validation of the ice 3g model of wurm wisconsin deglaciation using a global data base of relative sea level histories a global data base consisting of radiocarbon controlled relative sea level rsl histories from 392 different geographic locations has been compiled for use in analyses of the glacial isostatic adjustment process these data may be employed to constrain both the spatiotemporal characteristics of the last deglaciation event of the current ice age and the rheological structure of the planetary interior in a previous paper in this series tushingham and peltier 1991 we employed the rsl data in this set from sites that were once ice covered to refine the apriori model of deglaciation that had been delivered by past research in the area of pleistocene geomorphology peltier and andrews 1976 wu and peltier 1983 to produce a new global model of this event that we have called ice 3g in the present paper following a description of the full data base and of the methods used to compile it we employ data from the sites that were not ice covered 200 time series to verify the plausibility of this refined model of deglaciation and to test the extent to which the totality of the observations constrain the radial viscoelastic structure of the planet the analysis of solutions to the forward problem presented here reinforce previous inferences of a preference for a thick lithosphere by rsl data from sites along the u s east coast and a preference by data from most near field sites for an increase in viscosity across the 670 km discontinuity in the mantle by a factor of approximately 2 when the viscosity of the upper mantle is fixed to the value of 1021 pa s originally deduced by haskel 1935 on the basis of his analysis of the data from fennoscandia

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

the collision zone between the north d entrecasteaux ridge and the new hebrides island arc 2 structure from multichannel seismic data the d entrecasteaux zone dez collides with the central new hebrides island arc and consists of two subparallel ridges that strike east west stand 1 2 km above the surrounding oceanic plate and subduct obliquely 15 northward beneath the arc rocks dredged from the north ridge as well as reflections evident in multichannel seismic reflection data indicate that this ridge has a volcanic origin crystalline volcanic rocks are common along the lower flank of the ridge but sedimentary probably volcaniclastic rock caps the ridge seismic reflection data collected over the lower arc slope reveal that mass wasting deposits locally make up most of the accretionary wedge these deposits appear to form discrete bodies suggesting that mass wasting occurred episodically large anticlines and thrust faults having large vertical separation are not readily evident where the colliding ridge intersects the arc slope apparently slope rocks have low strength so that mass wasting deposits formed instead of large relief structures mass wasting is thought to occur as the accretionary wedge is uplifted in response to the northward oblique subduction of the north ridge the toe of the north ridge flank marks an abrupt transition in the lithologies that make up the footwall of the interplate decollement footwall lithologies change from ocean basin to volcaniclastic ridge material and this transition probably marks a discontinuity in friction along the decollement or in rock mechanical properties because north of the transition thrust faults deform the accretionary wedge whereas south of the transition steep reverse faults crosscut the wedge and pierce the north flank of the ridge this piercement means that the decollement at least locally lies within the ridge and that ridge material exotic to the new hebrides arc may be incorporated into the accretionary wedge

the sensitivity of post glacial sea level to viscosity structure and ice load history for realistically parameterized viscosity profiles the continuous variation of viscosity with depth expected from microphysical theories of silicate creep differs significantly from the layered structures typically used to model post glacial relative sea level variations and to refine models of ice load histories here we predict relative sea level rsl curves for a set of realistically parameterized continuous viscosity profiles with different amounts of depth dependence we demonstrate by forward modeling that different classes of realistically parameterized mantle viscosity structures are resolvable by rsl at the edge sites but the predicted rsl there is very sensitive to the assumed ice load history furthermore the sensitivity of rsl variations at these sites to the viscosity structure depends strongly upon the ice model at sites less sensitive to the ice model the resolving power for viscosity structure is also less when ice 1a an ice model derived without assumption of mantle viscosity structure is used to compute rsl variations some models with realistic continuous viscosity increases with depth fit the observations better than the standard model used to derive more recent ice models

xanthones novel aromatic oxygen containing compounds in crude oils abstract xanthone and its alkylated homologues were determined to be present in 64 of 69 investigated oils from offshore norway central graben viking graben haltenbanken this is the first description of xanthones in crude oils these compounds were identified by comparison with authentic standards by coinjection based on mass spectra and relative retention times on two different gc columns the elution order of the four methylxanthones was established as 1 4 2 3 by using a bpx 5 column about 2 3 of the oils contain concentrations of xanthone lower than 5 g g oil but some oils are clearly enriched in the parent compound the highest amount of xanthone in the sample set was 38 g g oil the relative abundance of xanthone the sum of the methylxanthones and the sum of the c 2 xanthones is mainly controlled by maturity partitioning processes may effect changes in the distribution of methylxanthones as observed for a biodegradation sequence from the gullfaks field molecular dynamics calculations support the observation of a better preservation of the shielded isomers 1 and to a lesser extent 4 methylxanthone in the oil phase compared to the non shielded isomers 2 and 3 methylxanthone the ratio of these two different isomer groups may be useful as an indicator of secondary migration distances as demonstrated for an oil sequence from the tampen spur and haltenbanken oils however biodegradation could also cause an increase of the shielded isomers relative to the non shielded isomers due to sterical hindrance by the methyl groups restricting access to the oxygen functionalities the origin of xanthones in crude oils and source rocks is not known but they could be generated as diagenetic products formed by oxidation of xanthenes in the reservoir or originate by geosynthesis from aromatic precursors

upb zircon and rutile chronology of archean greenstone formation and gold mineralization in the val d or region quebec abstract u pb geochronology provides an absolute time framework for the evolution of the sigma gold deposit and surrounding rocks at val d or southern abitibi subprovince the bourlamaque batholith the largest pluton in the area gives a 2699 8 1 0 ma u pb zircon age this pluton cuts the val d or formation which hosts the mineralization a u pb zircon age of 2704 9 1 1 ma on a felsic volcanic rock the colombiere rhyolite 13 km east of the mine dates that formation the gold bearing quartz vein system at sigma is hosted by andesites and two generations of porphyry intrusions all metamorphosed to the greenschist facies the oldest porphyry porphyritic diorite shows the same deformation as the volcanic rocks and has a 2703 7 2 5 ma u pb zircon age the porphyritic diorite and volcanic rocks are cut by feldspar porphyry dykes which post date regional folding and have a 2694 0 2 2 ma u pb zircon age regional greenschist metamorphism has been dated directly with a u pb date of 2684 7 ma on rutile in the colombiere rhyolite the mineralization and hydrothermal alteration in the mine are superimposed on the metamorphic minerals hydrothermal rutile from an alteration halo around the veins in andesite has a 2599 9 ma u pb age textural evidence clearly indicates that the wall rock alteration and vein filling are contemporaneous and hence the vein system and gold mineralization appear to have developed at least 80 m y after the formation and metamorphism of host greenstones

haskell 1935 revisited the haskell 1935 value of 1021 pa s for mantle viscosity is a classic and enduring constraint on the rheology of the earth s interior we revisit this inference using spherically symmetric self gravitating maxwell viscoelastic earth models our inference is based on both forward and inverse analyses of decay times associated with uplift at two sites considered by haskell angerman river sweden and oslo norway rather than the raw relative sea level rsl data at these sites we demonstrate that predictions of the decay time associated with the angerman river data are insensitive to variations in both the late pleistocene ice load history and the lithospheric thickness of the earth model the predictions at oslo are sensitive to both these inputs and hence decay times at this site provide a remarkably robust constraint on mantle viscosity we derive a constraint on the average viscosity of the mantle of 0 65 1 10 1021 pa s where the average resolved by the data encompasses a region which extends from the base of the lithosphere to a depth of near 1400 km this indicates that many previous analyses which have invoked the haskell value of 1021 pa s as a constraint on the average upper mantle i e above 670 km depth viscosity alone have misinterpreted the resolving power of the inference furthermore our analysis indicates that a number of apparently contradictory inferences of viscosity based on fennoscandian data satisfy the new rigorous interpretation of the haskell constraint finally we demonstrate how the ambiguity in the upper mantle lower mantle viscosity contrast associated with the haskell average may be reduced by invoking decay time constraints estimated from rsl curves in hudson bay a preliminary inversion of decay times at angerman river and richmond gulf in hudson bay suggests a contrast of approximately an order of magnitude between the average viscosities of the upper mantle and the top 1000 km of the lower mantle however a conclusive analysis in this regard must await the determination of consistent decay time estimates for the hudson bay region

