petrogenesis of late paleozoic volcanics from the zhaheba depression east junggar insights into collisional event in an accretionary orogen of central asia abstract the carboniferous to permian period marks an important transition from accretion to collision in the east junggar terrane nw china field and well fuqian 1 well core data from the zhaheba depression provide a better window for understanding the magmatic process during this period and its implications for the continental growth of central asia field investigations reveal structural features characterized by ne sw compression with lithology composed of basic and intermediate felsic volcanic rocks and pyroclastic rocks the core samples from well fuqian 1 show dominantly basalt basaltic andesite dacite and minor pyroclastic rocks we report zircon shrimp u pb ages of 276 0 279 8 ma from rhyolites and zircon la icp ms u pb ages of 315 4 317 4 ma from dacite and basaltic andesite our data suggest that the volcanic rocks from surface exposures and the well cores of well fuqian 1 formed in the early permian and the late carboniferous respectively the late carboniferous mafic rocks have geochemical characteristics similar to the intercalated early permian felsic rocks the mafic rocks show low initial 87 sr 86 sr 0 703162 0 703783 and high e nd t 5 5 7 5 enrichment in lree and some liles such as rb and th as well as hfses such as zr y and depletion in nb ta and ti furthermore they also display lower sm th 1 6 8 4 and higher th y 0 03 0 12 ratios than those of morb and variable th zr 0 004 0 016 ba th 61 839 ba la 6 13 48 77 and ba nb 10 101 ratios the geochemical data suggest that these rocks were derived dominantly from a 5 10 partial melting of a mainly garnet rich with minor spinel bearing iherzolite mantle source metasomatized by slab derived fluids the felsic rocks are rich in silica sio 2 57 43 78 07 and alkalis k 2 o na 2 o 5 33 9 28 and possess high tfe 2 o 3 0 70 6 95 contents and ga al ratios and low cao 0 18 5 11 and mgo 0 13 2 02 contents they represent typical high medium k calc alkaline a type rhyolite with enrichment of lree and hfse zr hf and depletion of ba sr eu nb and ta these rocks display high e nd t 6 9 7 3 and e hf t 10 3 14 6 values and young crustal model ages 348 557 ma integrating regional geological data from the east junggar terrane and the available data from the proximal ophiolite belt we propose that an arc arc or arc continent post collisional setting in the zhaheba area commenced at ca 317 ma the late carboniferous early permian felsic and mafic magmas were derived from the partial melting of the juvenile mafic lower crust and subcontinental lithospheric mantle metasomatized by pre carboniferous subduction related fluids through asthenospheric upwelling this post collisional event suggests that vertical accretion played an important role not only in the late carboniferous early permian continental growth of the east junggar but also in the final evolutionary phase of the accretionary orogen

a conceptual model for glaciogenic reservoirs from landsystems to reservoir architecture abstract glaciogenic sediments are present in many hydrocarbon producing basins across the globe but their complex nature makes it difficult to characterise the reservoir quality sedimentary units despite this ordovician glacial deposits in north africa and carboniferous permian glaciogenic sequences in the middle east have been proven to host significant economical hydrocarbon accumulations additionally discoveries have been made in the shallow

high resolution landform assemblage along a buried glacio erosive surface in the sw barents sea revealed by p cable 3d seismic data abstract the quaternary sedimentary record in the arctic captures a diverse and evolving range of landscapes reflecting climate changes here we study the geological landform assemblage of the upper regional unconformity uru in the sw barents sea the aims are i to characterize buried geological landforms on a meter scale resolution ii to understand their link with underlying structures and iii to reconstruct paleo ice sheet dynamics and configurations the data consist of a high resolution three dimensional 3d p cable seismic cube with an extent of c 200 km2 and an inline separation of 6 m dominant frequencies of c 150 hz allow to image landforms at uru with a vertical resolution of 1 5 m and a horizontal resolution of 3 6 m we conduct detailed horizon picking and seismic attribute analysis of the buried uru horizon we identified four sets of mega scale glacial lineations and shear band ridges located to the west of a shear margin moraine other characteristic features include hill hole pairs transverse ridges rhombohedral ridges and depressions iceberg ploughmarks and pockmarks polygonal faults below uru and deeper faults have a strong effect on the location of structures observed on uru bedrock packages deformed down to 30 m below uru and up to 5 m high transverse ridges at uru are imprints of glacio tectonic activity deformed strata below uru indicate normal faulting superimposed by glaciotectonic deformation the four sets of mega scale glacial lineations indicate four streaming events with thawed glacial beds with shear band ridges forming in the shearing zone during one of these streaming events hill hole pairs and rhombohedral ridges are frozen bed features which indicate a polythermal regime at the base of the barents sea ice sheet during multiple streaming phases this study therefore shows that paleo ice streams have been temporarily frozen to the ground in the sw barents sea and that landforms evidencing this freezing are associated with underlying faults

dynamic processes from plate subduction to intracontinental deformation insights from the tectono sedimentary evolution of the zhaosu tekesi depression in the southwestern chinese tianshan abstract the zhaosu tekesi depression located to the northern margin of the south tianshan orogenic belt stb is an ideal region for investigating paleozoic orogenic processes and later modifications of the southwestern chinese tianshan in this study we employ 2d seismic and borehole data revealing the geological structure and tectonic evolution of the zhaosu tekesi basin and we report new zircon u pb geochronological and hf isotopic data and whole rock elemental and sr nd isotopic analytical results of the late silurian magmatic rocks as well as the whole rock trace element data of the early carboniferous carbonate rocks borehole data wells zc1 and zc2 and seismic imaging suggest that the zhaosu tekesi depression is composed of silurian lower carboniferous permian jurassic upper cretaceous and paleogene strata with six unconformity surfaces c 1 a s 3 p 1 c 1 a p 2 t p 1 j p 2 t k 2 d j and e k 2 d the silurian strata exhibit southward thrust structures and consist of basalt andesite dacite tuff minor muddy limestone and diorite intrusions zircon shrimp u pb dating for the well zc1 diorites yield a crystallization age of 422 ma with positive e hf t values 3 3 10 6 the diorites and andesites are calc alkaline and show enrichment in liles such as th and u and depletion in nb ta and ti relatively high initial 87 sr 86 sr ratios 0 703376 0 706737 and low e nd t values 0 5 to 1 4 and high th yb 0 29 0 35 and ta yb 1 31 1 58 ratios indicating their formation in an active continental margin setting the lower carboniferous strata mainly comprise oolitic limestone bioclastic micritic limestone and interbedded calcareous siltstone high sr ba 1 31 2 33 v sc 10 4 18 6 and low th u 0 01 0 23 ratios suggest that they were potentially deposited in the mixing near shore marine environment these results in combination with previous data indicate that the southwestern chinese tianshan is controlled by northward subduction of the south tianshan ocean during the late silurian to early carboniferous the presence of the lower permian terrigenous strata and rift basin structure constrains the timing of collision between the ctb kyb and the tarim craton as the late carboniferous thrusting reactivation and syn tectonic growth strata in the basin suggest that the southwestern chinese tianshan experienced late cretaceous compression and neogene modifications after the late permian post faulting thermal subsidence triassic peneplanation and jurassic regional subsidence intracontinental subduction due to distant effect is the main tectonic control on the miocene rapid uplift of the tianshan the zhaosu tekesi basin evolution sheds light on dynamic processes of the southwestern chinese tianshan from plate subduction to intracontinental deformation

in situ u pb sr nd and hf isotopic analysis of eudialyte by la mc icp ms abstract eudialytes are a group of complex na ca zirconosilicate minerals that generally occur in peralkaline agpaitic syenites given that eudialytes are easily altered and commonly contain inclusions of earlier crystallized minerals in situ laser ablation is considered as the most suitable method to determine their u pb ages and sr nd and hf isotopic compositions electron microprobe and la icp ms analysis of eudialytes from nepheline syenites from ilimaussaq greenland khibiny and lovozero russia saima china tamazeght morocco kipawa and mont saint hilaire canada pocos de caldas brazil and langesund fjord norway indicate that this mineral typically has high contents of u pb nb ta zr hf and rare earth elements ree analysis of an in house standard eudialyte by both solution and laser ablation methods demonstrates that precise and accurate u pb ages can be obtained from eudialyte after correction for the common pb content the high sr nd and hf contents in eudialyte coupled with the generally low rb sr and lu hf ratios also permit the precise determination of in situ sr nd and hf isotopic ratios by la mc icp ms methods however some eudialytes with rb sr ratio of 0 02 and yb sr 0 1 and lu hf 0 08 or yb hf 0 4 0 5 cannot be used for in situ sr and hf isotopic measurement eudialyte is the only mineral investigated to date for which it is possible to determine simultaneously u pb ages and sr nd and hf isotopic compositions

in situ sims u pb dating of phanerozoic apatite with low u and high common pb abstract apatite is a common accessory mineral in various igneous metamorphic and sedimentary rocks it has strong potential to provide important information for geochronology and petrogenesis however precise u th pb dating of apatite especially young samples is difficult due to low abundances of u and less radiogenic pb posing significant challenges for accurate common pb correction an additional issue is the lack of suitable apatite to serve as a standard for in situ analyses here we present both analytical and data reduction protocols for sims in situ u pb analyses on apatite with low u and high common lead with nw 1 apatite as the u pb age standard which was separated from 1160 ma carbonatite in the prairie lake complex in canada apatites from the kovdor carbonatite in the kola peninsula which contains low u mostly 2 5 ppm and high common pb 20 80 yielded weighted average 207pb corrected u pb ages of 375 13 ma kv 8 and kv 18 and 377 11 ma kv a respectively apatites from the quruqtagh ultramafic intrusion in nw china containing low u 2 3 ppm and high common pb 70 yield 207pb corrected u pb age of 805 21 ma the cenozoic durango apatite was dated at 31 2 ma all these new apatite u pb ages are indistinguishable from independently known age constraints to within 2 4 our results demonstrate that a u pb age can be accurately and precisely measured for apatite with low u 50 by sims with a suitable standard and a careful choice of common pb composition

