape structure is preserved if flow then ceases the vigour of the burst out is greatest when the base layer material has a grain size 15 of the top layer material if the base layer grain size is less than 8 of the top layer then base layer material will pass through the top layer pore spaces without forming an escape structure if cohesive material is present escape structures form when a layer of fine grained cohesive material overlies a layer of cohesionless material at low flow rates small pipes with scattered angular bends pierce the top layer and base layer material passes through them the base layer material is ejected on to the top layer and builds up around the mouth of each pipe to form constructional structures sand volcanoes this is in contrast to the cohesionless experiments where the weight of material being deposited on the top layer caused an ejecta filled depression to form around the rupture if flow then ceases both the pipes and the sand volcanoes are preserved at high flow rates where the base layer fluidizes the top cohesive layer becomes fragmented small fragments circulate within the fluidizing base layer and are preserved as floating clasts large fragments sink to the bottom of the fluidizing base layer erosion of the bottom surface of these larger fragments causes this surface to become convex downward the experimentally derived structures are similar to pillar type structures observed in the field and the processes described can be used to investigate the development of these structures fluidization experiments also demonstrate the genesis of dish structures and the cohesive behaviour can be applied to the deformation of these structures after initial formation

large scale hydrocarbon driven sand injection in the paleogene of the north sea the detailed study of many diagenetic carbonates concretions cemented bioturbation burrows etc and dykes of a large scale sandstone injection complex which are preserved in a cored early eocene section recovered from the south viking graben north sea provides evidence for the dyke emplacement by gas driven sand injection and coeval methane seepage the morphology chemistry of fluid inclusions isotopic signature d 13 c as low as 35x and petrographic characteristics of the diagenetic carbonates reveal gradual carbonate precipitation with a contribution of carbon derived from methane oxidation stratigraphic and cross cutting relationships reveal that sand injection post dates the formation of the diagenetic carbonates and therefore the beginning of hydrocarbon migration fluorescing fluid inclusions carbonate cement isotopic signature d 13 c as low as 27x and petrographic observations of the injected sandstones indicate the persistence of hydrocarbons including methane after the injection process gas chromatography of fluid inclusions confirms the presence of methane in both diagenetic carbonates and injected sandstones carbonate cements we suggest that gas influx in the eocene deep water sandstones increased pore fluid pressures during early burial and decreased the grain framework stability inducing liquefaction and sand injection gas involvement in sand injection has been widely invoked to explain the large scale injection complexes recently recognised in the paleogene of the north sea but had previously never been proven large scale injection structures and hydrocarbon seepage appear linked in several localities with obvious great economic significance d 2005 elsevier b v all rights reserved

identification of calanco a badland landform in the northern apennines italy calanco plural calanchi is a term widely used in the northern apennines italy to define a type of badland formed in clayey bedrock however no precise geomorphological definition of calanco has been established and a variety of map symbols are used to indicate the presence of calanco landforms with the aim of developing an improved approach to identifying calanchi a group of experienced surveyors identified 24 catchments with calanco characteristics among 67 catchments located between bologna and faenza in the northern apennines the morphology of each catchment was classified using traditional quantitative geomorphic approaches including fieldwork map interpretation hypsometric curve construction and computation of the annual sediment yield consideration of the parameters produced by these approaches indicated that none was capable of representing the presence of calanchi unequivocally and the basins were grouped into five classes on the basis of number and type of calanco criteria that they met a characteristic of calanchi that is evident on topographic maps is crenulation of the contour lines and in this study a new topographic parameter was developed to represent the degree of contour crenulation this parameter lo lf is defined as the ratio of the actual length of a contour line lo to the length of the same line smoothed by an algorithm based on a moving average lf calculated values of lo lf ranged from 1 05 to 1 38 to test whether high values of the contour crenulation parameter were associated with calanchi lo lf values were added to other criteria for the five classes of catchment class 1 catchments consisting of 14 of the 24 calanchi catchments identified in the field displayed all of the criteria defining calanchi and were characterized by the highest values of lo lf mean value 1 27 0 15 it is proposed therefore that the contour crenulation ratio lo lf may be useful in identifying the calanco landform copyright 2000 john wiley sons ltd

tracking the prograde p t path of precambrian eclogite using ti in quartz and zr in rutile geothermobarometry a fe ti rich garnet clinopyroxene and quartz eclogite sample from the 1 0 ga sveconorwegian orogen sw sweden contains abundant quartz rutile and zircon in distinct micro textural sites garnet core garnet rim and matrix constituting an ideal case for investigation of the behavior of zr in rutile and ti in quartz at high pressure and temperature a p t path peaking at 16 5 19 kbar and 850 900 c has been constrained independently for the same rock by pseudosection modelling input pressures from this model were used for trace element geothermometry of each garnet micro textural domain trace element thermo baro metry based on in situ secondary ion mass spectrometry analyses of ti contents in quartz and zr contents in rutile yields p t estimates of progressive crystallization of quartz and rutile along the prograde metamorphic path for inclusions in the garnet cores zr in rutile geothermometry yields 700 715 c and ti in quartz 620 640 c at 7 kbar for inclusions in the garnet rims temperature estimates are 760 790 c zr in rutile and 740 920 c ti in quartz at 12 18 kbar finally matrix rutile records 775 800 c and locally 900 c and quartz records temperatures up to 900 c at 18 kbar ti in quartz estimates for the metamorphic peak inclusions in the garnet rims and matrix conform to the pseudosection but appear too low for the early prograde stage garnet cores possibly due to lack of equilibrium at t 700 c the pseudosection shows that rutile was produced by continuous ilmenite breakdown during the early stages of prograde metamorphism a reaction that was completed at 730 c rutile grains in the garnet rims and the matrix grew subsequently larger by recrystallization of previously produced rutile however recrystallized rutile does not predominantly record peak temperatures but instead yield 745 840 c between 12 and 18 kbar in the pseudosection this temperature range broadly coincides with a stage during which ti bearing hornblende was consumed and clinopyroxene produced i e dehydration the zr contents thus appear to reflect the last stage of efficient rutile recrystallization catalysed by fluids released by the dehydration of hornblende preceding the metamorphic peak concurrently combination of the isopleths for ti content in quartz and zr content in rutile i e independent from pseudosection modelling yields pressure and temperature conditions in almost perfect agreement with the p t path as deduced from the pseudosection the variation in ti concentration in quartz is small regardless of crystal size and the ti in quartz geothermometer provides both precise and accurate peak temperatures of 875 920 c without a significant diffusional reequilibration the lack of significant ti diffusion in quartz is consistent with an inferred short residence time at high temperature this study illustrates that zr in rutile and ti in quartz geothermobarometry can robustly constrain prograde p t conditions and yield further insights into recrystallization processes at high temperature the combination of these methods and integration of the results with pseudosection modelling is a versatile tool for investigating the petrologic history of high grade rocks less

factors underlying piping in the basilicata region southern italy abstract piping tunnelling erosion is a widely spread process in the plio pleistocene marine clays of the basilicata region in southern italy the pipes are often closely concentrated along the surface drainage networks at different depths with a tunnel length and a diameter varying from just a few centimetres to some metres the formation and evolution of pipes in the badlands can be explained through 1 geo structural characteristics of the clay 2 material properties such as a high exchangeable sodium percentage 3 favourable climatic conditions and 4 hydraulic gradient along the path controlled by the gully or ravine bottom that is acting as a local drain the exposure and the extension of joints at the surface and in the bedrock along the slope are the main factors required for development of the pipes the absence of the piping erosion on the slopes where a reasonably thick layer of the soil material covers the open joints shows that although certain material properties and climatic conditions play an important role they are not sufficient to develop extensive piping erosion in the area