interpretation and significance of combined trace element and u pb isotopic data of detrital rutile a case study from late ordovician sedimentary rocks of saxo thuringia germany the u pb age and trace element composition of detrital rutile provide information about the metamorphic history of the source region that cannot be constrained by traditional u pb dating of detrital zircon previous provenance investigations focussed on only one of these methods based on a large la icp ms trace element and u pb isotopic dataset of detrital rutile and u pb isotopic data of detrital zircon from late ordovician sedimentary rocks of saxo thuringia germany this paper discusses the application and significance of combining these methods in provenance investigations u pb age spectra from the detrital zircons analysed show multiple age components multimodal age spectra in all samples this is in contrast with the detrital rutile data as only one sample yielded a multimodal u pb age distribution multimodal age spectra of detrital rutile are most likely preserved in sediments from large catchment areas with complex geological histories they may also be related to specific sedimentation events such as glacial washout during the retreat of large ice shields e g the hirnantian glaciation of gondwana unimodal age spectra are however not restricted to small catchment areas if the provenance region is characterized by a pervasive thermal overprint such as the pan african orogeny throughout gondwana unimodal age distributions may further consist of overlapping age cluster detectable by different trace element composition of the detrital rutile grains the combined u pb age and trace element data from detrital rutile grains demonstrate that rutile sourced from metapelitic rocks yield reliable and precise u pb ages in contrast detrital rutile classified to be of metamafic origin generally has too low uranium concentrations to be dated reliably by la icp ms detrital rutile records low to medium grade metamorphic events in the source region and therefore has the potential to better constrain the maximum depositional age of sedimentary rocks in comparison to u pb dating of detrital zircon

a study of strontium diffusion in k feldspar na k feldspar and anorthite using rutherford backscattering spectroscopy abstract sr chemical diffusion has been measured in orthoclase anorthoclase and anorthite under dry 1 atm conditions a strontium oxide aluminosilicate powder mixture was used as the source material with rutherford backscattering spectroscopy rbs used to measure diffusion profiles over the temperature range 725 1075 c the following arrhenius relations were obtained orthoclase normal to 001 d 5 97 10 0 0060 0 0030exp 67900 1600rtcm 2 s 1 measurements of diffusion perpendicular to 010 and 100 indicate little diffusional anisotropy in orthoclase anorthoclase normal to 010 d 4 51 10 1 358 5 6exp 89100 4800rt cm 2 s 1 normal to 001 d 2 25 10 2 1615 31exp 89300 4600rt cm 2 s 1 anorthite normal to 010 d 3 85 10 2 0 380 0 0039 exp 78800 5400rt cm 2 s 1 the correlation of sr uptake with a reduction of k and ca in orthoclase and anorthite respectively indicates that sr is exchanging with these species nuclear reaction analysis nra measurements of al in orthoclase suggests that the coupled exchange sr 2 al 3 k 1 si 4 is taking place as expected sr closure temperatures for feldspars calculated with the above parameters are relatively high compared to those of some other minerals e g biotite muscovite apatite however closure temperatures of feldspars may be significantly depressed if they are exsolved or twinned leading to small effective diffusion lengths feldspar crystals of millimeter size should retain 87 sr 86 sr ratios except when subjected to thermal events of extreme temperature or duration

ti diffusion in quartz abstract we have measured ti diffusion in quartz under dry 1 atm conditions experiments were performed using synthetic and natural quartz and a tio2 powder source with ti profiles obtained by rutherford backscattering spectrometry rbs over the temperature range 700 1150 c the following arrhenius relation was obtained for diffusion parallel to 001 d ti 7 10 8 exp 273 12 kj mol 1 r t m 2 sec 1 similar diffusivities were obtained for both synthetic and natural quartz and for a range of ti source materials including natural titanite powder and rutile quartz single crystal diffusion couples although ti diffusion appears slightly slower in the direction normal to c this difference is not great using these diffusion parameters calculations indicate that distances over which diffusional alteration of ti concentrations in quartz could occur in a million years would be on order of 500 m at 800 c and 15 m at 600 c the arrhenius relation above should be broadly applicable and may find application in constraining metamorphic histories under conditions where the ti in quartz geothermometer can be reasonably applied this relation can also be used to constrain peak temperatures and cooling histories from observations of exsolved rutile needles in quartz and the width of the ti depleted zone that develops around the growing needles finally these findings may find utility in evaluating crystal residence times in magmatic systems when coupled with observations of the sharpness of zoning patterns in quartz

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

glacial isostatic adjustment i the forward problem summary the isostatic adjustment of a radially stratified visco elastic spheroid is treated using space time green functions for the associated surface mass load boundary value problem these impulse response functions are convolved with a heaviside function to give the time dependent deformation of the planet which would be produced by a unit point mass brought up from infinity at t 0 and allowed to remain on the surface the resulting heaviside green functions can be employed to simulate all of the important signatures of glacial isostatic adjustment given a space time dependent surface mass load consisting of ice sheet ablation histories and a model of the simultaneous filling of the ocean basins these source terms are simply convolved with the heaviside green function appropriate to a specific response signature a realistic model of the spatial distribution of the main late pleistocene ice loads and of their temporal disintegration is constructed the response of two visco elastic earth models is computed and compared to a global set of relaxation data relative sea level curves on the basis of this initial comparison of theory and observation the possibility that the lower mantle has a viscosity which is significantly in excess of the viscosity of the upper mantle is excluded in addition clear evidence of the presence of the lithosphere has been found in relaxation data from sites which were near the edge of the laurentide ice sheet such data should therefore prove useful as a basis for analysis of lateral variations in lithosphere thickness further extensions of the calculation are suggested

geochemical study of a series of biodegraded oils microtexture and structure of their coked asphaltenes abstract the asphaltenes extracted from eight oils and a bituminous sand were coked and studied by transmission electron microscopy and x ray diffraction to observe the microtextural and structural changes caused by increasing biodegradation the pyrolysis effluents of asphaltenes were analyzed by chromatography biodegradation causes an increase of aromatic hydrocarbons and sulfur during heat treatment of isolated asphaltenes during thermal treatment the more biodegraded the sample the earlier and the greater the release of aromatics the microtexture of the asphaltene coke is very sensitive to this early release of aromatics and is used to classify samples as to their degree of biodegradation in the series two groups were distinguished

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

insights into orogenic processes from drab schists and minor intrusions southern sao francisco craton brazil abstract minor altered intrusions and drab retrogressed schists can easily be overlooked in geological studies but this contribution explores these rocks within the archaean and palaeoproterozoic southern sao francisco craton ssfc brazil using geological relationships and accessory mineral in situ analyses in the context of cratonic assembly three magmatic pulses are documented i archaean and ii palaeoproterozoic felsic intrusions both hosted by archaean protoliths and iii palaeoproterozoic felsic intrusions in palaeoproterozoic supracrustal sequences archaean felsic intrusions confirm the palaeoarchaean age of the mafic ultramafic sequence of the rio das velhas greenstone belt and rhyacian intrusions mark the collisional stage of the mineiro belt with the sfc at c 2130 ma greenstone belt schists show a wide distribution of rounded soccer ball archaean detrital and metamorphic zircon grains ranging in age from 3200 to 2750 ma with an interpreted overprinting high grade metamorphic event at c 2700 to 2680 ma most high grade metamorphic rims have th u 0 1 negative ehf t values and ree pattern consistent with eclogite granulite metamorphic facies reinforcing the hypothesis of a dehydrated refractory crust formed during the stabilization of the ssfc even though no such protoliths are preserved this event links crustal thickening and partial melting of archaean lower crust archaean rutile crystals from the greenstone belt schist were reset during the palaeoproterozoic event but still preserve the early archaean high grade metamorphic signature the presence of unstable ilmenite replaced by rutile in the schist associated to felsic intrusions with the same age at c 2130 ma suggest high pressure low temperature prograde metamorphism during the collisional stage of the palaeoproterozoic orogen elongate and prismatic zircon grains from the rhyacian intrusions have low ehf t signature and crystallised from partial melting of sedimentary protoliths accretionary events produced thicker and more differentiated crust by the end of rhyacian time easily overlooked rocks in this study when studied have revealed a rich multi event history of cratonic evolution