properties of iron oxides in some new caledonian oxisols abstract oxisols from two toposequences of new caledonia formed from peridotite consist essentially of fe oxides goethite hematite maghemite these fe oxides were characterized by their mineralogy crystal size and morphology al substitution thermal behaviour and dissolution kinetics in 6 m hcl at 25 c in one toposequence the samples were free of hematite goethite only at 1050 m above sea level whereas at lower altitudes hematite was also present al substitution was generally low due to the low al content of the peridotite except in gibbsitic samples on rocks somewhat higher in al the surface areas of goethite and hematite ranged between 50 and 150 m 2 g 1 dithionite extractable ni and cr were between 0 2 and 2 2 ni and 0 3 and 2 3 cr the hematite containing samples tended to be higher in cr and lower in ni whereas the opposite held for samples containing goethite only maghemites had a low unit cell size 8 31 8 32 instead of 8 34 8 35 a which was attributed to al substitution dehydroxylation temperature of goethites was weakly correlated with al substitution dissolution kinetics could be described by a linear form of a modified first order reaction with one straight line for samples containing goethite only and two lines for samples containing goethite plus hematite

ice stream dynamics of the sw barents sea revealed by high resolution 3d seismic imaging of glacial deposits in the hoop area abstract recent developments in seismic acquisition systems and seismic data visualization have contributed to improve the imaging of seismic geomorphologies over a broad range of topics this study focuses on a new high resolution p cable 3d seismic cube located in the hoop area in the sw barents sea the scientific motivations of the study are 1 to document glacial landforms on a meter scale 2 to study the link of these landforms with the subsurface and 3 to understand ice stream dynamics by detailed interpretation of main horizons including the seabed intra glacial horizons and upper regional unconformity uru the horizons are assessed using the concept of seismic geomorphology and compared with interpretations derived from conventional 3d seismic and state of the art multibeam echosounder technologies to discuss the benefits and limitations of the different geophysical technologies a well defined intra glacial seismic reflection is imaged in the eastern part of the p cable cube this reflection has an overall ne trending ridge shaped morphology which is up to 50 m high and 5 10 km wide and interpreted as a shear margin moraine the top of the moraine displays well defined iceberg ploughmarks and clear slope failure events along its eastern flank the seabed geomorphology which has been directly shaped by glacial processes related to multiple phases of ice streaming appears to be influenced by the buried shear margin moraine mega scale glacial lineations msgls indicative of fast flowing ice streams characterize the seabed west of the moraine infilled msgls and different sets of iceberg ploughmarks with large berms dominate the seabed geomorphology above the moraine the seabed east of the moraine characterized by a smooth morphology and few pockmarks is inferred to reflect more slowly moving ice not resolved by other geophysical techniques seismic attribute maps of p cable 3d allowed the identification of smaller ploughmarks and corrugated ridges related to paleo tides eroded by the larger iceberg ploughmarks these small ploughmarks are suggested to be linked to an earlier rapid disintegration of the barents sea ice stream the new high resolution 3d seismic data have led to the development of a revised ice stream model of the barents sea linking the glacial deposits to different ice stream events

tectonic framework of the northern junggar basin part i the eastern luliang uplift and its link with the east junggar terrane abstract the luliang uplift preserves relatively complete carboniferous strata and is an important region to study the spatio temporal framework and tectonic evolution of the junggar basin here we report new shrimp sims u pb ages whole rock sr nd data and in situ zircon hf isotopic compositions for carboniferous strata samples in the eastern luliang uplift the gravity and magnetic data suggest that the carboniferous volcanics are distributed as nw trending bands and also bring out n s oriented parallel amalgamation the sedimentary units and structural deformation of the eastern luliang uplift suggest that the basin evolution involved late carboniferous extensional graben stage and latest carboniferous early permian compressional stage the carboniferous batamayineishan formation is divided into the lower volcanic unit followed up sedimentary unit and an upper volcanic unit as inferred from the lithology and unconformities the lower volcanic unit from the drill cores mainly consists of andesite dacite rhyolite and tuff intercalated with minor basalt the middle sedimentary unit is made up of sandstone and mudstone with tuff and tuffaceous sandstone and the upper volcanic unit is composed of basalt rhyolite tuff and breccia with minor clastic sedimentary rocks zircon shrimp u pb age 337 2 ma for the tuff and sims u pb age 308 6 ma for basalt suggest that the lower and upper volcanic units belong to lower carboniferous and upper carboniferous respectively the basalts from upper volcanic unit in the eastern luliang uplift show typical calc alkaline affinity with low nb y ratios 0 17 0 28 and sio2 contents 47 54 and moderate th abundances 0 45 3 74 ppm enrichment in lree and liles and depletion in nb ta and ti they have low initial 87sr 86sr ratios 0 703571 0 705122 and positive end t values 5 5 8 6 and constant sm yb ratios 1 56 2 03 and variable trace element ratios e g ba th ba la and ba nb suggesting that the parental magmas were mainly derived from 2 to 8 partial melting of a spinel iherzolite mantle source metasomatized by hydrous fluids and melts of subducted sediments furthermore relatively high tio2 1 52 3 76 and zr contents 172 414 ppm indicate that they were formed in an extensional setting taking into account the occurrence of coeval island arc related volcanics we propose an intra arc rift basin model for the eastern luliang uplift the eastern luliang uplift and east junggar terrane display different tectonic features during the closure of the junggar ocean during the late carboniferous continued northward subduction prevailed and generated a fault controlled intra arc basin in the eastern luliang uplift intra arc basin contraction in permian is probably indicative of the closure of junggar ocean in the northern junggar basin our study confirms the important role of subduction accretion process associated with the carboniferous crustal growth in the junggar terrane

the isotopic composition of yb and the precise and accurate determination of lu concentrations and lu hf ratios by isotope dilution using mc icpms 1 we report yb isotopic data for the purpose of accurately correcting measurements of lu and lu hf ratios during multicollector inductively coupled plasma mass spectrometer mc icpms analysis the yb isotopic ratios agree with recent results of chu et al 2002 and amelin and davis 2004 when corrected for mass fractionation to the same reference values protocols for lu measurement involving simultaneous subtraction of yb interference and application of a fractionation correction based on yb are described it is shown that lu concentrations and lu hf ratios determined by mc icpms using this methodology are more precise and potentially more accurate than results based on analysis of lu by thermal ionization mass spectrometry tims a number of mc icpms lu hf isotopic analyses of standard rocks and other geological samples previously analyzed by tims are presented these document reproducibility of lu hf within 0 2 where most discrepancies can be assigned to the unknown lu mass fractionation during tims analysis

age of carbonatite and phoscorite magmatism of the phalaborwa complex south africa abstract the phalaborwa complex south africa has been dated by u pb analysis of uranothorianite and baddeleyite yielding an age of 2047 11 8 ma for caronatite and phoscorite magmatism baddeleyite yields an age comparable to the age determined on uranothorianite and provides a reliable age indicator ages of carbonatite and silicate magmatism cannot be resolved as different events confirmation of k rich alkaline magmas produced in the mantle as early as 2047 ma suggests that significant chemical heterogeneities existed prior to 2000 ma

velocity and attenuation anisotropy implication of seismic fracture characterizations recent observations from several walkaround walkaway and 3d vsps from various parts of the world have shown that anisotropy symmetry directions or fracture orientations estimated from traveltime or velocity anisotropy do not necessarily agree with symmetry directions from amplitude or attenuation analysis we have also consistently found that attenuation anisotropy in reservoir intervals is generally stronger than in overburdens we argue in this article that instead of reconciling the differences between various attributes we should try to understand the mechanisms and use the difference in velocity and attenuation anisotropy which may contain additional information about subsurface fracture systems

dense arrays of short streamers for ultrahigh resolution 3d seismic imaging ultrahigh resolution 3d uhr3d seismic systems employing a dense array of short streamers represent a significant advancement in the field of marine seismic data acquisition and are an appropriate choice for many near surface survey applications data comparisons between conventional 3d reprocessed 3d high resolution 2d and uhr3d seismic data illustrate the benefits of a uhr3d acquisition strategy results from a recent study of seeps imaged in the gulf of mexico gom suggest that uhr3d data can serve as a comprehensive data source for some near surface geophysical characterizations satisfying many of the needs often addressed by integrating multiple separate types of survey data

na rich carbonate inclusions in perovskite and calzirtite from the guli intrusive ca carbonatite polar siberia carbonate phases some rich in na2o and comparatively rich in sro and bao occur as inclusions in perovskite and calzirtite ca2zr5ti2o16 in the carbonatite of the guli complex siberia this is the first record of alkali carbonates akin to nyerereite na2ca co3 2 in plutonic igneous rocks the inclusion populations suggest that the parental magma of the complex was ca rich but developed na rich differentiates during the latest stages this points to the dominant calcic carbonatites of the complex not being derivatives of alkali rich parental carbonatites these alkali rich carbonate inclusions and rare inclusions of djerfisherite have been preserved due to the resistance of perovskite and calzirtite to processes of leaching hydrothermal alteration and weathering

ion microprobe u pb dating of apatite abstract to illustrate in situ sensitive high resolution ion microprobe shrimp analysis of apatites pb isotopes and pb u ratios of five apatite samples with different ages have been measured using shrimp ii ion microprobe at hiroshima university the prap apatite from a carbonatite complex at prairie lake ontario with a 207 pb 206 pb age of 1156 45 ma 2 was used as the standard for 206 pb 238 u 238 u 16 o 238 u calibration apatites from the poohbah lake alkaline complex give 204 pb 206 pb 238 u 206 pb and 204 pb 206 pb 207 pb 206 pb isochron ages of 2726 145 ma 2 and 2701 86 ma 2 in agreement with a conventional tims 207 pb 206 pb age of 2667 10 ma 2 and a k ar isochron age of 2706 46 ma 2 for the remaining three apatite samples the 204 pb 206 pb 238 u 206 pb and 204 pb 206 pb 207 pb 206 pb isochron ages obtained by shrimp are consistent with radiometric and geological ages in the literature