geomorphic knobs of candor chasma mars new mars reconnaissance orbiter data and comparisons to terrestrial analogs high resolution imaging science experiment hirise imagery and digital elevation models of the candor chasma region of valles marineris mars reveal prominent and distinctive positive relief knobs amidst light toned layers three classifications of knobs types 1 2 and 3 are distinguished from a combination of hirise and thermal emission imaging system themis images based on physical expressions geometries spatial relationships and spectral data from compact reconnaissance imaging spectrometer for mars crism type 1 knobs are abundant concentrated topographically resistant features with their highest frequency in west candor which have consistent stratigraphic correlations of the peak altitude height these type 1 knobs could be erosional remnants of a simple dissected terrain possibly derived from a more continuous resistant capping layer of pre existing material diagenetically altered through recrystallization or cementation types 2 and 3 knobs are not linked to a single stratigraphic layer and are generally solitary to isolated with variable heights type 3 are the largest knobs at nearly an order of magnitude larger than type 1 knobs the variable sizes and occasional pits on the tops of type 2 and 3 knobs suggest a different origin possibly related to more developed erosion preferential cementation or textural differences from sediment water injection or intrusion or from a buried impact crater enhanced color hirise images show a brown coloration of the knob peak crests that is attributable to processing and photometric effects crism data do not show any detectable spectral differences between the knobs and the host rock layers other than albedo these intriguing knobs hold important clues to deducing relative rock properties timing of events and weathering conditions of mars history

interpreting zirconium in rutile thermometric results at first sight experimental results and observations on rocks suggest that the zr content in rutile where equilibrated with quartz and zircon should be a useful thermometer for metamorphic rocks however diffusion data for zr in rutile imply that thermometry should not for plausible rates of cooling give the high temperatures commonly observed in high grade metamorphic rocks it is suggested here that such observations can be accounted for by high t diffusive closure of si in rutile causing the interior of rutile grains to become insensitive to the thermometer equilibrium well above the temperature of zr diffusive closure paired with comparatively slow grain boundary diffusion and problematic zircon nucleation this allows for cases of zr retention in rutile through temperatures where zr is still diffusively mobile within rutile grains other observations that may be accounted for in this context are large inter grain ranges of rutile zr contents uncorrelated with rutile grain size and flat zr profiles across individual rutile grains counter to what would be expected from diffusive closure a consequence is that it is unlikely that zr in rutile thermometry will be useful for estimating rock cooling rates

thermobarometric constraints on burial and exhumation of 2 billion year old eclogites and their metapelitic hosts abstract one of the first appearances of eclogite facies mineral assemblages in the geological record occurs in the c 2000 ma palaeoproterozoic usagaran belt in central tanzania where the extended margin of the tanzanian craton is interpreted to have been subducted mafic rocks are interpreted to have contained the mineral assemblage garnet omphacite rutile quartz amphibole this high pressure assemblage has been overprinted by a secondary mineral assemblage containing clinopyroxene plagioclase hornblende ilmenite orthopyroxene mineral equilibria forward modelling indicates that the eclogite facies assemblages reached minimum peak pressure temperature p t conditions of 17 kbar and 700 c inclusions in garnet document a prograde p t history consistent with burial through upper amphibolite facies conditions and possible partial melting petrological and compositional evidence from garnet suggests that following peak metamorphism the eclogite facies rocks were heated while stalled at approximate peak pressures temperature estimates derived from zr concentrations in interpreted texturally retrograde rutile support a near isothermal post peak p t evolution for the eclogite facies rocks an evolution that terminates at retrograde p t conditions of approximately 7 6 8 2 kbar and 680 790 c the relict eclogite domains form part of a larger assemblage with enclosing migmatitic metapelitic lithologies the isimani suite the metapelitic gneisses contain garnet kyanite biotite staurolite hornblende plagioclase muscovite rutile quartz and preserve minimal evidence of a high pressure history conceivably due to post peak mineralogical recrystallisation p t modelling inclusion assemblages and compositional zonation patterns in porphyroblastic garnet suggests the metapelitic gneisses similarly to the relict eclogites experienced burial to minimum peak pressures of approximately 16 5 17 kbar compositional zoning patterns in eclogitic garnet suggest the isimani system was buried reached peak metamorphic conditions and was subsequently exhumed within a timeframe of up to 20 myr a tectonic regime involving crustal thickening and subduction followed by extensional exhumation of the entire isimani suite is our preferred model for the development of the c 2000 ma usagaran belt

petrology and geochronology of rutile rutile tio2 is an important accessory mineral that when present offers a rich source of information about the rock units in which it is incorporated it occurs in a variety of specific microstructural settings contains significant amounts of several trace elements and is one of the classical minerals used for u pb age determination here we focus on information obtainable from rutile in its original textural context we do not present an exhaustive review on detrital rutile in clastic sediments but note that an understanding of the petrochronology of rutile in its source rocks will aid interpretation of data obtained from detrital rutile for further information on the important role of rutile in provenance studies the reader is referred to previous reviews e g zack et al 2004b meinhold 2010 triebold et al 2012 coarse rutile is the only stable tio2 polymorph under all crustal and upper mantle conditions with the exception of certain hydrothermal environments smith et al 2009 as such we will focus on rutile rather than the polymorphs brookite anatase and ultrahigh pressure modifications in this chapter we first review rutile occurrences trace element geochemistry and u pb geochronology individually to illustrate the insights that can be gained from microstructures chemistry and ages then in the spirit of petrochronology we show the interpretational power of combining these approaches using the ivrea zone italy as a case study finally we suggest some areas of future research that would improve petrochronologic research using rutile rutile is a characteristic mineral in moderate to high pressure metapelitic rocks in high pressure metamorphosed mafic rocks and in sedimentary rocks e g force 1980 frost 1991 zack et al 2004b triebold et al 2012 rutile also occurs rarely in magmatic rocks e g anorthosites as well as in some hydrothermal systems coarse grained

heavy mineral sorting in downwards injected palaeocene sandstone siri canyon danish north sea abstract post depositional remobilization and injection of sand are often seen in deep water clastic systems and have been recently recognised as a significant modifier of deep water sandstone geometry large scale injectite complexes have been interpreted from borehole data in the palaeocene siri canyon near the danish central graben of the north sea hydrocarbon province the emplacement of large scale injectite complexes has been commonly attributed to seismic activity and consequent sand liquefaction however due to very small differences in textural and compositional properties and the lack of depositional structures in deep water sandstones the distinction between in situ and injected or remobilized sandstones is often ambiguous large scale heavy mineral sorting in 10 m thick units is observed in several reservoir units in the siri canyon and has been interpreted to represent the depositional sorting in this study we describe an example of effective shear zone sorting of heavy minerals in a thin downwards injected sandstone dyke which was encountered in one of the cores in the cecilie field siri canyon differences in sorting pattern of heavy minerals are suggested as a tool for petrographic geochemical distinction between in situ sandstones and their related injectites especially where primary sedimentary structures are removed by fluidization or minor remobilization

calculation of partial melting equilibria in the system na2o cao k2o feo mgo al2o3 sio2 h2o nckfmash a thermodynamic model for haplogranitic melts in the system na2o cao k2o al2o3 sio2 h2o nckash is extended by the addition of feo and mgo with the data for the additional end members of the liquid incorporated in the holland powell 1998 internally consistent thermodynamic dataset the resulting dataset with the software thermocalc is then used to calculate melting relationships for metapelitic rock compositions the main forms for this are p t and t x pseudosections calculated for particular rock compositions and composition ranges the relationships in these full system pseudosections are controlled by the low variance equilibria in subsystems of nckfmash in particular the solidus relationships are controlled by the solidus relationships in nkash and the ferromagnesian mineral relationships are controlled by those in kfmash however calculations in nckfmash allow the relationships between the common metapelitic minerals and silicate melt to be determined in particular the production of silicate melt and melt loss from such rocks allow observations to be made about the processes involved in producing granulite facies rocks particularly relating to open system behaviour of rocks under high grade conditions