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

chemical reactions and stability of biomarkers and stable isotope ratios during in vitro biodegradation of petroleum abstract petroleum from the gifhorn trough lower saxony f r g and the maracaibo basin venezuela were analyzed for microorganisms capable of biodegradation genetically related oils were inoculated with the isolated microorganisms and the degradation of the oils was followed by chromatographic techniques parameters important for the reactions ph oxygen concentration nitrogen and phosphorus reaction medium were monitored and optimized the degradation of n alkanes was followed closely it was shown that the microorganisms responsible for degradation yeasts and bacteria could easily survive a period of inactivity due to missing nutrients and could be reactivated within hours to degrade newly added petroleum under conditions in which oxygen or nitrogen was limited selectivity was observed medium chain n alkanes c18 c20 were degraded faster than long chain c30 or short chain c14 n alkanes branched chain alkanes were also degraded the physical parameters of the oils e g density viscosity average molecular weight were altered as expected during degradation in vitro degraded oil is very similar to oil degraded in nature it was found that biomarker molecules are resistant to degradation under the conditions used pyrolysis gc analysis of asphaltenes revealed no significant changes in the composition of pyrolyzates during biodegradation a small shift in the carbon isotope ratios in the aromatic hydrocarbon fraction was observed between biodegraded and unaltered samples

petroleum migration alteration and remigration within troll field norwegian north sea troll field represents the largest petroleum discovery within the entire north sea area in oil equivalents with 74 of the accumulated petroleum present as dry gas and 26 as a heavy biodegraded oil leg the field is divided into several provinces based on the distribution of gas and oil and the gas and oil have been suggested to be cogenetic the migration and filling model presented in this paper suggests that the oil and gas represent two different migration phases and that gas migration and filling predate oil emplacement two different oil populations have been characterized and mapped in troll field applying conventional geochemical techniques we suggest that the two oil populations migrated into the structure through two different migration systems oil and gas were subsequently biodegraded within the reservoir the two oil populations have been found in neighboring oil and gas discoveries and an oil oil correlation with these discoveries has been used to determine the location of field filling points and regional migration routes when oil biodegradation terminated fresh oil continued to migrate into the reservoir and mixed with the residue of the biodegraded oil the field was tilted downward to the west in the neogene and oil and gas remigrated within the field with a possible spillage of gas tilting resulted in a dominantly upward movement of the oil phase whereas gas migrated laterally residual oils in the water zone copyright 1997 the american association of petroleum geologists all rights reserved 1manuscript received july 18 1995 revised manuscript received march 14 1996 final acceptance august 16 1996 2saga petroleum a s kjorboveien 16 p o box 490 n 1301 sandvika norway 3newcastle research group drummond building university of newcastle upon tyne newcastle upon tyne ne1 7ru united kingdom we would like to thank the partners in the troll license who allowed us to publish these results per erling johansen and tone molvik are acknowledged for the analytical work and snorre olaussen nigel mills and terje hellem are thanked for helpful discussions and for assistance with the back tilting of the irap reservoir field model jill sonrier is acknowledged for typing we acknowledge k m wolgemuth john f brint and two anonymous reviewers for helpful comments that improved the paper significantly

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

titaniq a titanium in quartz geothermometer titanium is one of many trace elements to substitute for silicon in the mineral quartz here we describe the temperature dependence of that substitution in the form of a new geothermometer to calibrate the titaniq thermometer we synthesized quartz in the presence of rutile and either aqueous fluid or hydrous silicate melt at temperatures ranging from 600 to 1 000 c at 1 0 gpa the ti contents of quartz in ppm by weight from 13 experiments increase exponentially with reciprocal t as described by text log left x text qtz text ti right 5 69 pm 0 02 frac 3765 pm 24 t k application of this thermometer is straightforward typically requiring analysis of only one phase quartz this can be accomplished either by epma for crystallization temperatures above 600 c or by sims for temperatures down to at least 400 resulting temperature estimates are very precise usually better than 5 c potentially allowing detailed characterization of thermal histories within individual quartz grains although calibrated for quartz crystallized in the presence of rutile the thermometer can also be applied to rutile absent systems if tio2 activity is constrained

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

are the alteration halos of massive sulfide deposits syngenetic evidence from u pb dating of hydrothermal rutile at the kidd volcanic center abitibi subprovince canada the kidd volcanic complex is composed of felsic volcanic and subvolcanic rocks of archean age the felsic rocks are intercalated with sedimentary rocks and are in contact with komatiitic ultramafic rocks large diorite plutons were emplaced into the rhyolite and the complex is overlain by younger basalts metasomatic events affecting the lithology of the kidd volcanic complex include silicification extensive co 2 metasomatism carbonate k metasomatism sericite fuchsite and chlorite and minor carbonate alterations petrographic evidence supported by stable isotope and fluid inclusion studies suggests that silicification and early carbonate alteration were synvolcanic and therefore related to ore deposition during subsequent extensive k metasomatism sericite precipitated in the rhyolite and fuchsite precipitated in the ultramafic rocks although chlorite post dates k metasomatism the micas and chlorite are both found in anastomosing microfissures commonly occupying the same set of fractures hydrothermal rutile formed by the breakdown of magnetiteilmenite during k metasomatism and chlorite alteration gives an age of 2624 62 ma 95 confidence level by pb pb isotopic measurements it is therefore approximately 100 m y younger than syngenetic massive sulfide mineralization 2717 2 ma sulfide stringers within sericite and chlorite veins suggest some remobilization of the ores during these later events this alteration assemblage generally thought to be intimately associated with mineralization is identical to that found associated with many lode gold deposits in the superior province recent dating of micas and rutile associated with gold deposits in the abitibi subprovince gives comparable ages to the rutile in the kidd volcanic complex which must therefore record a widespread late hydrothermal event affecting mineralized rocks

a quantitative model of biological petroleum degradation within the brent group reservoir in the gullfaks field norwegian north sea abstract it has been documented that the degree of biological degradation of the petroleum in the brent group reservoir in the gullfaks field quadrant 34 10 norwegian north sea varies laterally the most severe degradation has taken place in the western part of the field where the brent group sediments are not eroded lack of erosion in the west suggests that this part of the reservoir has always been buried at greater depths than the eastern part of the field the geochemical description with the most severe biodegradation in the west seems therefore to conflict with the most obvious geological model with easiest access for bacteria with meteoric water from the east this suggests that we either do not understand the geology of the gullfaks field area or we do not understand the biological degradation process or perhaps both it is possible to give a reasonably good approximation of the amount of carbon that has been removed from the reservoired petroleum by bacterial degradation by comparing degraded and non degraded petroleum with a fill spill relationship in the area by assuming that the supply of an oxygenating agent is the rate limiting factor in biological degradation of petroleum within a reservoir it is possible to simplify the very complex processes and mechanisms involved in petroleum degradation and to reduce the number of variables to three these are the thickness of the supply zone below the reservoir from which an oxygenating agent can be supplied the flow of water within this supply zone below the oil water contact o w c and the time available to degrade the petroleum in the reservoir geochemical and geological observations and modelling have demonstrated that it is unlikely that the degradation involves sulphate reducing bacteria but that degradation is probably aerobic bacterially mediated and a supply of oxygen rich water with nutrients or is related to a yet unidentified process this mass balance based on the supply and demand of oxygen dissolved in meteoric water indicates that several thousand reservoir volumes are required to degrade the petroleum within the brent group to its present stage this is difficult to explain with the current geological model of the field however the biological degradation must be accounted for when establishing a realistic geological model in the gullfaks area the main advantage of our model is that it is quantitative and although some inaccuracies are inevitable it gives an order of magnitude estimate of the amount of water which must have been supplied into the reservoir