mitigation of overburden effects in fracture prediction using azimuthal avo analysis an example from a middle east carbonate field the ability to identify fracture clusters and corridors and their prevalent direction within many carbonates and unconventional shale gas tight gas reservoirs may have a significant impact on field development planning as well as on the placement of individual wells we believe seismic fracture prediction provides the best opportunity to identify the spatial distribution of fracture corridors but the reliability of seismic fracture detection technology is constantly being questioned the criticism results from the degree to which the acquisition footprint random and coherent noise in the seismic data and near surface overburden issues affect extracted seismic fracture attributes therefore a key issue is the separation of artifacts caused by the acquisition footprint and near surface or overburden anisotropy structural variations from the anomalies caused by the presence of fractures

mineral chemistry of a zircon bearing composite veined and metasomatised upper mantle peridotite xenolith from kimberlite zircon bearing veins in a harzburgite xenolith from kimberlite have imposed ca metasomatism on the harzburgite wall rock in addition to adding k fe ti and oh the zircon previously dated to have an age similar to that of the xenolith hosting kimberlite shows higher y nb ba ree th and u contents than other mantle derived zircons peripheral alteration of the zircon to baddeleyite and zirconolite and alteration of vein ilmenite to perovskite suggest reaction with an evolving carbonatitic kimberlite melt the high cr2o3 content 0 77 wt of the zirconolite extends the compositional range of terrestrial zirconolite

zirconolite allanite and hoegbomite in a marble skarn from the bergell contact aureole implications for mobility of ti zr and ree zirconolite allanite and hoegbomite are present as accessory phases in a metasomatically altered spinel calcite marble from the contact with the bergell intrusives switzerland italy textural relationships indicate a step wise alteration of spinel to 1 hoegbomite or corundum magnetite 2 margarite and 3 chlorite replacement of spinel by hoegbomite can be described by the substitution 1 94 mg2 fe2 zn2 mn2 ca2 ti4 0 12 oh where al3 and fe3 are held constant the average composition of the bergell hoegbomites is given by the formula fe 0 97 2 mg0 69zn0 04ti0 17al3 94fe 0 06 3 o7 98 oh 0 02 and seems to be imposed by the composition of pre existing spinel during the first two steps of spinel alteration calcite was replaced by anorthite phlogopite and the rare earth element ree bearing minerals zirconolite allanite and sphene were formed allanites have characteristic chondrite normalized ree patterns with enrichment in the light ree the zirconolite patterns show a marked increase in concentration from la to ce followed by an almost constant section sphene lacks detectable la and its ree patterns vary from grain to grain contemporaneous formation of phlogopite ree bearing minerals and hoegbomite during replacement of the spinel calcite marble indicates that the metamorphic fluid introduced potassium along with ree and other high valence cations ti4 zr4 u4 th4a3804265 nb5a3804265 y3a3804265 possibly as polynuclear complexes the abundance of fluorine bearing phlogopite and fluor apatite as well as their close association with ree bearing minerals and hoegbomite suggests f and po 4 3 as likely ligands for complexing of the above mentioned elements

in situ u pb and nd hf sr isotopic investigations of zirconolite and calzirtite abstract although the calcium and titanium bearing zirconsilicates zirconolite and calzirtite are common minerals in carbonatites little is known regarding their trace element or isotopic characteristics available data indicate that they can have significant contents of u pb nb ta zr hf rare earth elements rees minor sr and low rb sr and lu hf ratios their compositions indicate that they have potential for u pb age determination together with nd hf and possibly sr isotopic analyses in this study zirconolite and calzirtite from carbonatites occurring at phalaborwa south africa prairie lake canada afrikanda and kovdor kola russia guli siberia russia and jacupiranga brazil were selected for an isotopic analysis by in situ techniques ion microprobe analyses using a cameca 1280 ion microprobe show that reliable pb pb ages can be obtained from these minerals as they have extremely high u concentrations coupled with negligible common pb although these minerals have low rb sr ratios their low sr concentrations in most cases render in situ sr isotopic analyses difficult in contrast their high sm nd and hf concentrations with generally low lu hf ratios permit precise in situ isotopic analysis of nd and hf

magnetic enhancement is linked to and precedes hematite formation in aerobic soil 1 soil formation usually increases magnetic susceptibility most often by increasing the concentrations of magnetite and maghemite which are two ferrimagnetic iron oxides here we provide evidence that magnetic enhancement in aerobic soils not affected by detrital magnetic inputs or thermal transformation of other iron oxides is mostly due to the formation of maghemite which is later transformed into hematite the iron oxide that gives red color to soil we show that the maghemite hematite ratio is influenced by the particular environment and the degree of soil development so it constitutes an effective tool for paleoenvironmental and planetary studies

zirconolite and baddeleyite in an ultramafic suite from southern india early ordovician carbonatite type melts associated with extensional collapse of the gondwana crust abstract we report here the occurrence of rare zirconium bearing minerals zirconolite cazrti2o7 and baddeleyite zro2 from an unusual ultramafic suite within the achankovil shear zone acsz in southern india zirconolite occurs as inclusions within spinel in phlogopite graphite spinellite and shows characteristic development of radial cracks baddeleyite is commonly observed as an included phase within phlogopite from phlogopite dunite and graphite spinel glimmerite the mineral also occurs less commonly within spinel and graphite from graphite spinel glimmerite the composition of zirconolite is characterized by an enrichment of u and th over rare earth elements baddeleyite shows abundance of zr with minor hf ti and u the mode of occurrence along with the chemical composition of these minerals implies their formation as early stage crystallization products from a silica undersaturated melt that was enriched in carbonatite phile elements such as ca zr ti and volatiles co2 and h2o we report

relationships between phosphate sorption and iron oxides in alfisols from a river terrace sequence of mediterranean spain abstract phosphate sorption isotherms for samples of the a and upper b horizons of alfisols situated on a sequence of terraces of the river guadalquivir southern spain showed that phosphate sorbed at an equilibrium concentration of 0 3 g p ml 1 was correlated with several soil properties crystalline fe oxides goethite and hematite appeared to be the most important p sorbing components of the soil samples sorption was highly correlated with percent clay and with dithionite soluble fe this last property was as good a property to predict sorption as the specific surface of crystalline fe oxides which was estimated by line profile analysis of the x ray diffractograms probably because the range of surface areas for goethite and hematite was relatively narrow in the samples and because of the limited accuracy of the method of line profile analysis well drained and imperfectly drained soils differed little in sorption properties in imperfectly drained hematite free soils chroma was correlated with sorption this is promising for it would allow rapid field estimation of sorption the sorption maximum calculated from the fitted langmuir isotherm was about 1 7 mol p m 2 of fe oxides a value similar to those reported in the literature for natural and synthetic oxides

theoretical correlations between the elastic and electrical properties in layered porous rocks with cracks of varying orientations abstract cracks that are widely existing in geological formations play an important role in affecting the elastic and electrical rock properties which are remotely measured for detecting and characterizing cracked rocks joint interpretation of the complementary elastic and electrical data is expected to give a better assessment of the cracks however the correlations between the elastic and electrical rock properties which are the key to the successful joint interpretation remain poorly understood in layered porous rocks with cracks of varying orientations we reviewed and summarized the most recent advances in the theoretical models for the elastic and electrical properties of layered porous rocks with inclined and rotated cracks as well as with randomly orienting cracks the limitations of the models were identified by comparing the modeling results with available experimental data and we applied the models within their validity range to obtaining theoretically the correlations between the elastic and electrical properties in layered porous rocks with cracks of the above mentioned orientations in the horizontal and vertical directions respectively we showed that the elastic and electrical properties are systematically correlated with cracks of varying crack densities and aspect ratios different cracks orientations affect the correlations in varying ways the results not only illustrate the link between the elastic and electrical properties in cracked rocks but also have important practical applications when the seismic and electromagnetic exploration data are jointly interpreted to gain better knowledge about the subsurface earth although future work is required to extend the models to more realistic cracked formations and to experimentally test the validity of the models and the theoretically obtained joint correlations

vsp normal moveout stretch the vertical seismic profiling common depth point vspcdp transformation is a technique used to image the reflected waves in an offset vsp this coordinate transformation procedure maps reflection amplitudes from receiver depth and reflection times to lateral offset and reflector depth wyatt and wyatt 1981 the process involves the application of moveout correction followed by stacking this moveout correction results in a distortion of the original waveform and a smear of the reflection event that consequently degrades the lateral resolution of the transformation owusu 1991 therefore to determine the optimum processing parameters for the transformation we need to understand the effects of the vsp moveout stretch

the application of u pb geochronology to mafic ultramafic and alkaline rocks an evaluation of three mineral standards abstract a key to proving the accuracy of u pb age determinations by the various techniques available is routine analysis of an internal well characterized matrix matched mineral standard of known age in general there are very few well studied natural mineral standards available to the geological community in this study the nature geochemistry and u pb systematics of baddeleyite titanite and perovskite from three potential mineral standards are evaluated a compilation of concordant to near concordant analyses of a single phalaborwa baddeleyite crystal yields a precise u pb age of 2059 60 0 35 ma a large variation in uranium 51 2124 ppm thorium 0 5 73 ppm and lead 19 782 ppm concentrations and the presence of some u bearing mineral inclusions zircon monazite and baddeleyite zircon intergrowths require some caution when using aliquots of this phalaborwa baddeleyite crystal as a mineral standard the khan titanite crystal investigated here overall has a relatively uniform chemical composition e g u 584 95 ppm th 473 73 ppm pb 57 8 ppm th u 0 81 0 05 but parts of the crystal contain abundant mineral inclusions the model 1 upper intercept age of 522 2 2 2 ma for nine khan titanite analyses is considered the current best estimate for its crystallization age some variability in the u pb systematics with 207pb 206pb ages that vary between 508 and 560 ma was observed and could be related to the presence of tiny u bearing mineral inclusions such as rutile or allanite so careful selection of material from this titanite crystal is also required a single perovskite crystal from the ice river alkaline intrusion has a relatively uniform chemical composition uranium 141 25 ppm thorium 1954 270 ppm lead 41 5 ppm and th u 14 5 1 3 the u pb results for eight perovskite fractions yield a weighted average 206pb 238u age of 356 5 1 0 ma although there are always some limitations to using natural mineral crystals as u pb standards such as the presence of mineral inclusions alteration and geochemical heterogeneity the three crystals investigated here are considered suitable to be used as internal u pb standards for any of the currently used u pb dating techniques