zr and hf diffusion in rutile abstract chemical diffusion of zr and hf under anhydrous conditions has been measured in synthetic and natural rutile the sources of diffusant used were hafnon or zircon powders or a hafnon rutile mixture experiments were run in crimped pt capsules in air or in sealed silica glass capsules with solid buffers to buffer at nno or qfm rutherford backscattering spectrometry rbs was used to measure zr and hf diffusion profiles from these measurements the following arrhenius relations were obtained for zr diffusion parallel to c over the temperature range 750 1100 c d zr c 9 8 10 15 exp 170 30 kj mol 1 rt m 2 s 1 for hf diffusion parallel to c over the temperature range 800 1000 c d hf c 9 1 10 15 exp 169 36 kj mol 1 rt m 2 s 1 for hf diffusion normal to c over the temperature range 750 1050 c d hf c 2 5 10 12 exp 227 62 kj mol 1 rt m 2 s 1 diffusivities for experiments buffered at qfm and nno are similar to those run in air diffusivities in synthetic and natural rutile are likewise similar indicating that these findings can be applied directly in determining zr diffusivities in rutile in natural systems these data indicate that rutile should be moderately retentive of zr chemical signatures with zr diffusivities within an order of magnitude of those for pb in rutile over most geologic conditions when applied in evaluation of the relative robustness of the recently developed zr in rutile geothermometer t zack r moraes a kronz temperature dependence of zr in rutile empirical calibration of a rutile thermometer contributions to mineralogy and petrology 148 2004 471 488 e b watson d a wark j b thomas crystallization thermometers for zircon and rutile contributions to mineralogy and petrology 151 2006 413 433 these findings suggest that zr concentrations in rutile will be somewhat more likely to be affected by later thermal disturbance than the geothermometer based on zr concentrations in titanite l hayden e b watson d a wark a thermobarometer for sphene abstract 16th v m goldschmidt conference 2006 and much less resistant to diffusional alteration subsequent to crystallization than the ti in zircon geothermometer e b watson d a wark j b thomas crystallization thermometers for zircon and rutile contributions to mineralogy and petrology 151 2006 413 433 e b watson t m harrison zircon thermometer reveals minimum melting conditions on earliest earth science 308 2005 841 844

indicators of propagation direction and relative depth in clastic injectites implications for laminar versus turbulent flow processes clastic injectites are widely recognized in deep water stratigraphic successions although their sediment transport processes propagation direction and depth of injection are poorly constrained understanding how they form is important as injectites are increasingly being recognized as significant components of sedimentary basin fills yet are not predicted by standard sedimentary facies models here analysis of features on the margins of exhumed clastic sills and dikes and clasts within them enables their genesis to be determined a diverse array of diagnostic structures is found on the margins of injectites in the karoo basin south africa where the net direction of injection and position of the parent sand are well constrained injectite margin features include mudstone clast rich surfaces planar or smooth surfaces blistered surfaces and parallel and plumose ridged surfaces combined these features are critical in distinguishing injected sands where injectites are strata concordant from those of primary deposition all features are indicative of propagation through brittle very fine grained sediments at depths where the applied shear stress is at least four times the tensile strength of the host rock additionally the presence of parallel ridges plumose ridges and steps allows local fracture propagation to be constrained and in turn injection direction the features described provide evidence that sands were injected at considerable depth in closed fractures with limited capacity for flow dilution and turbulence enhancement calculated reynolds numbers lack of erosion at injectite walls and the presence of mud clasts at the top and base of sills indicate that many flows were likely fully laminar during injection the sedimentary features of these confined relatively deep laminar flow induced injectites are very different from injectites that reach the surface and produce extrudites surface linked injectites are associated with open conduits where a greater fraction of carrier fluid to particles can be accommodated enabling highly turbulent lower concentration flows

a systematic evaluation of the zr in rutile thermometer in ultra high temperature uht rocks the zr in rutile geothermometer is potentially a widely applicable tool to estimate peak metamorphic temperatures in rocks from diverse geological settings in order to evaluate its usefulness and reliability to record and preserve high temperatures in granulite facies rocks rutile from uht rocks was investigated to assess different mechanisms of zr re distribution following cooling from high temperature granulite facies paragneisses from the lowermost part of the ivrea zone italy incorporated as thin sheets into the extensive basaltic body of the mafic complex were selected for this study the results show that zr in rutile thermometry if properly applied is well suited to identify and study uht terranes as it preserves a record of temperatures up to 1190 c although the thermometer is susceptible to partial post peak metamorphic resetting by zr diffusion texturally homogeneous rutile grains preserve zr concentrations corresponding to temperatures of prograde rutile growth diverse rutile textures and relationships between some rutile host grains and included or adjacent zr bearing phases bear testimony to varying mechanisms of partial redistribution and resetting of zr in rutile during cooling and link zr in rutile temperatures to different steps of the metamorphic evolution rutile grains that equilibrated their zr concentrations at temperatures above 1070 c i e 1 1 wt zr could not retain all zr in the rutile structure during cooling and exsolved baddeleyite zro2 by subsequent reaction of baddeleyite exsolution lamellae with sio2 zircon needles formed before the system finally closed at 650 700 c without significant net loss of zr from the whole host rutile grain by reintegration of zircon exsolution needles peak metamorphic temperatures of up to 1190 c are derived for the studied rocks which demonstrates the suitability of this solution thermometer to record uht conditions and also confirms the extraordinary geological setting of the lowermost part of the ivrea zone

geometry and lithofacies of coarse grained injectites and extrudites in a late pliocene trench slope basin on the southern boso peninsula japan abstract this study investigates the geometry and internal structures of coarse to very coarse grained volcanic sandstones and volcanic breccias with many siltstone clasts interpreted to be sill like injectites and extrudites occurring in an upper pliocene trench slope basin succession on the southern boso peninsula japan the injectites occur in the uppermost shiramazu formation and pinch out laterally into siltstone dominated deposits of the mera formation their thicknesses vary from a few centimeters to 2 m the basal and upper contacts of the injectites with host muddy deposits are sharp and or erosional and are locally discordant with the bedding of the host deposits siltstone clasts which were ripped up or ripped down from the host muddy deposits are commonly incorporated into the injectites although some siltstone clasts have geological ages older than those of the host deposits seven lithofacies have been identified in the injectites based on the internal structures the combinations of internal structures are different from those of high density turbidity current deposits and debrites and suggest that injection was promoted by a combination of turbulent and laminar flow conditions the extrudites show an overall convex up geometry and possess lithological features similar to those of the injectites they have been identified in the rendaiji conglomerate member which is encased in the mera formation and which rests on the uppermost shiramazu formation the extrudites are characterized by gently undulating waveforms that show upstream migration and climbing stacking patterns similar to the cross sectional geometry of cyclic steps or upstream migrating antidunes the active eruption of solid liquid mixtures onto the seafloor and sedimentary piles may have subsequently collapsed to produce supercritical high density gravity currents down the flanks of a neptunian volcano the injectites and extrudites locally contain calyptogena shells and shell fragments as well as fragments of carbonate concretions that exhibit low carbon isotopic ratios suggesting that fluidization of the source sediments was triggered by a combination of seepage of cold methane bearing water into the source sediments and seismic shaking volcaniclastic deposits older than the host muddy deposits are present in the trench slope basin deposits and these are the likely source of the injectites and extrudites

the process of sand injection internal structures and relationships with host strata yellowbank creek injectite complex california u s a abstract the yellowbank creek injectite complex ycic has excellent exposure of the external geometries and internal structures in a large scale sandstone injectite the ycic has an irregular geometry that can be defined neither as a sandstone dike nor as a sill substantial erosion occurred along the margins between the ycic sandstone and host mudstones that includes scoured basal margins and a scalloped upper margin that cuts up to 5 m into the overlying host mudstones erosion of host mudstone has incorporated significant volumes of mudstone clasts into sandstones at the margins of the injectite using microtextural data corrasion is identified as a typical process by which mudstone is eroded during sand injection corrasion occurs when particles of mudstone are either cut or broken from a cohesive bed as the result of high velocity turbulent flow of sand grains acting as tools corrasion together with scouring and the general erosion of the host mudstone imply high velocity turbulent flow conditions and confirm that the fluidized sand had a sufficiently low viscosity during sand injection to allow turbulence internal structures include laminae of more tightly packed sand grains than occur in the surrounding sandstones and are interpreted to have formed by flow and deposition of injecting sands during waning of flow thus reflecting an overall reduction of pore fluid pressure deformation of laminae into folds defines bands which are aligned parallel to the margins of the sandstone the force driving deformation is likely to have been shear stresses induced between the injected sandstone and the more rigid host mudstone the principal style of deformation is hydroplastic oversteepened laminae and pipes are interpreted to have formed due to post sand injection consolidation and resulted in only minor mobilization of sand