vertical deformation and absolute gravity summary crustal deformation in the greenland and antarctic areas is strongly influenced by both postglacial rebound and contemporary mass redistribution we explore the relationship between the displacement field and the gravitational disturbance for a viscoelastic maxwell earth with an arbitrary radial viscosity profile we seek to determine whether the effects of viscous relaxation in the memory of surface mass change can be separated from the effects of present day mass variation by combined measurements of vertical displacement and absolute gravity when the viscosity profile in the earth s interior is unknown our conclusion is positive specifically the non elastic effects can be reduced substantially by combined measurements of displacement and gravity change for a maxwell viscoelastic earth regardless of its radial viscosity profile the underlying physics has nothing to do with the mathematical structure of viscous relaxation modes rather it is due to the fact that the non elastic response of a maxwell earth is nearly incompressible

the impact of severe biodegradation on the molecular and stable c h n s isotopic compositions of oils in the alberta basin canada abstract although the effects of biodegradation on the composition and physical properties of crude oil have been well studied effects of in reservoir petroleum biodegradation on molecular and isotopic compositions of crude oils are not yet clearly understood the alberta basin in western canada is one of the world s largest petroleum accumulations and constitutes an ideal example of a natural suite of sequentially biodegraded oils the basin hosts moderately to severely biodegraded petroleum regionally distributed and in single more or less continuous oil columns in this study a series of oil samples from the alberta heavy oil and oil sands provinces with varying degrees of biodegradation were analyzed to assess the impact of progressive biodegradation on the molecular and c h n and s isotopic compositions of oils the results of the molecular characterization of the hydrocarbon fraction of the studied oils show that the oils have suffered biodegradation levels from 2 to 10 toward the alberta saskatchewan border on the peters and moldowan scale of biodegradation abbreviated pm 2 to pm 10 and from tens to hundreds on the manco scale within single reservoirs increasing biodegradation was observed from top to bottom of the oil columns at all sites studied the whole oil stable isotopic compositions of the samples varied in the ranges 13 c 31 2 to 29 0 2 h 147 to 133 15 n 0 3 4 7 and 34 s 0 4 6 4 the maximum differences between values of samples within single oil columns were 13 c 1 4 2 h 7 15 n 1 7 and 34 s 1 0 regional variations in the isotopic compositions of oil samples from different wells averaged values from top to bottom were 1 2 for 13 c 12 for 2 h 4 1 for 15 n and 5 5 for 34 s and hence generally significantly larger variations were seen than variations observed within single oil columns especially for n and s it appears that even severe levels of biodegradation do not cause observable systematic variations in carbon nitrogen or sulfur isotope composition of whole oils this indicates that sulfur and nitrogen isotopic compositions may be used in very degraded oils as indicators for oil charge from different source rock facies

u pb zircon and rutile ages from granulite xenoliths in the slave province evidence for mafic magmatism in the lower crust coincident with proterozoic dike swarms zircon and rutile in two garnet bearing mafic granulite xenoliths from a kimberlite in the archean slave province record proterozoic ages similar to the 1 27 ga mackenzie dike swarm or similar to the ca 2 23 2 21 ga malley mckay diabase dike swarms the xenolith sample site currently overlies thick lithosphere more than 700 km to the southeast of the proposed mackenzie plume center because lower crust was effectively shielded from the thermal effects of an upwelling plume by thick lithospheric mantle heat was most likely advected into the lower crust by lateral intrusion of mafic sills over distances of hundreds of kilometres from magma generation zones nearer the plume center

application of ti in zircon and zr in rutile thermometers to constrain high temperature metamorphism in eclogites from the dabie orogen central china abstract ultrahigh pressure uhp eclogites from the northern dabie orogen central china underwent a complex metamorphic evolution during triassic continental deep subduction and subsequent exhumation the eclogites were strongly affected by multiple decompression and re crystallization processes during exhumation thus making the determination of peak metamorphic conditions particularly challenging the recently calibrated ti in zircon and zr in rutile thermometers provide new tools to estimate the peak and post peak temperatures rutiles within uhp mineral bearing domains of zircon have zr contents of 1030 4310 ppm and record a temperature range of 880 1080 c with a peak at 970 c rutiles within high pressure hp mineral bearing domains contain zr contents of 800 5800 ppm and define a temperature range of 780 1030 c with an average value of 873 c rutiles in granulite facies mineral bearing rims of zircon yield a temperature of 845 c in contrast rutile inclusions within garnet have lower zr contents of 100 800 ppm yielding lower temperatures of 600 850 c the uhp and hp mineral bearing mantle domains of zircon have ti contents of 2 15 97 8 ppm yielding ti in zircon temperatures of 620 1020 c ti contents in the rim domains of zircon are low 900 c for the uhp and hp domains of zircon therefore this study combined with the previously published data suggests that the eclogites in the region experienced a protracted high temperature ht metamorphic evolution from uhp eclogite facies to hp granulite facies metamorphic stages this long lived ht evolution coupled with slow cooling and partial melting may explain the rare preservation of uhp traces in the area hp uhp mineral inclusions in garnet and zircon experienced variable degrees of decompression breakdown or retrogression therefore also ti concentrations in zircons and zr concentrations in rutiles within garnet and zircon may have been strongly modified by re crystallization or partial melting as a result only few zircons record their actual crystallization temperatures in comparison the rutile inclusions in zircon generally define higher temperatures we therefore suggest that rutile inclusions in zircon are the most suitable candidates for ht estimates especially in strongly retrogressed eclogites

first application of titanium in zircon thermometry to ultrahigh temperature metamorphism titanium in zircon thermometry has been applied to evaluate the temperatures of metamorphism for two ultrahigh temperature uht granulite localities the neoproterozoic anapolis itaucu complex in central brazil and lower crustal xenoliths from the neo archean kaapvaal craton in south africa uht metamorphism in the anapolis itaucu complex occurred ca 640 ma ti in zircon thermometry on metamorphic zircon yields temperatures of 965 811 c a population of late zircon that formed from ilmenite and rutile breakdown records temperatures of 780 c maximum temperatures are less than those inferred from quantitative phase equilibria modeling based on textural setting inclusions in peak phases and as matrix grains these zircons likely record growth during the pro grade and or postpeak evolution in contrast the kaapvaal xenoliths record two phases of zircon growth during uht metamorphism at 2720 2715 ma followed by growth during isobaric cooling in kyanite bearing leucosomes ca 2690 ma temperatures recorded by the two phases of growth are 1024 878 c and 936 839 c respectively suggesting that zircon growth occurred during uht conditions and continued throughout the postpeak evolution over a 200 c interval these examples demonstrate that the ti in zircon thermometer is a powerful new tool with the potential to determine crystallization temperatures of zircon during granulite facies metamorphism throughout the prograde to postpeak evolution of such terranes