nonstretch moveout correction of long offset multichannel seismic data for subbasalt imaging example from the north atlantic we have developed a pragmatic new processing strategy to enhance seismic information obtained from long offset multichannel seismic data the conventional processing approach which treats data on a sample by sample basis is applied at a coarser scale on groups of samples using this approach a reflected event and its vicinity remain unstretched during the normal moveout correction isomoveout curves lines of equal moveout in the time velocity panel are employed to apply a constant moveout correction to selected individual events leading to a nonstretch stack a zigzag stacking velocity function is introduced as a combination of segments of appropriate isomoveout curves by employing a zigzag velocity function stretching of key events is avoided and thus information at far offset is preserved in the stack the method is also computationally cost effective however the zigzag stacking velocity field must be consistent with target horizons this method of horizon consistent nonstretch moveout has been applied to a wide angle data set from the north atlantic margin providing improved images of the basement interface which was previously poorly imaged

precise determination of phanerozoic zircon pb pb age by multicollector sims without external standardization 1 zircon has long been recognized as the best geochronometer and the most important timekeeper in geosciences modern microbeam techniques such as sims and la icpms have been successfully applied to in situ u pb zircon age determinations at spatial resolutions of 20 30 m or less matrix matched calibration by external standardization of well characterized natural zircon references is a principal requirement for precise microbeam u pb zircon age determination due to fractionation effects between pb and u which usually result in an external age error exceeding 1 alternatively zircons with a closed u pb system can be directly dated by measurement of 207pb 206pb isotopic ratio without external standardization which has been a common practice for zircons older than 1 0 ga but not for relatively young 1 0 ga and particularly phanerozoic ones because of limitations of analytical precision we describe in this paper a method of 207pb 206pb measurement on phanerozoic zircons using a new generation of large radius magnetic sector multicollector cameca ims 1280 sims in combination with multicollector mode a nuclear magnetic resonance nmr magnet controller and oxygen flooding techniques we achieve precisions of 207pb 206pb ratio of 0 1 and 0 1 0 2 propagating to pb pb age errors 0 4 and 1 3 excluding u decay constant uncertainties for zircons of latest neoproterozoic and late paleozoic to mesozoic age respectively therefore the multicollector sims is capable of direct determination of zircon pb pb ages as young as mesozoic age with uncertainties of geological significance this technique is useful for direct dating of zircons in thin sections moreover it has significance for dating of some other u rich minerals i e baddeleyite and zirconolite that are not suitable for sims u pb dating by external standardization

zirconolite a new u pb chronometer for mafic igneous rocks precise dates for mafic igneous events are essential for tectonic reconstructions and understanding mantle dynamics mass extinctions and paleoclimate zirconolite cazrti2o7 is a uranium bearing accessory mineral found in a wide range of terrestrial and lunar rocks that has been largely overlooked as a chronometer in situ u pb geochronology of zirconolite from three dolerite intrusions in western australia demonstrates that it yields emplacement ages that are more precise than those obtained from coexisting zircon and baddeleyite dikes in the stirling range formation give a zirconolite 207pb 206pb age of 1218 3 ma indistinguishable from the less precise dates obtained from zircon 1215 10 ma and baddeleyite 1217 39 ma and coincident with dike emplacement in the adjacent craton margin and peak metamorphism in the albany fraser orogen zirconolite from the 755 ma mundine well dike swarm yields a 207pb 206pb age of 754 5 ma sills intruding the proterozoic manganese group contain zirconolite crystals that give a 207pb 206pb age of 523 14 ma despite high u contents 550 ppm to 14 000 ppm and greenschist facies metamorphism zirconolite in these samples is apparently unaffected by loss of radiogenic pb because of its remarkable properties for u pb geochronology it may soon become the dominant tool for dating mafic igneous rocks as young as 500 ma by ion microprobe and thus will prove especially valuable in reconstructing precambrian geologic history

tectonostratigraphic evolution of the carboniferous arc related basin in the east junggar basin northwest china insights into its link with the subduction process abstract the junggar basin in northwest china is located in the southern part of central asian orogenic belt caob the tectonic mechanisms controlling sedimentary fill through space and geologic time within dynamic subduction environments remains poorly understood in the junggar basin this paper presents an integrated tectonostratigraphic and tectonic evolution of carboniferous volcanic arcs and associated basin in the east junggar basin using multichannel seismic reflection data well line data geochronological and geochemical data we propose a new tectonic sedimentary model for the east junggar basin during the carboniferous time based on geochemistry of volcanic rocks and four seismic tectonostratigraphic sequences the carboniferous succession of volcanogenic sediments represents progradational sequences mainly supplied from the northeast the negative ta nb and ti anomalies low rb ba ratios 0 01 0 15 and high incompatible trace element such as th u abundances of the basalts suggest that metasomatism may have occurred during the late carboniferous subduction the northeastward increase of the ba la ration k ca and decrease of na ti and fe indicate the northeast dipping subduction polarity in the east junggar basin during the early carboniferous tectonism in the east junggar basin took place in two stages deep marine sediments widely covered the junggar region and then the depocenter slightly shifted towards southwest which probably resulted from the northeast dipping subduction that led to the southwestward tilting of the dinan area during the early stage of the late carboniferous mixed marine and nonmarine deposits initially onlapped the volcanic arc towards the northeast and then gradually downlapped to the southwest at the end of the late carboniferous subduction of the junggar ocean continued towards northeast and depositional environment became nonmarine the main axis of the depocenter rapidly migrated towards southwest that resulted from the southwestward tilting of the luliang region

a 4 2 billion year old impact basin on the moon u pb dating of zirconolite and apatite in lunar melt rock 67955 abstract a sharp rise in the flux of asteroid size bodies traversing the inner solar system at 3 9 ga has become a central tenet of recent models describing planetary dynamics and the potential habitability of early terrestrial environments the prevalence of 3 9 ga crystallization ages for lunar impact melt breccias and u pb isotopic compositions of lunar crustal rocks provide the primary evidence for a short lived cataclysmic episode of late heavy bombardment at that time here we report u pb isotopic compositions of zirconolite and apatite in coarse grained lunar melt rock 67955 measured by ion microprobe that date a basin scale impact melting event on the moon at 4 22 0 01 ga followed by entrainment within lower grade ejecta from a younger basin approximately 300 million yr later significant impacts prior to 3 9 ga are also recorded by lunar zircons although the magnitudes of those events are difficult to establish other isotopic evidence such as 40 ar 39 ar ages of granulitic lunar breccias regolith fragments and clasts extracted from fragmental breccias and re os isotopic compositions of lunar metal is also suggestive of impact related thermal events in the lunar crust during the period 4 1 4 3 ga we conclude that numerous large impactors hit the moon prior to the canonical 3 9 ga cataclysm that some of those pre cataclysm impacts were similar in size to the younger lunar basins and that the oldest preserved lunar basins are likely to be significantly older than 3 9 ga this provides sample based support for dynamical models capable of producing older basins on the moon and discrete populations of impactors an extended period of basin formation implies a less intense cataclysm at 3 9 ga and therefore a better opportunity for preservation of early habitable niches and hadean crust on the earth a diminished cataclysm at 3 9 ga suggests that the similarity in the age of the oldest terrestrial continental crust with the canonical lunar cataclysm is likely to be coincidental with no genetic significance

volatile induced transport of hfse ree th and u in arc magmas evidence from zirconolite bearing vesicles in potassic lavas of lewotolo volcano indonesia potassium rich calc alkaline lavas of lewotolo volcano situated in the east sunda arc indonesia contain the rare mineral zirconolite cazrti2o7 samples in which tiny grains of this mineral 3 25 m in size were found span the entire range of lava compositions 47 62 wt sio2 to the best of our knowledge this is the first record of primary zirconolite in juvenile arc volcanics the mineral forms part of a vesicle filling assemblage consisting of a network of quenched feldspar crystals and an sio2 phase probably cristobalite high contents of th u and ree up to 9 3 4 3 and 15 6 wt oxide respectively and very high fe contents up to 13 5 wt fe2o3 distinguish these zirconolites from those of other rock types the extraction of volatile rich phases with changing compositions in successive stages is considered to be responsible for the zirconolite formation we hypothesise that a fluid capable of transporting hfse ree th and u was extracted from the magma and partly crystallised within voids which had formed earlier upon saturation of an aqueous fluid assuming that zirconolite compositions largely reflect trace metal contents of the coexisting fluid phase significant amounts of immobile elements must have been transported on a macroscopic scale our findings thus point to a late stage transfer of hfse ree th and u between different domains in a cooling magma body such a volatile induced redistribution of trace elements at shallow levels of high k volcanic systems may be significant for conventional geochemical modelling of magma evolution and for th u disequilibrium studies

estimation of interval anisotropic attenuation from reflection data knowledge of interval attenuation can be highly beneficial in reservoir characterization and lithology discrimination we combine the spectral ratio method with velocity independent layer stripping to develop a technique for the estimation of the interval attenuation coefficient from reflection seismic data the layer stripping procedure is based on identifying the reflections from the top and bottom of the target layer that share the same ray segments in the overburden the algorithm is designed for heterogeneous arbitrarily anisotropic target layers but the overburden is assumed to be laterally homogeneous with a horizontal symmetry plane although no velocity information about the overburden is needed interpretation of the computed anisotropic attenuation coefficient involves the phase angle in the target layer tests on synthetic p wave data from layered transversely isotropic and orthorhombic media confirm the high accuracy of 2d and 3d versions of the algorithm we also demonstrate that the interval attenuation estimates are independent of the inhomogeneity angle of the incident and reflected waves