implications of near rim compositional zoning in rutile for geothermometry geospeedometry and trace element equilibration in principle compositional profiling of the near rim region of minerals can provide insight into cooling rates but presumes that loss or gain of material from the crystal rim is not kinetically restricted trace element depth profiles collected for zr hf ta nb and u in amphibolite facies rutile grains of the catalina schist southern california show significant variability within a single rock profiles of the same element among different grains can have significantly different slopes grains with indistinguishable zr profiles show vastly different nb profiles and grains with indistinguishable nb profiles show different zr profiles textural and kinetic idiosyncrasies within the matrix apparently affect the ability of specific crystals to accept or release trace elements and impugn the common assumption that mineral surfaces maintain equilibrium at amphibolite facies conditions a new model that limits the flux of zr from rutile grains helps explain commonly observed compositional profiles and implies that inversion of compositional profiles assuming equilibrium among grain surfaces will invariably overestimate cooling rates few grains may record the low closure temperatures that experimentally determined diffusivities imply rather higher temperatures will be retained depending on the proximity of reactants and products in the matrix silicon diffusion does not control zr reequilibration in rutile and relative diffusion coefficients d s of trace elements in rutile are dzr dhf 10dnb 20dta 40du

mechanical control on patterns of overburden deformation induced by dyke fed sandstone intrusions insights from numerical experiments abstract conical sandstone intrusions as a distinct type of hydrocarbon reservoir remain poorly understood regarding their emplacement mechanics here we report a numerical modelling study of conical sandstone intrusions using the two dimensional discrete element method we built numerical models that contain bonded elastic particles with predefined mechanical properties in an open box as the overburden a thin tube filled with unbonded particles and connected to the upper box was used to model the feeder dyke the dynamic behavior of the assembly was enabled by the displacement of a driving wall that defines the lower boundary of the feeder dyke the results show that the model composed of soft materials produced a pair of conical opening mode fractures in the host sediments as the result of tensile stress concentrations in the fracture tip zones the overburden deformation was largely localised within the sediments adjacent to the sandbody and without the formation of a forced fold and significant uplift of the surface in contrast the model composed of stiffer materials produced conical fractures that have closed lower segments and opening upper segments with a reverse sense of shear the intrusion also caused a forced fold in the overburden with a vertical opening mode fracture generated in the fold hinge the modelling results demonstrate that dyke fed sand intrusions can significantly distort the local stress field and the overburden can be subjected to fracturing and or folding due to differential compaction during gradual inflation of the intrusive sandbody importantly deformation patterns of the overburden in response to sandstone intrusion largely depend on mechanical properties of the host sediments

a pliocene mega tsunami deposit and associated features in the ranquil formation southern chile abstract an exceptionally large tsunami affected the coastline of southern chile during the pliocene its backflow eroded coarse beach and coastal dune sediments and redistributed them over the continental shelf and slope sandstone dykes and sills injected from the base of the resulting hyperconcentrated flow into underlying cohesive muds assisted in plucking up large blocks of the latter and incorporating them into the flow locally the rip up intraclasts were fragmented further by smaller scale injections to form a distinct breccia of angular to rounded mudstone clasts within a medium to coarse sandstone matrix sandstone sills in places mimic normal sedimentary beds complete with structures resembling inverse gradation planar laminae as well as ripple and trough cross lamination these were probably formed by internal sediment flow and shear stress as the semi liquefied sand was forcefully injected into cracks in borehole cores such sills can easily be misinterpreted as normal sedimentary beds which can have important implications for hydrocarbon exploration

geomorphic features of a badland biancane area central italy characterisation distribution and quantitative spatial analysis abstract the biancana landscapes rather common in several italian areas have a very complex morphology different geomorphic features often occur along the same hillslope from a morphological survey of an experimental site in southern tuscany the forms were classified and their distribution analysed spatial analysis of the biancane provided insights into the range of forces responsible for their formation and evolution the results confirm an evolutionary trend from an original gently sloping surface to a complex biancana landform emphasising a trend from the taller bean forms to the terminal souffle like and cone forms the presence of scarp and sliding forms in the most sloping areas and along the residual surfaces supports the hypothesis of a process influenced by base level acting initially by small mass movements spatial analysis did not reveal any systematic trend in the variability of the erosional features along the slopes variographic analysis showed that selected morphological attributes are spatially auto correlated over a short range suggesting that the erosive processes responsible for morphogenic evolution of biancane act mostly on a local scale the strong geometric anisotropy detected in directions parallel to the main jointing systems also indicated a broader scale tectonic control of biancane evolution probably in an early stage of their formation

complex reservoir geometries in a deep water clastic sequence gryphon field ukcs injection structures geological modelling and reservoir simulation abstract the balder formation sandstone reservoir of the gryphon field was deposited during the late paleocene early eocene while the background sedimentation comprised pelagic shales and tuffs sediment gravity flows transported sands from the shelf area in the west the crawford ridge acted as a barrier to sediment transport in the east causing the sands to be deposited predominantly as massive sand bodies as flow velocities decreased during burial sand remobilisation and injection occurred possibly localised around faults cored intervals show a range of injection structures from thin cm scale dykes to more massive metre scale chaotic intrusive features the cross cutting nature of the injection structures as observed in core and in seismic sections accounts for the high degree of reservoir connectivity observed in the field a study was undertaken with the objective of constructing a 3d geological model for dynamic reservoir simulation in order to evaluate future development activities in the field as previous purely deterministic models had proven unsuitable the complex depositional and post depositional history of the gryphon field reservoir has resulted in a system for which there is no published analogue to aid in 3d reservoir modelling preliminary stochastic models based on analogues chosen to reflect the reservoir sand body geometries did not match the field production history the fact that both the deterministic and fully stochastic models were unsuitable suggested that a novel approach was required to model this field subsequent models constructed using a combination of stochastic and deterministic models have proven successful in matching the production history of the field and evaluating infill opportunities

compositional modification and trace element decoupling in rutile insight from the capricorn orogen western australia abstract the trace element composition of rutile is widely used to constrain the temperature and timing of geological events the provenance of detrital grains and as a potential indicator of proximal ore mineralisation understanding the processes of trace element mobility in rutile is therefore paramount to the successful application of rutile geochemistry to geological research using a combination of electron backscattered diffraction and laser ablation split stream icp ms we studied the microtextures trace element contents and u pb isotopes of rutile from the siliciclastic rocks of the mesoproterozoic edmund group capricorn orogen western australia the capricorn orogen experienced multiple tectonothermal events during the proterozoic under conditions spanning from low to high grade metamorphism rutile textures u pb ages trace element variations and calculated zr in rutile temperatures reveal different generations of rutile including detrital or metamorphic hydrothermal grains u pb age data of detrital rutile indicate a wide span of ages ca 2 7 1 7 ga of the source rocks and cr nb compositions point to metamafic metapelitic and granitic origins for this rutile the youngest detrital ages of 1 68 ga constrain the maximum depositional age of the sedimentary package the comparison of age spectra across the stratigraphy indicates a change in provenance with sourcing from circa 1 7 ga rocks during early stages of deposition followed by unroofing of older basement during deposition of the youngest units of the edmund group partial resetting of detrital rutile is observed in the increase of 207pb 206pb ratios accompanied by a decrease of zr in rutile calculated temperatures lower temperature metamorphic hydrothermal rutile yielded imprecise mesoproterozoic ages 1 3 1 1 ga this rutile has significant variations of zr hf and nb ta extending to values both lower and higher than primitive mantle which may record crystallisation from or interaction with hydrothermal fluids partial remobilisation of trace elements in metamorphic hydrothermal rutile is demonstrated by sub grain domains with sharp geochemical variations and by evidence of element diffusion at grain margins orders of magnitude differences in trace element concentrations including nb cr and zr in metamorphic hydrothermal rutile grains suggest thorough investigation of rutile textures needs to be carried out prior to using the trace element concentrations in rutile for provenance and zr in rutile temperature studies