a singularity free approach to post glacial rebound calculations calculating the post glacial response of a viscoelastic earth model using the exponential decay normal mode technique leads to intrinsic singularities if viscosity varies continuously as a function of radius we develop a numerical implementation of the complex real fourier transform crft method as an accurate and stable procedure to avoid these singularities using crft we investigate the response of a set of maxwell earth models to surface loading we find that the effect of expanding a layered viscosity structure into a continuously varying structure is to destroy the modes associated with the boundary between layers horizontal motion is more sensitive than vertical motion to the viscosity structure just below the lithosphere horizontal motion is less sensitive to the viscosity of the lower mantle than the vertical motion is when the viscosity increases at 670 km depth by a factor of about 60 the response of the lower mantle is close to its elastic limit any further increase of the viscosity contrast at 670 km depth or further increase of viscosity as a continuous function of depth starting from 670 km depth is unlikely to be resolved

the viscoelastic relaxation of a realistically stratified earth and a further analysis of postglacial rebound summary we discuss the isostatic adjustment of the earth in response to pleistocene deglaciation and derive constraints on the earth s viscosity profile we model the earth as viscoelastic self gravitating realistically stratified and spherically symmetric it is shown that the earth s relaxation eigenspectrum besides possessing a small set of well known discrete modes also includes infinitely dense sets of modes a continuous spectrum which separate into classes that depend on the principal restoring force of the mode methods for estimating the continuous spectrum are discussed and the effects on the predicted uplift are assessed we find that the effects of the continuous spectrum are far less important than those of the discrete modes though the presence of the continuous spectrum can make the discrete modes more difficult to identify the continuous spectrum does become important when computing the rebound due to more recent loading such as might be associated with present day changes in polar ice we use our model to refine predictions of the earth s response to pleistocene glacial loading with particular emphasis on implications for mantle viscosity we have used time histories that are consistent with the recently recalibrated 14c time scale a special effort is made to match the geologic records of sea level at sites in the vicinity of hudson bay we find consistent with the results of other authors that the curvatures of the records are sensitive indicators of lower mantle viscosity but that there are inconsistencies between the records at different sites however we find we are also able to change the predicted curvatures by modifying the temporal and spatial distribution of the ice loads if we assume a factor of 50 increase in viscosity between the upper and lower mantles and if we assume that the ice on the eastern side of hudson bay melted a few thousand years later than the ice on the western side a result consistent with recent geologic evidence we are able to match the observed sea level data about as well as we are able to if we use instead a uniform mantle viscosity profile a model with a factor of 50 jump in viscosity predicts a large free air gravity anomaly over northern canada that is reasonably consistent with what is observed whereas a uniform viscosity model does not though some authors have argued that the observed north american gravity anomaly may be mostly a consequence of mantle convection and largely unrelated to postglacial rebound our objective here is not to present a preferred ice model or viscosity profile rather we conclude only that the interpretation of the data is ambiguous and that the mantle viscosity profile can not yet be uniquely inferred from them

glacial rebound and relative sea level variations a new appraisal summary late pleistocene and holocene changes in sea level at technically stable shorelines contain information on the melting history of the ice sheets and on the response of the earth to changes in surface loads on time scales of 104yr some separation of parameters defining the ice loads and the earth s response can be achieved by examining sea level change at different sites around the world and at different epochs this paper examines the mathematical requirements for obtaining satisfactory solutions for the sea level equation rather than emphasizing results for the earth s response to the surface loads an examination of the equation expressing the sea level variation on a viscoelastic earth indicates that careful consideration needs to be given to both the definition of the ice load and the geometry of the redistributed water load if geophysically significant earth response parameters are to be deduced from observations of relative sea level the spectrum of the 5 x 5 area mean description of the ice load widely used in glacial rebound studies contains significant power at high degrees n 30 and can result in substantial spatial variations in sea level unless a thick lithosphere is introduced in the earth s response function a smoothed 1 1 description of the ice model avoids these high degree oscillations in relative sea level and produces satisfactory sea level results without requiring a thick lithosphere at far field sites the holocene sea levels are sensitive to the earth s response to the meltwater loading in the vicinity of the site and a high degree spatial resolution of coastline geometry is required to model the mantle flow driven by the differential loading about the site at some sites convergence of the solution to the sea level equation is not obtained even when the solution is expanded to degree 180 convergent solutions at lower degrees can be achieved by introducing earth models with a moderately thick lithosphere if high resolution ice and meltwater load models are not used then the tendency will be to overestimate the effective elastic thickness of the lithosphere estimates of mantle viscosity are also of questionable value if these high resolution models are not used a preliminary examination of sea levels at sites in both the near and far field places an upper limit of about 50 80 km on the effective lithospheric thickness these sea level observations are also consistent with an upper mantle viscosity of about 1021 pas with a lower mantle viscosity in the range of 1021 1023pa s

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

constraints on mantle viscosity from relative sea level variations in hudson bay a number of previous analyses have suggested that the relative sea level record in hudson bay constrains the viscosity of the lower mantle to be near 1021 pa s these conclusions have been based on a limited number of forward calculations which have assumed an isoviscous lower mantle region we compute frechet kernels for the rsl data in hudson bay to determine the detailed depth dependent sensitivity of the data to variations in a viscosity profile which is consistent with the past inferences we find that the rsl data provide a robust constraint on the average viscosity in the top half of the lower mantle only the average must be near 1021 pa s the data are less sensitive to variations in the viscosity below approximately 1800 km depth and in the upper mantle forward analyses included herein show that the data admit models whose average viscosity in the deep mantle below 1800 km depth and in the upper mantle can differ significantly from the value near 1021 pa s estimated for the top half of the lower mantle the total variation in the viscosity from the surface to the cmb can exceed an order of magnitude or more and still satisfy the constraint provided by the hudson bay rsl data set the necessity of invoking an isoviscous mantle model in previous studies is thus seen to be a consequence of the limited class of viscosity model solutions employed in those studies

glacial isostatic adjustment and the free air gravity anomaly as a constraint on deep mantle viscosity summary a gravitationally self consistent theory for relative sea level variations forced by pleistocene deglaciation events is employed to explore the extent to which rsl and free air gravity observations together constrain the viscosity of the mantle beneath the seismic discontinuity at 670 km depth a trade off is revealed between errors in the assumed deglaciation history and errors in the inferred value of the viscosity of the lower mantle taking full account of such uncertainty plausible values of the viscosity beneath the transition region are bounded above by 1023 poise cgs units the preferred value is at least a factor of 2 lower than this and is strongly constrained by the observed free air gravity anomaly over hudson bay the calculations described in detail here show for the first time that the relatively large gravity anomalies observed over sites of wurm wisconsin deglaciation do not require any pronounced increase of mantle viscosity with depth in order to explain them

microbial degradation of aromatic components of crude oils a comparison of laboratory and field observations abstract small aliquots of crude oil brent north sea were incubated aerobically for periods of up to 14 days with an inoculum of recent sediment the saturated and aromatic hydrocarbon components were then isolated and the latter were compared by capillary gas chromatography with similar fractions isolated from four oils from the barrow sub basin of western australia which had experienced different degrees of biodegradation biodegradation of the aromatic hydrocarbons of brent oil produced a series of altered oils whose compositions were comparable to those of the naturally reservoir degraded oils compounds such as naphthalene phenanthrene and alkylated homologues of these hydrocarbons were oxidised but individual isomers were oxidised to different extents

geochemical compositional gradients in a mixed oil reservoir indicative of ongoing biodegradation abstract this study reports the results of organic geochemical characterisation of oil extracts from cores through an oil reservoir column within the grane field north sea the results show small gradients in composition attributed to ongoing biodegradation occurring at the oil water contact biodegradation is affecting the labile constituents that have been replenished by recent charging of this mixed oil and there is no apparent ongoing biodegradation effect upon the resistant compounds associated with earlier oil charge the use of principal component analysis has allowed compositional changes due to evaporation during storage to be distinguished from the effects of biodegradation and has highlighted the c19 n alkanes hopanes steranes ratio as a biodegradation sensitive parameter that shows a gradient in composition through the oil column the concentration of the c19 n alkanes though the oil column confirms that the n alkanes are depleted towards the oil water contact this approach has shown that biodegradation related trends indicative of ongoing biodegradation can be identified in reservoirs that contain multiple altered oil charges even when affected by subsequent compositional changes during sample storage