nmo stretch and subtle traps introductory note the following paper shows the impact of cmp stacking on the search for subtle traps it appears that 14 years after the publication of aapg memoir 32 the search for the subtle trap is alive and well

nonstretching nmo correction of prestack time migrated gathers using a matching pursuit algorithm abstractwide azimuth long offset surveys are becoming increasingly common in unconventional exploration plays where one of the key routine processes is maintaining data fidelity at far offsets the conventional nmo correction that processes the data sample by sample results in the well known decrease of frequency content and amplitude distortion through stretch which lowers the seismic resolution and hinders and amplitude variation with offset and azimuth avaz analysis of the long offset signal to mitigate the stretch typically associated with large offsets we use a matching pursuit based normal moveout correction mpnmo to reduce nmo stretch effects in long offset data mpnmo corrects the data wavelet by wavelet rather than sample by sample thereby avoiding stretch we apply our technique 1 to a set of synthetic gathers and 2 as part of a residual velocity analysis workflow to a prestack time migrated data volume acquired over the northern chicontepec basin mexico test results show th

sm nd systematics of zircon abstract 147sm 143nd and 146sm 142nd systems were studied in nineteen 3 32 4 02 ga zircon grains from jack hills metaconglomerate 12 of which were previously analyzed for lu hf nd concentrations in the zircons are 0 9 20 ppm the amount of nd recovered was between 13 and 446 pg the analytical precision of 142nd 144nd and 143nd 144nd ratios varied between 0 004 and 0 08 2 m depending on the sample size the 147sm 144nd ratios vary from 0 4 to 1 2 143nd 144nd ratios are variably radiogenic from 0 5125 to 0 5346 combined interpretation of 147sm 143nd and u pb systems shows that lree in zircons are a mixture of a primary component with high sm nd 1 6 2 0 and a secondary younger component with low sm nd determination of initial 143nd of ancient zircons with a precision and accuracy sufficient for petrogenetic interpretations may not be possible because of large errors in the 147sm 144nd ratio which propagate to the uncertainty of 143nd additionally the 143nd values are biased by the presence of secondary nd of unknown age and isotopic composition in more altered zircons the 147sm 143nd system is more promising as a gauge for this secondary alteration related ree component in zircon application of the 146sm 142nd system in zircon to determine the timing of early terrestrial differentiation is promising it will require advancement of the analytical procedures to achieve the lowest possible blanks and maximum sensitivity ion yield as high as 20 30 will be required

ree bearing minerals in a ti rich vein from the adamello contact aureole italy zirconolite aeschynite ce titanite and apatite have been found as minor or accessory minerals in a ti rich tio2 2 1 4 5 wt hydrothermal vein occurring in dolomite marbles at the contact with a tonalite intrusion of the tertiary adamello batholith northern italy the vein consists of four distinct mineral zones comprising from margin to center 1 forsterite calcite 2 pargasite calcite titanite sulfides 3 phlogopite calcite titanite sulfides and 4 titanian clinohumite spinel calcite sulfides zirconolite occurs in two vein zones only in the phlogopite zone it is invariably anhedral often corroded and exhibits complex chemical zonation patterns in the titanian clinohumite zone zirconolite is idiomorphic and characterized by a pronounced discontinous chemical zoning but shows no evidence of corrosion the considerable compositional variation observed for zirconolite in wt ree2o3 0 74 16 8 uo2 0 59 24 0 tho2 0 67 17 1 is due to the zoning and may be attributed to four major substitutions described by the exchange vectors 1 th u mg fe2 ca 1 ti 1 2 ree al ca 1 ti 1 3 ree fe2 nb ta ca 1 ti 1 4 hf zr 1

quantifying the timing and rate of crustal evolution global compilation of radiometrically dated detrital zircon grains abstractmultiple models steady state episodic and early growth followed by crustal reworking have been postulated to explain the evolution of earth s continental crust an independent assessment of these models is now possible as a result of the massive numbers of detrital zircon grains that have been dated individually over recent years using u pb and hf isotopes a compilation of 200 000 published zircon dates reveals a global age distribution u pb with six prominent statistically significant peaks 3 2 3 0 2 7 2 5 2 0 1 7 1 2 1 0 0 7 0 5 and 0 3 0 1 ga in most cases these peaks are recorded on all seven continents most of the peaks are detectable also in modern sediments a comparison of grains with both u pb ages and hf isotope model ages available for 5100 detrital zircons suggests that the age frequency distribution of detrital grains reflects predominantly episodic crustal recycling rather than crustal growth the zircon age distributions and associated data provide consistent ev

do hf isotopes in magmatic zircons represent those of their host rocks abstract lu hf isotopic system in zircon is a powerful and widely used geochemical tracer in studying petrogenesis of magmatic rocks and crustal evolution assuming that zircon hf isotopes can represent initial hf isotopes of their parental whole rock however this assumption may not always be valid disequilibrium partial melting of continental crust would preferentially melt out non zircon minerals with high time integrated lu hf ratios and generate partial melts with hf isotope compositions that are more radiogenic than those of its magma source dissolution experiments with hotplate bomb and sintering procedures of zircon bearing samples demonstrate this disequilibrium effect where partial dissolution yielded variable and more radiogenic hf isotope compositions than fully dissolved samples a case study from the neoproterozoic jiuling batholith in southern china shows that about half of the investigated samples show decoupled hf isotopes between zircons and the bulk rocks this decoupling could reflect complex and prolonged magmatic processes such as crustal assimilation magma mixing and disequilibrium melting which are consistent with the wide temperature spectrum from 630 c to 900 c by ti in zircon thermometer we suggest that magmatic zircons may only record the hf isotopic composition of their surrounding melt during crystallization and it is uncertain whether their hf isotopic compositions can represent the primary hf isotopic compositions of the bulk magmas in this regard using zircon hf isotopic compositions to trace crustal evolution may be biased since most of these could be originally from disequilibrium partial melts

the tectonized central peak of the mjolnir impact crater barents sea abstract the mjolnir structure sw barents sea is one of the best preserved marine impact craters on earth after impact on the paleo seafloor about 142 ma ago this crater experienced an atypical deformation of its central peak which is now elevated 435 m above the crater rims here we investigate the effect of far field tectonic stresses on the central peak uplift based on interpretation of new high resolution p cable and conventional seismic reflection data nearby wells provided stratigraphic control on the interpreted horizons the reconstruction of the crater sedimentary infill supports a subdued original central peak relief with a 5 km wide gentle mound 15 m below the rim our interpretation shows that subvertical outward dipping impact induced faults were reactivated by uplifted segments of the central peak up to 500 m above the platform level during one or several contractional episodes we postulate that post albian tectonic compressional events triggered the structural uplift of the mjolnir central peak differential compaction previously seen as the main deformation process may have increased the original central peak height by only 10 m the mobilization of impact shattered rocks by tectonic compression provides a new and robust explanation for the structural rise of mjolnir s central peak

normal moveout in focus improving the accuracy of nmo corrections and of the corresponding interval velocities entails implementing a better approximation than the formula used since the beginning of seismic processing the exact equations are not practical as they include many unknowns the approximate expression has only two unknowns the reflection time and the rms velocity but becomes inaccurate for large apertures of the recording system and heterogeneous vertical velocities several methods of improving the accuracy have been considered but the gains do not compensate for the dramatic increase in computing time two alternative equations are proposed the first containing two parameters the reflection time and the focusing time is not valid for apertures much greater than is the standard formula but has a much faster computing time and does not stretch the far traces the other containing three parameters the reflection time like focusing time and the tuning velocity retains high frequencies for apertures about twice those allowed by the standard equation its computing time can be kept within the same limits nmo equations old and new are designed strictly for horizontal layering but remain reliable as long as the rays travel through the same layers in both the down and up directions more an equation similar to dix s formula is given to compute the interval velocities the entire scheme can be automated to produce interval velocity sections without manual picking less

phosphate sorption and desorption by thai upland soils abstract phosphate p sorption and desorption characteristics have been investigated for sixty two representative samples of the major thai upland agricultural soils which are oxisols and ultisols formed on diverse parent materials and under various climatic conditions p sorption characteristics are well described by langmuir and freundlich equations values of langmuir p sorption maximum xm and b coefficient range from 47 to 1250 g g 1 soil and 0 5 to 30 ml g 1 respectively and the freundlich k varies between 12 and 1694 g g 1 and b coefficient 0 09 and 0 67 soils derived from basalt have larger values of p sorption maximum than soils on other parent materials both p sorption maximum and freundlich k are closely related to ph naf ssa total titanium aluminum and iron dithionite and oxalate extractable fe and al and other soil properties that reflect specific surface area soil ph in naf is highly effective in predicting the p sorption capacity of thai upland soils explaining 79 of the variation in p sorption by these soils p desorption curves for adsorbed p are well described by the freundlich equation the freundlich kd coefficient for p desorption is highly linearly related to the freundlich k coefficient of p sorption indicating that the above soil factors that contribute to p sorption similarly affect p desorption