zirconium in rutile speedometry new constraints on lower crustal cooling rates and residence temperatures abstract the incorporation of zirconium into the mineral rutile tio2 has been both empirically and experimentally calibrated as a measure of rutile crystallization temperatures watson et al 2006 this temperature sensitive system has been employed as a geothermometer with applications to a number of different geologic settings and rock types experimentally measured kinetics for zr diffusion in rutile cherniak et al 2007 indicate that zr can be lost to temperature dependent diffusion warranting further investigation of the geologic significance of calculated temperatures coupling diffusion kinetics with numerical solutions to the diffusion equation provides a means to forward model the time and temperature dependency of the system modeled results indicate a strong dependency of zr concentration in rutile on both 1 initial cooling rate following high temperature metamorphism crystallization and 2 temperature and duration of long term geologic residence zr concentrations measured in rutile from lower crustal xenoliths that resided at 25 45 km depths for 2000 my reveal zr concentrations in the approximate grain center that are consistent with temperatures measured by independent thermometers forward models for zr diffusion show that preserving a zr record of these initial temperatures in the center of a rutile crystal with a 50 m radius requires rapid cooling 300 c ma from magmatic metamorphic temperatures followed by a long term residence 2000 my at temperatures

rutile saturation in hydrous siliceous melts and its bearing on ti thermometry of quartz and zircon the tio2 solubility of rutile saturated hydrous siliceous melts has been investigated at p 1 gpa and t 650 1000 c for several representative felsic compositions the dissolution of a rutile crystal into a tio2 undersaturated melt provides information on both tio2 solubility and ti diffusion results of this study confirm that tio2 solubility is strongly dependent on both temperature and melt composition but not on the amount of h2o present for a given t t io2 content decreases as the melts become more felsic the solubility of tio2 is given by log ti ppm 7 95 5305 t 0 124fm

saucer shaped intrusions occurrences emplacement and implications abstract magmatic intrusions and fluidized injected sands represent the two main types of sheet intrusions in the earth s crust in this paper we show that both intrusion types often display a saucer like geometry as revealed by 3d seismic imaging and field observations saucer shaped intrusions are fairly common in sedimentary basins as for example offshore in the norwegian and north sea basins and onshore in the karoo basin of south africa the formation of the saucer geometry is controlled by the low viscosity of the injected fluid and by the interaction between a growing shallow hydraulic fracture and overburden deformations statistics gathered from observations and modelling show a linear relationship between the depth of emplacement and the size of the saucer shaped intrusions we anticipate future cross disciplinary studies aiming to discover other occurrences of saucer shaped intrusions and to identify the physical processes controlling the development of this fundamental geometry

redistribution of hfse elements during rutile replacement by titanite titanite growth at the expense of rutile during retrograde hydration of eclogite into amphibolite is a common phenomenon we investigated an amphibolite sample from the tromso eclogite facies terrain in northern norway to gain insight into the trace element distribution between rutile and titanite during incomplete resorption of the rutile by titanite patchy compositional zoning of al ti and f in titanite relates to the presence of a fluid with variable ti al and or f during its growth laser ablation icp ms and electron microprobe data for high field strength elements hfse nb zr ta and hf of rutile resorbed by titanite indicate a pronounced enrichment of these elements in the rim of a large single rutile crystal 8 mm and a systematic decrease towards uniform hfse contents in the large core hfse contents of smaller rutile grains 0 5 mm and rutile inclusions 100 m in the titanite overgrowth are similar or higher than in the rims of large rutile crystals element profiles from the rim inward demonstrate that hfse enrichment in rutile is controlled by diffusion hfse ratios in diffusion altered rutile show systematic variations compared with the uniform core composition of the large rutile modelling of zr and nb diffusion in rutile indicates that diffusion coefficients in rutile in fluid dominated natural systems must be considerably higher than those determined experimentally at 1 bar in dry systems variations of hfse contents in the newly formed titanite show no systematic spatial distribution hfse ratios in titanite and the rims of rutile are different indicating different solid fluid distribution coefficients in these minerals element fractionation by diffusion into the relict rutile and during fluid mediated growth of new titanite could substantially change the hfse budget of these minerals and could affect their use for geochemical tracing and other applications such as zr based geothermobarometry

episodic fluid expulsion from geopressured sediments numerical simulation of fluid explusion from geopressured sediments using a one dimensional finite difference model shows that large volumes of fluid can be transported through a fractured seal during short lived 100 year expulsion events in this model abnormal fluid pressures are maintained by an impermeable seal when the fluid pressure exceeds 85 of the lithostatic pressure a vertical fracture opens in the seal providing a permeable pathway from the geopressured sediments into the overlying section fluid pressure in the seal decreases as fluid flows through the fracture closing the fracture as sediments in the seal compact once the fracture closes the seal remains impermeable until fluid flowing from deeper in the section increases fluid pressure to the fracture criteria a process that takes 10 000 500 000 years fractures emplaced in relatively incompressible seals such as compacted and or cemented sediments remain open for 20 50 years fluid fluxes through the seal integrated over the life of these events are 1 5 107 kg m2 and temperatures in the overlying sediments are increased by 5 20 c these temperature anomalies decay to less than half their original value in 300 years suggesting that the thermal anomalies observed in wells that are attributed to fluid expulsion formed in response to a very recent or currently active event

petrogenetic relations among titanium rich minerals in an anatectic high p mafic granulite the petrogenetic relations among ti rich minerals in high grade metabasites is illuminated here through a detailed petrological investigation of an anatectic garnet clinopyroxene granulite from the grenville province ontario canada containing rutile titanite and ilmenite in distinct microtextural settings garnet porphyroblasts exhibit zoned ti concentrations up to 0 15 wt tio2 in their cores as well as a variety of rutile inclusion types including clusters of small variably elongate grains and thin 1 m oriented needles calcite inclusions in garnet commonly observed surrounding garnet cores containing quartz and clinozoisite indicate the presence of evolving c o h fluids during garnet growth and suggest that the rutile clusters may have formed from subsequent ti diffusion and rutile precipitation within existing fluid inclusions titanite forms large subhedral crystals and typically occurs where the primary garnet clinopyroxene assemblage is in contact with leucosome containing megacrystic hornblende silvialitic scapolite and calcic plagioclase many titanite crystals exhibit marginal subgrains that correspond with sharp changes in their major and trace element composition likely related to a dissolution precipitation or recrystallization process following primary crystallization clinopyroxene ilmenite symplectite coronas surround titanite in most locations likely forming from reaction with the hornblende plagioclase matrix fluids melt integration of multi equilibria thermobarometry and zr thermometry in rutile and titanite with phase equilibrium modelling allows definition of a clockwise p t path evolving to peak pressures of 1 5 gpa at 750 c during garnet and rutile growth followed by peak temperature conditions of 1 2 gpa and 820 880 c associated with melt present titanite growth and finally cooling and decompression to regional amphibolite facies conditions 1 0 gpa and 750 c associated with the formation of clinopyroxene ilmenite symplectites surrounding titanite p t pseudosections calculated for the pristine leucosome and titanite free metabasite bulk composition reproduce much of the prograde phase relations but predict rutile as the stable ti rich mineral at the peak thermal conditions associated with melt present titanite growth the p m cao and t m cao models show that bulk cao concentrations have a significant effect on the stability ranges of titanite and rutile increased bulk cao tends to stabilize titanite to higher pressure and temperature at the expense of rutile with a 15 increase in cao producing the observed titanite bearing assemblage at high p granulite facies conditions thus the model results are consistent with the textural observations which suggest that titanite stability is associated with a chemical exchange between the host metabasite and a ca rich melt