pb diffusion in zircon abstract chemical diffusion of ti under anhydrous conditions at 1 atm and under fluid present elevated pressure 1 1 1 2 gpa conditions has been measured in natural zircon the source of diffusant for 1 atm experiments was a zro2 tio2 zircon mixture with experiments run in crimped pt capsules diffusion experiments done in the presence of h2o co2 fluid were run in a piston cylinder apparatus using a source of ground tio2 zrsio4 and sio2 with oxalic acid added to produce h2o co2 vapor and partially melt the solid source material yielding an assemblage of rutile zircon melt vapor nuclear reaction analysis nra with the resonant nuclear reaction 48ti p 49v was used to measure diffusion profiles for both sets of experiments the following arrhenius parameters were obtained for ti diffusion normal to cover the temperature range 1350 1550 c at 1 atm d ti 3 33 10 2 exp 754 56 kj mol 1 r t m 2 s 1 ti diffusivities were found to be similar for experiments run under fluid present conditions a fit to all of the data yields the arrhenius relation d 1 34 102 exp 741 46 kj mol 1 rt m2 s 1 these data suggest that zircon should be extremely retentive of ti chemical signatures indicating that the recently developed ti in zircon crystallization geothermometer watson e b harrison t m 2005 zircon thermometer reveals minimum melting conditions on earliest earth science 308 841 844 will be quite robust in preserving temperatures of zircon crystallization titanium diffuses somewhat faster in zircon than larger tetravalent cations u th and hf but considerably more slowly than pb the ree and oxygen hence ti crystallization temperatures may be retained under circumstances when radiometric ages or other types of geochemical information are lost

a u pb age for mineralized nipissing diabase gowganda ontario concordant baddeleyite and rutile analyses from mineralized nipissing diabase at gowganda s castle mine yield a u pb age of baddeleyite is a primary phase of the diabase therefore the age dates the magmatic emplacement the genesis of rutile is less certain rutile could have formed during an episode of alteration veining and ag mineralization in which case the u pb age would also date the secondary event and demonstrate that ag mineralization was related to the nipissing magmatism however a primary magmatic origin of the rutile cannot be completely excluded for now thus the u pb age may not constrain the time of ag mineralization further research is needed to clarify this point

the effect of spatially non uniform water loads on prediction of sea level change summary numerical modelling of postglacial rebound predics a spatially variable pattern of sea level change yet many previous models predicting late pleistocene sea level change either neglect the load of water added to the oceans or assume a spatially uniform time dependent load over the whole ocean this is a poor approximation of the load near the former ice sheet since sea level change varies geographically in addition the coastline goemetry changes through time a spectral technique has been used to solve the sea level equation on an earth model with axisymmetric distribution of ice and oceans and also for a realistic ice ocean configuration the axisymmetric model is useful for demonstrating the fundamental physics involved in sea level changes caused by changes in surface loads in particular it can be seen that the elastic and gravitational response to the load is spread over a great distance whereas the viscous response is more localized a realistic ice ocean configuration has been used to demonstrate that neglect of the melt water load underestimates the amount of uplift in fennoscandia and other regions where rebound occurs in the ocean as previously noted by wu peltier 1983 in hudson bay and that movement of the coastlines and spatially varying water loads must both be included in calculations for the north sea and other near field regions with shallow seas sea level calculations including these effects and careful analysis of the sea level and ice melting record are required to determine modifications to the viscosity profile and ice model inferred by previous inaccurate models of the ocean load in the near field

the controls on the composition of biodegraded oils in the deep subsurface part 1 biodegradation rates in petroleum reservoirs abstract biodegradation rates in oilfields have been assessed conservatively using whole oil column minimum rate estimates diffusion controlled oil column compositional gradient modelling and mixed oil kinetic models biodegradation rate constants first order are around 10 6 10 7 yr 1 for hydrocarbons in the degradation zones these corresponding well with zero order field wide minimum rate estimates of about 10 8 kg hydrocarbons kg oil year for the whole oil column with biodegradation induction times of around 1 2 ma to perturb an entire oil column for light oil reservoirs and 10 20 ma for heavy oil reservoir degradation the results indicate that where we see continuous gradients in the oil columns degradation must have been occurring episodically for many millions of years to remove the n alkanes from an oil i e about 10 of an oil around ca 15 ma is needed for a heavy oil ca 5 ma for a light n sea oil the timescales of oilfield degradation and filling are thus very similar and consequently the degree of biodegradation will be substantially controlled by oilfield charge history assessment of mixed degraded non degraded oil occurrence provides an independent confirmation that these rates are realistic and that timescales of degradation and field charging are similar the maximum effective rate constant of degradation ultimately controlled by the limiting effect of diffusion of alkanes to the oil water contact owc ca 10 4 yr 1 for a 130 m thick oil column first order rate constant is well above the estimated rate constants indicating oil biodegradation rate is not limited by electron donor supply i e hydrocarbons but by supply of nutrients or oxidants this suggests that diffusive transport of nutrients and electron acceptors in the aquifer to the site of biodegradation may be adequate to maintain the low rate biosphere

late pleistocene and holocene sea level change in the australian region and mantle rheology summary spatial and temporal variations in sea level are produced by the melting of the late pleistocene ice and by the earth s response to the redistribution in surface loads by examining different parts of the sea level curves of the past 20 000 yr from geographically widely distributed regions it becomes possible to constrain models of the melting history of the ice sheets and of the earth s rheology observations from sites away from the former arctic ice sheets such as the australian and south pacific region are particularly important for constraining the total meltwater volumes added into the oceans in the past 20 000 yr and the rates at which this occurred these observations indicate that the antarctic ice sheets provided a significant contribution to the sea level rise at a rate that was approximately synchronous with the melting of the laurentide ice sheet except for the interval 9000 6000 yr ago when it may have lagged behind minor melting of the antarctic ice sheet appears to have continued throughout the late holocene differential observations of the late holocene sea level change recorded at sites in the same region are particularly useful for estimating parameters describing the earth s non elastic response to surface loading the effective parameters used here are a lithospheric thickness an upper mantle viscosity and a lower mantle viscosity describing the response below 670 km depth with the observations used here it is not possible to separate the lithospheric thickness h from the upper mantle viscosity and the viscosity results are based on the assumption that 50 h 100 km neither do these observations provide a resolution of the depth dependence of viscosity in the upper mantle and the resulting estimates are effective parameters only differential sea levels along continental margins and along the shores of large gulfs and bays constrain the effective upper mantle viscosity to be about 1 2 1020 pa s 1 while differential values from islands of different sizes are suggestive of a somewhat lower value the lower mantle taken to be below 670 km depth viscosity is about two orders of magnitude greater than this the estimated ice and rheological models explain many of the holocene sea level observations throughout the australian and southern pacific region the tilting of continental margins as exemplified by observations of variable amplitudes of the holocene high stands and the variable times at which sea levels first reached their present level along the north queensland coast and great barrier reef is well represented by these models differential holocene sea levels observed along the narrow spencers gulf of south australia are also well explained by the models and in neither case is it necessary to invoke tectonic motions predicted late holocene sea levels at small to medium sized islands are characterized by small amplitude high stands that reached their maximum values about 4000 2000 yr ago consistent with observations from the society cook and tuamotu islands