pb pb geochronology petrography and chemistry of zr rich accessory minerals zirconolite tranquillityite and baddeleyite in mare basalt 10047 abstract in situ u pb isotopic measurements were carried out by ion microprobe on the zr rich accessory minerals zirconolite cazrti2o7 tranquillityite fe82 zry 2ti3si3o24 and baddeleyite zro2 in low k high ti mare basalt 10047 collected during the apollo 11 mission the analysed minerals are concentrated in pockets of late stage mesostasis that comprises an intergrowth of silica barian k feldspar and si al k glass from a phaneritic subophitic basalt comprising mainly pyroxene plagioclase ilmenite cristobalite and troilite most zr rich minerals are unaltered however some tranquillityite is replaced by a complex intergrowth of zirconolite baddeleyite ilmenite and fayalite suggesting that the mineral became unstable during crystallization several baddeleyite crystals have also undergone alteration to secondary zircon zirconolite was analysed in thin section 10047 11 and tranquillityite and baddeleyite in 10047 227 using a 6 m primary ion beam both zirconolite and tranquillityite have significant u and low initial pb contents and are highly suitable for pb pb dating fifteen analyses of zirconolite give a 207pb 206pb age of 3708 7 ma 207pb 206pb 204pb 206pb isochron 95 confidence including renormalisation of ratios and twenty five analyses of tranquillityite give 3710 6 ma the 207pb 206pb dates are consistent with each other and refine results from an earlier study baddeleyite data were less precise mainly due to lower secondary ionisation efficiency our results show that zirconolite and tranquillityite can provide precise isotopic dates and given their presence in other samples they represent important u pb chronometers for refining lunar geology

seismoacoustic signatures of fracture connectivity wave induced fluid flow wiff between fractures and the embedding matrix as well as within connected fractures tends to produce significant seismic attenuation and velocity dispersion while wiff between fractures and matrix is well understood the corresponding effects related to fracture connectivity and the characteristics of the energy dissipation due to flow within fractures are largely unexplored in this work we use oscillatory relaxation simulations based on the quasi static poroelastic equations to study these phenomena we first consider synthetic rock samples containing connected and unconnected fractures and compute the corresponding attenuation and phase velocity we also determine the relative fluid displacement and pressure fields in order to gain insight into the physical processes involved in the two manifestations of wiff in fractured media to quantify the contributions of the two wiff mechanisms to the total seismic attenuation we compute the spatial distribution of the local energy dissipation finally we perform an exhaustive sensitivity analysis to study the role played by different characteristics of fracture networks on the seismic signatures we show that in the presence of connected fractures both p wave attenuation and phase velocity are sensitive to some key characteristics of the probed medium notably to the lengths permeabilities and intersection angles of the fractures as well as to the overall degree of connectivity of the fracture network this in turn indicates that a deeper understanding of these two manifestations of wiff in fractured media may eventually allow for the extraction of some of these properties from seismic data

zirconolite and xenotime u pb age constraints on the emplacement of the golden mile dolerite sill and gold mineralization at the mt charlotte mine eastern goldfields province yilgarn craton western australia in situ shrimp u pb dating of magmatic zirconolite cazrti2o7 in the golden mile dolerite from the mt charlotte gold deposit yilgarn craton australia has yielded the first robust emplacement age 2 680 9 ma for the principle host rock of gold mineralization in the kalgoorlie district in contrast co magmatic zircon gave ages from 2 68 ga to 2 17 ga reflecting isotopic resetting of high u and th crystals in situ shrimp analysis of hydrothermal xenotime ypo4 which co exists with gold in alteration pyrite provided a pb pb isochron age of 2 655 13 ma this date indicates that the youngest deposit in the kalgoorlie district mt charlotte formed at 2 65 ga and provides a new minimum age for the structurally older golden mile deposit our results indicate that gold mineralization at mt charlotte is 50 million years older than indicated by recent 40ar 39ar dating and places new constraints on the timing of late stage regional faulting d4 in the province

petrochronology of zircon and baddeleyite in igneous rocks reconstructing magmatic processes at high temporal resolution zircon zrsio4 and baddeleyite zro2 are common accessory minerals in igneous rocks of felsic to mafic composition both minerals host trace elements substituting for zr among them hf th u y rees and many more the excellent chemical and physical resistivity of zircon makes this mineral a perfect archive of chemical and temporal information to trace geological processes in the past utilizing the outstanding power and temporal resolution of the u pb decay schemes baddeleyite is a chemically and physically much more fragile mineral it preserves similar information only where it is shielded from dissolution and physical fragmentation as an inclusion in other minerals or in a fine grained or non reactive rock matrix it offers the potential for dating the solidification of mafic rocks with high precision through its crystallization in small pockets of zr enriched melt after extensive olivine and pyroxene fractionation zircon and baddelelyite u pb dates are for an overwhelming majority of cases and where we can assume a closed system considered to reflect the time of crystallization the development of the u pb dating tool ca id tims chemical abrasion isotope dilution thermal ionization mass spectrometry since 2005 has led to unprecedented precision of better than 0 1 in 206pb 238u dates bowring et al 2005 increased sensitivity of mass spectrometers and low laboratory blanks due to reduction of acid volumes allow routine u pb age determinations of micrograms of material at sufficiently high radiogenic common lead ratios see schoene and baxter 2017 this volume in situ u pb age analysis using laser ablation or primary ion beam sputtering allows analysis of sub microgram quantities of zircon material from polished internal sections or zircon surfaces with spot diameters ranging from 30 m for laser ablation inductively coupled plasma mass spectrometry la icp ms to 10 m for secondary ion mass spectrometry sims lateral resolutions of 2 5 m for nanosims

insights into the patterns and locations of erosion in the himalaya a combined fission track and in situ sm nd isotopic study of detrital apatite understanding the role that climate erosion and tectonics play in determining the mean relief elevation and general form of a mountain range over time has become the focus of much recent research in the field of tectonic geomorphology a crucial constraint in these studies is the long term exhumation rate which is increasingly being examined using detrital minerals from the sedimentary rock record that represent the eroded remnants of the orogen a classic field area of such studies is the himalayan orogen the earth s largest mountain range we describe here a novel approach that uses the in situ analysis of nd isotopes by laser ablation multicollector inductively coupled plasma mass spectrometry of fission track dated apatite grains to unambiguously tie them to their source regions we demonstrate the capability of this new approach on several modern and holocene river sand samples from the himalayan orogen and determine because of the large isotopic differences in the constituent tectonostratigraphic units both the location and magnitude of long term erosion in agreement with previous studies we are able to show that in the central and eastern himalaya long term denudation is focussed within the high himalayan crystalline series hhcs at average rates of not vert similar 2 mm yr average long term rates are similar in the western himalaya sampled by the indus river and largely reflect erosional denudation of the western indian himalaya and the western syntaxis the nanga parbat haramosh massif and south karakoram metamorphic complex notably the asian continent supplies significantly more apatites to the mouth of the indus than they do to the bengal delta the ability to reconstruct the patterns of long term erosion in the himalaya using detrital apatites from a few samples collected from major transverse drainages provides confidence in the utility of this approach to examine the locations and magnitude of long term erosion in the past

provenance and tectonic setting of the carboniferous sedimentary rocks of the east junggar basin china evidence from geochemistry and u pb zircon geochronology abstract the modern junggar basin was located in the central asian orogenic belt caob during the devonian and carboniferous few data concerning the weathering provenance and tectonic setting of the carboniferous sedimentary rocks in the junggar basin have been published the recent discovery of an oil gas field in the east junggar basin provides the impetus for this study twenty eight sediment samples were recovered from eight boreholes and all were analysed for major and trace element geochemistry two samples of sedimentary rocks were selected for zircon u pb dating low chemical index of alteration cia values 44 71 and relatively high index of compositional variability icv values 0 72 1 83 suggested weak chemical weathering and an immature source for these samples the relatively low th u 2 16 10 55 and rb sr 0 03 5 44 ratios of the drill core samples reflect a simple recycling history two samples indicated upper carboniferous ages 314 6 ma and a lower middle devonian age 397 9 ma geochemistry and detrital zircon geochronology from the east junggar basin reveal a distinct difference in the composition and source rock ages of clastic rocks from the lower and the upper carboniferous major and trace element compositions of the lower carboniferous sedimentary rocks lcrs were derived from typical mafic rocks and an intermediate ocean island arc of early to middle devonian age whereas the upper carboniferous sedimentary rocks ucrs were derived from a continental island arc or active continental margin setting with a dominantly felsic to intermediate late carboniferous age the current data provide little support for tectonic models that show a passive continental margin of a precambrian crystalline basement our study suggests that a volcanic arc accretion or archipelago early carboniferous to early middle devonian model for the east junggar basin is more viable

toward one meter resolution in 3d seismic high resolution 3d hr3d seismic data are important for hydrocarbon exploration of shallow reservoirs site characterization and geohazard assessments the goal of this contribution is to identify and quantify the parameters to increase the resolution of hr3d seismic data to meter scale the main acquisition parameters controlling the resolution of the collected data are the spectrum of the seismic source source receiver offset range and trace density an evolution to one meter scale resolution of 3d seismic will rely on combining a reproducible seismic source with high frequencies up to at least 600 hz a high uniform trace density of more than 4 million traces per square kilometer and an offset range shorter than approximately 200 m the resulting 3d seismic data volume will reach meter scale resolution for water and target depths of less than 600 m the proposed hr3d system will be suitable for 3d and 4d characterization of seabed properties and shallow stratigraphy the identification of geohazards and hydrocarbon leakage and monitoring the environmental impact of offshore activities the p cable 3d system is an excellent starting point for achieving one meter scale resolution due to its flexible and tight meter scale shot and receiver spacing

seismic wave attenuation and dispersion resulting from wave induced flow in porous rocks a review one major cause of elastic wave attenuation in heterogeneous porous media is wave induced flow of the pore fluid between heterogeneities of various scales it is believed that for frequencies below 1 khz the most important cause is the wave induced flow between mesoscopic inhomogeneities which are large compared with the typical individual pore size but small compared to the wavelength various laboratory experiments in some natural porous materials provide evidence for the presence of centimeter scale mesoscopic heterogeneities laboratory and field measurements of seismic attenuation in fluid saturated rocks provide indications of the role of the wave induced flow signatures of wave induced flow include the frequency and saturation dependence of p wave attenuation and its associated velocity dispersion frequency dependent shear wave splitting and attenuation anisotropy during the last four decades numerous models for attenuation and velocity dispersion from wave induced flow have been developed with varying degrees of rigor and complexity these models can be categorized roughly into three groups according to their underlying theoretical framework the first group of models is based on biot s theory of poroelasticity the second group is based on elastodynamic theory where local fluid flow is incorporated through an additional hydrodynamic equation another group of models is derived using the theory of viscoelasticity though all models predict attenuation and velocity dispersion typical for a relaxation process there exist differences that can be related to the type of disorder periodic random space dimension and to the way the local flow is incorporated the differences manifest themselves in different asymptotic scaling laws for attenuation and in different expressions for characteristic frequencies in recent years some theoretical models of wave induced fluid flow have been validated numerically using finite difference finite element and reflectivity algorithms applied to biot s equations of poroelasticity application of theoretical models to real seismic data requires further studies using broadband laboratory and field measurements of attenuation and dispersion for different rocks as well as development of more robust methods for estimating dissipation attributes from field data