trace element systematics in granulite facies rutile implications for zr geothermometry and provenance studies metamorphic rutile from granulite facies metapelitic rocks of the archean pikwitonei granulite domain pgd manitoba canada provides constraints on the systematics of trace elements in rutile during high temperature conditions and subsequent slow cooling compositional profiles and maps of the zr concentrations in rutile grains 120 600 m from three metapelitic gneisses were acquired by electron probe micro analysis using a spatial resolution of down to 2 m simultaneously profiles were analysed for nb cr and v which have significantly different diffusion characteristics in rutile the profiles of all elements show relatively homogeneous concentrations within most grains but significant inter grain differences even within a single thin section some rutile grains display a slight concentration decrease from a neighbouring garnet towards the matrix for all measured elements the lack of diffusion profiles for all analysed elements shows that these are highly immobile in rutile and that distributions of these elements are primary and preserve prograde information the nb and cr concentrations overlap with ranges that are ascribed to different provenances indicating that source discrimination based on these elements is not possible in all cases high retentiveness for zr implies that the zr in rutile geothermometer is highly robust to diffusive re equilibration even during very slow cooling 2 c ma 1 from granulite facies conditions most grains have high zr contents 3000 4600 ppm differences between high zr contents suggest that during growth under vapour absent conditions there may not be saturation of zr in rutile even if zircon is present therefore several rutile grains need to be analysed in a sample to obtain a useful minimum peak temperature the highest zr concentrations correspond to 900 c this is significantly higher than previous peak temperature estimates of 820 c based on two feldspar thermometry on a regional scale this implies that part of the pgd was affected by ultra high temperature uht metamorphism it also implies that rutile is able to preserve primary compositions even to uht conditions this study shows that if combined with textural information zr in rutile has the potential to be a very useful tool for estimating rutile crystallization temperatures and peak metamorphic conditions for granulite facies rocks zr in rutile yields more reliable peak metamorphic temperatures than most other exchange geothermometers which tend to partially re equilibrate by diffusion during cooling

zoning patterns in orthopyroxene and garnet in granulites implications for geothermometry compositional maps of orthopyroxene and garnet of contrasting grain size and in contact with different minerals were made from two paragneiss granulites from the minto terrane of northern quebec the compositional maps provide clear evidence of late exchange of fe fe mg after ca in garnet and al in orthopyroxene had been quenched in the extent of late fe mg exchange was controlled by neighbouring minerals with negligible fe mg gradients against plagioclase and quartz and substantial gradients against exchangeable fe mg minerals cores of grains in contact with exchangeable fe mg neighbours are progressively more reset in fe fe mg as grain size decreases whereas cores of even small grains surrounded by only plagioclase and quartz are not significantly different in fe fe mg than cores of the largest grains gradients of ca in garnet and of al in orthopyroxene in grains of uniform fe fe mg preserve a high temperature retrograde history during which intergranular exchange effected compositional uniformity of mineral rims and intragranular fe mg diffusion in garnet and orthopyroxene was rapid enough to homogenize fe fe mg the transition from efficient intergranular exchange at relatively high temperatures to local fe mg exchange at lower temperatures may have been controlled by loss of an intergranular exchange medium in the rock possibly an internally generated dehydration melt phase implications for geothermometry of granulites include the following numerical values are particular to this study 1 core compositions of garnet and orthopyroxene grains in contact with exchangeable neighbours may be reset in fe fe mg relative to the most refractory compositions by an amount equivalent to 120d c 2 fe mg exchange thermometry using even the most refractory fe fe mg compositions may not record peak granulite conditions possibly recording instead the temperature at which an intergranular exchange medium was lost from the rock and 3 temperature sensitive net transfer equilibria involving al solubility in orthopyroxene yield temperatures up to 150d c higher than maximum fe mg exchange temperatures even in grains with flat fe fe mg compositional profiles making them a better means of estimating peak granulite temperatures than fe mg exchange thermometry

silicon diffusion in silicate minerals abstract recently obtained silicon self diffusion data dsi d0exp h rt in silicates quartz itreous silica forsterite san carlos olivine and diopside show a compensation law that is a linear relation log d0 logd h 2 303rt we find h 532 6 30 4 log d0 h in kj mol and d0 in cm2 s which corresponds to logd x02212 17 5 and t 1588k d represents a common value of dsi for all these silicates at t but also the value of dsi at h 0 it has therefore a pure entropic signification d fa2 exp s r f is a geometrical factor a the jump distance and the si o vibrational stretching optic frequency almost common to all these silicates despite the wide range of enthalpies for si diffusion in silicates we propose that the compensation law outlines a unique mechanism for si migration in minerals with structures based on the sio4 tetrahedron

experimental soft sediment deformation structures formed by the liquefaction of unconsolidated sands and some ancient examples the effects of liquefaction in saturated sand bodies under a variety of driving forces are described from shaking table experiments and structures from the geological record are presented which are analogous to the experimental structures the collapse of sloping heaps of cross bedded sand under a gravitational body force generates low angle essentially uncontorted stratification a basal zone of shearing may be present with steepened and folded foresets stretching of foresets may be accommodated on normal faults and bottomsets may be contorted into inclined folds in natural systems the substrate may also liquefy causing deformation driven by an unevenly distributed confining load stratification in the surface bedform is flattened and stratification in the substratum contorted experiments failed to produce relative displacement at the interface between stacked sand bodies liquefaction of gravitationally unstable systems in sands generates load structures comparable to those from sand mud systems recumbent folded deformed cross bedding is formed by current shear over a liquefied bed as has been inferred from field and theoretical analyses shear of nonliquefied sand forms angular folds other deformation mechanisms such as fluidization or seepage may generate structures similar to all of these local water escape structures driven by fluidization occur in the upper parts of some liquefied sand bodies they include cusps sand volcanoes and clastic dykes transient cavities formed in some experiments and seemed to be preserved as breached cusps although the experiments tried to isolate individual driving forces driving forces may operate together and there may be a continuum between deformation driven by water escape and deformation driven by loading different structures from those described here may form where liquefaction develops in a buried layer as opposed to at the sediment surface

geochemistry and origin of organic rich sediment veins in fractured granitic basement helmsdale sutherlandshire uk abstract black sediment veins up to 2 cm width penetrate the caledonian helmsdale granite in the vicinity of the helmsdale fault onshore moray firth the black colour and geochemistry of the veins reflect a high content of organic carbon both devonian and jurassic shales are conceivable available sources but sterane compositions relate the organic matter to the jurassic shales a content of extractable organic matter higher than in the shales suggests that the carbon in the veins represents oil rather than mechanically mobilized shale the oil was present during sediment vein emplacement the veins were emplaced forcefully which may reflect high fluid pressure associated with post jurassic movement on the helmsdale fault

nb and zr behavior in rutile during high grade metamorphism and retrogression an example from the ivrea verbano zone abstract detailed textural observations and in situ analyses emp sims and la icp ms are used to characterize trace element behavior during prograde and retrograde metamorphic reactions involving rutile the ivrea verbano zone is a classic granulite area and rocks from the strona and d ossola valleys are an example of the amphibolite to granulite facies transition although different rock types occur in the area detailed sampling and petrographic work show that rutile only occurs in granulite facies paragneisses these rocks show a rich inventory of textures that allow not only for the investigation of trace element behavior in response to prograde rutile growth but also for the effect of post peak processes on rutile chemistry nb concentrations in rutile from lower grade samples show a larger spread from 500 to 5000 ppm within one sample when compared to those from higher grades this pattern can be modeled using prograde rutile growth formed from biotite breakdown zr concentrations in rutile are characterized by an anomalously large spread and a bimodal distribution maximum zr concentrations increase according to the general metamorphic gradient known for this area temperatures from zr in rutile thermometry although feasible are considerably higher than previous calculations increasing from ca 850 to 930 c a second cluster of zr concentrations in rutile occurs at rather constant concentrations ca 1000 ppm for all localities and is interpreted to be related to intense fluid influx at high temperature and or to post peak diffusional resetting favored by slow cooling rates alteration textures characterized by a complex network of micro veins are evidence for the late fluid influx the fluid strongly affected the rutiles which is evidenced by corrosion of older rutile grains and formation of rutile veinlets