ice 3g a new global model of late pleistocene deglaciation based upon geophysical predictions of post glacial relative sea level change a new high resolution global model of late pleistocene deglaciation is inferred on the basis of geophysical predictions of postglacial relative sea level variations in which the ice ocean solid earth interaction is treated in a gravitationally self consistent fashion for the purpose of these analyses the radial viscoelastic structure of the planet is assumed known on the basis of previously published sensitivity tests on solutions of the forward problem only radiocarbon controlled relative sea level histories from sites that were actually ice covered with one or two additions are employed to constrain the model leaving relative sea level rsl data from sites that were not ice covered to be employed to confirm its consistency results for these confirmatory analyses are reported elsewhere here the new deglaciation model referred to as ice 3g is compared to previous models derived by several independent means and tested against a number of additional observations other than sea level histories including geologically controlled retreat isochrones oxygen isotope data from deep sea sedimentary cores and coral terrace elevations the latter two observations strongly constrain the net sea level rise that has occurred since the onset of deglaciation and therefore the mass of ice that melted during the last glacial interglacial transition

unusual high acidity oils from the great palogue field melut basin sudan abstract crude oils produced from the great palogue field in the melut basin sudan display unusually high total acid number values tan up to 10 4 mg koh g oil this field was discovered in 2002 and produces oils of highly variable 15 31 api gravity the main production comes from the paleogene samma and yabus formations with the upper cretaceous melut formation being a minor contributor the effective hydrocarbon source rocks are most likely within lower cretaceous lacustrine shales deposited during the syn rift stages of the basin s evolution this study addressed 20 crude oil samples from five exploration and appraisal wells in the great palogue field and four oil samples from other oil fields in the basin to represent the various production fluids from the upper cretaceous and paleogene pay zones these oil samples were characterized using routine molecular geochemical techniques to determine the primary geological and geochemical controls on oil acidity based on source and maturity constraints two genetic types of high acidity oils have been recognized from the melut basin the first group of high acidity oils is likely primary high tan oils with a tan value of 0 5 0 99 mg koh g oil they are buried deeper than 2000 m where the temperature is higher than 80 c these include the oils only in the upper cretaceous melut formation of the anbar 1 and palogue south 2 blocks the second group of high acidity oils show higher tan values 1 0 mg koh g oil and various levels of biodegradation these oils represent the dominant oil type in the melut basin occurring mainly in the paleogene yabus and samma formations a multiple phase oil charging model is proposed to explain the horizontal and vertical variation in the oil tan values across the great palogue field

a dynamic biodegradation model suggested by petroleum compositional gradients within reservoir columns from the liaohe basin ne china abstract a suite of petroleum reservoir extracts from the liaohe basin ne china was analyzed to investigate the effects and controls of biodegradation on petroleum composition systematic changes seen as marked gradients in petroleum bulk composition component concentrations and molecular indicators have been observed in two biodegraded oil columns in the es3 column 1700 1850 m biodegradation has removed substantial amounts of normal and isoprenoid alkanes more severe biodegradation occurs in the shallower es1 column 1500 1650 m with both steranes and hopanes being partially removed temperature has an overall control on biodegradation in the two columns a lower reservoir temperature leading to a higher degree of biodegradation however observed variation in the degree of biodegradation in the es3 column at different sites is controlled by water leg size with a higher level of degradation being associated with a thicker water leg the supply of nutrients from the water leg is thought to have a significant impact upon the degree of biodegradation in addition to water leg size nutrient supply the compositional gradients also are controlled by the relative rate of mixing of fresh oil charge gradients can only be conserved in biodegraded petroleum columns if the rate of diffusive mixing is similar to or lower than the rate at which the hydrocarbons are removed a biodegradation model is proposed that couples geochemical and geological factors to provide a coherent approach for assessing the impact of degradation on petroleum our geochemical study indicates that biodegradation occurs mainly within a narrow region at or near the base of the oil column the stable compositional gradients are produced after an initial induction period involving diffusive transport of alkanes to the oil water contact owc and diffusion of biodegradation products such as 25 norhopanes and other metabolites away from the reaction site the mixing of continuously charged oil with residential biodegraded oil by diffusion may be considered as one of the most important factors controlling the biodegradation process the conceptual model illustrates all of these processes and opens the possibility of model driven prediction of oil properties and sweetspot location in reservoirs

on postglacial sea level summary an exact method is presented for calculating the changes in sea level that occur when ice and water masses are rearranged on the surface of elastic and viscoelastic non rotating earth models the method is used to calculate the instantaneous elastic and delayed vi scoelastic sea level changes following the partial melting of late quaternary ice sheets we find that there can be large errors in the usual assumption that changes in sea level are uniform over the ocean basins if a quantity of ice equivalent to a uniform 100 m rise in sea level melts from the laurentide and fennoscandian ice sheets then in the south pacific the instantaneous rise in sea level can be as large as 120m in the north atlantic the instantaneous rise is always less than 100 m there is a zone in the north atlantic with almost no sea level change and near greenland and norway the sea level falls rather than rises by over 100 m one thousand years after the melting a forebulge migrating towards the ice loads causes water to flow from the south pacific into the north pacific suggesting that raised beaches should occur in the south pacific the gravitational attraction of an ice mass upon a nearby ocean tends to hold sea level high in the vicinity of the ice this extra load near the ice may have a significant influence on postglacial isostatic adjustment

controls on co2 fate and behavior in the gullfaks oil field norway how hydrogeochemical modeling can help decipher organic inorganic interactions oil degradation in the gullfaks field led to hydrogeochemical processes that caused high co2 partial pressure and a massive release of sodium into the formation water hydrogeochemical modeling of the inorganic equilibrium reactions of water rock gas interactions allows us to quantitatively analyze the pathways and consequences of these complex interconnected reactions this approach considers interactions among mineral assemblages anorthite albite k feldspar quartz kaolinite goethite calcite dolomite siderite dawsonite and nahcolite various aqueous solutions and a multicomponent fixed pressure gas phase co2 ch4 and h2 at 4496 psi 31 mpa reservoir pressure the modeling concept is based on the anoxic degradation of crude oil irreversible conversion of n alkanes to co2 ch4 h2 and acetic acid at oil water contacts these water soluble degradation products are the driving forces for inorganic reactions among mineral assemblages components dissolved in the formation water and a coexisting gas at equilibrium conditions the modeling results quantitatively reproduce the proven alteration of mineral assemblages in the reservoir triggered by oil degradation showing 1 nearly complete dissolution of plagioclase 2 stability of k feldspar 3 massive precipitation of kaolinite and to a lesser degree of ca mg fe carbonate and 4 observed uncommonly high co2 partial pressure 61 psi 0 42 mpa at maximum the evolving composition of coexisting formation water is strongly influenced by the uptake of carbonate carbon from oil degradation and sodium released from dissolving albitic plagioclase this causes supersaturation with regard to thermodynamically stable dawsonite the modeling results also indicate that nahcolite may form as a co2 sequestering sodium carbonate instead of dawsonite likely controlling co2 partial pressure

pb diffusion in rutile diffusion of pb was measured in natural and synthetic rutile under dry 1 atmosphere conditions using mixtures of pb titanate or pb sulfide and tio2 as the sources of diffusant pb depth profiles were then measured with rutherford backscattering spectrometry rbs over the temperature range 700 1100 c the following arrhenius relation was obtained for the synthetic rutile d 3 9 10 10exp 250 12 kj mol 1 rt m2s 1 results for diffusion in natural and synthetic rutile were quite similar despite significant differences in trace element compositions mean closure temperatures calculated from the diffusion parameters are around 600 c for rutile grains of 100 m size this is about 100 c higher than rutile closure temperature determinations from past field based studies suggesting that rutile is more resistant to pb loss through volume diffusion than previously thought