horizon based semiautomated nonhyperbolic velocity analysis abstractwith higher capacity recording systems long offset surveys are becoming common in seismic exploration plays long offsets provide leverage against multiples have greater sensitivity to anisotropy and are key to accurate inversion for shear impedance and density there are two main issues associated with preserving the data fidelity contained in the large offsets 1 nonhyperbolic velocity analysis and 2 mitigating the migration nmo stretch current nonhyperbolic velocity analysis workflows first estimate moveout velocity vnmo based on the offset limited gathers then pick an effective anellipticity eff using the full offset gathers unfortunately estimating vnmo at small aperture may be inaccurate with picking errors in vnmo introducing errors in the subsequent analysis of effective anellipticity we have developed an automated algorithm to simultaneously estimate the nonhyperbolic parameters instead of directly seeking an effective stacking model the algorithm finds an interval model t

in situ upb age determination and srnd isotopic analysis of perovskite from the premier cullinan kimberlite south africa abstract south africa is characterized by multiple episodes of kimberlite intrusion however the age and sr nd isotopic compositions of the primary magma of most of the earlier emplacement events remain unresolved using in situ secondary ion mass spectrometry and laser ablation multi collector inductively coupled plasma mass spectrometry the u pb ages and sr nd isotopic compositions were obtained for perovskite from the premier cullinan kimberlite one of the oldest diamondiferous kimberlites the u pb perovskite ages are 1150 16 1151 9 and 1156 12 ma for the brown black and green kimberlites respectively demonstrating that the different phases of the kimberlite were emplaced contemporaneously at 1150 ma in situ sr nd isotopic analyses of perovskite yield initial sr isotopic ratios and e nd t 1150 values of 0 7031 4 and 1 9 0 9 for the brown 0 7025 1 and 1 8 0 4 for the black and 0 7030 2 and 0 8 0 7 for the green kimberlites these are essentially identical within analytical uncertainties and suggest that the kimberlites were derived from a moderately depleted mantle source in contrast whole rock data yield variable sr nd isotopic compositions confirming that whole rock isotopic data cannot be used to constrain the character of the source of kimberlitic magma due to crustal contamination later alteration and or weathering our data also indicate that kimberlite emplacement might be considered as a prelude to mantle plume activity beneath a craton

phosphate sorption by calcium carbonate in some soils of the mediterranean part of spain abstract we studied the properties of caco3 and phosphate sorption of 36 calcareous soil samples collected across the mediterranean part of spain owing to its low surface area and to its relatively low phosphate sorption capacity caco3 did not influence sorption markedly other soil components of calcareous soils such as fe oxides or silicate clays appear to be quantitatively more important at least for sorption at low phosphate equilibrium concentrations

instantaneous spectral attributes to detect channels channels filled with porous rock and encased in a nonporousmatrixconstituteoneofthemoreimportantstratigraphic exploration plays although attributes such as coherence can be used to map channel width they are relatively insensitive to channel thickness in contrast spectral decomposition can beusedtomapsubtlechangesinchannelthickness thepeak spectral frequency derived by using the short window discrete fourier transform swdft is an excellent tool for mapping such changes along an interpreted horizon we show that by use of instantaneous spectral attributes we can generateequivalentmapsforcompleteseismicvolumes because we are often interested in mapping high reflectivity channelsencasedinalower reflectivitymatrix wefindthata composite plot of the peak frequency and the above average peak amplitude accentuates highly tuned channels finally by generating a composite volume using peak frequency peakamplitude andcoherence wecanestablishnotonlythe channelthickness butalsoitswidth wedemonstratethevalueofsuch3dvolumetricestimatesthroughapplicationto1 a marine survey acquired over tertiary channels from the gulfofmexicoand2alanddatasurveyacquiredoverpaleozoic channels from the central basin platform west texas united states the channels in both marine and land surveys canbehighlightedthroughcomposite volumeanalysis

mineralogy of iron oxides in two soil chronosequences of central spain abstract the iron oxide mineralogy of soils of two river terrace sequences of the rivers jarama and henares central spain which are in close proximity was studied the degree of weathering increases with age as shown by several mineralogical and geochemical indicators such as the increase in the ratio dithionite extractable free fe total fe low values for oxalate extractable fe indicate that the fe oxides are essentially crystalline in the jarama sequence goethite is the dominant pedogenic fe oxide in the henares sequence both goethite and hematite are present in significant amounts the difference is attributed to pedoenvironmental differences such as the lower ph and the moister pedoclimate of the jarama sequence soils the sensitivity of the goethite hematite system to pedoenvironmental factors shows the limited value of iron oxides for the estimation of paleoclimatic conditions or relative age in chronosequences even in relatively small geographical areas

the kola alkaline province of the cis and finland precise rbsr ages define 380 360 ma age range for all magmatism abstract twenty one new rb sr mineral and biotite whole rock isochrons are presented for intrusive rock complexes of the palaeozoic kola alkaline province in the cis and finland samples from the ultrabasic alkaline and nepheline syenite complexes khibina lovozero afrikanda turiy mys ozernaya varaka sokli and iivaara all yield ages in the very narrow range from 361 7 to 377 3 ma i e late middle devonian to upper devonian these data represent crystallization rather than intrusion ages but are nevertheless argued as marking very closely the time of intrusion there is no indication of bimodal age distribution the emplacement of the alkaline magmas is related temporally to the subsidence of the kontozero graben of the central kola peninsula sr initial ratios of the agpaitic nepheline syenites of the giant khibina and lovozero intrusions scatter between 0 703 and 0 704 because of high rb sr ratios of the rocks these isotope ratios exclude long term pre enrichment of alkalis in the sources of the magmas prior to segregation and intrusion and thus episodic enrichment during earlier rifting events in the northern baltic shield the magma formation may be related to wrench movements in the surroundings of the major trollfjord komagelv fault which forms part of the late caledonian arctic north atlantic megashear system

petrogenesis of orbicular ijolites from the prairie lake complex marathon ontario textural evidence from rare processes of carbonatitic magmatism abstract a unique occurrence of orbicular ijolite is hosted in a matrix of contemporaneous holocrystalline ijolite at the 1 1 ga prairie lake carbonatite complex marathon ontario canada and is the only known occurrence of this textural type in a rock of ijolitic composition this mineralogical and petrological study of this orbicular ijolite highlights many of the differences from other rare occurrences of orbicular rocks described from carbonatites granites diorites and lamprophyres the orbicules occur along distinct densely packed bands in equigranular nepheline rich ijolite and range up to 6 cm in diameter macroscopically the orbicules show variability in the mineralogy of their cores detailed imaging of the cores shows evidence of quench textures radial outward zoning is common near the cores with concentric banding occurring toward the margins of the orbicules the mineralogy of the orbicules consists of nepheline diopside calcite apatite andradite melanite garnet titanite fe rich phlogopite titaniferous magnetite perovskite with secondary natrolite calcite and cancrinite the mineralogy of the host ijolite is similar to that of the orbicules mineral compositions from the orbicular ijolite and the host ijolite are similar within the orbicules anhedral minerals are found occurring in a matrix of garnet throughout the distinct concentric bands the textures within the concentric bands of the orbicules are best described as annealing recrystallization textures the rims of the orbicules form interlocking crystals with the host ijolite resulting in near indistinguishable boundaries the orbicules are interpreted to represent interaction of a partially crystallized quenched ijolitic melt which was in contact with a second pulse of consanguineous ijolite magma immersion in the latter resulted in sub solidus diffusion and annealing recrystallization orbicular textures were produced from previously formed quenched ijolite which was recrystallized producing the monominerallic concentric layers sequentially from the margins toward the center of the orbicule this proposed model for the formation of orbicular ijolite from prairie lake highlights the complexities of these rock types and supports previous models of magma mixing during the later stages of carbonatite emplacement and crystallization

zircon u pb and pb isotope fractionation during stepwise hf acid leaching and geochronological implications abstract two homogeneous zircons zircon 91500 kuehl lake ontario and phalaborwa zircon south africa were analysed to study u and pb behaviour during stepwise hf acid leaching from the phalaborwa zircon 11 of radiogenic pb and 7 of u were extracted into solution at the first leaching step and a reverse discordance was obtained after extraction of 27 0 of the total radiogenic pb budget and 24 5 of the u the zircon residue gave concordant ages it contained 75 8 of total radiogenic 206pb budget 76 4 of total radiogenic 207pb budget and 68 0 of total radiogenic 208pb budget indicating different mobility of pb isotopes the 208pb 206pb ratios of the solutions and the residue decrease systematically from 1 10 to 0 60 this pattern probably demonstrates that domains with different th u ratios were successively sampled during acid attack in contrast to phalaborwa zircon only 1 of the total radiogenic pb budget was extracted in leaching steps from each of three zircon 91500 fragments highly reverse discordant ages are observed in the first leaching step of the phalaborwa zircon this phenomenon is consistent with the recent studies of mattinson partial dissolution analysis pdf of zircon past present future 11th annual v m goldschmidt conference abstract volume 3368 pdf 2001 and davis and krogh chem geol 172 2000 41 due to the fractionations between u and pb and between radiogenic pb isotopes observed in the first leaching step discordant domains or zonings of zircons have to be completely removed in the leaching steps to avoid any artificial high 207pb 206pb ratio in the residues evaluation of data from leaching studies shows that the extractability of pb is positively correlated with the total radiogenic pb budgets in zircons and subsequently with u contents and ages of zircons indicating an important role of radiation damage this correlation is consistent with the fact that old zircons with high u contents are much more susceptible to pb loss than younger ones with low u contents