numerical modeling of shallow magma intrusions with finite element method abstract a numerical approach for simulation of magma intrusion process considering the couplings of the stress distribution the viscous fluid flow of magma and the fracturing of host rock has been developed to investigate the mechanisms of fracture initiation and propagation in host rock during magma intrusion without pre placing a set of fractures the study focused on the dike intrusions filled with injected viscous magma in shallow sediments a series of numerical modellings were carried out to simulate the process of magma intrusion in host rocks with particular attention on the magma propagation processes and the formation of intrusion shapes the model materials were mohr coulomb materials with tension failure and shear failure the scenarios of both stochastically heterogeneous host rocks and layered host rocks were analyzed the injected magma formed intrusions shapes of a dyke b sill c cup shaped intrusion d saucer shaped intrusion the numerical results were in agreement with the experimental and field observed results which confirmed the adequacy and the power of the numerical approach

the impact of the farming practice of remodelling hillslope topography on badland morphology and soil erosion processes abstract badland landforms created in plio pleistocene clay landscapes of the basilicata region of southern italy form marginal features in a semi arid landscape dominated by the widespread cultivation of subsidised cereals these badland features are high relative relief forms exhibiting a high drainage density and steep slopes with slope angles typically in excess of 35 economic incentives to increase agricultural productivity have resulted in the practice of remodelling these marginal areas using heavy earth moving equipment remodelling the badland features creates longer slopes at lower angles which can be cultivated using conventional farm machinery these changes in hillslope morphology have altered the degree to which soil erosion processes operating in these areas are spatially coupled in the badland areas erosion and deposition are strongly localised with minimal sediment delivery to ephemeral or perennial channel systems the economically driven change in land use from visually striking badland areas to newly remodelled fields for agricultural use results in an increase in the coupling of drainage networks and a net increase in soil erosion

process form relationships in southern italian badlands erosion rates and implications for landform evolution characteristic badlands are incised into plio pleistocene clays in basilicata southern italy creating steep scarp slopes with knife edge ridges calanchi and small dome shaped forms biancane erosion pin data for the period 1997 2003 give mean annual erosion rates for dome shaped biancane in the range 9 19 mm a 1 while rates for the calanchi scarps are lower at 7 10 mm a 1 the erosion pin data also show a non linear relationship with slope angle maximum erosion rates coincide with a slope angle of 35 within an envelope defined by combining the theoretical effects of both rainsplash and surface weathering monitoring of surface changes and erosion rates for two 0 5 m 2 cleared swathes on biancane forms reveals a complex relationship between weathering and erosion characteristic forms can develop from large blocks of intact clay bedrock over a time period of less than 30 a the implications of the measured erosion rates for the landform association of mountain front pediment domed inselberg are explored copyright 2005 john wiley sons ltd

the alba field ocean bottom cable seismic survey impact on development alba field in the central north sea uk block 16 26 consists of eocene age high porosity unconsolidated turbidite channel sands sealed by low permeability shales at an average subsea depth of 1900 m the main channel is approximately 9 km long and 1 5 km wide and can be up to 100 m thick figure 1 the channel contains discrete bodies of intrareservoir shales that can cause significant drilling completion and production problems immediately overlying the main alba sand channel several wells have encountered thin discontinuous oil saturated brioc sands

the 2 1 ga old injectite network of the franceville basin gabon architecture origin and implications on manganese mineralization abstract detailed sedimentological investigations on numerous outcrops and drill core sections in the 2 1 ga old franceville basin gabon provide evidence for a large scale injectite network the injectites were formed by the injection of sands through a thickness of about 150 m of the fb1 member and now cover a minimum area of 70 km 2 corresponding to the bangombe plateau but are also recognized close to franceville 35 km farther south east the injectite lithology corresponds to a mud or carbonate supported sandstone characterized by a loose and uncompacted fabric contrasting with the host rock because the injectites are often parallel to subparallel to the stratification they were misinterpreted as depositional beds by previous authors at outcrop the injectite bodies exhibit sill dyke wing and protrusive geometries emplaced during early burial within poorly compacted material with partial wall erosion and dissociation the source of the sand material is attributed to a channel levee turbidite depositional system located in the lower part of the fb1 member these deposits were buried by a thick biochemical muddy cap deposited during a starvation phase which increased the seal capacity of the system this type of architecture has a high potential to develop compaction disequilibrium during burial moreover in the case of the francevillian injectites the abundance of microbial organic matter favoured early methane degassing and lateral charging of the sand reservoir the overpressure in the channels was periodically released during early burial through the effect of rapid sedimentary and tectonic loading and possible seismic activity the fluidized sand was injected according to a symmetrical wing pattern thus the injected masses caused a local decrease in the grade of the lateritic manganese ore deposit of the bangombe plateau

making a homogenite an outcrop perspective into the evolution of deformation within mass transport deposits abstract mass transport deposits mtds may show a variety of deformation aspects from poorly deformed layers to highly deformed and homogenized deposits as a result of the different kinds of mass transport processes involved in their evolution previous studies indicate that the downslope flow transformation of mtds is characterized by increasing disaggregation mixing and homogenization of a non to poorly lithified protolith which may ultimately generate a homogenite we here explore the role of deformation processes in the disaggregation and mixing of sediments that tend to lead to sediment homogenization and so may also control the evolution of mtds using the itarare group of the parana basin southern brazil as our case study we examine several types of structures in mtds with varying degrees of mass disaggregation and discuss the role of deformation process in the continuum homogenization of the sediment three deformational facies df 1 df 2 and df 3 were identified and interpreted as recording varying stages of homogenization of sediments disaggregation and mixing within the incipient mature and evolved flows respectively these different stages show transitional aspects that indicate a continuum homogenization the comparison between structural assemblages and the amount of matrix in the three different deformational facies indicates a close relationship between styles of deformation and the homogenization expected for mass flows the processes that promoted disaggregation include boudinage faulting layer parallel shearing and marginal deformation of intrabasinal clasts while mixing processes that generate matrix include shearing and liquefaction fluidization of sediments

fluid migration and fluid seepage in the connemara field porcupine basin interpreted from industrial 3d seismic and well data combined with high resolution site survey data this study documents the suite of processes associated with source to seafloor fluid migration in the connemara field area on the basis of 3d seismic data well logs 2d high resolution seismic profiles subbottom profiles short cores and sidescan sonar data the combination of datasets yields details about fluid migration pathways in the deep subsurface in the unlithified shallow subsurface and about the distribution of fluid and gas seeps pockmarks at the sea floor the connemara field area is characterized by vertical fluid migration pathways seismic chimneys or gas chimneys that extend from the top of the jurassic sequence cross cutting the entire cretaceous sequence to the upper tertiary deposits over a vertical distance of up to 1 5 km their localization is mainly structurally controlled to the crest of tilted fault blocks along the main hydrocarbon migration pathways these chimneys are important conduits for focused vertical fluid gas flow from the deep to the shallow subsurface however gas seeps pockmarks at the sea floor are almost randomly distributed which indicates a change from focused to diffuse fluid gas migration in shallow unconsolidated sediment where the vertical chimneys reach up to unlithified eocene to miocene sands widespread deformation interpreted as fluidization occurs around the main conduit this deformation affects about 32 of the entire unconsolidated tertiary section late eocene miocene a plio pleistocene glaciomarine drift with up to five horizons with iceberg ploughmarks seals the tertiary sands in the near surface sediments it is observed that gas accumulation occurs preferentially at iceberg ploughmarks it is inferred that lateral migration at five levels of randomly oriented ploughmarks dispersed gas over larger areas and caused random pockmark distribution at the sea floor independent from the underlying focused migration pathways this study demonstrates that fluid flow migration changes from structurally controlled focused flow in the deep consolidated subsurface to diffuse flow controlled by sediment variability in the shallow subsurface this result is relevant to a better understanding of the distribution of seepage induced features at the seafloor related to focused hydrocarbon migration pathways known from industry data and fluid flow modeling

preliminary study of the erosion mechanisms in a biancana badland tuscany italy abstract italian badlands are present along the appennini mountains with an annual precipitation which ranges from 400 to 1200 mm the genesis of these badlands has often been studied whereas current processes and erosion rates have only rarely been examined and measured this paper describes a preliminary study on a badland developed in temperate mediterranean climate and located in sw tuscany italy the selected site is characterized by biancane dome shaped features a few meters in height generally having a vegetated nne aspect and severely eroded ssw slope with a sub horizontal basal pediment field rainfall and runoff experiments were carried out field results were substantiated by data collected in specially devised laboratory tests it was concluded that near surface pipes which develop at the point of contact between a surficial layer of weathered and severely fractured regolith and the less fractured and weathered regolith underneath are the main drainage channels while rills play a secondary role soil detachment is largely due to mechanical and chemical slaking of the regolith during infiltration the role of runoff is almost solely transport in particular it was found that the runoff detachment rate is limited by the rate at which the water front penetrates into the regolith