reservoir geochemistry of south pass 61 field gulf of mexico compositional heterogeneities reflecting filling history and biodegradation abstract cluster analysis of gc data for gasoline and mid range hydrocarbon ratios from fifty one south pass 61 field oils reveals geochemically similar oil clusters corresponding to geographically coherent groups insight into the groupings is obtained from examination of indicators of geochemical processes e g anaerobic biodegradation aerobic biodegradation and extensive remigration of light ends six duplicate samples collected in 1986 and 1992 as well as replicate runs on a single sample showed excellent analytical reproducibility subtle but consistent differences in both gasoline and oil range hydrocarbon maturity indicators are observed between the east west and far west flanks of the field suggesting filling of different segments of the reservoir from different kitchens at slightly different stages of thermal maturity or with slightly different chemical character the west flank of the salt dome was charged with slightly more thermally mature petroleum than the east flank the stratigraphically oldest and deepest sand on the far west flank has received the most mature petroleum different fluid contacts and gors are observed in different sands and different fault blocks the stacked pay geometry of the field and widespread faulting have led to considerable remigration of gas and condensate as observed in other fields in the gulf of mexico thompson 1987 biodegradation varies in severity with depth and reservoir zone but is frequently overprinted by remigration of light end hydrocarbons anaerobic biodegradation by sulfate reducing bacteria is probably the cause of light to moderate alteration in intermediate depth pliocene sands which are hydraulically connected to the salt dome with dissolution of anhydrite from the salt dome providing the sulfate widespread late pyrite formation in reservoir sandstones is inferred to represent the ultimate sink for reduced sulfur from sulfate reduction during oil biodegradation co produced water compositions suggest no oxygenated freshwater infusion

aspects of petroleum basin evolution due to gas advection and evaporative fractionation abstract criteria are proposed for the recognition of depletion by evaporative fractionation in reservoir fluid analyses pvt data the characteristics of original as generated molar concentration profiles of marine oils are postulated oils derived from clastic or carbonate sediments bearing respectively type ii or iis kerogens in unaltered marine oils two decreasing exponential concentration series occur separated by a discontinuity between p5 the 5 carbon pseudo component and p6 such that p6 exceeds p5 rendering the profile abruptly bimodal a suite of 195 detailed pvt analyses c1 to p30 of reservoir fluid oils shows that concentrations in the p6 fraction are frequently perturbed the maximum migrating to p7 p8 or a higher carbon number alteration attributable to additive gas advection followed by evaporative fractionation in the subject oils four variables are adduced which track these changes c1 c2 p4 p8 e3 a light gas liquid heavy end ratio and e7 a gasoline range heavy end ratio increase in c1 c2 is accompanied by decreasing values of p4 p8 for which there is no a priori rationale other than the precepts of evaporative fractionation involving the advection of highly mature dry gas dividing a suite of 535 pvt analyses detailed analyses plus 340 analyzed to p7 of world wide provenance into seven subsets on the basis of c1 c2 ratios a well defined separate regression of gas oil ratio on saturation pressure is revealed in each subset such correlations depend primarily upon the processes involved in evaporative fractionation the curves embrace the full commonly encountered range of combinations of gas oil ratio and saturation pressure both of which correlate poorly with level of maturity expressed in a liquid fraction slope factor these observations lead to the hypothesis that progressive evaporative fractionation is a widespread if not universal evolutionary process in petroleum basins

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

alteration of crude oils from the troll area by biodegradation analysis of oil and water samples abstract biodegradation of crude oil in reservoirs has been extensively studied and is usually considered to be a quasi stepwise process the process is known to increase the acidity of the oil in this paper results from the analysis of crude oils and co produced waters from the reservoir surrounding the troll c platform in the norwegian north sea are presented based on the concentrations of light hydrocarbons in the troll oils simultaneous biodegradation of n alkanes branched alkanes cycloalkanes alkyl benzenes alkyl naphthalenes and methyl phenanthrenes is suggested pronounced relative enrichment of methylcyclopentane cyclohexane and methylcyclohexane provide evidence for a specific recalcitrance of cycloalkanes to biodegradation in this field biodegradation can also be seen in the carbon isotopic signature of the lighter hydrocarbons e g heavy signatures for n pentane and iso pentane the composition of the aromatic acids in the produced waters suggests biodegradation to be their predominant source in the reservoir the occurrence of reduced naphthoic acids previously shown to be specific indicators of anaerobic biodegradation of naphthalene 2 methylnaphthalene and tetralin indicates that the biodegradation took place under anoxic conditions

migration of hydrocarbons in the tampen spur area norwegian north sea a reservoir geochemical evaluation abstract this paper describes the application of reservoir geochemical protocols to a study of oil field and regional petroleum compositional variations in the major fields in the tampen spur area the tampen spur high is located in the middle of several oil mature to gas mature source rock kitchens and most of the structures might receive petroleum from several different directions based on the definition of several different petroleum populations within the tampen spur area we define five major petroleum charging systems correlating the petroleum population variations with geological information allows us to derive likely migration fill scenarios for many of the oil fields and requires us to invoke a new upper jurassic carrier system in parts of the area connecting brent group reservoirs across major faults based on this hypothesis two exploration wells were drilled on structures to test this carrier and petroleum was found in one of the structures an understanding of the migration pathways and petroleum drainage efficiency of the basins is of great economic interest because most of the smaller substructures are marginally economic thus it is important to provide an effective risk analysis and ranking of the satellite prospects prior to drilling this study has demonstrated that filling and migration in a geological province are controlled by a series of complex processes and that the filling history of the structures within the tampen spur is more complicated than suggested earlier

the controls on the composition of biodegraded oils in the deep subsurface part ii geological controls on subsurface biodegradation fluxes and constraints on reservoir fluid property prediction the principal controls on the fluid properties of biodegraded oil systems have been determined by a combination of petroleum geochemistry numerical modeling of oil biodegradation in reservoirs and analysis of oil property data sets from a variety of geological settings petroleum biodegradation proceeds under anaerobic conditions in any reservoir that has a water leg and has not been heated to temperatures more than 80c in most reservoirs with low concentrations of aqueous sulfate methanogenic degradation is a primary mechanism of petroleum degradation whereas in waters containing abundant sulfate sulfate reduction and sulfide production may dominate net degradation of petroleum fractions in reservoirs is primarily controlled by the reservoir temperature the chemical compounds being degraded and relationships between the oil water contact owc area and oil volume the relative volumes of water leg to oil leg prior level of oil biodegradation and reservoir water salinity act as second order controls on the process typically degradation fluxes kilograms of petroleum destroyed per square meter of oil water contact area per year or kg petroleum m2 owc yr1 for fresh petroleum in clastic reservoirs are in the range of 103 104 kg petroleum m2 owc yr1 and increase with decreasing reservoir temperature from zero near 80c to a maximum flux at the owc of less than 103 kg petroleum m2 owc yr1 at a temperature less than 40c at very low reservoir temperatures and with severely degraded oils such as are seen in the near surface canadian tar sands at the present day the net degradation fluxes are much less than maximum values nutrient supply from the aquifer and adjacent shales mostly buffered by mineral dissolution probably provides the ultimate control on the range of degradation flux values oil compositional gradients and resulting oil viscosity variations are common on both reservoir thickness and field scales in biodegraded oil reservoirs and are a defining characteristic of heavy oil fields produced by crude oil biodegradation continuous vertical gradients in the oil columns document episodic degradation for many millions of years suggesting that the time scales of oil field degradation and petroleum charging are similar the flux temperature relationship we have derived coupled with typical reservoir charge histories defines the range of variation of fluid properties seen in many biodegraded oil provinces and identifies oil charge mixing of biodegraded and fresh oils and reservoir temperature history as the primary controls on fluid properties these flux temperature relationships are easily integrated into prospect charge modeling procedures sensitivity analyses show that the limiting factor in fluid property predictions using even this first level approach are ultimately constrained by the accuracy of current oil charge modeling estimates the absence today of any functional geochemical proxies for assessing oil residence time in oil fields and the substantial uncertainty in petroleum charging times estimated by forward basin modeling is a major obstacle to more accurate fluid property predictions that needs to be addressed