sensitivity of 3d 3c synthetic seismograms to anisotropic attenuation and velocity in reservoir models abstractanisotropic attenuation in fluid saturated reservoirs with high fracture density may be diagnostic for reservoir characterization wave induced mesoscale fluid flow is considered to be the major cause of intrinsic attenuation at exploration seismic frequencies we perform tests of the sensitivity of anisotropic attenuation and velocity to reservoir properties in fractured hti media based on the mesoscale fluid flow attenuation mechanism the viscoelastic t matrix a unified effective medium theory of global and local fluid flow mechanisms is used to compute frequency dependent anisotropic attenuation and velocity for ranges of reservoir properties including fracture density orientation fracture aspect ratio fluid type and permeability the 3d 3c staggered grid finite difference anisotropic viscoelastic modeling with a crank nicolson scheme is used to generate seismograms using the frequency dependent velocity and attenuation computed by the viscoelastic t matrix a standard linear solid mo

seismic data processing in vertically inhomogeneous ti media the first and most important step in processing data in transversely isotropic ti media for which velocities vary with depth is parameter estimation the multilayer normal moveout nmo equation for a dipping reflector provides the basis for extending the ti velocity analysis of alkhalifah and tsvankin to vertically inhomogeneous media this nmo equation is based on a root mean square rms average of interval nmo velocities that correspond to a single ray parameter that of the dipping event therefore interval nmo velocities including the normal moveout velocity for horizontal events vnmo 0 can be extracted from the stacking velocities using a dix type differentiation procedure on the other hand which is a key combination of thomsen s parameters that time related processing relies on is extracted from the interval nmo velocities using a homogeneous inversion within each layer time migration like dip moveout depends on the same two parameters in vertically inhomogeneous media namely vnmo

mineralogy composition and alteration of mars pathfinder rocks and soils evidence from multispectral elemental and magnetic data on terrestrial analogue snc meteorite and pathfinder samples major element multispectral and magnetic properties data were obtained at ares vallis during the mars pathfinder mission to understand the compositional mineralogical and process implications of these data we obtained major element mineralogical and magnetic data for well crystalline and nanophase ferric minerals terrestrial analogue samples with known geologic context and snc meteorites analogue samples include unaltered palagonitic and sulfatetic tephra from mauna kea volcano hydrolytic and acid sulfate alteration steam vent material from kilauea volcano hydrolytic alteration and impactites from meteor crater relithification salient results for mars pathfinder include 1 band depths bd530b and bd600 and the reflectivity ratio r800 r750 are consistent with the dominant ferric mineral being nanophase ferric oxide associated with an unknown amount of h2o and occurring in composite particles along with subordinate amounts of other ferric minerals hematite and hematite plus nanophase goethite are most consistent with the data but maghemite akaganeite schwertmannite and nanophase lepidocrocite are also possible interpretations ferric oxides that are consistently not favored by the data as sole alteration products are jarosites and well crystalline goethite and lepidocrocite 2 the strength of the ferric adsorption edge r750 r445 implies the fe3 fe2 values for pathfinder rock and soil are within the ranges 0 7 3 and 3 20 respectively 3 ferrous silicates are indicated for subsets of pathfinder rocks and soils one subset has a band minimum near 930 nm that can attributed to low ca pyroxene alternatively the band could be a second manifestation of certain ferric oxides including nanophase goethite maghemite akaganeite and schwertmannite another subset has a negative spectral slope from 800 to 1005 nm which could result from the high energy wing of a high ca pyroxene and or olivine band a mixture of bright and dark materials and for rocks thin coatings of bright dust on dark rocks 4 chemical data on pathfinder rocks and soils are consistent with two component mixtures between an andesitic rock with low mgo and so3 concentrations soil free rock and a global basaltic soil with high mgo and so3 concentrations rock free soil pathfinder rock free soil can be modeled as a chemical mixture of snc meteorites and the pathfinder soil free rock 5 pathfinder soil cannot be obtained by chemical alteration of pathfinder rocks by any of the hydrolytic and acid sulfate alteration processes we studied presumably global mixing has obscured and possibly erased the elemental signatures of chemical alteration 6 the strongly magnetic phase in palagonitic and sulfatetic tephra is titanomagnetite and possibly its oxidation product titanomaghemite fe ti spinels the saturation magnetization of the tephra samples 0 5 2 0 am2 kg is at or below the low end of the range inferred for martian dust 4 2 am2 kg implying that lithogenic fe ti spinels are a possible candidate for the martian strongly magnetic phase 7 the predominantly palagonitic spectral signature and magnetic nature of martian soil and dust are consistent with glassy precursors with imbedded fe ti spinel particles comparison with lunar glass production rates suggests that production of sufficient quantities of glassy materials on mars by volcanic and impact processes is sufficient to account for these observations

sims pb pb and u pb age determination of eucrite zircons at 5 μm scale and the first 50 ma of the thermal history of vesta eucrites a subgroup of basaltic achondrites represent the remnants of the earliest magmatic stage of the solar system formation possibly on the asteroid 4 vesta the precise determination of their crystallization age is therefore important for constraining the evolutionary history of the asteroid including melting and differentiation processes of the parent body zircons would be the best mineral for such purpose however extra terrestrial zircons are rare and those found in eucrites are typically small 5 m using a cameca ims 1280 high resolution ion microprobe precise uranium lead u pb and pb pb ages of the non cumulate basaltic eucrite zircons in bereba cachari caldera camel donga and juvinas were determined successfully at scale of 5 m we obtained a weighted average 207pb 206pb age of 4541 11 ma and u pb concordia age of 4525 24 ma for the five eucrite samples studied a synthesis of available age data of howardites eucrites and diogenites indicate a protracted magmatic history on vesta with a most pronounced core mantle differentiation event marked at 4564 2 ma followed by a peak of basaltic magmatism at 4552 7 ma which gradually diminished over the next 50 ma thermal modeling of vesta suggests that partial melt fraction of greater than 10 with temperature well exceeding 1500 k could be maintained over this period throughout its interior this is consistent with the chronological records of eucrites suggesting persistent magmatism on vesta during the first 50 ma in the early solar system

modeling the effect of multiple sets of mesoscale fractures in porous rock on frequency dependent anisotropy this study models the seismic response of porous rock containing two fracture sets with different orientations sizes and connectivities modeling demonstrates frequency dependent anisotropy controlled by two characteristic frequencies that are defined by fluid mobility and the length scales of the fractures fracture related dispersion and attenuation typically occur over a wider frequency band than is seen in the case of a single fracture set when one set of fractures is modeled as being sealed the azimuthal variation of velocity and attenuation can be different with the azimuth of minimum attenuation coinciding with the strike direction of the open fracture set the results should support attempts to differentiate between open and closed fractures on the basis of seismic measurements

estimation of shear wave interval attenuation from mode converted data interval attenuation measurements provide valuable information for reservoir characterization and lithology discrimination we extend the attenuation layer stripping method of behura and tsvankin to mode converted ps waves with the goal of estimating the s wave interval attenuation coefficient by identifying pp and ps events with shared ray segments and applying the pp ps ss method we first perform kinematic construction of pure shear ss events in the target layer and overburden then the modified spectral ratio method is used to compute the effective shear wave attenuation coefficient for the target reflection finally application of the dynamic version of velocity independent layer stripping to the constructed ss reflections yields the interval s wave attenuation coefficient in the target layer the attenuation coefficient estimated for a range of sourcereceiver offsets can be inverted for the interval attenuation parameters the method is tested on multicomponent synthetic data generated with the anisotropic reflectivity method for layered vti transversely isotropic with a vertical symmetry axis and orthorhombic media

hf isotopic compositions of the standard zircons and baddeleyites used in u pb geochronology abstract zircon and baddeleyite u pb geochronological dating is widely used in solid earth sciences and the advent of rapid in situ methods of analysis such sims and icp ms has re emphasized the importance of having uniform standards recently it has been shown that hf isotopic data can provide important information on these minerals since they contain high concentrations of hf but have low lu hf ratios which results in negligible age correction however the complex internal structures that result from multiple thermal events such as inherited cores and metamorphic overgrowths require that the hf isotopic data be measured with high spatial resolution however the isobaric interferences of 176 yb and 176 lu on 176 hf hamper the precise determination of the 176 hf 177 hf ratio during in situ laser ablation mc icpms analysis it is shown here that mass biases of yb yb and hf hf change with time during analyses and behave differently for solutions and solid material therefore it is suggested that the mean yb value of the individual spot be used to obtain the precise isotopic composition for in situ zircon and baddeleyite hf isotopic analyses for low yb hf 176 yb 177 hf yb value have little effect on the accuracy of the hf isotopic composition however the appropriate yb isotopic abundance is necessary for high yb hf 176 yb 177 hf 0 001 zircons and baddeleyites since the interference of 176 yb on 176 hf is significant using the mean yb value of the individual spot and newly published yb isotopic abundance data six standard zircons and two standard baddeleyites have been investigated using a neptune mc icpms with 193 nm laser for zircons the obtained 176 hf 177 hf ratios are 0 282307 31 2sd for 91500 0 282680 31 2sd for temora 0 281729 21 2sd for cz3 282177 17 2sd for cn92 1 0 282983 17 2sd for fm0411 and 281234 11 2sd for phalaborwa the baddeleyites from phalaborwa and sk10 2 have 176 hf 177 hf ratios of 0 281238 12 and 0 282738 13 2sd these results agree well with the values obtained by the solution method and indicate that these standards have different hf isotopic compositions in which the extremely low 176 lu 177 hf and 176 yb 177 hf values of cz3 zircon and phalaborwa baddeleyite make them excellent standards for machine calibration during in situ zircon hf isotopic measurement with the other standards being more suitable for the development of the correction method