the origin of consolidation laminae and dish structures in some deep water sandstones abstract consolidation laminae and dish structures form high density zones that are interpreted to have formed by disruption of primary structures during gravitational collapse of the grain framework during water escape and consolidation they are not associated with higher contents of clay size material than adjacent units but the chloritic clay minerals associated with consolidation laminae and dish structures have a different microtexture than observed elsewhere clay mineral texture has a direct effect on petrophysical characteristics in particular water saturation and conductivity in hydrocarbon saturated intervals ct scans identify consolidation laminae and dish structures as zones of high density that correspond to tighter packing of sand grains and are unrelated to clay distribution dish structures may form independently of consolidation laminae or by further modification of fragmented consolidation laminae

use of liquefaction induced features for paleoseismic analysis an overview of how seismic liquefaction features can be distinguished from other features and how their regional distribution and properties of source sediment can be used to infer the location and strength of holocene paleo earthquakes abstract liquefaction features can be used in many field settings to estimate the recurrence interval and magnitude of strong earthquakes through much of the holocene these features include dikes craters vented sand sills and laterally spreading landslides the relatively high seismic shaking level required for their formation makes them particularly valuable as records of strong paleo earthquakes this state of the art summary for using liquefaction induced features for paleoseismic interpretation and analysis takes into account both geological and geotechnical engineering perspectives the driving mechanism for formation of the features is primarily the increased pore water pressure associated with liquefaction of sand rich sediment the role of this mechanism is often supplemented greatly by the direct action of seismic shaking at the ground surface which strains and breaks the clay rich cap that lies immediately above the sediment that liquefied discussed in the text are the processes involved in formation of the features as well as their morphology and characteristics in field settings whether liquefaction occurs is controlled mainly by sediment grain size sediment packing depth to the water table and strength and duration of seismic shaking formation of recognizable features in the field generally requires a low permeability cap above the sediment that liquefied field manifestations are controlled largely by the severity of liquefaction and the thickness and properties of the low permeability cap criteria are presented for determining whether observed sediment deformation in the field originated by seismically induced liquefaction these criteria have been developed mainly by observing historic effects of liquefaction in varied field settings the most important criterion is that a seismic liquefaction origin requires widespread regional development of features around a core area where the effects are most severe in addition the features must have a morphology that is consistent with a very sudden application of a large hydraulic force this article discusses case studies in widely separated and different geological settings coastal south carolina the new madrid seismic zone the wabash valley seismic zone and coastal washington state these studies encompass most of the range of settings and the types of liquefaction induced features likely to be encountered anywhere the case studies describe the observed features and the logic for assigning a seismic liquefaction origin to them also discussed are some types of sediment deformations that can be misinterpreted as having a seismic origin two independent methods for estimating prehistoric magnitude are discussed briefly one method is based on determination of the maximum distance from the epicenter over which liquefaction induced effects have formed the other method is based on use of geotechnical engineering techniques at sites of marginal liquefaction in order to bracket the peak accelerations as a function of epicentral distance these accelerations can then be compared with predictions from seismological models

soft sediment deformation structures as a tool to recognize synsedimentary tectonic activity in the middle member of the bakken formation williston basin north dakota abstract the bakken formation uppermost devonian lower carboniferous in north dakota consists of black shales with a middle member composed of mixed siliciclastics and carbonates millimeter to decimeter scale soft sediment deformation structures ssds are common in the upper third to quarter of the middle member having been observed in sixty three out of ninety cores studied the nine categories identified herein reflect brittle and ductile deformation and loss of sediment shear in compressional and extensional settings they are interpreted to form due to seismically induced folding liquefaction and fluidization of unconsolidated sediment as well as microfaulting and brecciation of consolidated sediment and reflect synsedimentary tectonic movements e g along faults that were active during deposition the distribution of ssds follows the orientation of the major structural elements rooted in the basement of the williston basin the stratigraphic and spatial distribution of ssds suggests variable tectonic activity cores near the most active fault systems have the highest net thickness of units with ssds whereas those farther from the most active faults exhibit only a few deformed units the predominance of ssds in the upper portion of the middle member suggests there was a change from relative tectonic quiescence to a more active regime which in turn led to modifications of basin geometry and new accommodation patterns synsedimentary deformation might have had a positive effect on reservoir quality in deformed units by increasing porosity and permeability as a result of cohesion loss and rearrangement of grains additionally multiple injection structures and complexes of small scale normal and reverse faults could contribute to better connectivity of reservoir units

episodic basin wide fluid expulsion from geopressured shale sequences in the north sea basin a proposed general model for the episodic dewatering of thick shale successions is based on the recognition of a pervasive polygonal extensional fault network developed in the dominantly fine grained lower tertiary of the north sea basin seismic data show that the faults are arranged in stratigraphically bound structural units tiers that are delimited vertically by almost undeformed condensed sections and are restricted in distribution to the lowest permeability slope and basin floor facies i propose an episodic three stage mechanism to explain the fault genesis involving 1 the development of basin wide overpressured compartments 2 a density inversion between the overpres sured units and the overlying seal and 3 natural hydraulic fracturing pressure bleed off and resealing of the pressure compartment leading to a repeat of the cycle

evolution of permeability in sand injectite systems abstract sand injectite complexes comprise kilometer scale clastic intrusion networks that act as effective conduits for the migration accumulation and then recovery of hydrocarbons and other fluids an equivalent continuum model is constructed to represent a sand injectite reservoir coupling stress and fluid flow in fractured rock using the continuum simulator toughreact coupled with flac3d to follow deformation and fluid flow a permeability model which uses staged percolation models is proposed to improve permeability estimation of fracture networks by accommodating four different levels of fracture connectivity this permeability model is confirmed against field and laboratory data corresponding to the different connectivities of fracture networks the new constitutive permeability model is incorporated into the coupled hydro mechanical simulator framework and applied to sand injectites with the analysis of permeability evolution mechanisms and mechanical sensitivity the results indicate that when the magnitudes of principal stresses increase in a constant ratio normal closure is the dominant mechanism in reducing fracture aperture and thereby permeability conversely the evolution of stress difference can accentuate aperture and permeability due to an increase in shear dilation for critically or near critically oriented fractures also the evolution of aperture and related permeability of fractured rock are more sensitive at lower stress states than at higher stress states due to the hyperbolic relationship between normal stress and normal closure of the fractures

application of zr in rutile thermometry a case study from ultrahigh temperature granulites of the khondalite belt north china craton zr in rutile thermometry was applied to ultrahigh temperature uht granulites from three localities dongpo tuguishan and dajing tuguiwula of the khondalite belt north china craton zr concentrations of analyzed rutiles were detected by la icp ms and emp which display a mutative composition zoning a large inter grain variation a bimodal distribution at around 1 500 and 6 000 ppm and no relationship with the textural setting matrix vs inclusion these characteristics were likely caused by post peak diffusional resetting associated with slow cooling rates and the presence of a co2 rich fluid the grains with lower zr concentrations 500 to 3 000 ppm and temperature estimates 650 to 850 c occur close to or in contact with zircon which was easily affected by post peak processes for example diffusion dissolution reprecipitation the lowest temperatures 650 to 700 c we obtained represent the closure temperature of zr in rutile rutiles with higher zr concentrations 3 000 to 8 000 ppm and calculated temperatures 850 to 1 000 c were least affected by late resetting giving near peak metamorphic temperatures these temperature results higher than 900 c even in excess of 1 000 c from the three localities reconfirm the presence of uht metamorphism our results also suggest that zr in rutile thermometry is valid for ultrahigh temperature estimates in addition there are positive correlations between concentrations of zr and hf nb and ta of the investigated rutiles but the correlations weaken as the concentrations increase especially for nb and ta implying fractionation of nb and ta